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Triazolylidene‐Iridium Complexes with a Pendant Pyridyl Group for Cooperative Metal–Ligand Induced Catalytic Dehydrogenation of Amines
Author(s) -
Valencia Marta,
Pereira Ana,
MüllerBunz Helge,
Belderraín Tomás R.,
Pérez Pedro J.,
Albrecht Martin
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201700676
Subject(s) - chemistry , substituent , iridium , ligand (biochemistry) , dehydrogenation , catalysis , denticity , medicinal chemistry , oxidative addition , amine gas treating , lewis acids and bases , substrate (aquarium) , hydrogen bond , stereochemistry , polymer chemistry , metal , molecule , organic chemistry , biochemistry , oceanography , receptor , geology
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 N pyr ⋅⋅⋅H−N interactions are demonstrated by X‐ray diffraction analysis, 1 H 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.