Hydroboration of Isocyanates: Cobalt-Catalyzed vs. Catalyst-Free Approaches

Hydroboration of isocyanates with HBPin was demonstrated using both catalytic and catalyst-free approaches. In arene solvents, reactions employed the commercially available and bench-stable Co(acac)2/dpephos (dpephos = bis[(2-diphenylphosphino)phenyl] ether) pre-catalyst and proved chemodivergent, showing formation of either formamides or N-methylamines, depending on concentration of HBPin and reaction conditions used. Catalytic monohydroboration of isocyanates to formamides was found to be highly chemoselective, tolerating alkenes, alkynes, aryl halides, esters, carboxamides, nitriles, nitroarenes and heteroaromatic functionalities. The catalyst-free hydroboration reactions have been demonstrated in neat HBPin. Whereas monohydroboration proved less selective compared to Co(acac)2/dpephos-catalyzed transformations, selective deoxygenative hydroboration of isocyanates to N-methylamines was observed under catalyst-free conditions.