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1、ExploitingNanospaceforAsymmetricCatalysis:ConfinementofImmobilized,Single-SiteChiralCatalystsEnhancesEnantioselectivity,,JOHNMEURIGTHOMAS*ANDROBERTRAJA*DepartmentofMaterialsScience,UniversityofCambridge,CambridgeCB23QZ,U.K.,SchoolofChemistry,UniversityofSouthampt
2、on,Highfield,SouthamptonSO171BJ,U.K.RECEIVEDONSEPTEMBER27,2007CONSPECTUSnthemid-1990s,itbecamepossibletopre-Iparehigh-areasilicashavingporediame-terscontrollablyadjustableintherangeca.20-200Å.Moreover,theinnerwallsofthesenanoporoussolidscouldbefunctionalizedtoyie
3、ldsingle-site,chiral,catalyticallyactiveorga-nometalliccenters,theprecisestructuresofwhichcouldbedeterminedusinginsituX-rayabsorptionandFTIRandmultinuclearmagicanglespinning(MAS)NMRspectroscopy.Thisapproachopeneduptheprospectofperformingheterogeneousenantiose-le
4、ctiveconversionsinanovelmanner,underthespatialrestrictionsimposedbythenanocavitieswithinwhichthereac-tionsoccur.Inparticular,itsuggestedanalternativemethodforpreparingpharmaceuticallyandagrochemicallyusefulasymmetricproductsbycapitalizingonthenotion,initiallyten
5、tativelyperceived,thatspatialconfinementofprochiralreac-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