Bis-zirconium and bis-hafnium catalysts for the strong activation of carbonyl substrates

(3,3′-Di-t-butyl-5,5′-dimethylbenzophenone-2,2′-dioxy)bis(triisopropoxyzirconium) and its hafnium derivative can be successfully utilized in organic synthesis as bimetallic Lewis acid catalysts. The high activation ability of such catalysts toward carbonyls is emphasized using several synthetic examples including the asymmetric allylation in comparison with the corresponding mono-Zr as well as bis-Ti catalysts.