-t s62s i The Mechanismof Formation of I2,3,4-Tetramethylnaphthalenefrom 2-Butyneand Triphenyltris( tetrahydrofuran ) chromium ( III )' GeorgeiVI. lVhitesidesand William J. Ehmann: Contributionfrom the Department of Chemistrv, MassachusettsInstitute of Technology, Cambridge, lvlassachusetts 02139. ReceiuedJanuary 3i,, 1970 .\bstract: Reacrion of triphenyltris(tetrahydrofuran)chromium(III)(f) with 2-butyne y'ields,inter alia, 1,2,3,4' tetremerhylnaphthalene(2). A freeor metal-complexedtetramethylcyclobutadiene has beenexclr-rded as an inter- mediarern rhis reactionby the observationthat 1,2-dimethyl-3,4-di(methyl-rir)naphthalene(6) is not a product of I and 2-burlne- 1,1,1-d3 (3). Examinationof the relativeyields of 1,2,3,4,5-pentamethylnaphthalene(15) and 1,2,3,' .1.6-pentamerhylnaphthalene(16) tbrmed in reactionof 2-butyne with tri-o-tolyl-, tri'nr-tolyl-,and tri-p-tolyltris- (terrahldroiuren)chromium(III)demonstrates thiit a iong-livedaryne-chromium complexis also not an intermedi- atc in fhe:e cyclizations. Labeling and kinericisotope experiments using partially deuteratedderivatives of 1 fur- rhcr drsercdir bcnzynecomplexes as intermediatesin the tbrmation of 2. The reactionof trimesityltris(tetrahydro- iurrn)chronrrumtlll) with 2-butyneto torm cis-2-mesitylbut-2-enesuggests that an initial stepin thesereactions may be rnserrronot'2-butyne into a carbon-chromiumbond rvirh formation of an intermediatevinylic chromium reagent (2{r. The additional observationsthat 2-biphenylmagnesiumbromide and trichlorotris(tetrahydrofuran)chro- mrum(lll) relct to form 5-(2-biphenyl)dibenzchromole(29), and that this chromocyclcreacts with 2-butyneto yield 9.lr.t-dimcthylphenanrhrene,impliclte an analogouschromocycle 3,4-dimethyt-5-phenylbenzchromole (34) in the l'ormarronof 2. Taken togetheiwith further deuteriumexchange and labelingexperiments. thcse obscrvations lead ro rhc proposalthar the reactionof I with 2-buryneproceeds by initial insertionof one molcculeol'2-butyne into a phcnll-chromium bond of l, cyclizationof thc resultingvinylic chromium contpoundrvith elimination of benzene to iorm chromocycle34, ancireaction of the chromocyclewith a secondmolecule of 2-butyneto yield 2 (Scheme VII ). rclooliuonrerizetionof acetyleneby transitionntetal butadienes'r0-r3 intermediates. or to proceedby a con- t t't3 clitllvsts prorides the basis for a number of certecl " n-ntulticenter" rcaction pat[. Of these useiulorslnic sl'ntheses.3Attenrpts to establishmech- suggestedand not necessarilyexclusive mechanistns, anisms ior this classof reactionshave been hindered only the nretallocyclicpathwxy has receivedpositire by' dif'hcultiesin identifyingthe activeorganometallic support.4'; Untbrtunately,without knowingeither thc catalvsts. Although a variety of structureshave been structuresoI the active catalysts.or, in most cases. postulatedtor these catalysts,it has proved possible evenelementary cietails of stoichionletry,reaction order. to isollte and characterizemechanistically significant or material balance,the designand interpretationof reectionintermcdiates or by-productsin only a small experimentsbearing on the rltech;,tnismsof these re- number oi reactions.{'; Precedcntsderived from the actionsremains a dillicultand subjectivematter. ertensirelv explored chemistry of transition-metalacety- Our interest in the mechanismof transition metal lenc conrplexessuggest that thesecyclooligomerization catalyzeclc.vclooligonrerization reections has promptc-d reactionsare initiatedby coordinationof one or more us to examine a related noncatalyticcyclization in- moleculesof acetylenicsubstrate to a metal atom or volvinga transitionmetal organometallic reagent: ui:.. metal atonr clusterof the catalyst.s'6 The process(es) the reaction of 2-butyne with triphenyltris(tetrahydro- b1'which the coordinatedacetylenes are subsequently furan)chromium(III) (l) to yield. inter alia, 1,2,3,-l- t t't:' tt conrerted to product has been variously suggested tetramethylnaphthalene(2;. This reaction is i-t to involre metallocyclic,r'z's ?r-allylic,s"'e'r0or cyclo- considerably more tractable subject for mechanistic examination than the catalytic cyclooligomerizations (l) Supportcdby thc National Institutcsot'Health, Grarrt No. GN{ - 160:0.by thc U. S.Army RescarchOtIice (Durham) Grant No. ARO-D- (8) For rclated proposals of mctrl-coordinittcd butadiene l,'l-dt I I - l l-1-G69l, and by Eli Lilly and Co. radicalsas reactionintcrnrcdiatcs, sec R. C. Cooksonand D. W. Jones. (l) Nattonll Sciencc FourrdatiorrTruince. 1965-1966; National Proc. Chem.'Soc., ll5 (1961); H' P. Throndscn'W. Metlesics'and H' Institutcsot' Hcalth PrccloctoralFellow. 1966-1969. Zeiss.-/. Organometal.Chem.,5, 176 ( 1966). (3) Rerrovs: (a) C. Hoogzandand W. Hiibcl in "Orglnic Svnthcscs (9) G. Wilkc,et al., Anqetv. Chem., tnr. Ed. Enql.,5,l5l (1966);A' T' via IIctaI Carbonyls,"L Wenderand P. Pino, Ed., Intcrscience,Ncrv Btomquistancl P. Il. \laitlis, J. Amer. Chen. Soc.,84, 2329(1961). York, N. \'., 1968.pp 3.{3ft'; (b) F. L. Bowdenand A. B. P. Lever, P. M. NIaitlis.et al.. ibid.,90,5l2l ( 1968). Orqunometal.Chem. Rec., Sccr. A,3,227 (1968); (c) E. Ochiai.Coord. (10) w. Schr.it'crancl H. Hcllm;rnn, '4nqerv.Chent.' Int. Ed. Enql'' 6, Citent.Rer'., J. -19( 1968); (d) J. P. Collmrn, Trattsitiort,lletal Chent., 518fl967). 2. | (1966t. (ll) H. Zcissin "OrglrtorrtctallicChemistrl'," H. Zciss,Ed., Amerr- (1) J. P. Collman.J, W.liang, W. F. Littlc,and i\I. F. Sullivarr,Inorg. canChcmical Socicty !{orrograph No. l{7, Rcinhold,Nerv York, N' Y ' Cltem.,7.l:9U ( 1968). 1960,pp 186fl (5) (a) O. S. llills and C. Robinsorr,Proc. Chen..Soc., 187 (196'l); (lli w. Hcrrvig,W. \Ictlcsics,and H' Zciss,J. Amer. Chem.Soc'. (b) R. P. Dodge and V. Schomaker,J. Organontetal.Chen., 3' :7'l 81.610l ( l9-59). (1965); (c)J. F. Blount,L. F. Dahl, C. Hoogzand,and W. Hiibcl, (13) G. N. Schrauzer,P. Glockner,and S. Eichtcr,Angew. Cherrt" J. Arner.Chem. Soc.,88,292(1966); J. T. lv{ague.ibid.,9l.198l (1969); Inr. Etl. Engl..3, 185 (196'1);G. N. Schr.tuzerrnd S. Eichler,Chettt' L. R. Bateman,P. M. Maitlis,and L. F. Dahl, ibid.,91,7292(1969). 8er..95.550( 196:). (6) W. Hijbcl, "Organic Synthesesvia Metal Carbon.'-ls."I. Wender (l-l) Rclatcclreactions have becp obscrycdwith diphenylnicket[\l. and P. Pino, Ed., Intt-'rscicrrce,Ncrv York, N. Y., 1968,p i73 ti. Tsutsui arrd H. Zciss,./. .{nter. Chenr.Sr-lc., El, 6090 (1959)land rvrtlr (7) L. S. IWerirvether,!1. F. Leto, E. C. Colthup,ancl G. W. Kcn- cycloperrtl{icnylmethylirortdicarborrl [ ;.rrtd c;-clopcltadiepylcthrt- nerly, Org. Chenr.,27. 3930( 1962); W. Keim, J. OrguncmetalChem., molybdcnum tricarbonyl [A. N.ku'rur.r .rrrd N. H.giharit, i\'lipp,trt "/. ( 16.l9 I ( 1969);E.-A. Rcinsch,Theor. Cltenr. .1cra, ll, 196( 1968). Kag'rt k tt Zos s lt i, 8.1.3'l'l ( I 961) ; Che nt. .1b s r r, 59' i'i0l I d 1963)l' LVlr i ra sidcs, Elrrnun n 5626 for severalreasons. First, the composition and struc- version of 3 ro retramethylnaphthalene-d6by way of ture of the starting organometallicreagent I are rea- r-allylic or metall,rcl'clicintermediates, represented sonablywell defined.rr'r2'rs Second,the fact that con- version of a o-bonded phenylchromium moiety into H | ( tl " \-,/'" L ft. tetramethylnaphthalenenecessarily involves the cleavage 3-'lrPh, of an ortho carbon-hydrogen bond providesan opportu- ^,-'-\ -r, Lrt ( n nity to apply a number of standard mechanistictests to {a those stepsof the reaction in which the carbon-hydro- gen bond is broken and the corresponding carbon- H I I t) ^-hr carbon bond formed. Finally, since the organochro- \'- ! r rit 6 mium reagent is directly involved as a reagent, and Hlll \\\ CH since it is not regenerated,there is no ambiguity con- 9H, {b I cerning the nature of the "active" organometallicspecies C in the reaction. Nonetheless,despite the obvious differ- llr r_-l ences between this noncatalytic cyclization and the U ilt V. CDt catalytic cyclooligomerization reactions,there are also I r.'._ph CD, I parallels suggest ,r^\'_ enough to that information concerning 3 the mechanismo[ the former should be pertinent to a:) QD, mechanisticquestions concerning the latter. JA r--lJ r'. / Resultsand Discussion D \.r'\ nt l\lechanismsInvolving a CyclobutadieneIntermediate. \.,' 1i'-rn The initial objectiveof this study was to determineif Dr'- \ either tetramethylcyclobutadieneor a chromium- r'H 'l tetramethylcyclobutadienecomplex were an interme- JO diate in the conversionof 1 to 2. Previousdeuterium- (-H Dr'. / labeling studiesof the cyclotrimerizationof 2-butyne \,zz\ to hexamethylbenzeneby an organochromiumcom- i .t-r'-Ph ..S-,/ tr -/ \ pound of unknown composition derived from I had rlr \ t'D CH, demonstratedthat a chromium-tetramethylcyclobuta- I dienecomplex wasnot an intermediatein the reaction.16 JC Although it seemedprobzrble that the same resultwould schematicallyby Sa-c. or by way of any other "linear" be found for the noncatalyticconversion of I into 2. cyclooligomerizarionpathway that does not allow thc the fact that these earlier labeling studiest6 had es- four methyl groups derivedfrom the two reactingmole- tablishedthat the mechanismof catalyticcyclotrimeriza- culesof 3 to becomeequivalent, will lead to 6,7,8, tion varied with the catalyst indicated that it would and 9 in relativeyields of 0/":50/":25ft:25f.t. be prudentto treatthis point explicitly. Thus, a clear distinction betweenthe mechanistical- The sameexperimental probe usedto testthe catalytic ternativesunder considcrationcan be made on thc cyclotrimerizationsof 2-butyne-l,l,l-& (31 to hexa- basisof the