Cooperative Heterobimetallic Substrate Activation Enhances Catalytic Activity and Amplifies Regioselectivity in 1,4-Hydroboration of Pyridines

Regioselective 1,4-hydroboration of pyridine derivatives and quinoline with pinacolborane is catalyzed efficiently by the heterobinuclear catalyst, (IPr)­CuFeCp­(CO)2, at only 2 mol % loading, providing access to valuable 1,4-dihydropyridine (1,4-DHP) products. A variety of reactive functional groups are tolerated in the pyridine 3-position, and sufficient catalytic activity was obtained for reduction of sterically hindered cases such as 3,5-disubstituted pyridines and even 4-substituted pyridines. Mechanistic experiments indicate that the superior catalytic activity and 1,4-regioselectivity of the Cu/Fe heterobinuclear catalyst, compared to the corresponding mononuclear Cu catalyst, is derived from biphilic cooperativity of two key catalytic intermediates: electrophilic CpFe­(CO)2(Bpin) activates the pyridine substrates toward regioselective nucleophilic addition by (IPr)­CuH.