Redox activity and π bonding in a tripodal seven-coordinate molybdenum(VI) tris(amidophenolate)

A tris(aminophenol), tris(2-(3', 5'-di-tert-butyl-2'-hydroxyphenyl)amino-4-methylphenyl)amine, MeClampH(6), is prepared in three steps from tri-p-tolylamine. The ligand reacts with dioxomolybdenum(VI) bis(acetylacetonate) to form an oxo-free heptadentate complex, (MeClamp)Mo, with a capped octahedral geometry. The molybdenum is formally in the +6 oxidation state, with significant pi donation of the amidophenolates, as judged by intraligand bond distances. Two ligand-based oxidations and one metal-centered reduction are observed by cyclic voltammetry. Analysis of the optical spectrum of the compound gives an estimate of the energetic stabilization of the ligand pi orbitals by bonding to the molybdenum of approximately 0.9 eV, corresponding to about 40 kcal mol(-1) per pi bond.