Chemoselective and efficient catalytic hydrogenation of furfural by iridium and ruthenium half-sandwich complexes†
The efficient hydrogenation reaction of furfural (FFR) to furfuryl alcohol (FFA) was achieved with new pyridyl-imine iridium(III) and ruthenium(II) complexes as catalyst precursors. The hydrogenation of furfural yielded furfuryl alcohol selectively with a turnover number (TON) of 2961 and turnover frequency (TOF) of 1481 h−1. The reactions were performed with formic acid as the source of hydrogen using a catalyst loading as low as 0.025 mol% and Et3N as base. The catalyst remained active for up to seven consecutive catalyst reuse cycles. Iridium outperformed the ruthenium analogues in terms of selectivity. Iridium hydride species were detected, during in situ 1H NMR spectroscopy studies, and are believed to be the active catalytic species. A mechanism of the hydrogenation reaction has hence been proposed.