Vinylidene transition-metal complexes. Part 13. The reactivity of [IrH5(PPri3)2] and [IrH2Cl(PPri3)2] toward Alk-1-ynes: synthesis of four-, five- and six-co-ordinate iridium complexes containing alkynyl, vinyl and vinylidene ligands

Abstract

Reaction of [IrH₅(PPrⁱ₃)₂]2 with excess of phenylacetylene in pentane gives the tris(alkynyl) complex [Ir(C₂Ph)₃(PPrⁱ₃)₂]3, whereas with acetylene and propyne the bis(alkynyl) vinyl compounds [Ir(C₂R)₂(CRCH₂)(PPrⁱ₃)₂](R = H, 4; or Me 5) are obtained. Complexes 3–5 react smoothly with H₂ to give 2 and the corresponding alkene and thus are supposed to be intermediates in the hydrogenation of alk-1-ynes catalysed by 2. Reaction of [IrH₂Cl(PPrⁱ₃)₂]8 with PhC₂H occurs stepwise leading to the formation of the mono-, bis- and tris-(alkynyl) iridium(III) derivatives [IrH(Cl)(C₂Ph)(PPrⁱ₃)₂]9, [IrCl(C₂Ph)₂(PPrⁱ₃)₂]10 and 3. From 8 and acetylene, the vinylidene complex [IrCl(CCH₂)(PPrⁱ₃)₂]11 is obtained. Treatment of 8 with an equimolar amount of HC₂CO₂Me gives first the alkynyl hydrido compound [IrH(Cl)(C₂CO₂Me)(PPrⁱ₃)₂]12 which on warming to 80 °C in benzene rearranges to give the substituted vinylidene isomer [IrCl(CCHCO₂Me)(PPrⁱ₃)₂]13 in virtually quantitative yield. The reaction of 8 with 2 equivalents of HC₂CO₂Me leads to the formation of the bis(alkynyl) complex [IrCl(C₂CO₂Me)₂(PPrⁱ₃)₂]14.