A Molecularly Defined Iron‐Catalyst for the Selective Hydrogenation of α,β‐Unsaturated Aldehydes

A selective iron‐based catalyst system for the hydrogenation of α,β‐unsaturated aldehydes to allylic alcohols is presented. Applying the defined iron–tetraphos complex [FeF(L)][BF₄] (L=P(PhPPh₂)₃) in the presence of trifluoroacetic acid a broad range of aldehydes are reduced in high yields using low catalyst loadings (0.05–1 mol %). Excellent chemoselectivity for the reduction of aldehydes in the presence of other reducible moieties, for example, ketones, olefins, esters, etc. is achieved. Based on the in situ detected hydride species [FeH(H₂)(L)]⁺ a catalytic cycle is proposed that is supported by computational calculations.