Oxidative addition of the imidazolium cation to zerovalent Ni, Pd, and Pt: a combined density functional and experimental study

Synthesis of Highly Stable 1,3-Diaryl-1H-1,2,3-triazol-5-ylidenes and their Applications in Ruthenium-Catalyzed Olefin Metathesis

The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions.

The measure of all rings--N-heterocyclic carbenes

Quantification and variation of characteristic properties of different ligand classes is an exciting and rewarding research field. N-Heterocyclic carbenes (NHCs) are of special interest since their electron richness and structure provide a unique class of ligands and organocatalysts. Consequently, they have found widespread application as ligands in transition-metal catalysis and organometallic chemistry, and as organocatalysts in their own right. Herein we provide an overview on physicochemical data (electronics, sterics, bond strength) of NHCs that are essential for the design, application, and mechanistic understanding of NHCs in catalysis.

Unexpected C(carbene)-X (X: I, Br, Cl) Reductive Elimination From N-Heterocyclic Carbene Copper Halide Complexes Under Oxidative Conditions

The non-innocent behaviors of NHC ligands have attracted wide attention due to their important implications for catalyst designs and reaction mechanisms. Herein, we report facile C(carbene)-halogen reductive eliminations from NHC copper halide complexes at RT under oxidative conditions. Density functional calculations on a simplified model system suggest that the reactions occur through oxidation of Cu(I) to Cu(III) species followed by C(carbene)-halogen reductive eliminations from NHC Cu(III) halide complexes. Remarkably short C(carbene)-chloride contacts and rare interactions between the chloride lone pair electrons and the C(carbene)p(π) orbital were found for the calculated NHC Cu(III) chlorides. The facile C(carbene)-X reductive elimination reported here warrants consideration as a potential decomposition pathway in reactions involving NHC-supported high-valent metal complexes, especially with late transition metals.