It should be noted that no BCP was found between the P and O2 atoms from calculations at the current level of theory. We also explored the reaction between 3a and CatBCl (Cat = catecholato, C6H4O2 2-) to examine whether the exchange of the B f unit with a CatB unit could proceed or not. However, the quantitative formation of a borenium species 10a including a Cl -counterion was unexpectedly observed (Figure ). This borenium 10a was isolated in 83% yield, and its molecular structure was unambiguously confirmed by NMR and SC-XRD analyses (vide infra).