Iron(II) Complexes for the Efficient Catalytic Asymmetric Transfer Hydrogenation of Ketones

Ferrous efficiency: New achiral and chiral iron complexes containing P‐N‐N‐P diiminodiphosphine ligands display high activity—and in the case of the catalyst shown, high enantioselectivity—in the catalytic transfer hydrogenation of ketones. This is an important step in the journey to replace precious and toxic platinum metal catalysts with cheap and environmentally friendly iron compounds. magnified image Iron(II) carbonyl compounds of the type trans‐[Fe(NCMe)(CO)(P‐N‐N‐P)][BF4]2 bearing the ethylenediamine‐derived diiminodiphosphine ligands (R,R)‐ or (S,S)‐1,2‐diphenyl‐1,2‐diaminoethane were synthesized and characterized, including by their crystal structures. The new complexes are suitable precatalysts for the transfer hydrogenation of ketones at room temperature, giving turnover frequencies of up to 2600 h−1 with low catalyst loadings (0.025–0.17 %). Screening experiments showed that the precatalysts are able to produce alcohols from a wide range of simple ketones. For sterically demanding prochiral ketones, excellent enantioselectivities were obtained (up to 96 % ee).