N-Heterocyclic Carbenes

Synthesis of Backbone P-Functionalized Imidazol-2-ylidene Complexes: En Route to Novel Functional Ionic Liquids

“…Since the discovery of “bottleable” 1,3-diadamantyl imidazol-2-ylidene, a representative of nowadays so-called N-heterocyclic carbenes (NHC’s), carbene chemistry has received enormous attention in coordination chemistry, stabilization of highly reactive main group molecules, homogeneous catalysis, and beyond . So far most of the frequently employed (unsaturated) imidazol-2-ylidene typically form metal complexes via the carbene carbon (C 2 position), while the C 4 and C 5 positions remain unsubstituted or bear only alkyl and/or aryl groups (the numbering of elements in the imidazole ring follows the IUPAC recommendation).…”

Synthesis and catalytic activity of cis-chelated palladium(II) complexes of biphenyl-linked bis(imidazolin-2-ylidene)

“…The present chelated bis-NHC-Pd complex catalysts attain both stability and activity in the Suzuki-Miyaura reaction of aryl chlorides. It is also noted that, compared to some palladium complexes of monocarbene ligands, 1,12 the structures of bis-NHC ligands still need modification to further improve the catalytic activity.…”

“…Various palladiumNHC complex catalysts have been successfully employed in this reaction. 1,12 Herein, we turned our interest to investigate the catalytic activity of the biphenyl-linked cis-chelated bisNHCPd(II) complexes 7a and 7b in the SuzukiMiyaura cross-coupling reactions of aryl chlorides which are more attractive from the view of economic cost, but more challenging due to the less active nature of the carbonchlorine bond. We chose to examine the coupling of 1-chloro-4-methoxybenzene with phenylboronic acid for the survey of the reaction parameters.…”

“…1 The reactivity and stability of NHCmetal complexes largely rely on the electronic and steric characteristics of the NHC ligands, which can be controlled by modifying the structures of NHC ligands. Among various NHC ligands, chelate bis-NHCs with a biaryl backbone not only yield more stable metal complexes, but also give interesting features that can provide fine-tuning of topological properties such as steric hindrance, bite angles and chirality.…”