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On the Electronic Impact of Abnormal C4‐Bonding in N‐Heterocyclic Carbene Complexes
Author(s) -
Heckenroth Marion,
Neels Antonia,
Garnier Michael G.,
Aebi Philipp,
Ehlers Andreas W.,
Albrecht Martin
Publication year - 2009
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.200900249
Subject(s) - carbene , chemistry , steric effects , reactivity (psychology) , oxidative addition , metal , electronic effect , catalysis , palladium , transition metal carbene complex , center (category theory) , density functional theory , reductive elimination , photochemistry , stereochemistry , crystallography , computational chemistry , organic chemistry , alternative medicine , pathology , medicine
Sterically similar palladium dicarbene complexes have been synthesized that comprise permethylated dicarbene ligands which bind the metal center either in a normal coordination mode via C2 or abnormally via C4. Due to the strong structural analogy of the complexes, differences in reactivity patterns may be attributed to the distinct electronic impact of normal versus abnormal carbene bonding, while stereoelectronic effects are negligible. Unique reactivity patterns have been identified for the abnormal carbene complexes, specifically upon reaction with Lewis acids and in oxidative addition‐reductive elimination sequences. These reactivities as well as analytical investigations using X‐ray diffraction and X‐ray photoelectron spectroscopy indicate that the C4 bonding mode increases the electron density at the metal center substantially, classifying such C4‐bound carbene ligands amongst the most basic neutral donors known thus far. A direct application of this enhanced electron density at the metal center is demonstrated by the catalytic H 2 activation with abnormal carbene complexes under mild conditions, leading to a catalytic process for the hydrogenation of olefins.