Synthesis of Tridentate 2,6-Bis(imino)pyridyl Ruthenium(II) Complexes with N-Heterocyclic Carbene Ligands: Activation of Imidazolium Salts

Low-valent Ru(0) complexes, [eta(2)-N-3]Ru(eta(6)-Ar) (1) or {[N-3]Ru}(2)(mu-N-2) (2), where Ar = C6H6 or C6H5Me, and [N-3] = 2,6-(2,4,6-(CH3)(3)C6H2N-CCH3)(2)C5H3N, activate C-H bonds in imidazolium salts to produce bis(imino)pyridyl ruthenium-(imidazolidin-2-ylidene) complexes, [N-3]Ru(H)(X)(NHC) (4) (X = halides and tosylate). Formation of 4 is most likely to proceed via C-H oxidative addition, followed by anion coordination, which is expected to be a useful pathway in synthesizing new complexes with both N-heterocyclic carbene (NHC) and hydride ligands. A zwitterionic ruthenium complex with an ylidic ligand, bis(imino)pyridyl ruthenium-(2-methyleneimidazoline) complex, 7, was also successfully isolated and fully characterized. The (1)H NMR spectra and the solid-state structure confirm that complex 7 is an ylidic transition-metal complex with both NHC and hydride ligands, which was formed through the activation of imidazolium salts.