Cyanoacetylenes and cyanoacetylides: versatile ligands in organometallic chemistry

The nitrile like lone pair of the cyanoacetylene PhC(identical)CC(identical)N (1) has been found to coordinate readily to the Ru(PPh3) 2Cp fragment, to give [Ru(N(identical)CC(identical)CPh)(PPh3)2Cp]PF6(2) which may be considered as an "extended" derivative of the more common benzonitrile complex [Ru(N(identical)CPh)(PPh3)2Cp]PF6(3). Reaction of 1 with [Co2(CO)6(dppm)] readily forms the (mu), (eta)^2 complex [Co2((mu),(eta)^2-PhC2C(identical)N)(CO)4(dppm)](4), which reacts with [RuCl(PPh3)2Cp] to give the mixed metal species [{Co2((mu),(eta)^2-PhC2C(identical)N){Ru(PPh3)2Cp}(CO)4((mu)-dppm)}]PF6(5). The 1(N) bonded PhC(identical)CC(identical)N ligand is labile, being displaced by NCMe at ambient temperature to afford [Ru(NCMe)(PPh3)2Cp]PF6, or by tcne to give trans-[{Ru (PPh3)2Cp}2((mu)-tcne)}][PF6]2(9). The metallocyanoacetylide [Ru(C(identical)CC(identical)N)(PPh3)2Cp](6) was prepared by lithiation (BuLi) of [Ru(C(identical)CH)(PPh3)2Cp] followed by treatment with PhOCN. Coordination of the metal fragments Ru(PPh3)2Cp or Fe (dppe)Cp to the N terminus in 6 occurs readily to give the homo- or hetero-bimetallic cations [{Cp(PPh3)2Ru}((mu)-C(identical)CC (identical)N){ML2Cp}]+, which were isolated as the PF6 salts [ML2Cp = Ru(PPh3)2Cp (7); Fe(dppe)Cp (8)]. The crystal structures of 25, 7 and 9 are reported. The electrochemical response of these complexes suggests there are considerable electronic interactions between the heterometallic end-caps in 8 through the polarised C3N bridge.