Versatile Iridicycle Catalysts for Highly Efficient and Chemoselective Transfer Hydrogenation of Carbonyl Compounds in Water

Cyclometalated iridium complexes are shown to be highly efficient and chemoselective catalysts for the transfer hydrogenation of a wide range of carbonyl groups with formic acid in water. Examples include alpha-substituted ketones (alpha-ether, alpha-halo, alpha-hydroxy, alpha-amino, alpha-nitrile or alpha-ester), alpha-keto esters, beta-keto esters and alpha, beta-unsaturated aldehydes. The reduction was carried out at substrate/catalyst ratios of up to 50000 at pH 4.5 and required no organic solvent. The protocol provides a practical, easy and efficient way for the synthesis of beta-functionalised secondary alcohols, such as beta-hydroxyethers, beta-hydroxyamines and beta-hydroxyhalo compounds, which are valuable intermediates in pharmaceutical, fine chemical, perfume and agrochemical synthesis.