Hydroboration of C=O Bonds Using an Iron-Borane complex: Isolation of an Iron(I) Ketyl Radical

An iron metalloborane complex [{(iPrDPBPh)Fe}2(μ-1,2-N2)] (A) has been demonstrated to be an efficient pre-catalyst for hydroboration of ketones, cyclic esters and CO2 with mild conditions. Mechanistic insights into the hydroboration of cyclohexylphenyl ketone via initial rate kinetics, kinetic isotope studies reveal an unprecedented iron-mediated ligand-to-ligand hydride transfer (LLHT) process is in operation with B–H bond breaking being be rate determining, indicating the importance of mechanistic studies on well-known transformations. Isolation of the first iron(I)-benzophenone ketyl radical with a unique S = 1 antiferromagnetic ground state has been achieved.