) v-
{Reprioted froo the Journal ol the Aoericen Cbeoiccl Society,91,20Og (1g0g).1 Copyrigbt 1969 by tbe Aoericra Cbcrnicel Socicty ead reprioted by pernissioo of tbe copyright orocr.
Irradiation of cis,cis-l ,S.Cyclooctadiene in the Presenceof copper(I) chloride
GeorgeM. Whitesides,Gerald L. Goe,and Arthur C. Cope Irradiationof cls,cis-l,5-Cyclooctadiene in the Presenceof Copper(I)Chloride'
George NI. \l'hitesides, Gerald L. Goe,:" and Arthur C. Cope2b
Contributiott J'rorn the Departntent oJ'Cltenti.strt', ilIassac'husetts Itrstirure of' Technologl', Canrhridge, Llassacltusetts 02139. Receivetl Septembar t0. 1968
Abstract: Irradiation of an oxygen-frcepent:.tne suspcnsion of di-tt-chloro-bis(crs.crs-1,5-cycloocradiene)dicopper- (l) (4) at 254-msyields, in addition to tricyclo[].1.0.0:'t,loctlnc(t). sigrrificilnrquantitics of insolublecopper(l) comple.resof cis,tratrs-and tratts,trons-1.5-cyclooctldienes.Exumination of the photocfternicalbehavior of these dienes,and of their yieldsrelative to the yield of I during thc irradiation ol {. indicatesthat a rlajor part of the I formed hlts cls,trarrs-1,5-cyclooctadieneas x prccursor. These data furrher suggestthat a significant part of the photoconversionof cis,tratrs-1,5-cyclooctadicneto I may take placc lrcr the intermedilrcy'of tratts,trytrrs-1,5- cyclooctadiene.
-rr I ransition metals catalyze the thermal and photo- /r---.' I chemicaldimerization of a widevariety of olefins.3-8 r--x// | One of the most interestingof the metal-catalyzedphoto- /-Jx--' chemicalreactions is the conversionof crs,cls-1,S-cyclo- 2a 2b octadieneto tricyclo[3.3.0.02'6]octane(l) by irradiation in the presenceof copper(l)chloride, or by photosensiti- servea varietyof functions: r'i:., as a photosensitizer,as zationwith mercury(3P,) atoms.s'a Althoughthe basic a "template" controlling the stereochemistryof reaction mechanismof the gas-phase,mercury-photosensitized of coordinatedexcited olefinic ligands,or as a catalysr reactionhas beenestablished,a neither the mechanism(s) facilitatingcarbon-carbon bond formation through mix- of the condensed-phase,copper-catalyzed photochemical ing of appropriatemetal orbitalswith olefinicmolecular reaction nor the nature of any intermediatesin this orbitals.t On the basisof quantumyield measurements. reactionhave yet beenclearly defined. Srinivasanhas su_egested that the primary photochemical The copper ion in the latter reaction might a priori step under the homogeneousreaction conditions of his experimentsinvolves absorption of light by uncomplexed (l) Supportedin part by the U. S. Army ResearchOffice (Durham), Grant ARO(D)-31-12.1-.135,and by the National ScienceFoundation, cis,cis-I,5-cyclooctadiene.He further proposedthat thc Crants GP-6222and CP-7266. copper(l)atom exertedits influencein the reactionin the (2) (a) National ScienceFoundation Predoctoral Fellow, 196l-1966: subsequentstabilization National Institutes of Health Predoctoral Fellow, 1966-1967. (b) of the initially tormed excited DeceasedJune 4, 1966. state of the olefin by formation of a complex of un- (3) R. Srinivasan,J. Arner.Chem. Soc., 86, 33lS (1964). specifiedstructure (representedschematically by 3).l (4) I. Haller and R. Srinivasan,ibid.,88,5084 (1966). (5) F. D. Mango and J. H. Schachtschneider,ibid., 89, 2485(1967). However, the appealinggeometrical relation betweenI (6) J. J. ivlrowcaand T. J. Katz, ibid.,88,4012(1966), and references and the racemic conformation of trans,trans-1,5-cyclo- therein. octadiene(2a), and the complicatedand quite different (7) W. Merk and R. Pettir,ibid.,89,4787,11-BB (1967). (8) D.J. Trecker, R. S. Foote, J. P. Henry, and J. E. McKeon, ibid., mechanismsuggested for the superficiallysimilar copper- 88, 302r 0966). catalyzedphotochemical dimerization of norbornene.s
Journal of the American Chemical Society I 9l:10 I Ntay 7, 1969 26()9 actually consists of a mixture of severalspecies. 3fltl * "CuCl" -> probably containsappreciable quantities of both com- plexedand uncomplexedcrs,crs- 1,5-cyclooctadiene ; horr'- /.\ol tf-\/"Cvcl" ever, accurate estimates of the relativequantities of n-'/) -_) t complexedand uncomplexeddiene cannot be obtained from the availabledata. 3 In a typical experiment,a stirred, degassedpentanc suspensionof complex.l was irradiatedfor ca.24 hr at room temperature using low-pressuremercury lanrps, have led us to examine in detail severalaspects of the and the solid material presentat the end of the reacrion photochemistry of crs,crs-1,5-cyclooctadienein the pres- was separatedby filtration. The filtered solution was ence of copper(I) chloride, under reaction conditions shown by glpc to contain cls,crs-1,5-cyclooc'adienetnd somewhat different from those describedby Srinivasan. tricyclooctaneI as major components,and cls,crs-l.-1- ln this paper we report the isolationof significantquan- cyclooctadiene,.l-vinylcyclohexene, and three unidenti- tities of cis,trans-and trans,trans-1,5-cyclooctadiene from fied componentsas minor constituents.t2The solid this reaction, and presentevidence pertinent to an under- materialwas composed of a mixtureof copper(l)chloridc standing of the role of thesecompounds in the conversion and copper(l) olefin complexes. Trearmentof this mix- of crs,cls- 1,5-cyclooctadieneto l.e ture with aqueoussodium cyanide solution liberated the olefinic components. E.xtractionand glpc analysis ot' Results the freed olefins indicated the presenceof both crs.cis- Isolation and Structure Proof of trans.trans-L,S-Cyclo- and cis,trans-I.5-cyclooctadiene,t3as well as a small octadiene. The starringmaterial tbr the majority of our quantityof anothercomponent, to whichwe haveassigned experimentshas been the crystallineand well-charac- the trans.trans-I,5-cyclooctadienestructure 2 on the basis -cyclooctadiene)di- terized di-pr-chloro-bis(crs,crs-1.5 of the chemicaland spectrcscopicevidence which follow's. copper(l)(.1).to Penranerather than diethylether was Compound 2 could be isolatedin pure form by glpc usedas themedium for our irradiations.in orderto avoid under ctrefully controlledconditions. This compt>und the complicatingfree-radical side reactionsencountered proved to be very sensitiveto tracesof oxygenor aciti. and slorvlypolymerized thermally even in the absencct)i' thcseagcnts. It was indc-finirelystable while tiozen rr -g\-..J'', 7ql - 78" under an inert atmosphere,and reasonablystablc I L___r- \.,/ in dilute solutionin degassedaprotic solvents. It polv- merizedexplosively on the additionof solventthat hati 4 not been deoxvgenated. It was characterizedby un odor similar to thoseof cis,trarrs-1,5-cyclooctadieneand trans-cyclooctene. by other worker_sduring the irracjiationof copper(l) I The infrared spectrum of 2 showed bands at l6t5 chloridein ether.r"r'r rhe useo[4 asstarting material - (C-C stretchingvibration) and 985cm L (trans-olelin and pentaneas mediumtbr the irradiationuntbrrunately bending vibrarion). No bands appearedin the 650- tntroducesseveral points of uncertaintyin our experi- 750-cm-t region.ra The observeddouble-bond stretch- ments. In particular,it hasnot beenpossible to measure ing frequency is lower than that of cis,trans-1,5-cvclo- rhesolubility of { in pentane,since a suspensionof 4 in -t octadiene(1630 cnt in their spectrum;peaks of equal this solvent dissociatesin part to tiee crs,cls-1,5-cyclo- intensityat 1622and 1635cm-t in the Raman spec- octadieneand a solid nonstoichiometric1,5-cycloocta- trumr3;, which in turn is lorverthan that of crs,crs-1,5- diene copper(t) complex. Further, we do not know cyclooctadiene(1655 cm-r in the ir spectrum,and l66J exactly what fraction of the total cls,cls-1.5-cycloocta-cm-r in the Ramanspectrumrr). dienepresent in the reactionmixture remainscomplexed The mass spectra of the I,3-, 1,4-, and 1,5-cyclo- with copper(l),either in solutionor as suspendedsolici. octadienesare strikingly similar in theregions corresoond- washing 4 with moderatequantities of pentaneresults in ing to fra*qmentscontaining three, five, six, and seven essentiallyquantitative extraction of cyclooctadienefrom carbon atoms (Figure l). However,while the 1,3-and the complex(see the E.rperimentalSection), and suggests 1,4-cyclooctadienesshow only small peaksin the region that 4 should be appreciably dissociatedunder the of m e 50-55, the base peak of the 1,5-cyclooctadienes conditionsof theseirradiations. Converserythe obser- occurs at mle ,s4 (butadienemolecular ion). The oc- vation (t,ideifia) that ca. 10,)(of the starting crs,cls-1,5- currenceof IVI* a,tmle 108for 2 demonstratesthat this cyclooctadienecan be recovered from the suspended compound has the same molecular formula as cls.cis- pentane-insolublecopper containing solids at the con- and cis,trans-I,5-cyclooctadienes.The observation ot' clusion of a typical irradiation, while ca. 50',,ois foun lVhitesides, Goe, Cope,i lrradiution of cis,cis-1,5-Cyclooct(t(/ictrc 26tO [/+\-1. t [sl. l|,i ill L\/J \ t/) co 60 mk lO8 mle 54 40 its base peak at mfe 54 supports the assignmentof 2 20 as a 1,5-cyclooctadieueisomer. The fact that the mass o spectra of 2 and cls,cls-and cls,rrans-\,5-cyclooctadienes are distinguishableonly by minor intensitydifferences is proposal 2 is trans,trans-1,5- consistent with the that 80 cyclooctadiene, since the mass spectra of cls and trans olefinsare usually almost identical.r5 60 Chemicaldemonstration of the 1,5arrangement of the 4O double bonds in 2 was provided when its ozonolysis ?o followed by oxidation with basic hydrogen peroxide afforded succinic acid in approximately 85% yield. Esterification of the crude acid with diazomethane yielded dimethyl succinate. The observation that no (< ca. 0.5%) dimethyl glutarate or adipate could be detectedby glpc in the esterifiedacids from the ozonolysis reactionexcludes a 1,4 or 1,3 arrangementof the double bondsin 2. The nmr spectrumof 2 showedresonances at E 4.88and 2.43 with relative areas l:2. The low-field olefinic resonanceis at higher field than the correspondingpeaks of cri,cri-1,5-cyclooctadiene(6 5.47) and cis,trans'|,5' cyclooctadiene(6 5.7),and thehigh-field peak is somewhat downfield from the correspondingpeaks of theseisomers (S 2.?5 and 2.1, respectively).Although the upfield shift of the low-field resonanceo[ 2 relative to the cor- responding peaks of crs,cls-and cis,rrans-1,5-cycloocta- dienesis undoubtedly due to the shieldingeffect of the opposingdouble bond, data concerningthe magnitude and anisotropy of shieldingeffects in the vicinity of carbon-carbon double bonds are not sufficientlyquanti- tative to permit theseshifts to be used in discussingthe conformationof the compound. In brief summary, these foregoing piecesof evidence clearly establishthe structure of 2 to be trans,trans-1,5- cyclooctadiene: its mass spectrum shows it to be a CrH,, isomerand suggeststhat it is a 1,5-cyclooctadiene; Figurel. Massspect*,,"",t,", voltage-80 eV; inletsystem at its presenceof one or more infrared spectrum shows the ambienttemperature; source temp€rature -80o) of cls,cts-1,5-, trans-disubstituteddouble bonds and demonstratesthat cis,trans-|,5-, trans,trans-I,5-, cis,cis-1,*, and cl's,cts-1,3-cyclo- it is neither crs,crJ-nor cls,/rans-|,5-cyclooctadiene;and octadienes. its ozonolysisestablishes the 1,5 positionof the double bonds. with potassiumamide in liquid The low yield of trans,trans-1,S-cyclooctadieneobtained ment of this methiodide yield cis,trans'andtrans,trans- in the photoreaction is a major practicalimpediment to ammonia did in fact both in approximately1.2 and 2.47;yields. any proposedinvestigation oiits chemistry. Accordingly, 1,5-cyclooctadienes No wasobserved. we brieflyinvestigated the low-temperaturemodificationr6 respectively. cls,cis-1 ,5-cyclooctadiene Hence,although this reactiondoes not provide a practical synthetic route to 2, it does at least provide further I- ,'-Jt**(cHr)3I- confirming evidencefor the assignedstructure. (cHr)rN-'\---,/ The ultraviolet spectrum of trans,trans'I,5-cycloocta- dieneis remarkable. In both isooctaneand diethylether ello/ - 5 2.47" solution the compound shows a peak at I.o, 246 mp (e - 1500). In addition, it exhibits normal end ab- - of the Hofmann degradationof 1,5-bis(N,N-dimethyl- iorption for u disubstitutedolefin (rrro -,. !?00).tt amino)cyclooctanedimethiodiderT (5) in an attempt to The oscillator strength of the 246mp transitiontn (-f - find a practicalsynthetic route to this compound. Treat- 0.05) is sufficiently high that it seemsunlikely that this transition is an olefin "mystery band" of unusually (15) K. Biemann. "Mass Spectrometry," McGraw-Hill Book Co., Inc., New York, N. Y., 1962,p l5l. (16) C. Wittig and R. Polster,Ann. Chem.,612,lO2 (1958). (17\ Z. Jacura. Ph.D. Thesis, MassachusettsInstitute of Technology, (18) P. Bladon,H. B. Henbest,and G. W. Wood,J. Chem.Soc.,2737 1962: A. C. Cope and Z. Jacura,unpublished. (r952). Journal of the American Chemical Society I 9l:10 | May 7, 1969 :6il nigh intensity.:o Furrher. cis,trans-I.5-cyclooctadiene, -cv 2r t.a tr ans clooctene.and 9,9':dehydrodianthracene, whose 1../l doublebonds are aiso highlystrained, show no abnormal /a 1 //"L uv L/ absorption. Hence, the anomaious absorption ex- I /a hibited by 2 is apparently nor peculiar to the strained t, .,4 t I .' oo trans double bond. Models suggesrthat the double I IOO-9- bonds in cis,trans-1,5-cyclooctadiene are held rather far i 3 w apart, while those of both the racemic and meso 751l\_.'- oi contormations2a and 2b of trans,trans-!,5-cyclooctadiene t\ are constrainedto be in closeproximity. We believe,in uoJ the absence of other obvious explanations for this I a' phenomenon,that the anomalousuv absorption in 2 is 25 -l l- a due to an interaction betweenthe transannular double i^- bonds.:2 ojLJ-:- Unfortunately, we are unable to determine unam- 0 i2 i biguouslyfrom either the uv or other availablespectro- houis scopr c evidence whe ther thet r ans,trens-i, 5-cyc Iooctad iene Figure 2. Yields of I (o), crs,crs-1,5-cyclooctadiene(c), orepared by the copper-catalyzedphotoreaction exists cis.rran.s- l,-S-cyclooctadiene (A), and trans,trans-l,5-cyclooctadiene ( V), rn contbrmation2t or 2b. The high opticarstabirities of during the irradiation of 4 in pentane. The insert gives yields or' I resolv'edtrans-cyciooctene23 and of cis,trars-1,5-cvclo- and cis,trans-1,5-cyciooctadiene on an expanded scale during rhc octadiene:+suggest that the rate of interconversionof 2t inirial sragesof the irradiarion. The data of the two sets oi;l()rs were obtained in different experiments, end 2b should be slow. on the basisof the r>bservation rnd are not directlv corn- ( parable, due to the effecls e.t aging ot'the lamps. t'ideirytia\ that 2 undergoesfacile conversionto I rather than to tricyclo[4.2.0.02.5]octaneon irradiation, we pro- posethat 2a is the conformation producedin the irradia- Samples of trans,trans-I.,i-cyclooctadienewhich hati tion::5 horvever, this proposalmust obviouslybe con- been kept at rocm temperatureuntii compieteiytlecorn- srderedtenrative at thisjuncture. posedthermally showedno traceof I or of other ot' rhc Irradiationof 1,5-c.vclooctadiene Isomers. In consider- cyclooctadieneisomers: onlv polymer was ibrmeti. rngpossible mechanisms for the copper-catalyzedphoto- Similarly, no trace oi I cr>uldbe detectedon gipc trt' chemicalconversion oi 4 to tricyclor>ctanel, it seemed purified irans,trans-1,5-cvclooctadieneusing an injectir.n conceivablethat I might arise trom an intramolecular biock temperatureof 30' tnd cr>iumntemperature r)t' :hermaicycloaddition reaction of the strainetiand highly 60-65'. The compounci,.vas never exposecito highcr rercti'e double boncis ot' photochemically produced temperatures. irans.trans- or cis,trans-|,5-cyclooctadiene. This hy- of samplesof cis,trans-1,5-cyclooctadieneby pothesisivas examined . .Pyr.glys.is and rejectedon the basisoia briei injectioninto a glpc instrumenrhaving an injectionp()rr ixaminationof the thermal behaviorof thesetwo dienes. temperatureof 275" resultedin the productionof cis.ci.r- 1,5-cyclot>ctadiene( l2|;,). 4-vin,llcyclohe,rene(5 ,?;,),i.r r l9) Calcuiated from an expression modified for unsymmetrical lbsorptronbands compound (possiblycrs-divinylc;rclobutane) which dc- j': (1.62 x l0- 8)r-".(v... _ v,) composed to clr.crJ-1,5-.:lrcioocta(lienein the detecr,rr ',,,'here - \'.r, and v, arc the frequencies(in cm t) of the absorption (l\fi),tu and unidentifiedminor componenrs; the rc- :rllxrmum and thc long-wavelengthside of the peakat halt'-bandwidth. mainder rtf the cis,trans-I,-<-cvclooctadienegave a sinrrlc ct c Brrc gleb, " Elektronen-Donator-.{.cceptor-Komplexe. " Springer- \ crlrg,Berlin. 1961. p 61. peak (84",;)and decomposecito crs,crs-1,5-cyclooctadienc {:01 L. Lubczkyand R. Kopelman.J. Chem.phvs.,45.2526 0966); and 4-vinylc;rclohexeneon passagethrough the detector Il. B. Robin. R. R. Hart, and N. A. Kuebler,ibid.,41, 1803(l966). (300"). Although the minor componentshad retenri()n ,ll) N ^\{.Weinshenker and F. D. Greene,J.Amer. Chem.Soc..90. 506r 1968). timessimilar to I on the columnused. no traceof I corrid tll) A transitionoccurring at ca.2lO mp (log e -4) in a number of bedetected in the infraredspectrum of coilectedmaterialrt iesqulrerpenelactones (e.g., (i), balchanolide germacrone,and costuno- These data provide convincing lrde)has beenattributed to a similar transiinnularinteraction: F. Sorm evidencethat I is not produced by an uncatalyzedthermal reaction of either cis,trans-ot trans.trans-\.5-cyclooctadiene.2sThe possi- bility that I mighr be produceciby a coDper-catalt':ei (26) The retentiontime ot'this material.,vas appreciably shortcr rhan that of cis,cis-1..<-cyclooctadiene:however. materiar collected from thc glpc I had an ir spectrumidentical with that oi cis.cis-1,S-cyclooctadiene (27) ziegler reporredthat heatinga diluresolution oi the compotrnri subsequentlyshownr3 to be cis.rrans-|,S-cyclooctadieneat I l0' yieltled ,rndL. Delo5,"cuaianolides and.cermacranolides," Holden-Day, Inc., dimer (20'11)),polymer G3o,/o),cis,cis-1,5-cvclooctadiene (12'i,). rrn,l San Francisco,Calif.. pure 1966; F. Sorm, Appl. Chem.,l. - *'.\iteside.s. Cue. Cope , Irrc:.:iurton o,t L.is,c:s-,.5-C;,'c!oocictlietr,' 26t2 TableI. lrraciiarionof 1,5-Cyclooctaciienes" Yietd. 7( /i I Irradiatron li',J lr N/'J ,l Substrate timc. hr 2 \_,, v-/ Other ,:ls,crs-1,5-CCD 100 0 (t 0 0 0 crs.crs-1.5-CODo Major Trace' 0 0 0 0 Poiyme: (t 93 + Iournal of the American Chemical Society I 9l:10 I May 7, ,t969 :6 tl conversionof cls,crs-1,5-cyclooctadieneto I on irradiation conversionsof 4 (Figure2) showthat therate of formetion in the presenceo[ coppei(l) chlorideestablished, among of I dependson the concentrationof this diene in the other things,that only a very small fractionof the diene irradiation mixture, and suggeststhat at leastpart of the I presentin the ether solution was complexedwith copper observedas a reaction product is derivedfrom a photo- ion. using argumentsbased on the opticaldensities of reaction of cis,trans-diene.The high steady-statecon- the variouscomponents of the irradiatedsorution. and on centrationof cis,trans-1,5-cyclooctadiene observed durin g estimatesof the quantum yieldswhich wourd be required the latter stagesof the irradiation (Figure 2), and the to describe the photochemical transformationof the relatively high efficiencywith.which it is converted to I complexedand uncomplexedforms of 1,5-cyclooctadiene on irradiation in the presence of copper(l) chloride into l, srinivasan was able to demonstratethat uncom- (Table I) indicate that a major portion of I has the ple-veddiene was the primary light-absorbingspecies in cis,trans-dieneas a precursor. Finally, the facile trans- solutionunder the conditionsof his irradiations. formation of trans,trans-\,5-cyclooctadieneto I on irradi- A choiceof the primary light-absorbingspecies in the ation, togetherwith the observationthat irradiation of heterogeneouspentane suspensionof 4 used in our cis,trans-I,5-cyclooctadienein the presenceof copperll) experimentsis unfortunately much more difficult, due chloride yields trans,trans-1,5-cyclooctadiene,raises thc both to the impracticabilityof meaningfulquanrum yield interesting possibility that the trans,trens-dieneitself, measurementsunder theseconditions and to our inability despiteits consistentlylow concentration,might give rise to estimateeither the solubilityor dissociationconstant of to a significantquanrity of l. { in pentane. The last of theseproblems is particularly Thus, we cannot rigorously exclude contributions ro 'e.ring,since 4, if anything,appears to be /essdissociated the conversionof 4 to I from eithera directphotochemical in heterogeneouspentane suspensionthan in homo- reaction or from a less direct pathway involving con- geneousether solution, and consequentlyappears rela- version of uncomplexed cls,crs-1,5-cyclooctadiene to I tivelymore likely to be rheprimary light-absorbing species ula someundetected copper-complexed intermediate, but rn pentanethan in ether. Nonetheless.both on the basis not involving cis,trans-or trans,trans-1,5-cyclooctadiene, of the qualitativeobservation that a significanttiaction on the basisof the relativelyqualitative data availablt--; of the crs,crs-1,5-cyclooctadienepresent in a pentane however,it is clear trom the accumulateddata that an suspensionof .f is freein solurion,and on the basisof the appreciablefraction of the I isolatedat the conciusionot' obviousanalogy between the system studieci by Srinivasan the reaction must hav'e come in some fashion tiom and that investigatedin this work, we rvill assumethat c is.trons-1,5-cyclooctad iene. uncomplexed cli,crs-1,5-cyclooctadienc is the primary On the basisof thesedata, we proposethat the con- light-absorbingspecies in irradiationof a pentanesus- versionof .{ to 1 should be describedby somevariant of pensionof 4. the mechanismoutlined in Scheme[. The most inrercst- Acceptingthis assumption,an uncomplexedelectroni- cally excited 1,5-cyclooctadieneis necessarilythe first Scheme I speciestormed on irradiation. This e.rcitedstate, what- ever its geometry, is certainly energeticallycapable of conversionto l. However,several observations suggest r.^O_CuC, #O]' that the initiallyformed excited 1,5-cycroocradiene, *hen generatedunder the conditionsof our experiment,is convertedto I in large measureby way of one or more stableintermediates. First, neitherdirect nor benzene-sensitizedirradiation h"bt,re oI crs,cls-1,5-cyclooctadiene,in the absenceol copper(l) chloride but under conditionsotherwise comparable to Q1.,., those of the copper-catalyzedphotoreaction, yields de- .ll tectablequantities of l.3a Srinivasanhas interpreteda tl il similar observationunder homogeneousconditions to | | hv.'b, tl tl mean that copper(t) functions in the photoreactionby IY coordination with I the exciteddiene, and has suggested that I is obtained directly fiom this excited complex nr) without a subsequentphotochemical step. Although we \_i '\/ -> + cannot excludea contribution lrom a pathway o[ this Q=z-."., LJ type in the irradiation of 4 in pentane,the isolationof B*' cis,trans- and trans,trans-1,5-cyclooctadiene from this photoreaction,and the demonstrationthat theseolefins ing problem posed by this schemeconcerns the role ot' are convertedto I under the conditionsof the reaction, trans,trans-1,5-cyclooctadiene in the formation of l. suggestthat it may be more profitableto rationalizethe Under the conditionsof the irradiations,both cis,trans- influenceof the copper(l) on the basisof its ability to and trans,trans-1,5-cvclooctadienesare present in xp- complex strongiy with the ground-statetrans double preciableconcentrations only as their copper(l) com- bonds of these dienes. Second, the reiativeyields of plexes. The major part of I mightthen be formed directly cis,trons-1,5-cyclooctadiene and of I observedat low by irradiationof the cis,trans-I,5-cyclooctadienecopper( l) comple,x,or it might result from photochemicalconver- sion of this comple.x to trans,trans-1,-<-cyclooctadienc (3.1)However Professor Harold Ward (Brown University) has obtained I on benzene-photosensitizedirradiation of cis.cls-1,5-cyclo- and subsequentphotolysis of this latter compound. octadienein the vapor phase: H. R. Ward, privatecommunicarron. Ideally,examination of the ratesof formationof 1 and or' lVhi tesides, Goe, Cope, I rrudiut ion of c is,cis-!,5 -Cyclooc tutlian t: 26t4 trans,trans-l,-<-cyclooctadiene at conversionswell below The correct descriptionof the detailedfunction of the the levelsof Figure 2 would p.rovidedata which could be copper(I) in the reactionsequence of SchemeI remains a used to answer this question. Unfortunately the low topic of speculation. The experimentsreported here are steady-stateconcentration of thc trans,trans-dienereached not helpful in judging the correctnessof Srinivasan's during the irradiation,and the appreciableexperimental suggestion that the copper(l) serves to stabilize an difficultiesinvolved in analyzingsmall quantitiesof this electronicexcited state of 1,5-cyclooctadiene.3How- compound, make a detailed quantitativeyield study at ever,an alternativeand attractivepossibility raised by the very low concentratignsimpractical. isolation and examination of cis,trans-and trans,trens- Alternativeiy, a knowledge of the absorption charac- 1,5-cyclooctadienesis that the ability of copper(I) to teristics of the copper(I) complexeswith cis,trans-and form strongcoordinate bonds with the ground-statetrans trens,trans-1,5-cyclooctaciienes, and of the quantumyields double bondsof thesedienes serves both to protectthem O1, @2,and @, (SchemeI) describingthe conversionof from polymerization,and to shift the position of the these complexes to I on irradiation, would permit an photoequilibria between the three 1,5-cyclooctadiene estimation of the relative rates of formation of I from isomerstoward the stericallystrained but stronglycom- each diene. Under the approximately steady-statecon- plexing cis,trans-and trans,trans-I,5-cyclooctadienesat ditions reachedin the later stagesof the photoreaction, the expenseof the relatively unstrained but weakly the concentration of cis,trans-1,5-cyclooctadieneis ap- coordinatingcrs,cls- 1,5-cyclooctad iene. proximately twenty times that of trans,trans-1,5-cyclo- octadiene. On the other hand, the extinctioncoefficient ExperimentalSection of the 246-mp transition of trans,trens-1,5-cyclooctadiene General. Melting points were determined on a Reichert hot- is sufficientlylarge that, if the extinctioncoeticients of the stage microscope and are uncorrected. All irradiations were con- copp€r complexesof these dienesin the region of the ducted in quartz vesselsusing a Rayonet Photochemical Reactor emissionmaximum of the lampsare in the sameratio as equipped with RPR 2537A lamps. Solutions were concentrated the extinctioncoefficients of the uncomplexeddienes in at 0-5' (50*100 mm) with the aid of a rotary evaporator, except as were Perkin-Elmer Model this region, the trens,trans-1,5-cyclooctadienecomplex noted. Infrared spectra taken on a 2378 spectrometer. Mass spectra were taken on a Hitachi Perkin- should absorba. Iarger traction of the incidentlight than Elmer Model RMU-6D mass spectrometer. Nmr spectra were the cis,transcomplex. The quantum yield, Or, charac- obtained using Varian A-60 and HA-60 spectrometers. Ultra- terizingthe internalcycloaddition of the trens,trens-1,5- violet spectra were taken on a Cary lvlodel l4 recording spectro- cyclooctadienecopper(l) complex would be expectedto photometer. Clpc analyses were carried out using the following columns and instruments: column A.8 ft x 0.25 in.25)(4-nitro- be high.35 Hence, with these assumptions,at one 4-methylpimelonitrile (NMPN) on Chromosorb P, glass column extreme of interpretation the rates of tormation of I operated isothermally at 65";r6 column B, 8 ft x 0.5 in. 10"; from cis,!rans-and trans.trans-I ,5-cyclooctadiene pre- 1,2.3-tris(2{yanoethoxy)propane (TCEOPt on Chromosorb P, cursors shouid be approximatelyequal; at the other glasscolumn operated isothermallyat 65';rn column C, l2 ft x 0.2-sin.57; XF (nitrile siliconetluid),40-65" (F & lvt Model extreme,the major fraction of I might be tormed from the ll50 810 gas chromatograph. thermal conductivity or flame ionization trans.trans-diene.Unfortunately, carrying this approach detector as noted); column D, 2 ft x 0.25 in. ?0)( silicone rubber through in a convincingquantitative manner requires a SE 30, temperature as noted (F & M Model 720 gas chromato- knowledgeof the extinction coeltcientsoi the diene- graph). The areas of glpc peaks were dctermined by planimeter (column copper(l)complexes, and of the quantum yieldsof the (columns A and B) or by Disc integrator C). Elemental analyses were perlbrmed by Dr. S. ivl. Nagy and associates. individual stepsin the presenceof copper,and it is less Pentane was purified by stirring with sulfuric acid, and distilled than obvious how these numbers might be obtained from barium oxide. All glasswarewas rinsed with concentratcd practicallyin the heterogeneousreaction system of this amnronium hydro,ride and distilled ,,'vater.and dried before use. Di-u-chloro-bis(crs,crs-1,S-cyclooctadiene)dicopper(I) (4) was pre- study. I o It is worthwhilepointing out explicitlythat the con- pared using published procedures. Anal. Calcd tbr C,6H2nCuzCl.: C. 46.38; H,4.57; Cl, l7.ll. clusionsreached in this paperare intendedto apply only Found: C, -15.67,45.48; H, 5.84,5.90: CI, 17.18,17.21. to the particular heterogeneousreaction system studied Pentane Washing of Complex .1. A 0.1-g sample of complex -1 here. The vapor phase studies of Srinivasan3'nand was washed with five 5-ml portions of pentaneand dried at 100 mm Wardsa have demonstratedclearly that the presenceof and room temperature tor 2 hr. Anal. Calcd for C, 46.38: H,4.57; Cl, l7.ll. prerequisite photochemical CroFIznCuzCl2: copper(l) is not a for the Found: C, 32.96; H, 4.57; CI, 21.57 (-297', low in 1,5-cyclo- conversion of 1,5-cyclooctadieneto l, and it seems octadiene). entirelypossible that the homogeneouscopper-catalyzed The procedure was repeatedwith l-s 5-ml portions of pentane. photoreactionstudied by Srinivasan*may proceedby Anal. Found: C, 1.42; H, 0.31; Cl, 34.04 (-977, lorv in still another mechanism. Thus, it appears probable 1,5-cyclooctadiene). Irradiation of Complex 4. Complex 4 (0.5 g, L2 mmol) and 70 ml that a number of reaction pathwavsconnect 1,5-cyclo- of pentane were placed in a 100-ml quartz vesselequipped with a octadieneand 1, and that mechanisticconclusions drawn nitrogen inlet and condenser, and irradiated for 24 hr with magnetic from studies of one system need necessarilyhave verv stirring. A stream of prepurified nitrogen previously saturated little pertinenceto other systems. with pentane was bubbled through the suspension vra a Teflon syringe needle; the agitation provided by this gas stream stirred (35) The quantum yield of formationof oxetanetrom benzaldehydc the rni.rture and prevented caking of the solid on the walls of the in 4 ,l/ 2,1-dimethvl-2-butenenas beenfound to be 0.527(N. C. Yang, vessel. The mi.rture was filtered and the solid was washed several R. Loeschen,and D. Mitchell, J. Amer. Chem.Soc.,89, 5465(196i)). times with pentane. Analysis oi the concentrated filtrate by glpc The photocycloaddition of rrans-srilbeneand 2,3-dimethy[-2-butene (4 'l{ in hexane)proceeds wilh a quantumyield of 0.538(O. L. Chapman privare communication). Although ihese quantum yields describe (36) in;ection port and detectorblock tempcratureswere maintained cycloadditionreactions proceeding from n * rtr lnd aromaticIt - tlr at 80'. The glpc instrument used wrs oi lvlassachusettsInstitute of' excited states. respectively,and as such are not necessarilydirectly Technoiogy Chemistry Department design. Attempts to use any ot' comparable to that descrrbing the olefinic ;t - rr' c;;cloaddition the avarlablecommercial instrumentswith metal columns for analysis presumedto be invoived in the conversionof 2 to l. their high values or separationof mixturescontaining 2 resultedin compietedestruction do suggestthat a low value lor the last processis unlikely. of this compound. Journal of tlrc American Chemical Societv I 9l:10 ,l ;Va)'7, 1969 2615 usrng c.,.:(\t\lri'lc as an inrernal stanciard(column A) indicateCthe stanC for iC min. Nitrogen was buhbled tnrough the solutiorr ro prcscn-!,r: -;,.-'rs-i.5rlclooctadiene(52i;), tricyclo[3.3.0.0t'6]- remove excess ozone. Ivlethanol /-ltl ml) was added and thc ()ctf,nc I , l,i .,. crr.clr-1,4+yclcloctadiene(1.3','"), and 4-vinyi- soiutron was alitrwed to warm to ice-bath lernperature. To tirc ;,,,:1,,-ga.-"c,1."'.,.l' stirrecisolulion was addcci 5 mi of 20'fu aeueous sodium hvdroxitic T:'c ,,.,:.i :::.trc.rralrEfrom the irradiation was slraken with a soiutron. then 5 ml of 309j hycirogenperoxicie wa^radded ciropwrsc :'\:r:. .'i'l-<;'ni tri pentaneand l5 ml of 15)j aqucoussodium over l0 ntirr. Water (10 ml) was addcci.and the resultingnrixrurr j;.i: J.;.ri'.;::.rn at 0-, and the hycirocarbclnphase was separated. was stirrcd, in the ice bath for I hr. l'he mixture was warrncd l:'c.r.:-.rc,)u)i.rrcr was again extractedwith 25 ml of cold pentane. gentlv on the sream bath. and mcthylene chlondc was removcd bv .1.r.::::c :-'n-llrncd i)cntane soiutions were washcciwith coici water distillation. Tlrc resulting sotution rvas ireatedunder reflux tirr Ii ::.,. :l:ercci qur::kly tirroughout Moicular Sieves(Linde 44,t. I irr. Mosr of thc methanoi was removed by distillation,and thu .1."1: --,'n:snt retetj. The solutions were stored unoer nitrogen at 0" ; resicirreu'as cooled and made acidic rvith concentratedhydrochionc .:,..r:l'lilcl's anJ manipulations were carried out rapidlv withour acici. fhis solution was extracted continuouslv with ethcr lirr ti,'li*Jlrrro l'rc)matmospheric oxygen. Analysis of the concentrate l5 hr. The ethcr cxtract was dried and evanorated tc yieid 2E rng :. g:lJ (,-oiunrn B) using cyciooctane as internal standard shclwed (85')( of 0.23 mmol) of cruciesuccinrc acrC, mp 169-176'(lit.aonrp :.-.c i:iicn!c oi c'rs',crs-,cis,lrans-, and Irans,trans-l ,5 lVhites ides. G oe, C,Lpe,' Irrudiut ion of c ls,t'is-!,5 -Cyclooctudt'( n ( 26t6 solurionshowed the preserccof cfcloocrane.nd ll.? m8-(70i,) appreciation tc Dr. A. S. Mehta for preliminary expert- of t c-vclooctane(2).r' and no othcrcomponents (limit ol dctcc' ments, to Mr. H' L. Mitchell for running massspectra. rnd tion lbout 2i1). to Professor John Baldwin (University of Oregon) for .{cknowl€dgm€nas. We would like to express our r heipful discussion'1000, (32) For a related study of the photochemicalisomerization of r, and 75 l. mol- respectively. cis,trans,trans- to cis,cis,trans- and trens,rrans,trans-1,5,9-cyclodo- (30) The giass-column,low-temperature glpc used of necessityfor the decatrienes,see H. Nozaki, Y. Nisikawa.Y. Kamatani, and R. Noyori, isolation and analysis of the cis,trans- and trans,trans-|,5-cycloocta- TetrahedronLetr., 216l (1965). dieneswas unsuitablefor reliablequantirative determinations of yields (31) The rapid formation of polymer in the benzenesensitized of thesecompounds lessthan approximately2oL. However,accurate reactions may in part reflect photoaddition of the cyclooctadienesro determinationsof the lesssensitive I were possibleusing conventional benzene: cf. D. Bryce-Smith and A. Cilbert, Chem. Commun., 613 glpc instruments (see Experimental Section). (re66).