Expanding the Catalytic Scope of (Cyclopentadienone)iron Complexes to the Hydrogenation of Activated Esters to Alcohols

Herein, we report the application of easy-to-make and bench-stable (cyclopentadienone) iron complexes (such as 1) as precatalysts for the hydrogenation of esters. After optimization of the reaction conditions (i.e., solvent, temperature, pressure), complex 1 was tested in the hydrogenation of a range of esters. With most of the activated trifluoroacetate esters, quantitative formation of 2,2,2-trifluoroethanol was obtained at low catalyst loadings. For nonactivated esters, no reaction was observed. Trifluoroacetic acid, a common impurity in hydrolytically labile trifluoroacetate esters, was shown to act as a poison for the catalyst. However, the simple addition of Et3N allowed the catalyst activity to be restored. Our study constitutes the first examples of ester hydrogenation with an Fe complex based on a non-pincer ligand.