Convenient hydrogenation of furfural to furfuryl alcohol in metal-catalyzed and organo-catalyzed environments

Palladium iminophosphorane (C1–C3) and pyridylimine (C4–C5) pincer complexes were evaluated for their activity in the conversion of furfural to furfuryl alcohol in the presence of triethylamine (Et3N) and formic acid (FA). A catalyst loading of 0.1 mol% Pd afforded conversions of >99% achieving TONs of up to 9996. Surprisingly, upon evaluating a control blank (no metal catalyst) the conversions remained at >99% under metal catalyst-free conditions. Various tertiary and secondary amines were also screened in place of Et3N and all proved efficient in furfural hydrogenation to furfural alcohol giving comparable conversions (>99%). Apart from furfural, metal catalyst-free hydrogenation was expanded to various other aldehydes all of which were converted to their corresponding alcohols in excellent yields of up to 100%. This work has led to a new discovery that would result in cost-effective metal catalyst-free processes for aldehyde hydrogenation.