Iron, cobalt and nickel boride as precursor of heterogeneous oxazaborolidine catalysts

Heterogeneous 1,3,2-oxazaborolidine catalysts FeB1.8-0.1(oxaza)(0.1), CoB2-0.1(oxaza)(0.1) and NiB2-0.1(oxaza)(0.1) were prepared by reacting iron, cobalt and nickel boride with (1S, 2R)-(+)-2-amino-1,2-diphenylethanol. Over these catalysts, acetophenone can be reduced with high enantioselectivity (ee = 97%) by using borane N,N-diethylaniline complex. The capacity to be used again depends on the Metal. The detrimental effect of residual water in the metallic salt before reduction, on the enantioselective properties of the catalyst is demonstrated. The formation of the oxazaborolidine ring is substantiated by IR spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.