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.