How To Enhance the Efficiency of Breslow Intermediates for SET Catalysis
Abstract
Oxidativecarbeneorganocatalysis,whichproceedsviasingleelectrontransfer(SET) pathways, hasbeen limitedby themoderately reducingpropertiesof deprotonatedBreslow intermediatesBI−sderivedfromthiazol-2-ylidene1and1,2,4-triazolylidene2.Usingcomputational methods,weassesstheredoxpotentialsofBI−sbasedontendifferenttypesofknownstablecarbenes andreportourfindingsconcerningthekeyparametersinfluencingthestepsofthecatalyticcycle. FromthecalculatedvaluesofthefirstoxidationpotentialofBI−sderivedfromcarbenes1to10,it appearsthat,apartfromthediamidocarbene7,alltheothersaremorereducingthanthiazol-2-ylidene 1andthe1,2,4-triazolylidene2.WeobservedthatwhilethereducingpowerofBI−ssignificantly decreaseswithincreasingsolventpolarity,theredoxpotentialoftheoxidantcanincreaseatagreater rate,thusfacilitatingthereaction.Thecation,associatedwiththebase,alsoplaysanimportantrole whenanonpolarsolventisused;largeandweaklycoordinatingcationssuchasCs+arebeneficial.The radical−radicalcouplingstepisprobablythemostchallengingstepduetobothelectronicandsteric constraints.Basedonourresults,wepredictthatmesoioniccarbene3andabnormalNHC4arethe mostpromisingcandidatesforoxidativecarbeneorganocatalysis.
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Chemical Sciences| Origin | Files produced by the author(s) |
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