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 sp2 C-sp3 C σ-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.