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ID:56432622
大小:1.36 MB
页数:51页
时间:2020-06-18
《基元反应(插入).ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、氧化加成和还原消除反应a)b)金属的氧化态及配位数均减少2;配位饱和的高价金属变为配位不饱和的低价金属。氧化加成反应的特点:A-B键发生断裂,同时加成到过渡金属上;金属的氧化态及配位数均增加2;配位不饱和的低价金属变为配位饱和的高价金属。还原消除反应的特点:A=B为C=C、R’RC=O、C=N等。:A–B为一氧化碳:CO、异氰:CN–R、卡宾:CR2等。插入反应和消除(反插入)反应插入反应是指不饱和键插入到M-H键或M-C键中。特点:金属的氧化态及配位数均没有变化。Oxidativeaddition/reductiveeliminationproces
2、sesarecentraltoavastarrayofsyntheticallyusefulorganometallicreactions(eg.“Heck”reaction),andoccurbecauseoftheabilityoftransitionmetalstoexistinseveraldifferentoxidationstates,incontrasttonontransitionmetalcompounds,whichusuallyhaveclosedshellconfigurations.Infact,itisthefacilesh
3、uttlingbetweenoxidationstatesthatmakestransitionmetalssousefulinorganicsynthesis.氧化加成和还原消除是以Vaska(1968)配合物IrCl(CO)(PPh3)2和Wilkinson配合物RhCl(PPh3)3的发现及反应性研究开始的,对了解催化反应机理非常重要。NotethatmanyoftheseresultintheformationofM-HandM-Cbonds,andinthe“activation”ofarangeoforganicsubstrates.Con
4、certedoxidativeadditionsarebestknownfornonpolarsubstrates,eg.H2,andC-Hbonds.OxidativeadditionviaSN2-typeprocessesismostoftenobservedwithstronglynucleophilic,lowvalentmetalsandclassicSN2substratessuchasorganichalidesandtosylates.Collman’sreagent,Na2Fe(CO)4,averypotentnucleophile,
5、reactswithRXviaSN2.Competingradicalchainmechanismforoxidativeaddition.Tracesofairsometimespromotethereactionofcomplexeswhichnormallyrequirestrictexclusionofair,andservesasawarningthatthemechanismbywhichareactionproceedsmaybeafunctionofthecarewithwhichitiscarriedout.Nicatalyzedco
6、uplingofarylhalidestobiaryls,whichwasoriginallythoughttoproceedbytwosequentialtwo-electronoxidativeadditions.However,carefulstudiesshowedthiswasnotthecase.Rather,acomplicatedradicalchainprocessinvolvingNi(I)toNi(III)oxidativeadditionisthetruecourseofthereaction.氧化加成和还原消除反应a)b)金属
7、的氧化态及配位数均减少2;配位饱和的高价金属变为配位不饱和的低价金属。氧化加成反应的特点:A-B键发生断裂,同时加成到过渡金属上;金属的氧化态及配位数均增加2;配位不饱和的低价金属变为配位饱和的高价金属。还原消除反应的特点:Reductiveeliminationisthereverseofoxidativeadditionandisusuallythelaststepofmanycatalyticprocesses.Itisexceptionallyimportantfororganicsyntheticapplicationsbecauseitis
8、themajorwayinwhichtransitionmetalsareusedtomake
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