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 [RuII(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.