Reversible cyclometalation at RhI as a motif for metal-ligand bifunctional bond activation and base-free formic acid dehydrogenation

Article abstract of DOI:10.1039/c5cy01505g

Reversible cyclometalation is demonstrated as a strategy for the activation of small protic molecules, with a proof-of-principle catalytic application in the dehydrogenation of formic acid in the absence of an exogenous base. The well-defined Rh^I complex Rh(CO)(L) 1, bearing the reactive cyclometalated PN(C) ligand L (L^H = PNC^H = 2-di(tert-butylphosphinomethyl)-6-phenylpyridine), undergoes protonolysis of the Rh-C_Ph bond with weak protic reagents, such as thiols and trifluoromethanesulfonamide. This system also displays bifunctional metal-ligand protonolysis reactivity with formic acid and subsequent decarboxylation of the formate complex. Density functional theory (DFT) calculations show that H₂ evolution from putative Rh(CO)(H)(L^H) complex A is very facile, proposedly encompassing formal C-H oxidative addition at Rh to give Cvia agostic intermediate B and subsequent reductive elimination of H₂. Complex 1 is a catalytically competent species for base-free formic acid dehydrogenation, with the intermediacy of formate complex 4. DFT calculations reveal accessible barriers for involvement of a flanking phenyl group for both initial activation of formic acid and release of H₂, supporting a cooperative pathway. Reversible C-H activation is thus a viable mechanism for metal-ligand bifunctional catalysis.

Full text of DOI:10.1039/c5cy01505g

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DOI: 10.1039/C5CY01505G
JournalꢀNameꢀ
ꢀ
ARTICLEꢀ
I
ReversibleꢀcyclometalationꢀatꢀRh ꢀasꢀMotifꢀforꢀMetal-Ligandꢀ
BifunctionalꢀBondꢀActivationꢀandꢀBase-freeꢀFormicꢀAcidꢀ
Dehydrogenationꢀ
Receivedꢀ00thꢀJanuaryꢀ20xx,ꢀ
Acceptedꢀ00thꢀJanuaryꢀ20xxꢀ
a
a
a
b
aꢀ
L.ꢀS.ꢀJongbloed, ꢀB.ꢀdeꢀBruin ,ꢀJ.ꢀN.ꢀH.ꢀReek, ꢀM.ꢀLutz ꢀandꢀJ.ꢀI.ꢀvanꢀderꢀVlugt
DOI:ꢀ10.1039/x0xx00000xꢀ
www.rsc.org/ꢀ
Reversibleꢀcyclometalationꢀisꢀdemonstratedꢀ asꢀaꢀstrategyꢀforꢀtheꢀactivationꢀofꢀproticꢀsmallꢀmolecules,ꢀwithꢀaꢀproof-of-
principleꢀcatalyticꢀapplicationꢀinꢀtheꢀdehydrogenationꢀofꢀformicꢀacid,ꢀinꢀtheꢀabsenceꢀofꢀexogenousꢀbase.ꢀTheꢀwell-definedꢀ
I
H
H
Rh ꢀcomplexꢀRh(CO)(L)ꢀ1,ꢀbearingꢀtheꢀreactiveꢀcyclometalatedꢀPN(C)ꢀligandꢀLꢀ(L ꢀ=ꢀPNC ꢀ=ꢀ2-di(tert-butylphosphinomethyl)-
-phenylpyridine)ꢀ undergoesꢀ protonolysisꢀ ofꢀ theꢀ Rh-CPhꢀ bondꢀ withꢀ weakꢀ proticꢀ reagents,ꢀ suchꢀ asꢀ thiolsꢀ andꢀ
trifluoromethanesulfonamide.ꢀThisꢀsystemꢀalsꢀdisplaysꢀbifunctionalꢀmetal-ligandꢀprotonolysisꢀreactivityꢀwithꢀformicꢀacidꢀ
6
andꢀ subsequentꢀ decarboxylationꢀ ofꢀ theꢀ formateꢀ complex.ꢀ DFTꢀ calculationsꢀ showꢀ thatꢀ H
2
ꢀ evolutionꢀ fromꢀ aꢀ putativeꢀ
H
Rh(CO)(H)(L )ꢀcomplexꢀAꢀisꢀveryꢀfacile,ꢀencompassingꢀformalꢀC-HꢀoxidativeꢀadditionꢀatꢀRhꢀtoꢀgiveꢀCꢀviaꢀagosticꢀintermediateꢀ
BꢀandꢀsubsequentꢀreductiveꢀeliminationꢀofꢀH
dehydrogenation,ꢀinvolvingꢀformateꢀintermediateꢀ4.ꢀDensityꢀfunctionalꢀtheoryꢀ(DFT)ꢀcalculationsꢀrevealꢀaccessibleꢀbarriersꢀ
forꢀinvolvementꢀofꢀtheꢀflankingꢀphenylꢀgroupꢀforꢀbothꢀinitialꢀactivationꢀofꢀtheꢀformicꢀacidꢀandꢀreleaseꢀofꢀH ,ꢀsupportingꢀaꢀ
2
.ꢀComplexꢀ1ꢀisꢀaꢀcatalyticallyꢀcompetentꢀspeciesꢀforꢀbase-freeꢀformicꢀacidꢀ
2
cooperativeꢀpathway.ꢀReversibleꢀC-Hꢀactivationꢀisꢀthusꢀaꢀviableꢀmechanismꢀforꢀmetal-ligandꢀbifunctionalꢀcatalysis.ꢀꢀ
asꢀpresentꢀinꢀcyclometalatedꢀspecies.ꢀReversibleꢀcyclometalationꢀatꢀ
lateꢀtransitionꢀmetalsꢀusingꢀstrongꢀacidsꢀhasꢀbeenꢀwell-documentedꢀ
Introductionꢀ
ꢀ
6,7,8
forꢀstoichiometricꢀscenarios, ꢀbutꢀexamplesꢀwithꢀlow-valentꢀmetalꢀ
Theꢀ applicationꢀ ofꢀ reactiveꢀ ligandsꢀ forꢀ metal-ligandꢀ bifunctionalꢀ
bondꢀ activationꢀ andꢀ subsequentꢀ cooperativeꢀ catalysisꢀ receivesꢀ
I
ionsꢀsuchꢀasꢀRh ꢀandꢀapplicationsꢀofꢀthisꢀtypeꢀofꢀreactivityꢀinꢀcatalyticꢀ
1
turnoverꢀ areꢀ rare,ꢀ toꢀ theꢀ bestꢀ ofꢀ ourꢀ knowledge.ꢀ Metal-ligandꢀ
bifunctionalꢀ catalysisꢀ byꢀ reversibleꢀ cyclometalationꢀ hasꢀ beenꢀ
postulatedꢀ asꢀ possibleꢀ mechanismꢀ withꢀ aꢀ fewꢀ systemsꢀ (Figureꢀ 1).ꢀ
Mashimaꢀ etꢀ al.ꢀ discussedꢀ thisꢀ strategyꢀ forꢀ theꢀ dehydrogenativeꢀ
silylationꢀofꢀphenylpyridinesꢀcatalyzedꢀbyꢀaꢀcyclometalatedꢀiridiumꢀ
muchꢀ attention. ꢀ Amongꢀ theꢀ differentꢀ reactiveꢀ ligandꢀ designs,ꢀ
systemsꢀ bearingꢀ aꢀ proton-responsiveꢀ groupꢀ (showingꢀ reversibleꢀ
deprotonationꢀ activity)ꢀ areꢀ particularlyꢀ attractiveꢀ andꢀ versatile.ꢀ
Generally,ꢀ twoꢀ strategiesꢀ toꢀ incorporateꢀ suchꢀ aꢀ fragmentꢀ (anꢀ
‘
internalꢀbase’)ꢀwithinꢀtheꢀligandꢀstructureꢀthatꢀcanꢀeasilyꢀactivateꢀ
9
complex. ꢀ Aꢀ similarꢀ ‘roll-over’ꢀ mechanismꢀ wasꢀ suggestedꢀ forꢀ theꢀ
substratesꢀco-exist:ꢀi)ꢀaꢀsiteꢀinꢀtheꢀcoordinationꢀsphereꢀofꢀaꢀmetalꢀ
10
base-freeꢀtransferꢀhydrogenationꢀwithꢀaꢀrutheniumꢀcatalyst. ꢀTheꢀ
cooperativityꢀofꢀaꢀcyclometalatedꢀfragmentꢀinꢀtheꢀligandꢀstructureꢀ
hasꢀalsoꢀbeenꢀproposed,ꢀonꢀtheꢀbasisꢀofꢀcomputationalꢀstudies,ꢀtoꢀ
centerꢀandꢀii)ꢀaꢀsiteꢀatꢀaꢀlocationꢀnotꢀdirectlyꢀconnectedꢀtoꢀtheꢀmetalꢀ
nd
centerꢀ(2 ꢀcoordinationꢀsphere).ꢀWell-knownꢀdesignsꢀimplementingꢀ
theꢀ latterꢀ strategyꢀ operateꢀ viaꢀ reversibleꢀ dearomatizationꢀ byꢀ
11,12,13
2
3
beꢀ suitableꢀ forꢀ theꢀ dehydrogenationꢀ ofꢀ ammonia-borane.
ꢀ
deprotonationꢀ ofꢀ functionalizedꢀ picoline, ꢀ aminopyridine, ꢀ orꢀ
4
However,ꢀitꢀwasꢀexperimentallyꢀprovenꢀthatꢀthisꢀmechanismꢀoccursꢀ
pyridoneꢀfragments. ꢀRegardingꢀtheꢀstrategyꢀencompassingꢀproton-
13
mostꢀ likelyꢀ onlyꢀ inꢀ theꢀ earlyꢀ stageꢀ ofꢀ catalysis ꢀ orꢀ asꢀ aꢀ wayꢀ toꢀ
responsiveꢀgroupsꢀinꢀtheꢀcoordinationꢀsphereꢀofꢀaꢀtransitionꢀmetal,ꢀ
12
5
generateꢀanꢀactiveꢀspecies. ꢀꢀ
reversibleꢀ deprotonationꢀ ofꢀ metal-boundꢀ functionalizedꢀ amines ꢀ
hasꢀ beenꢀ successfullyꢀ appliedꢀ inꢀ aꢀ varietyꢀ ofꢀ catalyticꢀ
transformations.ꢀꢀ
Metal-carbonꢀ bondsꢀ areꢀ typicallyꢀ ratherꢀ strong,ꢀ butꢀ theꢀ bondꢀ
energyꢀcanꢀbeꢀinfluencedꢀbyꢀe.g.ꢀstrainꢀorꢀnon-idealꢀorbitalꢀoverlap,ꢀ
ꢀ
Figureꢀ1.ꢀComplexesꢀthatꢀhaveꢀbeenꢀproposedꢀtoꢀactꢀasꢀcooperativeꢀcatalystsꢀforꢀ
differentꢀtypesꢀofꢀtransfomationsꢀviaꢀreversibleꢀcyclometalation.ꢀ
ComputationalꢀstudiesꢀbyꢀVankaꢀetꢀal.ꢀindicateꢀthatꢀreversibleꢀ
cyclometalationꢀ canꢀ notꢀ onlyꢀ beꢀ usefulꢀ forꢀ NH3BH3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ1ꢀꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

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ARTICLEꢀ
JournalꢀNameꢀ
I
dehydrogenationꢀbutꢀalsoꢀbeꢀaꢀsuitableꢀmechanismꢀforꢀformicꢀ coordinationꢀsphereꢀofꢀRh ꢀcouldꢀbeꢀemployedꢀasꢀinternalꢀbaseꢀforꢀ
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11
DOI: 10.1039/C5CY01505G
acidꢀ dehydrogenationꢀ toꢀ CO2ꢀ andꢀ H2. ꢀ Dihydrogenꢀ isꢀ aꢀ theꢀ activationꢀ andꢀ conversionꢀ ofꢀ functionalizedꢀ proticꢀ substratesꢀ
consideredꢀaꢀkeyꢀcomponentꢀofꢀmanyꢀfutureꢀrenewableꢀenergyꢀ andꢀtheꢀflexidentateꢀcharacterꢀofꢀtheꢀligandꢀcouldꢀbeꢀbeneficialꢀinꢀ
20
solutions,ꢀ butꢀ efficientꢀ andꢀ reversibleꢀ storageꢀ andꢀ releaseꢀ ofꢀ catalysis.ꢀ Weꢀ previouslyꢀ studiedꢀ theꢀ activationꢀ ofꢀ alkynes, ꢀ
2
H2,ꢀe.g.ꢀinꢀorganicꢀliquidsꢀsuchꢀasꢀformicꢀacidꢀ(FA),ꢀisꢀessentialꢀ activatedꢀ amines ꢀ andꢀ thiols
1
22,23
ꢀ usingꢀ proton-responsiveꢀ PNꢀ andꢀ
forꢀaꢀhydrogenꢀbasedꢀeconomy.ꢀMostꢀcatalyticꢀsystemsꢀforꢀtheꢀ PNPꢀ ligandsꢀ coordinatedꢀ toꢀ lateꢀ transitionꢀ metalsꢀ usingꢀ
dehydrogenationꢀ ofꢀ HCOOHꢀ toꢀ H2ꢀ andꢀ CO2ꢀ requireꢀ theꢀ dearomatization/aromatizationꢀ cooperativity.ꢀ Inꢀ thisꢀ articleꢀ weꢀ
14
presenceꢀ ofꢀ exogenousꢀ base, ꢀ whichꢀ notꢀ onlyꢀ decreasesꢀ theꢀ describeꢀtheꢀreactivityꢀofꢀtheꢀRh-Cꢀbondꢀtowardꢀrelatedꢀsubstratesꢀ
overallꢀhydrogenꢀcontentꢀfromꢀ4.4ꢀwt%ꢀ(forꢀpureꢀHCOOH)ꢀtoꢀ andꢀweꢀreportꢀonꢀtheꢀbase-freeꢀdehydrogenationꢀofꢀformicꢀacidꢀasꢀ
2
.3ꢀ wt%ꢀ (forꢀ aꢀ typicalꢀ 5:2ꢀ HCOOH/NEt3ꢀ mixture)ꢀ butꢀ alsoꢀ proof-of-principleꢀforꢀtheꢀuseꢀofꢀreversibleꢀcyclometalationꢀinꢀmetal-
necessitatesꢀpost-catalysisꢀprocessingꢀforꢀfuelꢀcellꢀapplicationsꢀ ligandꢀbifunctionalꢀcatalysis.ꢀ
1
5
(
removalꢀ ofꢀ volatileꢀ amines). ꢀ Hence,ꢀ catalyticꢀ formicꢀ acidꢀ
dehydrogenationꢀshouldꢀideallyꢀbeꢀperformedꢀinꢀtheꢀabsenceꢀ
ofꢀsuchꢀexogenousꢀbase,ꢀbutꢀtoꢀdateꢀonlyꢀaꢀhandfulꢀofꢀsystemsꢀ
capableꢀofꢀbase-freeꢀformicꢀacidꢀdehydrogenationꢀhaveꢀbeenꢀ
Resultsꢀandꢀdiscussionꢀ
Reactivityꢀ ofꢀ 1ꢀ towardꢀ weakꢀ proticꢀ donorsꢀ -ꢀ thiols.ꢀ Theꢀ
cyclometalatedꢀcomplexꢀ1ꢀwasꢀshownꢀtoꢀbeꢀsusceptibleꢀtoꢀRh-
I
CꢀcleavageꢀbyꢀetherealꢀHBF4ꢀasꢀstrongꢀacid.ꢀThisꢀgeneratesꢀaꢀRh ꢀ
16
reported. ꢀꢀ
Givenꢀ ourꢀ interestꢀ inꢀ theꢀ designꢀ ofꢀ reactiveꢀ ligandꢀ systemsꢀ forꢀ
complexꢀ withꢀ anꢀ agosticꢀ Rh-(CPh-H)ꢀ bondꢀ inꢀ theꢀ solidꢀ state,ꢀ
III
possiblyꢀviaꢀprotonationꢀofꢀtheꢀmetalꢀtoꢀcreateꢀaꢀRh (hydride)ꢀ
17
cooperativeꢀbondꢀactivationꢀreactionsꢀandꢀcatalyticꢀprocesses, ꢀweꢀ
wonderedꢀ whetherꢀ reversibleꢀ C-Hꢀ activationꢀ inꢀ theꢀ coordinationꢀ intermediate,ꢀ withꢀ subsequentꢀ C-Hꢀ reductiveꢀ elimination.ꢀ
sphereꢀofꢀaꢀmetalꢀcouldꢀserveꢀasꢀaꢀnewꢀmethodologyꢀtoꢀfacilitateꢀ Furthermore,ꢀfacileꢀmethylationꢀatꢀtheꢀcyclometalatedꢀcarbonꢀ
e.g.ꢀformicꢀacidꢀdehydrogenation.ꢀInꢀsuchꢀaꢀstrategy,ꢀaꢀmetal-carbonꢀ resultsꢀ fromꢀ reactionꢀ ofꢀ 1ꢀ withꢀ MeI.ꢀ Basedꢀ onꢀ theseꢀ initialꢀ
fragmentꢀshouldꢀfunctionꢀasꢀanꢀinternalꢀbaseꢀforꢀtheꢀactivationꢀofꢀaꢀ results,ꢀ theꢀ activationꢀ ofꢀ lessꢀ reactiveꢀ substratesꢀ wasꢀ
suitableꢀ proticꢀ substrate.ꢀ Aꢀ hypotheticalꢀ cooperativeꢀ mechanismꢀ investigated.ꢀ Initialꢀ attemptsꢀ toꢀ activateꢀ alcoholsꢀ orꢀ
phenylacetyleneꢀatꢀr.t.ꢀdidꢀnotꢀresultꢀinꢀRh-Cꢀcleavage,ꢀbasedꢀ
onꢀ NMRꢀ spectroscopy.ꢀ Thisꢀ mayꢀ pointꢀ towardꢀ eitherꢀ aꢀ pKaꢀ
mismatchꢀ betweenꢀ theseꢀ proticꢀ substratesꢀ andꢀ theꢀ metal-
carbonꢀ bondꢀ asꢀ ‘internalꢀ base’ꢀ orꢀ toꢀ unfavorableꢀ stericꢀ
interferenceꢀ thatꢀ preventsꢀ formalꢀ oxidativeꢀ additionꢀ atꢀ theꢀ
metalꢀcenter.ꢀ
basedꢀ onꢀ reversibleꢀ cyclometalationꢀ asꢀ aꢀ bond-activationꢀ conceptꢀ
involvesꢀ i)ꢀ M-Cꢀ bondꢀ assistedꢀ E-Hꢀ bondꢀ activationꢀ andꢀ ii)ꢀ ligand-
assistedꢀY-Hꢀbondꢀreductiveꢀeliminationꢀafterꢀproductiveꢀconversionꢀ
ofꢀ theꢀ activatedꢀ M-Eꢀ moietyꢀ intoꢀ aꢀ product-likeꢀ M-Yꢀ fragmentꢀ
(
Schemeꢀ1).ꢀReversibleꢀcyclometalationꢀbyꢀprotonationꢀofꢀtheꢀM-Cꢀ
1
8
bondꢀmightꢀresultꢀinꢀaꢀweaklyꢀcoordinatingꢀagosticꢀC-Hꢀbond. ꢀThisꢀ
fragmentꢀ couldꢀ beꢀ viewedꢀ asꢀ maskingꢀ aꢀ vacantꢀ siteꢀ atꢀ theꢀ metalꢀ
center,ꢀwithoutꢀsignificantꢀpertubationsꢀ(structuralꢀorꢀelectronic)ꢀofꢀ
theꢀglobalꢀligandꢀframework,ꢀunlikeꢀwhatꢀisꢀoftenꢀencounteredꢀforꢀ
otherꢀreactiveꢀligands.ꢀAnꢀagosticꢀC-Hꢀinteractionꢀmightꢀalsoꢀassistꢀinꢀ
stabilizingꢀ catalyticallyꢀ relevantꢀ intermediates,ꢀ withꢀ beneficialꢀ
implicationsꢀ forꢀ theꢀ overallꢀ energyꢀ profileꢀ ofꢀ aꢀ potentialꢀ reactionꢀ
path.ꢀ
ꢀ
ꢀ
I
Schemeꢀ 2.ꢀ Reactivityꢀ ofꢀ Rh ꢀ complexꢀ 1ꢀ towardꢀ 1,3-propanedithiolꢀ andꢀ
trifluoromethanesulfonamide.ꢀꢀ
ꢀ
Aliphaticꢀ thiolsꢀ didꢀ reactꢀ smoothlyꢀ withꢀ 1,ꢀ judgingꢀ fromꢀ theꢀ
rapidꢀ colorꢀ changeꢀ ofꢀ theꢀ solutionꢀ fromꢀ redꢀ toꢀ light-yellowꢀ
31
(
monitorꢀ theꢀ chemistryꢀ atꢀ theꢀ Rh-Cꢀ bondꢀ transꢀ toꢀ theꢀ
Schemeꢀ 2).ꢀ Pꢀ NMRꢀ spectroscopyꢀ provedꢀ veryꢀ usefulꢀ toꢀ
phosphineꢀ donor.ꢀ Hence,ꢀ whileꢀ 1ꢀ appearsꢀ asꢀ aꢀ doubletꢀ atꢀ δꢀ
7
1
6.31ꢀ ppmꢀ ( JRh-Pꢀ =ꢀ 101ꢀ Hz),ꢀ theꢀ reactionꢀ withꢀ 1,3-
1
propanedithiolꢀledꢀtoꢀaꢀdoubletꢀatꢀδꢀ69.75ꢀppmꢀ( JRh-Pꢀ=ꢀ151.7ꢀ
Hz)ꢀ forꢀ complexꢀ 2.ꢀ Aꢀ strongꢀ IR-bandꢀ forꢀ theꢀ carbonylꢀ wasꢀ
-
1
1
presentꢀatꢀνꢀ1938ꢀcm ꢀ(Δνꢀofꢀ5ꢀcm ꢀvsꢀ1),ꢀwhileꢀtheꢀpyridineꢀ
ꢀ
1
Schemeꢀ 1.ꢀ Proposedꢀ pathwayꢀ involvingꢀ reversibleꢀ cyclometalationꢀ forꢀ metal- signalsꢀ wereꢀ significantlyꢀ shiftedꢀ downfieldꢀ inꢀ theꢀ Hꢀ NMRꢀ
ligandꢀbifunctionalꢀbondꢀactivationꢀandꢀcatalysis.ꢀ
spectrum.ꢀTheseꢀdataꢀsuggestꢀdecoordinationꢀofꢀtheꢀpyridineꢀ
I
19
H
Recently,ꢀ weꢀ synthesizedꢀ cyclometalatedꢀ Rh ꢀ complexꢀ 1 ꢀ bearingꢀ donorꢀ andꢀ thusꢀ monodentateꢀ P-coordinationꢀ ofꢀ theꢀ PNC ꢀ
theꢀ deprotonatedꢀ derivativeꢀ ofꢀ ligandꢀ L ꢀ thatꢀ canꢀ actꢀ bothꢀ asꢀ aꢀ framework,ꢀinducedꢀbyꢀtheꢀtendencyꢀofꢀthiolateꢀfragmentsꢀtoꢀ
H
bridgeꢀtoꢀmetalꢀcenters.ꢀThisꢀhypothesisꢀwasꢀcorroboratedꢀbyꢀ
X-rayꢀ crystalꢀ structureꢀ determinationꢀ onꢀ singleꢀ crystalsꢀ ofꢀ 2ꢀ
grownꢀfromꢀaꢀconcentratedꢀacetone-d6ꢀsolutionꢀ(Figureꢀ2).ꢀTheꢀ
neutralꢀbidentateꢀPN-ligandꢀandꢀasꢀanionicꢀtridentateꢀPNC-system,ꢀ
dependingꢀonꢀtheꢀreactionꢀconditions.ꢀBasedꢀonꢀtheseꢀinitialꢀresults,ꢀ
weꢀspeculatedꢀthatꢀtheꢀligand-basedꢀreactiveꢀcarbonꢀcenterꢀinꢀtheꢀ
I
geometryꢀ aroundꢀ eachꢀ Rh -centerꢀ isꢀ squareꢀ planarꢀ andꢀ theꢀ
2
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
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ꢀARTICLEꢀ
-
1
overallꢀ structuralꢀ featuresꢀ withꢀ theꢀ gem-dithiolateꢀ coreꢀ barrierꢀ7.2ꢀkcalꢀmol .ꢀThisꢀdihydrideꢀsubsequent
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-1
DOI: 10.1039/C5CY01505G
resembleꢀthoseꢀreportedꢀinꢀliterature. ꢀ
smoothꢀreductiveꢀeliminationꢀofꢀH2ꢀ(6.9ꢀkcalꢀmol ꢀbarrier)ꢀtoꢀ
-1
generateꢀ1ꢀasꢀstableꢀproductꢀ(∆Gꢀ=ꢀ-7.6ꢀkcalꢀmol ).ꢀAsꢀaꢀresult,ꢀ
thisꢀ cyclometalatedꢀ complexꢀ mayꢀ thusꢀ beꢀ aꢀ catalyticallyꢀ
competentꢀspeciesꢀforꢀreactionsꢀthatꢀinvolveꢀH2ꢀproduction.ꢀ
ꢀ
Figureꢀ2.ꢀORTEPꢀplotꢀ(50%ꢀdisplacementꢀellipsoids)ꢀforꢀcomplexꢀ2.ꢀSelectedꢀbondꢀ
lengthsꢀ(Å)ꢀandꢀanglesꢀ(°):ꢀRh
Rh -S23ꢀ2.3784(5);ꢀRh -P ꢀ2.3154(6);ꢀRh
.3948(5);ꢀRh …Rh ꢀ3.0845(2);ꢀP -Rh -S13ꢀ94.682(18);ꢀS13-Rh
Rh -S23ꢀ 93.690(19);ꢀ S13-Rh -S23ꢀ 82.642(18).ꢀ Angleꢀ sumsꢀ Rh
60.44(12)ꢀ°.ꢀDihedralꢀangleꢀbetweenꢀS-Rh-Sꢀplanes:ꢀ61.27(3)°.ꢀ
1
-P
1
ꢀ2.3163(5);ꢀRh
1
-C211ꢀ1.827(2);ꢀRh
-S13ꢀ2.3833(5);ꢀRh
-S23ꢀ82.762(18);ꢀP
2
:ꢀ 359.99(10);ꢀ Rh :ꢀ
1
-S13ꢀ2.3940(5);ꢀ
1
2
2
1
-C212ꢀ1.808(2);ꢀRh
2
2
-S23
ꢀ
ꢀ
2
1
2
1
1
1
2
-
0
Figureꢀ3.ꢀDFTꢀ(BP86,ꢀdef2-TZVP,ꢀdisp3)ꢀcalculatedꢀfreeꢀenergyꢀprofileꢀ(∆G 298Kꢀinꢀ
kcalꢀmol )ꢀofꢀhydrogenꢀformationꢀfromꢀhydrideꢀintermediateꢀA ,ꢀwithꢀmethylꢀ
insteadꢀofꢀtert-butylꢀgroups.ꢀ
2
2
1
-
1
Me
3
ꢀ
Similarꢀspectroscopicꢀobservationsꢀwereꢀmadeꢀwhenꢀreactingꢀ1ꢀ
ꢀ
Catalyticꢀdehydrogenationꢀofꢀformicꢀacid.ꢀToꢀcapitalizeꢀonꢀtheꢀ
apparentꢀ facileꢀ lossꢀ ofꢀ H2ꢀ fromꢀ putativeꢀ speciesꢀ Aꢀ inꢀ
combinationꢀwithꢀtheꢀpotentialꢀreactivityꢀofꢀtheꢀmetal-carbonꢀ
bondꢀinꢀaꢀmetal-ligandꢀbifunctionalꢀdehydrogenativeꢀcatalysisꢀ
andꢀ toꢀ illustrateꢀ theꢀ conceptꢀ ofꢀ reversibleꢀ metalationꢀ forꢀ
cooperativeꢀbondꢀactivation,ꢀweꢀstudiedꢀtheꢀdehydrogenationꢀ
ofꢀ formicꢀ acidꢀ asꢀ proof-of-principleꢀ reaction.ꢀ Additionꢀ ofꢀ 20ꢀ
molarꢀequivꢀHCOOHꢀtoꢀ1ꢀinꢀMeCNꢀinstantaneouslyꢀresultedꢀinꢀaꢀ
yellowꢀ complexꢀ thatꢀ canꢀ beꢀ characterizedꢀ asꢀ formateꢀ
25
withꢀbenzylꢀmercaptan. ꢀThisꢀbehaviourꢀisꢀstrikinglyꢀdifferentꢀ
fromꢀ theꢀ chemistryꢀ observedꢀ forꢀ Ni-complexesꢀ withꢀ
dearomatizedꢀ PNPꢀ ligands,ꢀ byꢀ virtueꢀ ofꢀ theꢀ tridentateꢀ ligandꢀ
2
2
I
coordination, ꢀalthoughꢀforꢀCu ,ꢀthisꢀPNPꢀscaffoldꢀwasꢀshownꢀ
23
toꢀadoptꢀaꢀdinucleatingꢀcoordinationꢀmode. ꢀBecauseꢀofꢀtheꢀ
decoordinationꢀ ofꢀ theꢀ pyridineꢀ fromꢀ theꢀ metal,ꢀ weꢀ didꢀ notꢀ
pursueꢀ catalyticꢀ (hydroaddition)ꢀ transformationsꢀ involvingꢀ
thiols,ꢀ asꢀ theꢀ proposedꢀ cooperativeꢀ natureꢀ ofꢀ reversibleꢀ
cyclometalationꢀisꢀaidedꢀbyꢀcloseꢀproximityꢀofꢀtheꢀC-Hꢀbondꢀtoꢀ
theꢀ metalꢀ byꢀ theꢀ directingꢀ forceꢀ ofꢀ theꢀ pyridineꢀ group.ꢀ Alsoꢀ
trifluoromethylsulfonamideꢀreactsꢀrapidlyꢀwithꢀtheꢀRh-Cꢀbondꢀ
31
1
derivativeꢀ4ꢀ(Schemeꢀ3).ꢀComplexꢀ4ꢀ( P:ꢀδꢀ105ꢀppm,ꢀ JRh-Pꢀ167ꢀ
Hz)ꢀisꢀtheꢀonlyꢀspeciesꢀpresentꢀatꢀr.t.,ꢀbutꢀuponꢀwarmingꢀtoꢀ55ꢀ
°Cꢀ inꢀ aꢀ closedꢀ NMRꢀ tube,ꢀ deep-redꢀ speciesꢀ 1ꢀ isꢀ regeneratedꢀ
withinꢀ 45ꢀ minutes.ꢀ Noꢀ traceꢀ ofꢀ remainingꢀ HCOOHꢀ wasꢀ
31
(
complexꢀ 3ꢀ atꢀ δꢀ 103.7ꢀ ppmꢀ ( JRhPꢀ =ꢀ 152ꢀ Hz).ꢀ Theꢀ combinedꢀ
Schemeꢀ2),ꢀwhichꢀresultedꢀinꢀaꢀ Pꢀshiftꢀforꢀtheꢀresultingꢀamideꢀ
1
observed,ꢀandꢀtheꢀformationꢀofꢀH2ꢀwasꢀdetectedꢀ(Figureꢀ4).ꢀ
ꢀ
spectroscopicꢀ dataꢀ areꢀ similarꢀ toꢀ previouslyꢀ reportedꢀ
R
21
Pd(CH3)( PN)(triflamide)ꢀspecies, ꢀsoꢀaꢀsimilarꢀgeometry,ꢀwithꢀ
theꢀ triflamideꢀ transꢀ toꢀ phosphorus,ꢀ isꢀ proposed,ꢀ althoughꢀ
singleꢀ crystallineꢀ materialꢀ couldꢀ notꢀ beꢀ obtainedꢀ forꢀ thisꢀ
compound.ꢀꢀ
ꢀ
DFTꢀ calculationsꢀ onꢀ H2ꢀ activationꢀ withꢀ 1.ꢀ Havingꢀ
I
demonstratedꢀ thatꢀ cyclometalatedꢀ Rh -systemꢀ 1ꢀ isꢀ reactiveꢀ
ꢀ
I
Schemeꢀ3.ꢀReactivityꢀofꢀRh ꢀcomplexꢀ1ꢀtowardꢀ10ꢀmolarꢀequivꢀofꢀHCOOH.ꢀꢀ
towardꢀ (weakly)ꢀ proticꢀ substrates,ꢀ weꢀ soughtꢀ toꢀ applyꢀ theꢀ
conceptꢀofꢀreversibleꢀcyclometalationꢀinꢀcooperativeꢀcatalysis.ꢀ
Speciesꢀ1ꢀappearedꢀstableꢀunderꢀanꢀH2ꢀatmosphereꢀ(20ꢀbar)ꢀatꢀ
r.t.,ꢀindicatingꢀaꢀrelativelyꢀhighꢀbarrierꢀforꢀheterolyticꢀcleavageꢀ
H
ofꢀH2,ꢀwhichꢀwouldꢀgenerateꢀputativeꢀspeciesꢀA,ꢀRh(H)(CO)(1 ).ꢀ
HeatingꢀanꢀNMRꢀsampleꢀforꢀ1ꢀhourꢀatꢀ70ꢀ°Cꢀunderꢀ35ꢀbarꢀofꢀH2ꢀ
didꢀ notꢀ resultꢀ inꢀ anyꢀ observableꢀ hydrideꢀ species.ꢀ Thisꢀ
‘
inertness’ꢀ towardꢀ heterolyticꢀ H2ꢀ activationꢀ canꢀ beꢀ takenꢀ asꢀ
indicationꢀthatꢀtheꢀreverseꢀreaction,ꢀi.e.ꢀH2ꢀevolutionꢀfromꢀCꢀtoꢀ
generateꢀ 1,ꢀ mayꢀ beꢀ aꢀ favourableꢀ pathway.ꢀ Toꢀ confirmꢀ thisꢀ
hypothesis,ꢀweꢀperformedꢀDFTꢀcalculationsꢀ(BP86,ꢀdef2-TVZP,ꢀ
disp3ꢀcorrections)ꢀonꢀmonohydrideꢀcomplexꢀAꢀ(Figureꢀ3).ꢀThisꢀ
speciesꢀ mayꢀ convert,ꢀ viaꢀ agosticꢀ intermediateꢀ Bꢀ andꢀ
subsequentꢀCPh-Hꢀoxidativeꢀaddition,ꢀtoꢀdihydrideꢀCꢀwithꢀaꢀlowꢀ
ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ3ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Ca tP al el ya ss ies ꢀ dS o cꢀ ni eo nt cꢀ a ed &j u sTt eꢀ mc ha rn g oi nl os gꢀ y
Page 4 of 9
ARTICLEꢀ
JournalꢀNameꢀ
Figureꢀ4.ꢀCatalyticꢀexperimentꢀ(0.02ꢀmmolꢀcat.ꢀ1,ꢀ0.4ꢀmmolꢀHCOOH,ꢀ2ꢀmLꢀMeCN,ꢀ
5
spectroscopyꢀ(right)ꢀoverꢀaꢀtime-spanꢀofꢀ45ꢀmin.ꢀNMRꢀspectraꢀareꢀstackedꢀunderꢀ
anꢀangleꢀofꢀ15°.ꢀ
1 31
5ꢀ°Cꢀ→ꢀ60ꢀ°C)ꢀinꢀ10mmꢀHP-NMRꢀtube,ꢀmonitoredꢀbyꢀ HꢀNMRꢀ(left)ꢀandꢀ PꢀNMRꢀ
View Article Online
DOI: 10.1039/C5CY01505G
UseꢀofꢀHCOODꢀresultedꢀinꢀselectiveꢀdeuterationꢀofꢀbothꢀortho-
C-Hꢀ groupsꢀ onꢀ theꢀ phenylꢀ ringꢀ inꢀ 1,ꢀ whichꢀ isꢀ inꢀ lineꢀ withꢀ
cooperativeꢀ activationꢀ ofꢀ FAꢀ overꢀ theꢀ Rh-Cꢀ bond.ꢀ Noꢀ
deuterationꢀ ofꢀ theꢀ methyleneꢀ spacerꢀ wasꢀ observedꢀ underꢀ
I
Figureꢀ 6.ꢀ Otherꢀ Rh ꢀ complexesꢀ thatꢀ wereꢀ studiedꢀ inꢀ theꢀ dehydrogenationꢀ ofꢀ
formicꢀacid.ꢀ
2
theseꢀconditions,ꢀasꢀconfirmedꢀbyꢀ HꢀNMRꢀstudies,ꢀexcludingꢀaꢀ
ꢀ
roleꢀ forꢀ thisꢀ reactiveꢀ siteꢀ duringꢀ turnover.ꢀ Smoothꢀ catalyticꢀ Mechanisticꢀconsiderations.ꢀBasedꢀonꢀtheseꢀcatalyticꢀresultsꢀ
dehydrogenationꢀofꢀHCOOHꢀwasꢀestablishedꢀusingꢀ0.5ꢀmol%ꢀofꢀ andꢀ supportedꢀ byꢀ DFTꢀ calculations,ꢀ twoꢀ catalyticꢀ cyclesꢀ areꢀ
speciesꢀ1ꢀinꢀdioxaneꢀatꢀ75ꢀ°C,ꢀwithꢀaꢀturnoverꢀfrequencyꢀ(TOF)ꢀ conceivableꢀ (Schemeꢀ 4).ꢀ Theꢀ firstꢀ intramolecularꢀ pathꢀ involvesꢀ
-1
-1
ofꢀ169ꢀmol⋅mol ⋅h ꢀ(seeꢀFigureꢀ5ꢀandꢀESI).ꢀAdditionꢀofꢀexternalꢀ reversibleꢀ cyclometalationꢀ asꢀ keyꢀ element.ꢀ Cooperativeꢀ activationꢀ
27
baseꢀ (NEt3)ꢀ didꢀ notꢀ affectꢀ theꢀ catalyticꢀ activity. ꢀ Catalystꢀ 1ꢀ ofꢀ formicꢀ acidꢀ overꢀ theꢀ reactiveꢀ Rh-Cꢀ fragmentꢀ toꢀ formꢀ formateꢀ
-
1
showedꢀ reproducibleꢀ performanceꢀ duringꢀ eightꢀ consecutiveꢀ speciesꢀ4ꢀproceedsꢀwithꢀaꢀmoderateꢀbarrierꢀofꢀ17.4ꢀkcalꢀmol .ꢀTheꢀ
3
0
runsꢀ (totalꢀ TONꢀ ofꢀ 1024).ꢀ Theꢀ gaseousꢀ fractionꢀ producedꢀ transitionꢀstateꢀforꢀaꢀconcertedꢀhydride-proton-transferꢀstep ꢀcouldꢀ
duringꢀ reactionꢀ wasꢀ analyzedꢀ byꢀ GCꢀ andꢀ noꢀ COꢀ wasꢀ foundꢀ notꢀbeꢀfound,ꢀmostꢀlikelyꢀbecauseꢀtheꢀhydrideꢀwouldꢀbeꢀlocatedꢀinꢀ
2
z
withinꢀ theꢀ detectionꢀ limitꢀ (δꢀ =ꢀ 10ꢀ ppm).ꢀ Althoughꢀ theꢀ TOFꢀ anꢀunfavourableꢀaxialꢀpositionꢀ(filledꢀd
ꢀorbital)ꢀatꢀRh.ꢀAlternatively,ꢀ
III
achievedꢀ isꢀ stillꢀ moderateꢀ underꢀ theseꢀ (unoptimized)ꢀ HCOOHꢀcouldꢀalsoꢀoxidativelyꢀaddꢀtoꢀformꢀaꢀRh ꢀintermediateꢀthatꢀ
conditions,ꢀ thisꢀ representsꢀ theꢀ firstꢀ exampleꢀ ofꢀ base-freeꢀ canꢀ undergoꢀ reductiveꢀ eliminationꢀ ofꢀ theꢀ CPh-Hꢀ bond.ꢀ Thisꢀ optionꢀ
I 27
formicꢀacidꢀdehydrogenationꢀusingꢀaꢀRh ꢀcomplex. ꢀ
couldꢀ notꢀ beꢀ ruledꢀ outꢀ byꢀ DFTꢀ calculations,ꢀ asꢀ chargedꢀ speciesꢀ
cannotꢀ beꢀ comparedꢀ toꢀ neutralꢀ speciesꢀ inꢀ gasꢀ phaseꢀ calculationsꢀ
-
1
(
seeꢀESI).ꢀRestingꢀstateꢀ4,ꢀwhichꢀliesꢀ-1.9ꢀkcalꢀmol ꢀlowerꢀinꢀenergyꢀ
thanꢀ1,ꢀconvertsꢀtoꢀmonohydrideꢀAꢀviaꢀrate-limitingꢀβ-Hꢀeliminationꢀ
-
1
(
18.2ꢀ kcalꢀ mol ꢀ relativeꢀ toꢀ 4)ꢀ concomitantꢀ withꢀ CO
2
ꢀ release.ꢀ
I
SubsequentꢀC-HꢀoxidativeꢀadditionꢀviaꢀtheꢀRh (C-H)ꢀagosticꢀspeciesꢀBꢀ
19
(
aꢀcloseꢀanalogueꢀofꢀaꢀpreviouslyꢀisolatedꢀcationicꢀderivative )ꢀandꢀ
III
2
facileꢀreleaseꢀofꢀH ꢀfromꢀRh ꢀintermediateꢀCꢀregeneratesꢀ1ꢀasꢀtheꢀ
activeꢀcatalyst.ꢀTheꢀreversibleꢀC-Hꢀmetalationꢀpathway,ꢀprovidingꢀaꢀ
hemilabileꢀarylꢀmoiety,ꢀisꢀalsoꢀproposedꢀtoꢀstabilizeꢀtheꢀRh-speciesꢀ
betweenꢀturnovers.ꢀ
ꢀ
Figureꢀ5.ꢀCatalyticꢀdehydrogenationꢀcurves.ꢀ
H
Controlꢀ experimentsꢀ usingꢀ complexꢀ 5ꢀ ([Rh(Cl)(CO)(PN ])ꢀ
H
bearingꢀ aꢀ bidentateꢀ PN ꢀ ligandꢀ (Figureꢀ 6),
20,21
ꢀ lackingꢀ theꢀ
flankingꢀphenylꢀarm,ꢀshowedꢀveryꢀlowꢀconversionꢀinꢀabsenceꢀofꢀ
base,ꢀlikelyꢀdueꢀtoꢀblockingꢀofꢀtheꢀfourthꢀcoordinationꢀsiteꢀbyꢀ
theꢀchlorideꢀligand.ꢀUponꢀadditionꢀofꢀoneꢀequivalentꢀofꢀstrongꢀ
H
baseꢀ toꢀ deprotonateꢀ theꢀ PN ꢀ ligand,ꢀ theꢀ systemꢀ showedꢀ aꢀ
similarꢀTOFꢀbutꢀaꢀdifferentꢀreactionꢀprofileꢀincludingꢀsignificantꢀ
substrateꢀ inhibition,ꢀ suggestingꢀ aꢀ differentꢀ catalyticꢀ pathwayꢀ
forꢀthisꢀcatalystꢀcomparedꢀtoꢀcomplexꢀ1ꢀ(Figureꢀ4).ꢀThisꢀspeciesꢀ
likelyꢀfollowsꢀaꢀpathwayꢀinvolvingꢀligandꢀ‘dearomatization’.ꢀTheꢀ
Schemeꢀ4.ꢀProposedꢀmechanismꢀforꢀtheꢀbase-freeꢀcooperativeꢀdehydrogenationꢀ
ofꢀ formicꢀ acidꢀ usingꢀ 1ꢀ asꢀ catalyst.ꢀ Theꢀ DFTꢀ calculatedꢀ valuesꢀ forꢀ theꢀ relativeꢀ
I
28
-1
knownꢀ Rh -pincerꢀ complexesꢀ [Rh(CO)(PNN*)] ꢀ (6)ꢀ andꢀ transitionꢀstateꢀbarriersꢀareꢀshownꢀinꢀkcalꢀmol .ꢀꢀ
2
9
[
Rh(CO)(PCP)] ꢀ(7)ꢀ(PNN*ꢀ=ꢀ6-di(tert-butyl)phosphinomethine-
,2’-bipyridine;ꢀ seeꢀ Figureꢀ 5)ꢀ barelyꢀ gaveꢀ activity,ꢀ suggestingꢀ
thatꢀlow-coordinateꢀgeometriesꢀandꢀtheꢀpresenceꢀofꢀaꢀligandꢀ
Aꢀ second,ꢀ non-cooperative,ꢀ pathꢀ hasꢀ veryꢀ similarꢀ reactionꢀ
barriersꢀandꢀsharesꢀtheꢀsameꢀrate-limitingꢀstepꢀ(fromꢀ4ꢀtoꢀA),ꢀ
followedꢀbyꢀoxidativeꢀadditionꢀofꢀaꢀsecondꢀmoleculeꢀofꢀHCOOHꢀ
2
-1
withꢀadaptableꢀdenticityꢀareꢀimportant.ꢀ
ꢀ
toꢀ formꢀ dihydrideꢀ intermediateꢀ D,ꢀ whichꢀ liesꢀ 0.8ꢀ kcalꢀ mol ꢀ
higherꢀ inꢀ energyꢀ thanꢀ A.ꢀ Dihydrideꢀ Dꢀ generatesꢀ H2ꢀ viaꢀ
-1
reductiveꢀeliminationꢀwithꢀaꢀTSꢀbarrierꢀofꢀ5.3ꢀkcalꢀmol .ꢀGivenꢀ
theꢀnear-identicalꢀoverallꢀreactionꢀprofilesꢀ(withꢀaꢀsharedꢀrateꢀ
-1
limitingꢀstepꢀwithꢀaꢀbarrierꢀofꢀ~18ꢀkcalꢀmol ),ꢀbothꢀmechanismsꢀ
likelyꢀ areꢀ catalyticallyꢀ competentꢀ andꢀ thusꢀ co-existꢀ underꢀ
4
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Page 5 of 9
Ca tP al el ya ss ies ꢀ dS o cꢀ ni eo nt cꢀ a ed &j u sTt eꢀ mc ha rn g oi nl os gꢀ y
JournalꢀNameꢀ
catalyticꢀconditions,ꢀregeneratingꢀredꢀspeciesꢀ1ꢀduringꢀand/orꢀ PC(CH
ꢀARTICLEꢀ
-
1
3
)
3
).ꢀ IRꢀ (ATR,ꢀ cm ):ꢀ vCOꢀ 1938.ꢀ HRMSꢀ (FD):ꢀ mVie
/
w
zꢀAr
c
t
a
ic
l
lecd
O
ꢀ
nl
f
in
o
e
rꢀ
+
DOI: 10.1039/C5CY01505G
afterꢀ catalysis.ꢀ Theꢀ involvementꢀ ofꢀ theꢀ cooperativeꢀ pathꢀ isꢀ
supportedꢀ byꢀ selectiveꢀ deuterationꢀ experiments,ꢀ isolationꢀ ofꢀ
C
ꢀ
44
H
62
N
2
OP
2
Rh
2
S
2
:ꢀ966.18888ꢀ[M-CO] ;ꢀfound:ꢀ966.18386.ꢀ
19
2
H
anꢀagosticꢀC-Hꢀmodelꢀcomplexꢀasꢀaꢀrelevantꢀintermediate, ꢀtheꢀ Complexꢀ3,ꢀRh(NHSO CF )(CO)(κ -P,N-1 )ꢀ
2
3
spectroscopicꢀ observationꢀ ofꢀ 4ꢀ inꢀ theꢀ presenceꢀ ofꢀ 10ꢀ Toꢀ aꢀ solutionꢀ ofꢀ 1ꢀ (12ꢀ mg,ꢀ 27ꢀ µmol)ꢀ inꢀ CH Cl ꢀ (1ꢀ mL)ꢀ wasꢀ addedꢀ
equivalentsꢀofꢀformicꢀacid,ꢀfollowedꢀbyꢀregenerationꢀofꢀ1ꢀwithꢀ
conversionꢀofꢀHCOOHꢀandꢀreleaseꢀofꢀH2.ꢀꢀ
2
2
trifluoromethylsulfonamideꢀ (4ꢀ mg,ꢀ 27ꢀ µmol),ꢀ resultingꢀ inꢀ aꢀ colorꢀ
changeꢀfromꢀredꢀtoꢀorangeꢀwithinꢀ5ꢀmin.ꢀatꢀroomꢀtemperature.ꢀTheꢀ
1
solventꢀwasꢀevaporatedꢀtoꢀyieldꢀ3ꢀinꢀquantitativeꢀyieldꢀ(16ꢀmg).ꢀ Hꢀ
NMRꢀ(300ꢀMHz,ꢀ298ꢀK,ꢀCD
t,ꢀJꢀ=ꢀ7.8ꢀHz,ꢀ1H,ꢀPy),ꢀ7.68ꢀ–ꢀ7.59ꢀ(m,ꢀ3H,ꢀPh),ꢀ7.52ꢀ(t,ꢀJꢀ=ꢀ8.3ꢀHz,ꢀ2H,ꢀ
Py),ꢀ3.75ꢀ(d,ꢀJꢀ=ꢀ9.3ꢀHz,ꢀ2H,ꢀCH P),ꢀ1.41ꢀ(d,ꢀJꢀ=ꢀ14.1ꢀHz,ꢀ18H,ꢀPtBu ),ꢀ
.14ꢀ(s,ꢀ1H,ꢀNH).ꢀ PꢀNMRꢀ(121ꢀMHz,ꢀ298ꢀK,ꢀCD Cl ,ꢀppm):ꢀδꢀ103.70ꢀ
Cl ,ꢀppm):ꢀδꢀ-78.68ꢀ.ꢀ
,ꢀppm):ꢀδꢀ189.59ꢀ(dd,ꢀJRhCꢀ=ꢀ75.5ꢀHz,ꢀ
CPꢀ=ꢀ17.7ꢀHz,ꢀCO),ꢀ161.58ꢀ(s,ꢀPy-C),ꢀ161.50ꢀ(dd,ꢀJꢀ=ꢀ4.7,ꢀ1.8ꢀHz,ꢀPy-C),ꢀ
2 2
Cl ,ꢀppm):ꢀδꢀ8.20ꢀ–ꢀ8.12ꢀ(m,ꢀ2H,ꢀPh),ꢀ7.90ꢀ
Conclusionsꢀ
(
Inꢀ summary,ꢀ weꢀ haveꢀ shownꢀ thatꢀ reversibleꢀ cyclometalationꢀ
mayꢀbeꢀsuccessfullyꢀemployedꢀasꢀmotifꢀforꢀcooperativeꢀbondꢀ
activationꢀprocesses.ꢀComplexꢀ1ꢀreadilyꢀreactsꢀwithꢀthiolsꢀandꢀ
2
2
31
19
1
2
2
(
d,ꢀJꢀ=ꢀ152.0ꢀHz).ꢀ FꢀNMRꢀ(282ꢀMHz,ꢀ298ꢀK,ꢀCD
2
2
activatedꢀ amines,ꢀ whichꢀ leadsꢀ toꢀ protonationꢀ ofꢀ theꢀ anionicꢀ 13
2 2
CꢀNMRꢀ(75ꢀMHz,ꢀ298ꢀK,ꢀCD Cl
31
carbonꢀofꢀtheꢀreactiveꢀflexidentate ꢀligandꢀL.ꢀDFTꢀcalculationsꢀ
showꢀ thatꢀ releaseꢀ ofꢀ dihydrogenꢀ isꢀ facileꢀ fromꢀ aꢀ putativeꢀ
monohydrideꢀcomplexꢀA.ꢀReactionꢀofꢀcyclometalatedꢀcomplexꢀ
J
1
1
1
3
39.03ꢀ (s,ꢀ Py-CHꢀ andꢀ Ph-C),ꢀ 130.57ꢀ (s,ꢀ Ph-CH),ꢀ 128.62ꢀ (s,ꢀ Ph-CH),ꢀ
28.52ꢀ(s,ꢀPh-CH),ꢀ124.17ꢀ(s,ꢀPy-CH),ꢀ121.48ꢀ(d,ꢀJꢀ=ꢀ9.2ꢀHz,ꢀPy-CH),ꢀ
1
4
ꢀwithꢀaꢀsmallꢀexcessꢀofꢀformicꢀacidꢀresultsꢀinꢀformateꢀadductꢀ
.ꢀToꢀdemonstrateꢀtheꢀpotentialꢀofꢀreversibleꢀcyclometalationꢀ
20.88ꢀ(q,ꢀJCFꢀ=ꢀ325.5ꢀHz,ꢀCF
4.78ꢀ(d,ꢀJꢀ=ꢀ20.1ꢀHz,ꢀPC(CH
3
),ꢀ35.32ꢀ(dd,ꢀJꢀ=ꢀ20.8,ꢀ2.3ꢀHz,ꢀCH
2
P),ꢀ
3
)
3
),ꢀ28.92ꢀ(d,ꢀJꢀ=ꢀ4.2ꢀHz,ꢀPC(CH ).ꢀIRꢀ
3 3
)
inꢀ metal-ligandꢀ bifunctionalꢀ catalysis,ꢀ weꢀ haveꢀ successfullyꢀ
I
employedꢀ Rh ꢀcatalystꢀ1ꢀinꢀtheꢀbase-freeꢀdehydrogenationꢀofꢀ
-1
-1
(ATR,ꢀ cm ):ꢀ v ꢀ 1973ꢀ cm .ꢀ HRMSꢀ (FD):ꢀ m/zꢀ calcdꢀ forꢀ
CO
+
C
ꢀ
22 30 3 2 3
H F N O PRhS:ꢀ593.07219ꢀ[M] ;ꢀfound:ꢀ593.07219.ꢀ
formicꢀ acid.ꢀ Experimentalꢀ observationsꢀ inꢀ combinationꢀ withꢀ
DFTꢀ studiesꢀ supportꢀ aꢀ cooperativeꢀ modeꢀ ofꢀ actionꢀ basedꢀ onꢀ
reversibleꢀcyclometalationꢀasꢀaꢀfeasibleꢀmechanism.ꢀ
2
H
Complexꢀ4,ꢀRh(OCH(O)(CO)(κ -P,N-1 )ꢀ
Toꢀ aꢀ solutionꢀ ofꢀ 1ꢀ (4.4ꢀ mg,ꢀ 10ꢀ µmol)ꢀ inꢀ CDCl3ꢀ (0.6ꢀ mL)ꢀ wasꢀ
addedꢀ formicꢀ acidꢀ (9.2ꢀ mg,ꢀ 200ꢀ µmol),ꢀ resultingꢀ inꢀ anꢀ
immediateꢀ colorꢀ changeꢀ fromꢀ redꢀ toꢀ yellowꢀ atꢀ roomꢀ
temperature.ꢀDueꢀtoꢀitsꢀunstableꢀnature,ꢀthisꢀspeciesꢀwasꢀonlyꢀ
Experimentalꢀ
Generalꢀconsiderationsꢀ
1
characterizedꢀ inꢀ situꢀ usingꢀ NMRꢀ spectroscopy.ꢀ Hꢀ NMRꢀ (400ꢀ
MHz,ꢀ298ꢀK,ꢀCDCl3,ꢀppm):ꢀδꢀ8.01–7.94ꢀ(m,ꢀ2H,ꢀo-Ph),ꢀ7.82ꢀ(ddd,ꢀ
Jꢀ=ꢀ7.8,ꢀ7.8,ꢀ1.0ꢀHz,ꢀ1H,ꢀPy),ꢀ7.57–7.39ꢀ(m,ꢀ5H,ꢀ2Py,ꢀm-Ph,ꢀp-Ph),ꢀ
Allꢀ reactionsꢀ wereꢀ carriedꢀ outꢀ underꢀ anꢀ atmosphereꢀ ofꢀ nitrogenꢀ
usingꢀstandardꢀSchlenkꢀtechniques.ꢀReagentsꢀwereꢀpurchasedꢀfromꢀ
commercialꢀ suppliersꢀ andꢀ usedꢀ withoutꢀ furtherꢀ purification.ꢀ THF,ꢀ
2
3
.73ꢀ(d,ꢀ JP-Hꢀ=ꢀ9.6ꢀHz,ꢀ2H),ꢀ1.38ꢀ(d,ꢀ JP-Hꢀ=ꢀ14.3ꢀHz,ꢀ18H).ꢀ Pꢀ
31
3
NMRꢀ(162ꢀMHz,ꢀ298ꢀK,ꢀCDCl3,ꢀppm):ꢀδꢀ105.29ꢀ(d,ꢀJRh-Pꢀ=ꢀ166.8ꢀ
pentane,ꢀ hexaneꢀ andꢀ Et
benzophenoneꢀketyl.ꢀCH Cl ꢀwasꢀdistilledꢀfromꢀCaH
sodiumꢀunderꢀnitrogen.ꢀNMRꢀspectraꢀ( H,ꢀ H{ P},ꢀ P,ꢀ P{ H},ꢀ P- Hꢀ
2
Oꢀ wereꢀ distilledꢀ fromꢀ sodiumꢀ
2
2
2
,ꢀtolueneꢀfromꢀ
1
1
31
31 31
1
31
1
Hz).ꢀ
ꢀ
13
1
andꢀ C{ H})ꢀwereꢀmeasuredꢀonꢀaꢀBrukerꢀDRXꢀ500,ꢀBrukerꢀAVꢀ400,ꢀ
Brukerꢀ DRXꢀ 300ꢀ orꢀ onꢀ aꢀ Brukerꢀ AVꢀ 300ꢀ spectrometer.ꢀ IRꢀ spectraꢀ
2
Complexꢀ6,ꢀRh(Cl)(CO)(κ -P,N-2-methyl-6-((di-tert-
butylphosphino)-methyl)pyridine))ꢀ
(
ATRꢀ mode)ꢀ wereꢀ recordedꢀ withꢀ aꢀ Brukerꢀ Alpha-pꢀ FT-IRꢀ
Toꢀ aꢀ solutionꢀ ofꢀ 2-methyl-6-((di-tert-butylphosphino)methyl)-
pyridineꢀ(0.025ꢀg,ꢀ0.010ꢀmmol)ꢀinꢀCH2Cl2ꢀ(0.5ꢀmL)ꢀwasꢀaddedꢀaꢀ
solutionꢀofꢀ[Rh(CO)2(µ-Cl)]2ꢀ(0.019ꢀg,ꢀ0.005ꢀmmol)ꢀinꢀCH2Cl2ꢀ(2ꢀ
mL)ꢀ andꢀ theꢀ reactionꢀ mixtureꢀ wasꢀ stirredꢀ overnight.ꢀ Afterꢀ
evaporationꢀ ofꢀ theꢀ solvent,ꢀ theꢀ productꢀ wasꢀ washedꢀ withꢀ
spectrometer.ꢀ Highꢀ resolutionꢀ massꢀ spectraꢀ wereꢀ recordedꢀ onꢀ aꢀ
JMS-T100GCVꢀmassꢀspectrometerꢀusingꢀfieldꢀdesorptionꢀ(FD).ꢀ
1
H
Complexꢀ2,ꢀRh
2
(SCH
2
CH
2
CH
2
S)(CO)
2
(κ -P-1 )
Cl
2
ꢀ
Toꢀaꢀsolutionꢀofꢀ1ꢀ(10ꢀmg,ꢀ23ꢀµmol)ꢀinꢀCH
2
2
ꢀ(1ꢀmL)ꢀwasꢀaddedꢀ1,3-
pentaneꢀ(1ꢀmL),ꢀyieldingꢀtheꢀdesiredꢀcomplexꢀasꢀyellowꢀpowderꢀ
(
propanedithiolꢀ (1.1ꢀ µL,ꢀ 23ꢀ µmol),ꢀ resultingꢀ inꢀ anꢀ immediateꢀ colorꢀ
changeꢀ fromꢀ redꢀ toꢀ darkꢀ yellow.ꢀ Theꢀ solventꢀ wasꢀ evaporatedꢀ toꢀ
1
0.038ꢀ g,ꢀ 0.092ꢀ mmol,ꢀ 92%).ꢀ Hꢀ NMRꢀ (300ꢀ MHz,ꢀ 298ꢀ K,ꢀ
1
acetone-d6,ꢀppm):ꢀδꢀ7.77ꢀ(t,ꢀJꢀ=ꢀ7.7ꢀHz,ꢀ1H,ꢀPy),ꢀ7.46ꢀ(d,ꢀJꢀ=ꢀ7.7ꢀ
2
Hz,ꢀ1H,ꢀPy),ꢀ7.23ꢀ(d,ꢀJꢀ=ꢀ7.7ꢀHz,ꢀ1H,ꢀPy),ꢀ3.93ꢀ(d,ꢀ JP-Hꢀ=ꢀ9.6ꢀHz,ꢀ
yieldꢀ 2ꢀ inꢀ quantitativeꢀ yieldꢀ (11ꢀ mg).ꢀ Hꢀ NMRꢀ (300ꢀ MHz,ꢀ 298ꢀ K,ꢀ
CD
2
Cl
2
,ꢀppm):ꢀδꢀ8.44ꢀ(d,ꢀJꢀ=ꢀ6.3ꢀHz,ꢀ2H),ꢀ8.14ꢀ–ꢀ8.07ꢀ(m,ꢀ4H),ꢀ7.63ꢀ–ꢀ
2
H,ꢀCH2P),ꢀ3.10ꢀ(s,ꢀ3H,ꢀPy-CH3),ꢀ1.32ꢀ(d,ꢀ JP-Hꢀ=ꢀ13.9ꢀHz,ꢀ18H,ꢀ
2
7
.40ꢀ(m,ꢀ10H),ꢀ4.21ꢀ–ꢀ3.82ꢀ(m,ꢀ4H),ꢀ2.95ꢀ–ꢀ2.69ꢀ(m,ꢀ4H),ꢀ2.42ꢀ–ꢀ2.30ꢀ
31
CH3)CP).ꢀ PꢀNMRꢀ(121ꢀMHz,ꢀ298ꢀK,ꢀCDCl3,ꢀppm):ꢀδꢀ106.12ꢀ(d,ꢀ
(
1
31
(
m,ꢀ2H),ꢀ1.53ꢀ(d,ꢀJꢀ=ꢀ12.7ꢀHz,ꢀ18H),ꢀ1.41ꢀ(d,ꢀJꢀ=ꢀ12.9ꢀHz,ꢀ18H).ꢀ Pꢀ
13
JRh-Pꢀ=ꢀ165.0ꢀHz).ꢀ CꢀNMRꢀ(75ꢀMHz,ꢀ298ꢀK,ꢀacetone-d6,ꢀppm):ꢀδꢀ
13
NMRꢀ(121ꢀMHz,ꢀ298ꢀK,ꢀCD
2
Cl
,ꢀppm):ꢀδꢀ190.58ꢀ(dd,ꢀJRhCꢀ=ꢀꢀ73.4ꢀHz,ꢀJCP
ꢀ14.9ꢀHz,ꢀCO),ꢀ157.28ꢀ(s,ꢀPy-C),ꢀ155.81ꢀ(s,ꢀPy-C),ꢀ139.48ꢀ(s,ꢀPh-C),ꢀ
36.22ꢀ(s,ꢀPy-CH),ꢀ128.71ꢀ(s,ꢀPh-CH),ꢀ128.58ꢀ(s,ꢀ2C,ꢀPh-CH),ꢀ126.75ꢀ
2
,ꢀppm):ꢀδꢀ69.75ꢀ(d,ꢀJꢀ=ꢀ151.7ꢀHz).ꢀ Cꢀ
1
=
9
3
91.85ꢀ(dd,ꢀJꢀ=ꢀ73.4,ꢀ14.5ꢀHz,ꢀCO),ꢀ163.78ꢀ(s,ꢀPy-C),ꢀ162.52ꢀ(d,ꢀJꢀ
ꢀ3.9ꢀHz,ꢀPy-C),ꢀ139.74ꢀ(s,ꢀPy-CH),ꢀ124.56ꢀ(Py-CH),ꢀ121.46ꢀ(d,ꢀJꢀ=ꢀ
NMRꢀ(75ꢀMHz,ꢀ298ꢀK,ꢀCD
2
Cl
2
ꢀ
1
2
=
1
.0ꢀ Hz,ꢀ Py-CH),ꢀ 36.05ꢀ (dd,ꢀ JC-Pꢀ =ꢀ 20.3,ꢀ JRh-Cꢀ =ꢀ 2.3ꢀ Hz,ꢀ CH2P),ꢀ
1
2
5.42ꢀ (dꢀ JC-Pꢀ =ꢀ 20.7ꢀ Hz,ꢀ PC(CH3)3),ꢀ 29.48ꢀ (d,ꢀ JC=Pꢀ =ꢀ 4.5ꢀ Hz,ꢀ
-1
(
(
s,ꢀ2C,ꢀPh-CH),ꢀ124.71ꢀ(d,ꢀJꢀ=ꢀ2.8ꢀHz,ꢀPy-CH),ꢀ117.89ꢀ(s,ꢀPy-CH),ꢀ38.67ꢀ PC(CH ) ),ꢀ 28.19ꢀ (s,ꢀ Py-CH ).ꢀ IRꢀ (ATR,ꢀ cm ):ꢀ ν ꢀ 1958.ꢀ
3 3 3 CO
+
s,ꢀSCH
2
CH
2
),ꢀ37.31ꢀ(d,ꢀJꢀ=ꢀ16.2ꢀHz,ꢀPC(CH
3 3
16 26
) ),ꢀ36.93ꢀ(dd,ꢀJꢀ=ꢀ15.7,ꢀ1.3ꢀ HRMS(FD):ꢀm/zꢀcalcdꢀC H ClNOPRh:ꢀ417.04956ꢀ[M] ;ꢀfound:ꢀ
Hz,ꢀCH
2
P),ꢀ31.71ꢀ(d,ꢀJꢀ=ꢀ13.0ꢀHz,ꢀSCH
2
CH ),ꢀ30.16ꢀ(dd,ꢀJꢀ=ꢀ17.4,ꢀ3.8ꢀHz,ꢀ 417.04984.ꢀ
2
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ5ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Ca tP al el ya ss ies ꢀ dS o cꢀ ni eo nt cꢀ a ed &j u sTt eꢀ mc ha rn g oi nl os gꢀ y
Page 6 of 9
ARTICLEꢀ
JournalꢀNameꢀ
ꢀ
Catalyticꢀdehydrogenationꢀexperimentsꢀ
ewꢀ i
Article On e
frequencyꢀ inꢀ bothꢀ directionsꢀ (IRC).ꢀ Allꢀ minimaꢀ (nVio maginalinryꢀ
DOI: 10.1039/C5CY01505G
frequencies)ꢀ andꢀ transitionꢀ statesꢀ (oneꢀ imaginaryꢀ frequency)ꢀ
wereꢀcharacterizedꢀbyꢀcalculatingꢀtheꢀHessianꢀmatrix.ꢀZPEꢀandꢀ
gas-phaseꢀthermalꢀcorrectionsꢀ(entropyꢀandꢀenthalpy,ꢀ298ꢀK,ꢀ1ꢀ
bar)ꢀ fromꢀ theseꢀ analysesꢀ wereꢀ calculatedꢀ usingꢀ standardꢀ
thermodynamics.ꢀ
Inꢀaꢀtypicalꢀexperiment,ꢀcompoundꢀ1ꢀ(10ꢀμmol)ꢀwasꢀaddedꢀtoꢀ
theꢀ solventꢀ (1ꢀ mL)ꢀ inꢀ aꢀ 5ꢀ mLꢀ Schlenkꢀ equippedꢀ withꢀ aꢀ
condenserꢀandꢀconnectedꢀtoꢀaꢀwaterꢀreplacementꢀset-up.ꢀTheꢀ
reactionꢀmixtureꢀwasꢀheatedꢀtoꢀtheꢀdesiredꢀtemperatureꢀ(e.g.ꢀ
ꢀ
7
5ꢀ°C)ꢀandꢀstirredꢀforꢀ10ꢀminutes.ꢀFormicꢀacidꢀ(75ꢀμL,ꢀ2ꢀmmol)ꢀ
orꢀtheꢀazeotropeꢀHCOOH/NEt3ꢀ(187ꢀμL,ꢀ2ꢀmmolꢀHCOOH)ꢀwasꢀ
addedꢀ toꢀ theꢀ reactionꢀ mixtureꢀ andꢀ theꢀ evolvedꢀ gasꢀ wasꢀ
collected.ꢀ Inꢀ theꢀ caseꢀ ofꢀ complexꢀ RhCl(CO)(PN),ꢀ firstꢀ oneꢀ
Acknowledgementsꢀ
equivalentꢀofꢀpotassiumꢀtert-butoxideꢀinꢀTHFꢀ(1M)ꢀwasꢀaddedꢀ ThisꢀworkꢀwasꢀfundedꢀbyꢀtheꢀEuropeanꢀResearchꢀCouncilꢀ(ERC,ꢀ
atꢀr.t.ꢀtoꢀabstractꢀtheꢀchlorideꢀligand.ꢀAfterꢀstirringꢀthisꢀmixtureꢀ StartingꢀGrantꢀ279097,ꢀEuReCatꢀtoꢀJ.I.v.d.V.).ꢀWeꢀthankꢀSanderꢀ
forꢀ5ꢀmin,ꢀ75ꢀμLꢀHCOOHꢀwasꢀadded.ꢀTheꢀmixtureꢀwasꢀrapidlyꢀ Oldenhofꢀ forꢀ usefulꢀ discussionsꢀ andꢀ practicalꢀ tipsꢀ onꢀ FAꢀ
heatedꢀtoꢀ75ꢀ°Cꢀandꢀtheꢀevolvedꢀgasꢀwasꢀcollected.ꢀTheꢀsetupꢀ dehydrogenationꢀchemistry,ꢀEdꢀZuidingaꢀforꢀMSꢀmeasurementsꢀ
wasꢀ calibratedꢀ withꢀ aꢀ Brooksꢀ flowmeterꢀ typeꢀ 1054-3Cꢀ andꢀ andꢀChristopheꢀRebreyendꢀandꢀSandraꢀdeꢀBoerꢀforꢀsupplyingꢀ
evolvedꢀ gasesꢀ wereꢀ analyzedꢀ withꢀ aꢀ G·A·Sꢀ Compactꢀ GCꢀ (Rt- compoundsꢀ7ꢀandꢀ8,ꢀrespectively.ꢀTheꢀX-rayꢀdiffractometerꢀatꢀ
MSieveꢀ5Aꢀ20ꢀmꢀ×ꢀ0.32ꢀmmꢀ+ꢀRt-Q-bondꢀ2ꢀmꢀ×ꢀ0.32ꢀmm).ꢀꢀ
ꢀ
X-rayꢀcrystalꢀstructureꢀdeterminationꢀofꢀcomplexꢀ2ꢀ
UtrechtꢀUniversityꢀwasꢀfundedꢀbyꢀNWO.ꢀ
Notesꢀandꢀreferencesꢀ
C45H62N2O2P2RhS2,ꢀ Fwꢀ =ꢀ 994.85,ꢀ yellowꢀ block,ꢀ 0.25ꢀ ×ꢀ 0.19ꢀ ×ꢀ
3
.09ꢀ mm ,ꢀ monoclinic,ꢀ P21/nꢀ (no.ꢀ 14),ꢀ aꢀ =ꢀ 12.7487(4),ꢀ bꢀ =ꢀ
1
Reviews:ꢀD.ꢀL.ꢀJ.ꢀBroere,ꢀR.ꢀPlessiusꢀandꢀJ.ꢀI.ꢀvanꢀderꢀVlugt,ꢀ
Chem.ꢀ Soc.ꢀ Rev.,ꢀ 2015,ꢀ 44,ꢀ 6886-6915;ꢀ D.ꢀ Milstein,ꢀ Phil.ꢀ
Trans.ꢀ R.ꢀ Soc.ꢀ A,ꢀ 2015,ꢀ 373,ꢀ 20140189;ꢀ O.ꢀ R.ꢀ Luca,ꢀ R.ꢀ H.ꢀ
Crabtree,ꢀChem.ꢀSoc.ꢀRev.,ꢀ2013,ꢀ42,ꢀ1440-1459;ꢀJ.ꢀI.ꢀvanꢀderꢀ
Vlugt,ꢀ Eur.ꢀ J.ꢀ Inorg.ꢀ Chem.,ꢀ 2012,ꢀ 363-375;ꢀ V.ꢀ Lyaskovskyyꢀ
andꢀB.ꢀdeꢀBruin,ꢀACSꢀCatal.,ꢀ2012,ꢀ2,ꢀ270-279;ꢀT.ꢀIkariya,ꢀTop.ꢀ
Organomet.ꢀ Chem.,ꢀ 2011,ꢀ 37,ꢀ 31-54;ꢀ d)ꢀ D.ꢀ Milstein,ꢀ Top.ꢀ
Catal.,ꢀ2010,ꢀ53,ꢀ915-923.ꢀ
0
1
9.7725(6),ꢀcꢀ=ꢀ18.4361(5)ꢀÅ,ꢀβꢀ=ꢀ103.046(1)ꢀ°,ꢀVꢀ=ꢀ4527.3(2)ꢀ
3
3
-1
Å ,ꢀZꢀ=ꢀ4,ꢀDxꢀ=ꢀ1.460ꢀg/cm ,ꢀµꢀ=ꢀ0.93ꢀmm .ꢀ60826ꢀReflectionsꢀ
wereꢀmeasuredꢀonꢀaꢀBrukerꢀKappaꢀApexIIꢀdiffractometerꢀwithꢀ
sealedꢀtubeꢀandꢀTriumphꢀmonochromatorꢀ(λꢀ=ꢀ0.71073ꢀÅ)ꢀatꢀaꢀ
temperatureꢀ ofꢀ 150(2)ꢀ Kꢀ upꢀ toꢀ aꢀ resolutionꢀ ofꢀ (sinꢀ θ/λ)maxꢀ =ꢀ
-1
0.65ꢀÅ .ꢀX-rayꢀintensitiesꢀwereꢀmeasuredꢀonꢀaꢀBrukerꢀKappaꢀ
ApexIIꢀ diffractometerꢀ withꢀ sealedꢀ tubeꢀ andꢀ Triumphꢀ
monochromatorꢀ(λꢀ=ꢀ0.71073ꢀÅ)ꢀatꢀaꢀtemperatureꢀofꢀ150(2)ꢀK.ꢀ
2
Reviews:ꢀJ.ꢀI.ꢀvanꢀderꢀVlugtꢀandꢀJ.ꢀN.ꢀH.ꢀReek,ꢀAngew.ꢀChem.ꢀ
Int.ꢀEd.,ꢀ2009,ꢀ48,ꢀ8832-8846;ꢀC.ꢀGunanathanꢀandꢀD.ꢀMilstein,ꢀ
Acc.ꢀ Chem.ꢀ Res.,ꢀ 2011,ꢀ 44,ꢀ 588-602;ꢀ C.ꢀ Gunanathanꢀ andꢀ D.ꢀ
Milstein,ꢀ Chem.ꢀ Rev.,ꢀ 2014,ꢀ 114,ꢀ 12024-12087;ꢀ J.ꢀ R.ꢀ
KhusnutdinovaꢀandꢀD.ꢀMilstein,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.ꢀ2015,ꢀ
32
Theꢀ intensitiesꢀ wereꢀ integratedꢀ withꢀ theꢀ Eval15ꢀ software. ꢀ
Multi-scanꢀ absorptionꢀ correctionꢀ andꢀ scalingꢀ wasꢀ performedꢀ
5
4,ꢀ12236-12273.ꢀ
H.ꢀLi,ꢀB.ꢀZheng,ꢀK.-W.ꢀHuang,ꢀCoord.ꢀChem.ꢀRev.,ꢀ2015,ꢀ293-
94,ꢀ 116-138;ꢀ B.ꢀ Bichler,ꢀ C.ꢀ Holzhacker,ꢀ B.ꢀ Stöger,ꢀ M.ꢀ
Puchberger,ꢀL.ꢀF.ꢀVeiros,ꢀK.ꢀKirchner,ꢀOrganometallics,ꢀ2013,ꢀ
2,ꢀ 4114-4121;ꢀ D.ꢀ Benit-Garagorri,ꢀ K.ꢀ Kirchner,ꢀ Acc.ꢀ Chem.ꢀ
33
withꢀSADABS ꢀ(correctionꢀrangeꢀ0.67-0.75).ꢀ10392ꢀReflectionsꢀ
wereꢀ uniqueꢀ (Rintꢀ =ꢀ 0.039),ꢀ ofꢀ whichꢀ 8330ꢀ wereꢀ observedꢀ
3
4
2
[
superpositionꢀ methodsꢀ usingꢀ SHELXT. ꢀ Least-squaresꢀ
I>2σ(I)].ꢀ Theꢀ structureꢀ wasꢀ solvedꢀ withꢀ Pattersonꢀ
34
3
35
2
Res.,ꢀ2008,ꢀ41,ꢀ201-213.ꢀ
refinementꢀwasꢀperformedꢀwithꢀSHELXL-97 ꢀagainstꢀF ꢀofꢀallꢀ
reflections.ꢀ Non-hydrogenꢀ atomsꢀ wereꢀ refinedꢀ freelyꢀ withꢀ
anisotropicꢀ displacementꢀ parameters.ꢀ Allꢀ hydrogenꢀ atomsꢀ
wereꢀ locatedꢀ inꢀ differenceꢀ Fourierꢀ mapsꢀ andꢀ refinedꢀ withꢀ aꢀ
ridingꢀmodel.ꢀ508ꢀParametersꢀwereꢀrefinedꢀwithꢀnoꢀrestraints.ꢀ
R1/wR2ꢀ[Iꢀ>ꢀ2σ(I)]:ꢀ0.0255ꢀ/ꢀ0.0542.ꢀR1/wR2ꢀ[allꢀrefl.]:ꢀ0.0396ꢀ/ꢀ
Overview:ꢀ W-H.ꢀ Wang,ꢀ J.ꢀ T.ꢀ Muckerman,ꢀ E.ꢀ Fujitaꢀ andꢀ Y.ꢀ
Himeda,ꢀNewꢀJ.ꢀChem.,ꢀ2013,ꢀ37,ꢀ1860-1866.ꢀSeeꢀalso:ꢀC.ꢀM.ꢀ
MooreꢀandꢀN.ꢀK.ꢀSzymczak,ꢀChem.ꢀCommun.,ꢀ2013,ꢀ49,ꢀ400-
402;ꢀ J.ꢀ F.ꢀ Hull,ꢀ Y.ꢀ Himeda,ꢀ W.-H.ꢀ Wang,ꢀ B.ꢀ Hashiguchi,ꢀ R.ꢀ
Periana,ꢀD.ꢀJ.ꢀSzalda,ꢀJ.ꢀT.ꢀMuckermanꢀandꢀE.ꢀFujita,ꢀNatureꢀ
Chem.,ꢀ 2012,ꢀ 4,ꢀ 383-388;ꢀ R.ꢀ Kawahara,ꢀ K.ꢀ Fujitaꢀ andꢀ R.ꢀ
Yamaguchi,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.,ꢀ2012,ꢀ51,ꢀ12790-12794.ꢀ
Reviews:ꢀB.ꢀZhao,ꢀZ.ꢀHanꢀandꢀK.ꢀDing,ꢀAngew.ꢀChem.ꢀInt.ꢀEd.,ꢀ
0
0
.0580.ꢀSꢀ=ꢀ1.023.ꢀResidualꢀelectronꢀdensityꢀbetweenꢀ-0.32ꢀandꢀ
3
.32ꢀ e/Å .ꢀ CCDCꢀ 1422009ꢀ containsꢀ theꢀ supplementaryꢀ
5
2013,ꢀ 52,ꢀ 4744-4788;ꢀ S.ꢀ Schneider,ꢀ J.ꢀ Meinersꢀ andꢀ B.ꢀ
Askevold,ꢀEur.ꢀJ.ꢀInorg.ꢀChem.,ꢀ2012,ꢀ412-429;ꢀS.ꢀKuwataꢀandꢀ
crystallographicꢀ dataꢀ forꢀ thisꢀ paper.ꢀ Theseꢀ dataꢀ canꢀ beꢀ
obtainedꢀfreeꢀofꢀchargeꢀfromꢀTheꢀCambridgeꢀCrystallographicꢀ
DataꢀCentreꢀviaꢀwww.ccdc.cam.ac.uk/data_request/cif.ꢀ
T.ꢀIkariya,ꢀDaltonꢀTrans.,ꢀ2010,ꢀ39,ꢀ2984-2992.ꢀ
Rh :ꢀ J.ꢀ R.ꢀ Krumper,ꢀ M.ꢀ Gerisch,ꢀ A.ꢀ Magistrato,ꢀ U.ꢀ
III
6
7
Rothlisberger,ꢀR.ꢀG.ꢀBergmanꢀandꢀT.ꢀD.ꢀTilley,ꢀJ.ꢀAm.ꢀChem.ꢀ
Soc.,ꢀ2004,ꢀ126,ꢀ12492–12502.ꢀ
DFTꢀCalculationsꢀ
III
Ir :ꢀY.ꢀGloaguen,ꢀL.ꢀM.ꢀJongens,ꢀM.ꢀLutz,ꢀJ.ꢀN.ꢀH.ꢀReek,ꢀB.ꢀdeꢀ
Bruinꢀ andꢀ J.ꢀ I.ꢀ vanꢀ derꢀ Vlugt,ꢀ Organometallics,ꢀ 2013,ꢀ 32,ꢀ
GeometryꢀoptimizationsꢀwereꢀcarriedꢀoutꢀwithꢀtheꢀTurbomoleꢀ
36
37
programꢀ package ꢀ coupledꢀ toꢀ theꢀ PQSꢀ Bakerꢀ optimizer ꢀ viaꢀ
4284–4291;ꢀ F.ꢀ Morandini,ꢀ B.ꢀ Longatoꢀ andꢀ S.ꢀ Bresadola,ꢀ J.ꢀ
Organomet.ꢀ Chem.,ꢀ 1977,ꢀ 132,ꢀ 291–299;ꢀ J.ꢀ A.ꢀ Raskatov,ꢀ S.ꢀ
38
39
theꢀ BOptꢀ package, ꢀ atꢀ theꢀ ri-DFTꢀ levelꢀ usingꢀ theꢀ BP86 ꢀ
40
Spiess,ꢀC.ꢀGnamm,ꢀK.ꢀBrödner,ꢀF.ꢀRomingerꢀandꢀG.ꢀHelmchen,ꢀ
Chem.ꢀEur.ꢀJ.,ꢀ2010,ꢀ16,ꢀ6601–6615.ꢀPt ꢀ(andꢀIr ):ꢀS.ꢀMusa,ꢀR.ꢀ
Romm,ꢀC.ꢀAzerraf,ꢀS.ꢀKozuchꢀandꢀD.ꢀGelman,ꢀDaltonꢀTrans.,ꢀ
functionalꢀ andꢀ theꢀ resolution-of-identityꢀ (ri)ꢀ method. ꢀ Weꢀ
optimizedꢀtheꢀgeometriesꢀofꢀallꢀstationaryꢀpointsꢀatꢀtheꢀdef2-
II
III
41
TZVPꢀ basisꢀ setꢀ level, ꢀ usingꢀ Grimme’sꢀ dispersionꢀ correctionsꢀ
III
011,ꢀ40,ꢀ8760–8763.ꢀAu :ꢀꢀD.ꢀA.ꢀSmith,ꢀD.-A.ꢀRoşcaꢀandꢀM.ꢀ
2
Bochmann,ꢀOrganometallics,ꢀ2012,ꢀ31,ꢀ5998–6000.ꢀPd :ꢀA.ꢀD.ꢀ
42
II
(disp3ꢀversion) ꢀandꢀaꢀtightꢀenergyꢀgridꢀ(m5).ꢀTheꢀidentityꢀofꢀ
theꢀtransitionꢀstatesꢀwasꢀconfirmedꢀbyꢀfollowingꢀtheꢀimaginaryꢀ
GettyꢀandꢀK.ꢀI.ꢀGoldberg,ꢀOrganometallics,ꢀ2001,ꢀ20,ꢀ2545–
2
II
551.ꢀRu :ꢀJ.ꢀBecker,ꢀT.ꢀModlꢀandꢀV.ꢀH.ꢀGessner,ꢀChem.ꢀEur.ꢀJ.,ꢀ
6
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Page 7 of 9
Ca tP al el ya ss ies ꢀ dS o cꢀ ni eo nt cꢀ a ed &j u sTt eꢀ mc ha rn g oi nl os gꢀ y
JournalꢀNameꢀ
ꢀARTICLEꢀ
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014,ꢀ20,ꢀ11295–11299.ꢀNi :ꢀD.ꢀVꢀGutsulyak,ꢀW.ꢀE.ꢀPiers,ꢀJ.ꢀ
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1776–11779.ꢀꢀꢀꢀ
I.ꢀvanꢀderꢀVlugtꢀꢀandꢀJ.ꢀN.ꢀH.ꢀReek,ꢀChem.ꢀCommVuienw.,Aꢀ2rt0ic1le5O,nꢀ5lin1e,ꢀ
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18 M.ꢀ Brookhart,ꢀ M.ꢀ L.ꢀ H.ꢀ Green,ꢀ J.ꢀ Organomet.ꢀ Chem.,ꢀ 1983,ꢀ
250,ꢀ395-408;ꢀM.ꢀBrookhart,ꢀM.ꢀL.ꢀH.ꢀGreen,ꢀG.ꢀParkin,ꢀProc.ꢀ
Natl.ꢀAcad.ꢀSci.ꢀUSA,ꢀ2007,ꢀ104,ꢀ6908-6914.8ꢀ
DOI: 10.1039/C5CY01505G
1
8
Roll-overꢀcomplexes:ꢀL.ꢀMaidich,ꢀG.ꢀZuri,ꢀS.ꢀStoccoro,ꢀM.ꢀA.ꢀ
Cinellu,ꢀM.ꢀMasia,ꢀA.ꢀZuccaꢀandꢀU.ꢀSassari,ꢀOrganometallics,ꢀ
2
2
013,ꢀ32,ꢀ438–448;ꢀB.ꢀButschkeꢀandꢀH.ꢀSchwarz,ꢀChem.ꢀSci.,ꢀ 19 L.ꢀS.ꢀJongbloed,ꢀB.ꢀdeꢀBruin,ꢀJ.ꢀN.ꢀH.ꢀReek,ꢀM.ꢀLutzꢀandꢀJ.ꢀI.ꢀvanꢀ
012,ꢀ3,ꢀ308–326;ꢀJ.ꢀKwak,ꢀY.ꢀOhk,ꢀY.ꢀJungꢀandꢀS.ꢀChang,ꢀJ.ꢀ derꢀVlugt,ꢀChem.ꢀEur.ꢀJ.,ꢀ2015,ꢀ21,ꢀ7297-7305.ꢀ
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Petretto,ꢀ M.ꢀ L.ꢀ Cabras,ꢀ S.ꢀ Stoccoro,ꢀ M.ꢀ A.ꢀ Cinellu,ꢀ M.ꢀ Inorg.ꢀChim.ꢀActa,ꢀ2012,ꢀ380,ꢀ336-342.ꢀ
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94,ꢀ3753–3761.ꢀ derꢀVlugt,ꢀDaltonꢀTrans.,ꢀ2012,ꢀ41,ꢀ11276–11283;ꢀꢀ
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35,ꢀ13149-13161.ꢀ DaltonꢀTrans.,ꢀ2009,ꢀ1016–1023.ꢀ
0 L.ꢀ Taghizadehꢀ Ghoochany,ꢀ C.ꢀ Kerner,ꢀ S.ꢀ Farsadpour,ꢀ F.ꢀ 23 J.ꢀI.ꢀvanꢀderꢀVlugt,ꢀE.ꢀA.ꢀPidko,ꢀR.ꢀC.ꢀBauer,ꢀY.ꢀGloaguen,ꢀM.ꢀK.ꢀ
6
9
1
1
Menges,ꢀY.ꢀSun,ꢀG.ꢀNiedner-SchatteburgꢀandꢀW.ꢀR.ꢀThiel,ꢀEur.ꢀ
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1 K.ꢀGhatak,ꢀM.ꢀManeꢀandꢀK.ꢀVanka,ꢀACSꢀCatal.,ꢀ2013,ꢀ3,ꢀ920-
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24 M.ꢀA.ꢀF.ꢀHernandez-Gruel,ꢀG.ꢀGracia-Arruego,ꢀA.ꢀB.ꢀRivas,ꢀI.ꢀT.ꢀ
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1
1
1
9
27.ꢀ
2 C.ꢀ Boulhoꢀ andꢀ J.-P.ꢀ Djukic,ꢀ Daltonꢀ Trans.,ꢀ 2010,ꢀ 39,ꢀ 8883-
905.ꢀ
3 P.ꢀBhattacharya,ꢀJ.ꢀA.ꢀKrauseꢀandꢀH.ꢀGuan,ꢀJ.ꢀAm.ꢀChem.ꢀSoc.,ꢀ
014,ꢀ136,ꢀ11153-11161.ꢀ
8
2
25 Notably,ꢀ reactionꢀ ofꢀ 1ꢀ withꢀ thiophenolꢀ gaveꢀ differentꢀ
1
4 Selectedꢀ recentꢀ examples:ꢀ R.ꢀ Tanaka,ꢀ M.ꢀ Yamashita,ꢀ L.ꢀ W.ꢀ
Chung,ꢀK.ꢀMorokuma,ꢀK.ꢀNozaki,ꢀOrganometallicsꢀ2011,ꢀ30,ꢀ
spectralꢀfeatures,ꢀwithꢀaꢀdoubletꢀatꢀ99ꢀppmꢀ( JRh-Pꢀ=ꢀ136.3ꢀHz)ꢀ
3 6 6
inꢀ MeCN-d .ꢀ Whenꢀ C D ꢀ wasꢀ usedꢀ asꢀ solvent,ꢀ twoꢀ speciesꢀ
6
742–6750;ꢀ E.ꢀ A.ꢀ Bielinski,ꢀ P.ꢀ O.ꢀ Lagaditis,ꢀ Y.ꢀ Zhang,ꢀ B.ꢀ Q.ꢀ
withꢀsimilarꢀshiftsꢀandꢀcouplingꢀconstantsꢀasꢀcomplexꢀ2ꢀwereꢀ
1
observed,ꢀi.e.ꢀdoubletsꢀatꢀ66ꢀppmꢀ( JRh-Pꢀ=ꢀ152.1ꢀHz)ꢀandꢀ72ꢀ
1
Mercado,ꢀ C.ꢀ Würtele,ꢀ W.ꢀ H.ꢀ Bernskoetter,ꢀ N.ꢀ Hazariꢀ andꢀ S.ꢀ
Schneider,ꢀJ.ꢀAm.ꢀChem.ꢀSoc.,ꢀ2014,ꢀ136,ꢀ10234-10237;ꢀG.ꢀA.ꢀ
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Ed.,ꢀ 2008,ꢀ 47,ꢀ 3962–3965;ꢀ S.ꢀ Enthaler,ꢀ J.ꢀ vonꢀ Langermannꢀ
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solventꢀisꢀchangedꢀinꢀtheꢀsameꢀsample.ꢀTheseꢀresultsꢀindicateꢀ
thatꢀmonomericꢀcomplexesꢀareꢀformedꢀwhenꢀpolarꢀsolventsꢀ
areꢀusedꢀinꢀtheꢀreaction,ꢀbutꢀnoꢀconclusiveꢀevidenceꢀcouldꢀbeꢀ
obtained.ꢀꢀ
1
1
andꢀT.ꢀSchmidt,ꢀEnergyꢀEnviron.ꢀSci.,ꢀ2010,ꢀ3,ꢀ1207–1217;ꢀA.ꢀ 26 Theꢀ catalyticꢀ dehydrogenationꢀ ofꢀ formicꢀ acidꢀ isꢀ notꢀ fasterꢀ
3
whenꢀ theꢀ azeotropeꢀ HCOOH/Et Nꢀ 5:2ꢀ isꢀ used,ꢀ butꢀ theꢀ TOFꢀ
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canꢀbeꢀincreasedꢀasꢀmoreꢀequivalentsꢀofꢀtheꢀazeotropeꢀareꢀ
addedꢀunderꢀtheꢀsameꢀconditions.ꢀIncreasingꢀtheꢀformicꢀacidꢀ
concentrationꢀ withoutꢀ aꢀ baseꢀ presentꢀ resultsꢀ inꢀ aꢀ lossꢀ ofꢀ
activity,ꢀpresumablyꢀbecauseꢀdormantꢀspeciesꢀ5ꢀisꢀformedꢀatꢀ
tooꢀhighꢀconcentrationsꢀofꢀacid.ꢀꢀꢀꢀ
5
,ꢀ8907-8911.ꢀ
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Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ7ꢀ
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Ca tP al el ya ss ies ꢀ dS o cꢀ ni eo nt cꢀ a ed &j u sTt eꢀ mc ha rn g oi nl os gꢀ y
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ARTICLEꢀ
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View Article Online
DOI: 10.1039/C5CY01505G
1
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ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
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Page 9 of 9
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C5CY01505G
The first example of base-free catalytic dehydrogenation of formic acid using reversible cylcometalation at
Rh(I) is discussed, using a combination of experimental and computational methods.
Graphical Abstract
HCOOH
H2
H
N
N
H
O
O
Rh
H
Rh
P
(
P
tBu)2
H
(tBu)2
OC
OC
H
N
CO2
Rh
H
P
(
tBu)2
OC