N ‐Heterocyclic Carbene‐Containing Metal Complexes

Abstract

In the last decade, coordination chemistry has witnessed the advent of a new class of ligands: the N ‐heterocyclic carbenes (NHCs). The “success story” associated with this ligand family can be explained by the unique stereoelectronic properties of the NHCs; these unique properties have led to their numerous applications in catalysis. This article provides an overview of developments and recent advances in the syntheses of NHCs and NHCtransition metal complexes. For these NHC ligand‐containing complexes, an analysis focuses on stability and reactivity patterns is provided. Reactions such as the cleavage of NHCmetal bond, CH and CC activations, NHC migration, and NHC insertion are presented.

Pd‐Catalyzed Z‐Selective Semihydrogenation of Alkynes: Determining the Type of Active Species

“…[4,108] Efficient well-defined molecular catalysts ystems are expected to give values greatert han 40 %o fa ctive metal.However,i f also inactive NPs are formed, ap art of the added palladium is deactivated, thus leadingt oal ower percentage of active Pd atoms. Furthermore, we previously proposed that the phosphine coordinationt ot he [Pd 0 (NHC)] species leads to an inactive state, [102] which was also proposed for aP d(NHC)PCy 3 system by Cazin et al [41,109] The presence of an inactive species could also explainw hy al ower fraction of Pd that is active in the reactioni so btained for am olecular catalyst. The degree of Pd that is in ap oison-independent inactive state depends on the bindings trength of the phosphine ligand compared to that of the alkynes ubstrate.…”

Synthesis of palladium(0) and -(ii) complexes with chelating bis(N-heterocyclic carbene) ligands and their application in semihydrogenation

“…13,14 We are interested in the properties and reactivity of low-valent late transition metal complexes, notably electron rich zero-valent palladium NHC complexes, as these often play a vital role in the catalytic cycles of many reactions. [15][16][17][18] Although a lot of research has been devoted to bis-carbene Pd II (halide) 2 complexes, usually obtained by treating a bisimidazolium salt with Pd(OAc) 2 at elevated temperatures, 7,[19][20][21][22][23] we are not aware of any previous reports on chelate [Pd 0 (bis-NHC)L] or [Pd II (bis-NHC)(η 3 -C 3 H 5 )]Cl complexes. Moreover, reports on zero-valent d 10 metal complexes bearing a chelating bis-NHC ligand have not appeared in the literature at all.…”