Ruthenium(II) N,S-heterocyclic carbene complexes and transfer hydrogenation of ketones

A series of ruthenium(II) N, S-heterocyclic carbene (NSHC) complexes (RuX)-X-II(RCOO)(PPh3)(2)(3-R'BzTh) (BzTh = benzothiazol-2-ylidene; R = Me, R'/X = Bz/Br (4), Pr-i/I (6), Bu-i/I (8); R = Et, R'/X = Bz/Br (5), Pr-i/I (7), Bu-i/I (9)) have been synthesized and characterized. Single-crystal X-ray structural analysis revealed that in each case the Ru(II) center adopts an essentially octahedral geometry, coordinated by two trans-oriented PPh3 completed by an NSHC, chelating carboxylate and halide X (X = Br (4-5), X = I (6-9)) ligands. Although thiazol-2-ylidiene Ru(II) complexes are established and applied in metathesis, these benzothiazol-2-ylidene complexes (4-9) are the first of its kind. Their catalytic activities towards transfer hydrogenation of ketones have been examined and discussed.