nature chem[1].(Zhang-Jie Shi)(2)

施老师的代表作

ARTICLES

NATURECHEMISTRY

DOI:10.1038/NCHEM.862

thedevelopmentofacross-couplingbetweenaryliodides/bromidesandgeneralarenesintheabsenceofsupplementaltransitionmetals.

Results

Initially,wehadidenti edacobalt-catalysedcross-couplingbetween4-iodoanisole(1a–I)andbenzene(2a).Inthepresenceofsuitableligandstopromotethecross-coupling,thedesiredproduct3aawasobservedinmoderateyieldsat808C.Systematic

a

10.90.80.7Conversion

0.60.50.40.30.20.10Time (h)

examinationsoftheconditionsledustoidentifythecombinationofCo(acac)3and1,10-phenanthrolineinthepresenceofKOt-Bu(asabase)asmostef cient:.99%conversionof1a–Ioccurred,andproduct3aacouldbeisolatedin71%yield(entry2,Table1).N,N′-dimethylethylenediamine(DMEDA)demonstratedasimilarreactivityasaligand.Furtherstudiesindicatedthatlessreactive4-bromoanisole(1a–Br)wasalsosuitableforthiscobalt-catalysedtransformation(entry3,Table1).

Initially,wehypothesizedthatthiscatalyticprocessmightproceedthroughasingleelectrontransfer(SET)pathway.Wewere,however,surprisedbythecontrolreactions,inwhichthedesiredcross-couplingproduct3aawasobservedinaconsiderableyieldevenintheabsenceofanyadditionalcobaltspecies(thatis,withjustthe‘ligand’andbaseat808C(entry4,Table1)).Theef -ciencywasdramaticallydecreasedwhen4-bromoanisole(1a–Br)wasusedtoreplace1a–I,despitethefactthatithadreactedinthepresenceofCo(acac)3catalyst(entry5,Table1).Theseresultssuggestedthatthecobaltspeciesplayedavitalroleinthecross-couplingundertheseconditionsbecausetheadditionofthecobaltspeciessigni cantlyimprovedthereactionef ciency.

Wethenbegansearchingfortheoptimumconditionsforthecouplingreaction.Consideringthehigherreactivityofaryliodides,we rstexploredthereactivityof1a–I,andfoundthatthestartingmaterialwascompletelyconsumedwithan83%isolatedyieldoftheproductinthepresenceof20mol%catalystat1008C(entry6,Table1).Weweretakenbysurpriseonceagainwhenreactionof1a–Bratthehighertemperatureof1008Cinthepresenceofonly1,10-phenanthroline(20mol%)andKOt-Buaffordeda99%conver-sionofthestartingmaterialanda48%isolatedyield(entry7,Table1).Notably,theconversionandyieldwereaffectedbytheamountof1,10-phenanthrolineused.Increasingtheamountof1,10-phenanthrolineto40mol%resultedincompleteconversionofthestartingmaterialandanisolatedyieldof87%(entry8,Table1).Othertypesoforganic‘ligand-type’catalystswerealsotested.Wefoundthatthestructurallysimilarcompoundsshowedgoodreactiv-ity(entry10,Table1).However,aloweref ciencywasobservedwithbothhighlysterichinderedL3andtheelectron-de cientL4,whichmighthaveariseneitherfromastericeffectorelectroniceffects(entries11and12,Table1).Moreover,compoundssuchasDMEDAdidnotshowgoodreactivityinthistransformationof1a–Br(entry9,Table1),despitethefactthattheyservedasgood

b

Yield

Time (h)

Figure2|Kineticstudiescomparingthereactionpro lewithvariousaddedtransition-metalcatalysts.a,Comparisonofstartingmaterialconversion

versustimeforreactionsruninthepresenceofadditionaltransitionmetals(Cu,Fe,Co,Ni,Pd,Ru,Rh),differentcoppersources,andwithdifferentloadingsofCu(OAc)2.b,Comparisonofcross-couplingproductyieldversustimeforreactionsruninthepresenceofadditionaltransitionmetals(Cu,Fe,Co,Ni,Pd,Ru,Rh),differentcoppersources,anddifferentloadingsofCu(OAc)2.Exponentialdecayof4-bromoanisole(la–Br)andformationof4-methoxy-1,1′-biphenyl(3aa)wasobserved,indicatingthezero-orderdependenceondifferentmetalcatalysts.Furthermore,reactionyieldswithaddedtransitionmetalswerefoundtobelowerthanthemetal-freereaction.

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