Photochemical isomerization of N-heterocyclic carbene ruthenium hydride complexes: in situ photolysis, parahydrogen, and computational studies.

Low-temperature UV irradiation of the N-heterocyclic carbene complex Ru(IEt2Me2)(PPh3)2(CO)H2 (IEt2Me2 = 1,3-bis(ethyl)-4,5-dimethylimidazol-2-ylidene) leads to a remarkable photoisomerization reaction. By combining in situ photolysis and parahydrogen experiments to characterize the ultimate photoproducts and DFT calculations to interrogate the structures of the key 16-electron intermediates, the importance of both PPh3 and H2 loss pathways has been established.