Metal Amidoboranes: Superior Double-Hydrogen-Transfer Agents in the Reduction of Ketones and Imines

Metal amidoboranes (MABs), such as lithium amidoborane (LiAB), show superior ability in reducing ketones and imines directly into their corresponding secondary alcohols and amines, respectively, at room temperature with high conversion and yields. A mechanistic study indicates that the reduction proceeds through a double-hydrogen-transfer process. Both protic H(N) and hydridic H(B) protons in the amidoborane participate in the reaction. Theoretical investigations show that the first (and rate-determining) step of the reduction reaction is the elimination of LiH from LiAB, followed by the transfer of H(Li) to the C site of the unsaturated bond.