Oxidation of cyanide-bridged dimanganese(I) complexes: redox-induced isomerisation as a probe of intermetallic interaction

Abstract

The reaction of [Mn(CN)(CO)₂L(L–L)] with [MnBr(CO)₂L′(L′–L′)] in the presence of TlPF₆ gives [(L–L)L(OC)₂Mn(µ-CN)Mn(CO)₂L′(L′–L′)][PF₆] which may have trans,trans; cis,trans; trans,cis or cis,cis geometries depending on the structures of the mononuclear precursors. The trans,trans complexes undergo two reversible one-electron oxidations, the first at the N-bonded Mn(CO)₂L′(L′–L′) site to give dications which IR carbonyl and ESR spectroscopy and cyclic voltammetry suggest to be localised mixed-valence species. The oxidation of the cis,trans and trans,cis monocations occurs first at the trans site and then at the cis site. Where the difference in potential, Δ, between the two redox processes (which depend on the ligands L, L–L, L′ and L′–L′) is large the first oxidation occurs with retention of geometry; subsequent oxidation at the cis site results in isomerisation and the formation of the trans,trans trications. Where Δ is small, oxidation of the trans site is accompanied by isomerisation at the cis centre implying some delocalisation in the mixed-valence dication. The oxidative-isomerisation process therefore provides a probe of the intermetallic interactions in the Mn₂(µ-CN) core.