Selective Benzylic CH‐Borylations by Tandem Cobalt Catalysis

Metal‐catalyzed C−H activations are environmentally and economically attractive synthetic strategies for the construction of functional molecules as they obviate the need for pre‐functionalized substrates and minimize waste generation. Great challenges reside in the control of selectivities, the utilization of unbiased hydrocarbons, and the operation of atom‐economical dehydrocoupling mechanisms. An especially mild borylation of benzylic CH bonds was developed with the ligand‐free pre‐catalyst Co[N(SiMe(3))(2)](2) and the bench‐stable and inexpensive borylation reagent B(2)pin(2) that produces H(2) as the only by‐product. A full set of kinetic, spectroscopic, and preparative mechanistic studies are indicative of a tandem catalysis mechanism of CH‐borylation and dehydrocoupling via molecular Co(I) catalysts.