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, [η2-N3]­Ru­(η6-Ar) (1) or {[N3]­Ru}2­(μ-N2) (2), where Ar = C6H6 or
C6H5Me, and [N3] = 2,6-(2,4,6-(CH3)3­C6H2NCCH3)2­C5H3N, activate C–H
bonds in imidazolium salts to produce bis­(imino)­pyridyl ruthenium–(imida­zolidin-2-ylidene)
complexes, [N3]­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 1H 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.