Photo‐promoted Skeletal Rearrangement of Phosphine‐Borane Frustrated Lewis Pairs Involving Cleavage of Unstrained C–C σ‐Bonds

An unprecedented photo-promoted skeletal rearrangement reaction of phosphine-borane frustrated Lewis pairs, o -(borylaryl)phosphines, involving cleavage of an unstrained sp 2 C-sp 3 C sigma-bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium-borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine-borane FLPs.