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The solid-state crystal structure of Na[Y(dota)(H2O)]·4H2O (H4dota = 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid) at 115 K has been obtained together with the solution structure of the neutral zirconium complex. The yttrium complex shows a mono-capped (H2O) square-antiprismatic structure while the solution 1H NMR spectra of [Zr(dota)(H2O)] suggest that a structure of lower symmetry is adopted and a minor isomer is observed. The crystal structure of the yttrium complex of N,N″-bis(benzylcarbamoylmethyl)diethylenetriamine-N,N′,N″-triacetic acid has revealed amide carbonyl ligation in a distorted mono-capped square-antiprismatic structure, with one metal-bound water molecule.

The complexes [W(CR)(CO)2(η-C5H5)](R = C6H4Me-2 or C6H3Me2-2,6) react with 2 equivalents of CF3CO2H in CH2Cl2 to afford [W(O2CCF3)2(CO)(η2-COCH2R)(η-C5H5)], and with 2 equivalents of HBF4·Et2O in NCMe to give the salts [W(CO)(NCMe)2(η2-COCH2R)(η-C5H5)][BF4]2. Treatment of [W(CC6H4OMe-2)(CO)2(η-C5H5)] with ca. 0.5 equivalent of HBF4·Et2O in CH2Cl2 at ca. –78 °C gives the salt [W{C(H)C6H4OMe-2}(CO)2(η-C5H5)][BF4]. However, if the reaction of [W(CC6H4OMe-2)(CO)2(η-C5H5)] with 1 equivalent of HBF4·Et2O is carried out in the presence of PPh3 or Ph2PCH2PPh2 the complexes [W{σ,η2-CH(PPh3)C6H4OMe-2}(CO)2(η-C5H5)][BF4] and [[graphic omitted]Ph2}(CO)2(η-C5H5)][BF4], respectively, are obtained. The structure of the former has been established by X-ray diffraction. In the cation the tungsten atom is ligated by the cyclopentadienyl group, two CO molecules (W–C–O average 176°), and by a CH(PPh3)C6H4OMe-2 fragment. The latter is attached to the metal in a σ,η2-bonding mode via a W–CH(PPh3) linkage [2.16(3)A] and connectivities to two carbon atoms of the C6H4OMe-2 ring [W–C1 2.31(3) and W–C6 2.65(4)A].

The electronically unsaturated dimetal compound [WFe(µ-CC6H4Me-4)(CO)5(η-C5Me5)] reacts with the phospha-alkynes R′CP (R′= But or Pri) in thf (tetrahydrofuran) below room temperature to give the complexes [WFe{µ-C(C6H4Me-4)PC(R′)}(CO)5(η-C5Me5)]. The structure of the species with R′= But has been determined by X-ray diffraction. The metal–metal bond [W–Fe 2.720(2)A] is spanned by the bridging group such that all three atoms of the CPC chain are attached to the iron atom [Fe–CC6H4Me-4 2.11 (2), Fe–CBut 2.14(1), and Fe–P 2.336(5)A] but only the terminal carbons ligate the tungsten centre [W–CC6H4Me-4 2.18(2), W–CBut 2.22(1)A]. The iron carries three CO groups, and the tungsten is co-ordinated by two CO ligands and the C5Me5 ring. Reactions between the phospha-alkynes and the dimetal compounds [MFe(µ-CC6H4Me-4)(CO)4(PMe3)(η-C5H5)](M = Mo or W) in thf afford under mild conditions the complexes [MFe{µ-C(C6H4Me-4)PC(R′)}(CO)4(PMe3)(η-C5H5)](M = Mo, R′= But or Pri; M = W, R′= But), containing a similar bridge system. The two molybdenum–iron compounds readily isomerise in solution, yielding the species [MoFe{µ-C(C6H4Me-4)C(R′)P}(µ-CO)(CO)3(PMe3)(η-C5H5)]. An X-ray diffraction study on one of the isomers (R′= But) revealed an asymmetric unit containing two crystallographically independent molecules of similar geometry. The Mo(1)–Fe(1) bond [2.710(1)A] is bridged by a carbonyl ligand and by the C(C6H4Me-4)C(But)P unit. All these atoms of the CCP group are bonded to the molybdenum atom [Mo(1)–CC6H4Me-4 2.290(4), Mo(1)–CBut 2.353(5), and Mo(1)–P(1) 2.527(2)A], but only the P and CC6H4Me-4 groups are attached to the iron [Fe(1)–CC6H4Me-4 2.017(5), Fe(1)–P(1) 2.302(2)A]. The Mo atom carries the η-C5H5 ring and a CO ligand but the latter is bent [Mo(1)–C–O 168.4(4)°] towards the µ-P atom [C ⋯ P 2.380(5)A]. The Fe atom is co-ordinated by two terminally bound CO groups and the PMe3 ligand [Fe(1)–P(2) 2.246(2)A]. The n.m.r. spectra (1H, 13C-{1H}, and 31P-{1H}) of the new compounds are reported and discussed.

Treatment of a thf (tetrahydrofuran) solution of K[Rh(PPh3)2(η5-C2B9H11)] with ButCP, followed by addition of NEt4Cl, affords the salt [NEt4][Rh(η4-But2C2P2)(η5-C2B9H11)](3), the structure of which has been established by X-ray diffraction. Compound (3) reacts with [AuCl(PPh3)] and with [Co(CO)2(NCMe)(η4-C4Me4)][PF6] to afford, respectively, the complexes [Rh{η4-But2C2P2Au-(PPh3)}(η5-C2B9H11)](4) and [Rh{η4-But2C2P2Co(CO)2(η4-C4Me4)}(η5-C2B9H11)](5). The structures of the products (4) and (5) have also been determined by X-ray diffraction. In all three compounds the rhodium is η5 ligated by a nido-icosahedral C2B9H11 fragment, and by a 1,3-diphosphacyclobutadiene group. Within the latter the P–C distances are equal, and the four-membered CPCP rings are close to planar. In the compounds (4) and (5) a phosphorus atom in the η4-But2CP2 group co-ordinates to the Au(PPh3) and the Co(CO)2(η4-C4Me4) groups, respectively. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) are reported, and where appropriate discussed.

Treatment of [MoW2(µ-CC6H4Me-4)2(µ-CO)2(CO)4(η-C5H5)2] with PhCCPh in n-hexane at reflux temperatures affords a chromatographically separable mixture of the two trimetal compounds [MoW2{µ-σ,σ′ : η4-C(Ph)C(Ph)C(C6H4Me-4)C(C6H4Me-4)}(CO)6(η-C5H5)2](2) and [MoW2(µ-C2Ph2){µ-C2(C6H4Me-4)2}(CO)4(η-C5H5)2](3), the structures of which have been established by X-ray diffraction. In the molecule of (2) there is a bent W–Mo–W [143.2(1)°] spine with one short [2.562(1)A] and one long [2.987(1)A] metal–metal bond. The longer of the two Mo–W linkages is bridged by a C(Ph)C(Ph)C(C6H4Me-4)C(C6H4Me-4) fragment, with all four carbon atoms of the C4 chain ligating the molybdenum atom, and with the two terminal carbon atoms σ bonded to the tungsten. Each tungsten atom carries two CO groups and a C5H5 ring, and the molybdenum is also co-ordinated by two CO ligands. All six CO groups deviate slightly from linearity [M(Mo or W)–C–O 171.4–173.9°] due to their weakly semi-bridging the metal–metal bonds. The structure of compound (3) is based on an essentially equilateral triangle of metal atoms with the W–W bond [2.752(1)A] weakly semi-bridged by two CO groups (mean W–C–O 170°) and with the Mo–W bonds (mean 2.706 A) bridged, respectively, by the alkynes C2Ph2 and C2(C6H4Me-4)2. Each tungsten atom is co-ordinated by a C5H5 ring, and the molybdenum atom is ligated by two CO groups. The molecule is an interesting example of an unsaturated trimetal cluster with 44 valence electrons. The n.m.r. data (1H and 13C-{1H}) for complexes (2) and (3) are in agreement with the structures established by X-ray diffraction.

The salt [NEt4][Rh(CO)(PPh3)(η5-C2B9H11)](1) reacts with the complexes [Co(CO)2(NCMe)(η4-C4Me4)][PF6], [Rh2(µ-Cl)2(CO)4], and [IrCl(CO)2(NH2C6H4Me-4)] to afford, respectively, the dimetal compounds [CoRh(CO)2(PPh3)(η4-C4Me4)(η5-C2B9H11)](2), [Rh2(CO)2(PPh3)2(η5-C2B9H11)](3), and [RhIrH(µ-σ : η5-C2B9H10)(CO)3(PPh3)2](4). Complex (3) is also obtained in an unusual reaction involving addition of BH3·thf (thf = tetrahydrofuran) to (2). Treatment of (4) with K[BH(CHMeEt)3] in the presence of NEt4Cl gives the salt [NEt4][RhIr(µ-σ : η5-C2B9H10)(CO)3(PPh3)2], a process which can be reversed by addition of HBF4·Et2O to the latter. The structures of complexes (2)–(4) have been established by single-crystal X-ray diffraction studies. In (2) and (3) the metal–metal bonds [Co–Rh 2.746(3), Rh–Rh 2.692(3)A] are bridged by the C2B9H11 group such that the latter is η5co-ordinated to a rhodium atom while forming a three-centre two-electron B–H⇀M (M = Co or Rh) with the other metal centre. However, whereas in (2) it is a BH group which is α to a CH fragment in the pentagonal face of the cage which forms the B–H⇀Co bond, in (3), the B–H⇀Rh bond is formed by a BH group which is β to a CH group. In complex (3) both metal centres are co-ordinated by a CO and a PPh3 ligand. This is also true for the rhodium atom in (2), while the cobalt atom in the latter carries the tetra-methylcyclobutadiene ring and a CO group. Compound (4) has a Rh–Ir bond [2.781(1)A] bridged by a C2B9H10 moiety. The latter is η5 co-ordinated to the rhodium atom and forms an exopolyhedral B–Ir bond using a boron atom in the pentagonal face of the ligand which is α to a CH fragment. The iridium centre is ligated by two CO groups, and by a PPh3 and a hydrido ligand, while the rhodium atom carries a CO and a PPh3 group. The n.m.r. spectra (1H, 13C-{1H}, 31P-{1H}, and 11B-{1H}) of the new compounds are reported and discussed.

The reaction between [NEt4][Rh(CO)(PPh3)(η5-C2B9H11)] and [PtCl(H)(PEt3)2] in acetone, in the presence of TIBF4, affords the dimetal compound [RhPt(µ-H)(µ-CO)(PEt3)2(PPh3)(η5-C2B9H11)]. The structure of this complex has been established by an X-ray diffraction study. The Rh–Pt bond [2.734(2)A] is bridged by a hydrido ligand [Rh–H 1.7(2), Pt–H 1.8(2)A] and by a carbonyl group [Rh–CO 1.99(1), Pt–CO 1.99(1)A; Rh–C–O 133(1), Pt–C–O 141(1)°]. The platinum atom carries the two PEt3 ligands [Pt–P 2.275(4) and 2.335(4)A], while the rhodium atom is co-ordinated by the PPh3 molecule [Rh–P 2.257(4)A] and the five atoms [graphic omitted] in the pentagonal face of the nido-C2B9H11 cage. Treatment of this dimetal compound with the alkynes RCCR (R = Ph or C6H4Me-4) in tetrahydrofuran at room temperature affords the complexes [RhPt{σ-C(R)C(R)H}(CO)(PEt3)(PPh3)(η5-C2B9H11)]. An X-ray diffraction study on the species with R = C6H4Me-4 revealed the following structural features. The Rh–Pt bond [2.762(1)A] is bridged by the C2B9H11 cage such that the latter is η5 co-ordinated to the rhodium atom while forming an exopolyhedral bond to the platinum via a three-centre B–H ⇀ Pt linkage. The boron atom involved lies in the pentagonal face of the cage ligating the rhodium, and is in the β site with respect to the two carbon atoms. The rhodium atom is co-ordinated by a PPh3[Rh–P 2.294(2)A] and a CO [Rh–CO 1.845(8)A] group. The platinum atom carries the PEt3 ligand [Pt–P 2.221(2)A] and a σ bonded cis-C(C6H4Me-4)C(C6H4Me-4)H vinyl group [Pt–C 2.036(7)A]. N.m.r. data (1H,13C-{1H},31P-{1H}, and 11B-{1H}) for the compounds are reported and discussed.

The naphthaleneruthenium complex [Ru(η6-C10H8)(η4-cod)](1)(cod = cyclo-octa-1,5-diene) has been synthesised and characterised by X-ray crystallography. Compound (1) contains a ruthenium atom η6-bonded to naphthalene and η4-bonded to a cyclo-octa-1,5-diene ligand. Slip distortions in the naphthalene ring are discussed. Spectroscopic data for the norbornadiene complex [Ru(η6-C10H8)(η4-nbd)](2) are also presented.

The compounds [Mo(CO)3(NCMe)3] and [M(CR)(CO)2(η-C5H5)](M = MO or W) in Et2O at room temperature afford the trimetal complexes [MoM2(µ-CR)2(CO)6(η-C5H5)2](M = MO or W, R = C6H4Me2-2,6; M = MO, R = C6H4OMe-2). In contrast, [Mo(CO)3(NCMe)3] and [Mo(CC6H4Me-4)(CO)2(η-C5H5)] yield the µ-alkyne complex [Mo2{µ-C6H4Me-4)2}-(CO)4(C5H5)2]. An X-ray diffraction study established the structure of [MO3(µ-CC6H3Me-2,6)2(CO)6(η-C5H5)2]. The three metal atoms form the spine of the molecule [Mo–Mo 2.802(1)A, MO–MO–MO 124.8(1)°], and the metal–metal bonds are bridged in an essentially symmetrical manner by the alkylidyne groups [µ-C–MO 1.986(5) and 2.100(5)A]. Each metal atom carries two carbonyl groups, but one of these ligands on each of the terminal molybdenum atoms semi-bridges a metal-metal bond [Mo–C–O 169.8(5)°]. The molecule has crystallographic C2 symmetry. The two almost isosceles µ-CMo2 triangles share an Mo apex, with a dihedral angle of 79° between the planes defined by the triangles. Moreover, the two carbonyl groups attached to the central MO atom are each, respectively, coplanar with one of the µ-CMo2 triangles. The arrangement of the ligating groups around the central MO atom is in agreement with extended-Huckel molecular orbital calculations on the model isolobal molecule [Mo(CO)2(η-C2H2)2]. The lowest energy results for a structure in which the alkyne ligands are orthogonal to each other, and are each parallel to one of the CO groups. The reactions of the species [M(CC6H3Me2-2,6)(CO)2(η-C5H5)](M = MO or W) with [Cu(thf)(η-C5Me5](thf = tetrahydrofuran) were also investigated and shown to give the dimetal compounds [MCu(µ-CC6H3Me2-2,6)(CO)2(η-C5H5)(η-C5Me5)].

Treatment of [Rh(CO)2(η-C5Me5)] with [Mn(CO)2(thf)(η-C5H5)](thf = tetrahydrofuran) affords [MnRh(µ-CO)2(CO)2(η-C5H5)(η-C5Me5)], the structure of which has been determined by an X-ray diffraction study. The crystals are orthorhombic, space group Pnam(non-standard setting of Pnma, No. 62), in a unit cell with a= 16.851(12), b= 9.338(5), c= 11.566(9)A, U= 1 820(2)A3 at 220 K, and Z= 4. The structure was solved to R 0.057 (R′ 0.058) from 1 860 observable independent reflections [I 3.0σ(I)]. The molecule possesses C, symmetry; one terminal carbonyl ligand on each of the metal atoms, together with the Rh–Mn bond [2.703(2)A], define the mirror plane. The cyclopentadienyl ligand on the Mn atom is in a trans relationship to the pentamethylcyclopentadienyl ligand on the Rh atom and both lie astride (perpendicular to) the mirror plane. The two other carbonyl ligands are terminal to the Mn atom but are strongly semi-bridging to the Rh atom [Mn–C(9) 1.866(7), Rh–C(9) 2.172(7)A], and define planes which are nearly perpendicular to the mirror plane. A distortion of the Rh–C5 geometry towards a ‘diolefin’ type attachment is discussed.Reaction of [Rh(CO)2(η-C5Me5)] with [Fe2(CO)9] in thf affords the compounds [FeRh(µ-CO)2(CO)4(η-C5Me5)] and [Fe2Rh(µ-CO)2(CO)7(η-C5Me5)]. The latter is also formed, together with [FeRh2(µ3-CO)(µ-CO)2(CO)3(µ-C5Me5)2], on treatment of [Rh2(µ-CO)2(η-C5Me5)2] with excess [Fe2(CO)9].The trirhodium complex [Rh3(µ3-CO)(µ-CO)2(η-C5Me5)3] was obtained in high yield by pyrolysis of [Rh(CO)2(η-C5Me5)] and undergoes dynamic behaviour in solution. Protonation of the trirhodium cluster or [Rh2(µ-CO)2(η-C5Me5)2] affords quantitatively the cation [Rh3(µ-H)(µ3-CO)(µ-CO)2(η-C5Me5)3]+ which can be deprotonated with NaOMe in MeOH.

Tris(ethylene)platinum, prepared in situ from [Pt(cod)2](cod = cyclo-octa-1,5-diene), reacts with the compounds [W(CR)(CO)2L] to give the complexes [PtW2(µ-CR)2(CO)4L2](R = Me or Ph, L =η-C5H5; R = Me, Ph, or C6H4Me-4, L =η-C5Me5). The analogous nickel compounds [NiW2(µ-CR)2(CO)4L2] have also been prepared using [Ni(cod)2]. Treatment of the trinuclear metal species [MW2(µ-CR)2(CO)4L2] with one equivalent of [Pt(cod)2] affords the tetranuclear metal compounds [MPtW2(µ-CR)(µ3-CR)(CO)4(cod)L2](M = Ni or Pt, R = C6H4Me-4, L =η-C5H5 or η-C5Me5; M = Pt, R = Me, L =η-C5Me5), while with two equivalents of [Pt(cod)2] the pentanuclear metal complexes [Pt3W2(µ3-CR)2(CO)4(cod)2L2](R = C6H4Me-4, L =η-C5H5; R = Me, L =η-C5Me5) are obtained. These tetra- and penta-nuclear metal compounds were generally isolated as isomeric mixtures, as revealed by n.m.r. measurements (1H, 13C-{1H}, and 195Pt-{1H}). An X-ray diffraction study structurally characterised a symmetrical isomer of [Pt3W2(µ3-CC6H4Me-4)2(CO)4(cod)2(η-C5H5)2], a molecule having a crystallographic two-fold rotation axis. The structure comprises two ‘butterfly’µ3-CPt2W fragments sharing a wing-tip platinum vertex, with isosceles metal triangles [Pt–W 2.751(1) and 2.748(1), Pt ⋯ Pt 3.089(1)A] capped by the CC6H4Me-4 groups. The terminal Pt atoms each carry a cod ligand, and the four CO groups semi-bridge Pt–W bonds. The pentanuclear metal compounds [Pt2W3(µ-CR)2(µ3-CR)(CO)6L3](R = C6H4Me-4, L =η-C5H5; R = Me or C6H4Me-4, L =η-C5Me5), [Pt2W3(µ-CMe)(µ-CC6H4Me-4)(µ3-CMe)(CO)6(η-C5H5)(η-C5Me5)2], and [Pt2W3(µ-CC6H4Me-4)2(µ3-CC6H4Me-4)(CO)6(η-C5H5)(η-C5Me5)2] have also been prepared by treating the appropriate tetranuclear metal compound [Pt2W2(µ-CR)(µ3-CR)(CO)4(cod)L2] with an alkylidynetungsten complex so as to displace the cod ligand. Again isomeric mixtures were produced, and identified by n.m.r. spectroscopy. An X-ray diffraction study established the molecular structure of one of the three isomers of [Pt2W3(µ-CC6H4Me-4)2(µ3-CC6H4Me-4)(CO)6(η-C5H5)3]. The molecule has an essentially planar five-metal atom framework, with two edge-bridging and one triply bridging tolylmethylidyne groups. Four of the six CO ligands semi-bridge W–Pt bonds [W–C–O 163–168(2)A] and each tungsten carries an η-C5H5 group, with each terminal W atom having one linearly bound CO. The Pt ⋯ Pt separation [2.949(2)A] implies little direct metal-metal bonding between these atoms. Bond lengths to the central µ3-CC6H4Me-4 ligand are µ3-C–Pt 2.02(3) and 2.09(2), µ3-C–W 1.99(3)A, while those to the edge-bridging CC6H4Me-4 groups are µ-C–W 1.96(2)(mean) and µ-C–Pt 2.03(2)A(mean).

Treatment of [Mo(CO)5(thf)](thf = tetrahydrofuran) with [CoRh(µ-CO)2(η-C5Me5)2] affords the heterotrimetallic complex [MoCoRh(µ-CO)2(CO)5(η-C5Me5)2]. Variable-temperature 13C-{1H} n.m.r. studies on this species revealed that in solution rotation of the CoRh(µ-CO)2(η-C5Me5)2 fragment occurs about an axis through the Mo and the midpoint of the Co–Rh vector, and that the preferred orientation of the Co–Rh vector with respect to the four equatorial carbonyl ligands of the square-pyramidal Mo(CO)5 moiety is staggered. The estimated barrier to rotation (ΔG‡258= 52.3 ± 1.3 kJ mol –1) is in the range observed and calculated for the hindered rotation of alkenes in related d6 ML5 alkene complexes where, however, the orientational preference of the alkene is to lie so as to eclipse an LML vector. The structure of the analogous trinuclear compound [MoRh2(µ-CO)2(CO)5(η-C5Me5)2] has been determined by a single-crystal X-ray diffraction study. The core of the molecule consists of an MoRh2 isosceles triangle [Mo–Rh (mean) 3.009(1), Rh–Rh 2.623(1)A]. The molybdenum atom carries five carbonyl groups, the rhodium atoms are each ligated by an η-C5Me5 group, and the Rh–Rh vector, staggered with respect to the four equatorial carbonyl groups of the Mo(CO)5 fragment, is symmetrically bridged by two CO ligands. Relatively short non-bonded contacts between the oxygen atoms of the equatorial CO ligands and the hydrogen atoms of the η-C5Me5 groups suggest a significant steric barrier to the ‘alkene-like’ rotation of the Rh2(µ-CO)2(η-C5Me5)2 fragment. Extended-Huckel molecular-orbital calculations on the model species [MoRh2(µ-CO)2(CO)5(η-C5H5)2] indicate that the dirhodium fragment and an alkene bond to an Mo(CO)5 moiety in a similar fashion. However, whereas the barrier to alkene rotation in d6 ML5 alkene complexes derives from electronic effects, no significant electronic contribution to the barrier of rotation of the trinuclear metal complex is indicated.

Cyclo-octatetraenes C8H7R(R = H, Me, Ph, or SiMe3) react with [Ru(SiMe3)2(CO)4] in hexane at reflux to give trimethylsilyl migration products [Ru(SiMe3)(CO)2{C8H7R(SiMe3)}] and ring-closed tetrahydropentalenyl complexes [Ru(SiMe3)(CO)2{C8H8R)}]. The molecular structure of complexes of the former type has been established by a single-crystal X-ray diffraction study of [Ru(SiMe3)(CO)2{C8H8(SiMe3)}]. Crystals are triclinic, space group P with Z= 2 in a unit cell of dimensions: a= 9.972(3), b= 16.082(6), c= 6.662(2)Aα= 89.46(2), β=110.44(2). and γ= 82.46 (2)°. The structure has been determined by heavy-atom methods from diffractometer data and refined to R 0.035 for 3 146 independent reflections The results establish that one SiMe3 group is bonded to ruthenium and one to the C8 ring. The hydrocarbon ligand is co-ordinated to the ruthenium through η3-ally1 and η2-ethylenic interactions within a C8 ring, with another ethylenic bond unco-ordinated. The complex exhibits luxional behaviour in solution, which has been investigated by variable-temperature 1H and 13C n.m.r. spectroscopy. Heating cyclo-octatetraenes C8H7R with [Ru(SiMe3)2(CO)4] in heptane, or heating [Ru(SiMe3)(CO)2{C8H7R(SiMe3)}] directly in heptane or octane, effects ring closure with ejection of the C-bonded SiMe3 group, producing diruthenium pentalene complexes [Ru2(SiMe3)2(CO)4(C8H5R)] in moderate yield. Under mild conditions (hexanereflux)[Ru(GeMe3)2(CO)4] with cyclo-octatetraene yields small amounts of [Ru(GeMe3)(CO)2{C8H8(GeMe3)}] whereas [Ru(SiMe3)(GeMe3)(CO)4] readily gives [Ru(GeMe3)(CO)2{C8H8(SiMe3)}]. In heptane or octane [Ru(GeMe3)2(CO)4] undergoes more complex reactions, affording [Ru(GeMe3)(CO)2(C8H9)], [Ru2(GeMe3)2(CO)4(C8H8)], and [Ru2(GeMe3)2(CO)4(C8H6)]. The mechanism of pentalene-ruthenium complex formation is discussed.

The salts [X][W(CR)(CO)2(η5-C2B9H9Me2)][X = NEt4, R = Ph; X = P(CH2Ph)Ph3 or PPh4, R = C6H4Me-4] have been prepared, and an X-ray diffraction study has been carried out on the tetraphenylphosphonium compound. There are two very similar crystallographically independent anions, together with their associated counter ions, in the asymmetric unit of the structure. In the anion the tungsten atom carries two terminally bound carbonyl ligands (W–CO mean 2.019 A, W–C–O mean 176.9°), a p-tolylmethylidyne ligand [WCC6H4Me-4 mean 1.83(3)A], and the η5-7,8-C2B9H9Me2 cage [mean W–ligated cage atoms, 2.424 A(mean of 10)]. Treatment of the species [X][W(CR)(CO)2(η5-C2B9H9Me2)][X = P(CH2Ph)Ph3, R = C6H4Me-4; X = NEt4, R = Ph] in thf (tetrahydrofuran) with [Pt(cod)2](cod = cyclo-octa-1,5-diene) affords the complexes [P(CH2Ph)Ph3][PtW(µ-CC6H4Me-4)(CO)2(cod)(η5-C2B9H9Me2)](2a) and [NEt4][PtW(µ-CPh)(CO)2(cod)(η5-C2B9H9Me2)](2b), respectively. The cod ligand in the compounds (2) may be displaced with tertiary phosphines, but crystalline products were not obtained. Moreover, protonation of (2) led to decomposition. However, treatment of (2a) with [AuCl(PPh3)] and TIPF6, and (2b) with the gold reagent and KPF6, in thf, affords the trimetal compounds [AuPtW(µ3-CR)(CO)2(PPh3)(cod)(η5-C2B9H9Me2)](R = C6H4Me-4 or Ph), which were fully characterised. The n.m.r. data (1H, 13C-{1H}, 195Pt-{1H}, and 31P-{1H}) for the complexes are reported.

Treatment of di-µ-chloro-dichlorobis(η-ethylene)diplatinum with Mg(C5H5)2 affords the compounds [Pt(η-C2H4)(σ-C5H5)(η-C5H5)] and [Pt2(µ-C10H10)(η-C5H5)2]. Reaction between [NBun4]2[Pt2Cl4(CO)2] and Mg(C5H5)2 affords [Pt2(CO)2(η-C5H5)2] in good yield, as well as the compound [Pt(CO)(σ-C5H5)(η-C5H5)]. Protonation of [Pt(η-C2H4)(σ-C5H55)(η-C5H5)] yields the salt [Pt(η-C2H4)(η2-C5H6)(η-C5H5)][BF4]. Reaction of [Pt(η-C2H4)(σ-C5H5)(η-C5H5)] with PhCCPh affords (η-cyclopentadienyl)(σ: 2–3-η-2,3-diphenylbicyclo[2.2.1 ] hepta-2,5-dien-7-yl) platinum. The compound [Pt2(CO)2(η-C5H5)2] on treatment with PhCCPh in the presence of Me3NO gives [Pt2{µ-C(Ph)C(Ph)C(O)}(η-C5H5)2], and on similar treatment with ButCCBut and Me3NO affords [Pt2(µ-ButC2But)(η-C5H5)2]. The complex [Pt2{µ-C(Ph)C(Ph)C(O)}(η-C5H5)2] was structurally characterised by a single crystal X-ray diffraction study. The metal–metal bond [Pt–Pt 2.590(1)A] is bridged by the C(Ph)C(Ph)–C(O) ligand, in such a manner that the terminal carbon atoms are each σ-bonded to one platinum centre, while the C(Ph)C(Ph) fragment is η2-co-ordinated to the other. Both metal atoms carry C5H5 ligands, but one is asymmetrically bound. The n.m.r. data (1H, 31C-{1H}, and 195Pt-{1H}) for the new compounds are reported and discussed, and this information used to suggest mechanisms for the dynamic behaviour of [Pt(η-C2H4)(σ-C5H5)(η-C5H5)], [Pt2(CO)2(η-C5H5)2], and [Pt(η-C2H4)(η2-C5H6)(η-C5H5)]+.

The compounds [W(CR)(CO)2(η-C5H5)](R = C6H4Me-4 or Me) and [[graphic omitted]H2}(η-C5H5)2] react in toluene, in the presence of tetrahydrofuran, to afford the bridged vinyl complexes [TiW{µ-C(R)CH2}(µ-CO)(CO)(η-C5H5)3]. The compound with R = C6H4Me-4 may also be prepared by treating [TiW(µ-CC6H4Me-4)(µ-CO)(CO)(µ-C5H5)3] with the titanium reagent. It has been structurally characterised by X-ray diffraction. The Ti–W bond [3.082(2)A] is spanned by a σ:η2-CO ligand [W–C–O 173.4(3)°, Ti–C 2.222(4), Ti–O– 2.285(3)A] and by a σ:η2-C(C6H4Me)CH2 group, σ bonded to titanium and η2 co-ordinated to tungsten [Ti–C 2.290(4), CC 1.441(6), W–C 2.199(5) and 2.268(6)A]. The tungsten atom carries a terminally bound CO ligand and a C5H5 group, and the titanium atom is ligated by two C5H5 groups. Reactions between the dimetal compounds [PtW(µ-CR)(CO)2(PMe3)2(η-C5H5)] and [[graphic omitted]H2}(η-C5H5)2] afford the complexes [PtW{µ-C(R)CH2}(CO)2(PMe3)2(η-C5H5)]. An X-ray diffraction study on the platinum–tungsten species with R = C6H4Me-4 established the structure as one in which the Pt–W bond [2.820(1)A] is bridged by a C(C6H4Me-4)CH2 group, as in the titanium–tungsten compound, being σ bonded to the platinum and η2 co-ordinated to the tungsten. The metal–metal bond is semi-bridged by one CO ligand [W–C–O 166(1)°], while the remaining CO is terminally bound to tungsten, which also carries the C5H5 group. The platinum is ligated by two PMe3 ligands, and is in a distorted square-planar environment defined by the two phosphorus atoms, and the µ-C atoms of the semi-bridging carbonyl and the vinyl group. Spectroscopic properties of the new dimetal compounds are reported, and their mechanisms of formation discussed in the light of 1H and 13C-{1H} n.m.r. studies on reaction mixtures.

The mononuclear manganese–carbene complex [Mn{C(OMe)Ph}(η-C5H5)(CO)2] reacts with the compound [Pt(cod)2](cod = cyclo-octa-1,5-diene) to give the dimetal complex [(OC)2(η-C5H5)[graphic omitted]t(cod)]. Similarly, [Pt(C2H4)3], [Pd(dba)2](dba = dibenzylideneacetone), and [Ni(cod)2], each treated with 2 mol of PMe3, react with the mononuclear manganese compound to yield heteronuclear dimetal complexes [(OC)2(η-C5H5)[graphic omitted](PMe3)2](M = Ni, Pd, or Pt). The PMe3 ligand trans to the µ-C(OMe)Ph group in the palladium and platinum compounds is readily replaced by CNBut. The binuclear manganese–carbene complex [(OC)5Mn–Mn([graphic omitted])(CO)4] reacts with [Pt(C2H4)3], treated with 2 mol of PMe3, to form two crystalline forms of a compound [(OC)4[graphic omitted]t(PMe3)2]. Single-crystal X-ray diffraction studies have been carried out (200 K) on these geometrical isomers. The red form is monoclinic, space group P21/n, Z= 4, in a unit cell with lattice parameters a= 9.357(5), b= 12.844(10), c= 15.989(9)A, and β= 98.14(4)°. The structure has been refined to R 0.023 (R′ 0.030) for 3 274 reflections to 2θ⩽ 50°(Mo-KαX-radiation). The yellow form is triclinic, space group P, Z= 2, in a unit cell with lattice parameters a= 9.429(5), b= 12.113(4), c= 9.729(6)A, α= 93.97(14), β= 115.45(4), and γ= 98.83(3)°. The structure has been refined to R 0.055 (R′ 0.073) for 3 350 reflections to 2θ⩽ 50°(Mo-KαX-radiation). In both isomers a cyclic 1-σ,1–2-η-[graphic omitted] ligand bridges a platinum–manganese bond such that the manganese atom is η2-co-ordinated by the CCH group, which is σ-bonded to the platinum. The two forms differ in the relative orientation of some least-squares planes involving various groups of atoms comprising the molecules and in the Mn–Pt distances [2.6909(7)A red form, 2.659(2)A yellow form]. The 1H, 13C, and 31P n.m.r. spectra of the various compounds are discussed.

Treatment of a mixture of the salts [N(PPh3)2][W2{µ-CH(C6H4Me-4)}(CO)7(η-C5H5)] and TIPF6 in tetrahydrofuran (thf) with [AuCl(PPh3)] affords the bridged p-tolylmethylidene complex [AuW{µ-CH(C6H4Me-4)}(CO)2(PPh3)(η-C5H5)], the structure of which has been established by a single-crystal X-ray diffraction study. As expected, the Au–W bond [2.729(1)A] is spanned by the CH(C6H4Me-4) group. The µ-C–W separation is relatively short [2.058(14)A] whereas the µ-C–Au distance is relatively long [2.268(14)A]. To account for these features a three-centre two-electron µ-C–Au–W interaction is postulated. Addition of [Au(PR′3)]+[PR′3= PPh3 or P(cyclo-C6H11)3] fragments, generated in situ from [AuCl(PR′3)] and TIPF6 in dichloromethane, to the alkylidynetungsten compounds [W(CR)(CO)2(η-C5H5)](R = C6H4Me-4 or Me) affords the salts [AuW(µ-CR)(CO)2(PR′3)(η-C5H5)][PF6][R = C6H4Me-4, PR′3= PPh3or P(C6H11)3; R = Me, PR′3= PPh3]. N.m.r. studies (1H, 31P-{1H}, and 13C-{1H}) on solutions of these salts, however, reveal that the cations dissociate, affording equilibrium mixtures containing the species [Au{W(CR)(CO)2(η-C5H5)}2]+ and [Au(PR′3)2]+. The trimetal compound [AuPtW(µ3-CR)(CO)2(PMe3)3(η-C5H5)][PF6](R = C6H4Me-4) has been prepared by two routes: from the reaction between [Au{W(CR)(CO)2(η-C5H5)}2][PF6] and [Pt(C2H4)(PMe3)2], and by addition of [Au(thf)(PMe3)][PF6] to [PtW(µ-CR)(CO)2(PMe3)2-(η-C5H5)]. The structure of [AuPtW(µ3-CR)(CO)2(PMe3)3(η-C5H5)][PF6] has been established by X-ray crystallography. A triangular array of metal atoms [Au–W 2.801 (2), Au–Pt 2.956(2), and Pt–W 2.770(2)A] is asymmetrically bridged by the CR ligand [µ3-C–Au 2.21 (4), µ3-C–Pt 1.97(4), and µ3-C–W 2.01 (4)A]. The Au–Pt separation suggests that there is little or no direct metal–metal bonding between these two metal atoms. The tungsten atom carries the cyclopentadienyl ligand and two CO groups, but the latter are appreciably non-linear. The gold and platinum atoms are ligated by one and two PMe3 groups, respectively.

Treatment of [W(CC6H4Me-4)(CO)2(η-C5H5)] with [N(PPh3)2][WH(CO)5] in thf (tetrahydrofuran) affords the salt [N(PPh3)2][W2{µ-C(H)C6H4Me-4}(CO)7(η-C5H5)], the structure of which has been established by X-ray diffraction. In the anion, the W–W bond [3.111 (1)A] is asymmetrically spanned by the C(H)C6H4Me-4 group [µ-C–W 2.127(7) and 2.436(8)A]. One tungsten atom carries five CO groups at octahedral sites around the metal, while the other tungsten atom is ligated by two CO groups and the cyclopentadienyl ring. The latter and the tolyl group are positioned on opposite sides of the µ-CW2 ring. The reaction between [AsPh4][WH(CO)5] and [W(CMe)(CO)2(η-C5H5)] affords [AsPh4][W2{C(H)Me}(CO)7(η-C5H5)], and evidence was obtained for the existence in related syntheses of the anions [MW{µ-C(H)C6H4Me-4}(CO)6(L)(η-C5H5)]–[M = Cr, L = CO; M = W, L = P(OMe)3]. Treatment of [W2{µ-C(H)C6H4Me-4}(CO)7(η-C5H5)] with SnPh3Cl in thf affords the stable alkylidene complex [W{C(H)C6H4Me-4}(SnPh3)(CO)2(η-C5H5)], the structure of which has been established by a single-crystal X-ray diffraction study. The W–C and W–Sn separations are 2.032(7) and 2.837(1)A, respectively, with the SnPh3 and C(H)C6H4Me-4 groups in a transoid configuration. The molecule is orientated such that the alkylidene hydrogen substituent is adjacent to the cyclopentadienyl ligand. The n.m.r. data for the new compounds are reported and discussed.

Reactions between the poly(pyrazol-1-yl)borato-salts K[R′B(pz)3](pz = C3H3N2; 1a, R′= C3H3N2; 1b, R′= H) and the bromo(alkylidyne)tungsten complexes [W(CR) Br(CO)4] afford the compounds [W(CR)(CO)2{R′B(pz)3}](2a, R = C6H4Me-4, R′= C3H3N2; 2b, R = C6H4Me-4, R′= H; 2c, R = Me, R′= H). The structure of (2a) has been established by X-ray diffraction. The tungsten atom is in an essentially octahedral environment ligated by two CO groups, the alkylidyne fragment CC6H4Me-4 [CW 1.821(7)A], and the [B(pz)4]– anion functioning as a tridentate ligand. Interestingly, the three N-W distances in the latter are not equal, that trans to the alkylidyne carbon being significantly longer [2.284(6)A] than those traps to the CO ligands [2.219(6) and 2.186(5)A]. The compounds (2) have been used to prepare the cluster complexes [Co2W(µ3-CR)(CO)8-{R′B(pz)3}][3a, R = C6H4Me-4, R′= C3H3N2; 3b, R = C6H4Me-4, R′= H; 3c, R = Me, R′= H), [RhW(µ-CC6H4Me-4)(CO)3(η-C9H7){HB(pz)3}](4), [Rh2W(µ3-CR)(µ-CO)(CO)2(η-C9H7)2{HB(pz)3}](5a, R = C6H4Me-4; 5b, R = Me), [FeRhW(µ3-CR)(µ-CO)(CO)5(η-C9H7){HB(pz)3}](6a,R = C6H4Me-4; 6b, R = Me), and [PtW(µ-CC6HaMe-4)(CO)2(L)(PMe3){HB(pz)3}](8a, L = PMe3; 8b, L = CO). The structure of (5a) was determined by X-ray diffraction. The almost isosceles metalatom triangle [Rh–Rh 2.646(2), Rh–W mean 2.848 A] is capped by the tolylmethylidyne group [µ3-C–Rh mean 2.072, µ3-C–W 2.010(6)A]. The Rh–Rh bond is symmetrically bridged by a CO ligand, and the two carbonyl groups on tungsten semibridge the two Rh–W bonds [W–C–O 168.0(6) and 164.5(6)°]. The indenyl group attached to each rhodium shows slippage to an η3-bonding mode. The tridentate tris(pyrazol-1-yl)borato ligand is co-ordinated to the tungsten with the N–W separation [2.245(5)A]transoid to the alkylidyne carbon being somewhat longer than the other two N–W distances [mean 2.222 A]. The trimetal compounds (6) react with but-2-yne to give the alkylidyne- and alkyne-bridged complexes [FeRhW(µ3-CR)(µ-MeC2Me)(CO)4(η-C9H7){H B(pz)3}](7a, R = C6H4Me-4; 7b, R = Me); the structure of (7a) being established by X-ray diffraction. The metal atoms form a triangle [Fe–Rh 2.577(2), Fe–W 2.756(2), Rh–W 2.677(2)A] the face of which is bridged asymmetrically by the µ3-CC6H4Me-4 ligand [µ3-C–Fe 1.926(3), µ3-C-Rh 2.202(4), µ3-C–W 2.042(4)A]. The Rh–W edge is bridged transversely on the opposite face of the triangle by the MeCCMe ligand. The iron atom carries three terminal carbonyl groups, while the remaining CO attached to the tungsten semibridges the Fe–W bond [W–C–O 165.3(4)°]. The [HB (pz)3]– ligand is bonded to the tungsten with three essentially equal N–W distances, while the indenyl group on the rhodium shows the customary slippage towards η3 bonding. The spectroscopic properties (i.r. and n.m.r.) of the new compounds are reported and discussed.

The compounds MCl3(M = Al, Ga, or In) yield electrically conducting solutions in acetonitrile. Boron trichloride gives non-conducting solutions and, contrary to previous work, this is interpreted as due to the presence of a molecular solute BCl3·MeCN. The electrical-conductivity data for AlCl3 in acetonitrile are discussed in detail and it is shown that from the results obtained it is not possible to differentiate between 1 : 1 and 1 : 2 electrolyte behaviour. Quantitative Raman and 27Al n.m.r. spectra demonstrate that ca. 70% of the aluminium in solutions of AlCl3 in acetonitrile is present in the form of [AlCl4]–. An X-ray single-crystal study of the solid adduct AlCl3·2MeCN crystallizing from such a solution shows that this adduct is correctly formulated as the auto-complex [AlCl(NCMe)5]2+2[AlCl4]–·MeCN. Further 27Al n.m.r. studies on solutions of Al[ClO4]3 in acetonitrile and of the solute AlCl[ClO4]2, in conjunction with the work on AlCl3 demonstrate that [AlCl(NCMe)5]2+ is the major cationic constituent of aluminium trichloride solutions in acetonitrile. The electrical-conductivity, Raman, and n.m.r. data on these solutions are all satisfactorily interpreted by the principal ionization scheme [AlCl(NCMe)5]2+2[AlCl4]– which is the formulation found for the crystal. The ionization of AlCl3, but the non-ionization of BCl3, in solution in acetonitrile is attributed principally to the ability of aluminium to adopt a co-ordination number of greater than four in ions such as [AlCl(NCMe)5]2+.

Purple crystals of the compound [RuW(µ-Cl)(µ-CMe)(Cl)(CO)2(PPh3)2(η-C5H5)] are obtained by placing a diethyl ether solution of [W(CMe)(CO)2(η-C5H5)] above a tetrahydrofuran (thf) solution of [RuCl2(PPh3)3]. The ruthenium–tungsten complex has been characterised by an X-ray diffraction study. The Ru–W bond [2.769(1)A] is spanned by the Cl and CMe ligands [C–W 1.942(11), C–Ru 2.021(9), Ru–Cl 2.447(3), W–Cl 2.497(3)A]. In addition to the cyclopentadienyl ligand the W atom carries terminal Cl and CO ligands which exhibit a positional disorder between two effectively interchangeable sites in the complementary ratios 3: 1. The ruthenium atom is ligated by two PPh3 groups and a CO group. Treatment of the ruthenium–tungsten complex with MeCCMe affords [RuW(µ-Cl)(µ-CMe)(Cl)(CO)2(PPh3)(η-C2Me2)(η-C5H5)], possible structures for which are discussed on the basis of n.m.r. data. The compound [W(CMe)(CO)2(η-C5H5)] reacts with the species [Ru(CO)n(PPh3)5–n](n= 2 or 3) to afford an insoluble trimetal complex [RuW2(µ3-C2 Me2)(CO)6(PPh3)(η-C5H5)2]. The PPh3 group in the latter may be displaced with CO or PEt3 to give the species [RuW2(µ3-C2Me2)(CO)6(L)(η-C5H5)2](L = CO or PEt3), but the reaction with CO is reversed unless the PPh3 is removed by complexation. The structure of the heptacarbonyl complex has been established by X-ray diffraction. The molecule has a triangular metal core [Ru–W 3.026(1) and 2.835(1), W–W 2.944(1)A] bridged by the MeCCMe ligand in such a manner that the alkyne lies essentially parallel to one of the Ru–W vectors. Hence this ligand is σ bonded to the ruthenium atom and to one tungsten centre [C–RU 2.068(9), C–W 2.169(9)A] while being η2 co-cordinated to the other tungsten atom [C–W mean 2.281 (9)A]. The ruthenium atom carries three terminally bound CO ligands, while the tungsten atoms are each ligated by a C5H5 and two CO groups. Three of the four CO ligands bound to tungsten semi-bridge the edges of the metal–atom triangle. The complexes [RuW2(µ3-C2Me2)(CO)6(L)(η-C5H5)2] undergo dynamic behaviour in solution, as revealed by n.m.r. studies.

Ultra-violet irradiation of diethyl ether solutions of [Fe(CNR)5](R = Et or Pri) affords the dinuclear complexes [Fe2(CNR)9]. In contrast, sodium amalgam reduction of trans-[RuCl2(CNPri)4] in the presence of an excess of isopropyl isocyanide affords directly [Ru2(CNPri)9]. In order to establish the molecular structure of these dimetal complexes, an X-ray diffraction study was carried out on [Fe2(CNEt)9], crystals of which are monoclinic, space group P21/n, Z= 4, in a unit cell with lattice parameters a= 22.193(14), b= 12.762(6), c= 12.332(8)A, and β= 104.60(5)°. The structure has been refined to R 0.08 (R′ 0.11) for 3 062 observed intensities to 2.9 ⩽ 2θ⩽ 50°(Mo-KαX-radiation) collected at 223 K. The structure is similar to that previously established for [Fe2(CO)9], i.e. two iron atoms separated by 2.461 (2)A are spanned by three isocyanide ligands in bridging modes, while the remaining isocyanide molecules are terminally bound, three to each metal atom. Whereas for the terminal ligands the angles C–N–C range over 165–179°, for the bridging groups the angles C–N–C are 123(1)°. In the bridge system one ligand bends at its nitrogen atom in a direction anti with respect to the other two CNEt groups, with the Fe–C distances syn to the ethyl groups being ca. 0.03 A longer than those which are anti. Examination of the 1H and 13C n.m.r. spectra of the di-iron and -ruthenium complexes at various temperatures reveals dynamic behaviour in solution involving bridge–terminal isocyanide exchange with ΔGTc‡= 63 ± 1, 65 ± 1, and 61 ± 1 kJ mol–1 for [Fe2(CNEt)9], [Fe2(CNPri)9], and [Ru2(CNPri)9] respectively, this process occurring via synchronous pair-wise exchange with inversion at nitrogen. Reaction of [Fe2(CNEt)9] with methyl or ethyl iodide affords salts [Fe2-(CNEt)7{CNEt(R)}2]l2(R = Me or Et), which are formulated as having bridging carbyne ligands. Ultraviolet irradiation of solutions of [Fe(CNBut)5] yields trans-[Fe(CN)2(CNBut)4], whereas in the presence of cyclo-octatetraene the complex [Fe(CNBut)3(η4-C8H8)] is produced.

Reactions between [RuX(PPh3)2(η-C5H5)](X = H, Me, or CH2Ph) and the alk-1-ynes RC2H (R = CO2Me, COMe, CF3, or C6F5) have given products resulting from interaction of one, two, or three alkyne molecules per molecule of ruthenium complex. Methyl propiolate and the hydrido-compound afford the η1-alkynyl complex [Ru(C⋮CCO2Me)(PPh3)2(η-C5H5)], the 1,3,4-η3-buta-1,3-dienyl complex [[graphic omitted]CH(CO2Me)}-(PPh3)(η-C5H5)], and the 1,4,5-η3-penta-1,3,4-trienyl complex [[graphic omitted]CMe-(CO2Me)}(PPh3)(η-C5H5)]. The methyl- and benzyl-ruthenium complexes give only the corresponding η3-but-adienyl complexes. Ethynyl methyl ketone and the methylruthenium complex afforded [[graphic omitted]-Me]:CHMe}(PPh2)(η-C5H5)]. The structure of the 1,3,4,5-tetraenyl complex [[graphic omitted]C:CHCF3}(PPh3)(η-C5H5)], obtained from HC2CF3 and [RuMe(PPh3)2(η-C5H5)], was determined by a single crystal X-ray study. This shows that the acetylenic fragments have joined head-tail, head-tail, tail-head, and that whereas the first carbon atom of the chain (head, carrying a CF3 group) is directly bonded to the ruthenium atom, the other attachment is an η-interaction at the tail-tail juxtaposition. The whole unsaturated system, including the metal atom, is essentially planar.The product [[graphic omitted]Ph2}(η-C5H5)] from HC2C6F5 and the hydride contains a 10-membered RuPC8 heterocycle. Possible mechanisms for the formation of these complexes are discussed.

The reaction between [Pt3W4(µ-CC6H4Me-4)2(µ3-CC6H4Me-4)2(CO)8(η-C5H5)4] and [Pt(cod)2](cod = cyclo-octa-1,5-diene) in tetrahydrofuran (thf) affords the compound [Pt4W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4]. The latter may also be obtained from the reaction between the tetranuclear metal cluster [Pt2W2(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(cod)(η-C5H5)2] and ethylene under pressure. The structure of [Pt4W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4] has been established by X-ray diffraction. The molecule has a ring of eight metal atoms with the four platinum and four tungsten atoms in alternating positions, such that the tungsten atoms form the four points of a ‘star’, and the platinum atoms lie in an essentially square arrangement (mean Pt ⋯ Pt 2.954, mean Pt–W 2.754 A). Three of the tolylmethylidyne groups triply bridge Pt2W triangles, while the fourth edge-bridges a Pt–W bond. Two of the µ3-CC6H4Me-4 groups lie on one side of the Pt4W4 ring, while the third is on the other side. On this side also a CO ligand asymmetrically bridges the Pt2W triangle which in a symmetrical isomer would have been occupied by a µ3-CC6H4Me-4 fragment. One CO group bridges the Pt–W bond adjacent to that spanned by the edge-bridging tolylmethylidyne ligand. The remaining six carbonyl groups semi-bridge the other six Pt–W bonds. The reaction between the trimetal compound [PtW2(µ-CC6H4Me-4)2(CO)4(η-C5H5)2] and an excess of [Ni(cod)2] affords the compound [Ni2Pt2W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4]. The latter is formed as a mixture of two isomers by interchange of the platinum and nickel sites. In one isomer a tolylmethylidyne ligand edge-bridges a Ni–W bond, and in the other a Pt–W bond. An X-ray diffraction study showed that in the crystal both isomers are present, leading to disorder at the nickel and platinum sites. In the Ni2Pt2W4 rings there is a trans-Ni ⋯ Ni and a trans-Pt ⋯ Pt arrangement, as expected from the mode of synthesis. Treatment of [PtW2(µ-CPh)2(CO)4(η-C5H5)2] with an excess of [Ni(cod)2] yields an octanuclear Ni2Pt2W4 metal complex formed as a separable mixture of three isomers: [Ni2Pt2W4(µ-CPh)(µ3-CPh)3(µ-CO)(CO)7(η-C5H5)4](two isomers) and [Ni2Pt2W4(µ3-CPh)4(CO)8(η-C5H5)4]. An X-ray diffraction study on the latter species confirmed the presence of the eight-membered metal ring in which four tungsten atoms are at the points of a ‘star’ and there is a central Ni ⋯ Pt ⋯ Ni ⋯ Pt fragment. Four CPh ligands triply bridge the NiPtW triangles, two lying above the mean plane through the eight metal atoms, and two below this plane. The structure has a crystallographic two-fold axis through the centre of the ring. A cluster compound [NiPt3W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4](two isomers) has been prepared by addition of [Ni(cod)2] to the seven-metal-atom chain complex [Pt3W4(µ-CC6H4Me-4)2(µ3-CC6H4Me-4)2(CO)8(η-C5H5)4]. In thf at reflux temperatures, the species [Pt4W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4] and [Ni2Pt2W4(µ-CR)(µ3-CR)3(µ-CO)(CO)7(η-C5H5)4](R = Ph or C6H4Me-4) readily isomerise to their respective symmetrical forms with four triply bridging alkylidyne groups. The 13C-{1H} and 195Pt-{1H} n.m.r. data for the various compounds are reported, and are discussed in relation to the molecular structures.

A series of complexes [Pt(η2-quinone)(C2H4){P(cyclo-C6H11)3}] has been prepared by treating [Pt(C2H4)2{P(cyclo-C6H11)3}] with benzo-1,4-quinones. Carbon-13 n.m.r. studies on the compounds containing the ligands 2,3-dimethyl-, 2,5-dimethyl-, 2,5-diphenyl-benzo-1,4-quinone, and naphtho-1,4-quinone revealed that although the C2H4 group is undergoing rapid rotation, the η2-bonded quinone is rigid on the n.m.r. time scale. In contrast, in the derivatives from 2,6-dimethyl-, 2,6-di-t-butyl-, 2,6-dimethoxy-, and 2,3,5,6-tetramethyl-benzo-1,4-quinone, the quinone ligands are also undergoing dynamic behaviour. The η2 ground-state structure was established by an X-ray diffraction study on the compound [Pt(η2-C6Me4O2)(C2H4){P(cyclo-C6H11)3}]. Crystals are triclinic, space group P, Z= 2, in a unit cell with lattice parameters a= 9.818(3), b= 10.489(3), c= 14.486(3)A, α= 97.27(2), β= 97.93(2), and γ= 91.33(3)°. The structure has been refined to R 0.027 (R′ 0.033) for 6 467 independent reflections collected at 200 K for 2.9 ⩽ 2θ⩽ 55°(Mo-KαX-radiation). The results establish that the 2,3,5,6-tetramethylbenzo-1,4-quinone ligand is attached to the platinum by two carbon atoms of one C(Me)C(Me) group, and the metal is in a trigonal planar environment with the midpoint of this group, the phosphorus atom, and the midpoint of the C–C bond of the ethylene ligand, with all these co-ordinated atoms lying within 0.1 A of the co-ordination plane.

Reaction of [Fe(CNBut)5] with MeI in thf (tetrahydrofuran) affords [[graphic omitted]But}(CNBut)3], whereas with diethyl ether as solvent the salt [FeMe(CNBut)5]I is formed, which on dissolving in thf is transformed into the former product. Cationic complexes [Fe(CH2CHCH2)(CNBut)5]X are formed on reaction of [Fe(CNBut)5] in thf with allyl halides or benzyl bromide. However, EtI, EtBr, PriI, and [Me3O][BF4] afford η2-iminoacyl complexes [[graphic omitted]But}(CNBut)4]X. Reaction of [Fe(CNC6H3Me2-2,3)5] with MeI or EtI gives [FeI{C(R)N(C6H3Me2-2,3)}(CNC6H3Me2-2,3)4]. n-Heptafluoropropyl iodide and bromopentafluorobenzene readily react with [Fe(CNBut)5] to give [FeI{CF(CF3)2}(CNBut)4] and [Fe(C6F5)(CNBut)5]Br respectively. Diphenylacetylene reacts with [Fe(CNBut)5] to give [Fe(CNBut)3{1–4-η-C(NBut)C(Ph)C(Ph)C(NBut)}], which was structurally identified by a single-crystal X-ray diffraction study. The crystals are monoclinic, space froup P21/c, Z= 4 in a unit cell of dimensions a= 9.724(4), b= 42.11(3), c= 11.330(4)A, β= 113.57(5)7°. The structure has been refined to R= 0.092 (R′= 0.123) for 4 327 reflections to 2.9 ⩽ 2θ⩽ 50.0° at 183 K. The dynamic behaviour of the complex in solution and its mode of formation are discussed.

The compound [Rh2(µ-CO)2(η-C5Me5)2] reacts with [Pt(C2H4)3] to give the pentanuclear cluster complex [PtRh4(µ-CO)4(η-C5Me5)4], the structure of which has been established by X-ray diffraction. Crystals grown from light petroleum–dichloromethane belong to the monoclinic system but on cooling to 200 K and rewarming to room temperature undergo an irreversible phase change to the orthorhombic system. Data were collected for both phases: (I) orthorhombic, space group Pnma, with Z= 4 in a unit cell of dimensions a= 17.945(5), b= 17.978(6), and c= 13.764(4)A; (II) monoclinic, space group A2a, with Z= 4, a= 17.826(4), b= 13.944(3), c= 18.112(5)A, and β= 97.19(2)°. Intensities were measured to 2θ⩽ 45° for (I) and to 2θ⩽ 40° for (II), and were refined for (I) to R 0.048 (R′ 0.050) and for (II) to R 0.066 (R′ 0.070) for 1 606 and 1 718 independent reflections respectively. The two molecules have very similar structures, based on the platinum atom being ‘co-ordinated’ to two Rh2(µ-CO)2(η-C5Me5)2 fragments. The four rhodium atoms are disposed around the platinum in an essentially tetrahedral arrangement, with the dihedral angles between the PtRh2 planes being 90°for (I) and 100° for (II). In both molecules the PtRh2 groups form essentially equilateral triangles [Rh–Rh(mean) and Pt–Rh(mean) 2.618(2)A]. The four CO ligands, in addition to bridging the Rh–Rh vectors, weakly interact with the platinum atom, a feature which persists in solution, as deduced from 195Pt–13C coupling observed in the 13C n.m.r. spectrum of [PtRh4(µ-CO)4(η-C5Me5)4].

Reaction of t-butyl isocyanide with bis(cyclo-octa-1,5-diene)platinum gives the orange crystalline complex [Pt3(ButNC)6] in essentially quantitative yield. Methyl, ethyl, and cyclohexyl isocyanides react with [Pt(1,5-C8H12)2] in a similar manner to give [Pt3(RNC)6](R = Me, Et, or C6H11). The structural identity of [Pt3(ButNC)6] has been established by analysis of single-crystal X-ray data recorded at room temperature on a four-circle diffractometer. The complex is monoclinic, space group P21/n, Z= 4, a= 18.213(7), b= 11.811 (5), c= 21.996(6)A, β= 110·21(3)°. Using 3 543 reflections, the refinement has converged to R 0.057 (R′0.070). The molecule contains an essentially equilateral triangle of platinum atoms each of which carries a terminal isocyanide ligand, with the remaining three isocyanide groups bridging the sides of the triangle. The former are effectively linear and the latter bent [CNC(mean) 132.7°]. The platinum atoms and the six attached carbon atoms are effectively coplanar with maximum deviation 0.08 A. Hydrogen-1 and 13C n.m.r. studies between room temperature and 120 °C reveal that [Pt3(ButNC)6] undergoes dynamic behaviour via an intermolecular process involving terminal and bridge isocyanide site exchange catalysed by free ligand.

The compounds [Os3Pt(µ-H)2(CO)10(PR3)] react with CO, PPh3, or AsPh3 to give complexes [Os3Pt(µ-H)2(CO)10(PR3)L][PR3= P(cyclo-C6H11)3, L = CO; PR3= PPh3 or AsPh3]. Hydrogen-1 and 31P n.m.r. data for the compounds are discussed, and a single-crystal X-ray diffraction study has been carried out on the compound [Os3Pt(µ-H)2(CO)10(PPh3)2], crystals of which are triclinic, space group P1, Z= 2, in a unit cell with lattice parameters a= 14.427(7), b= 12.793(5), c= 14.151(6)A, α= 92.33(3), β= 120.87(3), and γ= 91.06(4)°. The structure has been refined to R 0.041 (R′ 0.044) for 5 794 independent reflections (2.9 ⩽ 2θ⩽ 60°, Mo-KαX-radiation) collected at 200 K. The four metal atoms adopt a butterfly arrangement in contrast to the tetrahedral cluster structure of the 58-electron precursors [Os3Pt(µ-H)2(CO)10(PR3)]. In [Os3Pt(µ-H)2(CO)10(PPh3)2] the metal–metal bonding distances are Os–Pt 2.717(1) and 2.848(1)A, and Os–Os 2.773(1), 2.914(1), and 3.043(1)A. Evidence is presented for the two hydrido-ligands bridging the longer Os–Pt and Os–Os bonds. One triphenylphosphine ligand is attached to platinum and the other to osmium, and all the carbonyl ligands are terminally bound. Reaction of [Os3Pt(µ-H)2(CO)10(PPh3)] with but-2-yne affords a mixture, from which five polynuclear metal complexes were isolated and studied by i.r. and n.m.r. spectroscopy. None of these products contained the Os3Pt cluster of the precursor. One of the complexes was characterised as [OsPt2(CO)5(PPh3)2(µ3-MeC2Me)] and its structure established by X-ray diffraction. Crystals are monoclinic, space group P21/c, Z= 4, in a unit cell of dimensions a= 11.143(8), b= 17.458(12), c= 23.443(15)A, and β= 113.82(5)°. The structure has been refined to R 0.031 (R′ 0.033) for 4 438 independent reflections (2.9 ⩽ 2θ⩽ 55°, Mo-KαX-radiation) collected at 200 K. The metal atoms form an isosceles triangle [Os–Pt 2.662(2)(mean), Pt–Pt 3.033(2)A] bridged by a face-bonding but-2-yne molecule whose orientation with respect to the triangle is µ3(η2-‖). The osmium atom carries three terminal CO ligands, and each platinum a CO and PPh3 group such that there is a cisoid arrangement OCPtPtCO; the Pt–Pt separation of 3.033(2)A, however, suggests that there may be little direct metal–metal interaction.

Tetraethylammonium or bis (triphenylphosphine)iminium salts of the anion [Fe2(µ-H)(µ-CO)2(CO)6]– react with the complex [Pt(C2H4)2(PPh3)] in tetrahydrofuran to give the di-irondiplatinum compounds [R][Fe2Pt2(µ-H)-(µ-CO)3(CO)5(PPh3)2][R = NEt4+ or N(PPh3)2+]. The structure of the N(PPh3)2+ salt was established by a single-crystal X-ray diffraction study; the crystals are monoclinic, space group P21/c, Z= 4, in a unit cell with lattice parameters a= 25.05(3), b= 14.28(1), c= 23.99(2)A, and β= 106.84(7)°. The structure has been refined to R 0.059 (R′ 0.061) for 8 768 independent reflections to 2θ⩽ 50°[(Mo-Kα)X-radiation] collected at 200 K. The N (PPh3)2+ cation is bent [P–N–P 138.1(8)°], while the metal framework of the anion consists of a cluster of Fe2Pt2 atoms [Pt–Pt 2.966(1); Pt–Fe 2.756(2), 2.626(2), 2.555(2), and 2.562(2); Fe–Fe 2.522(2)A], arranged such that a Fe2 Pt triangle, edge-bridged by three CO ligands, is capped by a platinum atom carrying a terminal CO ligand and PPh3 group. The four remaining CO ligands are terminally bonded in pairs to the two iron atoms, while the platinum atom in the triangle carries a PPh3 group. Although not located in the X-ray diffraction study, evidence is presented that the hydrido-ligand bridges the longest of the four Fe–Pt separations. Protonation of the salts affords the neutral complex [Fe2Pt2(µ-H)2(CO)8(PPh3)2], also characterised by an X-ray diffraction study. Crystals are monoclinic, space group P21/c, Z= 4, in a unit cell with lattice parameters a= 10.83(2), b= 16.00(4), c= 27.88(4)A, and β= 99.40 (11)°. The structure has been refined to R 0.056 (R′ 0.060) for 2 474 independent reflections to 2θ⩽ 40° at 200 K. The structure consists of an Fe2Pt2 core [Pt–Pt 2.998(2); Pt–Fe 2.696(3), 2.694(3), 2.631(3), and 2.604(3)A], with each iron atom bonded to three CO ligands and each platinum atom bonded to a CO and a PPh3 group. The hydrido-ligands are considered to bridge the two longer Fe–Pt edges. The X-ray studies allow an understanding of the 1H and 31P n.m.r. data for the two Fe2Pt2 species, both of which undergo dynamic behaviour in solution. Reactions of the compound [Pt(C2H4)2(PPh3)] or [Pt(cod)(C8H13)][BF4](cod = cyclo-octa-1,5-diene) with the salt [NEt3H][Fe3(µ-H)(µ-CO)(CO)10] afford the compounds [NEt3H][Fe3Pt(µ-H)(µ-CO)(CO)10(PPh3)] and [Fe2Pt(CO)8(cod)], respectively. The latter was studied by X-ray crystallography; crystals are orthorhombic, space group P2121, Z= 4, in a unit cell of dimensions a= 12.321 (11), b= 9.442(7), and c= 15.707(16)A. The structure has been refined to R 0.050 (R′ 0.050) for 1 637 independent reflections to 2θ⩽ 55° at 200 K. The molecule consists of a triangle of metal atoms [Fe–Pt 2.561 (3) and 2.553(3); Fe–Fe 2.704 (4)A]; each iron atom carries four terminally bound CO ligands, and the platinum atom is η4 bonded to the cod group.

Bis(trimethylsilyl) acetylene in excess reacts with [Pt(cod)2](cod = cyclo-octa-1,5-diene) to give the diplatinum complex [Pt2(µ-Me3SiC2SiMe3)(Me3SiC2SiMe3)(cod)], whereas [Pt(C2H4)3] and the alkyne afford [Pt2(µ-Me3-SiC2SiMe3)(Me3SiC2SiMe3)2]. Reactions of [Pt(cod)2] with the alkynes RCCSiMe3(R = SiMe3, SiMe2But, CF3, or Ph) in 2 : 1 mol ratio, or excess of alkyne in the case of CF3CCSiMe3, yields the diplatinum complexes [Pt2(µ-RC2SiMe3)(cod)2]. The nickel compounds [Ni2(µ-RC2SiMe3)(cod)2](R = SiMe3 or Ph) have also been prepared. Reaction of PhCCSiMe3 with [Pt(cod)2] in 1 : 1 mol ratio gives the triplatinum complex [Pt3(µ-PhC2SiMe3)2(cod)2], which like [Pt2(µ-PhC2SiMe3)(cod)2] undergoes dynamic behaviour in solution, as revealed by variable-temperature n.m.r. studies. An X-ray crystallographic study on the latter was carried out. Crystals are monoclinic, space group P21/c, Z= 4, in a unit cell of dimensions a= 14.93(1), b= 10.38(1), c= 17.463(8)A, β= 112.79(6)°. The structure has been refined to R 0.038 (R′ 0.038) for 5 464 unique reflections to 2θ⩽ 60°(Mo-Kα, X-radiation) collected at 200 K. The PhC2SiMe3 ligand transversely bridges the Pt ⋯ Pt vector (2.914 A) such that the dihedral angel between the two planes formed by the two Pt–µ–C2 units is 97°. This, together with the long metal–metal distance and the essentially planar geometry about each platinum atom, is taken to imply little or no direct Pt–Pt bonding, with the two halves of the molecule held together by orthogonal π orbitals of the shared PhCCSiMe3 ligand.

Bis(ethylene)(tertiary phosphine)platinum complexes [Pt(C2H4)2(PR3)][PR3= P(cyclo-C6H11)3, PMe2Ph, PMePh2, PPh3, or PPri2Ph] react with bis(cyclopentadienyl)bis(phenylethynyl)titanium to give compounds [Pt{η-(PhC[triple bond, length half m-dash]C)2Ti(η-C5H5)2}(PR3)] in which the PhC[triple bond, length half m-dash]C–Ti–C[triple bond, length half m-dash]CPh group acts as a bidentate ligand to platinum. In contrast, dimethylbis(phenylethynyl)silane reacts with [Pt(C2H4)2(PR3)][PR3= P(C6H11)3, PMeBut2, or PPri2Ph] to give diplatinum complexes [Pt2(σ-C[triple bond, length half m-dash]CPh){µ-(1-σ:1–2-η-C[triple bond, length half m-dash]CPh)}(µ-SiMe2)(PR3)2]. A single-crystal X-ray diffraction study has established the structure of the product from [Pt(C2,H4)2{P(C6H11)3}] and [Si(C[triple bond, length half m-dash]CPh)2Me2]. Crystals are monoclinic, space group P21/c(no. 14), with a= 12.44(1), b= 26.12(4), c= 15.832(8)Å, β= 97.99(6)°, and Z= 4. The structure has been determined by analysis of 5 131 unique data with F > 4σ(F) collected to 2θ⩽ 50°(Mo-Kα radiation) at 200 K on a four-circle diffractometer, and refined to R 0.053 (R′0.041). The results establish a molecular structure with an SiMe2 group asymmetrically bridging a Pt–Pt separation of 2.703(1)Å. Two C[triple bond, length half m-dash]CPh groups are σ-bonded to one metal atom (formally PtIV) but one is also η2-co-ordinated to the other platinum (formally PtII). The P–Pt–Pt–P skeleton is non-linear with PPtPt angles of 165.2(1) and 148.0(1)°. Dimethylbis(phenylethynyl)silane reacts with [Pt(C2H4)(PPh3)2], without carbon–silicon bond cleavage, to give mono- and di-platinum η2 complexes [Pt{η-PhC[triple bond, length half m-dash]CSi(C2Ph)Me2}(PPh3)2] and [Pt2{η-(PhC[triple bond, length half m-dash]C)2SiMe2}(PPh3)4]., We thank the S.R.C. for support and the Studienstiftung des deutschen Volkes for the award of a scholarship (to H. W.).

The cycle-octatetraene (cot) complexes [M(CO)3(η4-cot)](M = Fe or Ru) undergo electrophilic addition reactions with arylcyclopropenium ions as their [BF4]– salts, [C3Ph2R][BF4](R = H or Ph), togive [M(CO)3(η2:η3-C11H8Ph2R)][BF4](1; M = Fe or Ru, R = H or Ph); hydride addition to (1; M = Fe, R = Ph) yields [Fe(CO)3(σ,η3-C11H9Ph3)](2). The X-ray structure of compound (2) shows the ring-opened cyclopropenium ion to be bonded to the original cot ring via three new carbon–carbon bonds. The resulting polycyclic hydrocarbon ligand is attached to the iron atom by a σ,η3-bonded eight-membered ring, and also contains substituted cyclopentene, cyclohexane, and cyclohexenyl moieties. Complex (2) crystallises in the monoclinic space group P21/n, and the structure has been refined to R(R′)= 0.073 (0.077) for 2 484 reflections [I 3.0σ(I)].

The tungsten–carbyne complex [W(C·C6H4Me-p)(CO)2(η-C5H5)] reacts with the compounds [Pt(C2H4)(PR3)2](PR3= PMe2Ph or PMe3) to give the dimetal species [PtW(µ-C·C6H4Me-p)(CO)2(PR3)2(η-C5H5)]. A related complex [PtWBr(µ-C·C6H4Me-p)(CO)4(PMe3)2] is produced quantitatively from [W(C·C6H4Me-p)(Br)(CO)4] and [Pt(C2H4)(PMe3)2]. In order to establish the molecular structure of this class of complex a single-crystal X-ray diffraction study was made on [PtW(µ-C·C6H4Me-p)(CO)2(PMe2Ph)2(η-C5H5)], crystals of which are monoclinic, space group P21/c, Z= 4, in a unit cell with lattice parameters a= 12.212(11), b= 9.339(6), c= 26.125(24)A, and β= 92.77(7)°. The structure has been refined to R 0.031 (R′ 0.029) for 3 803 reflections measured at 200 K for 2.9 ⩽ 2θ⩽ 55°(Mo-KαX-radiation). In the molecule a Pt–W bond [2.751(1)A] is bridged by a C·C6H4Me-p Group forming a ‘dimetallacyclopropene’ ring with Pt–C 1.997(9)A and W–C 1.967(6)A. The least-squares plane defined by the carbon atoms of the C·C6H4Me-p ligand is at 88.1° to the plane [graphic omitted]. The 1H, 31P, and 13C n.m.r. spectra of the compounds are discussed in relation to their structures.

Treatment of [Rh2(µ-PPh2)2(cod)2](cod = cyclo-octa-1,5-diene) in thf (tetrahydrofuran) at room temperature with 2 equivalents of [W(CMe)(CO)2(η-C5H5)] rapidly affords the tetranuclear metal complex [W2Rh2(µ-CMe)2(µ-PPh2)2(CO)4(η-C5H5)2](4). If the same reaction is carried out using an excess of the ethylidynetungsten complex two metal cluster compounds are obtained: [W2Rh2(µ-CO){µ-C(Me)C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)2](5)(formed as a separable mixture of two diastereoisomers) and [W3Rh2(µ-CO)2(µ-CMe){µ-C(Me) C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)3](6). The structure of the latter was established by X-ray diffraction. The molecule has an essentially planar W(1), Rh(1), W(2), Rh(2), W(3) framework. Carbonyl groups bridge the Rh(1)–W(1) and Rh(2)–W(2) bonds, and PPh2 ligands span the Rh(1)–W(2) and Rh(2)–W(3) linkages. Ethylidyne groups edge-bridge the Rh(1)–W(1) bond and triply bridge the atoms Rh(1)W(2)Rh(2), but the Rh(1)⋯ Rh(2) separation [3.115(4)A] is non-bonding. The Rh(2)–W(3) bond is bridged by a C(Me)C(O) ketenyl group, and the terminal W atoms in the chain each carry a CO ligand and a C5H5 ring. A third C5H5 group ligates W(2). The metal–metal distances fall into two groups [Rh(1)–W(2) 2.791(6), Rh(2)– W(3) 2.813(4); and Rh(1)–W(1) 2.696(5), Rh(2)–W(2) 2.664(5)A], with the shorter separations corresponding to double bonds and the longer to single bonds. Compound (6) is produced by addition of a molecule of [W(CMe)(CO)2(η-C5H5)] to (5), while the latter is formed by isomerisation of (4), a process necessitating migration of µ-CMe and µ-PPh2 between the metal centres. After several hours solutions of (6) in thf afford quantitatively the complex [W3Rh2(µ-CO)3(µ-C(Me){µ-C(Me)PPh2}(µ-PPh2)(µ-CMe)(CO)2(η-C5H5)3](7) an isomer of (6). The structure of (7) was established by X-ray diffraction. An essentially planar metal atom chain W(1), Rh(1), W(2), Rh(2), W(3) forms the spine of the molecule. The various ligands ligate the rhodium and tungsten atoms in a similar manner to those in (6), with the exception of the groups which span the Rh(2)–W(3) bond. This bond is now bridged by a λ5- phospha-alkyne C(Me) PPh2 fragment such that the phosphorus atom ligates W(3) and the carbon atom CMe is bonded to Rh(2) and W(3). The Rh(2)–W(3) bond is also bridged by a CO ligand. Thus the conversion of (6) into (7) involves a novel interchange of CO and PPh2 fragments such that in the former a µ-C(Me)C(O) group is present and in the latter a µ- C(Me)PPh2 moiety. The n.m.r. data (1H, 13C-{1H), and 31P-{1H}) for the new compounds are reported and discussed.

The compounds [M{C(OMe)Ph}(CO)5](M = Cr or W) react with [Pt(cod)2](cod = cyclo-octa-1,5-diene) to give metal—metal-bonded complexes [(OC)5[graphic omitted]t(cod)]. Ethylene-saturated light petroleum solutions of [Pt(cod)2], treated with 2 mol of tertiary phosphine, react with the mononuclear metal compounds [M{C(OMe)Ph}(CO)5](M = Cr, Mo, or W) and [W{C(OMe)Me}(CO)5] to afford the carbene-bridged dimetal complexes [(OC)5[graphic omitted]t(PR3)2](M = Cr or Mo, PR3= PMe3 or PMe2Ph; M = W, PR3= PMe3) and [(OC)5[graphic omitted]t(PMe3)2]. Phosphorus-31, 1H and 13C n.m.r. studies support the structures proposed, and for [(OC)5[graphic omitted]t(PMe3)2] the structure has been confirmed by a single-crystal X-ray diffraction study. Crystals are triclinic, with space group P and Z= 2 in a unit cell of dimensions a= 9.728(5), b= 16.002(13), c= 9.611(6)Aα= 109.86(6), β= 116,34(4), and γ= 83.77(6)°. The structure has been determined by heavy-atom methods from automated diffractometer data for 2.9 ⩽ 2θ⩽ 50° and refined to R 0.049 (R′ 0.048) for 3 735 independent reflections. A tungsten–platinum bond (2.861 (1)A] is asymmetrically bridged by a C(OMe)Ph group [C–Pt 2.04(1), C–W 2.48(1)A]. Reaction of the compounds [(OC)5[graphic omitted]t(PMe3)2](M = Cr or W) with trimethylphosphine gives the complexes [(Me3P)(OC)4[graphic omitted]t(PMe3)2], while the chromium compound with ButNC yields [(ButNC)2(OC)3[graphic omitted]t(CNBut)(PMe3)]. The n.m.r. data for these products are discussed.

The dimetal compounds [PtW(µ-CR)(CO)2(PR′3)2(η-C5H5)](R = C6H4Me-4, PR′3= PMe3, PMe2Ph, PMePh2, or PEt3) react with [Fe3(CO)9] in tetrahydrofuran at room temperature to afford trimetal complexes [FePtW(µ3-CR)(η-CO)(CO)5(PMe2Ph)2(η-C5H5)], [FePtW(µ3-CR)(CO)5(PMePh2)2(η-C5H5)], and [FePtW(µ3-CR)(CO)6(PR′3)(η-C5H5)](PR′3= PMe3, PMePh2, or PEt3). The reaction involving [PtW(µ-CR)(CO),(PEt3)2(η-C5H5)] also gave the non-iron containing compound [Pt2W(µ3-CR)(CO)4(PEt3)2(η-C5H5)]. Pathways for the formation of these heteronuclear trimetal complexes are discussed, and n.m.r. data (1H, 31 P-{1H}, 13C-{1H}) are reported for the dynamic platinumirontungsten species which contain a µ3-CFePtW core. X-Ray diffraction studies on [FePtW(µ3-CR)(CO)5(PMePh2)2(η-C5H5)] and on [FePtW(µ3-CR)(CO)6(PEt3)(η-C5H5)] confirm that the molecular skeleton is the same for both; the Pt atom in the former carries two PMePh2 ligands whereas in the latter it carries one terminal CO and one PEt3 ligand. Interesting differences in detailed structure are revealed, however. The Fe–Pt bond lengths are similar [2.556(2) and 2.542(3)A] for [FePtW(µ3-CR)(CO)5(PMePh2)2(η-C5H5)] and [FePtW(µ3-CR)(CO)6(PEt3)(η-C5H5)] respectively, but the Fe–W and Pt–W bond lengths are significantly different [2.694(2)versus 2.784(3), and 2.883(1)versus 2.775(1)A]. The Pt–W bond in [FePtW(µ3-CR)(CO)5(PMePh2)2(η-C5H5)] is among the longest so far observed. These differences, and those between the bonds of the µ3-CR ligand, are discussed. In the pentacarbonyl species the two P–Pt distances differ, that trans to the µ3-C atom [2.331(4)A] being notably longer than the other [2.289(3)A]. Both molecules are chiral and both crystallise in non-centrosymmetric space groups. Crystals of [FePtW(µ3-CR)(CO)5(PMePh2)2(η-C5H5)] are monoclinic, space group P21(no. 4) with Z= 2 in a unit cell of dimensions a= 10.005(2), b= 17.240(3), c= 12.928(4)A, β= 115.98(2)°, and the structure has been refined to R 0.050 for 4 490 reflections. Crystals of [FePtW(µ3-CR)(CO)6(PEt3)(η-C5H5)] are orthorhombic, space group Pna21(no. 33) with Z= 4 in a unit cell of dimensions a= 16.106(5), b= 8.958(5), c= 18.429(7)A, and the structure has been refined to R 0.050 for 2 703 reflections.

Reactions between the bromo(alkylidyne)tungsten complex [W(CR) Br(CO)4](R = C6H4Me-4) and the salts Na2[7,8-C2B9H9R′2](R′= Me or H), followed by treatment with [N(PPh3)2]Cl afford the compounds [N(PPh3)2][W(CR)(CO)2(η5-C2B9H9R′2)](1a, R′= Me; 1b, R′= H). The salt [NEt4][W(CMe)(CO)2(η5-C2B9H9Me2)](1c) was prepared from [W(CMe)Br(CO)4] and Tl2[7,8-C2B9H9Me2], with subsequent addition of [NEt4]Cl. Treatment of (1a) or (1b) with [AuCl(PPh3)], in the presence of TIPF6 yields the gold–tungsten complexes [AuW(µ-CR)(CO)2( PPh3)(η5-C2B9H9R′2)](2a, R′= Me; 2b, R′= H). Similarly, (1c) with [AuCl( PPh3)] affords [AuW(µ-CMe)(CO)2( PPh3)(η5-C2B9H9Me2)](2c). The structure of (2a) has been established by X-ray diffraction. The Au–W bond [2.780(8)A] is asymmetrically bridged by the CC6H4Me-4 group [µ-C–Au 2.19(3), µ-C–W 1.88(3)A]. Treatment of [AuCl(tht)](tht = tetrahydrothiophene) with (1a) gives the salt [N( PPh3)2][AuW2(µ-CR)2(CO)4(η5-C2B9H9Me2)2](3). The rhodium–tungsten compound [RhW(µ-CR)(CO)2(PPh3)2(η5-C2B9H9Me2)](4a) has been prepared by two routes: from the reaction between (1a) and [RhCl(PPh3)3] or from (1a) and [Rh(PPh3)2(cod)][PF6](cod = cyclo-octa-1,5-diene). The latter with (1b) yields [RhW(µ-CR)(CO)2(PPh3)2(η5-C2B9H11)](4b). Compounds (1a) and (1b) react with [Rh(PPh3)2(nbd)][PF6][nbd = norbornadiene (bicyclo[2.2.1] hepta-2,5-diene)] to give the complexes [RhW(µ-CR(CO)2(PPh3)2{η5-C2B9(C7H9)H8R′2}][5a,R′= Me; 5b, (two isomers), R′= H]. The structures of (4a) and (5a) have been established by X-ray diffraction. Both molecules have Y-shaped WRhP2 cores with the Rh–W bonds [4a, 2.681 (l), 5a, 2.662(2)A] bridged by CC6H4Me-4 groups [4a, µ-C–Rh 2.068(5), µ-C–W 1.880(6); 5a, µ-C-Rh 2.12(2), µ-C–W 1.84(2)A], and semibridged by a CO ligand [W–C-O, 4a, 160.2(5); 5a, 156( 1 )°] In (4a), the tungsten atom is ligated by a terminal CO group and the η5-C2B9H9Me2 cage. In (5a), the tungsten also carries a terminal CO group but the carbaborane ligand has a C7H9[nortricyclene (tricyclo[2.2.1.02,6] heptane)] fragment attached to the unique boron atom in the open face of the cage. Thus in the formation of (5a) an unprecedented hydroboration reaction has occurred, a cage B–H bond having added to the norbornadiene ligand with concomitant C–C bond formation. In contrast, treatment of the norbornadiene-containing salt (Rh(dppe)(nbd)[PF6](dppe = Ph2PCH2CH2PPh2) with (1a) gives [RhW(µ-CR)(CO)2(dppe)(η5-C2B9H9Me2)](4c). Reactions of (4a) with PEt3, PMe2Ph, dppe, and CO are reported. Examination of the 13C-{1H} and 31P-{1H} n.m.r. spectra of the complexes (4) and (5) reveal that they undergo dynamic behaviour in solution and possible mechanisms are described and discussed.

The salts [N(PPh3)2][W(CC6H4Me-4)(CO)2(η5-7,8-C2B9H9R2)](R = Me or H) and [M (CO)2(NCMe)2(η5-C9H7)][BF4](M = Mo or W, C9H7= indenyl) react in CH2Cl2 at ambient temperatures to give the dimetal compounds [MW(µ-CC6H4Me-4)(CO)3(η5-C9H7)(η5-7,8-C2B9H9R2)](2a, M = Mo, R = Me; 2b, M = W, R = Me; 2c, M = Mo, R = H). X-Ray diffraction studies on (2a) and (2b) showed they were isostructural, with the metal–metal bonds bridged by the p-tolylmethylidyne group and by a three-centre two-electron B–H⇀M bond involving the carbaborane group ligating the tungsten atom. The tungsten atom carries two terminally bound CO groups while the other metal centre (2a, Mo; 2b, W) is bonded by one CO ligand and the indenyl group. Structural parameters for (2a) and (2b) are essentially identical; for (2a), Mo–W 2.657(2), µ-C–Mo 1.95(2), µ-C–W 2.03(l), B–µ-H 1.02, and µ-H–Mo 1.719 A. In toluene at 80 °C, compounds (2a) and (2b) isomerise. The isomerisation involves a polytopal rearrangement of the carbaborane ligand, thereby affording the species [MW(µ-CC6H4Me-4)(CO)3(η5-C9H7)(η5-7,9-C2B9H9Me2)](3a, M = Mo; 3b,M = W). Compound (3a) was identified and structurally characterised by an X-ray diffraction study. Apart from migration of the carbon atoms within the carbaborane cage, (3a) retains the structural features of (2a) with the Mo–W bond [2.669(1)A] bridged by CC6H4Me-4 [µ-C–Mo 1.963(4), µ-C–W 2.056(4)A] and B–H⇀Mo [µ-H–Mo 1.93(3)A] groups. Treatment of (2a) with K[BH-(CHMeEt)3] followed by [N(PPh3)2]Cl gives the salt [N(PPh3)2][MoW{µ-CH(C6H4Me-4)}(CO)3(η5-C9H7)(η5-7,8-C2B9H9Me2)](4), with p-tolylmethylidene and B–H⇀Mo groups bridging the Mo–W bond. Reactions of the compounds (2) with PMe3 affords the complexes [MW(µ-CC6H4Me-4)(CO)n(PMe3)(η5-C9H7)(η5-7,8-C2B9H9R2)](5a, M = Mo, R = Me, n= 3; 5b, M = W, R = Me, n= 3; 6, M = Mo, R = H, n= 2). Whereas in (5a) and (5b) the groups M(PMe3)(η5-C9H7) are present and exo-polyhedral B–H⇀M bonds are absent, in contrast, in (6) the PMe3 ligand is attached to the tungsten atom and a three-centre two-electron B–H⇀Mo linkage is present. The latter bridge system is also found in [W2(µ-CC6H4Me-4)(CO)2( PMe3)(η5-C9H7(η5-7,8-C2B9H9Me2)] which contains a W( PMe3)(η5-C9H7) group, and was prepared by displacing the ligand N2C(C6H4Me-4)2 from [W2(µ-CC6H4Me-4)(CO)2{(N2C(C6H4Me-4)2}(η5-C9H7)(η5-7,8-C2B9H9Me2)]. Treatment of (2a) with dmpm (Me2PCH2PMe2) gives the compound [MoW(µ-CC6H4Me-4)(µ-CO)(µ-dmpm)(CO)(η5-C9H7(η5-7,8-C2B9H9Me2)]. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) for the new complexes are reported, and discussed in relation to structures proposed or established by X-ray diffraction.

Reaction of the compound [Pt(PhC2Ph)2] with [Pt(C2H4)(PPh3)2] or [Pt2(µ-cod)(PEt3)4](cod = cyclo-octa-1,5-diene) affords diplatinum complexes [Pt2(µ-PhC2Ph)(PhC2Ph)(PR3)2](R = Ph or Et). The triphenylphosphine compound has also been prepared by treating PhCCPh with [Pt(C2H4)2(PPh3)]. The terminal alkyne ligand in [Pt2(µ-PhC2Ph)(PhC2Ph)(PPh3)2] bonds a third platinum atom on treatment with [Pt(C2H4)(PPh3)2] to give the triplatinum complex [Pt3(µ-PhC2Ph)2(PPh3)4]. The latter can also be prepared by addition of 2 mol equivalents of [Pt(C2H4)(PPh3)2 to [Pt(PhC2Ph)2], and the triethylphosphine-triplatinum analogue is similarly obtained using [Pt2(µ-cod)(PEt3)4]. In view of the novelty of these compounds, a single-crystal X-ray diffraction study has been carried out on [Pt3(µ-PhC2Ph)2(PEt3)4], crystals of which are monoclinic, space group C2/c(no. 15), with Z= 4 in a unit cell of dimensions a= 17.047(2), b= 13.677(2), c= 25.073(3)A, and β= 105.79(1)°. The structure has been solved by heavy-atom methods from 3 038 intensity data [I 3.0σ(I)] measured on a four-circle diffractometer at 300 K, and refined to R 0.047 (R′ 0.046). The three platinum atoms adopt an open V-shaped configuration with an internuclear distance of 2.904A and an interbond angle of 144°, while the acetylenic units form transverse bridges across the two Pt–Pt vectors on the convex side of the V. The phenyl groups bend away from the metal atoms to give a C–C–Ph angle of 139°, and the whole molecule is constrained crystallographically to C2 symmetry. The ethyl groups of the phosphine ligands are ill defined and possibly disordered.The diplatinum complexes [Pt2(µ-RC2R)(PMe3)4](R = Ph or C6F5) have also been prepared, and [Pt2(µ-PhC2Ph)(PEt3)4] characterised spectroscopically. Reaction of [Pt(PhC2Ph)(CNBut)2] with [Pt(C2H4)(PPh3)2] yields trans-[Pt2(µ-PhC2Ph)(CNBut)2(PPh3)2], scrambling of the CNBut and PPh3 ligands having occurred. The stereochemistry of this complex, and its PhCCC6H4OMe-4 analogue, has been established by 31P and 13C-labelling n.m.r. studies. The modes of formation of the various compounds are discussed.

Treatment of copper(I) chloride with Li(C5Me5) in tetrahydrofuran at low temperatures affords a reagent which is a useful source of the Cu(η-C5Me5) fragment in syntheses. The preparation of the compounds [CuW{µ-C(OMe)R}(CO)5(η-C5Me5)], [Cu2W(µ3-CR)(CO)2(η-C5H5)(η-C5Me5)2], [CuPtW(η3-CR)(CO)2(PMe3)2(η-C5H5)(η-C5Me5)], [Cu2PtW2(µ3-CR)2(CO)4(η-C5H5)2(η-C5Me5)2](R = C6H4Me-4), [CuPt(µ-PhC2Ph)(PMe3)2(η-C5Me5)], and [CuRh2(µ-CO)2(η-C5Me5)3] is described, and spectroscopic data (i.r. and n.m.r.) for the new species are reported and discussed. Single-crystal X-ray diffraction studies have been carried out on the compounds [CuPtW(µ3-CC6H4Me-4)(CO)2(PMe3)2(η-C5H5)(η-C5Me5)] and [CuRh2(µ-CO)2(η-C5Me5)3]. In the former compound, the µ-CCuPtW core atoms adopt a butterfly configuration with an angle of fold of 90.6° between the C,W,Pt and C,W,Cu planes. The Cu ⋯ Pt separation [2.807(3)A] implies little or no metal–metal bonding between these centres. The tungsten atom carries an η-C5H5 group and two CO ligands, one of which semi-bridges [W–C–O 162(2)°] the Pt–W bond [2.779(2)A]. The C5Me5 ligand on copper is η5-bonded to the metal, and the Cu–W distance is 2.648(3)A. The structure of [CuRh2(µ-CO)2(η-C5Me5)3] is based on a triangle of metal atoms which, however, proved to be positionally disordered. The data obtained are limited, but the mean metal–metal separation is 2.56(1)A and the two CO groups are tilted in a way which implies semi-triply bridging behaviour. The important feature that the C5Me5 ligand on copper is η5-co-ordinated is confirmed.

Treatment of the compounds [N( PPh3)2[W(CR)(CO)2(η5-C2B9H9Me2)](R = C6H4Me-4 or Me) with [Ru(CO)(NCMe)2(η-C5H5)][BF4] in CH2Cl2 affords the dimetal complexes [RuW(µ-CR)-(CO)3(η-C5H5)(η5-C2B9H9Me2)]. The structure of the product with R = C6H4Me-4 has been established by a single-crystal X-ray diffraction study. The Ru–W bond [2.803(2)A] is spanned by the p-tolymethylidyne group [Ru–µ-C 2.20(7); W–µ-C, 1.890(6)A]. The tungsten atom carries two CO ligands and the η5-C2B9H9Me2 cage. The ruthenium atom is ligated by a CO group and the cyclopentadienyl anion, and also by the unique B–H bond of the open pentagonal face of the icosahedral η5C2B9H9Me2 fragment [B–Ru, 2.400(7); B–H, 1.33; Ru–H, 1.67 A]. Deprotonation of [RuW(µ-CC6H4Me-4)(CO)3(η-C5H5)(η5-C2B9H9Me2)], on basic alumina or by n-butyl-lithium, in the presence of [N( PPh3)2] Cl gives the salt [N( PPh3)2][RuW(µ-CC6H4Me-4)(µ-σ,η5-C2B9H8Me2)-(CO)3(η-C5H5)] which was structurally characterised by X-ray diffraction. The structure of the anion [Ru–W, 2.748(l); Ru–µ-C, 2.100(6); W–µ-C,1.941(5)A] is very similar to that of its neutral precursor, the major difference being replacement of the B–H⇀Ru three-centre two-electron bond by a direct B–Ru linkage [2.155(6)A]. The C2B9H8Me2 cage thus adopts an unusual µ-σ,η5 bonding mode at the WRu centre. Some reactions of the ruthenium–tungsten dimetal species are described, and spectroscopic data are reported and discussed.

Addition of [Pt(cod)2](cod = cyclo-octa-1,5-diene) in ethylene-saturated thf (tetrahydrofuran) to the compound [Mo2WPt3(µ-CMe)(µ3-CC6H4Me-4)2(CO)6(cod)(η-C5H5)3] in the same solvent affords the heptanuclear metal complex [Mo2WPt4(µ3-CMe)(µ3-CC6H4Me-4)2(CO)6(cod)2(η-C5H5)3]. The cod ligands in the latter species were displaced upon treatment with the reagents [W(CR)(CO)2(η-C5H5)](R = C6H4Me-4 or Me) to give the nonanuclear metal compounds [Mo2W3Pt4(µ-CC6H4Me-4)2(µ3-CMe)(µ3-CC6H4Me-4)2(CO)10(η-C5H5)5] and [Mo2W3Pt4(µ-CMe)2(µ3-CMe)(µ3-CC6H4Me-4)2(CO)10(η-C5H5)5], respectively. Complexes containing chains of ten or eleven metal atoms have also been prepared. Thus [Mo2W3Pt4(µ-CC6H4Me-4)2(µ3-CMe)(µ3-CC6H4Me-4)2(CO)10(η-C5H5)5] reacts with an excess of [Pt(cod)2] to yield a mixture of [Mo2W3Pt5(µ-CC6H4Me-4)(µ3-CMe)(µ3-CC6H4Me-4)3(CO)10(cod)(η-C5H5)5], and [Mo2W3Pt6(µ3-CMe)(µ3-CC6H4Me-4)4(CO)10(cod)2(η-C5H5)5]; and [Mo2W3Pt6(µ3-CMe)3(µ3-CC6H4Me-4),(CO)10(cod)2(η-C5H5)5] is obtained by treating [Mo2W3Pt4(µ-CMe)2(µ3-CMe)(µ3-CC6H4Me-4)2(CO)10(η-C5H5)5] with an excess of [Pt(cod)2]. Displacement of the cod ligands from [Mo2W3Pt6(µ3-CMe)3(µ3-CC6H4Me-4)2(CO)10(cod)2(η-C5H5)5] by PMe2Ph yields the complex [Mo2W3Pt6(µ3-CMe)3(µ3-CC6H4Me-4)2(CO)10(PMe2Ph)4(η-C5H5)5], structurally characterised by an X-ray diffraction study. The latter established that the spine of the molecule consisted of eleven metal atoms arranged in the sequence PtWPtMoPtMoPtWPtWPt. Each PtMPt (M = Mo or W) triangle (mean distances: Pt–W 2.751, Pt–Mo 2.745, and Pt ⋯ Pt 3.040 A) is capped by an alkylidyne fragment (mean distances: µ3-C–Pt 2.05, µ3-C–W 2.04, and µ3-C–Mo 1.98 A), and the terminal platinum atoms are each ligated by two PMe2Ph groups.

The reaction between the salts [PtH(Me2CO)(PEt3)2][BF4] and [NEt4][W(CC6H3Me2-2,6)(CO)2(η5-C2B9H9Me2)] in acetone at low temperature (ca. –30 °C) affords the dimetal compound [WPtH(µ-CC6H3Me2-2,6)(CO)2(PEt3)(η5-C2B9H9Me2)], in which the carbaborane ligand forms a B–H⇀Pt three-centre bond by employing a BH group in the pentagonal face of the cage. This product readily affords, via loss of hydrogen, the complex [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(µ-σ:η5-C2B9H8Me2)] as a mixture of two isomers. The structure of the major isomer (ca. 80%) has been established by X-ray diffraction. The W–Pt bond [2.728(1)A] is asymmetrically bridged by the CC6H3Me2-2,6 group [µ-C–W 1.88(2), µ-C–Pt2.15(2)A]. Indeed with a W–µ-C–C1(C6H3) angle of 175(1)° these three atoms are nearly linear. The carbaborane ligand has undergone ‘slippage’ along the W–Pt vector to accommodate formation of a direct exopolyhedral B–Pt σ bond [2.01(2)A]. This linkage involves the central boron in the [graphic omitted] face of the icosahedral fragment η5 bonded to tungsten. The PEt3 ligand attached to the platinum atom [Pt–P, 2.251(7)A] is transoid to the µ-C and W atoms [µ-C–Pt–P, 160.6(4)°, W–Pt–P 155.9(1)°]. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) are in accord with the structure established by the X-ray diffraction study. Similar data for the minor isomer reveal that this species had a structure in which the B–Pt σ bond involves a boron atom [graphic omitted] in the face of the cage, adjacent to a CMe group. The two isomers may be separated by column chromatography, but solutions equilibrate on standing. Formation of the major isomer from [WPtH (µ-CC6H3Me2-2,6)(CO)2(PEt3)(η5-C2B9H9Me2)] can be partially reversed by treating solutions of the former with hydrogen. Mechanisms are proposed for these various transformations based in part on deuteriation studies employing [PtD(Me2CO)(PEt3)2][BF4] as a precursor to the W–Pt species. The compound [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(µ-σ:η5-C2B9H8Me2)](major isomer) is relatively inert to the addition of ligands at the formally 14-electron platinum centre, presumably due to the presence of the bulky xylyl group. However, reactions very readily occur with rod-like ligands (L = CO or CNBut) to give the compounds [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(L)(µ-σ:η5-C2B9H8Me2)]. Indeed the tricarbonyl complex is a major constituent of the mixture of products obtained by treating the complex [NEt4][W(CC6H3Me2-2,6)(CO)2(η5-C2B9H9Me2)] with [PtH(Me2CO)(PEt3)2][BF4]. An X-ray study of the carbon monoxide adduct revealed a structure similar to the precursor with parameters W–Pt, 2.728(1),µ-C–W 1.89(1), µ-C–Pt 2.29(1), B–Pt 2.16(1)A, W–µ-C–C1(C6H3) 160.0(8), and P–Pt–W 138.5(1)°. The significantly lower W–µ-C–C1(C6H3) angle (ca. 160°) compared with that in the precursor is presumably a consequence of the presence of the additional CO ligand terminally bound to the platinum and cisoid to the alkylidyne group [µ-C–Pt–CO 83.5(4)°].

Reaction of [Pt3(CNBut)6] with diphenylcyclopropenone in toluene affords the yellow crystalline title complex [Pt2{µ-(PhC)2CO}(CNBut)4], the structural identity of which has been established by a single-crystal X-ray diffraction study. The complex is monoclinic, space group P21/n, Z= 4, with unit-cell dimensions a= 11.283(8), b= 19.821(6), c= 17.534(7)A, and β= 90.23(4)°. Using 4 494 independent reflections, the refinement has converged to R 0.070 (R′ 0.069). The molecule shows the unusual feature of ring opening at the carbon–carbon double bond of the cyclopropenone, the resulting C3 fragment symmetrically bridging the two platinum atoms. Reaction between cyclo-octa-1,5-dienebis(methyl vinyl ketone)platinum and diphenylcyclopropenone at –50 °C yields an analogous complex [Pt2{µ-(PhC)2CO}(cod)2](cod = cyclo-octa-1,5-diene). Protonation of this species gives the cation [Pt2{µ-(PhC)2C(OH)}(cod)2]+, while treatment with CNBut or P(OMe)3 leads to displacement of the cod ligands.

Reactions between [OS3(µ-H)2(CO)10] and the compounds [Pt(C2H4)2(PR3)][PR3= P(cyclo-C6H11)3, PPh3, or PBut2Me] afford tetranculear metal complexes [Os3Pt(µ-H)2(CO)10(PR3)]. Examination of the variable-temperature 1H n.m.r. spectra of these ‘58-electron’ clusters reveals dynamic behaviour with site exchange of the two hydrido-ligands, the energy barrier for this process for the PBut2Me derivative being ca. 58 kJ mol–1. In order to establish the molecular structure of these complexes a single-crystal X-ray diffraction study was made on the compound containing the P(cyclo-C6H11)3 ligand. Crystals are monoclinic, space group P21/c, Z= 4, in a unit cell of dimensions a= 11.822(4), b= 16.584(5), c= 17.763(9)A, and β= 108.10(4)°. The structure has been refined to R 0.035 (R′ 0.038) for 5 737 reflections to 2θ < 60°(Mo-Kα, X-radiation) collected at 200 K. The metal atoms adopt a slightly asymmetric tetrahedral structure [Os–Os 2.777(1), 2.741(1), and 2.789(1)A; Os–Pt 2.791(1), 2.832(1), and 2.863(1)A]. The platinum atom is bonded to a CO group and to the P(cyclo-C6H11)3 ligand, and each osmium is attached to three CO groups. The hydrido-ligands bridge the longer of the Os–Os and Os–Pt bonds, as deduced from observation of residual electron densities, from widening of certain Pt–Os–CO and Os–Os–CO angles, from staggered conformations of two of the Os(CO)3 groups with respect to the two longer edges of the tetrahedron, and from calculation of potential energy minima.

The alkylidyne complex [W(CC6H4Me-4)(CO)2(η-C5H5)] reacts in 1 : 2 mol ratio with the compounds [Pt-(C2H4)3], [Pd(C7H10)3], and [Ni(cod)2](cod = cyclo-octa-1,5-diene) to give the trimetalla species [MW2(µ-CC6H4Me-4)2(CO)4(η-C5H5)2](M = Pt, Pd, or Ni), characterised spectroscopically. Additionally, the structures of the platinum and nickel compounds have been established by single-crystal X-ray diffraction studies. Crystals of the platinum compound are monoclinic, space group P21/c, with Z= 4 in a unit cell of dimensions a= 12.187(6), b= 13.404(7), c= 16.938(9)A, and β= 96.42(4)°. The structure has been solved by heavy-atom methods and refined by least squares to R 0.047 (R′ 0.048) for 4 369 independent diffracted intensities measured at 200 K. For the nickel compound the crystals are monoclinic, space group P21/n, with Z= 4, in a unit cell of dimensions a= 7.980(2), b= 22.080(6), c= 16.025(3)A, and β= 103.45(2)°. Intensities were measured at room temperature to 2θ= 65° and the structure has been refined to R 0.053 (R′ 0.063) for 5 246 unique reflections. The two molecules have similar structures with a metal atom sequence W–Pt(Ni)–W in which the Pt–W or Ni–W bonds are bridged by alkylidyne ligands, CC6H4Me-4, affording two three-membered orthogonal ring systems sharing a common vertex (Pt or Ni). In the nickel compound the W–Ni–W sequence is nearly linear (175°), whereas in the platinum complex the angle W–Pt–W is 165°. The W–µ-C bond lengths in both compounds are very similar [1.91(1) and 1.89(1)A], and suggest a bond order of ca. 2 between the tungsten atom and the bridging carbon atom. The metal–metal distances [mean Ni–W 2.584(1), mean Pt–W 2.713(1)A] also imply multiple bonding within the dimetallacyclopropene rings. Each tungsten atom carries two carbonyl groups, one of which is semi-bridging to the Pt(Ni) atom and lies in the plane of the corresponding cyclopropene ring, while the other is orthogonal to this plane. The dihedral angle between the two dimetallacyclopropene rings is ca. 97°. A fascinating difference between these two molecules is that, whereas in the nickel compound the terminal carbonyl groups on the tungsten atoms each lie trans to the tolyl group of the second metallacyclopropene ring, in the platinum compound the corresponding carbonyl ligands lie one cis and one trans.

In CH2Cl2, at room temperature, the salt [NEt4][W(CMe)(CO)2(η5-C2B9H9Me2)] reacts with [Co2(CO)8] to give the trimetal complex [NEt4][Co2W(µ3-CMe)(CO)8(η5-C2B9H9Me2)]. The latter is partially decarbonylated in vacuo to the hexacarbonyl species [NEt4][Co2W(µ3-CMe)(CO)6(η5-C2B9H9Me2)]. In contrast, treatment of the salts [X][W(CR)(CO)2(η5-C2B9H9Me2)](X = NEt4, R = Ph, C6H4Me-4, or C6H4Me-2; X = PPh4, R = Ph) with [Co2(CO)8] affords the hexacarbonyl–trimetal compounds [X][Co2W(µ3-CR)(CO)6(η5-C2B9H9Me2)]via the intermediacy of initially formed octacarbonyl products [X][Co2W(µ3-CR)(CO)8(η5-C2B9H9Me2)]. In the presence of carbon monoxide, the hexacarbonyl–trimetal compounds revert to the octacarbonyl, and a single-crystal X-ray diffraction study has been carried out on [PPh4][Co2W(µ3-CPh)(CO)8(η5-C2B9H9Me2)], which crystallises with half a molecule of CH2Cl2 per asymmetric unit. The anion consists of a triangle of metal atoms [Co–Co 2.502(3), Co–W 2.767(2) and 2.769(2)A] capped by the phenylmethylidyne ligand [µ3-C–Co 1.89(2) and 1.93(2), µ3-C–W 2.07(1)A]. The cobalt atoms each carry three terminal CO groups, but the two CO ligands attached to the tungsten semibridge the Co–W bonds [W–C–O 169(2) and 165(1)°]. The carbaborane ligand is η5-co-ordinated to the tungsten atom, and lies on the same side of the metal triangle as the µ3-CPh group. The salts containing the anions [Co2W(µ3-CR)(CO)6(η5-C2B9H9Me2)]– were shown by n.m.r. studies (1H, 11B-{1H}, 11B, and COSY 11B–11B) to have structures in which the carbaborane ligand forms two B–H⇀Co exopolyhedral bonds, one to each cobalt atom.

Addition of light petroleum solutions of [M{C(OMe)C6H4R-4}(CO)5](M = Cr or W, R = Me or CF3) to ethylene-saturated solutions of [Pt(cod)2](cod = cyclo-octa-1,5-diene), to which two molar equivalents of tertiary phosphine had been added, afforded the heteronuclear dimetal complexes [(OC)5[graphic omitted](PR3)2](R = Me, PR3 PMe3 or PMe2Ph; R = CF3, PR3= PMe3) and [(OC)5[graphic omitted](PR3)2](R = Me or CF3, PR3= PMe3 or PMe2Ph), characterised by 31P and 1H n.m.r. spectroscopy. The compounds [(OC)5[graphic omitted](PMe2Ph)2], [(OC)5[graphic omitted](PMe2Ph)2], and [(OC)5[graphic omitted](PMe3)2] were similarly obtained from [W{C(OMe)Me}(CO)5], [Cr([graphic omitted]H2)(CO)5], and [W(CPh2)(CO)5], respectively. Although [PtW(µ-CPh2)(CO)5(PMe3)2] is a relatively unstable complex, reaction with trimethylphosphine affords air-stable [(Me3P)(OC)4[graphic omitted](PMe3)2] as a single isomer. A similar enhanced thermal and oxidative stability relative to the pentacarbonyl species is also observed with the compounds [(Me3P)(OC)4[graphic omitted](PMe3)2] and [(R3P)(OC)4[graphic omitted](PR3)2](PR3= PMe3 or PMe2Ph). A single-crystal X-ray diffraction study on the complex [PtW{µ-C(OMe)-C6H4Me-4}(CO)4(PMe3)3]shows that the tungsten–platinum bond [2.825(1)A] is asymmetrically bridged by a C(OMe)C6H4Me-4 group [C–W 2.37(1)A; C–Pt 2.03(1)A], that the co-ordination of the W atom is close to octahedral, and that the Pt atom is in a near-planar environment. The crystals are orthorhombic, space group Pna21(no. 33), with Z= 4 in a unit cell of dimensions a= 18.180(6), b= 10.720(3), c= 14.697(4)A. The structure has been elucidated by heavy-atom methods from 3 882 independent intensities measured to 2θ= 60° at 200 K, and refined to R 0.044.