DFT studies on reactions of boroles with carbon monoxide

Boroles can react with CO to give Lewis acid-base adduct 1AD, tricyclic boracycle 1TB or ketene derivative 1KD depending on the substituents on the borole. DFT calculations at the M06-2X level of theory were performed to study systematically the influence of borole substituents on these reactions. It was found that the Lewis acid-base adduct 1AD is a kinetic product, which can further transform to the tricyclic boracycle 1TB or ketene derivative 1KD. The computational results show that strong electron-withdrawing perfluorophenyl substituents significantly stabilise the Lewis acid-base adduct 1AD, allowing its successful isolation. In most cases, the tricyclic boracycle 1TB is both kinetically and thermodynamically more favourable than the ketene derivative 1KD. However, a -B(C6F5)(2) substituent at the 4-position and a silyl substituent at the 5-position together are able to lower the barrier leading to the formation of the ketene derivative 1KD.