Synthesis of a polyisobutylene-tagged fac-Ir(ppy)3 complex and its application as recyclable visible-light photocatalyst in a continuous flow process

Article abstract of DOI:10.1039/c5gc01792k

The facile synthesis and application of a polyisobutylene-polymer-tagged, iridium(iii) photocatalyst is described. The catalytic performance of this complex remains consistently high, while the installed tether allows for its convenient separation from reaction products through a thermomorphic solvent system. Excellent recycling properties were observed both in batch and in flow reactions, and especially in the latter the continuous, automatic recovery and reuse of the catalyst either from a mono- or a biphasic reaction solution is realised, making this approach attractive for large-scale applications.

Full text of DOI:10.1039/c5gc01792k

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Page 1 of 6
Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀ ha ed mj u si st ꢀt mr yarginsꢀ
View Article Online
DOI: 10.1039/C5GC01792K
GreenꢀChemistryꢀManuscript No. GC-ART-08-2015-001792; 3.8.2015ꢀ
ꢀ
ARTICLEꢀ
SynthesisꢀofꢀaꢀPolyisobutylene-Taggedꢀfac-Ir(ppy) ꢀComplexꢀandꢀ
3
itsꢀApplicationꢀasꢀRecyclableꢀVisible-LightꢀPhotocatalystꢀinꢀaꢀ
ContinuousꢀFlowꢀProcessꢀꢀ
Receivedꢀ00thꢀJanuaryꢀ20xx,ꢀ
Acceptedꢀ00thꢀJanuaryꢀ20xxꢀ
*ꢀ
DanielꢀRackl,ꢀPeterꢀKreitmeier,ꢀandꢀOliverꢀReiser
DOI:ꢀ10.1039/x0xx00000xꢀ
Theꢀ facileꢀ synthesisꢀ andꢀ applicationꢀ ofꢀ aꢀ polyisobutylene-polymer-tagged,ꢀ iridium(III)ꢀ photocatalystꢀ isꢀ described.ꢀ Theꢀ
catalyticꢀ performanceꢀ ofꢀ thisꢀ complexꢀ remainsꢀ consistentlyꢀ high,ꢀ whileꢀ theꢀ installedꢀ tetherꢀ allowsꢀ forꢀ itsꢀ convenientꢀ
separationꢀfromꢀreactionꢀproductsꢀthroughꢀaꢀthermomorphicꢀsolventꢀsystem.ꢀExcellentꢀrecyclingꢀpropertiesꢀwereꢀobservedꢀ
bothꢀ inꢀ batchꢀ andꢀ inꢀ flowꢀ reactions,ꢀ andꢀ especiallyꢀ inꢀ theꢀ latterꢀ theꢀ continuous,ꢀ automaticꢀ recoveryꢀ andꢀ reuseꢀ ofꢀ theꢀ
catalystꢀeitherꢀfromꢀaꢀmono-ꢀorꢀaꢀbiphasicꢀreactionꢀsolutionꢀisꢀrealizedꢀforꢀtheꢀfirstꢀtime,ꢀmakingꢀthisꢀapproachꢀattractiveꢀ
forꢀlarge-scaleꢀapplications.ꢀ
www.rsc.org/ꢀ
Relevantꢀtoꢀourꢀwork,ꢀBergbreiterꢀetꢀal.ꢀachievedꢀtheꢀsynthesisꢀ
2
+
Introductionꢀ
3
ofꢀ 1ꢀ representingꢀ aꢀ recyclableꢀ versionꢀ ofꢀ [Ru(bpy) ] ꢀ (bpyꢀ =ꢀ
2
,2’-bipyridine)ꢀ byꢀ installingꢀ multipleꢀ polyisobutyleneꢀ (PIB)ꢀ
Visibleꢀ lightꢀ photoredoxꢀ catalysisꢀ rejuvenatedꢀ asꢀ aꢀ powerfulꢀ
1
syntheticꢀtoolꢀwithinꢀtheꢀlastꢀdecade. ꢀManyꢀtransformationsꢀ
14
chainsꢀ (Fig.ꢀ 1,ꢀ rightꢀ side), ꢀ whichꢀ couldꢀ beꢀ separatedꢀ andꢀ
resusedꢀ byꢀ selectiveꢀ precipitationꢀ ofꢀ theꢀ polymericꢀ reactionꢀ
productꢀfromꢀtheꢀreactionꢀsolution.ꢀꢀ
thatꢀ previouslyꢀ requiredꢀ harshꢀ reactionꢀ conditions,ꢀ toxicꢀ
reagents,ꢀorꢀwereꢀunprecedentedꢀcouldꢀbeꢀachievedꢀwithꢀthisꢀ
technique.ꢀ Asꢀ catalystsꢀ canꢀ beꢀ employedꢀ inorganicꢀ semi-
Inꢀ aꢀ complementaryꢀ approach,ꢀ aꢀ heterogeneousꢀ polypyridylꢀ
iridiumꢀcomplexꢀ2ꢀwasꢀpreparedꢀbyꢀpolymerizationꢀofꢀaꢀvinyl-ꢀ
ꢀ
2
conductorsꢀ typicallyꢀ offeringꢀ highꢀ stabilities, ꢀ organicꢀ dyesꢀ
3
beingꢀcomparablyꢀlowꢀpriced, ꢀandꢀtransition-metalꢀcomplexesꢀ
4
beingꢀ mostꢀ versatileꢀ forꢀ aꢀ broadꢀ rangeꢀ ofꢀ reactionꢀ classes. ꢀ
5
Whereasꢀalsoꢀcopper, ꢀchromium ꢀandꢀotherꢀnon-nobleꢀmetalꢀ
6
7
complexesꢀ haveꢀ beenꢀ utilizedꢀ asꢀ photoredoxꢀ catalysts, ꢀ theꢀ
mostꢀ commonlyꢀ employedꢀ transitionꢀ metalꢀ complexesꢀ areꢀ
basedꢀ onꢀ priceyꢀ rutheniumꢀ orꢀ iridiumꢀ (Fig.ꢀ 1,ꢀ leftꢀ side).ꢀ
Especially,ꢀtris-phenylpyridineꢀcyclometalatedꢀfac-Ir(ppy)3ꢀ(ppyꢀ
8
=
ofꢀphotochemicalꢀtransformations,ꢀe.g.ꢀinꢀtheꢀdirectꢀarylationꢀ
ꢀphenylpyridine) ꢀshowsꢀsuperiorꢀapplicabilityꢀinꢀaꢀvastꢀvarietyꢀ
9
ofꢀ sp3ꢀ C–Hꢀ bonds, ꢀ trifluoromethylationꢀ ofꢀ alkynes, ꢀ decar-
10
11
boxylativeꢀcouplingꢀreactions, ꢀandꢀmanyꢀmore.ꢀNevertheless,ꢀ
possibleꢀlarge-scaleꢀapplicationsꢀwithꢀthisꢀcatalystꢀareꢀseverelyꢀ
impededꢀbyꢀitsꢀhighꢀcostꢀinꢀcombinationꢀwithꢀcatalystꢀloadingsꢀ
ofꢀ typicallyꢀ aroundꢀ 1ꢀ mol%,ꢀ makingꢀ theꢀ developmentꢀ ofꢀ
efficientꢀrecyclingꢀstrategiesꢀdesirable.ꢀꢀ
Immobilizedꢀ photosensitizersꢀ haveꢀ beenꢀ knownꢀ sinceꢀ almostꢀ
4
12ꢀ
0ꢀ years. Commonꢀ strategiesꢀ towardsꢀ recoverableꢀ ofꢀ
otherwiseꢀhomogeneouslyꢀoperatingꢀcatalysts,ꢀbeingꢀespeciallyꢀ
desirableꢀforꢀphotocatalyticꢀprocessesꢀtoꢀensureꢀefficientꢀlightꢀ
intake,ꢀ callꢀ forꢀ theirꢀ attachmentꢀ eitherꢀ toꢀ anꢀ insolubleꢀ poly-
13
mericꢀresinꢀorꢀtoꢀtagꢀthemꢀwithꢀaꢀphaseꢀselectiveꢀtether. ꢀꢀ
Fig.ꢀ1ꢀ Commonlyꢀusedꢀmetal-basedꢀphotocatalysts,ꢀtheirꢀcurrentꢀprices,ꢀandꢀ
strategiesꢀtoꢀimmobilizeꢀthem. ꢀ
1
5
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ1ꢀꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀ ha ed mj u si st ꢀt mr yarginsꢀ
Page 2 of 6
ARTICLEꢀ
substitutedꢀ iridiumꢀ photocatalystꢀ withꢀ partiallyꢀ cross-linkedꢀ
JournalꢀNameꢀ
View Article Online
DOI: 10.1039/C5GC01792K
16
acrylates, ꢀallowingꢀtheꢀrecoveryꢀofꢀtheꢀcatalystꢀbyꢀfiltrationꢀ
fromꢀtheꢀreactionꢀsolution.ꢀ
WeꢀreportꢀhereꢀtheꢀsynthesisꢀandꢀapplicationꢀofꢀPIBꢀtaggedꢀ3,ꢀ
beingꢀ theꢀ firstꢀ recyclableꢀ versionꢀ ofꢀ tris-cyclometalatedꢀ fac-
Ir(ppy)3,ꢀ Thisꢀ catalystꢀ featuresꢀ highꢀ activityꢀ dueꢀ toꢀ itsꢀ homo-
geneousꢀ natureꢀ inꢀ solution,ꢀ butꢀ moreꢀ importantlyꢀ allowsꢀ
automaticꢀrecoveryꢀandꢀreuseꢀinꢀflowꢀsystemsꢀmakingꢀuseꢀofꢀaꢀ
thermomorphicꢀ orꢀ biphasicꢀ solventꢀ system.ꢀ Theꢀ technologyꢀ
developedꢀ shouldꢀ beꢀ significantꢀ forꢀ aꢀ broadꢀ varietyꢀ ofꢀ
photocatalyticꢀprocessesꢀgoingꢀbeyondꢀtheꢀbenefitsꢀofꢀflowꢀasꢀ
Schemeꢀ1ꢀꢀ
Upperꢀpart:ꢀsynthesisꢀofꢀPIB-Iꢀ(6)ꢀstartingꢀfromꢀBASFꢀGlissopal®ꢀ1000ꢀ(4,ꢀ
17ꢀ
aꢀmeansꢀofꢀscalingꢀupꢀaꢀreaction.
nꢀ~ꢀ17).ꢀLowerꢀpart:ꢀtwoꢀexploredꢀmethodsꢀtoꢀsynthesizeꢀPIB-taggedꢀphotocatalystꢀ3.ꢀ
[
Ir]ꢀ=ꢀ[Ir(ppy)
2 2
(MeOH) ]OTfꢀ(7).ꢀRegentsꢀandꢀconditions:ꢀa)ꢀ4-methyl-2-phenylpyridineꢀ
(
1.05ꢀequiv),ꢀ LDAꢀ (1.10ꢀ equiv),ꢀ THF,ꢀ hexanes,ꢀ -78ꢀ °Cꢀ toꢀ rt,ꢀ on,ꢀ 83%ꢀ 8.ꢀ b)ꢀ [Ir]ꢀ (7)ꢀ (1.0ꢀ
equiv),ꢀphenylpyridineꢀ8ꢀ(1.0ꢀequiv),ꢀdioxane,ꢀreflux,ꢀ7ꢀd.ꢀc)ꢀcomplexꢀ10ꢀ(1.0ꢀequiv),ꢀLDAꢀ
1.3ꢀequiv),ꢀPIB-Iꢀ(6)ꢀ(1.4ꢀequiv),ꢀTHF,ꢀhexanes,ꢀ-78ꢀ°Cꢀtoꢀrt,ꢀon,ꢀ54%ꢀ3.ꢀd)ꢀcomplexꢀ10ꢀ
Resultsꢀandꢀdiscussionꢀ
(
Onꢀ theꢀ outsetꢀ weꢀ aimedꢀ toꢀ developꢀ aꢀ homogenousꢀ catalystꢀ (1.0ꢀequiv),ꢀLDAꢀ(13ꢀequiv),ꢀPIB-Iꢀ(6)ꢀ(14ꢀequiv),ꢀTHF,ꢀhexanes,ꢀ-78ꢀ°Cꢀtoꢀrt,ꢀon,ꢀ84%ꢀ9.ꢀ
systemꢀ toꢀ avoidꢀ anyꢀ massꢀ transportꢀ problemsꢀ commonlyꢀ
encounteredꢀ inꢀ heterogeneousꢀ systems.ꢀ Moreover,ꢀ withꢀ
specialꢀ relevanceꢀ toꢀ photocatalysts,ꢀ heterogeneousꢀ supportsꢀ
areꢀ impenetrableꢀ byꢀ visibleꢀ light,ꢀ thusꢀ greatlyꢀ reducingꢀ theꢀ
quantumꢀyieldꢀforꢀaꢀgivenꢀreaction.ꢀInꢀfact,ꢀtheꢀmostꢀefficientꢀ
approachꢀ forꢀ photocatalyticꢀ processesꢀ isꢀ toꢀ conductꢀ themꢀ inꢀ
transformationsꢀwithꢀfac-Ir(ppy)3ꢀareꢀDMFꢀandꢀacetonitrile.ꢀAsꢀ
itꢀturnedꢀoutꢀIr(ppy)2(PIB-ppy)ꢀ(3)ꢀisꢀsolubleꢀinꢀneither,ꢀevenꢀatꢀ
elevatedꢀtemperatures.ꢀThisꢀsolubilityꢀprofileꢀappearedꢀtoꢀbeꢀ
idealꢀtoꢀcarryꢀoutꢀhomogenousꢀphotochemicalꢀtransformationsꢀ
21
usingꢀaꢀthermomorphicꢀsolventꢀsystemꢀ(TMS). ꢀSuchꢀaꢀsystemꢀ
comprisesꢀofꢀaꢀpolarꢀandꢀaꢀnonpolarꢀsolventꢀthatꢀhaveꢀaꢀhugeꢀ
miscibilityꢀ gapꢀ atꢀ ambientꢀ temperatures.ꢀ Atꢀ elevatedꢀ
temperaturesꢀ theꢀ miscibilityꢀ gapꢀ disappearsꢀ andꢀ theꢀ formerꢀ
biphasicꢀ systemꢀ becomesꢀ homogeneous.ꢀ Afterꢀ cooling,ꢀ theꢀ
formerꢀ twoꢀ phasesꢀ reappear,ꢀ makingꢀ theꢀ processꢀ fullyꢀ
reversible.ꢀAcetonitrileꢀandꢀheptaneꢀformꢀsuchꢀaꢀTMSꢀwithꢀaꢀ
upperꢀ criticalꢀ solutionꢀ temperatureꢀ (UCST),ꢀ theꢀ temperatureꢀ
18
flowꢀ inꢀ homogeneousꢀ phase, ꢀ butꢀ toꢀ theꢀ bestꢀ ofꢀ ourꢀ
knowledge,ꢀ thereꢀ areꢀ noꢀ reportsꢀ thatꢀ demonstrateꢀ theꢀ
automaticꢀ separationꢀ andꢀ refeedꢀ ofꢀ aꢀ homogeneousꢀ
photocatalystꢀ underꢀ suchꢀ conditions.ꢀ Weꢀ thereforeꢀ choseꢀ toꢀ
tagꢀoneꢀorꢀmoreꢀofꢀtheꢀppyꢀligandsꢀwithꢀpolyisobutylene,ꢀwhichꢀ
hasꢀ provedꢀ toꢀ conferꢀ excellentꢀ solubilityꢀ toꢀ catalystsꢀ andꢀ
19
reagentsꢀ inꢀ variousꢀ organicꢀ solventsꢀ inꢀ earlierꢀ studies. ꢀ Ourꢀ
initialꢀ strategyꢀ wasꢀ toꢀ synthesizeꢀ Ir(ppy)(PIB-ppy)2ꢀ (3)ꢀ byꢀ
reactionꢀ ofꢀ [Ir(ppy)2(MeOH)2]OTfꢀ (7)ꢀ withꢀ polyisobutylene-
taggedꢀppyꢀligandꢀ8;ꢀtheꢀlatterꢀwasꢀreadilyꢀobtainedꢀbyꢀreactingꢀ
lithiatedꢀ 4-methyl-2-phenylpyridineꢀ withꢀ polyisobutyleneꢀ
22
whereꢀ fullꢀ miscibilityꢀ isꢀ achieved,ꢀ ofꢀ 84.6ꢀ °C. ꢀ Thus,ꢀ forꢀ theꢀ
photochemicalꢀreactionsꢀinvestigated,ꢀsubstratesꢀandꢀreagentsꢀ
wereꢀ dissolvedꢀ inꢀ acetonitrileꢀ atꢀ roomꢀ temperatureꢀ andꢀ
catalystꢀ 3ꢀ containingꢀ heptaneꢀ wasꢀ addedꢀ (Schemeꢀ 2,ꢀ (1)),ꢀ
formingꢀaꢀbiphasicꢀsolution.ꢀHeatingꢀtheꢀreactionꢀmixtureꢀtoꢀ85ꢀ
20
iodideꢀ (6)ꢀ (Schemeꢀ 1). ꢀ Unfortunatelyꢀ thisꢀ procedureꢀ gaveꢀ
noneꢀofꢀtheꢀdesiredꢀPIB-taggedꢀ3,ꢀinsteadꢀonlyꢀminorꢀamountsꢀ
ofꢀ Ir(ppy)(PIB-ppy)2ꢀ couldꢀ beꢀ isolatedꢀ (seeꢀ Supportingꢀ
Information).ꢀ Sinceꢀ allꢀ attemptsꢀ ofꢀ optimizationꢀ ofꢀ thisꢀ routeꢀ
wereꢀ unsuccessful,ꢀ theꢀ strategyꢀ towardsꢀ Ir(ppy)2(PIB-ppy)ꢀ (3)ꢀ
wasꢀchangedꢀtoꢀfirstꢀformꢀtheꢀcatalystꢀcoreꢀstructureꢀ10ꢀandꢀ
thenꢀ toꢀ attachꢀ theꢀ polyisobutyleneꢀ chainꢀ inꢀ aꢀ secondꢀ step:ꢀ
Gratifyingly,ꢀthisꢀstrategyꢀfurnishedꢀeitherꢀIr(ppy)2(PIB-ppy)ꢀ(3),ꢀ
orꢀ theꢀ twofoldꢀ alkylatedꢀ Ir(ppy)2(PIB2-ppy)ꢀ (9)ꢀ dependingꢀ onꢀ
theꢀstoichiometryꢀofꢀtheꢀreagentsꢀinvolvedꢀinꢀgoodꢀyieldꢀ(54%ꢀ
forꢀ 3,ꢀ 84%ꢀ forꢀ 9).ꢀ Sinceꢀ theꢀ tertiary,ꢀ benzylicꢀ positionꢀ inꢀ
Ir(ppy)2(PIB2-ppy)ꢀ(9)ꢀmightꢀhaveꢀadversaryꢀpropertiesꢀdueꢀtoꢀ
itsꢀ potentiallyꢀ veryꢀ activatedꢀ C–Hꢀ bond,ꢀ weꢀ focusedꢀ ourꢀ
followingꢀ investigationsꢀ onꢀ theꢀ mono-alkylatedꢀ Ir(ppy)2(PIB-
ppy)ꢀ(3).ꢀ
°
Cꢀ ledꢀ toꢀ aꢀ homogeneousꢀ mixtureꢀ whichꢀ wasꢀ thenꢀ irradiatedꢀ
withꢀ blueꢀ LEDꢀ lightꢀ (455ꢀ nm)ꢀ untilꢀ theꢀ transformationꢀ wasꢀ
completedꢀ (2).ꢀ Coolingꢀ toꢀ roomꢀ temperatureꢀ (3)ꢀ andꢀ phaseꢀ
separationꢀ(4)ꢀgaveꢀbackꢀanꢀacetonitrileꢀphaseꢀcontainingꢀtheꢀ
photochemicalꢀ productsꢀ andꢀ aꢀ heptaneꢀ phaseꢀ withꢀ catalystꢀ
Ir(ppy)2(PIB-ppy)ꢀ(3)ꢀthatꢀcouldꢀbeꢀaddedꢀtoꢀtheꢀnextꢀreactionꢀ
runꢀ (5).ꢀ Whileꢀ thisꢀ protocolꢀ requiresꢀ heatingꢀ inꢀ additionꢀ toꢀ
irradiatingꢀtheꢀreactionꢀmixture,ꢀitꢀshouldꢀbeꢀnotedꢀthatꢀquiteꢀaꢀ
numberꢀofꢀphotoredoxꢀcatalyzedꢀprocessesꢀhaveꢀbeenꢀrepor-
23ꢀ
tedꢀthatꢀrequireꢀelevatedꢀtemperaturesꢀtoꢀbeginꢀwith.
Toꢀ demonstrateꢀ theꢀ feasibilityꢀ ofꢀ aboveꢀ mentionedꢀ concept,ꢀ
weꢀappliedꢀpolyisobutylene-taggedꢀIr(ppy)2(PIB-ppy)ꢀ(3)ꢀtoꢀtheꢀ
photochemicalꢀdeiodationꢀreactionꢀofꢀ11,ꢀoriginallyꢀdevelopedꢀ
24
byꢀ Stephensonꢀ etꢀ al.ꢀ (Tableꢀ 1,ꢀ entryꢀ 1). ꢀ Usingꢀ aꢀ mixtureꢀ ofꢀ
acetonitrileꢀandꢀheptaneꢀatꢀ85ꢀ°Cꢀinsteadꢀsolelyꢀacetonitrileꢀatꢀ
roomꢀ temperatureꢀ hadꢀ littleꢀ influenceꢀ onꢀ theꢀ reactionꢀ
outcome,ꢀ andꢀ PIB-taggedꢀ Ir(ppy)2(PIB-ppy)ꢀ (3)ꢀ wasꢀ ableꢀ toꢀ
catalyzeꢀtheꢀreactionꢀessentiallyꢀwithꢀtheꢀsameꢀefficiencyꢀasꢀitsꢀ
non-taggedꢀ counterpartꢀ fac-Ir(ppy)3ꢀ (entryꢀ 2,3).ꢀ Theꢀ catalystꢀ
wasꢀ recycledꢀ asꢀ describedꢀ aboveꢀ andꢀ resubjectedꢀ toꢀ aꢀ newꢀ
reactionꢀrun,ꢀforꢀwhichꢀanꢀincreaseꢀofꢀproductꢀyieldꢀfromꢀ78ꢀtoꢀ
Polymer-boundꢀ Ir(ppy)2(PIB-ppy)ꢀ (3)ꢀ exhibitsꢀ anꢀ almostꢀ iden-
ticalꢀ UV-Visꢀ spectrumꢀ likeꢀ itsꢀ parentꢀ complexꢀ fac-Ir(ppy)3.ꢀ
Photochemicalꢀreactionsꢀcanꢀthereforeꢀbeꢀcarriedꢀoutꢀwithoutꢀ
theꢀ needꢀ ofꢀ adjustingꢀ theꢀ excitationꢀ wavelength.ꢀ Asꢀ theꢀ firstꢀ
approach,ꢀ weꢀ envisionedꢀ toꢀ performingꢀ photochemicalꢀ
reactionsꢀ underꢀ theirꢀ originallyꢀ publishedꢀ conditionsꢀ andꢀ
recoverꢀ PIB-taggedꢀ catalystꢀ 3ꢀ byꢀ aꢀ subsequentꢀ liquidꢀ /ꢀ liquidꢀ
extractionꢀ withꢀ heptane.ꢀ Typicalꢀ solventsꢀ forꢀ photochemicalꢀ
ꢀ
9
6%ꢀwasꢀobservedꢀ(entryꢀ4).ꢀThisꢀriseꢀcanꢀbeꢀexplainedꢀbyꢀtheꢀꢀ
2
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Page 3 of 6
Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀ ha ed mj u si st ꢀt mr yarginsꢀ
JournalꢀNameꢀ
ꢀARTICLEꢀ
Tableꢀ2ꢀ Deiodation/cyclizationꢀofꢀ13ꢀwithꢀreusableꢀIr(ppy)
2
(PIB-ppy)ꢀ(3).ꢀꢀ
View Article Online
DOI: 10.1039/C5GC01792K
H
I
Photocat. (2.5 mol%), Bu
3
N (10 equiv),
HCO H (10 equiv)
2
O
O
MeCN, 455 nm LED, 3 h
MeO
MeO
1
4
15
ꢀ
ꢀ
a
Entryꢀ
Catalystꢀ
Conditionsꢀ
Runꢀ
-ꢀ
Yieldꢀ[%] ꢀ
Schemeꢀ2ꢀ
Photoreactionsꢀ withꢀ Ir(ppy)
2
(PIB-ppy)ꢀ (3)ꢀ inꢀ aꢀ thermomorphicꢀ solventꢀ
b
1
ꢀ
fac-Ir(ppy)
3
ꢀ
MeCN,ꢀroomꢀtemp.ꢀ
80 ꢀ
systemꢀofꢀacetonitrileꢀandꢀheptane.ꢀ
Ir(ppy)
2
(PIB-ppy)ꢀ
c
2
ꢀ
MeCN/heptaneꢀ85ꢀ°Cꢀ
1ꢀ
47+17 ꢀ
(
3)ꢀ
residualꢀsolubilityꢀofꢀproductꢀ12ꢀinꢀtheꢀheptaneꢀphase.ꢀAsꢀtheꢀ
heptaneꢀ phaseꢀ isꢀ thenꢀ addedꢀ toꢀ theꢀ nextꢀ reactionꢀ run,ꢀ alsoꢀ
extractedꢀproductꢀfromꢀtheꢀlastꢀreactionꢀrunꢀisꢀadded,ꢀleadingꢀ
toꢀ aꢀ steadyꢀ stateꢀ ofꢀ extractedꢀ andꢀ addedꢀ productꢀ afterꢀ theꢀ
secondꢀ catalystꢀ run.ꢀ Theꢀ catalystꢀ containingꢀ heptaneꢀ phaseꢀ
wasꢀthoroughlyꢀextractedꢀwithꢀadditionalꢀacetonitrileꢀafterꢀtheꢀ
Ir(ppy)
2
(PIB-ppy)ꢀ
3
ꢀ
MeCN/heptaneꢀ85ꢀ°Cꢀ 2–10ꢀ
60–76ꢀ
(
3)ꢀ
a
b
ꢀ
Determinedꢀ byꢀ GC-FIDꢀ withꢀ diphenylmethaneꢀ asꢀ internalꢀ standard.ꢀ ꢀ 8ꢀ hꢀ
c
reactionꢀ time,ꢀ isolatedꢀ yield;ꢀ takenꢀ fromꢀ referenceꢀ 22.ꢀ ꢀ Additionalꢀ amountꢀ ofꢀ
productꢀextractedꢀfromꢀheptaneꢀphaseꢀafterꢀtheꢀlastꢀrun.ꢀ
lastꢀrun,ꢀgivingꢀanꢀadditionalꢀ12%ꢀofꢀ12ꢀ(relativeꢀtoꢀoneꢀrun).ꢀ Inꢀ additionꢀ toꢀ aꢀ simpleꢀ deiodation,ꢀ weꢀ alsoꢀ examinedꢀ theꢀ
Thisꢀcorrespondsꢀtoꢀtheꢀamountꢀofꢀextractedꢀproductꢀafterꢀtheꢀ catalyticꢀperformanceꢀandꢀrecyclingꢀcapabilitiesꢀofꢀIr(ppy) (PIB-
2
4
2
firstꢀ runꢀ (entryꢀ 3).ꢀ Inꢀ theꢀ followingꢀ runsꢀ theꢀ productꢀ yieldꢀ ppy)ꢀ (3)ꢀ inꢀ theꢀ deiodation/cyclizationꢀ ofꢀ 13ꢀ (Tableꢀ 2). ꢀ Alsoꢀ
stayedꢀconstantlyꢀhighꢀandꢀitꢀwasꢀpossibleꢀtoꢀrunꢀtheꢀreactionꢀ hereꢀ theꢀ reusableꢀ catalystꢀ variantꢀ 3ꢀ performedꢀ wellꢀ (entryꢀ 2ꢀ
forꢀatꢀleastꢀ10ꢀtimesꢀwithꢀtheꢀsameꢀbatchꢀofꢀcatalystꢀwithoutꢀ andꢀ 3).ꢀ Theꢀ amountꢀ ofꢀ extractedꢀ cyclizationꢀ productꢀ 14ꢀ isꢀ
anꢀevidentꢀdeclineꢀinꢀefficiencyꢀ(entryꢀ4).ꢀAꢀcontrolꢀexperimentꢀ higherꢀdueꢀtoꢀitsꢀlessꢀpolarꢀnature,ꢀneverthelessꢀtheꢀrecyclingꢀ
whereꢀ onlyꢀ oneꢀ tenthꢀ ofꢀ theꢀ catalystꢀ wasꢀ usedꢀ yieldedꢀ onlyꢀ behaviourꢀofꢀ3ꢀwasꢀnotꢀimpaired.ꢀ
3
4%ꢀproductꢀafterꢀirradiationꢀ(entryꢀ5).ꢀ
Encouragedꢀ byꢀ theꢀ catalyticꢀ performanceꢀ andꢀ excellentꢀ
recyclabilityꢀ ofꢀ PIB-taggedꢀ 3ꢀ inꢀ previousꢀ batchꢀ reactions,ꢀ weꢀ
envisionedꢀ aꢀ continuouslyꢀ operatingꢀ processꢀ inꢀ whichꢀ theꢀ
catalystꢀ isꢀ constantlyꢀ recycledꢀ andꢀ reused.ꢀ Forꢀ hydroformyl-
ationsꢀ conceptuallyꢀ relatedꢀ flowꢀ systemsꢀ withꢀ continuousꢀ
ꢀ
ꢀ
2
Tableꢀ1ꢀ Deiodationꢀofꢀ11ꢀwithꢀrecyclableꢀIr(ppy) (PIB-ppy)ꢀ(3).ꢀ
25
catalystꢀrecyclingꢀhaveꢀbeenꢀdevelopedꢀpreviously. ꢀInꢀthoseꢀ
studiesꢀ aꢀ polarꢀ rhodiumꢀ catalystꢀ isꢀ retainedꢀ inꢀ aꢀ DMFꢀ phaseꢀ
whileꢀ theꢀ productꢀ (long-chainedꢀ aldehydes)ꢀ dissolvesꢀ inꢀ
decane.ꢀAlso,ꢀlatentꢀmonophasicꢀfluorousꢀsystemsꢀareꢀknownꢀ
O
H
O
H
H
O
Photocat. (1 mol%), Bu3N (2.0 equiv),
Hantzsch ester (2.0 equiv),
O
O
O
O
O
O
MeCN, 455 nm LED, 3 h
O
I
26
1
2
13
inꢀflow. ꢀInꢀourꢀsetupꢀforꢀphotochemicalꢀtransformationsꢀinꢀaꢀ
thermomorphicꢀsolventꢀsystemꢀweꢀranꢀtheꢀreactionsꢀinꢀaꢀtrans-
ꢀ
a
Runꢀ Yieldꢀ[%] ꢀ parent,ꢀ heatableꢀ microreactorꢀ andꢀ therebyꢀ enableꢀ theꢀ irra-
Entryꢀ
Catalystꢀ
Conditionsꢀ
b
diationꢀ ofꢀ theꢀ reactionꢀ mixtureꢀ whileꢀ itꢀ isꢀ homogeneousꢀ
1
2
ꢀ
ꢀ
fac-Ir(ppy)
3
3
ꢀ
ꢀ
MeCN,ꢀroomꢀtemp.ꢀ
–ꢀ
–ꢀ
83 ꢀ
27
(
Schemeꢀ 3). ꢀ Substrateꢀ andꢀ reagentsꢀ dissolvedꢀ inꢀ heptane-
28
fac-Ir(ppy)
MeCN/heptane,ꢀ85ꢀ°Cꢀ
MeCN/heptane,ꢀ85ꢀ°Cꢀ
73ꢀ
saturatedꢀacetonitrile ꢀ(1)ꢀareꢀpumpedꢀ(2)ꢀintoꢀaꢀmicroreactorꢀ
(3)ꢀalongꢀwithꢀaꢀsolutionꢀofꢀIr(ppy)2(PIB-ppy)ꢀ(3)ꢀinꢀheptaneꢀ(4).ꢀ
Throughꢀ heatingꢀ toꢀ 90ꢀ °Cꢀ theꢀ biphasicꢀ systemꢀ becomesꢀ aꢀ
homogeneousꢀ solutionꢀ whichꢀ isꢀ thenꢀ irradiatedꢀ withꢀ visibleꢀ
light.ꢀ Aꢀ throttleꢀ valveꢀ (5)ꢀ ensuresꢀ thatꢀ theꢀ solventsꢀ areꢀ notꢀ
boiling.ꢀ Afterꢀ theꢀ photoreactionꢀ isꢀ completedꢀ theꢀ mixtureꢀ
reachesꢀaꢀcooledꢀphaseꢀseparatorꢀunitꢀ(6).ꢀWhileꢀtheꢀcatalystꢀ
Ir(ppy)
Ir(ppy)
Ir(ppy)
2
2
2
(PIB-ppy)ꢀ
c
3
4
5
ꢀ
ꢀ
ꢀ
1ꢀ
78+12 ꢀ
(
3)ꢀ
(PIB-ppy)ꢀ
ꢀ
MeCN/heptane,ꢀ85ꢀ°Cꢀ 2–10ꢀ
MeCN/heptane,ꢀ85ꢀ°Cꢀ –ꢀ
86–96
(
3)ꢀ
(PIB-ppy)ꢀ
d
34 ꢀ
(
3)ꢀ
a
b
ꢀ
Determinedꢀ byꢀ GC-FIDꢀ withꢀ diphenylmethaneꢀ asꢀ internalꢀ standard.ꢀ ꢀ 5ꢀ hꢀ containingꢀ phaseꢀ isꢀ recycledꢀ (4),ꢀ theꢀ product-containingꢀ
c
reactionꢀ time,ꢀ isolatedꢀ yield;ꢀ takenꢀ fromꢀ referenceꢀ 22.ꢀ ꢀ Additionalꢀ amountꢀ ofꢀ acetonitrileꢀisꢀcollectedꢀ(7).ꢀꢀ
productꢀextractedꢀfromꢀheptaneꢀphaseꢀafterꢀtheꢀlastꢀrun.ꢀ ꢀ0.1ꢀmol%ꢀofꢀcatalystꢀ3ꢀ
d
Weꢀ appliedꢀ thisꢀ reactionꢀ setupꢀ inꢀ theꢀ photochemicalꢀ
generationꢀ ofꢀ Z-alkenesꢀ fromꢀ readilyꢀ availableꢀ E-alkenesꢀ
wasꢀused.ꢀ
29
throughꢀ uphillꢀ catalysisꢀ asꢀ demonstratedꢀ byꢀ Weaverꢀ etꢀ al. ꢀ
Theꢀdoubleꢀbondꢀinꢀ15ꢀisꢀpresumablyꢀbrokenꢀthroughꢀenergyꢀ
transferꢀ fromꢀ theꢀ excitedꢀ photocatalystꢀ formingꢀ aꢀ biradicalꢀ
speciesꢀ17ꢀthatꢀrapidlyꢀundergoesꢀintersystemꢀcrossingꢀtoꢀgiveꢀ
theꢀisomerizedꢀcompoundꢀ16ꢀ(Tableꢀ3).ꢀControlꢀexperimentsꢀinꢀ
aꢀbatchꢀprocessꢀshowedꢀthatꢀthisꢀreactionꢀcouldꢀbeꢀcarriedꢀoutꢀꢀ
ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ3ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀ ha ed mj u si st ꢀt mr yarginsꢀ
Page 4 of 6
ARTICLEꢀ
JournalꢀNameꢀ
View Article Online
5
ꢀ
DOI: 10.1039/C5GC01792K
8
6
4
2
0
0
0
0
0
4ꢀ
3ꢀ
2ꢀ
1ꢀ
Schemeꢀ3ꢀ
Continuouslyꢀoperating,ꢀcatalystꢀrecycling,ꢀphotoreactionꢀsetup.ꢀ
0ꢀ
0
5
10
15
20
25
30
atꢀelevatedꢀtemperaturesꢀwithoutꢀaꢀdetrimentalꢀeffectꢀonꢀtheꢀ
n(converted substrate 15) [mmol]
E/Zꢀ ratioꢀ (entryꢀ 2).ꢀ Also,ꢀ neitherꢀ aꢀ switchꢀ ofꢀ solventꢀ toꢀ aꢀ Fig.ꢀ2.ꢀ PhotochemicalꢀE/Zꢀisomerizationꢀinꢀaꢀflowꢀprocessꢀwithꢀcontinuousꢀcatalystꢀ
acetonitrileꢀ /ꢀ heptaneꢀ mixtureꢀ norꢀ theꢀ employmentꢀ ofꢀ recycling.ꢀZ-isomerꢀratioꢀdepictedꢀinꢀblueꢀ(determinedꢀbyꢀGC-FID,ꢀshowingꢀaꢀrangeꢀfromꢀ
8
3:17ꢀtoꢀ81:19),ꢀiridiumꢀcontentꢀlostꢀnormalizedꢀforꢀ1ꢀmmolꢀsubstrateꢀdepictedꢀinꢀredꢀ
Ir(ppy)2(PIB-ppy)ꢀ(3)ꢀdeterioratedꢀtheꢀreactionꢀoutcomeꢀ(entryꢀ
),ꢀ promptingꢀ usꢀ toꢀ setꢀ upꢀ thisꢀ reactionꢀ inꢀ aꢀ continuousꢀ
process.ꢀꢀ
2
5
(
determinedꢀbyꢀICP-OES).ꢀReactionꢀparameters: ꢀ30ꢀmmolꢀE-alkeneꢀ15ꢀ(1.0ꢀequiv),ꢀ3ꢀ
3
i
mmolꢀ Pr
2
NEtꢀ(0.1ꢀequiv),ꢀ7ꢀµmolꢀIr(ppy)
2 2
(PIB -ppy)ꢀ(3)ꢀ(0.023ꢀmol%),ꢀMeCN,ꢀheptane,ꢀ
9
0ꢀ°C,ꢀflowrateꢀ20ꢀµmolꢀ15/min.ꢀ
Theꢀresultsꢀofꢀtheꢀisomerizationꢀofꢀ15ꢀinꢀaꢀflowꢀprocessꢀwithꢀ
continuousꢀcatalystꢀrecyclingꢀareꢀdepictedꢀinꢀFig.ꢀ2.ꢀAsꢀcanꢀbeꢀ
seenꢀtheꢀZ/Eꢀratioꢀremainsꢀatꢀconstantꢀhighꢀlevelsꢀthroughoutꢀ
theꢀwholeꢀreactionꢀprocess.ꢀTheꢀamountꢀofꢀcatalystꢀemployedꢀ
correspondsꢀtoꢀtheꢀamountꢀusedꢀinꢀaꢀ1ꢀmmolꢀbatchꢀreactionꢀ
30
setup, ꢀdemonstratingꢀthatꢀthisꢀsetupꢀcanꢀeffectivelyꢀdecreaseꢀ
theꢀcatalystꢀloadingꢀbyꢀaꢀfactorꢀofꢀatꢀleastꢀ30.ꢀCatalystꢀleachingꢀ
isꢀcomparablyꢀhighꢀatꢀtheꢀbeginningꢀofꢀtheꢀreactionꢀwithꢀ2.6%ꢀ
ofꢀtheꢀtotallyꢀemployedꢀiridiumꢀlostꢀrelativeꢀtoꢀtheꢀfirstꢀmmolꢀ
ofꢀ convertedꢀ substrateꢀ 15ꢀ asꢀ determinedꢀ byꢀ ICP-OES.ꢀ
Gratifyingly,ꢀtheꢀiridiumꢀlossꢀseverelyꢀdeclinesꢀinꢀcourseꢀofꢀtheꢀ
furtherꢀreaction,ꢀreachingꢀlevelsꢀwellꢀbelowꢀ0.1%ꢀiridiumꢀlostꢀ
perꢀ mmolꢀ ofꢀ convertedꢀ substrateꢀ 15,ꢀ correspondingꢀ toꢀ anꢀ
iridiumꢀ contaminationꢀ belowꢀ 2ꢀ ppmꢀ ofꢀ theꢀ reactionꢀ product.ꢀ
4
mm
1
H-NMRꢀanalysisꢀperformedꢀforꢀtheꢀcatalystꢀafterꢀtheꢀreactionꢀ
suggestsꢀthatꢀmainlyꢀcatalystꢀmoleculesꢀthatꢀwereꢀconnectedꢀ
toꢀshorterꢀPIBꢀchainsꢀbeingꢀpresentꢀfromꢀtheꢀstartꢀinꢀGlissopal®ꢀ
Fig.ꢀ3ꢀ
Photochemicalꢀ isomerizationꢀ ofꢀ 15ꢀ inꢀ aꢀ microreactorꢀ underꢀ biphasicꢀ
(PIB-ppy)ꢀ (3)ꢀ isꢀ containedꢀ inꢀ theꢀ fluorescent-greenꢀ heptaneꢀ phaseꢀ
conditions.ꢀ Ir(ppy)
2
whileꢀ 15ꢀ isꢀ locatedꢀ inꢀ theꢀ colourlessꢀ acetonitrileꢀ phase.ꢀ Theꢀ averageꢀ lengthꢀ ofꢀ eachꢀ
phaseꢀisꢀapproximatelyꢀ2ꢀmm.ꢀResultsꢀasꢀinꢀFig.ꢀ2ꢀatꢀaꢀflowrateꢀofꢀ10ꢀµmolꢀ15/min.ꢀ
1
000,ꢀi.e.ꢀhavingꢀhigherꢀpolarity,ꢀwereꢀlost.ꢀꢀ
Whileꢀ weꢀ demonstratedꢀ thatꢀ higherꢀ reactionꢀ temperaturesꢀ
haveꢀnoꢀadversaryꢀeffectsꢀonꢀtheꢀexaminedꢀreactions,ꢀitꢀmightꢀ
beꢀdisadvantageousꢀforꢀotherꢀphotochemicalꢀtransformations.ꢀꢀ
ꢀ
Toꢀ obliterateꢀ suchꢀ demur,ꢀ weꢀ alsoꢀ carriedꢀ outꢀ theꢀ
isomerizationꢀ reactionꢀ ofꢀ 15ꢀ atꢀ roomꢀ temperature.ꢀ Thisꢀ
31
resultedꢀinꢀaꢀbiphasicꢀreactionꢀsystem. ꢀLightꢀisꢀabsorbedꢀbyꢀ
theꢀ photocatalystꢀ inꢀ theꢀ heptaneꢀ phaseꢀ whileꢀ reactionꢀ
presumablyꢀ takesꢀ placeꢀ atꢀ theꢀ interfaceꢀ toꢀ theꢀ substrate-
containingꢀ acetonitrileꢀ phase.ꢀ Throughꢀ theꢀ employmentꢀ ofꢀ aꢀ
microreactorꢀ aꢀ sufficientlyꢀ highꢀ surfaceꢀ areaꢀ wasꢀ generatedꢀ
dueꢀ toꢀ lamellarꢀ flowꢀ andꢀ aꢀ phaseꢀ alternationꢀ approximatelyꢀ
everyꢀ2ꢀmmꢀ(Fig.ꢀ3).ꢀAlbeitꢀslightlyꢀlowerꢀflowꢀ(10ꢀµmolꢀinsteadꢀ
ofꢀ20ꢀµmolꢀ15/minꢀratesꢀwereꢀneeded,ꢀtheꢀproductꢀyieldꢀandꢀ
Tableꢀ3ꢀ
ꢀ
PhotocatalyzedꢀE/Zꢀisomerizationꢀinꢀaꢀcontinuousꢀprocess.ꢀ
Photocat. (0.7 mol%),
iPr
NEt (0.1 equiv)
via:
H
OAc
2
Ph
OAc
MeCN, 455 nm LED, 4 h
OAc
H
1
6
17
18
ꢀ
ꢀ
a
recyclingꢀ capabilitiesꢀ wereꢀ notꢀ impaired, demonstratingꢀ thatꢀ
Entryꢀ
Catalystꢀ
Conditionsꢀ
ꢀ
Z/Eꢀratio ꢀ
Ir(ppy)2(PIB-ppy)ꢀ(3)ꢀcanꢀbeꢀusedꢀinꢀboth,ꢀmono-ꢀandꢀbiphasicꢀ
reactionꢀconditions.ꢀ
1
2
3
ꢀ
ꢀ
ꢀ
fac-Ir(ppy)
fac-Ir(ppy)
3
3
ꢀ
ꢀ
MeCN,ꢀroomꢀtemp.ꢀ
MeCN,ꢀ90ꢀ°Cꢀ
ꢀ
ꢀ
ꢀ
82:18ꢀ
82:18ꢀ
82:18ꢀ
Ir(ppy)
2
(PIB-ppy)ꢀ(3)ꢀ
MeCN/heptane,ꢀ90ꢀ°Cꢀ
a
1
ꢀ
Ratioꢀdeterminedꢀbyꢀ H-NMRꢀ/ꢀGC-FIDꢀintegrationꢀofꢀtheꢀcrudeꢀreactionꢀmixture.ꢀ
Conclusionꢀ
TheꢀstandardꢀdeviationꢀforꢀtheꢀGC-FIDꢀmeasurementsꢀwasꢀbelowꢀ1%.ꢀ
Inꢀ summary,ꢀ aꢀ shortꢀ andꢀ efficientꢀ synthesisꢀ forꢀ
polyisobutylene-taggedꢀ Ir(ppy)2(PIB-ppy)ꢀ (3)ꢀ wasꢀ established.ꢀ
Thisꢀcatalystꢀshowedꢀexcellentꢀcatalyticꢀperformanceꢀasꢀwellꢀasꢀ
recyclabilityꢀinꢀbatchꢀandꢀinꢀflowꢀreactions.ꢀAꢀprocessꢀcouldꢀbeꢀ
developedꢀ whereꢀ theꢀ photocatalystꢀ 3ꢀ isꢀ constantlyꢀ recycled,ꢀ
allowingꢀ toꢀ useꢀ drasticallyꢀ lowerꢀ amountsꢀ ofꢀ highꢀ pricedꢀ
4
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
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Page 5 of 6
Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀ ha ed mj u si st ꢀt mr yarginsꢀ
JournalꢀNameꢀ
ꢀARTICLEꢀ
Pascie, G. Koch, M. Eberle, M. B. Berry and K. I. Booker-Milburn,
iridiumꢀ comparedꢀ toꢀ theꢀ batchꢀ process.ꢀ Catalystꢀ 3ꢀ thereforeꢀ
providesꢀ anꢀ alternativeꢀ toꢀ fac-Ir(ppy)3ꢀ whenꢀ large-scaleꢀ
View Article Online
Chem. Eur. J. 2014, 20, 15226-15232.
DOI: 10.1039/C5GC01792K
1
1
8
9
For leading reviews on photocatalyzed reactions in flow see: (a) Z. J.
Garlets, J. D. Nguyen and C. R. J. Stephenson, Isr. J. Chem., 2014, 54,
reactionꢀsetupsꢀareꢀrequired.ꢀ
ꢀ
3
51–360; b) Y. Su, J. W. Straathof, V. Hessel and T. Noel, Chem. Eur.
J., 2014, 20, 10562-10589.
Polyisobutylene was introduced as non-polar hydrocarbon support for
reagents and catalysts by Bergbreiter et al.: (a) D. E. Bergbreiter and J.
Li, Chem. Commun., 2004, 1, 42–43; (b) J. Li, S. Sung, J. Tia and D. E.
Bergbreiter, Tetrahedron, 2005, 61, 12081–12092.
Acknowledgementsꢀ
Thisꢀ workꢀ wasꢀ supportedꢀ byꢀ theꢀ GRKꢀ 1626ꢀ (“Chemicalꢀ
Photocatalysis”)ꢀofꢀtheꢀDFG.ꢀTheꢀauthorsꢀthankꢀA.ꢀWimmerꢀandꢀ 20 Polyisobutylene bromide is commercially available from Strem.
2
1
(a) D. E. Bergbreiter, ACS Macro Lett., 2014, 3, 260–265; (b) A. Behr,
M.ꢀTautzꢀ(Univ.ꢀofꢀRegensburg)ꢀforꢀtheirꢀhelpꢀwithꢀpreliminaryꢀ
studiesꢀandꢀTehshikꢀP.ꢀYoonꢀ(Univ.ꢀofꢀWisconsin-Madison)ꢀforꢀ
helpfulꢀdiscussions.ꢀ
G. Henze and R. Schomäcker, Adv. Synth. Catal., 2006, 348, 1485–
1
495; (c) D. E. Bergbreiter and S. D. Sung, Adv. Synth. Catal., 2006,
48, 1352–1366.
3
2
2
A. W. Francis, Critical Solution Temperatures, American Chemical
Society, Washington, DC, 1961.
Notesꢀandꢀreferencesꢀ
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P. Yoon, Science, 2014, 343, 985.
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ARTICLEꢀ
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Table of Contents
View Article Online
DOI: 10.1039/C5GC01792K
•
•
catalyst in heptane phase
substrate (and reagents)
in acetonitrile phase
immiscible at rt,
• automatic recovery & reuse of cataly
• advantages of homogen. catalysis
• continuous phase seperation
• 30 times batch scale reaction
with constant product yields
[
Ir]
•
homogeneous with ΔT
ΔT + hν
A protocol for photoredox catalysed reactions in homogeneous solution
mono- or biphasic) was developed that allows automatic recycling of
(
the catalyst.
6
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