The chemistry of functionalised N-heterocyclic carbenes.pdf

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1、ViewArticleOnline/JournalHomepage/TableofContentsforthisissueTUTORIALREVIEWwww.rsc.org/csr

2、ChemicalSocietyReviewsThechemistryoffunctionalisedN-heterocycliccarbenes{OlafKu¨hl*Received8thJune2006FirstpublishedasanAdvanceArticleontheweb8thSeptember2006DOI:10.1039/b603

3、765hThistutorialreviewpresentsthesynthesis,chemistryandapplicationsoffunctionalisedN-heterocycliccarbenesNHCandtheirtransitionmetalcomplexes.FunctionalisedNHCcomprisethosecarryingaphosphino-,amino-,imino-oroxygen-containingfunctionalityontheimidazolesidechain.Maina

4、pplicationshavebeenthemodificationofcatalystsandtheirimmobilisationbyfixationonapolymericsupportusingthefunctionalgroup.WhereasthefunctionalisationoftheNHChasnotimprovedtheirperformanceincatalysis,newdevelopmentshaveoccurredintheuseofimidazole-containingbiomolecule

5、ssuchasL-histidineorcaffeineasprecursorsforNHC.IntroductionForanOrganicChemistcarbeneshavetraditionallybeentransient,highlyreactiveandshortlivedspeciesthatareuseful1tointroduceasinglecarbonatomintoamolecule.Theirreactivitycomesmainlyfromtheirelectronicunsaturation,

6、i.e.carbonasgroup14elementhasfourelectrons,fourvalenceorbitalsandascarbenetwovalencebonds.ItisthereforeleftFig.1Electronicstructureofcarbenes.withthechoicetoplaceeitheroneelectronintoeachofthetworemainingorbitals(thusbecomingatripletcarbene)orbothsituationpresented

7、itselfasachallengetosynthesiseastableelectronsintooneorbitalandleavingthefourthorbitalemptycarbenethatcanbestoredforaprolongedperiodoftime.For(singletcarbene)(seeFig.1).Althoughatripletcarbeneisoveracentury,allattemptstodosoprovedunsuccessful,moreunstablethanasingl

8、etcarbene,botharehighlyreactivealthoughFischerandSchrockwereabletogeneratestableandcannotbeisolated.Tothepreparativechemistthiscarbenesinthecoordinationsphereoftransitionmetals.2Thequestforstableuncoordinatedcarbenes,however,wentonandDownloadedbySunYat-Sen(Zhongsha

9、n)Universityon11December2012ledtothesynthesisofanumberofolefinsthatresultedfromPublishedon08September2006onhttp://pubs.rsc.org

10、doi:10.1039/B60376