Anionic Group 6 Transition-Metal Carbonyl Hydrides as Reducing Agents. Ketones, Aldehydes, and Epoxides

Article abstract of DOI:10.1021/ja00294a038

Studies of the reducing ability of anionic group 6 transition-metal hydrides HM(CO)5(1-) and cis-HM(CO)4P(OMe)3(1-) (M = Cr, W) toward aldehydes and ketones are reported.Formaldehyde (as paraformaldehyde) reacts with all hydrides used, yielding spectroscopically observable addition products, presumed to be alkoxide intermediates, which are quenched by Broensted acids, yielding alcohols.Other aldehydes are unreactive with HM(CO)5(1-) except inthe presence of acid, in which case reduction occurs readily.With the more active cis-HM(CO)4P(OMe)3(1-) reagents aldehydes react to yield observable intermediates which are readily hydrolyzed to alcohols.Ketones are unreactive with all hydrides studied except in the presence of Broensted acids.A variety of ketones have been investigated, and the problem of balancing acid assistance of ketone reduction vs. acid destruction of the reactive hydrides has been addressed.A facile H/D exchange reaction using methanol-d₁ as the deuterium source to generate DM(CO)4L(1-) permits deuterium delivery to the carbonyl carbon of ketones and aldehydes.