Solid-State Dynamic Behavior of the Boron–Nitrogen Bond Enables Mechanophotocatalysis of a [2 + 2]-Photocycloaddition

We report reversible B←N coordinate bond formation and cleavage in the organic solid state. The dynamic behavior was probed using the [2 + 2]-photodimerization of 4-(1-naphthylvinyl)pyridine (4-nvp) as a chemical reporter under concurrent mechanochemical vortex grinding and ultraviolet light-emitting diode (UV-LED) irradiation. Phenylboronic acid catechol ester (pbe) templates the regio- and stereoselective formation of 1,3-bis(4-pyridyl)-2,4-bis(1-naphthyl)cyclobutane (pncb), and the reaction proceeds efficiently even when pbe is used in substoichiometric amounts (50%, 30% and 5% mol). The catalytic turnover demonstrates that B←N bonds can break and reform dynamically under mechanical stress in the organic solid state, establishing B←N coordination as a design element for responsive molecular materials.