Electron distribution within bis(quinone)ruthenium complexes. Structural characterization on delocalized (bipyridine)bis(quinone)ruthenium and on the localized trans-bis(3-chloropyridine)bis(3,5-di-tert-butyl-1,2-semiquinone)ruthenium(III) cation

Abstract

Structural information obtained on complexes containing semiquinone and catecholate ligands has provided insights on charge distribution. Ligand CO lengths found for trans-Ru(4-t-Bupy) 2(DBQ) 2 averaged 1.321(5) Å, midway between values of 1.34 and 1.29 Å expected for localized catecholate and semiquinone ligands. This value may arise from crystallographic disorder of a localized Ru III(SQ)(Cat) species or it may result from charge delocalization over both quinone ligands. Crystallographic characterization of Ru(bpy)(Q) 2, where Q is the unsubstituted o-quinone ligand, has shown that the complex molecule crystallizes without imposed symmetry on the molecule, in a crystal structure that places both quinone ligands in different solid-state environments. The four independent CO lengths average 1.321(5) Å, without significant variation, strongly suggesting charge delocalization over both quinone ligands. Characterization on the trans-Ru(3-Clpy) 2(DBQ) 2 + cation, formed by one-electron oxidation of a neutral species that would be expected to show ligand charge delocalization, has shown ligand CO lengths of 1.293(4) Å, exactly the value expected for semiquinone ligands. Oxidation of the neutral complex appears to occur at a ligand delocalized electronic level to give a ligand localized bis(semiquinone) product, Ru III(SQ) 2 +.