Mixed heteropentadienyl and N-heterocyclic carbene ruthenium(II) complexes: Synthesis and transfer hydrogenation catalysis

Two synthetic methodologies for obtaining novel mixed heteropentadienyl and N-heterocyclic carbenes (NHC) ruthenium(II) complexes have been explored. A synthetic strategy involving the addition of heteropentadienyl precursors to [Ru-II]-NHC complexes proved to be a successful route for the isolation of four novel mixed ligand complexes, namely stereoisomers [(p-cymene)Ru-II(BuImMe)(eta(3)-exo-syn-CH2CHCHCHO)]BF4 (3 and 3', BulmMe = 1-butyl-3-methylimidazolyl-2-idene) and [(eta(1)-CH(2)CHCRCHS02) Ru-II(PylmMe)(CH3CN)(3)](A) (PylmMe = 3-methyl-1-(2-pyridyl)imidazolyl-2-idene, R = H, A = BF4, 6; R = CH3, A = PF6, 7). Moreover complex 6 has been characterised by X-ray crystallography confirming the sulphur-bound monodentate nature of CH2CHCHCHSO2 ligand adopting an S-conformation. Complexes 6 and 7 were tested as pre-catalysts in the transfer hydrogenation reaction of benzophenone, showing moderate and good activities, respectively. (C) 2016 Elsevier B.V. All rights reserved.