Chemoselective boron-carbon bond cleavage by hydroboration of borirenes

We report on the hydroboration of 1-[bis(trimethylsilyl)amino]-2,3- diethylborirene (3) with 9-borabicyclo-[3.3.1]nonane (9-BBN), which led through ring-opening to an amino-(vinyl)borane. The viscous borane was subsequently converted into a crystalline borate on treatment with MeLi.Both compounds were fully characterized by multinuclear NMR spectroscopy and in case of the latter by singlecrystal X-ray diffraction analysis. To elucidate the reaction mechanism of the unexpected boron-carbon bond cleavage, DFT calculations of energy minima and transition states for the hydroboration were carried out.