Cyanoacetylenes and cyanoacetylides : versatile ligands in organometallic chemistry.

Abstract

The nitrile like lone pair of the cyanoacetylene PhCequivalent toCCequivalent toN (1) has been found to coordinate readily to the Ru(PPh3)(2)Cp fragment, to give [Ru(Nequivalent toCCequivalent toCPh)(PPh3)(2)Cp]PF6 (2) which may be considered its an "extended" derivative of the more common benzonitrile complex [Ru(Nequivalent toCPh)(PPh3)(2)Cp]PF6 (3). Reaction of 1 with [Co-2(CO)(6)(dppm)] readily forms the mu,eta(2) complex [Co-2(mu,eta(2)-PhC(2)Cequivalent toN)(CO)(4)(dppm)] (4), which reacts with [RuCl(PPh3)(2)Cp] to give the mixed metal species [{Co-2(mu,eta(2)-PhC(2)Cequivalent toN) {Ru(PPh3)(2)Cp}(CO)(4)(mu-dppm)}]PF6 (5). The eta(1)(N) bonded PhCequivalent toCCequivalent toN ligand is labile, being displaced by NCMe at ambient temperature to afford [Ru(NCMe)(PPh3)(2)Cp]PF6, or by tcne to give trans-[{Ru(PPh3)(2)Cp}(2)(mu-tcne)}][PF6](2) (9). The metallocyanoacetylide [Ru(Cequivalent toCCequivalent toN)(PPh3)(2)Cp] (6) was prepared by lithiation (BuLi) of [Ru(Cequivalent toCH)(PPh3)(2)Cp] followed by treatment with PhOCN. Coordination of the metal fragments Ru(PPh3)(2)Cp or Fe(dppe)Cp to the N terminus in 6 occurs readily to give the homo- or hetero-bimetallic cations [{Cp(PPh3)(2)Ru}(mu-Cequivalent toCCequivalent toN){ML2Cp}](+), which were isolated as the PF6 salts [ML2Cp=Ru(PPh3)(2)Cp (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.