Palladium Complexes of N-Heterocyclic Carbenes as Catalysts for Cross-Coupling Reactions—A Synthetic Chemist's Perspective

C4-bound imidazolylidenes: from curiosities to high-impact carbene ligands

This feature article summarizes the progress achieved thus far in using C4-bound imidazolylidenes as a new class of ligands for transition metals. Since the discovery of this unusual carbene bonding mode in 2001, various rational routes towards complexes containing C4-bound carbenes have evolved. These advances allowed for studying the impact of this new type of ligand on the transition metal center, both from a fundamental point of view as well as from a more applied perspective, in particular for catalytic applications. The promising results accomplished in this relatively short period of time demonstrate the potential of C4-bound imidazolylidenes as unique carbene ligands for inducing catalytic activity and for mediating unprecedented transformations.

Efficient and selective syntheses of (all-E)- and (6E,10Z)-2'-O-methylmyxalamides D via Pd-catalyzed alkenylation--carbonyl olefination synergy

Highly efficient and selective syntheses of both (all- E) and (6 E,10 Z)-isomers of 2'- O-methylmyxalamide D ( 2 and 3), in which the crucial conjugated pentaene moieties were assembled in > or =98% stereoselectivity through the use of two Pd-catalyzed alkenylation reactions, the Horner-Wadsworth-Emmons (HWE) olefination, and either the Corey-Schlessinger-Mills modified (CSM-modified) Peterson olefination for 2 or the Still-Gennari olefination for 3, are reported. Either 2 or 3 was prepared in 16% yield in seven steps from propargyl alcohol.

Heterocyclic carbenes: synthesis and coordination chemistry

The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of beta-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

Cyclic (amino)[bis(ylide)]carbene as an anionic bidentate ligand for transition-metal complexes

The 3-(triphenylphosphonio)-N-(2,6-diisopropylphenyl)pyrrole reacts with 2 equiv of methyllithium to afford a lithium adduct in which a cyclic (amino)[bis(ylide)]carbene, a novel type of NHC, acts as a 1,4-bidentate ligand via the carbene center and the exocyclic ylidic carbon. This species readily undergoes transmetalation reactions, which allows for the synthesis of a variety of transition-metal complexes.