Group IV Coordination Chemistry of a Tetradentate Redox-Active Ligand in Two Oxidation States

The redox-active ligand N,N'-bis(3,5-di-tert-butyl-2-phenoxy)-1,2-phenylenediamide [N2O2red](4) reacts with group IV metal salts to form six- and seven-coordinate complexes [N2O2red]MLn (M = Ti, L = py, n = 2; M = Zr, Hf, L = thf, n = 3). The redox-dctive ligand occupies four equatorial coordination sites in these complexes. In the case of the zirconium and hafnium complexes, two axial solvent molecules coordinate to the metal center with a third solvent molecule coordinating in the equatorial plane. In the Case of the smaller titanium metal center, only two pyridine solvent molecules coordinate to the metal atom, leaving an open coordination site. All three complexes react with halogen oxidants to afford oxidative addition products [N2O2OX]MCl2Ln (M = Ti, n = 0; M = Zr, Hf, L = thf, n = 1), in which the redox-active ligand is oxidized by two electrons to the cyclohexadienediimine state. ((C) Wiley-VCH Verlag GmbH & Co, KGaA, 69451 Weinheim, Germany, 2009)