Nuclear magnetic resonance and cryoscopic studies on some alkoxides of titanium, zirconium, and hafnium

Abstract

Cryoscopic and n.m.r. studies show that the ethoxide, n-propoxide, and n-butoxide of titanium are trimeric in solution over wide ranges of concentrations and temperature. Intramolecular exchange of terminal and bridging alkoxide groups is too rapid even at –90° to be resolved by n.m.r. at 60 Mc.sec. N.m.r. studies revealed reversible depolymerization of the trimers at high temperatures and low concentrations. Titanium isobutoxide and neopentoxide showed a concentration and temperature dependence of n.m.r. chemical shift due to the presence of monomers, dimers, and trimers. Zirconium and hafnium isopropoxides contain mixtures of trimers and tetramers, but the cryoscopically determined molecular weights are independent of concentration.