Exploiting Nanospace for Asymmetric Catalysis# Confinement of Immobilized, Single-Site Chiral Catalysts Enhances Enantioselectivity

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1、ExploitingNanospaceforAsymmetricCatalysis:Con?nementofImmobilized,Single-SiteChiralCatalystsEnhancesEnantioselectivity,,JOHNMEURIGTHOMAS*ANDROBERTRAJA*DepartmentofMaterialsScience,UniversityofCambridge,CambridgeCB23QZ,U.K.,SchoolofChemistry,UniversityofSouthampt

2、on,High?eld,SouthamptonSO171BJ,U.K.RECEIVEDONSEPTEMBER27,2007CONSPECTUSnthemid-1990s,itbecamepossibletopre-Iparehigh-areasilicashavingporediame-terscontrollablyadjustableintherangeca.20-200?.Moreover,theinnerwallsofthesenanoporoussolidscouldbefunctionalizedtoyie

3、ldsingle-site,chiral,catalyticallyactiveorga-nometalliccenters,theprecisestructuresofwhichcouldbedeterminedusinginsituX-rayabsorptionandFTIRandmultinuclearmagicanglespinning(MAS)NMRspectroscopy.Thisapproachopeneduptheprospectofperformingheterogeneousenantiose-le

4、ctiveconversionsinanovelmanner,underthespatialrestrictionsimposedbythenanocavitieswithinwhichthereac-tionsoccur.Inparticular,itsuggestedanalternativemethodforpreparingpharmaceuticallyandagrochemicallyusefulasymmetricproductsbycapitalizingonthenotion,initiallyten

5、tativelyperceived,thatspatialcon?nementofprochiralreac-tants(andtransitionstatesformedatthechiralactivecenter)wouldprovideanaltogethernewmethodofboostingtheenan-tioselectivityoftheanchoredchiralcatalyst.Initially,weanchoredchiralsingle-siteheterogeneouscatalysts

6、tonanoporescovalentlyviaaligandattachedtoPd(II)orRh(I)centers.Later,weemployedamoreconvenientandcheaperelectrostaticmethod,relyinginpartonstronghydrogenbonding.ThisAccountprovidesmanyexamplesoftheseprocesses,encom-passinghydrogenations,oxidations,andaminations.O

7、fparticularnoteisthefacilesynthesisfrommethylbenzoylformateofmethylmandelate,whichisaprecursorinthesynthesisofpemoline,astimulantofthecentralnervoussystem;ourpro-cedureoffersseveralviablemethodsforreducingketocarboxylicacids.Inadditiontorelyingonearlier(synchrot

8、ron-based)insitutechniquesforcharacterizingcatalysts,wehaveconstructedexperimentalproceduresinvolvingroboticallycontrolledcatalyticreactorsthatallowthekineticsofconve