Bis(hydroxyphenyloxazolinato)-titanium(IV) and -zirconium(IV) triflates as novel transition metal-based Lewis acids

Abstract

The preparation of novel titanium, 3, and zirconium, 4, organometallic Lewis acids by treatment of the readily available [M(L)₂(C1)₂] complexes (M = Ti, Zr; L = hydroxyphenyl-4,5-dihydrooxazole) with AgOSO₂CF₃ are described. The new homogeneous organometallic Lewis acids, prepared in situ, are active in promoting aldol reactions, additions to imines and catalytic allylations. In addition, some examples of the use of 3 and 4 in other reactions (i.e. Mukaiyama–Michael reaction, addition of Me₃SiCN, Diels–Alder, and hetero Diels–Alder reaction) are presented. Some mechanistic studies on the aldol reaction and on the catalytic allylation have been performed in order to show some of the characteristics of the present Lewis acid system.