Titanocene and ansa-titanocene complexes bearing 2,6-bis(isopropyl)phenoxide ligand(s). Syntheses, characterization and use in catalytic dehydrocoupling polymerization of phenylsilane
Abstract
Aryloxychloro and bis(aryloxy) titanocenes of general formula L2TiCl2-x(OAr')(x) where L = eta(5)-C5H5 (x = 1 (1) and 2 (2)), L-2 = SiMe2(eta(5)-C5H4)(2) (x = 1 (3) and 2 (4)), and Ar' = 2,6-(CHMe2)(2)C6H3 were prepared by the reaction of corresponding titanocene dichloride with LiOAr' and characterized by spectroscopic methods and compound 3 by single crystal X-ray diffraction analysis. The bulky aryloxy ligand in 1 and 3 exerts a hindered rotation around the Ti-O bond on the H-1 NMR time scale, resulting in its dynamic behavior in CDCl3 solution.
Variable temperature NMR measurements proved the rotation barrier in 3 (Delta G(298)(double dagger) = 13.9 +/- 0.3 kcal/mol) to be lower than that in 1 (Delta G(298)(double dagger) = 14.7 +/- 0.2 kcal/mol) as a consequence of the more open titanocene shell in the ansa-structure of 3.