Efficient Hydrogenation of Ketones Catalyzed by an Iron Pincer Complex

摘要

The catalytic reduction of ketones to the corresponding alcohols is an important reaction in organic chemistry, which is usually catalyzed by complexes of precious metals (e.g. Rh, Ir, Ru) using either H2 or iPrOH as hydrogen source. In particular, the reduction of ketones with gaseous hydrogen provides an atom-economical synthetic method. The development of iron-based catalysts with similar activity is desirable due to their low toxicity, lower price, and the benign environmental impact of iron compounds.Although considerable progress has been made in iron-catalyzed transfer hydrogenations and hydrosilylations, only a few studies have been published on iron-catalyzed hydrogenations. Chirik and co-workers recently described the synthesis of the well-defined catalyst [(iPrPDI)Fe(N2)2] (iPrPDI = ((2,6-CHMe2)2C6H3N=CMe)2C5H3N), which was capable of hydrogenating alkenes and alkynes with 0.3 mol % catalyst loading and 4 atm hydrogen pressure at ambient temperature. Turnover frequencies of up to 1814 h~(-1) were reached with this system for the hydrogenation of 1-hexene. We are aware of only two iron complex systems that are capable of catalyzing the hydrogenation of ketones to alcohols. Casey et al. described the bifunctional complex [{2,5-(SiMe3)2-3,4-(CH2)4(η~5-C4COH)}Fe(CO)2H], which catalyzes hydrogenation of ketones under mild conditions with high chemo- and diastereoselectivity, resulting in 50 turn-overs. The diiminodiphosphine and diaminodiphosphine iron complexes described by Morris and co-workers were studied in the catalytic hydrogenation of acetophenone, leading to high conversion at high pressure and excess of base (T=50 ℃, p(H2) = 25 atm, TON 225; catalyst:base = 15).