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Treatment of the compounds [MoW(µ-CC6H4Me-4)(CO)2(η7-C7H7)(η5-C2B9H10R)](R = H or Me) in CH2Cl2with PHPh2 affords the complexes [MoW(µ-PPh2){µ-C(OH)C(C6H4Me-4)}(CO)(η7-C7H7)-(η5-C2B9H10R)]. The structure of the species with R = H was established by X-ray diffraction. The Mo–W bond [2.713(1)A] is spanned by the PPh2 group [Mo–P 2.439(3), W–P 2.360(3)A], and in a transverse manner by the alkyne. However, the latter is twisted so that the C(OH) atom lies appreciably closer to the tungsten [µ-C–W 2.067(8)A] than the molybdenum [µ-C–Mo 2.352(8)A], whereas the C(C6H4Me-4) atom is essentially symmetrically bridging [µ-C–Mo 2.224(9), µ-C–W 2.251(8)A]. The molybdenum atom carries the η7-C7H7 group (C–Mo av. 2.27 A), and the tungsten atom is η5 co-ordinated by the C2B9H11 cage and a CO group. The reaction between [MoW(µ-CC6H4Me-4)(CO)3(η5-C9H7)(η5-C2B9H9Me2)] and PHPh2in CH2Cl2 gives the complex [MoW(µ-CC6H4Me-4)(CO)2(PHPh2)(η5-C9H7)(η5-C2B9H9Me2)]. The latter on heating in toluene at 70 °C yields the compound [MoW(µ-PPh2)(CO)3(η5-C9H7){η5-C2B9H8(CH2C6H4Me-4)Me2}], the structure of which was established by X-ray diffraction. The Mo–W bond [2.708(1)A] is bridged by the PPh2 group [Mo–P 2.357(2), W–P 2.456(2)A]. The tungsten atom is ligated by two CO groups, and η5 co-ordinated by the C2B9 cage. In the open face of the latter a BH group in the α position to a CMe fragment forms a B–H⇀Mo exopolyhedral bond, while the boron atom β to the CMe groups in the pentagonal ring carries a CH2C6H4Me-4 substituent. The molybdenum atom is ligated by a CO molecule and the indenyl group. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) for the new compounds are reported and discussed.

Treatment of CO-saturated CH2Cl2 solutions of the salts [X][Rh(CO) L(η5-C2B9H9R′2)][X = NEt4, L = PPh3, R′= H; L = CO, R′= Me; X = N(PPh3)2, L = CO, R′= H] with the reagents [Mn(CR)-(CO)2(η-C5H4Me)][BCl4](R = C6H4Me-4 or C6H3Me2-2,6) affords the rhodium complexes [Rh{σ,η5-CH(R)C2B9H8R′2}(CO)L](R = C6H4Me-4, R′= H, L = PPh3 or CO; R = C6H4Me-4, R′= Me, L = CO; R = C6H3Me2-2,6, R′= H, L = PPh3). The structure of the compound [Rh{σ,η5-CH(C6H4Me-4)C2B9H10}(CO)(PPh3)] was established by X-ray diffraction. The rhodium atom is ligated by the CO and PPh3 groups [Rh–CO 1.854(3), Rh–P 2.302(1)], and by the CH(C6H4Me-4)C2B9H10 fragment. In the latter the CH(C6H4Me-4) moiety forms a bridge between the rhodium [Rh–C 2.374(3)A] and a boron atom [B–C 1.501 (4)A] in the pentagonal face of the cage. This boron atom is in the β site ([graphic omitted]) with respect to the carbon atoms, and all the atoms of the ring are bonded to the rhodium, but the connectivities are somewhat asymmetric [Rh–C 2.373(3) and 2.341 (3)A, Rh–B 2.205(3), 2.165(3), and 2.237(3)A]. In the molecule the PPh3 and C6H4Me-4 groups are transoid to one another about the Rh–CH(C6H4Me-4)σ bond, but n.m.r. studies on solutions reveal the presence of a second isomer with a cisoid configuration for the PPh3 and C6H4Me-4 groups. Reactions of the rhodium compounds with K[BH(CHMeEt)3] in tetrahydrofuran led to rupture of the Rh–C(H)R σ bonds and formation, in the presence of NEt4Cl, of the salts [NEt4][Rh(CO)L{η5-C2B9H8(CH2R)R′2}](L = PPh3, R = C6H4Me-4 or C6H3Me2-2,6, R′= H; L = CO, R = C6H4Me-4, R′= Me). The n.m.r. data (1H, 13C-{1H}, 31P-{1H}, and 11B-{1H}) for the new complexes are reported and discussed.

The nine-vertex ferracarborane salt [N(PPh3)2][7,7,7-(CO)3-closo-7,1-FeCB7H8] (1) reacts with an excess of [IrCl(CO)(PPh3)2] in the presence of Tl[PF6] to form, successively, the bimetallic species [7,7,9,9,9-(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7] (3), in which one {BH}- vertex has formally been subrogated by an {Ir(CO)2(PPh3)} unit, and the trimetallic complex [6,7,9-{Ir(CO)(PPh3)2}-7,9-(mu-H)2-7,9,9-(CO)3-7-PPh3-closo-7,9,1-IrFeCB6H6] (5), which contains an {FeIr2} triangle. The {FeIrCB6} core in 5 resembles that in 3 with, in addition, the Fe...Ir connectivity being spanned by an {Ir(CO)(PPh3)2} fragment and the consequent Fe-Ir and Ir-Ir bonds bridged by hydrido ligands. In contrast to the above, treatment of the 10-vertex diferracarborane salt [N(PPh3)2][6,6,6,10,10,10-(CO)6-closo-6,10, 1-Fe2CB7H8] (2) with the same reagents yields two very different, trimetallic complexes, namely [8,10-{Ir(mu-PPh2)(Ph)(CO)(PPh3)}-8-(mu-H)-6,6,6,10,10-( CO)5-closo-6,10,1-Fe2CB7H7] (6) and [6,7,10-{Fe(CO)3}-6-(mu-H)-6,10,10,10-(CO)4-6-PPh3-closo-6,10,1-IrFeCB7H7] (7). In 6, an exo-polyhedral {IrPh(CO)(PPh3)} moiety is attached to a {closo-6,10,1-Fe2CB7} framework via a PPh2-bridged Fe-Ir bond and a B-HIr agostic-type linkage, the iridium center formally having inserted into one P-Ph bond of a PPh3 unit. Complex 7 contains an {IrFeCB7} cluster core, with an exo-polyhedral {Fe(CO)3} moiety bridging a {BIrFe} triangular face and with an additional Ir-H-Fe bridge. However, this metal atom arrangement reveals that iridium and iron moieties have exchanged exo- and endo-polyhedral sites with respect to the 10-vertex metallacarborane. X-ray diffraction studies upon 3, 5, 6, and 7 confirmed their novel structural features; some preliminary reactivity studies upon these compounds are also reported.

Insertion of {M(CO)4} fragments (M = Fe, Ru, Mn, Re) into the eight-vertex monocarborane anion [closo-1-CB7H8]- affords ten-vertex metal-dicarbollide complexes.

The reagent [arachno-4-CB8H14] reacts with [Fe3(CO)12] in tetrahydrofuran (THF) at reflux temperatures, followed by addition of [N(PPh3)2]Cl, to afford [N(PPh3)2][4,9-{Fe(CO)4}-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (3). In the anion of 3, one iron atom is part of the open CBBFeBB face of a 10-vertex {arachno-9,6-FeCB8} cage, to which the second iron atom is attached via an Fe-Fe bond and an additional exo-polyhedral Fe-B sigma bond. Upon heating 3 in refluxing toluene, the closed 10-vertex species [N(PPh3)2][2,2,2-(CO)3-closo-2,1-FeCB8H9] (4) is obtained, whereas the isomeric compound [N(PPh3)2][6,6,6-(CO)3-closo-6,1-FeCB8H9] (5) is isolated upon heating [closo-4-CB8H9]- and [Fe3(CO)12] in refluxing THF with subsequent addition of [N(PPh3)2]Cl. Protonation of 3 using CF3SO3H in CH2Cl2 gives the charge-compensated compound [4,9-{Fe(CO)4}-4-(mu-H)-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (6), in which the B-Fe sigma bond of the precursor has been converted to a B-H right harpoon-up Fe linkage. In contrast, 3 with {M(PPh3)}+ gives the trimetallic species [1,3,4,9-{MFe(CO)4(PPh3)}-1,3-(mu-H)2-9,9,9-(CO)3-arachno-9,6-FeCB8H9] (M = Cu (7), Ag 8) in which the three metal centers form a V-shaped M-Fe-Fe unit. Compound 6 reacts with PEt3 in the presence of Me(3)NO to yield [4,9-(PEt3)2-9,9-(CO)2-nido-9,6-FeCB8H10] (9). In the latter, the formerly exo-polyhedral {Fe(CO)4} fragment has been replaced by a PEt3 ligand, with a second PEt3 substituting one CO group at the remaining cluster iron vertex. The novel structural features of compounds 3-9 have been confirmed by single-crystal X-ray diffraction studies.

The trinuclear osmium complex [Os3(CO)8(η5-7-NMe3-7-CB10H10] (1) has been synthesized by heating [Os3(CO)12] with nido-7-NMe3-7-CB10H12 in bromobenzene. The structure has been established by X-ray diffraction.

Treatment of 7-NH(2)Bu(t)-nido-7-CB(10)H(12) in tetrahydrofuran (THF) with LiBu(n)(3 equiv) and then [ReBr(CO)(3)(THF)(2)] gives the rhenacarborane dianion [1-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)](2-), isolated as the bis-[N(PPh(3))(2)](+) salt (4). Iodine oxidation of this Re(I) intermediate gives the Re(III) complex [1,2-mu-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)] 6 in which the carborane functions formally as an 8-electron (6pi+ 2sigma) donor. Reaction of with ligands L in the presence of Me(3)NO gives substituted products [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-closo-2,1-ReCB(10)H(10)][L = PPh(3)(7a), CNXyl (7b; Xyl = C(6)H(3)Me(2)-2,6), or Bu(t)C triple bond CH (7c)]. Formation of complex 7c is unexpectedly accompanied by [1,2-mu-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)] 8a, in which an alkyne-derived dienyl group is bound to both the rhenium centre and to an adjacent boron vertex. Complex 8a is also obtained from 7c with Bu(t)C triple bond CH and Me(3)NO. The same reaction of 7c, using PhC triple bond CH or CNXyl instead of Bu(t)C triple bond CH, gives, respectively, [1,2-micro-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHPh}-closo-2,1-ReCB(10)H(9)] 8b and [1,2-micro-NHBu(t)-2-Bu(t)C triple bond CH-2-CO-2-CNXyl-closo-2,1-ReCB(10)H(10)] 9. Addition of donors L to results in displacement from rhenium of the pendant dienyl moiety, yielding [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-3-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)][L = PMe(3)(10a), CNBu(t)(10b)]. Single-crystal X-ray diffraction analyses have confirmed the novel structural features of compounds 6, 7c, 8b and 9.

The compound [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8] 1a reacts with PMe3 or PCy3(Cy = cyclo-C6H11) to give the structurally different species [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)5(PMe3)}-closo-2,1-RuCB10H8] 4 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)5(PCy3)}-closo-2,1-RuCB10H8]5, respectively. A symmetrically disubstituted product [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)4(PMe3)2}-closo-2,1-RuCB10H8] 6 is obtained using an excess of PMe3. In contrast, the chelating diphosphines 1,1'-(PPh2)2-Fe(eta-C5H4)2 and 1,2-(PPh2)2-closo-1,2-C2B10H10 react with 1a to yield oxidative-insertion species [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(micro-[1',1''-(PPh2)2-Fe(eta-C5H4)2])(CO)4}-closo-2,1-RuCB10H8] 7 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)4(1',2'-(PPh2)2-closo-1',2'-C2B10H10)}-closo-2,1-RuCB10H8] 8, respectively. In toluene at reflux temperatures, 1a with Bu(t)SSBu(t) gives [1-SMe2-2,2-(CO)2-7-(mu-SBu(t))-11-(mu-H)-2,7,11-{Ru2(mu-H)(mu-SBu(t))(CO)4}-closo-2,1-RuCB10H8] 9, and with Bu(t)C [triple bond] CH gives [1-SMe2-2,2-(CO)2-7-{mu:eta2-(E)-CH=C(H)Bu(t)}-11-{mu:eta2-(E)-CH=C(H)Bu(t)}-2,7,11-{Ru2(CO)5}-closo-2,1-RuCB10H8] 10. In the latter, two alkyne groups have inserted into cage B-H groups, with one of the resulting B-vinyl moieties involved in a C-H...Ru agostic bond. Oxidation of 1a with I2 or HgCl2 affords the mononuclear ruthenium complex [1-SMe2-2,2,2-(CO)3-closo-2,1-RuCB10H10] 11.

Icosahedral metal–monocarbollide complexes in which the carbon atom of the {nido-CB10} fragment carries an exo-polyhedral –NR3 or –NR2 group have an extensive chemistry. This is illustrated with complexes of ruthenium, osmium, rhodium, molybdenum, tungsten and rhenium. Many complexes with molecular structures new to the metallacarborane field have been discovered, and it has been shown that it is possible to introduce functional groups into the {nido-CB10} cage system in many different ways.

The nickelacarboranes [NEt(4)][2-(eta(3)-C(3)H(4)R)-closo-2,1,7-NiC(2)B(9)H(11)] (R = H (1a), Ph (1b)) have been synthesized via reaction between [Na](2)[nido-7,9-C(2)B(9)H(11)] and [Ni(2)(micro-Br)(2)(eta(3)-C(3)H(4)R)(2)] in THF (THF = tetrahydrofuran), followed by addition of [NEt(4)]Cl. Protonation of 1a in the presence of a donor ligand L affords the complexes [2,2-L(2)-closo-2,1,7-NiC(2)B(9)H(11)] (L = CO (2), CNBu(t) (3)). Addition of PEt(3) (1 equiv) to 2 produces quantitative conversion to [2-CO-2-PEt(3)-closo-2,1,7-NiC(2)B(9)H(11)], 4. Species 2-4 exhibit in solution hindered rotation of the NiL(2) fragment with respect to the eta(5)-C(2)B(9) cage unit. Protonation of 1a in the presence of a diene affords the neutral complexes [2-(eta(2):eta(2)-diene)-closo-2,1,7-NiC(2)B(9)H(11)] (diene = C(5)Me(5)H (5), dcp (6), cod (7), nbd (8), chd (9), and cot (10a); dcp = dicyclopentadiene, cod = 1,5-cyclooctadiene, nbd = norbornadiene, chd = 1,3-cyclohexadiene, and cot = cyclooctatetraene). Variable temperature (1)H NMR experiments show that the [Ni(diene)] fragments are freely rotating even at 193 K. A small quantity of the di-cage species [2,2'-micro-(1,2:5,6-eta-3,4:7,8-eta-cot)-(closo-2,1,7-NiC(2)B(9)H(11))(2)] (10b) is formed as a coproduct in the synthesis of 10a. This species can be rationally synthesized by protonation of 1a and subsequent addition of 10a.

The reagent Li(2)[7-NMe(3)-nido-7-CB(10)H(10)] reacts with [Mo(CO)(3)(NCMe)(3)] in THF-NCMe (THF = tetrahydrofuran) to give a molybdenacarborane intermediate which, upon oxidation by CH(2)[double bond]CHCH(2)Br or I(2) and then addition of [N(PPh(3))(2)]Cl, gives the salts [N(PPh(3))(2)][2,2,2-(CO)(3)-2-X-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (X = Br (1) or I (2)). During the reaction, the cage-bound NMe(3) substituent is transferred from the cage-carbon atom to an adjacent cage-boron atom, a feature established spectroscopically in 1 and 2, and by X-ray diffraction studies on several of their derivatives. When [Rh(NCMe)(3)(eta(5)-C(5)Me(5))][BF(4)](2) is used as the oxidizing agent, the trimetallic compound [2,2,2-(CO)(3)-7-mu-H-2,7,11-[Rh(2)(mu-CO)(eta(5)-C(5)Me(5))(2)]-closo-2,1-MoCB(10)H(9)] (10) is formed, the NMe(3) group being lost. Reaction of 1 in CH(2)Cl(2) with Tl[PF(6)] in the presence of donor ligands L affords neutral zwitterionic compounds [2,2,2-(CO)(3)-2-L-3-NMe(3)-closo-2,1-MoCB(10)H(10)] for L = PPh(3) (4) or CNBu(t) (5), and [2-Bu(t)C[triple bond]CH-2,2-(CO)(2)-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (6) when L = Bu(t)C[triple bond]CH. When 1 is treated with CNBu(t) and X(2), the metal center is oxidized, and in the products obtained, [2,2,2,2-(CNBu(t))(4)-2-Br-3-X-closo-2,1-MoCB(10)H(10)] (X = Br (7), I (8)), the B-NMe(3) bond is replaced by B-X. In contrast, treatment of 2 with I(2) and cyclo-1,4-S(2)(CH(2))(4) in CH(2)Cl(2) results in oxidative substitution of the cluster and retention of the NMe(3) group, giving [2,2,2-(CO)(3)-2-I-3-NMe(3)-6-[cyclo-1,4-S(2)(CH(2))(4)]-closo-2,1-MoCB(10)H(9)] (9). The unique structural features of the new compounds were confirmed by single-crystal X-ray diffraction studies upon 6, 7, 9 and 10.

The butadienyl moiety in the title compound is bound to both cage-boron and rhenium vertices, and arises from coupling of two alkyne molecules at the rhenium centre, unprecedented in metallacarbaborane chemistry.

Upon protonation, salts of the anionic complexes [closo-1,2-R’2-3-(≡CR)-3,3-(CO)2-3/l,2-MC2B9H9]≡ (1) and [closo-1,6-R’2-4-(≡CR)-4,4-(CO)2-4,1, 6-MC2B10H10]− (2) (M = W or Mo, R = alkyl, aryl or alkynyl; R’ = H or Me) afford a remarkable variety of unusual mono-or di-metal complexes, resulting from the juxtaposition of M≡CR and B-H groups on the surface of the respective metallacarbaborane cages. The nature of the products isolated depends on many factors including: (i) whether one or one-half of a molar equivalent of acid is used, (ii) whether the anion of the acid employed has ligating properties, e.g. HBF4 versus HC1 or HI, (iii) whether Lewis bases (L = CO, PPh3, CNBut, Ph2P(CH2)nPPh2 or PhC≡CPh) or donor molecules [M(≡CR)(CO)2(η-C5H5)] are present, (iv) whether the carbaborane cages contain CH or CMe vertices, and (v) whether the substituent R in the ≡CR fragment contains a functional group.

Intramolecular hydroxyl attack upon iron-coordinated nitriles in a {closo-2,1,10-FeC2B7} system forms imidates that allow construction of a tetra-cluster {FeC2B7}-{C2Co2}-{C2Co2}-{FeC2B7} molecule.

The first examples of rhenacarborane complexes with nitrosyl ligands have been prepared and used to synthesise alkylidene(nitrosyl)rhenacarboranes and a novel complex in which a conjoined carboranyl–iminium group is bound to rhenium both through the η5-C2B3 face of the cage and the iminium carbon atom.

The ferracarborane [N(PPh3)2][6,6,6,10,10,10-(CO)6-closo-6,10,1-Fe2CB7H8] (2) reacts in CH2Cl2 with 3 molar equivalents of Ag[PF6] to yield the trifluoro-substituted species [N(PPh3)2][7,8,9-F3-6,6,6,10,10,10-(CO)6-closo-6,10,1-Fe2CB7H5] (3). Compound 3 undergoes structural rearrangement in toluene at reflux temperatures, forming [N(PPh3)2][8,9,10-F3-6,6,6,7,7,7-(CO)6-closo-6,7,1-Fe2CB7H5] (4). Alternatively, reaction of either 2 or 3 with a 10-fold excess of Ag[PF6] in CH2Cl2 forms two species: namely, [N(PPh3)2][2,7,9,10-F4-6,6,6,8,8,8-(CO)6-closo-6,8,1-Fe2CB7H4] (5), in which one further B–F substitution has occurred and the {Fe2CB7} cluster core has rearranged, plus a mono-iron co-product, [N(PPh3)2][3,8,9-F3-7,7,7-(CO)3-closo-7,1-FeCB7H5] (6) that is formed by polyhedral contraction. Treatment of 3 with [NO][BF4] in CH2Cl2 results in CO substitution at the 4-connected iron vertex [Fe(10)], producing the zwitterionic complex [7,8,9-F3-6,6,6,10,10-(CO)5-10-NO-closo-6,10,1-Fe2CB7H5] (7). Addition of Me3NO to a mixture of 3 and PEt3 in CH2Cl2 also results in CO substitution, forming the isomeric species [N(PPh3)2][7,8,9-F3-6,6,m,10,10-(CO)5-n-PEt3-closo-6,10,1-Fe2CB7H5] [m = 6, n = 10 (8a); m = 10, n = 6 (8b)] in a 5 : 1 ratio. Treatment of 8a with [NO][BF4] and then CNBut in CH2Cl2 allows further, successive CO substitution at Fe(10) to yield first a neutral, zwitterionic complex [7,8,9-F3-6,6,6,10-(CO)4-10-NO-10-PEt3-closo-6,10,1-Fe2CB7H5] (9) and then [7,8,9-F3-6,6,6-(CO)3-10-CNBut-10-NO-10-PEt3-closo-6,10,1-Fe2CB7H5] (10). The molecular structures of compounds 3, 4, 5, 6, and 10 have been established by X-ray diffraction.

The title trianion reacts successively with cationic transition-metal fragments to afford a heterotrimetallic Mn-Mo-Pt species.

Treatment of the isomeric 12-vertex nickelacarbaborane salts [NEt(4)][3-(eta3)-C(3)H(5))-closo-3,1,2-NiC(2)B(9)H(11)] and [NEt(4)][2-(eta3)-C(3)H(5))-closo-2,1,7-NiC(2)B(9)H(11)] with [CuCl(PPh(3))](4) and Tl[PF(6)] affords the zwitterionic bimetallic species [3-(eta3)-C(3)H(5))-3,4,8-[Cu(PPh(3))]-4,8-(mu-H)(2)-closo-3,1,2-NiC(2)B(9)H(9)] and [2-(eta3)-C(3)H(5))-2,6,11-(Cu(PPh(3)))-6,11-(mu-H)(2)-closo-2,1,7-NiC(2)B(9)H(9)], respectively. Similarly, the 13-vertex nickelacarbaborane [NEt(4)][4-(eta3)-C(3)H(5))-closo-4,1,6-NiC(2)B(10)H(12)] reacts with sources of mono-cationic metal fragments to form [4-(eta3)-C(3)H(5))-7,8,13-(Cu(PPh(3)))-7,8,13-(mu-H)(3)-4,1,6-closo-NiC(2)B(10)H(9)], [4-(eta3)-C(3)H(5))-3,8-(Rh(PPh(3))(2))-3,8-(mu-H)(2)-4,1,6-closo-NiC(2)B(10)H(10)] and [4-(eta3)-C(3)H(5))-3,7,8-(RuCl(PPh(3))(2))-3,7,8-(mu-H)(3)-4,1,6-closo-NiC(2)B(10)H(9)]. The molecular structures of these five new bimetallic compounds were determined by X-ray diffraction studies, confirming that exopolyhedral Cu, Rh and Ru fragments are attached to the cluster via B-H[right harpoon up]M agostic-type interactions and, in the case of the (NiC(2)B(9)) species, by a metal-metal bond.

The salt [NEt4][10-endo-{Au(PPh3)}-nido-7,8-C2B9H9Me2] reacts with trans-[IrCl(CO)(PPh3)2] in thf (tetrahydrofuran), in the presence of TIBF4, to afford the complex [IrAu(CO)(PPh3)2(η5-7,8-C2B9H9Me2)]. The structure of this product was established by X-ray crystallography. The iridium is co-ordinated on one side by the open pentagonal face of a nido-icosahedral 7,8-C2B9H9Me2 group in an η5 bonding mode, and on the other by the PPh3 and CO ligands and an Au(PPh3) fragment [Ir–Au 2.616(2), Au–P 2.251(3)A, Ir–Au–P 175.8(1)°]. The related compound [IrAu(CO)2(PPh3)(η5-7,8-C2B9H9Me2)] is formed in the corresponding reaction using cis-[IrCl(CO)2(NH2C6H4Me-4)]. Small and variable amounts of a metal cluster species [Ir2Au4(µ-σ:η5-7,8-C2B9H8Me2)(CO)3(PPh3)4][7,8-C2B9H10Me2] are also produced in the latter reaction. Treatment of [IrCl(PPh3)3] with [NEt4][10-endo-{Au(PPh3)}-nido-7,8-C2B9H9Me2] affords the dimetal complex [IrAuH(µ-σ:η3-7,8-C2B9H8Me2)(PPh3)3], the structure of which was determined by X-ray crystallography. The Ir–Au bond [2.739(1)A] is spanned by a 7,8-C2B9H8Me2 group. The open [graphic omitted] pentagonal ring of the cage is attached to the iridium via its three boron atoms, while also being σ bonded to the gold atom through the boron atom in the β site with respect to the two carbons [Au–B 2.200(9)A]. The gold atom carries a PPh3 ligand [Au–P 2.320(2)A, P–Au–Ir 164.6(1)°], and the iridium is co-ordinated by two such groups [Ir–P 2.293 A(average), P–Ir–P 100.3(1)°] and a hydride ligand transoid to the gold [Ir–H 1.58(9)A, H–Ir–Au 168(3)°]. The NMR data (1H, 13C-{1H}, 31P-{1H} and 11B-{1H}) of the new compounds are reported and discussed in relation to the structures.

Treatment of thf (tetrahydrofuran) solutions of [MBr(CO)2(NCMe)2(η3-C3H5)](M = Mo or W) with Na2[7,8-C2B9H9R′2](R′= H or Me), followed by addition of [N(PPh3)2]Cl or [NEt4]Cl, afforded the salts [Y][M(CO)2(η3-C3H5)(η5-7,8-C2B9H9R′2)][Y = N(PPh3)2, R′= Me, M = Mo 1a or W 1b; Y = NEt4. R′= H, M = Mo 1c] in high yield. These species may be synthesised, but in lower yield, from allyl bromide and Tl2[M(CO)3(η5-7,8-C2B9H9R′2)] generated in situ. Protonation of the salts 1a and 1b with HBF4·Et2O in the presence of CO or PPh3 yielded the compounds [M(CO)2L2(η5-7,8-C2B9H9Me2)](M = Mo 2a or W 2b, L = CO; M = Mo 2c or W 2e, L = PPh3). The synthesis of 2c was accompanied by formation of the tricarbonyl species [Mo(CO)3(PPh3)(η5-7,8-C2B9H9Me2)]2d. Treatment of the salt 1c with HBF4·Et2O in the presence of buta-1,3-diene afforded the species [Mo(CO)2(η4-C4H6)(η5-7,8-C2B9H11)]5. When reactions of 1a–c with HBF4·Et2O were carried out in the presence of alkynes, the bis(alkyne) complexes [M(CO)(RC2R)2(η5-7,8-C2B9H9R′2)](M = Mo, R = R′= Me 6a; M = W, R = Ph, R′= Me 6b; M = Mo, R = Me, R′= H 6c) are formed. The compounds 6a and 6c can also be obtained from reactions between Tl2[Mo(CO)3(η5-7,8-C2B9H9R′2)] generated in situ, MeC≡CMe, and AgBF4. Reaction of the complex 6a with PMe2Ph gives the species [Mo(CO)(PMe2Ph)(MeC2Me)(η5-7,8-C2B9H9Me2)]6e. Treatment of the reagent Tl2[Mo(CO)3(η5-7,8-C2B9H9Me2)] with AgBF4 in the presence of [W(≡CC6H4-Me-4)(CO)2(η-C5H5)] afforded the dimetal complex [MoW(µ-CC6H4Me-4)(CO)3(η-C5H5)(η5-7,8-C2B9H9Me2)]7.

The reaction between the salt [Rh(NCMe)3(η-C5Me5)][BF4]2 and the reagents Na2[M(CO)3(η5-7,8-C2B9H9R′2)](M = Mo or W, R′= H or Me) in tetrahydrofuran affords [Rh(CO)2(η-C5Me5)] and the trimetal complexes [MRh2(µ-H)(µ-CO)(µ-σ:η5-7,8-C2B9H8R′2)(CO)2(η-C5Me5)2]. An X-ray diffraction study of the compound with M = W and R′= Me revealed a structure based on a triangulated metal core [Rh(1)–Rh(2) 2.859(1), W–Rh(1) 2.736(1), W–Rh(2) 2.822(1)A] with the Rh–Rh bond bridged by a hydrido ligand. Two of the carbonyl groups are terminally attached to the tungsten atom, while the third [W–C–O 154(1)°] semi-bridges a W–Rh bond. The open pentagonal C2B3 face of the carbaborane framework is η5 co-ordinated to the tungsten, but the cage also bridges the metal triangle through exopolyhedral B–Rh and B–H⇀Rh bonds, using boron atoms in the C2B3 ring attached to the tungsten. The B–Rh bond bridges the W–Rh vector which is asymmetrically bridged by the CO group, and involves the boron atom α to the carbons in the CCBBB ring. The B–H⇀Rh three-centre two-electron bond utilises the boron atom which is β to the carbons in the CCBBB ring. Examination of the NMR spectra (1H, 13C-{1H}, 11B-{1H}, 11B) of the trimetal complexes revealed that the structures of these molecules at –60 °C were similar to that established in the solid state for M = W and R′= Me. However, at ambient temperatures three of the complexes (M = Mo, R′= H or Me; M = W, R′= Me) isomerised to a structure [MRh2(µ-H)2(µ-CO)(µ-σ:σ′:η5-7,8-C2B9H7R′2)(CO)2(η-C5Me5)2] in which the carbaborane cage bridged the metal triangle via two B–Rh bonds.

In CH2Cl2 solutions at ca.–78 °C the salts [PPh4][W(CC6H4Me-4)(CO)2(η5-C2B9H9R′2)](R′= Me or H) upon treatment with HBF4·Et2O, in the presence of dppm (Ph2PCH2PPh2) or dppe (Ph2PCH2CH2PPh2), afford the complexes [[graphic omitted]Ph2}(CO)2(η5-C2B9H9R′2)](n= 1 or 2, R′= Me; n= 2, R′= H). The compound [[graphic omitted]Ph2}(CO)2(η5-C2B9H11)] was similarly prepared from [NEt4][W(CMe)(CO)2(η5-C2B9H11)], dppe and HBF4·Et2O. In contrast, treatment of [NEt4][W(CMe)(CO)2(η5-C2B9H9Me2)] in CH2Cl2 at –78 °C with HBF4·Et2O and dppe or dmpe (Me2PCH2CH2PMe2) gives the complexes [W(CO)2L2{η5-C2B9H8(Et)Me2}](L2= dppe or dmpe). The molecular structure of [[graphic omitted]Ph2}(CO)2(η5-C2B9H9Me2)] has been established by a single-crystal X-ray diffraction study. Within the five-membered [graphic omitted] ring the bond distance are W–C 2.342(9), C–P 1.802(9), P–C 1.81 (1) and P–W 2.482(3)A. The ligated carbon and phosphourus atoms of the ring, and the two essentially linearly bound CO ligands, form a pyramidal arrangement with the tungsten atom, the other side of which is co-ordinated by the nido-icosahedral C2B9H9Me2 cage in the usual η5 manner. The NMR spectra (1H, 13C-{1H}, 31P-{1H} and 11B-{1H}) of the new compounds are reported and discussed in relation to their structures.

Protonation (HBF4·Et2O) of equimolar mixtures of the compounds [M(CC6H4Me-4)(CO)2(η-C5H5)](M = Mo or W) and [NEt4][W(CCCBut)(CO)2(η5-7,8-C2B9H11)] in CH2Cl2 at –78 °C affords the dimetal complexes [MW{µ-η3 : η2-C(But)CC[C(H)C6H4Me-4]}(CO)4(η5-7,8-C2B9H11)(η-C5H5)]. The ditungsten compounds was also obtained by protonating equimolar mixtures of [W(CCCBut)(CO)2(η-C5H5)] and [NEt4][W(CC6H4Me-4)(CO)2(η5-7,8-C2B9H11)], and the species [W2{µ-η3 : η2-C(But)CC[C(H)C6H4Me-4]}(CO)4(η5-7,9-C2B9H11)(η-C5H5)] was similarly prepared by treating equimolar mixtures of [W(CC6H4Me-4)(CO)2(η-C5H5)] and [NEt4][W(CCCBut)(CO)2(η5-7,9-C2B9H11)] with HBF4·Et2O. The structure of [MoW{µ-η3 : η2-C(But)CC[C(H)C6H4Me-4]}(CO)4(η5-7,8-C2B9H11)(η-C5H5)] has been established by X-ray diffraction. The Mo–W bond [3.031(2)A] is bridged by a C(But)CC[C(H)C6H4Me-4] unit [average C–C 1.40(3)A]. All three carbon atoms of the chain ligate the Mo atom but only two carbons of the C(But)CC fragment ligate the W atom. The latter is also co-ordinated by the nido-icosahedral 7,8-C2B9H11 cage and two CO groups, and the Mo atom is co-ordinated by a C5H5 ring and two CO ligands, as expected. Solutions of the compounds [MW{µ-η3 : η2-C(But)CC[C(H)C6H4Me-4]}(CO)4(η5-7,8- or -7,9-C2B9H11)(η-C5H5)] slowly (days) convert into new species of formulation [MW{µ-η3 : η2,η5-C(H)(C6H4Me-4)CC[C(H)(But)(7,8- or 7,9-C2B9H10)]}(CO)4(η-C5H5)], a process accelerated by refluxing in tetrahydrofuran. The 1H and 13C{1H} NMR data of the new compounds are reported and discussed in relation to the structures proposed.

Treatment of carbon monoxide-saturated solutions of the salts [NEt4][W(CR)(CO)2(η5-C2B9H9Me2)](R = C6H4Me-4 or Me) at ca.–78 °C with HBF4·Et2O affords the complexes [W(CO)4{η5-C2B9H8(CH2R)Me2}]. If these protonation reactions are carried out in the presence of PhCCPh, the alkynetungsten complexes [W(CO)(PhC2Ph)2{η5-C2B9H8(CH2R)Me2}] are formed via the intermediacy of dicarbonyl species [W(CO)2(PhC2Ph)2{η5-C2B9H8(CH2R)Me2}]. The latter (R = C6H4Me-4) with PMe3 yields the compound [W(CO)(PMe3)(PhC2Ph){η5-C2B9H8(CH2C6H4Me-4)Me2}]. Treatment of [NEt4][W (CC6H4Me-4)(CO)2(η5-C2B9H9Me2)] with HBF4·Et2O in the presence of CNBut yields [W(CO)2(CNBut)2{η5-C2B9H8(CH2C6H4Me-4)Me2}], whereas if PPh3 is used instead of CNBut a tricarbonyl species [W(CO)3(PPh3){η5-C2B9H8(CH2C6H4Me-4)Me2}] is isolated. However, the latter disproportionates in solution to afford the bis(triphenylphosphine) complex [W(CO)2(PPh3)2{η5-C2B9H8(CH2C6H4Me-4)Me2}], crystals of which have been analysed by X-ray crystallography. The tungsten atom is η5 co-ordinated by the C2B9H8(CH2C6H4Me-4) Me2 ligand and is ligated by two CO and two PPh3 groups, having transoid arrangements. The CH2C6H4Me-4 substituent on the cage is bonded to the boron atom which is in the β site with respect to the two carbons in the open pentagonal [graphic omitted] face of the nido-icosahedral C2B9 fragment. This geometry accounts for the NMR data (1H, 13C-{1H} and 11B-{1H}) for all the new complexes reported containing the C2B9H8(CH2R)Me2 cage system.

The salt [NEt4][10-endo-{Au(PPh3)}-7,8-nido-C2B9H9Me2] has been used to synthesise several complexes in which gold forms bonds with rhodium and iridium, including [IrAuH(µ-σ,η3-C2B9H8Me2)(PPh3)3], [exo-nido-5,10-{Rh(PPh3)2}-5,10-µ-(H)2-10-endo-{Au(PPh3)}-7,8-C2B9H7Me2]·CH2Cl2, and [RhAu2(µ-H)(PPh3)3(η5-C2B9H9Me2)]·2(CH2Cl2).

The alkylidynemetal complexes [M(CR)(CO)2{HC(pz)3}][BF4][HC(pz)3= tris(pyrazol-1-yl)methane; M =W, R =Me, C6H4Me-4, or C6H3Me2-2,6; M = Mo, R = Me or C6H4Me-4], [W(CMe)(CO)2{MeC(pz)3}][BF4][MeC(pz)3=1,1,1 -tris(pyrazol-1 -yl)ethane], and [W(CMe)(CO)3{H2C(pz)2}][BF4][H2C(pz)2= bis(pyrazol-1-yl)methane] have been prepared by treating the complexes [MBr(CR)(CO)4] in thf (tetrahydrofuran) with TIBF4 and HC(pz)3, MeC(pz)3, and H2C(pz)2, respectively. Reactions of the salts [W(CR)(CO)2{HC(pz)3}][BF4](R = Me or C6H4Me-4) with the compounds [Co2(CO)8], [Pt(nb)3](nb = norbornene = bicyclo[2.2.1]heptene), and [Pt(nb)(PMe2Ph)2] afford the mixed-metal complexes [WCo2(µ3-CR)(CO)8{HC(pz)3}][BF4], [W2Pt(µ-CR)2(CO)4{HC(pz)3}2][BF4]2, and [WPt(µ-CR)(CO)2(PMe2Ph)2{HC(pz)3}][BF4], respectively. A trimetal complex [WPtAu(C6F5)(µ3-CMe)(CO)2(PMe2Ph)2{HC(pz)3}][BF4] has been prepared by addition of [Au(C6F5)(tht)](tht = tetrahydrothiophene) to [WPt(µ-CMe)(CO)2(PMe2Ph)2{HC(pz)3}][BF4] in thf. The n.m.r. data (1H, 13C-{1H}, and 31P-{1H}) for the new compounds are reported and discussed in relation to the structures proposed.

The trimetal compounds [MWAu(µ-CR)(µ-CR′)(CO)4(η-C5H5)(η5-C2B9H9Me2)](M = Mo or W, R = R′= C6H4Me-4; M = W, R = R′= Me; R = Me, R′= C6H4Me-4) have been prepared by treating the complexes [MAuCl(µ-CR′)(CO)2(η-C5H5)](M = Mo or W, R′= C6H4Me-4; M = W, R′= Me) with the reagents [NEt4][W(CR)(CO)2(η5-C2B9H9Me2)](R = C6H4Me-4 or Me) in CH2Cl2 in the presence of TIBF4. The trimetal compounds react with [Pt(cod)2](cod = cyclo-octa-1,5-diene) or [Pt(PMe2Ph)2(nb)](nb = norbornene = bicyclo [2.2.1]heptene) to afford, respectively, the complexes [W2PtAu(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(cod)(η-C5H5)(η5-C2B9H9Me2)] and [MWPtAu(µ-CR′)(µ3-CR)(CO)4(PMe2Ph)2(η-C5H5)(η5-C2B9H9Me2)](M = W, R = R′= C6H4Me-4; R = Me, R′= C6H4Me-4; M = Mo, R = R′= C6H4Me-4). The cod complex was prepared by an alternative method, by treating [NEt4][WPt(µ-CC6H4Me-4)(CO)2(cod)(η5-C2B9H9Me2)] with [WAuCl(µ-CC6H4Me-4)(CO)2(η-C5H5)], in the presence of TIBF4. Addition of an excess of PMe2Ph in thf (tetrahydrofuran) to [W2PtAu(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(cod)(η-C5H5)(η5-C2B9H9Me2)] in the same solvent results in displacement of both cod and W(CC6H4Me-4)(CO)2(η-C5H6) groups, and formation of the trimetal complex [WPtAu(µ3-CC6H4Me- 4)(CO)2(PMe2Ph)3(η5-C2B9H9Me2)]. The i.r. and n.m.r. (1H and 13C-{1H}) data for the compounds are reported and discussed.

Treatment of the complex [Mo(CO)2(NCMe)2(η5-C9H7)][BF4](C9H7= indenyl) with the salts [NEt4][W(CCCBut)(CO)2(η5-C2B9H9Me2)]and [NEt4][Mo(CC6H4Me-4)(CO){P(OMe)3}(η5-C2B9H9Me2)] in CH2Cl2 affords, respectively, the dimetal compounds [MoW(µ-CCCBut)(CO)3(η5-C9H7)(η5-C2B9H9Me2)]and[Mo2(µ-CC6H4Me-4)(CO)2{P(OMe)3}(η5-C9H7(η5-C2B9H9Me2)]. Similarly, reactions between the salts [NEt4][M(CR)(CO)2(η5-C2B9H9R′2)](M = Mo or W, R = C6H4Me-4, R′= H; M = W, R = C6H4Me-4 or C6H4Me-2, R′= Me; M = W, R = CCBut, R′= Me) and [Mo(CO)2(NCMe)(η7-C7H7)][BF4] yield the dimetal complexes [MMo(µ-CR)(CO)2(η7-C7H7)(η5-C2B9H9R′2)](M = W, R = C6H4Me-4, C6H4Me-2, or CCBut, R′= Me; M = Mo or W, R = C6H4Me-4, R′= H). The compounds [MoW(µ-CC6H4Me-4)(CO)2(η7-C7H7)(η5-C2B9H10Me)] and [MoW(µ-CC6H4Me-4)(CO)2(η7-C7H7)(η6-C2B10H10Me2)] have also been prepared using the reagents [NEt4][W(CC6H4Me-4)(CO)2(η5-C2B9H10Me)] and [NEt4][W(CC6H4Me-4)(CO)2(η6C2B10H10Me2)]. All the dimetal compounds have structures in which the metal–metal bonds are bridged by an alkylidyne group and by a B–H⇀Mo three-centre two-electron bond. The latter involves a boron atom lying in the face of the nido-carbaborane fragment which is co-ordinated to the other metal centre in the η5(for C2B9H9R′2) or η6(for C2B10H10Me2) bonding mode. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, 11B, and 31P-{1H}) for the new compounds are reported and discussed in the context of the structures proposed.

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.

Tricarbonyl(η7-cycloheptatrienyl)molybdenum tetrafluoroborate reacts with halogenotrimethyl silanes to give initially the complexes [MoX(η7-C7H7)(CO)2](X = Cl, Br, or I). These complexes undergo further reaction to yield the dimolybdenum species [Mo2X3(η7-C7H7)2]. The tri-iodo-complex has also been obtained by treating [Mo(η6-C6H5Me)(η7-C7H7)][BF4] with SiMe3I. Electrochemical studies suggest the existence of cationic complexes [Mo2X3(η7-C7H7)2]+, and this has been chemically accomplished with the mild oxidising agents p-NO2C6H4N2BF4, PhN2PF6, and I2. Moreover, [Mo(η7-C7H7)(CO)3][BF4] reacts with iodine to give [MO2-(µ-I)3(η7-C7H7)2][I3].

The title compound can be prepared in good yield by heating either [Ru4(μ-H)4(CO)12] or [Au2Ru4(μ3-H)2(CO)12(PPh3)2] with [AuMe(PPh3)] in toluene. The related compound [Au3Ru4(μ3-H)(μ-dppm)(CO)12(PPh3)] has also been prepared. Both trigoldtetraruthenium clusters undergo dynamic behaviour in solution, involving intramolecular rearrangement of the metal core, as revealed by variable temperature NMR studies. The crystal structure of [Au3Ru4(μ3-H)(CO)12(PPh3)3] has been established by an X-ray diffraction study. The metal atom core comprises a trigonal bipyramidal AuRu4 unit with two AuRu2 faces capped by gold atoms.

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.