Upgrading Light Hydrocarbons via Tandem Catalysis: A Dual Homogeneous Ta and Ir System for Alkane / Alkene Coupling

Transcription

1 Upgrading Light Hydrocarbons via Tandem Catalysis: A Dual Homogeneous Ta and Ir System for Alkane / Alkene Coupling David C. Leitch, Yan Choi Lam, Jay A. Labinger, and John E. Bercaw Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California, 91125, United States SupportingInformation TableofContents I:ExperimentalProcedures.S2 GeneralConsiderations S2 GCAnalysis...S2 Dimerizationof1CHexeneusing1.S4 Dimerizationof1CHepteneusing1...S4 CoCdimerizationof1CHexene/1CHepteneusing1.S5 AttemptedTandemCatalysiswith1and2a...S5 GeneralProcedureforReactionsfromTable1.S6 ExpandedResultsfor1CHexene/nCHeptaneDimerization..S7 ProcedureforMonitoringReactionsoverTime S7 ProcedureforMonitoringReactionsIndividualReactionswith1or2boverTime...S9 ProcedureforSyringePumpAddition.S10 ProcedureforCatalyticDimerizationofnCHeptane...S11 GC/MSCharacterizationofC13Product...S12 II:ThermodynamicAnalysis...S15 III:References S17 S1

2 I:ExperimentalProcedures GeneralConsiderations: All experiments were performed under an argon inert atmosphere using standard Schlenk line,highcvacuumline,orgloveboxtechniques.solventsforroutinesyntheses(pentane,toluene, diethylether,thf)weredriedbypassagethroughactivatedalumina,degassedundervacuum by several freezecpumpcthaw cycles, and stored over activated 4 Å molecular sieves under an inert atmosphere. ncheptane for use in catalytic reactions(hplc grade, >99%, SigmaCAldrich) wasprecdriedbystirring~400mlovercah2(~10g)foratleast48hours.thesolventwasthen vacuum transferred onto titanocene 1 (~1 g) and stirred overnight; the solution remained blackcgreen throughout. ThenCheptane was collected from this titanocene solution by a final vacuum transfer and stored under an argon atmosphere. 1CHexene, 1Cheptene, and neohexene (isoprenecfree)weredistilledunderargonfromcah2afterstirringforseveraldays.precatalysts 1, 2 2a, 3 2b, 4 and 2c 5 are known compounds, and were prepared according to published procedures.complexes2band2cwerepurifiedbywashingwithpentane(3x5c10mlfora 300 mg batch) and dried under vacuum prior to use in catalytic experiments; failure to do so resulted in substantial alkene isomerization immediately upon mixing the crude Ir compound with1chexene. 6 GCAnalysis: GaschromatographywasperformedonanAgilent6890Ninstrumentusingaflameionization detectorandadbc1capillarycolumn(10mlength,0.10mmdiameter,0.40μmfilm).runsused thefollowingprogram:holdat35 Cfor2minutes,ramptemperatureat2 Cmin C1 to50 C,hold at50 Cfor2minutes,ramptemperatureat100 Cmin C1 to290 C,holdat290 Cfor5minutes. Response factors for linear hydrocarbonsranging from C5 to C18 versus adamantane were determined by the following procedure. Two standard samples were prepared containing known amounts of ten compounds (ncpentane, 1Chexene, ncheptane, ncoctane, 1Cdodecene, 1C tridecene, 1Ctetradecene, 1Chexadecene, ncoctadecane, and adamantane) dissolved in dichloromethane. Analysis of these two solutions by GC generated data used to calculate individualresponsefactorsforeachcompoundversusadamantaneusingthefollowingformula: Resp.factor=([Areaanalyte]X[mmoladamantane])/([Areaadamantane]X[mmolanalyte]) Thefollowingresponsefactorswereobtained: Run1 Run2 ncpentane" CHexene ncheptane" ncoctane" CDodecene CTridecene CTetradecene CHexadecene ncoctadecane" These data were plotted versus carbon number, giving a linear correlation in the range analyzed(figures1). S2

3 FigureS1:Linearcorrelationofresponsefactorsversuscarbonnumber. Theequationofthelinewasusedtodetermineresponsefactorsforallofthehydrocarbons analyzed(thebranchinginthec12cc14dimersgeneratedincatalyticreactionsisassumedtohave negligibleeffectontheresponse). C C C C The response factor for neohexene versus adamantane was established to lie outside this correlation, and was determined independently from two separate runs. The response factors were0.5982(run1)and0.5853(run2)foranaveragevalueof GC/MS analysis was performed on an HP Model 6890N instrument using an HP5C1 column (30mlength,25mmdiameter,0.40μmfilm)andanHP5973massCselectiveEIdetector. S3

4 Dimerizationof1BHexeneusing1: Precatalyst 1 (6.6 mg, mmol) and adamantane (internal standard, 9.6 mg, mmol) weredissolvedin2mlofncheptaneina4mlscrewctopvialcontainingateflonccoatedstirbar. 1CHexene(36.8mg,0.437mmol)wasadded,andthevialsealedwithaTeflonClinedscrewcap. The vial was stirred at 100 C in an aluminum block heater for 4 hours. After cooling to room temperature, the brown solution was passed through a short plug of silica gel into a GC autosampler vial. The mixture was analyzed by GC to determine the retention times of the C12 dimers (Figure S2). The identities of the isomers produced by precatalyst 1 have been definitively established by Schrock and cocworkers; 7 therefore, all of the products here are assignedbyanalogytothispreviouswork. C 4 H 9 C 4 H 9 C 4 H 9 C 4 H 9 ncheptane C 4 H 9 C 4 H 9 C 4 H 9 C 4 H 9 FigureS2:GCtraceofthedimerizationof1ChexenetoproduceC12dimers." Dimerizationof1BHepteneusing1: As for the dimerization of 1Chexene with the following reagents: 1 (6.6 mg, mmol), adamantane(14.9 mg, mmol), 1Cheptene(40.0 mg, mmol), and ncheptane(2 ml). ThisreactionwasalsoanalyzedbyGCtodeterminetheretentiontimesoftheC14dimers(Figure S3). ncheptane FigureS3:GCtraceofthedimerizationof1CheptenetoproduceC14dimers. S4

5 CoBdimerizationof1BHexene/1BHepteneusing1: Precatalyst 1 (6.6 mg, mmol) and adamantane (internal standard, 9.6 mg, mmol) weredissolvedin2mlofncheptaneina4mlscrewctopvialcontainingateflonccoatedstirbar. 1CHexene(22.1mg,0.263mmol)and1Cheptene(24.9mg,0.254mmol)wereadded,andthevial sealedwithateflonclinedscrewcap.thevialwasstirredat100 Cinanaluminumblockheater for4hours.aftercoolingtoroomtemperature,thebrownsolutionwaspassedthroughashort plugofsilicagelintoagcautosamplervial.themixturewasanalyzedbygctodeterminethe retentiontimesofthec13crosscdimersbetween1chexeneand1cheptene(figures4). C12 C13 C14 ncheptane FigureS4:GCtraceofthecoCdimerizationof1Chexeneand1Cheptenetoproduce C12/C13/C14dimers. AttemptedTandemCatalysiswith1and2a: The following is a representative example. 1 (15.0 mg, mmol), 2a (12.8 mg, mmol),andadamantane(33.2mg,0.244mmol)weredissolvedin2mlofncheptaneina5ml glassreactiontube(kontescvalve)containingateflonccoatedstirbar.1chexene(218.9mg,2.60 mmol)wasadded,andthetubesealedwithatefloncplug.themixturewasstirredat125 Cin anoilbathfor24hours.aftercoolingtoroomtemperature,thebrownsolutionwasdilutedwith dichloromethane and passed through a short plug of silica gel into a GC autosampler vial. The mixture was analyzed by GC, indicating >98% conversion.the major products were nchexane (113.2mM,8.7%)andtheC12dimers(583.6mM,89.8%).NoC13orC14productswereobserved (FigureS5). DCM ncheptane C12 nchexane FigureS5:GCtraceofattempted1Chexene/nCheptanedimerizationwith1and2a. S5

6 GeneralProcedureforReactionsfromTable1: Thefollowingisarepresentativeexample(entry1,Table1,maintext).1(6.6mg,0.016mmol) and 2b(5.9 mg, mmol) were dissolved in 1 ml of a standard solution of 1Chexene(250 mm) and adamantane (24.8 mm) in ncheptane in a 4 ml screw top vial containing a TeflonC coated stir bar. The vial was sealed with a TeflonClined screw cap. The mixture was stirred at 125 Cinanaluminumblockheaterfor5hours.Aftercoolingtoroomtemperature,thebrown solution was diluted with ncheptane and passed through a short plug of silica gel into a GC autosamplervial.themixturewasanalyzedbygc,indicating>99%conversion.thec13andc14 dimersareclearlyobservedinthiscase(figures6,comparetofigures4). nchexane C12 C13 C14 ncheptane FigureS6:GCtraceforreactionfromentry1a,TableS1. S6

7 ExpandedResultsfor1BHexene/nBHeptaneDimerization TableS1.Resultsforstandardbatchreactions(Table1,maintext,entries1C6) Entry [1BHexene]0 mm a (FinalConc.) 1a 250 (0.7) 1b 250 (0.6) 2a 250 (0.8) 2b 250 (0.7) 3a 250 (0.4) 3b 250 (0.7) 3c 250 (0.9) 4a 250 (0.7) 4b 250 (0.6) 5a 250 (0.3) 5b 250 (0.4) 6a 1000 (3.4) 6b 1000 (3.4) solvent [1]/[2b] mm Temp. C 1 and 2b 5 hours nbhexane mm(%) 16/ (46.2) 16/ (45.2) 8/ (43.2) 8/ (41.5) 8/ (20.5) 8/ (22.6) 8/ (21.2) 5/ (30.5) 5/ (31.4) 12/ (22.3) 12/ (22.4) 8/ (8.6) 8/ (8.7) tb2bhexene/ cb2bhexene mm(%) 3.2(1.3)/ 1.6(0.7) 3.0(1.2)/ 1.3(0.5) 7.4(2.9)/ 3.4(1.4) 8.0(3.2)/ 3.5(1.4) 11.3(4.6)/ 8.0(3.3) 11.0(4.5)/ 5.0(2.1) 10.8(4.4)/ 4.8(2.0) 6.1(2.4)/ 3.2(1.3) 6.9(2.8)/ 3.5(1.4) 3.3(1.4)/ 2.2(0.9) 3.0(1.3)/ 2.0(0.8) 17.4(1.7)/ 9.6(1.0) 18.5(1.8)/ 10.0(1.0) C12 mm(%) 56.5 (46.0) 57.6 (47.1) 57.7 (46.0) 59.1 (47.5) 81.3 (66.3) 78.6 (64.9) 81.7 (66.9) 75.5 (60.3) 73.8 (58.9) 84.5 (71.5) 85.0 (71.5) (86.5) (86.2) Observed products C13/ C14 mm(%) 13.7(11.1)/ 12.4(10.1) 14.0(11.5)/ 12.7(10.4) 15.4(12.3)/ 13.0(10.3) 15.2(12.2)/ 13.0(10.4) 12.6(10.3)/ 9.6(7.8) 13.8(11.4)/ 10.0(8.2) 12.6(10.3)/ 9.9(8.1) 13.0(10.4)/ 9.4(7.5) 13.1(10.5)/ 9.3(7.4) 8.8(7.4)/ 7.8(6.6) 9.2(7.7)/ 8.1(6.9) 18.7(3.7)/ 10.2(2.0) 18.8(3.8)/ 10.2(2.0) C6Mass Balance mm b TON TON 1 c 2b c Coop. (%) d (2) 11(4) (2) 11(4) (4) 22(8) (4) 21(8) (3) 10(6) (3) 11(7) (3) 10(6) (4) 15(6) (4) 16(6) (1) 11(5) (1) 11(5) (4) 17(8) (4) 17(8) 45.0 adeterminedfromconcentrationofstandardsolution. b [1Chexene][nChexane][tC2Chexene][cC2Chexene]2[C12][C13] ctonsinparenthesesareforproductionofc13/c14. d See Ref.19inthemaintext. ProcedureforMonitoringReactionsoverTime: 1 (6.6 mg, mmol) and 2b (5.9 mg, mmol) were dissolved in 2 ml of a standard solutionof1chexene(250mm)andadamantane(24.8mm)inncheptaneina4mlscrewtopvial containing a TeflonCcoated stir bar. The vial was sealed with a TeflonClinedscrewcap.The mixture was heated briefly with a heat gun to dissolve the precatalysts and ensure a homogeneous solution. The solution was then split into ten aliquots of 0.2 ml each in ten separate 4 ml vials containing stir bars. These vials were sealed and stirred at 100 C in an aluminum block heater (except for one vial representing t0). At specified time intervals, vials were removed from the heat block, immersed in a drycice/acetone bath to rapidly cool the contents,andthendilutedwithdichloromethanetoquenchthereaction.thesesolutionswere passed through a short plug of silica gel into a GC autosampler vial, and analyzed by GC. Concentrationswereplottedversustime(FigureS7). R R' R R' C 12 : R = R' = n-c 4 H 9 C 13 : R = n-c 4 H 9, R' = n- or R = n-, R' = n-c 4 H 9 C 14 : R = R' = n- S7

8 FigureS7:Plotsofreactionprogressovertimeforentries3aand3binTableS1.Top:Overlayof both data sets. Bottom) left: Expansion of product concentration range for entry 3a. Bottom) Right:Expansionofproductconcentrationrangeforentry3b.Linesaredrawnasvisualguides. S8

9 ProcedureforMonitoringIndividualReactionswith1or2boverTime: 1(6.6mg,0.016mmol)or2b(5.9mg,0.010mmol)wasdissolvedin2mLofastandardsolution of 1Chexene (250 mm) and adamantane (24.8 mm) in ncheptane in a 4 ml screw top vial containing a TeflonCcoated stir bar. The vial was sealed with a TeflonClinedscrewcap.For reactionsinvolving1,themixturewasheatedbrieflywithaheatguntodissolvetheprecatalyst and ensure a homogeneous solution. The solution was then split into aliquots (5 aliquots for reactionswithcatalyst1,8forreactionswithcatalyst2b)inseparate4mlvialscontainingstir bars.thesevialsweresealedandstirredat100 Cinanaluminumblockheater(exceptforone vial representing t0). At specified time intervals, vials were removed from the heat block, immersed in a drycice/acetone bath to rapidly cool the contents, and then diluted with dichloromethanetoquenchthereaction.thesesolutionswerepassedthroughashortplugof silica gel into a GC autosampler vial, and analyzed by GC. Concentrations were plotted versus time(figures8).runswererepeatedintriplicate(catalyst1)orduplicate(catalyst2b). FigureS8:Overlayofreactionprogressfortandemcatalyticreactionfromentries3aand3bin TableS1,initialratefor1ChexenedimerizationtoC12catalyzedby1(3runs),andnChexane formedby1chexene/ncheptanetransferhydrogenationcatalyzedby2b(2runs).thesedata clearlyshowthatthecatalyticratesexhibitedby1and2bareunchangedunderthetandem catalysisconditions,andhencethetwocatalystsdonotundergomutualinhibition/ deactivation. ([1CHexene]forindividualruns,[C13]and[C14]fortandemruns,and[2Chexenes]forallrunsnot shownforclarity). S9

10 ProcedureforSyringeBPumpAddition: 1(6.6mg,0.016mmol),2b(5.9mg,0.010mmol)andadamantane(14.5mg,0.106mmol)were dissolved in 2 ml of ncheptane in a 10 ml roundcbottom flask containing a TeflonCcoated stir bar.threedropsof1chexenewereadded.theflaskwasconnectedtoarefluxcondenserwith ApiezonHCgreaseandfixedwithrubberbands.A90 adapterwith14/20and24/40jointsanda Kontes TeflonCplug was attached to the top of the condenser with HCgrease and fixed with rubber bands. With the plug sealed, the apparatus was removed from the glovebox and connectedtoanargonline.withastrongflowofargon(mercurybubbler),theteflonplugwas replaced with a rubber septum that was fixed with copper wire. After this, the apparatus was subject to a constant, slow stream of argon and vented through an oil bubbler to prevent overpressure.agastighthamiltonsyringe(500μl)withalong(~30cm)needlewasfilledwith 300μL1Chexene(~200mg,~2.38mmol)intheglovebox.WiththeneedleCtipinsidearubber stopper,thesyringewasremovedfromthegloveboxandquicklyinsertedintotheseptumatthe topoftherefluxcondenser.theflaskwasloweredintoanoilbathat120 C.Theneedlewas threadedthroughtherefluxcondensersuchthatthetipwasattherefluxlevel.thesyringewas placedinsideasyringecpumpandsettodeliverthe1chexeneat~12.5μlh C1 (~50mM1Chexene h C1 ),correspondingto~24hadditiontime,whilethereactionwasrunforatotalof32hours (run 1) or 36 hours (run 2). After completion, the flask was cooled to room temperature,the brown solution passed through a short plug of silica gel into a GC autosampler vial, and the contentsanalyzedbygc.theresultsoftwoseparaterunsaregivenintables2. TableS2.Resultsforslowadditionprotocol(Table1,maintext,entry7) 1200 mm added over 24 h Run [1BHexene]0 mm a (FinalConc.) 1 ~1200 (32.4) 2 ~1200 (83.8) 1 ~1200 (32.4) 2 ~1200 (83.8) solvent 1 (8 mm) 2b (5 mm) reflux hours nbhexane mm(%) (22.5) (17.2) e (27.8) e (27.0) tb2bhexene/ cb2bhexene mm(%) 28.8(2.4)/ 21.0(1.8) 24.1(2.0)/ 18.5(1.5) 28.8(2.4)/ 21.0(1.8) 24.1(2.0)/ 18.5(1.5) C12 mm(%) (50.4) (47.2) (50.4) (47.2) C13/ C14 mm(%) 179.6(29.9)/ 59.1(9.9) 182.2(30.4)/ 59.1(9.9) 179.6(29.9)/ 59.1(9.9) 182.2(30.4)/ 59.1(9.9) C6Mass Balance mm b (30) (30) (30) (30) TON TON 1 c 2b c adeterminedfromtotalamountof1chexeneadded. b [1Chexene][nChexane][tC2Chexene][cC2Chexene]2[C12][C13] c TONs inparenthesesareforproductionofc13/c14. d See Ref.19inthemaintext. e Correctedvalues,seediscussionbelow. Asanalyzed,thesetworunsaredeficientinnChexane,presumablyduetoevaporationduringthe prolonged reflux. This gives apparent cooperativity percentages that are over 100%, and a C6 mass balance below the anticipated value of ~1200 mm (runs 1 and 2 in Table S2). As acceptorless dehydrogenationof ncheptane is extremely unlikely under these conditions, we haveestimatedthetotalamountofnchexanegeneratedbasedontheexpectedc6massbalance of1200mm(runs1 and2 intables2).thus,the missing nchexaneis63.2mminrun1and 117.9mMinrun2.ApplyingthiscorrectiongivesTONsforcatalyst2bandcooperativityvalues thatareinexcellentagreementbetweenthetworuns. R R' Observed products R R' C 12 : R = R' = n-c 4 H 9 C 13 : R = n-c 4 H 9, R' = n- or R = n-, R' = n-c 4 H 9 C 14 : R = R' = n- 54 (60) 41 (60) 67 (60) 65 (60) Coop. (%) d S10

11 C12 C13 C14 nchexane ncheptane tc2chexene 1Chexene cc2chexene FigureS9:GCtraceforreactionfromrun1,TableS2. ProcedureforCatalyticDimerizationofnBHeptane: 1(6.6mg,0.016mmol),2c(2.1mg,0.0039mmol)weredissolvedin2mLofastandardsolution of neohexene (252 mm) and adamantane (34.7 mm) in ncheptane in a 4 ml screw top vial containing a TeflonCcoated stir bar. The vial was sealed with a TeflonClinedscrewcap.The mixturewasstirredat100 Cinanaluminumblockheaterfor18hours.Aftercoolingtoroom temperature, the brown solution was passed through a short plug of silica gel into a GC autosampler vial. The mixture was analyzed by GC, indicating ~50% conversion (Table S3). Longerreactiontimesgivesimilarresults,indicatingcatalystdecomposition. TableS3.ResultsforcatalyticnCheptanedimerization(Eq.4,maintext) Observed products mm 1 (8 mm) t-bu 2c (2 mm) t-bu 100 o C 18 h TBE solvent Run Final[TBE] mm t-bu TBA [TBA] %Conv. C13 mm mm(%) C14 mm(%) TON TON 1 a 2c a Coop. (%) b (1.6) 20.6(16.9) (3) 55(22) (1.3) 21.4(18.3) (3) 62(22) 35.5 atonsinparenthesesareforproductionofc13/c14. b See Ref.19inthemaintext. R t-bu R = n- R R R alkene isomers C 13 C 14 R S11

12 t-bu C14 ncheptane FigureS10:GCtraceforcatalyticnCheptanedimerization(run1,TableS3). GC/MSCharacterizationofC13Product: Inordertoconfirmtheproposedstructureoftheneohexene/nCheptaneheterodimer(C13),the reactionmixturewasanalyzedbygc/ms(figures9).thetracegivesasimilarpatterntothegc analysis carried out with the FID (Figure S8). The peak at 8.38 min, corresponding to the C13 product,hasamolecularionofm/z=182.6(calc.forc13h26:182.20).furthermore,diagnostic fragmentsareobserved.thebasepeakcorrespondstoatcbuc=ch2fragment(m/z=83.1found, 83.09calc.),confirmingthepresenceoftheC6neohexenecouplingpartner. S12

13 FigureS11:GC/MSanalysisofcatalyticnCheptanedimerization(Eq.4,maintext).Top:GCtrace, indicatingproducts.middle:msforpeakcorrespondingtoc13productwithdiagnosticfragment indicated.bottom:averagemsforc14region. S13

14 The regioisomer shown for the C13 product is proposed based on steric arguments in the tantallacyclopentaneintermediate(figures10). Ta Cl Cl Ta Cl Cl Ta Cl Cl Head-Head Isomer: Steric clash between t-bu and n- Head-Tail Isomer 1: Steric clash between t-bu and Cp Head-Tail Isomer 2: Minimum steric repulsion Figure S12:StericrationalefortheproposedregiochemistryoftheC13neohexene/nCheptane dimer. S14

15 II:ThermodynamicAnalysis TableS4.Gibbsenergiesofformationforpropane,propene,andC6alkanesinthegasphase(1 atm).dataobtainedfromref.8. Temp.& K"( C) ΔfG m Propane Propene Hexane 2BMethylB pentane 3BMethylB pentane 2,3BDimethylB butane 0 (C273.15) C C130.5 C135.3 C132.5 C (C73.15) C C52.8 C58.8 C56.6 C (25) C C5.1 C3.2 C (26.15) C C4.1 C2.1 C (126.15) (226.15) C 600 (326.15) (426.15) TableS5.Calculatedfreeenergiesofreactionforpropane/propenecoupling. or Temp.& K"( C) or or ΔGorxn ΔG rxn Hexane 2BMethylB pentane 3BMethylB pentane 2,3BDimethylB butane 0 (C273.15) C82.8 C87.6 C84.8 C (C73.15) C52.4 C58.4 C56.2 C (25) C37.7 C43 C41.1 C (26.15) C37.5 C42.8 C40.8 C (126.15) C22.7 C27.2 C25.4 C (226.15) C8.2 C12 C10.3 C 600 (326.15) (426.15) S15

16 Figure S13:PlotsofΔG rxnforpropane/propenecouplingtogeneratefourc6alkaneisomers. ThelinearcorrelationscrossthexCaxisbetween~260 Cfor2,3Cdimethylbutane,and~310 C for2cmethylpentane;thus,thesereactionscanbeexpectedtobespontaneousbelow250 C. S16

17 III:References (1)Bercaw,J.E.;Marvich,R.H.;Bell,L.G.;Brintzinger,H.H.J."Am."Chem."Soc.1972,94,1219C (2)McLain,S.J.;Wood,C.D.;Schrock,R.R.J."Am."Chem."Soc."1979,101,4558C4570. (3)GöttkerCSchnetmann,I.;Brookhart,M.J."Am."Chem."Soc.2004,126,1804. (4) Goldman, A. S.; Ghosh, R. In Handbook" of" C<H" Transformations Applications" in" Organic" Synthesis;Dyker,G.,Ed.;WileyCVCH:NewYork,2005;p616. (5)Liu,F.;Pak,E.B.;Singh,B.;Jensen,C.M.;Goldman,A.S.J."Am."Chem."Soc.1999,121,4086C (6)ForadiscussionoftheimportanceofpurifyingpincerCIrhydridespriortouseincatalytic experiments,see:jensen,c.m.chem."commun.1999,2443c2449. (7)McLain,S.J.;Sancho,J.;Schrock,R.R.J."Am."Chem."Soc."1980,102,5610C5618. (8) Frenkel, M.; Kabo, G. J.; Marsh, K. N.; Roganov, G. N.; Wilhoit, R. C. Thermodynamics" of" Organic" Compounds" in" the" Gas" State; Thermodynamics Research Center: College Station, TX, S17