Highly Efficient and Selective Hydrogenation of Aldehydes: A Well-Defined Fe(II) Catalyst Exhibits Noble-Metal Activity

The synthesis and application of
[Fe­(PNPMe-iPr)­(CO)­(H)­(Br)] and [Fe­(PNPMe-iPr)­(H)2(CO)] as catalysts for
the homogeneous hydrogenation of aldehydes
is described. These systems were found to be among the most efficient
catalysts for this process reported to date and constitute rare examples
of a catalytic process which allows selective reduction of aldehydes
in the presence of ketones and other reducible functionalities. In
some cases, TONs and TOFs of up to 80000 and 20000 h–1, respectively, were reached. On the basis of stoichiometric experiments
and computational studies, a mechanism which proceeds via a trans-dihydride intermediate is proposed. The structure
of the hydride complexes was also confirmed by X-ray crystallography.