Reduction of aldehydes catalyzed by oxo-rhenium(V) complexes containing heterocyclic ligands

This work describes the catalytic activity of several oxo-rhenium complexes containing the heterocyclic ligands 2-(2-hydroxy-5-methylphenyl)benzotriazole (Hhmpbta), 2-(2-hydroxyphenyl)benzothiazole (Hhpbt), 2-(2-hydroxyphenyl)benzoxazole (Hhpbo), 2-(2-hydroxyphenyl)-1H-benzimidazole (Hhpbi), isoquinoline-1-carboxylic acid (iqcH), and 4-methoxy-2-quinolinecarboxylic acid (mqcH) in the reduction of 4-nitrobenzaldehyde using phenylsilane as reducing agent. In general, all of the catalysts tested gave good to excellent yields of the 4-nitrobenzyl alcohol. Although, the best result was obtained with the catalytic system PhSiH3/[ReOBr2(hmpbta)(PPh3)] (5 mol %). This system was also applied to the reduction of a large variety of aldehydes, producing the corresponding primary alcohols in good to excellent yields and good chemoselectivity.