Titanium and ruthenium binaphthyl Schiff base complexes as catalysts for asymmetric trimethylsilylcyanation of aldehydes

Abstract

Investigations on the catalytic behaviour of titanium complexes formed in situ from Ti(OPri)4 and a variety of Schiff bases, mainly the binaphthyl derivatives 2,2′-bis(3-R1-5-R 2-2-hydroxybenzylideneamino)-1,1′-binaphthyl, toward the asymmetric trimethylsilylcyanation of some aromatic and aliphatic aldehydes demonstrated that the titanium complex of the binaphthyl Schiff base with R1 = R2 = But is one of the best catalysts for such a process, with an enantiomeric excess (e.e.) as high as 96% obtained for m-tolualdehyde. Crystal structure determination of a nitrosylruthenium complex, [RuII(L)(NO)Cl] (L is the dianion of the binaphthyl Schiff base with R1 = R2 = Cl), revealed that the complex assumes a cis-β configuration with the binaphthyl moiety having a dihedral angle of 70.2°. After treatment with AgPF6, the ruthenium complex also exhibited a good catalytic property for the trimethylsilylcyanation of benzaldehyde albeit with a lower e.e. (24%). © The Royal Society of Chemistry 1999.