Cyanoacetylenes and cyanoacetylides: versatile ligands in organometallic chemistry

Abstract

The nitrile like lone pair of the cyanoacetylene PhCCCN (1) has been found to coordinate readily to the Ru(PPh3)2Cp fragment, to give [Ru(NCCCPh)(PPh3)2Cp]PF6 (2) which may be considered as an “extended” derivative of the more common benzonitrile complex [Ru(NCPh)(PPh3)2Cp]PF6 (3). Reaction of 1 with [Co2(CO)6(dppm)] readily forms the μ,η2 complex [Co2(μ,η2-PhC2CN)(CO)4(dppm)] (4), which reacts with [RuCl(PPh3)2Cp] to give the mixed metal species [{Co2(μ,η2-PhC2CN){Ru(PPh3)2Cp}(CO)4(μ-dppm)}]PF6 (5). The η1(N) bonded PhCCCN 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(μ-tcne)}][PF6]2 (9). The metallocyanoacetylide [Ru(CCCN)(PPh3)2Cp] (6) was prepared by lithiation (BuLi) of [Ru(CCH)(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}(μ-CCCN){ML2Cp}]+, which were isolated as the PF6 salts [ML2Cp = Ru(PPh3)2Cp (7); Fe(dppe)Cp (8)]. The crystal structures of 2–5, 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.