title: Triazolylidene-Iridium Complexes with a Pendant Pyridyl Group for Cooperative Metal-Ligand Induced Catalytic Dehydrogenation of Amines.
abstract: Two iridium(III) complexes containing a C,N-bidentate pyridyl-triazolylidene ligand were prepared that are structurally very similar but differ in their pendant substituent. Whereas complex 1 contains a non-coordinating pyridyl unit, complex 2 has a phenyl group on the triazolylidene substituent. The presence of the basic pyridyl unit has distinct effects on the catalytic activity of the complex in the oxidative dehydrogenation of benzylic amines, inducing generally higher rates, higher selectivity towards formation of imines versus secondary amines, and notable quantities of tertiary amines when compared to the phenyl-functionalized analogue. The role of the pyridyl functionality has been elucidated from a set of stoichiometric experiments, which demonstrate hydrogen bonding between the pendant pyridyl unit and the amine protons of the substrate. Such Npyr⋅⋅⋅H-N interactions are demonstrated by X-ray diffraction analysis,1H NMR, and IR spectroscopy, and suggest a pathway of substrate bond-activation that involves concerted substrate binding through the Lewis acidic iridium center and the Lewis basic pyridyl site appended to the triazolylidene ligand, in agreement with ligand-metal cooperative substrate activation.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012, Bern, Switzerland.|School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Marta
authors.initials: M
authors.lastname: Valencia
authors.affiliation: School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.|Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC, Centro de Investigación en Química Sostenible, Departamento de Química, Universidad de Huelva, 21007, Huelva, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Pereira
authors.affiliation: School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Helge
authors.initials: H
authors.lastname: Müller-Bunz
authors.affiliation: Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC, Centro de Investigación en Química Sostenible, Departamento de Química, Universidad de Huelva, 21007, Huelva, Spain.
authors.forename: Tomás R
authors.initials: TR
authors.lastname: Belderraín
authors.affiliation: Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC, Centro de Investigación en Química Sostenible, Departamento de Química, Universidad de Huelva, 21007, Huelva, Spain.
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Pérez
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012, Bern, Switzerland.|School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0001-7403-2329
authors.initials: M
authors.lastname: Albrecht
keywords: amine dehydrogenation; hydrogen bonding; iridium; ligand-metal cooperativity; triazolylidene