Formation of exceptionally weak C-C bonds by metal-templated pinacol coupling.

The ability of the bis(imidazolyl)ketone ligand BMdiPh IK (bis(1-methyl-4,5-diphenylimidazolyl)ketone) to function as a redox active ligand has been investigated. The reduction of [M(BMdiPh IK)Cl2 ] (M = Fe and Zn) complexes resulted in a pinacol-type coupling to form dinuclear complexes featuring very weak and abnormally elongated C-C bonds (1.729(5) and 1.708(3) Å for Fe and Zn, respectively). Oxidation of these complexes using ferrocenium in the presence of Cl- ions regenerated the original [M(BMdiPh IK)Cl2 ] complexes, showing the reversibility of the coupling process. This makes it a potentially interesting approach for the storage of electrons and application of the BMdiPh IK ligand as a redox active ligand.