Redox-active complexes containing group 8 metal centers linked by C2 bridges

Abstract

A series of complexes containing dicarbon ligands bridging redox-active group 8 metal-ligand fragments M(dppe)Cp′ (M = Fe, Ru, Os; Cp′ = Cp, Cp*) have been prepared. These complexes give up to four one-electron anodic processes at a platinum electrode, with separations of successive oxidation potentials of ca. 850 mV, giving rise to large comproportionation constants, K c (ca. 10 12). Examples of the 36-electron neutral, 35-electron monocationic, and 34-electron dicationic species, together with some related monoprotonated complexes, have been isolated. Structural studies of the 36-, 35-, and 34-electron species derived from the dicarbon complex featuring two Ru(dppe)Cp end-caps (7) show that shortening of the M - C and lengthening of the C - C bonds occur upon oxidation. A complementary spectroelectrochemical investigation has revealed an intense band near 14 300 cm -1 associated with [7]PF 6, which is tentatively attributed to a Ru(d) - [Ru(d)/C 2(π)]* transition, rather than a genuine IVCT band. These observations have been rationalized using DFT calculations and collectively indicate that the frontier orbitais are delocalized over both group 8 metal centers and the carbon chain. © 2007 American Chemical Society.