Silver carbenes, review

Several reviews on the synthesis of aziridines have been published in the previous year. These publications include a review on the silver catalyzed addition of nitrenes (among other intermediates such as carbene) across a double bond <06EJOC4313> a review on sulfur ylide addition to imines to form aziridines <06SL181> a review on nitrogen addition across double bonds <06ACR194> a general review on functionalization of a,p-unsaturated esters with some discussion of aziridination <06TA1465>... 

Reports on the coordination chemistry of A-heterocyclic carbene-containing metal complexes started to appear as long ago as 1968,50,51 while metal-free carbenes have only been isolated very recently.52 In view of the fact that the general chemistry and applications of organic carbenes and related metal complexes in chemical synthesis have been reviewed several times recently,53-57 examples limited only to those carbene complexes with silver(i) have been discussed. Nevertheless, it is worth mentioning that the developments in silver(i) A-heterocyclic carbenes have also been reviewed recently by Lin.5... 

Alternatively, NHC ligands can also be transferred from triethylborane-carbene adducts [103] or complexes of the type [M(NHC)(CO)5] (M = Cr, Mo, W) [104], but these procedures are limited to special cases and are of less importance. The coordination chemistry of silver NHC complexes [105] and the advantages and applications of the Ag20 method [106] have recently been reviewed. 

Silver is often used as a halophile. In the context of six-electron species, the role of silver atoms in carbene, nitrene, and silylene transfer reactions, including aziridination, CH insertion, ring expansion, and silacyclopropanation, has been reviewed.9... 

Due to its high efficiency and regioselectivity, the Wolff rearrangement was extensively studied and reviewed, with copper or silver being the most efficient metals for this transformation (121). Similar reactivity can be achieved via ultraviolet (UV) light, sonication, or microwave irradiation (122). A free carbene-based pathway was proposed as a general mechanism. Basic additives are usually required when silver is used as the catalyst Silver nanoclusters are known to form under such conditions, which may serve as the real catalyst (Fig. 24) (123,124). 

Similarly, dichlorocarbene adds to substituted 2-arylpropenes with a p of -0.62, which is indicative of an electrophilic species. The magnitude of p is similar to that-observed for TT-complex formation of substituted styrenes by silver ion (-0.77), but significantly less than that for hydration (-4) or bromination (-4.3) of substituted styrenes. The relative reactivity of many carbenes and carbenoids with alkenes has been examined and the data accumulated and critically discussed in a comprehensive review. ... 

A review on the Simmons-Smith cyclopropanation has appeared. The involvement of silver carbenoids in various reactions (including Wolff rearrangement, car-benoid additions, and insertions) has been discussed. Benzannulation carried out by addition of a Fischer carbene to an alkyne (Doetz reaction) has been presented in an historical perspective featuring mechanistic details and synthetic applications. ... 

A review of silver carbenoid reactions including the Wolff rearrangement, carbene-transfer reactions, aziridination, cyclopropanation, formation and reactions of... 

Reviews.—Recent reviews involving olefin chemistry include olefin reactions catalysed by transition-metal compounds, transition-metal complexes of olefins and acetylenes, transition-metal-catalysed homogeneous olefin disproportionation, rhodium(i)-catalysed isomerization of linear butenes, catalytic olefin disproportionation, the syn and anti steric course in bi-molecular olefin-forming eliminations, isotope-elfect studies of elimination reactions, chloro-olefinannelation, Friedel-Crafts acylation of alkenes, diene synthesis by boronate fragmentation, reaction of electron-rich olefins with proton-active compounds, stereoselectivity of carbene intermediates in cycloaddition to olefins, hydrocarbon separations using silver(i) systems, oxidation of olefins with mercuric salts, olefin oxidation and related reactions with Group VIII noble-metal compounds, epoxidation of olefins... 

In this review, the applications in homogeneous catalysis of N-heterocyclic carbene-containing copper, silver and gold complexes will be presented. N-Heterocyclic carbenes (NHCs) are two-electron a-donor ligands that share a... 

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