Synthesis and Reactivity of Cationic Boron Complexes Distorted by Pyridine-based Pincer Ligands: Isolation of a Photochemical Hofmann-Martius-type Intermediate.

A family of cationic boron complexes was synthesized, using a dianilidopyridine pincer ligand, which imposes in-plane distortion of the geometry at boron towards T-shaped. Reactivity of these cations toward hydride and base was investigated, and the utility of these cations as precursors to a variety of π-conjugated BN heterocycles was demonstrated. 300 nm irradiation of a deprotonated pincer boron complex triggered a C-N cleavage/C-C formation yielding a dearomatized boryl imine, which has a structure akin to the long-proposed intermediate in the photochemical Hofmann-Martius rearrangement. The photo-rearrangement triggers relief of the distortion imposed by the pincer ligand.