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

Abstract

A series of ruthenium(II) N,S-heterocyclic carbene (NSHC) complexes Ru^IIX(RCOO)(PPh₃)₂(3-R′BzTh) (BzTh = benzothiazol-2-ylidene; R = Me, R′/X = Bz/Br (4), Prⁱ/I (6), Buⁱ/I (8); R = Et, R′/X = Bz/Br (5), Prⁱ/I (7), Buⁱ/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.