Abstract
Rollover cyclometalation constitutes a particular case of cyclometallation reaction. This reaction occurs when a chelated heterocyclic ligand loses its bidentate coordination mode and undergoes an internal rotation, after which a remote C–H bond is regioselectively activated, affording an uncommon cyclometalated complex, called “rollover cyclometalated complex”. The key of the process is the internal rotation of the ligand, which occurs before the C–H bond activation and releases from coordination a donor atom. The new “rollover” ligand has peculiar properties, being a ligand with multiple personalities, no more a spectator in the reactivity of the complex. The main reason of this peculiarity is the presence of an uncoordinated donor atom (the one initially involved in the chelation), able to promote a series of reactions not available for classic cyclometalated complexes. The rollover reaction is highly regioselective, because the activated C–H bond is usually in a symmetric position with respect to the donor atom which detaches from the metal stating the rollover process. Due to this novel behavior, a series of potential applications have appeared in the literature, in fields such as catalysis, organic synthesis, and advanced materials.
Highlights
Metal-mediated activation and functionalization of C–H bonds are fundamental topics in organometallic chemistry
The key of the process is the internal rotation of the ligand, which occurs before the C–H bond activation and releases from coordination a donor atom
Starting from the usual NN adduct, detachment of the nitrogen and internal rotation are the crucial differences between classical and rollover cyclometalation; in the latter, a coordination position is liberated by the nitrogen, alation) which do not involve a direct C–H bond activation but require a starting organometallic compound for the exchange reaction M-C + M’-X → M-X + M’-C
Summary
Metal-mediated activation and functionalization of C–H bonds are fundamental topics in organometallic chemistry. CTlheeavcaogme)p,roexhiednastiiovne aodf dthiteiomn,eachnadnσis-mbonisdcmometpaltihceasteisd[1b,y2,t2h0e].fact that sttisobstsrhhutufeaueeobbintndphttrrsllgieeCeTeieeetaarhisd–scsLacoHetettttonnrriiitMonuouovembnnpreccaomttefepepuurrntrosiaaaarradnpmgltaattsheheillmandaswcwmmcugtie.taiaancoioTclmyvyhtlddh.yCa.eaiiaetfif–csiniinocHchcpdoaanatamtthntbliivhlooeiopasiennandcmrssaednieuhsiiadlnnemaeeteucncott(ptthhrsIfireIeiveeoC)on,apolnld(aitisfhgginsopoiatadlfohn2nni,)cnetdd–throaHeCseoocves–rrtmoveaiHimavecinentrlacieeabttvthdlhioehaoafxenettnnatihdmoecimsai,tnnsometeatstr,ctneasaaioilnd,lsllemscsccacoiuetemnorrncpnomohtomltmneaenprat-roaildsmnfsitmocoitutcaarhnacmtyreyaaeei(tsdnldeIdieenIglecse)besge.t,ecyr.TpptiosMtrhltlunyohyiie-bsnseipicsnipnffchotaflaafioatrnltcuuunhrtafeeewirtltnsnnuaohtactctmriayeecseet on thCe–rHingbofnadvoarcstitvhaetimonetvaila-meeledcitartoepdhailcictivaacttiiovnat,ioinn aisnacloomgymtoonefloercterolepchtriolinc-parooomr alatitce struabnsstiittiuotniomnsetinalsorsguacnhicascopmalplaoduinudms(.II), and, to some extent, platinum(II) This pathway Iins ocopnetrraatsivt,eoxesidpaetciivaellaydidnittihoen cpaastehwofaCys(srpeq2)u–iHreaeclteicvtarotino-nrischinloawro-mvaalteinctrminegtsa.l MceenctherasannisdticissctuodmiemsoonnfaorrolmataetitcraCn–sHitiobnonmdeatcatlisv, astuiocnh raesvReaul,eOd st,hRathe, lIerc, tProt;na-dlsoon, aittisnegemsusbtsotitbuepenretsfeornretdhienriCn(galfkayvlo)–rsHthbeonmdetaaclt-imvaetdioiantse.d activation, in analogy to electrophilic aromatic substTithuetiσo-nbsoinndomrgeatnaitchceosims ppoatuhnwdas.y has been considered a prevalent mechanism in the case oInf ecloencttrroanst-,pooxoirdmatievtaelacdednitteirosnspuachthawsahyisghre-vqaulierneteeleacrltyrotnra-rnicsihtiloonwm-veatlaelns.tImn ethtael ccaesneotefrlsataentdrainsscitoimonmmoentaflosr, slautcehtarasnPsti(tIiIo)nanmdePtadl(sI,I)s,uthche maseRtaul ,suOpsp, oRrhts, Itrh,ePstt;aablisloiz,aittioseneomf sthteo σbecopmrepfelerrxeadnidn tCh(ealpkryolc)e–sHs hbaosndbeaecntidveastiiognnsa.ted σ-CAM, σ-complex assisted metathesis. Starting from the usual NN adduct, detachment of the nitrogen and internal rotation are the crucial differences between classical and rollover cyclometalation; in the latter, a coordination position is liberated by the nitrogen, alation) which do not involve a direct C–H bond activation but require a starting organometallic compound for the exchange reaction M-C + M’-X → M-X + M’-C. Quite recently, a C–H bond rollover activation which precedes nitrogen coordination was proposed for the reactions of 2,2 -bipyridines with a hexahydride bipyridine osmium complex (see Section 4.1.7, Osmium). Comparable considerations are likely true for the corresponding reaction of a pentahydride iridium complex [29]
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