Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 73. Reactions of [WCo(CR)(CO)8](R = C6H4Me-4 or Me) with alkynes. Crystal structures of [WCo{µ-C(C6H4Me-4)C(Me)C(Me)C(O)}(CO)6(PPh3)] and [WCo{µ-C(Ph)C(Me)C(Me)C(OH)}(CO)6(PPh3)][BF4]

Abstract

In light petroleum at room temperature the compound [WCo(CR)(CO)₈](R = C₆H₄Me-4) reacts with MeCCMe or EtCCEt to give the complexes [WCo{µ-C(R)C(R¹)C(R¹)C(O)}(CO)₇](R¹= Me or Et), whereas MeCCEt affords an inseparable mixture of the species [WCo{µ-C(R)C(R¹)C(R²)C(O)}(CO)₇](R¹= Me, R²= Et; R¹= Et, R²= Me). Reactions between [WCo(CMe)(CO)₈] and MeCCMe or MeCCPh yield the compounds [WCo{µ-C(Me)C(Me)C(Me)C(O)}(CO)₇] and [WCo{µ-C(Ph)C(Me)C(Me)C(O)}(CO)₇], respectively. Treatment of these various products with PPh₃ leads to substitution of a CO ligand on the cobalt atom by the phosphine, and the structure of one of these derivatives [WCo{µ-C(C₆H₄Me-4)C(Me)C(Me)C(O)}(CO)₆(PPh₃)] has been established by X-ray diffraction. The W–Co bond [2.737(1)Å] is spanned by the C(C₆H₄Me-4)C(Me)C(Me)C(O) fragment, with the terminal carbon atoms of the chain σ bonded to the cobalt, and with the carbon atoms of the C(C₆H₄Me-4)C(Me)C(Me) moiety η³ co-ordinated to the tungsten. The latter carries four terminal CO groups, and the cobalt two such ligands and the PPh₃ group [Co–P 2.237(2)Å, P–Co–W 146.4(1)°]. Protonation of the complex [WCo{µ-C(Me)C(Me)C(Me)C(O)}(CO)₇] with HBF₄·Et₂O affords the salt [WCo{µ-C(Me)C(Me)C(Me)C(OH)}(CO)₇][BF₄]. Three PPh₃ derivatives of the alkyne-adducts of [WCo(CR)(CO)₈](R = C₆H₄Me-4 or Me) have also been protonated, and the structure of the salt [WCo{µ-C(Ph)C(Me)C(Me)C(OH)}(CO)₆(PPh₃)][BF₄] has been established by X-ray diffraction. The results confirm that in the latter the phenyl group is attached to the carbon atom at the end of the µ-C₄ chain, and that this carbon atom and that of the C(OH) group are σ bonded to the cobalt. The tungsten atom is ligated by all four carbon atoms of the bridging ligand, by the cobalt atom [W–Co 2.660(1)Å], and by four terminal carbonyl groups. The cobalt atom carries two terminal carbonyl ligands and the PPh₃ group [Co–P 2.261(1)Å] with the latter sited transoid to the W–Co bond [P–Co–W 144.8(1)°]. The n.m.r. data (¹H, ¹³C-{¹H}, ³¹P-{¹H}) for the new compounds are reported and discussed in relation to their structures.