An Isolable Phosphaborene Stabilized by an Intramolecular Lewis Base

Phosphaborenes are P/B analogs of alkynes. Herein, we describe the isolation of a phosphaborene stabilized by an intramolecular Lewis base. This species is achieved via the installation of the phosphaborene with a sterically encumbering phosphino substituent. Although this species features an aromatic P2B three-membered ring, the ring strain allows the hemi-labile behavior of the P-B donor-acceptor bond, thereby exhibiting frustrated Lewis pair reactivity. Our finding paves the way for further exploration of the reactivity patterns of monomeric phosphaborenes.