title: Solvent-dependent switch of ligand donor ability and catalytic activity of ruthenium(II) complexes containing pyridinylidene amide (PYA) N-heterocyclic carbene hybrid ligands.
abstract: Chelating ligands incorporating both N-[1-alkylpyridin-4(1H)-ylidene]amide (PYA) and N-heterocyclic carbene (NHC) donor sites were prepared and used for the synthesis of ruthenium(II) complexes. Cyclic voltammetry, NMR, and UV-vis spectroscopy of the complexes indicate a solvent-dependent contribution of the limiting resonance structures associated with the ligand in solution. The neutral pyridylidene imine structure is more pronounced in apolar solvents (CH2Cl2), while the mesoionic pyridinium amide form is predominant in polar solvents (MeOH, DMSO). The distinct electronic properties of these hybrid PYA-NHC ligands in different solvents have a direct influence on the catalytic activity of the ruthenium center, e.g., in the dehydrogenation of benzyl alcohol to benzaldehyde. The activity in different solvents qualitatively correlates with the solvent permittivity.
authors.affiliation: School of Chemistry & Chemical Biology, University College Dublin , Belfield, Dublin 4, Ireland.
authors.forename: Vivienne
authors.initials: V
authors.lastname: Leigh
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Carleton
authors.forename: Juan
authors.initials: J
authors.lastname: Olguin
authors.forename: Helge
authors.initials: H
authors.lastname: Mueller-Bunz
authors.forename: L James
authors.initials: LJ
authors.lastname: Wright
authors.forename: Martin
authors.initials: M
authors.lastname: Albrecht