Lewis Base Activation of Lewis Acids - Group 13. In Situ Generation and Reaction of Borenium Ions.

A variety of Lewis bases were combined with 9-BBN-NTf2 to establish the requirements for the generation of borenium cations. Five different types of behavior were found, but the most interesting was the combination of Et3N, DABCO, 2,6-lutidine, or Ph3P=S which formed borenium ions exclusively even in sub- or superstoichiometric quantities. The 9-BBN borenium ion complex of 2,6-lutidine was found to rapidly catalyze the hydrosilylation of a variety of ketones in the presence of Et3SiH. Preliminary mechanistic experiments suggest that the reduction involves borenium ion activation of Et3SiH and not the ketone.