On the Mechanism of Frustrated Lewis Pair Catalysed Hydrogenation of Carbonyl Compounds

We have explored the reaction mechanism of the metal-free B(C₆ F₅ )₃ -catalysed hydrogenation of carbonyl compounds to the corresponding secondary alcohols by density functional theory calculations. Possible reaction routes have been investigated in detail and the results provide solid support for the mechanism proposed on the basis of experimental observations. The critical role of the ethereal solvent, as an active participant in the hydrogenation process, is highlighted with the ether-borane Lewis pair shown to be involved in the heterolytic activation of H₂ . The feasiblity of an alternative direct hydrogenation route featuring carbonyl-borane-mediated H₂ cleavage has also been examined. We have also investigated the moisture sensitivity of the catalyst and possible decomposition routes. We found that the catalyst shows appreciable water-tolerance and that even in the presence of moisture the hydrogenation proceeds through the same mechanism as that followed under anhydrous conditions.