Expanding the catalytic scope of (cyclopentadienone)iron complexes to the hydrogenation of activated esters to alcohols

Herein, we report the application of the 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 (solvent, temperature, pressure), complex 1 was tested in the hydrogenation of a range of esters. With most of the activated trifluoroacetate esters, a quantitative formation of TFE was obtained at low catalyst loadings. For non-activated esters, no reaction was observed. Trifluoroacetic acid, a common impurity in hydrolytically labile trifluroacetate esters, was shown to act as a poison for the catalyst. However, the simple addition of Et3N allowed to restore the catalyst activity. Our study constitutes the first example of ester hydrogenation with an Fe complex based on a non-pincer ligand.