Visible-light-induced reversible C–C bond formation of an imidazole-derived scandium complex

An unusual [3+3] cycloaddition between two scandium complexes formed by the ring-opening of 1-methylimidazole is reported. The two C–C bond formations were found to be reversible and temperature dependent. A higher temperature favored the dissociation process, while formation of the dimer by cycloaddition was favored at ambient conditions. It was found that the cycloaddition took place only in the presence of visible light, while the reverse, dissociation reaction could be induced by UV light. The effect of solvents, Lewis acids, and Brønsted bases on the reaction was also studied.