Manganese-Catalyzed Hydrogenation of Ketones under Mild and Base-free Conditions

In this paper, several
Mn­(I) complexes were applied as catalysts
for the homogeneous hydrogenation of ketones. The most active precatalyst
is the bench-stable alkyl bisphosphine Mn­(I) complex fac-[Mn­(dippe) (CO)3(CH2CH2CH3)]. The reaction proceeds at room temperature under base-free conditions
with a catalyst loading of 3 mol % and a hydrogen pressure of 10 bar.
A temperature-dependent selectivity for the reduction of α,β-unsaturated
carbonyls was observed. At room temperature, the carbonyl group was
selectively hydrogenated, while the CC bond stayed intact.
At 60 °C, fully saturated systems were obtained. A plausible
mechanism based on DFT calculations which involves an inner-sphere
hydride transfer is proposed.