N-Heterocyclic Carbenes:  Synthesis, Structures, and Electronic Ligand Properties^,

Abstract

N-Heterocyclic carbene (NHC) rhodium(I) complexes of general formula Rh(COD)X(NHC) are synthesized and structurally characterized (spectroscopy, X-ray diffraction). The relative σ-donor/π-acceptor quality of various NHC ligands was examined and classified by means of IR spectroscopy at the corresponding Rh(CO)2I(NHC) complexes. The first single-crystal X-ray diffraction studies of rhodium pyrazolin- and tetrazolinylidene complexes are reported. A wide variety of different azolium salts was applied to obtain rhodium and iridium complexes with two and four carbene ligands.

Platinum(ii) N-heterocyclic carbene complexes: coordination and cyclometallation.

“…The reagent PtMe 2 (DMSO) 2 has been reported 26 to induce facile cyclometallation reactions and we thus tried it. Reaction of the silver NHC complexes 2 with PtMe 2 (DMSO) 2 has not previously been documented, but we can report that it works well as another method of selectively introducing a single NHC ligand to a platinum(II) centre, giving excellent yields, Scheme 3. …”

Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

“…157 In contrast, donor quantification based on RhCl(CO) 2 (L) complexes have long been on weak grounds, despite the fact that many studies use this RhCl(CO) 2 synthon for the assessment of donor ability. 41,56,131,132,158,159 To the best of our knowledge, the correlation between the TEP (or LEP) and the CO vibrations in these Rh complexes has not yet been established. In a recent study, Wolf and Plenio succeeded, for the first time, in demonstrating a linear relationship of the ν CO frequencies between complexes of the type IrCl(CO) 2 (L) and RhCl(CO) 2 (L).…”

“…This is also the situation for metal-carbon coupling constants 1 J MC . Often they do not follow a consistent trend 56 and their discussion has been contradictory. 93,110 Inherent in the association of a larger 13 C chemical shift with more "carbene character" is the assumption that metalto-carbene π-back-donation does not effect the same amount of carbon shielding to the donor C atom as participation in π-bond formation within the heterocyclic ring.…”

Preparation and characterisation of a Ni2+/Co2+-cyclam modified mesoporous cellular foam for the specific immobilisation of His6-alanine racemase

“…Gradually, NHeterocyclic carbenes (NHCs) have become the most successful class of ligand in organometallic chemistry. This is partially due to their o-donating ligands similar to phosphate (P), nitrogen (N) and partially because they are chemically and thermally more inert towards the cleavage than P and N ligands 149 . The properties of NHCs based heterogeneous catalysts can be easily modified in order to increase selectivity 149,150 .…”