Hydroboration of Nitriles and N-Heteroarenes by Cooperative Iron Catalysis: A Kinetic and Mechanistic Study

We present a novel iron-catalyzed approach of synthesizing amines through reduction of nitriles through hydroboration and establish the factors that influence the selectivity and turnover. The kinetics and mechanism of the iron-catalyzed hydroboration of benzonitrile to bis(boryl)benzylamine has been investigated by initial rates, temperature dependence, kinetic isotope effects and DFT studies. In contrast to other iron-catalyzed nitrile hydroboration, this study reveals that B–H bond activation is not rate-determining. Moreover, the rate determining step was revealed to be C–H bond reductive elimination with equilibrium isotope effects in operation. Through this combined approached, an Fe(0)/(II) catalytic manifold proceeding via metal-ligand cooperativity has been determined. The iron-catalyzed hydroboration was extended to a range of nitriles and N-heteroarenes with low-catalyst loadings.