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Solar cells (SCs) are of considerable current research interest because of their potential as a clean alternative to fossil fuels. Researchers across the globe are developing novel polymeric materials with enhanced power conversion efficiency (PCE). Conjugated poly-ynes and poly(metalla-ynes) incorporating late transition metals and thiophene-based spacers have played a very important role in this strategic area of materials research. The performance of the SCs can be optimized by varying the conjugated spacers and/or the metal ions along the polymer backbone. Therefore, an analysis of structure-photovoltaic property relationships in poly-ynes and poly(metalla-ynes) is desirable as a guide for the development of new functional materials for use in SCs. Keeping the importance of this strategic topic in mind, herein we present a brief review on conjugated poly-ynes and poly(metalla-ynes) incorporating thiophene-based spacers that have potential SC applications. Attempts have been made to correlate the photovoltaic performance of the SCs to the chemical structure of thiophene-incorporated poly-ynes and poly(metalla-ynes). The performance of SCs is also strongly influenced by other factors such as morphology and device structure.

The reactions of [Os-3(mu-CO)(CO)(9){mu(3)-eta(2)-Me3SiCCC CSiMe3}] with phosphorus donor ligands (PPh3, PEt3, P(OEt)(3), PHPh2 and a diphosphine; Ph2PCH2PPh2 (dppm)) afford carbonyl mono-substitution products [Os-3(mu-CO)(CO)(8){mu(3)-eta(2)-Me3SiC2C2SiMe3}] even in the case of the bidentate phosphine dppm. All the complexes have been characterized by IR and multinuclear NMR spectroscopy and for 2 (L = PPh3), 3 (L = PEt3), 4 (L = P(OEt)(3)) and 5 (L = eta(1)-dppm) the structures have been confirmed by single- crystal X- ray analysis. The structural analyses show that in all four clusters the substitution has occurred at one of osmium equatorial sites that is sigma- bonded to the mu(3)-eta(2)-alkyne. (C) 2009 Published by Elsevier B.V.

A series of aromatic ethynyl-bridged ferrocenes with the general formula Fc–CC–R–CC–Fc (Fc=ferrocenyl, R=C6H2(-p-CH3)2 (1), C6H4-p-C6H4 (2), C5H3N (3), 9,10–C14H8 (4), C4H2S (5), (C4H2S)2 (6) and (C4H2S)3 (7)) has been synthesised by the reaction of ethynyl ferrocene with the appropriate dibromo-arenes. The new complexes have been characterised by spectroscopic techniques. The structures of 3 and 7 were determined via X-ray crystallography, and both show the trans–trans configuration of the two ethynyl ferrocene groups with respect to the central R group. The electronic properties of the compounds have been studied via optical spectroscopy and cyclic voltammetry.

The reaction between [Os3H2(CO)10] and 1,4-diphenylbuta-1,3-diyne yields two isomers of the triosmium cluster [Os3(μ-H)(CO)10{μ3-η1:η3:η1-Ph(C)C9H6)}] 1, 2, the structures of which involve an ‘open’ metal triangle and exhibit an unusual pseudo-allylic interaction involving a fused six- and five-membered ring system obtained from a ring-closure reaction of the diyne. Thermal decarbonylation of 1 and 2 produces [Os3(μ-H)(CO)9{μ3-η1:η3:η1-Ph(C)C9H6)}] (3) which has a ‘closed’ Os3 triangular core and the same formal μ3-η1:η3:η1-allylic coordination mode. The reaction of 1 with trimethylamine-N-oxide in the presence of acetonitrile affords [Os3(μ-H)(CO)8(MeCN){μ3-η1:η3:η1-(Ph(C)C9H6)}] (4), an acetonitrile-substituted derivative of 3. The structures of clusters 1–4 have been established by X-ray crystallography, and all the new clusters have been characterised spectroscopically.

Reaction of the sulphur-capped dicobalt–iron complex [Co 2 Fe(μ 3 -S)(CO) 9 ] with cyclo -(PhAs) 6 in toluene at 70 °C gives [Co 2 Fe(μ 3 -S){μ- cyclo -(PhAs) 6 }(CO) 7 ] ( 1 ) as the only product in good yield. Conversely, treatment of [Co 2 Fe(μ 3 -S)(CO) 9 ] with cyclo -(PhP) 6 under the same reaction conditions gives two isomers [Co 2 Fe(μ 3 -S){μ- cyclo -(PhP) 6 }(CO) 7 ] ( 2 ) and [Co 2 Fe(μ 3 -S){μ- cyclo -(PhP) 6 }(CO) 7 ] ( 3 ) in ca. 1:1 ratio. Single crystal X-ray analysis shows 1 and 2 to be isostructural with the intact six-membered ring adopting a chair conformation and bridging a cobalt–cobalt edge via either two arsine ( 1 ) or two phosphorus ( 2 ) atoms in the 1,5 positions of the respective rings. Thermolysis of 2 or of 3 in toluene at 120 °C gives [Co 2 Fe(μ 3 -SPPh)(μ-η 2 :η 2 :η 1 -P 5 Ph 5 )(CO) 5 ] ( 4 ) in moderate yield, while thermolysis of 1 under the same conditions leads to complete decomposition. A single crystal X-ray diffraction study performed on 4 reveals the cyclo -hexaphosphane rings in 2 or 3 to have cleaved to give a P 5 Ph 5 chain and a PPh group, the latter of which has additionally undergone coupling with the sulphur cap.

The reaction between [Os3(CO)10(NCMe)2] and MeC2C2Me yields the known cluster [Os3(CO)9(μ-CO)(μ3-η2-MeC2C2Me)] (1) and three previously uncharacterised products [Os3(CO)9(μ-CO){μ3-η2:μ3-η1:η1:η3-MeC2C2MeOC5Me2)Os3(μ-CO)(CO)9] (2), [Os3(CO)9{μ3-η4-[(MeC2)C2(Me)]CO[(Me)C2(C2Me)]}] (3) and [Os3(CO)9{μ3-η4-[(MeC2)C2(Me)]CO[(MeC2)C2(Me)]}] (4). The structures of 2 and 3 have been determined by X-ray crystallography. Cluster 2 incorporates two linked triosmium clusters joined by an unsaturated five-membered metallacycloether ring and 3 exhibits an alkyne-functionalised metallacyclohexadieneone ring. 1–4 and [Os3(CO)9(μ-CO)(μ3-η2-PhC2C2Ph)] (5) react with [Co2(CO)8] to form products 6–11 in which one free alkyne function coordinates to a Co2(CO)6 unit in each case; the cluster [{Os3(CO)10}{Co2(CO)6}{μ3-η2-‖-(MeCC)(μ2-η2(CCMe)}] (6) has been structurally characterised. The reaction of 1 and 5 with Me3NO–MeCN leads to the replacement of one CO ligand with MeCN, the products 12 and 13 reacting with H2O to form [Os3(CO)9(μ-OH)(μ3-η1:η2:η2-RC3CHR)] (R=Me (two isomers 14, 15), Ph (16)); the X-ray structure of 16 is reported. Reaction of 3 with Me3NO–MeCN results in the substitution of a CO ligand with either a MeCN or NMe3 ligand at the metallocyclic Os atom to afford the clusters [Os3(CO)8(L)(μ3-η1:η1:η2:η2-{(MeC2)C2(Me)}2CO)] (L=NCMe (17), NMe3 (18)).

Thermolysis of the tetranuclear cobalt cluster [Co4(μ3-AsPh)(μ4-η2:η2:η1-As4Ph4)(μ-CO)2(CO)8] (1) at 60°C in benzene for two days gives [Co4(μ3-AsPh)2(μ3-η2:η1-As2Ph2)(μ-CO)(CO)9] (2), in which the tetraarsine chain in 1 has been cleaved to give the bridging As2Ph2 unit in 2. Similar fragmentation of the As4Ph4 chain occurs on treatment of 1 with [Fe2(CO)9] in benzene at room temperature for 3 days affording [Co4(μ3-AsPh)2{(μ3-η2:η1-As2Ph2)Fe(CO)4}(μ-CO)(CO)9] (3), in which one arsine atom of the As2Ph2 bridging ligand is additionally bound to an Fe(CO)4 unit. Conversely, reaction of 1 with excess P(OMe)3 at room temperature in benzene for 3 days gives the trisubstituted trimethylphosphite derivative [Co4(μ3-AsPh)(μ4-η2:η2:η1-As4Ph4)(μ-CO)2(CO)5{P(OMe)3}3] (4), in which the As4Ph4 unit remains intact. Single crystal X-ray diffraction studies have been performed on 2, 3 and 4 and possible reaction pathways for the formation of the new complexes are proposed and discussed.

Reduction of the mixed-metal octanuclear cluster [Os6(CO)17(Au2dppm)] (1) with Na–Hg amalgam and subsequent reaction with one equivalent of [Au2dppm][NO3] affords two isomers of the neutral decanuclear cluster [Os6(CO)17(Au2dppm)2] (2a, 2b). In a similar reaction between the reduced form of 1 with two equivalents of [AuPPh3][NO3] gives two isomers of the related cluster [Os6(CO)17(Au2dppm2)(AuPPh3)2] (3a, 3b). All the new clusters have been characterised by IR and NMR spectroscopy and FAB mass spectrometry. The molecular and crystal structure of 2a has been established by a single-crystal X-ray structure. In 2a the six Os atoms define an octahedron, in contrast to the bicapped tetrahedral osmium core previously observed for 1. Two of the Au atoms in 2a cap adjacent triangular faces of the Os6 octahedron while the third spans an open OsAu2 triangle, and the fourth caps a closed OsAu2 triangle. Overall the decametal core may be viewed as an octahedron fused with a capped square based pyramid.

The reaction of [Os3H2(CO)10] with Me3SiC2C2SiMe3 affords both [Os3(μ-H) (CO)10{μ-η1-η2-HC2(SiMe3)C2(SiMe3)}] (1) and [Os3(μ-CO)(CO)9(μ3-η2-Me3SiC2C2SiMe3)] (2) in good yield, 2 being favoured with an excess of diyne. In 1, one edge of the triosmium unit is bridged by the vinyl moiety of a transformed bis(trimethylsilyl)-1,4-butadiyne ligand that has undergone a hydride transfer and a 1,2-trimethylsilyl shift. Compound 2 is selectively desilylated in methanol to produce a single isomer of the known cluster [Os3(μ-CO)(CO)9{μ3-η2-HC2C2SiMe3}] (3). Whereas reaction of 3 with [Co2(CO)8] results in the production of the previously reported cluster [Os3{μ3-η2-:μ-η2-(Me3SiC2C2H)[Co2(CO)6]}(μ-CO)(CO)9] (4) and a second product [Os3(μ-H)(CO)9{μ3-η1:η2-;μ-η2-Me3SiC2C2[Co2(CO)6]}] (5), the reaction of 1 and 2 results in recovery of the starting material or transfer of the alkyne ligand to the Co2 unit. Compound 4 undergoes a transformation to 5 in visible light. All the cluster complexes have been characterized spectroscopically, and the solid-state structures of 1, 2 and 5 have been determined by single-crystal X-ray diffraction.

The iron–cobalt phosphido-bridged complex [(OC)4Fe(μ-PPh2)Co(CO)3] (1) can be prepared conveniently and in good yield from the reaction of [Co2(μ-PPh2)2(CO)6] with [Fe(CO)5]. A study of the reactivity of 1 towards symmetrical and unsymmetrical alkynes, R1CCR2 (R1=R2=CO2Me, Ph; R1=H, R2=Ph), has been undertaken. In all cases, five-membered ferracycle-containing products of the type [(OC)3Fe{μ-PPh2C(O)CR1CR2}Co(CO)3] (R1=R2=CO2Me (2a), Ph (2c); R1=H, R2=Ph (2b)), are initially obtained in which a molecule of CO and a molecule of R1CCR2 have been inserted regiospecifically into a CoP bond in 1. Decarbonylation of 2a occurs during its preparation or in low yield on its thermolysis to give the four-membered ferracyclic species [(OC)3Fe{μ-PPh2C(CO2Me)C(CO2Me)}Co(CO)3] (3a). Similar thermolysis of 2b results not only in the related decarbonylation product [(OC)3Fe(μ-PPh2CHCPh)Co(CO)3] (3b), but additionally in three other products all in low yield, namely the regioisomer of 3b, [(OC)3Fe(μ-PPh2CPhCH)Co(CO)3] (4b), the aldehyde-substituted complex [(OC)3Fe{μ-PPh2C(CHO)CPh}Co(CO)3] (5b) and the five-membered ferracycle-containing species [(OC)3Fe{μ-PPh2CHCPhC(O)}Co(CO)3] (6b). Treatment of 2a and 2b with PPhMe2 and P(OMe)3 results in substitution of an iron-bound carbonyl group to give, respectively, [(PhMe2P)(OC)2Fe{μ-PPh2C(O)C(CO2Me)C(CO2Me)}(μ-CO)Co(CO)2] (7a) and [{(MeO)3P}(OC)2Fe{μ-PPh2C(O)CHCPh}(μ-CO)Co(CO)2] (7b) in high yield. In contrast, substitution of a cobalt-bound carbonyl is achieved on reaction of 3a with PPhMe2 or PPh2H to give [(OC)3Fe{μ-PPh2C(CO2Me)C(CO2Me)}Co(CO)2(L)] (L=PPhMe2 (8a), PPh2H (9a)). Thermolysis of the secondary phosphine-substituted complex 9a results in phosphorushydrogen bond cleavage to give [(OC)3Fe{μ-PPh2C(CO2Me)CH(CO2Me)}(μ-PPh2)Co(CO)2] (10a). Single-crystal X-ray diffraction studies have been performed on complexes 7b, 8a and 10a.

Reaction of the hexaosmium cluster [Os 6 (CO) 18 ] with 1.1 equivalents of Me 3 NO, in CH 2 Cl 2 , in the presence of one equivalent of [Au 2 dppm]Cl 2 (dppm=Ph 2 PCH 2 PPh 2 ), at room temperature, affords the new mixed-metal cluster [Os 6 (CO) 17 (Au 2 dppm)] ( 1 ), in high yield. Subsequent reduction of 1 with Na–Hg amalgam, and subsequent treatment with [Ru(η 5 -C 5 H 5 )(MeCN) 3 ][PF 6 ] ( 2 ) afforded two decanuclear clusters [Os 6 (CO) 17 (Au 2 dppm){Ru(η 5 -C 5 H 5 )} 2 ] ( 3 ) and [Os 6 (CO) 16 (Au 2 dppm){Ru(η 5 -C 5 H 5 )} 2 ] ( 4 ) in moderate yield. Cluster 3 loses CO under reflux in toluene to produce 4 . The new clusters have been fully characterised by IR, 1 H- and 31 P-NMR spectroscopies, and mass spectrometry. The molecular and crystal structures of 1 and 3 have been established by single-crystal X-ray analyses. In 1, the bicapped tetrahedral osmium core of [Os 6 (CO) 18 ] is retained and the two Au atoms of the Au 2 dppm group cap one Os 3 face in a μ 3 -η 2 bonding mode. In 3 the metal core consists of a capped square-based pyramidal arrangement of Os atoms that is capped over the square face by the Au 2 dppm group. One Ru atom caps another face of the Os 5 square-based pyramid, and the second Ru atom caps the Ru atom, two Os atoms and an Au atom to form a trigonal bipyramidal arrangement.

The thioarsine, AsMe 2 (SPh), reacts thermally with [Fe(CO) 5 ] to give the new bimetallic butterfly complex, [Fe 2 (CO) 6 (μ-AsMe 2 )(μ-SPh)] ( 1 ). Similarly, thermolysis of the thioarsine AsPh 2 (SPh) with [Fe 2 Cp 2 (CO) 4 ] and [Mn 2 (CO) 10 ] affords, respectively [Fe 2 Cp 2 (CO) 2 (μ-AsPh 2 )(μ-SPh)] ( 2 ) and [Mn 2 (CO) 8 (μ-AsPh 2 )(μ-SPh)] ( 3 ). At room temperature, AsPh 2 (SPh) reacts rapidly with [Co 2 (CO) 8 ] to yield the trimetallic product, [Co 3 (μ 3 -S)(μ-AsPh 2 )(CO) 6 AsPh 3 ] ( 4 ). The crystal structures of these four products have been determined by X-ray crystallography. Arsenic–sulfur bond cleavage is a feature of all these reactions; concomitant arsenic–carbon bond formation is observed in the production of complex 4 .

The synthesis of a series of metal mono-acetylides trans-[(dppe)2Ru(Cl)(CC–R)] (R=C6H4-p-C6H5, C6H4-p-CH3, C6H4-p-NO2, C6H3-o-CH3-p-NO2, dppe=Ph2PCH2CH2PPh2), and unsymmetrical metal bis-acetylides trans-[(dppm)2M(CC–R)(CC–R′)]; (M=Ru, Os; R=C6H4-p-NO2, R′=C6H5, C6H4-p-CH3; R=C6H5, R′=C6H4-p-CH3) using a variety of σ-acetylide coupling reactions is reported. Three compounds have been structurally characterised, including the unsymmetrical trans-[(dppm)2Os(CC–R)(CC–R′)] (R=C6H4-p-CH3, R′=C6H4-p-NO2] which shows the ‘rigid-rod’ nature of the acetylide-metal-acetylide linkage. The electrochemistry of symmetrical and unsymmetrical Ru(II) complexes demonstrates the role of the acetylide and the auxiliary ligands in determining the ease of oxidation at the metal centre whilst UV–vis spectral changes illustrate the influence of electron-withdrawing and -donating ligands.

Reaction of (4,4′–bis–tert–butyl–2,2′–dipyridyl) platinum bis–alkynyl [(tBu2bipy)Pt(CCR)2] (R=C6H4Me 1a, SiMe3 1b) with Group 11 metal thiocyanate salts (M=Cu, Ag) affords 1:1 mixed-metal complexes [(tBu2bipy)Pt(CCR)2M(SCN)] (M=Cu, R=C6H4Me 2a, SiMe3 2b; M=Ag, R=C6H4Me 3a, SiMe3 3b). X-ray analyses of the complexes 2a and 3b show that the group 11 metal is bonded in an η2 fashion to two carbon–carbon triple bonds so that the co-ordination geometry is trigonal planar. The Pt atom geometry in both complexes is square planar. An electrochemical study of the copper complexes 2a and 2b reveals one fully reversible one electron reduction that is consistent with the first reduction of the co-ordinated bipyridyl ligand. There is also an irreversible one electron oxidation that corresponds to the CuI to CuII transition.

The reaction of [Os4H4(CO)11]2− 2, formed by the reduction of [Os4H4(CO)12] 1 with K/Ph2CO, with the cation [Rh(η5-Cp*)(MeCN)3]2+ (Cp*C5Me5) 3, affords a number of penta- and hexanuclear mixed-metal clusters depending on the reaction conditions. If only sufficient K/Ph2CO is added to dissolve all of 1, and the dication 3 added, a low yield of a blue cluster [Os4Rh(μ-H)3(MeCNH)(CO)11(η5-Cp*)] (Cp*C5Me5) 4 is obtained in addition to large quantities of 1. If an excess of K/Ph2CO is added so that reduction of 1 is complete, and then the dication 3 added, two new products [Os4Rh(μ-H)2(CO)13(η5-Cp*)] 5 and [Os4Rh2(μ-H)2(CO)11(η5-Cp*)2] 6 are obtained in low yield. The three new complexes have been characterised spectroscopically and crystallographically. Cluster 4 contains the uncommon MeCNH group coordinated to an edge-bridged tetrahedral metal framework. The metal framework in 5 is also a Rh edge-bridged Os4 tetrahedron while that of 6 is a bicapped tetrahedron, with two Rh atoms face capping two faces of an Os4 tetrahedron.

Reaction of the mixed-metal alkyne-bridged complexes [(η5-C5H5)(OC)2M{μ-C2(CO2Me)2}Co(CO)3] (M=Mo or W) with Ph2PCCtBu in refluxing toluene gives the complexes [(η5-C5H5)(OC)2M{μ-tBuCCC(CO2Me)C(CO2Me)PPh2}Co(CO)2], [(η5-C5H5)(OC)2M{μ-C2(CO2Me)2}Co(CO)2(Ph2PCCtBu)] (MMo or W) and [(η5-C5H5)(OC)W{μ-C(CO2Me)C(CO2Me)CCtBu}(μ-PPh2)Co(CO)2]. The structures of the two complexes, [(η5-C5H5)(OC)2Mo{μ-tBuCCC(CO2Me)C(CO2Me)PPh2}Co(CO)2] and [(η5-C5H5)(OC)W{μ-C(CO2Me)C(CO2Me)CCtBu}(μ-PPh2)Co(CO)2], have been determined by X-ray analysis. Possible reaction pathways for the formation of the new complexes are proposed and discussed.

Treatment of [Os 4 H 4 (CO) 11 ] 2− , [Os 10 C(CO) 24 ] 2− and [Ru 10 C(CO) 24 ] 2− with [Au 2 (Ph 2 PCH 2 PPh 2 )Cl 2 ] in the presence of an excess of TIPF 6 , gave [Os 4 H 4 (CO) 11 (Au 2 Ph 2 PCH 2 PPh 2 )] 1 , [Os 10 C(CO) 24 (Au 2 Ph 2 PCH 2 PPh 2 )] 2 and [Ru 10 C(CO) 24 (Au 2 Ph 2 PCH 2 PPh 2 )] 3 , respectively, all of which were obtained in high yield. The structures of the clusters l and 3 have been established by X-ray crystallography, both exhibiting novel coordination modes of the bidentate gold fragments. Cluster 1 contains a tetrahedral Os 4 core with one of the Au atoms of the Au 2 (Ph 2 PCH 2 PPh 2 ) ligand bridging an edge of the tetrahedron, and the second Au atom coordinated to a third Os atom. In 3 the two Au atoms of the Au 2 (Ph 2 PCH 2 PPh 2 ) ligand cap two adjacent, vertex sharing, triangular faces of the Ru 10 tetracapped octahedral core.

The reaction of [PhCCLi] n with Se metal (1:1 equivalents) in THF/TMEDA gives the insertion product [PhCCSeLi · TMEDA · THF] 1 , which is monomeric in the solid state. The reaction of PhCCPh with Li metal, generating dilithium tetraphenylbutadiene in situ, followed by the addition of elemental Se gives the selenophene [{PhC} 4 Se] 2 , as a result of insertion of Se followed by the elimination of Li 2 Se. The latter provides a clean and direct route to compounds of this type.

Terminal metal acetylide complexes trans -[(dppm) 2 (Cl)Os(–C C-R-C C–H)] (dppm=Ph 2 PCH 2 PPh 2 , R=- p -C 6 H 4 – ( 1 ), - p -C 6 H 4 –C 6 H 4 - p - ( 2 )) and trans -[(Et 3 P) 2 (Ph)Pt(C C- p -C 6 H 4 –C CH)] ( 3 ) have been synthesised by the application of established synthetic routes. Acetylide bridged mixed-metal complexes trans -[(dppm) 2 (Cl)Os–C C- p -C 6 H 4 –C C–Ru(Cl)(dppm) 2 ] ( 4 ), trans -[(Et 3 P) 2 (Ph)Pt–C C- p -C 6 H 4 –C C–Ru(Cl)(dppm) 2 ] ( 5 ), trans -[(Et 3 P) 2 (Ph)Pt–C C- p -C 6 H 4 –C C–Ru(Ph 3 P) 2 ( η 5 -C 5 H 5 )] ( 6 ) and trans -[(Et 3 P) 2 (Ph)Pt–C C- p -C 6 H 4 –C C–Ru(Ph 3 P) 2 ( η 5 -C 5 H 4 –CH 3 )] ( 7 ) have been formed by the reaction of 1 , 2 and 3 with the appropriate metal chlorides. Complex 6 is less soluble in common organic solvents than the other complexes but this insolubility has been overcome by introducing a methylcyclopentadienyl group on the ruthenium centre to form complex 7 . Complexes 1 , 2 , 4 , 6 and 7 have shown reversible redox chemistry and in the di-metallic complexes, intramolecular electronic communication has been investigated by cyclic voltammetry. The shift in the lowest energy band in the UV–vis spectra of the mixed-metal complexes 4 , 5 , 6 and 7 is largely dependent on the various metal fragments.

Two alternative reaction pathways have been identified in the nucleophilic substitution reactions of Group 14 metallocenes with lithiated primary amines [RNHLi]. These are exemplified by the syntheses and structures of the tris(amido)stannate [(MANH)Sn(μ-NHMA)2Li·2THF] 1, obtained by the reaction of [(MA)NHLi] with [Cp2Sn] (MA=2-MeOC6H4), and the cubanes [E(NCy)]4 (E=Sn 2, Pb 3; Cy=C6H11), prepared from [CyNHLi] and [Cp2E]. The latter furnishes a new route to Group 14 imido cubanes.

The reaction of the nona-osmium cluster dianion [(Ph3P)2N]2[Os9(CO)24] with the electrophilic gold reagents “AuPR + 3 ” and “Au2L2+” (where R=Ph (2a, 3a), Cy (2b, 3b) and L=bis-(diphenylphosphino)methane (DPPM) (1a) or 1,2-bis-(diphenyl)ethane (DPPE) (1b)) has been studied. The monogold fragment reacts to give both the mono- and di-substituted products [(Ph3P)2N][Os9(CO)24{Au(PR3)}] and [Os9(CO)24{Au(PR3)}2]. The structure of the latter cluster (R=Cy (2b)) has been determined by a single crystal X-ray diffraction analysis and a major rearrangement of the metal core geometry was found to have occurred on coordination of the gold fragments. In contrast, reaction with the digold reagent “Au2L2+” results in the isolation of only one product of formulation [Os9(CO)23(Au2L)], where coordination of the heteroatom moiety has been accompanied with the loss of a carbonyl ligand. From a single crystal X-ray diffraction analysis (L=DPPE (1b)) this compound was shown to have retained its original cluster geometry, with the gold atoms coordinated in close proximity to each other.

A 1:1:1 reaction of 3-methylpyridine, 1 , with LDA and PhCN in the presence of PMDETA gives the title complex 6 , shown by X-ray crystallography to be the first monomeric iminolithium. The isolation of 6 , and of a cyclised product 8 when a 3:10:3 reaction of 1 :LDA:PhCN is carried out, suggest a mechanism for previously published cyclisation reactions of β -methylazines.

Dilithiation of 2-methylpyridine followed by PhCN insertion affords the complex [C5H4N · CHC(Ph)N]2− · 2Li+6 · (THF)4, 5. The crystal structure of 5 reveals an unusual Li12 aggregate containing four types of Li+ cation and two types of dianionic ligand which bond to the metal centres via exclusively N-Li interactions or via combinations of C-Li and N-Li coordinations.

Starting from the well known N,N-dimethylaminoethylferrocene ( 1 ) {or N,N-dimethyl(1-ferrocenylethyl)amine}, further substitution of the cyclopentadienyl ring in an adjacent position enables formation of -iodo ( 2 ), -trimethylsilylethynyl ( 3 ) and -ethynyl ( 4 ) derivatives in good yields. From 4 , fac -[manganese 1,2-bis(diphenylphosphinomethane)(tricarbonyl)acetylide] ( 5 ), trans -[rutheniumdi(1,2-bis(diphenylphosphinomethane))chloro-acetylide] ( 6 ) and trans -[osmiumdi(1,2-bis(diphenylphosphinomethane))chloro-acetylide] ( 7 ) have been synthesised and characterised. Electrochemical experiments in solution indicate that there is a decrease in polarisation and a decrease in the degree of metal-to-metal interaction in the chiral ferrocenyl metal-acetylides as opposed to the non-chiral analogues. Second harmonic generation (Kurtz powder) measurements are reported on the chiral metal complexes, but unfortunately negligible second-order non-linear activity was observed.

The room temperature reaction of [( η 5 -C 5 H 5 )W(CO) 3 (PPh 2 )] with [Mn(CO) 5 ] in tetrahydrofuran (THF) followed by protonation with H 3 PO 4 gives [( η 5 -C 5 H 5 )(OC) 2 W( μ -H)( μ -PPh 2 )Mn(CO) 4 ] 1 as the major product. Among the identified minor products from this reaction are [Mn 2 (CO) 9 (PPh 2 H)] 2a , [Mn 2 (CO) 9 (PPh 2 PPh 2 )] 2b , [Mn 2 ( μ -H)( μ -PPh 2 )(CO) 8 ] 2c , and [Mn 2 ( μ -PPh 2 ) 2 (CO) 8 ] 2d . 13 CO reacts with complex 1 substituting both the manganese and tungsten carbonyl groups. In contrast, other two-electron donor ligands, L, only substitute the manganese carbonyl groups to give the substituted products [( η 5 -C 5 H 5 )(OC) 2 W( μ -H)( μ -PPh 2 )Mn(CO) 3 L] (L = P(OMe) 3 3a , PMe 2 Ph 3b , PMePh 2 3c , PPh 2 H 3d ), [( η 5 -C 5 H 5 )(OC) 2 W( μ -H)( μ -PPh 2 )Mn(CO) 2 L 2 ] (L = P(OMe) 3 4a or PMe 2 Ph 4b ). In the case of the photolytic reaction of 1 with the diphosphine, dppm (dppm = Ph 2 PCH 2 PPh 2 ), two products are obtained, one in which the ligand is chelated to the manganese centre, [( η 5 -C 5 H 5 )(OC) 2 W( μ -H)( μ -PPh 2 )Mn(CO) 2 (dppm)] 5 , and the other in which the ligand bridges the tungsten manganese centres, [( η 5 -C 5 H 5 )(OC)W( μ -H)( μ -PPh 2 )( μ -dppm)Mn(CO) 3 ] 6 . Conversion of complex 5 to 6 can be achieved by prolonged UV irradiation of 5 . A single crystal X-ray diffraction study for [( η 5 -C 5 H 5 )(OC) 2 W( μ -H)( μ -PPh 2 )Mn(CO) 4 ] 1 is presented.

The mononuclear complex [Ru(CO) 4 (C 2 H 4 )] ( 1 ) reacts with bidentate phosphines to yield the corresponding [Ru(CO) 4 (η 1 -bidentate phosphine)] ( 3 ) complex in quantitative yield thereby offering a new route to this class of compound. Broadband UV photolysis of dichlorometharie solutions of the 1,2- bis (diphenylphosphino)propane (dppp) complex [Ru(CO) 4 (η 1 -dppp)] ( 3d ) under an atmosphere of ethene yields the dksubstituted complex [Ru(CO) 3 (η 1 -dppp)(η 2 -C 2 H 4 )] ( 9d ) in quantitative yield. Both 3d and 9d show potential in selective cluster capping reactions as illustrated by their reactivity with [Ru 5 C(CO) 15 ] ( 4 ) and [Ru 3 (CO) 12 ] ( 2 ).

The reactions of Ph 2 PCH 2 SR (R = Me, Ph) in toluene with the dicobalt complexes [Co 2 (μ-R 1 CCR 2 (CO) 6 ] (R 1 = R 2 = CO 2 Me and R 1 = H, R 2 = CO 2 Me) give the monosubstituted complexes [Co 2 (μ-R 1 CCR 2 )(CO) 5 PPh 2 CH 2 SMe] 1 and [Co 2 (μ- R 1 CCR 2 (CO) 5 PPh 2 CH 2 SPh] 2 . On heating 1 and 2 in toluene solution, loss of CO leads to the bridged species [Co 2 (μ-R 1 CCR 2 )(μ- PPh 2 CH 2 SMe)(CO) 4 ] 3 and [Co 2 (μ -R 1 CCR 2 )(μ-PPh 2 CH 2 SPh)(CO) 4 ] 4 . This transformation is readily reversed by treatment of 3 and 4 with CO, showing the Co-S bond in these complexes to be relatively weak. Similar reactions of Ph 2 PCH 2 SR (R = Me, Ph) with [Co 2 Fe(μ 3 -S)(CO) 9 ], however, give only the ligand bridged species [Co 2 Fe(μ 3 -S)(μ-Ph 2 PCH 2 SR)(CO) 7 ] (R = Me 5 and R = Ph 6 ). Treatment of 5 and 6 with CO causes cleavage of the Co-S bond but, in contrast to 3 and 4 , the ligand bridged species readily reform when the CO purge ceases. The structures of 3a and 6 have been confirmed by single-crystal X-ray analysis.

The alkylidyne-capped complexes [Co3(μ3−CR)(CO)9] (R = Me 1a, CO2Me 1b) react with PPh2CHCH2 in heptane at 308 K to give the phosphine-substituted complexes [Co3(μ3−CR)(CO)8(PPh2CHCH2)](R = Me 2a, CO2Me 2b), [Co3(μ3−CR)−(CO)7(PPh2CHCH2)2](R = Me 3a, CO2Me 3b) and, in the case of R = CO2Me, the tris-substituted complex [CO3(μ3−CCO2Me)(CO)6(PPh2CHCH2)3] 4. Heating of complexes 2a and 2b at 343 K results in loss of a CO group and coordination of the vinyl moiety of the PPh2CHCH2 ligand to afford [Co3(μ3−CR)(μ−PPh2CHCH2)(CO)7](R = Me 5a, CO2Me 5b). In contrast, reaction of [Co3(μ3−CR)(CO)9](R = Me 1a, CO2Me 1b) with cis-Ph2PCHCHPPh2 (dppee) gives [Co3(μ3−CR)(μ−Ph2PCHCHPPh2)(CO)7] (R = Me 6a, CO2Me 6b) in which the dppee ligand bridges two adjacent cobalt atoms via both phosphino moieties. Nuclear magnetic resonance studies on 5a and 5b indicate that two isomeric structures in a ratio of 7:3 are present in solution at 293 K. Conversion of [Co3(μ3−CR)(μ−PPh2CHCH2)(CO)7] 5a and 5b back to [Co3(μ3−CR)(CO)8(PPh2CHCH2)] 2a and 2b can be achieved by purging with CO at 293 K while further purging at 343 K results in conversion to [Co3(μ3−CR)(CO)9] 1a and 1b. The structure of [Co3(μ3−CCO2Me)(μ−Ph2PCHCHPPh2)(CO)7] 6b was determined by single-crystal X-ray diffraction. All the complexes have been characterized spectroscopically and by elemental analysis.

The room-temperature photolysis of Ru3(CO)12 (1) in dichloromethane under a flow of ethylene affords the highly reactive complex Ru(CO)4(C2H4) (2) in a quantitative yield. The addition of MeCN to the reaction mixture, while the photolytic conditions and the ethylene flow are maintained, gives Ru(CO)3(C2H4)(NCMe) (3). If the irradiation is continued but the ethylene flow stopped, a different product, namely Ru(CO)3(NCMe)2 (4) is obtained. The addition of an excess of triphenylphosphine to a dichloromethane solution of 2 in the absence of ethylene and of light gives two phosphine-substituted products: Ru(CO)4(PPh3) (5) and Ru(CO)3(PPh3)2 (6). Under similar conditions, 3 affords 6 and the cluster Ru3(CO)9(PPh3)3 (7) while, if MeCN is added instead of PPh3, the reactive cluster Ru3(CO)9(NCMe)3 (8) is obtained. If an excess of acrylonitrile is used instead of ethylene, the photolysis of 1 in dichloromethane yields Ru(CO)4(NCCHCH2) (9) which reacts under photolytic conditions but in the absence of an excess of acrylonitrile with MeCN to give Ru(CO)3(NCCHCH2)(MeCN) (10) and this product reacts with a second equivalent of acrylonitrile to afford Ru(CO)3(NCCHCH2)2 (11). All the products have been characterized by IR spectroscopy and their structures established from symmetry considerations.

The development of transition metal cluster chemistry is traced from the early discoveries of metal-metal bonded systems through to some recent developments made in the area of high nuclearity osmium and rutherium cluster carbonyls. Emphasis is placed on developments made in the physical techniques used to establish the structures of the cluster complexes in the solid state and in solution. Recent developments in synthetic methods which lead to “rational” cluster synthesis are described, and the electron counting rules used to rationalise the observed structures of carbonyl clusters are reviewed. New high nuclearity cluster structures are described, and emphasis is placed on the ability of these systems to undergo reversible redox chemistry without the metal frameworks rearranging. This contrasts the situation observed for low nuclearity clusters, and illustrates the potential of the higher nuclearity clusters to act as electron sinks.

Cp 2 Cd.TMEDA 1 and Cp 2 Cd.PMDETA 2 have been synthesized and characterized by spectroscopic studies and by X-ray diffraction studies at low-temperature (153 K). The adducts are present in the crystals as mononuclear complexes. When the denticity of the Lewis base ligands in these adducts is increased (from two in 1 to three in three in 2 ) the Cd 2+ centre requires less electron density from the Cp ligands and the hapticity changes from η 2 − in 1 to η 1 − in 2 . Complexes 1 and 2 are the first compounds for which π-bonding of Cp ligands to Cd 2+ has been observed in the solid state.

Some Group 6 transition metal complexes with bridging alkyne ligands [MM′(μ-HCCMe)(CO)4(η5-C5H5)2] [MM′ = W2 1; WMo 2; Mo2 3] and [WMo(μ-HCCPh)(CO)4(η5-C5H5)2] (5) were treated with hydrogen chloride to afford respectively [MM′Cl(μ-HCCHMe)(CO)4(η5-C5H5)2] [MM′=W2 (6); WMo (7a); Mo2 (8)] and [WMoCl(μ-HCCHPh)(CO)4(η5-C5H5)2] (9a). Similarly, the complexes [WMo(μ-HCCMe)(CO)4(η5-C5H5)2] (2) and [MM′(μ-HCCPh)(CO)4(η5-C5H5)2] [MM′=W2 (4); WMo (5)] were treated with trifluoroacetic acid to give respectively [WMo(CF3COO)(μ-HC=CHMe)(CO)4(η5-C5H5)2] (7b) and [MM′(CF3COO)(μ-HC=CHPh)(CO)4(η5-C5H5)2] [MM′ = W2 (10)]. All the products 6–10 result from anti Markovnikov addition of a proton to the bridging alkyne groups in 1–5, and contain (E)-alkenyl ligands, μ-HC=CHR, σ-bonded to one metal centre and π-bonded to the other. The metal centre to which the alkenyl ligand is σ-bonded in 6–10 is also coordinated by a conjugate base (Cl− or CF3COO−). In the case of 9a a single-crystal X-ray diffraction study shows that the W centre has been formally oxidised from W(+1) to W(+3), with both the alkenyl and chloro groups σ-bonded to it, while the Mo centre is π-coordinated by the alkenyl group and remains in oxidation state (+1).

The synthesis of vinylidene, trans -[(dppm) 2 ClMCC(H)(R)]PF 6 , and σ-acetylide complexes, trans -[(dppm) 2 ClMCCR] (M = Ru , Os ; dppm = bis(diphenylphosphino)methane, Ph 2 PCH 2 PPh 2 ; R = p -C 6 H 5 , p -C 6 H 4 C 6 H 5 , p -C 6 H 4  2 , C 6 H 3 2-(CH 3 )-4-NO 2 , p -C 6 H 4 CH 3 ), and a single-crystal X-ray determination of trans -[(dppm) 2 ClRuCCC 6 H 4 - p -NO 2 ] are reported. The metal-phosphine fragment in these complexes acts as a donor and communicates with the para -substituted nitro acceptor group through the backbone. Such an interaction helps create a delocalized charge-transfer state from the donor to the acceptor.

Some novel tetrayne complexes RC 2 [Co 2 (CO) 4 dppm]CCCCC 2 [Co 2 (CO) 4 dppm]R ( 5 ) (where R = SiMe 3 , a ; 4-MeC 6 H 4 , b ; C 6 H 5 , c ; 4-MeOC 6 H 4 , d ; 4-FC 6 H 4 , e ; dppm = 1,2-bis(diphenylphosphino)methane) have been synthesized either by oxidative coupling of RC 2 [Co 2 (CO) 4 dppm]CCH ( 4 ) or by lithiation and subsequent hydrolysis of RC 2 [Co 2 (CO) 4 dppm]CH  CHCl ( 8 ). An X-ray structure determination of 5a reveals that the two Co 2 (CO) 4 dppm units are trans to each other. The cobalt units can be removed from 5 by oxidizing reagents.

The complexes trans -[Ru(dppm) 2 (CCPh 2 ] and trans -[Ru(LL) 2 CCRCC] n − [LL = bis-diphenylphosphino)methane (dppm) or bis-(diphenylphosphino)ethane (dppe), R = p -C 6 H 4 or p -C 6 H 2 (CH 3 ) 2 ] have geen prepared by the reaction of the corresponding trans -[Ru(LL) 2 Cl 2 ] compound with Me 3 SnCCPh or Me 3 SnCCRCCSnMe 3 . Reactions between cis -[Ru(LL) 2 Cl 2 ], acetylenes and the salt NaPF 6 have yielded complexes of the type [CI(LL) 2 RuCCPhH] + PF 6 − . These were converted into the corresponding mono-acetylides, [Ru(LL) 2 Cl(CCPh)] by treatment with 1,8-diazabicyclo[5.4. Ojundec-7-ene(DBU) or alumina. Ale single crystal X-ray structure of [Ru(dppe) 2 Cl(CCPh)] confirms that during the reaction of the cis -dihalide species rearrangement takes place to give trans products.

The reaction of the dianionic cluster [PPN] 2 [Os 8 (CO) 22 ] {[PPN] + =[N(PPh 3 ) 2 ] + } with Au 2 Cl 2 L {L=chelating phosphines bis -(diphenylphosphino)methane (dppm), 1,2- bis -(diphenylphosphino)ethane (dppe) or 1,4- bis -(diphenylphosphino)butane (dppb)} in the presence of an excess of the halide acceptor TlPF 6 , affords the neutral digold-substituted clusters [Os 8 (CO) 22 (Au 2 L)] {(1) L = dppm; ( 2 ) L = dppe; ( 3 ) L = dppb} in almost quantitative yield. The 31 P{1H} NMR spectra of these compounds indicate that the gold atoms are in non-equivalent environments and therefore cannot have a metal geometry similar to that previously reported for the related cluster [Os 8 (CO) 22 (AuPPh 3 ) 2 ]1 (4). A reinvestigation of the reaction between [PPN] 2 [Os 8 (CO) 22 ] and monogold fragment ‘AuPPh 3 + ’ has shown that, in addition to ( 4 ), a second isomer of Os 8 (CO) 22 (AuPPh 3 ) 2 ] ( 5 ) is formed, which on the basis of the spectroscopic data is thought to have the same metal geometry as compounds ( 1-3 ). A single crystal X-ray diffraction study of the compound [Os 8 (CO) 22 (Au 2 dppb)] ( 3 ) has shown that the metal core consists of a bicapped octahedron of osmium atoms, with one of the gold atoms capping the osmium octahedron, and the other gold atom bridging an edge of the osmium core.

Syntheses of the mono-, bis- and poly-nuclear Ru-σ-acetylide complexes, trans-[Ru(CO)2(PnBu3)2(CC C6H5)2], trans-[ClRu(CO)2(PnBu3)2CCpC6H4C6H4 pCCRu(CO)2(PnBu3)2Cl] and trans-[Ru(CO)2(PnBu3)2CC RCC]n(R = p-C6H4, p(CH3)2C6H2) are reported. A study of the electronic structure of model metal-acetylide complexes of Group 8, M(L)2,(L′)2(RH)2, ClRu(L or L′)4RRu(L or L′)4 Cl, [M(PH3)4(RH)]2R and [M(L)(L)2(R)]n, (M  Fe, Ru; L  L′ PH3, PMe3; L  CO, L′ PH3; R  CC, CCC6H4CC, CH CHpC6H4CHCH) has been carried out using the Fenske-Hall molecular orbital model. These results and a comparison of the IR (vCC stretching frequencies) and optical absorption (π-π★ energy band gap) spectra of these complexes provide evidence for the role of (i) auxiliary ligands, (ii) metal, and (iii) the bridging alkyne units in determining the extent of π-electron conjugation in the backbone of these rigid rod organometallic complexes.

The reactions of alkynyltrimethylstannanes with 1,1′-dilithioferrocene have given several ferrocenylacetylides, namely 1-pheny]-ethynyl-1′-iodo-ferrocene ( 1 ), 1,1′-bis(phenylethynyl)ferrocene ( 2 ), 1,4-di(1′-iodoferrocenylethynyl)benzene ( 3 ) and poly[1,4-(1′-ferrocenylethynyl)ethynylbenzene] ( 4 ). The versatility of this reaction for the formation of ferrocenylacetylides is demonstrated. The crystal structure of 2 has been determined, and shown to involve a linear array of the groups with a cis arrangement of the phenylethynyl ligands.

Reactions of [(η5-C5Me5)TiCl3] with dialkyl and diarylamido-lithium complexes in 1:1, 1:2 or 1:3 molar ratios afford the mono(pentamethylcyclopentadienyl)titanium(IV) dialkylamido- complexes [(η5-C5Me5)TiCl3-n(NR2)n (n = 1; R = Me or SiMe3) (n = 2, R = Me or Ph) (n = 3, R = Me or Et). Similar reactions of [(η5-C5Me5)TiCl 22(μ-O)] and [(η5-C5Me5)TiCl3(μ-O)3] gave the corresponding complexes [(η5-C5Me5)TiCl2-n(NR2)ni2(μ-O)] (n = 1; R = Me or Ph) (n = 2, R = Me) and [(η5-C5Me5)3Ti3Cl3-n(NMe2)n(μ-O) 3] (n = 1 or 3). The crystal structure of [(η5-C5Me5)Ti(NMe2)3] has been established by X-ray crystallography and is shown to be monomeric with the typical three-legged piano- stool structure.

The synthetic utility of bis(trimethylstannyl)alkynyls in the preparation of Group 8 metal (Fe 2+ , Ru 2+ , Os 2+ ) σ-acetylide monomeric, M(DEPE) 2 (CCC 6 H 5 ) 2 (M  Fe 2+ , Ru 2+ ; DEPE = 1,2-bis(diethylphosphino)ethane), Ru(DPPE) 2 (CCC 6 H 5 ) 2 (DPPE = 1,2-bis(diphenylphosphino)ethane), Os(DPPM) 2 (CCC 6 H 5 ) 2 (DPPM = 1,2-bis(diphenylphosphino)methane) and polymeric, [M(DEPE) 2 CCRCC] n (M  Fe 2+ , Ru 2+ ), [Os(DPPM) 2 CCRCC-] n (R = p -C 6 H 4 - C 6 H 4 - p , p -C 6 H 4 , p -C 6 H 2 (CH 3 ) 2 ) complexes is demonstrated. The linear arrangement of the acetylenic units around octahedral metal centres is confirmed by a single crystal X-ray structure determination of the model complex trans -[Ru(DPPE) 2 (CCC 6 H 5 ) 2 ].

The reaction of the carbido dianion [Ru 6 C(CO) 16 ] 2− with Au 2 {Ph 2 PCH 2 PPh 2 }Cl 2 , in dichloromethane, in the presence of TIPF 6 , affords the neutral cluster Ru 6 C(CO) 16 Au 2 {Ph 2 PCH 2 PPh 2 } ( 1 ) in 90% yield. An X-ray analysis of 1 shows that the octahedral ruthenium core has remained intact, and that the two Au atoms of the chelating gold phosphine bridge two adjacent edges of one of the triangular faces of the Ru 6 octahedron. In marked contrast, the reaction of the non-carbido dianion [Ru 6 (CO) 18 ] 2− with Au 2 {Ph 2 PCH 2 PPh 2 }Cl 2 under similar reaction conditions leads to the breakdown of the octahedral ruthenium core and the formation of Ru 5 (CO) 15 Au 2 {Ph 2 PCH 2 PPh 2 } ( 2 ) in ca . 50% yield. The X-ray analysis of 2 shows that the ruthenium atoms adopt a trigonal bipyramidal framework with the Au atoms of the Au 2 {Ph 2 PCH 2 PPh 2 } ligand μ 3 - capping adjacent faces of the trigonal bipyramid in a manner not previously observed for mixed ruthenium-gold clusters.

The reaction of the activated triosmium cluster, [Os3(CO)11(NCMe)] with bis(diphenylphosphinoacetylene) (dppa) at room temperature affords the linked cluster [{Os3(CO)112}(dppa)] (1), while the reaction of [Os3(CO)10(NCMe)2] with an excess of dppa affords the di-, tri- and tetrameric clusters [{Os3(CO)10(dppa)}2] (2), [{Os3(CO)10(dppa)}3] (3) and [{Os3(CO)10(dppa)}4] (4) in moderate yields. Similarly, the reaction of the anion [Os4H3(CO)12]− with Au2(dppa)Cl2, in the presence of excess Et3N and TIPF6, under reflux, in chloroform affords [{Os4H(CO)12Audppa}2] (5) as the only extractable product. Single crystal X-ray structural analyses of 1 and 2 show that the two triosmium cluster units are linked via coordination of one Os centre to each of the two phosphorus centres of the intact dppa ligand, while the structure of 5 shows the two tetraosmium units are linked via two μ2-bridging Au centres and terminal phosphorus centres of the two Au(dppa) ligands.

The synthesis of a bulky chelating bis(phosphine) ligand, 1,2-bis(di n butylphosphino)ethane, n Bu 2 PCH 2 CH 2 P n Bu 2 ( 1 ) (Bu = Butyl = C 4 H 9 ) (DBPE) is reported. This ligand was coordinated to iron by treatment with FeCl 2 to yield Fe(DBPE) 2 Cl 2 ( 2 ) which is an important precursor of a variety of σ-acetylide complexes, e.g. Fe(DBPE) 2 (CCC 6 H 5 ) 2 ( 3 ). Complex 2 is paramagnetic in solution at room temperature and diamagnetic in the solid state. The optical absorption spectrum of 3 shows strong absorptions associated with π-π★ transition of the acetylenic unit.

The compound [Ru4(μ-Se)2(CO)8(μ3-CO)3] (1), has been obtained in good yield by vacuum pyrolysis of [RU3(CO)12] with [Ph2Se2] at 185°C. Reaction of 1 with 1,3-bis(diphenylphosphino)propane at room temperature affords the novel cluster [RU3(μ3-Se)2(CO)7(Ph2P(CH2)3PPh2)] (2). The structures of 1 and 2 have been determined by an X-ray diffraction study.

The reaction of [Os3(CO)12 with [12]aneS3 ([12]aneS3  {(CH2)3S}3) in octane for 6 h, under reflux, led to isolation of two products [Os3(CO)11([12]aneS3)] (1) and [Os4(CO) 13([12]aneS3)] (2), while with [Ru3(CO)12] under similar conditions, in THF, a number of products were obtained, including [Ru4(CO)11([12]aneS3)] (3), [Ru5(CO)13([12]aneS3)] (4), and [Ru6(CO)16([12]aneS3)] (5). An X-ray diffraction study of 2 shows that the macrocycle is coordinated to the ‘wingtips’ of an Os4 butterfly through the two electron pairs on one sulphur atom, while in 5 all three sulphur atoms of the macrocycle coordinate to two of the Ru atoms in a spiked edge-bridged tetrahedral metal framework.

The synthesis and characterisation of a new triosmium cluster, Os 3 (CO) 10 (μ 2 -η 3 -C 3 H 5 )(AuPEt 3 ) ( 1 ) are reported. The cluster is formed most efficiently by the deprotonation of HOs 3 (CO) 10 (HCCHMe) followed by reaction with Et 3 PAuCl, a step that stabilises the anion [Os 3 (CO) 10 (μ 2 -η 3 -C 3 H 5 )] − . This anion is also the product of the reaction between the cluster anion [HOs 3 (CO) 11 ] − and 1propyne. The molecular structure of 1 has been determined. The allylic moiety bridges one OsOs edge of the triosmium triangular cluster core in a μ 2 -η 3 fashion. The electronic structure of 1 has been investigated by the FenskeHall quantum chemical technique; the results illustrate the primary involvement of the allyl nonbonding MO and have been used to suggest possible orientations for the allylic hydrogen atoms.

Triosmium clusters with the formulation Os3(μ-H)2(CO)9Ar[Ar  C6H4 (1), C9H6 (2), C4H3N (3), or C4H2NMe (4)] can be chemically activated by reaction with Me3NO/MeCN to produce the reactive species Os3(μ-H)2(CO)9−n(MeCN)nAr[n = 1, Ar = C6H4 (5), C9H6 (6), C4H3N (7), or C4H2NMe (8); n = 2, Ar = C6H4 (9), C9H6 (10), C6H3N (11), or C4H2NMe (12)], which then react with phosphine or phosphite molecules to give substituted products Os3(μ-H)2(CO)9−n(PR3)nAr (n = 1, or 2, R = Ph, Et, or OMe). These clusters have been characterised by spectroscopic techniques, and Os3(μ-H)2(CO)7[P(OMe)3]2(C4H3N) (24) has been structurally characterised by an X-ray analysis. In this complex one of the phosphite ligand occupies an axial site on the osmium triangle while the second occupies a more conventional equatorial site. The C4H3N ligand capts the triangle and is coordinated through the nitrogen and one carbon atom.

Reaction of 1,1,1-tris(isocyanomethyl)ethane (trisNC) (3) with [Os3(CO)10(NCMe)2] gives the tripod-capped cluster [Os3(CO)9(trisNC)] (4), which has been fully characterised by spectroscopic and X-ray crystallographic techniques.

An acetylene-linked dimeric complex has been prepared from the reaction of [Co 2 (CO) 8 ] with PhC 2 MPPh 3 (M  Ag or Au) or [Hg(C 2 Ph) 2 ] in Ch 2 Cl 2 . An X-ray structure determination revealed that the product was not the expected aceteylene derivative [Co 2 (CO) 6 (PhC 2 MPPh 3 )] or [{Co 2 (CO) 6 PhC 2 } 2 Hg)], but contained two [Co 2 (CO) 6 PhC 2 ] units linked by a CC bond to give the dimer [{Co 2 (CO) 6 PhC 2 } 2 ].