Aldehyde Reduction by a Pyridone Borane Complex through Boron-Ligand-Cooperation: Concerted or Not?

Abstract

The reduction of benzaldehyde by a pyridone borane complex was investigated by NMR, X-ray analysis as well as DFT and DLPNO-CCSD(T) computations. The reaction leads to the formation of a pyridone boronic ester complex stabilized by an NH···O hydrogen bond. The computations show that the hydrogenation takes place in a concerted fashion, yielding a transient benzyl alcohol boroxypyridine complex that undergoes a barrierless O–H addition. The concerted hydrogen transfer is associated with a transformation of a pyridone borane to a boroxypyridine, and thus with the interconversion of a neutral donor ligand to a covalently bound substituent.