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, duringin situ¹H NMR spectroscopy studies, and are believed to be the active catalytic species. A mechanism of the hydrogenation reaction has hence been proposed.