N‑Alkylation and N,C-Dialkylation of Amines with Alcohols in the Presence of Ruthenium Catalysts with Chelating N‑Heterocyclic Carbene Ligands

A series
of new benzimidazolium salts and ruthenium­(II) complexes
containing chelating N-heterocyclic carbenes (NHCs) functionalized
with a benzylic group and an acetal group were prepared. All of the
synthesized compounds were characterized by elemental analysis and
NMR spectroscopy, and the molecular structures of 2c and 2d were determined by X-ray crystallography. All of the complexes
were tested in the alkylation of cyclic amine derivatives with alcohols
and showed excellent activity in this reaction. Cyclic amines were
alkylated with primary and heteroaromatic alcohols. The Ru–NHC
complexes also catalyzed N,C3-dialkylation of cyclic amines.