Formation of 1:1, 2:1, and 2:2 Complexes between Carbonyl Compounds and Titanium Tetrachloride. An ab Initio Study

Abstract

Carbonyl compounds can be activated through coordination to a Lewis acid. The formation of these complexes has important consequences in the reactivity and selectivity in many organic reactions. These include nucleophilic additions' and Diels-Alder reactions.2 The knowledge of the structure and properties of such complexes is necessary to understand the mechanism of activation and to obtain information useful for the design of effective catalysts. Crystal structures of several complexes between carbonyl compounds and Lewis acids have been determined in the last few years3 When the Lewis acid has several empty coordination sites, different kinds of complexes can be formed. This is the case of Tic4 and other Ti(IV) Lewis acids, which show a preference for six-coordinate complexes. The Tic4 complexes that have been characterized by X-ray diffraction are of two different types: chelate complexes with bidentate carbonyl compounds and complexes containing dimeric TiCLS4 Complexes between Lewis acids and carbonyl compounds have also been the object of theoretical ~ tud ie s .~ '~ Complexes