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1、PublishedonWeb10/14/2009InsertionofMolecularOxygenintoaPalladium(II)MethylBond:ARadicalChainMechanismInvolvingPalladium(III)IntermediatesLucBoisvert,MelanieC.Denney,SusanKloekHanson,andKarenI.Goldberg*DepartmentofChemistry,UniVersityofWashington,Box351700,Seat
2、tle,Washington,98195-1700ReceivedJuly23,2009;E-mail:goldberg@chem.washington.eduAbstract:Thereactionof(bipy)PdMe2(1)(bipy)2,2′-bipyridine)withmolecularoxygenresultsintheformationofthepalladium(II)methylperoxidecomplex(bipy)PdMe(OOMe)(2).Theidentityoftheproduct
3、2hasbeenconfirmedbyindependentsynthesis.Resultsofkineticstudiesofthisunprecedentedoxygeninsertionreactionintoapalladiumalkylbondsupporttheinvolvementofaradicalchainmechanism.Reproduciblerates,attainedinthepresenceoftheradicalinitiator2,2′-azobis(2-methylpropion
4、itrile)(AIBN),revealthatthereactionisoverallfirst-order(one-half-orderinboth[1]and[AIBN],andzero-orderin[O2]).Theunusualratelaw(half-orderin[1])impliesthatthereactionproceedsbyamechanismthatdifferssignificantlyfromthosefororganicautoxidationsandfortherecentlyrep
5、ortedexamplesofinsertionofO2intoPd(II)hydridebonds.Themechanismfortheautoxidationof1ismorecloselyrelatedtothatfoundfortheautoxidationofmaingroupandearlytransitionmetalalkylcomplexes.Notably,thechainpropagationisproposedtoproceedviaastepwiseassociativehomolytic
6、substitutionatthePdcenterof1withformationofapentacoordinatePd(III)intermediate.59Introductionoxygenase”catalysis)remainscarce.OnepossiblemechanismTheneedtodevelopmoreefficient,cost-effective,andfortheincorporationofmolecularoxygenintoanorganicsubstrateenvironme
7、ntallybenignprocessesfortheselectiveoxidationinvolvestheinsertionofO2intoapalladiumalkylbond.However,oforganiccompoundshasledtoagrowinginterestinthesuchreactivityinvolvingoxygenhasnotbeenreportedforreactivityoforganometalliccompoundstowardmolecularpalladiumalk
8、ylcomplexesand,infact,therearefewdocumentedoxygen.1,2Frombothenvironmentalandeconomicperspectives,examplesofO2insertionsintolatetransitionmetal-alkylbonds.oxygenrepresentsanidealox
