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.