New aqua N-heterocyclic carbene Ru(II) complexes with two-electron process as selective epoxidation catalysts: an evaluation of geometrical and electronic effects.

New ruthenium complexes with general formula [Ru(II)(T)(CN-Me)X](n+) (X = Cl(-) or H2O; T = 2,2':6',2″-terpyridine, trpy, or N,N-bis(2-pyridyl)ethylamine, bpea; CN-Me = N-methyl-N'-2-pyridylimidazolium) have been prepared. The complexes obtained have been characterized in solution by spectroscopic (1D- and 2D-NMR and UV-vis) techniques, mass spectrometry, and elemental analysis. The chloro complexes have also been characterized by X-ray diffraction analysis. The redox properties of all the compounds were studied by CV revealing, for the reported Ru-OH2 complexes, bielectronic Ru(IV/II) redox processes throughout a wide pH range. The catalytic activity of aquo complexes was evaluated in the epoxidation of olefins using PhIO as oxidant, displaying in general good yields and high selectivities for the epoxide product. The influence of electronic and geometrical factors on the spectroscopic and electrochemical properties as well as on the catalytic activity is discussed.