ORGANOMETALLIC CHEMISTRYOF FIVE-MEMBERED HETEROCYCLES
ALEXANDER SADIMENKO
ProfessorofChemistry,UniversityofFortHare,Alice,RepublicofSouthAfrica
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Abbreviationsvii Introductionix
1.Furansandbenzannulatedforms1
1.1Coordinationmodes 1 1.2Reactivityofcoordinatedfuran17
1.3Derivativesoffuran 25 1.4Conclusion 41 References 41
2.Thiophenes,benzannulatedforms,andanalogs47
2.1Coordinationmodes 48
2.2Reactivityofthe η5-coordinatedthiophenes110
2.3Reactivityofthe η6-coordinatedcomplexes121
2.4Reactivityofthe η4-coordinatedcomplexes126
2.5Reactivityofthe η2-coordinatedthiophenes134
2.6Derivatives 136 2.7Conclusion 212 References 213
3.Pyrrolesandbenzannulatedforms239
3.1Coordinationmodes 239
3.2Reactivityofthecoordinatedpyrroles291
3.3Derivatives 318 3.4Conclusion 529
4.Phospholes,benzannulatedforms,andanalogs565
4.1Coordinationmodes 566
4.2Reactivityofthecoordinatedphospholesandanalogs620
4.3Mixedheterocyclescontainingphospholeorphospholylmoiety674 4.4Conclusion 679 References 679
Contents
References
Furtherreading
531
564
v
5.Silolesandanalogs691
5.1Conclusion
707 References 708
6.1Conclusion 740 References 740 Generalconclusion745 Index 761 vi CONTENTS
6.Borolesandanalogs711
Introduction
Forthepast20years,wepreparedachapterseriesinorganometallicchemistryofheterocyclespublishedin AdvancesofHeterocyclicChemistry.Thisworkledtoanideaofpreparingasetofmonographs.Thesubjectisofcourseenormous,andthemainpurposefor uswasanappreciationofthevastnumberofpublishedworksontheelectronicstructure, geometry,coordinationmodes,reactivity,widevarietyoffunctionalderivatives,and importanceinmedicine,catalysis,materialschemistry,photochemistry,andnumerous otherfields.Thebooksetisthusabroadreferencework.Chemistsatalllevelsmightfind itusefultoassistthemwhenfirstenteringthefield,orwhenassessingthestateofart; researchersintherelatedfieldslikemedicinal,materials,orcatalyticchemistrywouldalso getusefulinformation.Theimportanceandextentofthesubjectmattercontinuestogrow sothatitisoneofthelargestsubdivisionsoforganometallicchemistry,whichhascontributedessentiallytotheprogressofdiversefieldsofscienceandtechnology.Thereforethe bulkofmaterialcannotbesqueezedintoonebookofreasonablesizeandmaybesubdividedintothefollowingparts:
Organometallicchemistryoffive-memberedmonoheterocycles
Organometallicchemistryofazoles
Organometallicchemistryofsix-memberedmonoheterocycles
Organometallicchemistryofazines
Appliedorganometallicchemistryofheterocycles
Inthecurrentvolumeorganometallicchemistryoffive-memberedmonoheterocyclesis inthefocus.
Five-memberedringswithnitrogen,phosphorus,arsenic,orantimony;andoxygen,sulfur,selenium,ortelluriumhavefour π-electronsfromthetwodoublebondsandtwononbonded π-electronsontheheteroatom,sothatthefive-memberedaromaticheterocycles pyrrole,phosphole,furan,andthiophenearearomatic.TheyarerelatedtothecyclopentadienylanionbyreplacementofoneCH groupwithNH,PR,O,orSheteroatoms,each contributingtwoelectronstothearomaticsextet.Heteroatomsofthistypehaveonlysinglebondsandarecalledpyrrole-like.Sixelectronsareassociatedwiththefiveringatoms. The π-excessofthesefive-memberedringsisaccompaniedbyhigh π-donorcharacterand adiversityofthe η5-coordinatedorganometalliccompounds.Forfive-memberedrings withoneheteroatom,benzannulationgenerallystabilizesanaromaticsystem,forexample, carbazole . indole . isoindole . pyrrole.Theborolesystemisisoelectronictothecyclopentadienylcationandfour π-electronsleadtoantiaromaticity,whichtransformstoaromaticityinorganometallicenvironment.Siloleisanalogoustocyclopentadienebutreveals thepropertiesnotonlyofadienebutalsoofaheteroaromaticligand.
Heteroaromaticligandsaresubdividedinto π-excessive,five-memberedringsexemplifiedbypyrrole,furan,andthiophene,and π-deficientsix-memberedrings,forexample,
ix
pyridine.The π-excessiveheterocyclesareextremelyreactivetowardelectrophilicattack and,withtheexceptionofthiophene,donotexhibitthechemicalinertnessassociatedwith aromaticbenzenederivatives.Conversely,the π-deficientheterocyclesareinertwith respecttoelectrophilicattack.
Thereactivityofthefive-memberedheterocyclespyrrole,furan,thiophene,andimidazoleischaracterizedbyinteractionswithelectrophilicreagents.Theprecisenatureofthese reactionsdependsontheparticularringsystem.Thiophenesundergofacileelectrophilic substitution,whereastheothercompoundsexhibitarangeofpolymerizationandother Lewisacid-initiatedreactionsupontreatmentwithelectrophiles.Organometalliccompoundsoffive-memberedheterocyclicligandshavetheirownfeaturesofreactivity, enhancingtheirsyntheticpotential.
Typicalderivativesoffive-memberedheterocyclesincludethosewithO (S ,Se ) functionalgroups,amines,aminomethyls,variousSchiffbases,andphosphines.Forpyrrolesthereisatendencytoformdipyrro-,tripyrro-,andmacrocycliccompoundsofvarioustypes.Porphyrinsandphthalocyaninesareasubjectofseparatediscussion,although organometalliccompoundsofsuchmacrocyclicligandsareexceptionallyscarce.Dipyrrins areregardedashalf-porphyrins.N-Confusedporphyrinshaveatleastoneinvertedpyrrolesubunit.Carbaporphyrinoidscontaincarbocyclicringsinsteadofthepyrrolerings andincludeoxybenzi-,carba-,tropi-,andazuliporphyrins.Porphyrinoids(includingcarbaporphyrinoids)aremacrocyclessuitableforstudyingorganometallicchemistryinaconfinedenvironment.TheCHorCCbondsareveryclosetothemetalionandleadtoa uniquecoordinationgeometryandreactivity.Thustheinternalcarboncanbemodifiedby alkylation,halogenation,nitration,acetoxylation,C-cyanideaddition,oxygenorsulfur insertion,formationofketal,pyridination,amination,orphosphinylation.Triphyrinscontainthreepyrroleringslinkedthrough meso-sp 2 carbonatoms.Carbaporphyrinshaveone ormorecarbonatomsinplaceofnitrogenringatomsincludingtheporphyrinandphthalocyanineisomers:N-confusedporphyrinandbenziphthalocyaninewhereoneoftheisoindolineringsisreplacedwithabenzenering.Organometalliccompoundsareremarkable especiallyduetothestabilizationofunusualmetaloxidationstates.
Referencesaredesignatedbyanumber-lettercodingofwhichthefirstnumbersrecord theyearofpublication,thenextonetofourlettersdenotethejournal,andthefinalnumbersgivethepage.Alistofjournalcodesisgiveninalphabeticalorder.Forjournalsthat arepublishedinseparateparts,thepartletterornumberisgiven(whennecessary)in parenthesesimmediatelyafterthejournalcodeletters.Journalvolumenumbersarenot includedinthecodenumbersunlessmorethanonevolumewaspublishedintheyearin question,inwhichcasethevolumenumberisincludedinparenthesesimmediatelyafter thejournalcodeletters.
TheauthorwillalwaysrememberProfessorAlanRoyKatritzkywhoeditedmy numerouschaptersin AdvancesofHeterocyclicChemistry andinspiredmetostartworking onthemonographseries,ProfessorAlexanderDmitrievichGarnovskiiinappreciationof ourlong-standingcollaborationresultinginmutuallycomplementarypapers,books,and chaptersinthebooks,ProfessorPavelAleksandrovichSadimenkoforhislessonsindedicatedandhardworkstyle.ProfessorVladimirIsaakovichMinkinismymainchemistry teacherandhestimulatedmeforwritingandmanyideashavearisenfromcommunicationwithhim.
x Introduction
TheauthorgratefullyacknowledgesthecooperationwithandthesupportoftheeditorialstaffofElsevier.ParticularlyIthankEmilieMcCloskey,TashaFrank,AlexRomano, EmeraldLi,andDivyaKrishnakumarforguidanceinpreparationandproductionof themanuscript.
Nobookisfreeoferrorsandthisonewillbenoexception.Thereforetheauthorwould begratefultoreaderswhopointthemoutandsuggestanyimprovement.
xi Introduction
Furansandbenzannulatedforms
Thescopeissynthesis,coordinationmodes,andreactivityofthecoordinatedfuran, someofitsderivatives,andbenzannulatedforms.Thiols,amines,Schiffbases,phosphine derivatives,andmixedheterocyclesoffuransareconsideredinseparatesections.
Furanisaplanarheteroaromaticligand,morereactivethanbenzeneduetothe electron-donatingeffectsofheteroatom.Itisoflowaromaticityandchemicallyresembles 1,3-dienes.Itundergoeselectrophilicsubstitutionpredominantlyatthe α-position,polymerizesinthepresenceofelectrophiles,andundergoesDiels Alderreactions.Onlyseldomis2,5-functionalizationpossible.Thescopeofchemicaltransformationsisapparently narrowdespitethehighdemandforvariouslyderivatizedfuransinsyntheticorganic chemistry(naturalproducts,pharmaceuticals,flavororfragrancecompounds).Furanis formallyclassifiedasa π-excessiveligand,althoughitisnotproneto π-complexformation withfewexceptions (01AHC1).
Althoughbenzofuranisconsideredtobearomatic,itselectronicdistributionissuch thatthe π-donorabilityislowerthaninfuran,that is,itislessaromaticthanfuran.The influenceoftheheteroatomislimitedbythefive-memberedcycle.Theoxygenatomisa stronger σ-acceptorandaweaker π-donorthaninfuran.Thefuranringofbenzofuranis less π-excessivethantheparentheterocycle,andthebenzeneandfuranringsarefairly independent.Dibenzofuranisverystable;itsfirstionizationpotentialis π innature.The HOMO LUMOtransitionreflectsthedieniccharacterofthefive-memberedring.This leadstoageneralviewoftheelectronicdistributioninbenzannulatedfive-membered heterocycles.The π-electrondelocalizationiscompleteonlyforthecarbocyclicconstituentofthemolecule.Thusonemayexpectthatcoordinationofmetalcarbonylsshould occurviathe π-conjugatedcarbocyclicsystemandtheheteronucleusshouldtakepartin π-complexformationonlywithdifficulty.
1.1Coordinationmodes
1.1.1 η1(C)-mode
Cocondensationoffuranwithlithiumatomsinthevaporphaseleadstothesequential C Hactivationatthe α-carbonatoms(Eq.1.1) (04EJI4525).Withcalciumatoms,similar Ca Hderivativesareproduced (06JOM1110) 1
CHAPTER
1
OrganometallicChemistryofFive-MemberedHeterocycles DOI: https://doi.org/10.1016/B978-0-08-102860-5.00001-8 © 2020ElsevierLtd.Allrightsreserved.
Dibromodifuranwithtrimethylsilylgroupsatthe2-and6-positionsoftheadjacent five-memberedringswithp-block(silicon,germanium,orphosphorus)dichloridesgive stabledifurans,bridgedbydiphenylsilyl,diphenylgermyl,or,andphenylphosphinoxide groups η1(C)-coordinatedwithrespecttothefuranrings( Eq.1.2) (17OM2565).
3,30 -Diiodobi(benzofuran)with n-butyllithiumfollowedbydialkylchlorosilaneor-germaneaffordedthe η1(C)-coordinatedpolycycle(Eq.1.3) (16OM2327)
2-Lithiofuranwithtintetrachlorideaswellastetrakis(2-benzofuryl)tinwithpotassium givehomolepticsix-coordinatewithrespecttotinandtwo-coordinatewithrespecttoan alkalimetaltrinuclear2-furyl-and2-benzofuryltin(IV)wheretinis η1(C)-coordinatedand lithiumorpotassium η1(O)-coordinated(Eq.1.4) (17D8279).2-Lithiofuran(Eq.1.5)and2benzofuran(Eq.1.6)withtetrakis(2-furyl)tinortetrakis(2-benzofuryl)tingivehomoleptic pentacoordinatetinanions,inwhichcationsarealkalimetalscoordinatedbysolvents (Eq.1.7).
O Li( g ) O Li Li( g ) O Li Li ð1:1Þ
O O Me3 Si Br Br SiMe3 Bu n Li PhPCl2 H 2 O2 OO P Me3 SiSiMe3 (O)Ph Ph 2 GeCl 2 Ph 2 SiCl 2 OO Ge Me3 SiSiMe3 Ph 2 OO Si Me3 SiSiMe3 Ph 2 ð1 2Þ
O O I I Bu n Li,R2 MCl 2 OO M R2
12 n ð1:3Þ
M=Si,Ge;R=Ph M=Ge,R=2-EtC 6H
O Li SnCl 4 Et 2 O Sn O O (Et 2O)Li O O O O Li(OEt) 2 ð1 4Þ 2 1.Furansandbenzannulatedforms
H 3O) 4
H5O) 4 THF
Li(THF) 4
2
Furaniscoordinatedtothe ansa-molybdoceneinan η1(C)-mannerformingC2-andC3coordinatedisomers(Eq.1.8),whilebenzofuranissolely η1(C3)-coordinated(Eq.1.9) (06POL499). η1(C2)-coordinationisrealizedin[(η5-Cp)Mo(CO)2(PPh3)(2-C4H3O)],whichis theresultofcouplingbetweencoordinatedCOofNa[(η5-Cp)Mo(CO)3]andepibromohydrin (BrCH2CHOCH2)inthepresenceofanexcessPPh3 (87OM1821).
Sn O O O O O Li Sn(2-C4
O
ð1 5Þ Sn O O O O O Li Sn(2-C8
O
ð1 6Þ
Sn O O (THF)
K O O O O K(THF)n ð1 7Þ
TMEDA
Li(TMEDA)
Sn(2-C8 H 5O) 4 +K+THF
n
O [( η 5 : η 5-Me 4C5 Si(Me 2)C 5Me4 )Mo(H) 2 ],h ν ( η 5 : η 5-Me 4C5 Si(Me 2)C 5Me4 )Mo H O +( η 5 : η 5 -Me4 C5 Si(Me2 )C5 Me 4 )Mo H O ð1:8Þ O ( η 5 : η 5-Me 4C5 Si(Me 2)C 5Me4 )Mo [( η 5 : η 5-Me 4C5 Si(Me 2)C 5Me4 )Mo(H) 2 ],h ν H O ð1:9Þ 3 1.1Coordinationmodes
MercuriatedfuranwithFe2(CO)6-basedcompoundgivestheproduct,inwhichfuran performsthe η 1 :η 2 bridgingfunctionbetweentwoironsites(Eq.1.10) (92OM3262).
HgCl (Et 3NH)[Fe 2(CO) 6( μ -CO)( μ -RS)] R=Ph,Bu t
FacileC Hactivationoffuranand2-methylfurantakenastriphenylphosphineadducts occurswiththeFe(II)organometallicprecursor(Eq.1.11) (13OM1797).
R [( η5-Cp * )Fe(CO)(AN)Ph] O R Fe(CO)(PPh 3) PPh 3 R=H,Me
Deprotonationoftherutheniumcarbeneleadstothecyclizationandgenerationofthe 2-furyl(Eq.1.12) (10OM38).Intheprocessofruthenium-catalyzedcyclizationof1,3butyne-2-diolsleadingtosubstitutedfurans,the η1(C2)-coordinatedfuranispostulated (08OM3614).Thewholeseriesofsuchreactionshasbeenreviewed (13CRV3084).
Cp(Ph 3 P) 2Ru
3 P) 2Ru O OR1
R=Ph,Me,R1 =Et
R=R1 =Me
Deprotonationoftheruthenium α,β-unsaturatedpropargyloxycarbenegivesthe η1(C)coordinatedbenzannulatedfuran(Eq.1.13) (00OM4).
Cp(CO)Ru(PPr i 3 )
2C CH CPh 2 =CH
Al 2 O3 Cp(CO)(Pr i 3P)Ru Ph O
Furans(Eq.1.14)andbenzo[b]furan(Eq.1.15)enterintotheC Hbondcleavageaccompaniedbythecoordinationmodechangeofcyclooctadieneintheruthenium(0)precursor (03ICA160).
O Fe
Fe (CO)
SR ð1 10Þ
O
(CO) 3
3
ð1:11Þ
O
C
R
OR1
O R R Bu n 4NOH Cp(Ph
R
ð
Þ
1 12
OCH
BF4
ð
Þ
1 13
4
1.Furansandbenzannulatedforms
[( η8-COT)Ru( η 4 -cod)],PEt 3 or [( η 4 -1,4-COT)Ru(PEt 3 ) 3 ]
RRu(PEt 3 ) 2 R=H,COMe
3 ) 2 [( η8-COT)Ru( η 4 -cod)],PEt 3 or [( η 4 -1,4-COT)Ru(PEt 3 ) 3 ]
Theprocessbelow(Eq.1.16)representstheC Hactivationofthefuranmolecule (04OM5514).
Furanoxidativelyaddstothetriosmiumcluster;itismetalatedatposition2ofthe heteroringandleadstothehydridoclusterpresentedasamixtureofthe exo-and endoisomers(Eq.1.17)wheretheligandplaystheroleofan η 1 :η 2 bridge (85JOM(297)141, 89OM1408,90CC1568,91JOM(412)177).Theproductofmoredeepinteraction, thetriosmiumfuryne(85JOM(297)141)reactsfurtherandgivesthebis-triosmiumcontainingabridgingfuryenylligandformedbytherouteofC HactivationattheuncoordinatedC Cdoublebond( Eq.1.18) (18CC3464).ThermolysisleadstofurtherC H activationtoyieldthefurdiyneC4O,whichsubsequentlyring-opensanddecarbonylates toyieldproductscontainingbridgingC 3 andCHCCHCC 5 Oligands.
O
R
O
ð
14
O
O
ð1:15Þ
1
Þ
R=H,COMe
Ru(PEt
O HB NN N N N N Ru(AN)(CO)Me + HB NN N N N N Ru O (CO)(AN) ð1:16Þ
O [Os3 (CO) 10(AN)
] (OC)
Os Os(CO) 3 Os (CO) 3 H O (OC) 4 Os Os(CO) 3 Os (CO) 3 H O ð1:17Þ 5 1.1Coordinationmodes
2
4
2-Formylfuranoxidativelyaddstothetriosmiumcluster(Eq.1.19) (86JOM(311)371). Decarbonylationleadsthe μ3-furan-2,3-diylbridge.
Substitutedfuranis η1(C)-coordinatedasfarastheheteroringisconcernedandissubjectedtothecarbene-typeactivationinaldolcondensation(Eq.1.20) (02D827).
O Os (OC) 3 Os Os(CO) 3 H H (CO) 3 [Os3 (CO) 10(AN) 2 ] O Os (OC) 3 Os Os(CO) 3 H H (CO) 3 H Os (OC) 3 Os Os(CO) 3 H (CO) 4 Os (OC) 3 Os Os(CO) 3 O Os (OC) 3 Os Os(CO) 3 H H (CO) 3 H H (CO) 3 + (OC) 3 Os Os(CO) 3 (CO) 3 Os H H C C C Os (OC) 3 Os Os(CO) 3 H H (CO) 3 + (OC) 3 Os Os(CO) 3 Os (CO) 4 H C (OC) 3 Os Os(CO) 3 Os (CO) 3 C C H H H + Os (OC) 3 Os Os(CO) 3 H (CO) 3 H-C C C H (OC) 3 Os Os(CO) 3 Os (CO) 4 H C O +
ð1 18Þ
O CHO [Os3 (CO) 10(AN) 2 ] (OC) 4 Os Os(CO) 3 Os (CO) 3 O O H Δ (OC) 3 Os Os(CO) 3 Os (CO) 3 H H O ð
1:19Þ
O (OC) 3 Os Os(CO) 3 H Os (CO) 4 Y X CHO O (OC) 4 Os Os(CO) 3 (CO) 3 Y X Os H X=Y=H;X=H,Y=NO 2 X=NO 2 ,Y=H;X=H,Y=OH X=OH,Y=H ð
Þ 6 1.Furansandbenzannulatedforms
1 20
Furanoxidativelyaddstotheiridium(I)compoundwithelimination,whichisaccompaniedbytheC Hactivationoftheheterocycle(Eq.1.21) (93OM3800,12JOM163).Sametypeof reactionisobservedforfuranand2-methylfuranwith[(η5-Cp*)Rh(PMe3)(Ph)H] (95OM855).
[(η4-cod)Ir(PMe3)3]Cl
TheC Hactivationoffuraninorganoiridiumchemistryisshownin Eq.(1.22) (08JOM3375).
Furanoxidativelyaddson[Pt(PEt3)4]atthe α-positionoftheheteroring(Eq.1.23) (04JOM1315)
3 ) 4 ]
Tin palladiumtransmetalationisanotherroutetotheC-coordinatedfuran(Eq.1.24) (98JA11016).C3-palladationisthefeatureofPd-catalyzedtandemintramolecularoxypalladation/Heck-typecoupling (09OL1083).2-Furfurylchloridewith[Pd(PPh3)4]gives[Pd(η 1CH2-2-C4H3O)] (81JOM(209)123).
α-BromoacetylferrocenewithlithiumdiisopropylamideinTHFgives3-bromo-2,4-bis (ferrocenyl)furanforming η1(C)palladium(II)byoxidativeadditionofthepalladium(0) precursor(Eq.1.25) (01JOM(637)258).
O
O Ir(H)(Cl)(PMe3)3 ð1:21Þ
O [( η
)(H)Ir( μ -dmpm)( μ-H)Ir(Ph)( η5-Cp * )]OTf Ir Me2 P PMe 2 IrCp* H Cp * (H) O OTf ð1:22Þ
5-Cp *
O [Pt(PEt
O Pt(PEt 3 ) 2 H ð1:23Þ
O SnBu 3 n Pd(C6
O Pd Ph 2 P Ph 2 P ð1:24Þ
H 3 (CH 2 PPh 2 ) 2 )(OTf)
O Fe Fe Br [Pd(PPh
4 ] O Fe Fe Br(Ph 3P) 2 Pd ð1:25Þ 7 1.1Coordinationmodes
3 )
The2-and3-furylmercuryderivativesaredescribed (79D2037).Theoreticalaspectsof cycloaurationintheprocessofgold-catalyzedderivatizationoffuranswerepresented (09OM741,10JA7645).
Metalationoffuranbyytterbocenes,O-coordinationinheteronuclearcomplex,aswell as η2(C,O)-coordinationareillustratedin Eqs.(1.26) (1.28)(02OM1759).
C Hbondactivationoffuranisachievedbyalabileyttriumhalf-sandwich(Eq.1.29) (01EJI73).2-Methylfuranissimilarlymetalated (02JOM(647)158). [( η 5 : η 1-C5Me4 SiMe2 NCMe3 )Y(CH 2 SiMe3 )(THF)]+
5 Me4 SiMe 2 NBu
1.1.2 η2(C2)-mode
Photolysisof[(η5-Cp)Mn(CO)3]inthepresenceoffurangivesthe η2-coordinated[(η 5Cp)Mn(CO)2L] (07IC7787).Anumberofthe η2-coordinatedderivativesoffuranwhose syntheticschemesareshownin Eqs.(1.30)(89JA5969),(1.31) (01OM3661),(1.32) (99JA6499,00OM728),(1.33) (06OM435),and(1.34) (03JA2024) servethepurposeofthe studyofcoordinatedfuranreactivitypattern.
O Li [( η5-Cp * ) 2YCl 2Li(OEt 2) 2 O Cp * 2Y Li(THF) 2 Cl THF ð1 26Þ O Li [( η5-Cp * ) 2 YCl 2 Li(OEt 2 ) 2 ] O Cp * 2Y TMEDA O Li(TMEDA) ð1:27Þ [( η5-Cp * ) 2 YH] 2 Cp * 2Y Cp * 2Y O O –H2 O THF THF ð1:28Þ
O
t )Y O Y(NBu t SiMe2 C5 Me 4) O THF (C 5 Me4 SiMe 2 NCMe 3)Y O THF ð1:29Þ
(C
8 1.Furansandbenzannulatedforms
R1 R2
[Os(NH 3 ) 5 ](OTf) 3
L=Bu t NC,Py, 1-MeIm
3 ) 5 (OTf) 2
[TpW(NO)(PMe3 )Br],Na N N NN N N HB W O R2 R1 PMe 3 NO R1 =R2 =H,Me; R1 =Me,R2 =H
[TpMo(NO)(1-MeIm)Br]
R=H,Me
Furanis η 2 :η2-coordinated(Eq.1.35)inironcarbenes (01OM2387).
2
OEt Ar=Ph, p -Tol, o-MeOC6 H 4 , p -MeOC6 H 4, p -CF3 C6 H 4
3 ArLi/Et 2O,Et 3OBF4
O
O Os(NH
ð
30
N N NN
N HB
CO L O O + N N NN
N HB Re CO
L
ð1 31Þ N N NN N N HB Re CO PMe 3 O O + N N NN N N HB Re CO PMe 3 ð1 32Þ O
1:
Þ
N
Re
N
AgOTf,Na/Hg
ð
O
1:33Þ
R R
Me ð1
34
O NPh Fe
O NPh Fe (CO)
ð
35
9 1.1Coordinationmodes
N N NN N N HB Mo O R R NO
N N
:
Þ
(CO)
Ar
1:
Þ
Maleicanhydrideformsthe η2-pentacoordinatedadductwithrhodium(I)precursor (Eq.1.36) (05OM5634).
Thepresenceofthe η6-coordinatingtricarbonylmanganeseatthebenzofuranring makespossibletheformationoftwotypesofadductswithorganoplatinumprecursor (99AGE2206).Oneofthemis η2-coordinatedviathedoublebondofthefuranheteroring, whereasanotherisformedviatwocarbonylgroupsherebybecomingbridginggroups. StandingallowsthepreparationoftheproductofinsertionintotherelativelystrongC O bondofthefive-memberedheteroring(Eq.1.37).
Dipalladium(I)terphenyldiphosphinebridgesfuranand2-methylfuraninan μ-η 2 :η 2 manner(Eq.1.38) (13JA15830).
1.1.3 η5-Coordination
Furanformsthe η5-ruthenium(II)(Eq.1.39) (88CC711). [( η5-Cp * )RuCl] n ,KPF6 or [( η5-Cp * )Ru(Me 2CO)(H2O) 2 ]PF6
O O O [Rh(CNC6
O O O Rh(CNC6
3Me2
ð1:36Þ
H 3Me2 -2,6) 2 (PPh 3)(CF3 )]
H
-2,6) 2 (PPh 3)(CF3 )
O (OC) 3 Mn BF4 [( η2-C2H4 )Pt(PPh 3) 2] O (OC) 3 Mn BF4 Pt(PF3 ) 2 Pt(PPh3)
O BF4 O Mn BF4 CO C O C O (Ph 3 P) 2 Pt [( η2-C2H4)Pt(PPh3)2] ð1:37Þ
2
Pd O R + Pr i 2P Pd PPr i 2 Pd Pr i 2P Pd PPr i 2 R=H,Me O (BF4 ) 2 R (BF4 ) 2 ð1 38Þ
Ru Cp * PF6 O O ð1 39Þ 10 1.Furansandbenzannulatedforms
1.1.4 η6-Coordinationofbenzannulatedfurans
Chromiumtricarbonylcomplexeswithbenzofuran(Eq.1.40),dibenzofuran(Eq.1.41), andbenzo[b]naphtho[2,3-d]furan(Eq.1.42)containthe η6-coordinatedCr(CO)3 fragment viathebenzenering (68JOM(14)359,75ADOC47).
The η6-coordinatedbenzofuranfollowsfromtheAlCl3-catalyzedexchangebetweenheteroaromaticbenzannulatedligandsandferrocene(Eq.1.43) (80JOM(186)265).Similarreactionsweredescribedforotherheterocycles (76ZN(B)525).
[( η5-Cp) 2 Fe],Al,AlCl 3 ,NH 4 PF6
[( η5-Cp) 2Fe],Al,AlCl 3 ,NH 4 PF6
1.1.5O-coordination
Cp PF6
Weakandshort-livingO-coordinatedproductsareformedin Eq.(1.44)(99D115,00JPC (A)10587,01OM3314).
L 5 2-methylfuran,2,5-dimethylfuran
O [Cr(CO) 6] O (OC) 3 Cr ð1:40Þ O [Cr(CO) 6] O (OC) 3 Cr ð1:41Þ O [Cr(CO)
(AN) 3 ] O (OC) 3 Cr ð1:42Þ
3
O
O Fe
O Fe Cp Fe Cp (PF6
ð1 43Þ
) 2
½WðCOÞ5 ðCyHÞ 1 L-½WðCOÞ5 L (1.44)
11
1.1Coordinationmodes
Organozinccompoundof2-phenylfuranisthesourceoftheheteroleptictriscyclometalatediridium(III)containing1-(2,4-difluorophenyl)pyrazoleor2-phenylpyridine (Eq.1.45) (09OM6079).
[(2,4-F2C6H2-1-Pz)2Ir(μ-Cl)]2
[(2-PhC5H4N)2Ir(μ-Cl)]2
1.1.6 η4(C4)-mode
Photochemicaldecarbonylationofthe2,5-dimethylfurantungstenpentacarbonylleads tothe η4-coordinatedcomplex(Eq.1.46) (03AGE2179).
1.1.7Peripheralcoordination
In2-furyl-substitutedbis(indenyl)zirconium, η5-coordinationisviathefive-membered carbocyclicringoftheindenylmoiety (00OM4095).Thesamesituationisobservedfor2(2-furyl)indene(Eq.1.47) (01JOM(622)143,01OM5067) and1-(5-methyl-2-furyl)indene (Eq.1.48) (01JOM(621)197).
O Br Bu n Li ZnCl 2 O ZnCl
or
F F N N F F N N Ir O or N Ir N O ð1:45Þ
O W(CO) 5 h ν O W(CO) 4 ð1:46Þ
O Li O ZrCl 4 O ZrCl 2 MeLi O O ZrMe 2 ð1:47Þ 12
1.Furansandbenzannulatedforms
2-LithiofuranformsstableFischercarbenes(Eq.1.49) (92JA2985).
Lithiatedfuranprecursorsandchromiumandtungstenhexacarbonylsyieldcarbenes withabridgingfuransubstituentandbinuclearbis-carbenes(Eq.1.50) (05D1649). Benzannulationofthemonocarbenesisachievedusing3-hexyne.
6 ] M=Cr,W O Li Li
M(CO) 5
(CO) 3 M = Cr, W O
O Li ZrCl 4 O ZrCl 2 O ð1 48Þ
O
E
ð1:49Þ
Li [M(CO) 6 ]
M=Cr,W X=H,Li M(CO) 5 XO
O Li
EtO
O LiO
OLi M'(CO)
O
[M(CO) 6 ] O LiO M(CO) 5 M=Cr,W LiNPr i 2 O LiO M(CO) 5 Li [M(CO)
Et 3 OBF4 O
M(CO) 5 [M'(CO) 6 ] M=M'=Cr,W M=Cr,M'=W
M(CO) 5
5 [M(CO) 6 ]M=Cr,W O LiO M(CO) 5 OLi M(CO) 5 Et 3 OBF4
EtO
M(CO) 5 OEt M'(CO) 5 EtCCEt M=Cr,M'=Cr,W O EtO
EtO
Et
ð1:50Þ 13 1.1Coordinationmodes
HO OEt Et Et Cr
M(CO) 5 HO OEt
Et M = Cr, W
Therangeofsuchcarbenesmaybeextendedtoethoxyandaminocompounds (Eq.1.51) (13OM5491,14JOM(752)171,15JCC2388).
Carbeneformationisobservedfordibenzofuran(Eq.1.52),buttheproductentersinto furthertransformations:[3 1 2 1 1]benzannulationwithalkynestogeneratehydroquinoid naphthobenzofurans,andhaptotropicchromiummigrationresultinginnaphthofuran complexes (02JOM(641)185).
R1 R2 ,Bu t Me 2 SiX,Et 3 N
R1 =R2 =Et,Ph,R3 =SiMe 2Bu t ,X=Cl
R1 =R2 =Ph,R3 =H,X=Cl
R1 =Pr n ,R2 =H,R3 =SiMe 2Bu t ,X=OTf R1 =Bu t ,R2 =R3 =H,X=Cl
(17JOM218)
3 Cr
R1 =R2 =Et,R3 =SiMe 2Bu t R1 =R2 =Ph,R3 =H
O
Et
O M(CO)
EtO M=Cr,W CyNH 2 O M(CO) 5 CyNH EDA O M(CO) 5 NH NH 2 NH 3 O M(CO) 5 NH 2 dppe M=Cr Y=OEt,NHCy O M(CO) 3 (dppe) Y ð1
51
Bu n Li [M(CO) 6 ]
3 OBF4
5
:
Þ
O Br
O MeO Cr(CO) 5
2,Bu n Li,Cr(CO) 6 ,Me 3OBF4
O R3 O R! R2 Cr(CO)
OMe Bu
3
n 2O
O R3 O R! R2 OMe
ð
14 1.Furansandbenzannulatedforms
(OC)
1 52Þ Lithiatedbenzofuranwithtricarbonylmanganesearenesgive η5-dienyls(Eq.1.53)
R1 =R3 =H,R2 =Me
R2 =R3 =H,R1 =Me
R3 =H,R1 =R2 =Me
R2 =H,R1 =R3 =Me
Furaninteractswiththetricarbonyl(cyclohexadienyl)ironcationtoyieldtheproductof electrophilicsubstitution,whichis η4-coordinated(Eq.1.54) (74JOM(71)C11).
[( η4-C6 H 7 )Fe(CO) 3 ] +
Thecopper-catalyzedreactionofazibenzilwithtricarbonyl(cycloheptatriene)irongives the η2-coordinatedannulatedfuran(Eq.1.55) (84JOM(260)105)
2,5-Bis-(trimethylsilylethynyl)-functionalizedfurangivesrisetothealkynylhalfsandwich(Eq.1.56) (15OM2826). O Me3 Si SiMe3
[( η5-Cp)M(dppe)Cl],KOBu t M=Fe,Ru O Cp(dppe)M M(dppe)Cp
Thefurancarboxylateligandformsthe η3-furfurylpalladiumoftheallyltype(Eq.1.57) (10OM4431,12OM5599) intheruthenium-catalyzed5-hydroxymethylfurfural,coordinationoftheCH2OHgroupsplaysaroleinthecatalyticcycle (14D10224).
ClOMe O [Pd(PPh3)4],AgBF4
(PPh 3) 2
O + Mn(CO) 3 OMe R3 R1 OMe R2 Bu n Li O Mn(CO) 3 OMe R3 R1 OMe
R2 ð1:53Þ
O
O Fe(CO)
ð1
54Þ
3
:
N N + O[( η3-cycloheptatriene)Fe(CO) 3] O Fe (CO) 3 ð1:55Þ
ð1
56
:
Þ
O
O OMe
Pd
BF4 ð1 57Þ 15 1.1Coordinationmodes
O
1-Dibenzofuranyl-3-methylbenzimidazol-2-ylideneformscyclometalatedplatinum(II) containingdimesitylacetylacetonatewithphosphorescentproperties(Eq.1.58) (15CEJ12881,16ACR2680).
1.1.8Coordinationwithring-opening
AluminumhydridescausethesplittingoftheC ObondandformationofthesixmemberedO Alcontainingring (13OM5260).Furanentersintothering-openingreaction (Eq.1.59)leadingtothe η5-oxapentadienyl (83CC813).
ThefollowingexamplecombinesperipheralandO-coordination,aswellasringopening.Furyl-derivedcyclopentadienylsmaybecoordinatedbyrareearthelements eitherviaexclusivelythe π-systemofthecyclopentadienylorformthechelateswherethe oxygenheteroatomisinvolved(Eq.1.60) (03OM775,07OM3227).However,bothtypesof productsundergothering-openingtoyielddinuclearyne-enolates.
[Ln(CH 2SiMe 3) 3 (THF) x ]
(CH 2 SiMe3 ) 2 THF Ln
(CH 2 SiMe3 ) 2 THF
Ln=Sc,Lu, x =2; Ln=Y, x =3 Ln=Sc,R=H,Me; Ln=Lu,R=Me Ln=Lu,Y,R=H –SiMe 4
2 SiMe3 )(THF) x
O N N Me I Ag 2 O,[( η 4 -cod)PtCl2 ],Mes(acac),Bu t OK Pt O O O Mes Mes N N Me ð1 58Þ
O
O H (Ph3P)2Re(CO) ð1 59Þ
[(Ph3P)2ReH(CO)]
Si
O
Me2
R
O
SiMe2 O R
SiMe2
R or
Ln
CH
SiMe2
Ln SiMe2 R
ð
16
2 SiMe3 Ln
O R O
CH 2 SiMe3 +THF –THF Ln SiMe2 O R (CH
1 60Þ
1.Furansandbenzannulatedforms
1.2Reactivityofcoordinatedfuran
Theoverallimpressionofthepoordonorabilityoffuranwaschangedsomewhatwhen itsorganoosmiumandlaterorganomolybdenum,tungsten,andrheniumcompoundswere studied.Thereactivityofthe η2-coordinatedspeciesappearedtobesodiversethatmany syntheticproblemsofderivatizationweresuccessfullysolved.Wegiveadetailedaccount ofthetransformationsoforganometallicspecieswithoutpayingattentiontothedecomplexationreactionsandpreparationofthecorrespondingsubstitutedfurans.Thisinformationcanbeeasilyfoundelsewhere (97CRV1953).
1.2.1Electrophilicaddition
Forfurans,electrophilicattackisdirectedpredominantlytoposition2.Onlyunderspecialconditionsdoesthethreeorientationbecomepossible.The η2-complexationenhances thenucleophiliccharacterofC3 atom,eventuallyenablingfacile β-electrophilicattacks.In addition,derivatizationoffuranispossiblewithsomecarbenecomplexes (99JA3065). η 2Coordinatedfuranisthesourceofinterestingderivatizationsandtransformationsofthe furanheteroring (00CCR3).ThusprotonationinDMFleadstothecleavageoftheO C2 bondtoafford3-oxopropylcarbyne(Eq.1.61) (94JA5499).Applicationofthecatalytic amountsoftheprotonatingagentinmethanolleadstoacetal.Electrophilicadditionof methylacetonitriliumtriflategoestothe β-positionoftheheteroringandformsiminium derivativeof4-acetylfuran.Benzaldehydedimethylacetalormethylvinylketoneaddsto theposition4inthepresenceoftheLewisacidandtheprocessisaccompaniedbyformationof4H-furanium,andsubsequentnucleophilicattackofMeOonC5 (95OM2861, 96JA5672).Hydrogenationgoestothe4,5-positions.
Incontrast,thecoordinated5-methylfuranwithbenzaldehydedimethylacetalgenerates thering-openedproduct(Eq.1.62).
O Os(NH3
(OTf)
HOTf MeOH OMe OMe MeO Os(NH3 ) 5 (OTf) 2 O Os(NH3 ) 5 (OTf) 3 N H (MeCNMe)OTf Ph(OMe) 2 BF3 OEt 2 . MeCOCH=CH2 BF3 MeOH . H2 /Rh O Os(NH3
5 (OTf) 2 O Os(NH3 ) 5 MeO MeO Ph O Os(NH3
5 (OTf) 2 O MeO (OTf) 2 ð1
) 5
2
)
)
:61Þ
17 1.2Reactivityofcoordinatedfuran
3 ) 5 (OTf) 2
3 ) 5
Withotheraldehydes,thereactiontakesasimilarcourse,althoughinsomespecial cases,cyclizationoftheinitialaldolproductgivesbicyclicdiacetalorketal(Eq.1.63).
3 ) 5 (OTf) 2 R1 =H,R2 =Me,R3 =CCPh,Ph R1 =H,R2 =R3 =Me R1 =R2 =Me,R3 =Ph
3 ) 5 (OTf)
3 ) 5
(OTf) 2
R1 =R2 =H,R3 =Me R1 =H,R2 =R3 =Me
Acetoneorbenzophenoneisnotincorporatedinthistypeofreaction,buttheprotonassisteddimerizationoccurs(Eq.1.64).
3 ) 5
One-electronoxidationagentscatalyzeanintramolecularcondensationoftheacetyl groupandcoordinatedammineandformationofthemetallacycleannulatedtothedihydrofuranring(Eq.1.65).
O Os(NH
PhCH(OMe)
BF3 OEt
Ph OMe Os(NH
OMe O
ð
2
2 .
(OTf) 2
1:62Þ
O R1 R2 Os(NH
2 R3 CHO O R1 R3 Os(NH
O R2 H O O O R1 Os(NH
R3
R3
H R2
ð1
63Þ
:
O Os(NH
H + O Os(NH
O Os(NH
ð
3 ) 5 (OTf) 2
3 ) 5 (OTf) 4
1:64Þ
O R O Os(NH
H (OTf) 2 R = Me, Ph, CCPh DDQ O N Os(NH
4 R H H (OTf)
O N Os(NH
4 R H H (OTf) 2 ð
18
3 ) 5
3 )
3
3 )
1:65Þ
1.Furansandbenzannulatedforms
