Study on the Reactions of Long Chain (Cnh2n+1) Azolium Chloride and Bromide Salts |

ABSTRACT:

Metal–NHCchemistry has been reviewed by pioneers in the field. When Herrmann andBertrand published excellent reviews in 2000 concerning the synthesis ofmetal–NHCs, few Ag(I)–NHCs were known [1,3b]. Indeed interest in the synthesisof Ag(I)–NHCs and their application in transmetallation reactions has onlygreatly increased in recent years. In this regard, we reviewed Ag(I)–NHCs in2004 [77] providing general trendsin Ag(I)–NHC chemistry. Arnold also had amini review onAg(I)–NHCs in 2002 [78]. Recently, Garrison and Youngs publisheda review on Ag(I)–NHCs in 2005 [79], focusing mainlyon the structuralparameters. We note that 62 papers dealingwith Ag(I)–NHCs have been publishedsince the Youngs’review. When we look at the present trends in the chemistry ofmetal–NHCs(up to 31 July 2006), the Ag(I)–NHCs comprise various NHC systems ranging fromfive membered to seven membered rings, including imidazolium, benzimidazolium,imidazolinium, triazolium, pyrazolium, quinoxaline and naphthaanellatedimidazolium, imidazo[1,5-a]pyridine, bipiperidine and biisoquinoline derivedimidazolium, bisimidazoliums with arene backbone, six-membered ringpyrimidinium, sevenmembered ring amidinium moieties, etc. (Scheme 1).Therefore, it was our intention to provide an updated and comprehensive reviewon the subject of Ag(I)–NHCs, which may further accelerate work on this topic.The main features of this review were to evenly focus on (a) the ease andlimitations in the synthesis of Ag(I)–NHCs, (b) the parameters influencing thesolid state structures of Ag(I)–NHCs, and (c) the efficacy of transmetallationreaction by Ag(I)–NHCs. In particular, the authors would like to evaluate thewidely applied Ag2O technique in the synthesisof Ag(I)–NHCs and theirtransmetallation efficiency to afford other important metal–NHCs.