Reactions of the co-ordinatively unsaturated cluster [Os₃(µ-H)(CO)₈{Ph₂PCH₂P(Ph)C₆H₄}] with alkynes RCCR (R = Ph, C₆H₄Me, Me or CF₃); crystal structures of [Os₃(CO)₈{µ₃–η²(∥)–RC₂R}(Ph₂PCH₂PPh₂)](R = Me or CF₃) and electrochemical behaviour of triosmium–alkyne clusters

Abstract

Treatment of the unsaturated triosmium cluster [Os3(µ-H)(CO)8{µ-Ph2PCH2P(Ph)C6H4}]1 with diphenylacetylene leads to the formation of [Os3(CO)7(PhC2Ph)(Ph2PCH2PPh2)]2a in which the alkyne is bonded in a µ3-η2(⊥) mode. Addition of CO to 2a gives [Os3(CO)7(µ-CO)(RC2R)(Ph2PCH2PPh2)]3a(R = Ph) in which the alkyne is bonded in a µ3-η2(∥) mode. Two-electron electrochemical reduction of 2a also causes this change in co-ordination mode of the alkyne ligand. Protonation of the electrochemically produced dianion [Os3(CO)7{µ3-η2(∥)PhC2Ph}(Ph2PCH2PPh2)]2– gives [Os3(µ-H)2(CO)7{µ3-η2(∥)-PhC2Ph}(Ph2PCH2PPh2)]4. The same product 4 has also been obtained by direct hydrogenation of 2a. A similar chemical and electrochemical behaviour is observed for the ditolylacetylene derivative [Os3(CO)7(p-MeC6H4C2C6H4Me-p)(Ph2PCH2PPh2)]2b, where the two p-methyl substituents are diagnostic in 1H NMR spectroscopy. With the alkynes RCCR (R = Me or CF3), analogous complexes to 2 are not observed, instead complexes [Os3(CO)8{µ3-η2(∥)-RR}(Ph2PCH2PPh2)]3c(R = Me) and 3d(R = CF3) are obtained. Single-crystal X-ray structure determinations of 3c and 3d have been performed.