Influence of Ligand Architecture on Bridging Bond Strength in Dimeric Titanium Aminoalkoxy-Diolates

Abstract

A series of mixed-ligand–titanium complexes is reported which incorporate a tridentate N-methyldiethoxoamine (mdea) ligand in conjunction with chelating diolate ligand. X-ray crystal structures of the complexes [Ti(mdea) (O-O)]₂ (where O-O = OC(CH₃)₂C(CH₃)₂O (1), OC(C₂H₅)₂C(C₂H₅)₂O (2), OC(CH₃)₂CH₂CH(CH₃)O (3), and OC(CH₃)₂CH₂C(CH₃)₂O (4)) show them to exist as dimers in the solid state, with one arm of the aminodialkoxy ligand μ-bridging two titanium centres. Solution-state ¹H and ¹³C NMR studies concur with the solid-state structures of (1)–(4) at low temperature. The room-temperature spectra of (3) and (4) suggest that bridging bond scission and reformation occurs increasing the apparent symmetry of the complexes. Complexes (3) and (4) dissociate into monomers in the vapour phase. The influence of the diolate ligand on the bridging bond strengths is discussed.