Photochemical Activation of Ruthenium Complexes Containing Unsymmetrical Unsaturated N-Heterocyclic Carbenes for Olefin Metathesis

Olefin metathesis is a fundamental transformation in organic chemist’s toolbox. Herein we report a methodological study on a set of bench stable, latent, ruthenium-indenylidene catalysts bearing two unsymmetrical unsaturated N-heterocyclic carbene (NHC) ligands. These complexes are successfully ‘activated’ and applied to ring-closing metathesis (RCM), cross-metathesis (CM), and ring-opening cross metathesis (ROCM) upon light irradiation in the presence of an organic photoactivator. The transformations could be performed at lower catalyst loading (down to 1 mol%) compared to the state-of-the-art photochemical activation methods, providing good yields in shorter reaction time.