摘要:
1706 J.C.S. DaltonThe Chemistry of Polynuclear Compounds. Part XXVII.l Activation ofC h I o roet h a nes by Dodecaca r bo n y I - trianguio - t r i - i r o n a n d - t r i rut hen i u mBy Colin R. Eady, Brian F. G. Johnson, and Jack Lewis," University Chemical Laboratory, Lensfield Road,The action of [Fe,(CO),,] and [ R U ~ ( C O ) ~ , ] on chloroethanes in the presence of alkanes leads to the formationof a large number of organic products the majority of which have been isolated and characterized by variousspectroscopic techniques. In general, the chloroethanes are converted into the corresponding chloroethylenes.whilst the alkanes are transformed into the monochloroalkanes and alkenes. Possible mechanisms for thesesomewhat complex reactions are described.Cambridge CB2 I EWTHE first reaction of a chloroalkane with a metalcarbonyl was reported in 1928 by Mittasch,2 in which hefound that [Fe(CO),] reacted with carbon tetrachlorideto give phosgene, iron@) chloride, some hexachloro-ethane, but mostly tars.More recently334 it has beenshown that the reaction of [M,(CO),,] (M = Mn or Re)with carbon tetrachloride leads to the formation in highyield of [M(CO),Cl] species. Halogen abstraction byiron carbonyls or their anionic equivalents has beenused extensively in both organometallic and organicsynthesis (Scheme 1) .5-12 Collman 13*14 in particularhas expounded the use of Na,[Fe(CO),] as an inexpensiveselective reagent for the high yield conversion, involvinghalogen abstraction, of aliphatic halides and tosylatesinto aldehydes and unsymmetrical ketones.A similartype of reaction has been reported by other workers l57 c1of [Fe(CO),] at 30 "C, is quantitatively converted intothe hydrocarbon polymer (CH2C6H& (a ca. 62). Bothgroups provide experimental evidence which suggestsXYY 4; ' Y)=( + 2 FeX, + 10 CO0 R' f R '/. \R3 R lSCHEME 1 (i) thf; (ii) [Fe2(CO),]who found that benzyl chloride, when stirred in abenzene solution of [Fe,(CO)$ at 30 "C, gives dibenzylketone in good yield. However, the same organicchloride, when stirred in a tetrahydrofuran (thf) solution1 Part XXVI, C. R. Eady, B. F. G. Johnson, and J. Lewis,2 A. Mittasch, Angew. Chem., 1928, 41, 827.J. C. Hileman, D. K. Huggins, and H. D. Kaesz, Inorg.M.Wrighton and D. Bredesen, J . Organometallic Chem.,R. G. Amiet, P. C. Reeves, and R. Pettit, Chem. Comm.,J. S . Ward and R. Pettit, Chem. Comm., 1970, 1419.J.C.S. Dalton, 1975, 2606.Chem., 1962, 1, 933.1973, 50, C35.1967, 1208.' R. Noyori, S. Makino, and H. Takaya, J . Amer. Chem. Soc.,* K. Ehrlich and G. F. Emerson, J . Amer. Chem. Soc., 1972, M,1971,93, 1272.2464.YSCHEME 2 X = C1, Y = H, Me, C1, CMe,, or OMe; X = Br,Y = NO,that ketone synthesis is preceded by the formation of aa-bonded alkyl iron carbonyl unit and that this, beingthermally unstable, decomposes to give the ketone.A simple preparation of tetra-arylethylenes involvingthe treatment of particular gem-dihalides with [Fe(CO),]in refluxing benzene has been reported by Coffey16(Scheme 2).Under similar conditions, no reaction wasobserved with t-butyl bromide, 2,2-dibromopropane,benzyl chloride, benzal chloride, triphenylmethylchloride, 1,2-dibromo-l,2-diphenylethane, chloroform, ormethylene chloride. Amongst other metal carbonylswhich converted dichlorodiphenylmethane to tetra-phenylethylene were [FeHg(CO),], [(Fe(CO),(cp)},], and[Ni(CO),] (cp = q-cyclopentadienyl). This work byH. A. Brune, W. Schwab, and H. P. Wolff, 2. Naturforsch.,10 H. A. Brune and G. Horlbeck, 2. Naturforsch., 1971, B26,11 H. A. Brune and G. Horlbeck, 2. Naturforsch., 1972, B27,12 H. A. Brune, H. P. Wolff, W. Klein, and U. I. Zahorszky,13 J. P. Collman, S. R. Winter, and D. R. Clark, J . Amer. Chem.14 W. 0. Siegl and J.P. Collman, J . Amer. Chem. SOC., 1972,94,16 I. Rhee, M. Ryang, and S. Tsutsumi, J . Organometallic1970, B25, 892.222.505.2. Naturforsch., 1972, B27, 639.Soc., 1972, 94, 1788.2516.Chem., 1967, 9, 361.C. E. Coffey, J . Amer. Chem. Soc., 1961, 83, 16231976 1707Coffey was taken to suggest that [Fe(CO),] will onlyreact with organic halides (under reflux in benzene) iftwo conditions are met: (a) the halogen atom must beactivated by at least one, and preferably two, groupssuch as CYano, alkoxycarbonY19 PhenYl, Or halogeno(in decreasing order of effectiveness); (b) there must beat least two halogens on the same carbon atom. Con-dition (b) suggested that the reactions of gem-dihalidestion of two chlorine atoms occurs to give the correspon-ding ethylene, e.g.as in equation (1). This appears to beone of the major reaction paths. (b) Chloroethanes[Fe,(CO)l,] + Cl,CCCl, -* Cl,C=CCl, + FeCl,containing a CCl, group undergo exchange presumablywith the n-heptane and this leads to the formation ofn-C7H16(1)TABLE 1n-GH16[Fe,(CO),,] + chloroethane -+ organic products +re0ux1, 1, 1,2-Tetrachloroethane HexachloroethaneOrganic productsmixture of isomeric heptenes (good yield)rMixture of isomeric heptenes (small yield)Vinyl chloride (trace)1 ,l-Dichloroethylene (major product)cis-l,%Dichloroethylene (trace butfrans-l,2-Dichloroethylene (trace) tram-l,2-dichloroethylene (trace)l,l, 2-Trichloroethane (second highest~is-1,2-dichloroethylene (trace buttrichloroethylene (third highest yield)cis 9 tvans) cis s trans)yield)1-, 2-, 3-, and 4-Chloroheptane (smallyield)with metal carbonyls involvedand indeed some experimentalin support of this mechanism.>mixture of isomeric heptenes (moderate1, l-dichloroethane (moderate yield)trans-2,3-dichlorobut-2-ene (moderatecis-2,3-dichlorobut-2-ene (trace)2,2,3-trichlorobutane (small yield)trichlorobutene (trace, isomer notyield)yield)determined)yield)tetrachloroethylene (second highest yield)1-.2-, 3-, and 4-chloroheptane (major2 2,3,3-tetrachlorobu tane (moderate1,1,3,3-tetrachlorobutane (trace)1-, 2-, 3-, and 4-chloroheptane (majorproduct) product)a carbene intermediateevidence was availablecliloroheptanes and the corresponding CC1,H group ; this,if possible, will once again undergo 1,2-abstraction of twoMore particularly, the n validity of condition (b) appeared to be beyond questionsince in no case was reaction with monohalogenatedcompounds observed even in the strongly halogen-activated triphenylmet h yl chloride.Ketone formationappeared to be negligible.Thus, despite the existence of a considerable volumeof literature associated with halogen abstraction,particularly by iron carbonyl species, very few if anystudies of chloroethanes have been made. This obvi-ously represents a large gap in the knowledge of thisrelatively cheap and simple class of organic compounds.In this paper, apart from providing basic information ofrelevance to the more significant alkane systems, wedescribe the reactions of iron and ruthenium carbonylswith chloroethanes and attempt to rationalize most ofthe products mechanistically.RESULTS AND DISCUSSIONDodecacarboutyZ-triangulo-tl.i-iron.-When [Fe,(CO),,]was heated under reflux in n-heptane with 1,1,1,2-tetrachloroethane, hexachloroethane, or 1,1, l-trichloro-ethane for 24 h a light brown solid was slowly depositedfrom the deep green solutions.Gas-liquid chromato-graphy (g.1.c.) on the resulting solutions showed a con-siderable number of organic products (Figure), themajority of which, after separation, were identified by acombination of lH n.m.r., i.r., and mass spectroscopicdata as well as their standardized g.1.c. retention times.The results of these studies (Table 1) suggest a numberof general conclusions.(a) Where possible, 1,2-abstrac-Gas-liquid chromatograph of the solution resulting from thereaction of [Fe,(CO),,] with 1, 1, 1-trichloroethane in n-heptane.Stationary phase, LAC 1R 296. Peaks: (1) n-heptane (sol-vent) ; (2) truns-hept-3-ene; (3) cis-hept-3-ene; (4) trans-hept-2-ene; (5) cis-hept-2-ene; (6) 1,l-dichloroethane; (7) un-changed 1, 1, l-trichloroethane ; (8) trans-2,3-dichlorobut-2-ene ;(9) 1,2-dichloroethane (original impurity) ; (10) 4-chlorohep-tam; (1 1) 3-chloroheptane ; (12) 2-chloroheptane; (13) cis-2,3-dichlorobut-2-ene; (14) l-chloroheptane; (15) 2,2,3-trichloro-butane; (16) a trichlorobutene; (17) 2,2,3,3-tetrachlorobutane;and (18) 1,1,3,3-tetrachlorobutanechlorine atoms to give the ethylene, e.g.as in equation (2).(c) Products corresponding to dehydrochlorination of theIFe,(CO), 21 ClCH,CCl, + n-C,H,, _____tCH,=CCl,, C,H,,Cl, ClCH,CHCl,[Fe, (CO),,l J (2)CH,=CHClchloroethane are formed in only trace amounts, e.g. as inequation (3). (d) Where 1,2-abstraction of two chlorinen-GHiarFe,(CO),,] + CH,CCl, +- CH,=CCl, (31708 J.C.S. Daltonatoms is not possible, dimerization OCCUIS and the pro-duct is then subject to 2,3-abstraction of two chlorineatoms, e.g. as in equation (4). This accounts for theformation of 2,2,3,3-tetrachlorobutane (dimerization ofn-C7% [Fe,(CO),,] + CH,CCl, ___t CH,CC12CC12CH,ILFe3(co),*l (4)CH,CCl=CClCH,1,l ,l-trichloroethane) , the 2,3-dichlorobut-2-ene isomers,and the 2,2,3-trichlorobutane (coupling of 1 ,l,l-trichloro-ethane and 1,l-dichloroethane). A number of the minorproducts are probably the result of positional isomerismwithin the ch10robutenes.l~The validity of conclusion (a) was further demon-strated by independently synthesizing 2,2,3,3-te tra-chlorobutane and then reacting this with [Fe,(CO),,] inn-heptane.trans-2,3-Dichlorobut-2-ene was the majorproduct of the reaction together with a trace amount ofthe corresponding cis isomer. The heptenes remain theonly significant products which are not encompassedby conclusions (a)-(d) . Contrasting directly withconclusion (c), it was found that each of the four isomericmonochloroheptanes, when heated separately underreflux in n-heptane with [Fe3(CO)12], gave a mixture ofheptenes the isomeric yields of which were identical andcorresponded to the ratio shown in the Figure.Sucha mixture of heptenes could be expected since it is nowwell established that [Fe,(CO),,] is capable of isomerizingolefins to give mainly the trans internal isomer~.l**~~Furthermore, whereas l-chloroheptane gave only traceamounts of isomeric heptenes together with unchangedl-chloroheptane, the reaction separately of either 2-, 3-,or 4-chloroheptane gave much higher yields of isomericheptenes together with a mixture of unchanged 2-, 3-,and 4-chloroheptane, e.g. as in equations (5) and (6).trace amountsheptenesof isomeric + unchanged C7H15C1-1 (5)moderateOf + unchanged C7H15C1-2, -3, and -4 (6) isomericheptenesThus [Fe,(CO),,] appears to be capable of reversiblydehydrochlorinating and isomerizing alkyl halides.Under conditions necessary for the reactions in Table 1to occur, [Fe,(CO),,] decomposes quite readily to givemetallic iron. It is possible that, like metallic zinc ornickel,20 metallic iron rather than an organometallic17 G.Henrici-Olivd and S. Olivd, J . Organometallic Chem., 1971,29, 307.T. A. Manual, J . Org. Chem., 1962,27, 3941.species could dechlorinate the organic molecule. In anattempt to clarify this situation, two reactions werestudied: (a) the reaction of metallic iron, produced byheating rFe,(CO),,] under reflux in n-nonane for 24 h,with 1,1,1,2-tetrachloroethane at 80 “C; and (6) thereaction of [Fe(CO),] with 1,1,1,2-tetrachloroethane inn-heptane.No reaction was observed in (a) whereas in(b) 1, l-dichloroethylene remained the major product ofthe reaction. Furthermore, for all reactions describedin this paper, control experiments, omitting the metalcarbonyl, were carried out and in each case the onlydetectable products were minute traces of the mono-chloroalkanes (e.g. nionochloroheptanes) . These resultssuggest that iron carbonyl units (possibly [Fe(CO)J)are significant species in the reactions discussed in thissection. The use of n-hexane rather than n-heptane assolvent gave products which generally satisfied con-clusions (a)-(d) presented earlier.DodecacarbonyZ-triangulo-trirztthevcium.--‘IVhereas arylhalides show low thermal reactivity towards [Fe(CO),][e.g. iadobenzene fails to react l5 at 30-60 “C], [Ni(CO),]is far more reactive towards halogen-containing mole-cules.Thus Bauld 21 reported that aryl iodides can beconverted into arylcarboxylic acid esters by nickelcarbonyl in the presence of alcoholic solvents [equation(7)]. These results suggested that the choice of metal0 1RII ___t [R1-C-Ni(CO),] ------t“i(CO),I I I I R20HRaOH0I IR1-C-OR2 + HI + [Ni(CO)J (7)carbonyl can be critical and that possibly the use of[Ru,(CO),,] rather than [Fe,(CO),,] may lead to asubstantially more active system.A detailed examination of the organic productsformed in the reaction of [Ru,(CO),~] with selectedchloroethanes was therefore undertaken and theseresults are presented in Table 2.They show that in thecase of 1,1,1,2-tetrachloroethane little difference existsbetween the use of iron or ruthenium carbonyls, whilstwith hexachloroethane no 1 ,2-dichloroethylenes or tri-chloroethylene could be detected. With l,l, l-trichloro-ethane, dimerizat ion products (chlorobut anes andbutenes) were absent. In general, reactions with[RU,(CO)~~] gave g.1.c. spectra consistent with a largenumber of very low yield organic products the character-ization of which in many cases was not possible. Sig-nificantly, the ruthenium residues of these reactionsgave complex i.r. spectra in the carbonyl-stretchingregion and t.1.c. revealed at least six major components.Their further identification was not effected because ofthe already highly complex nature of the organicproducts. However, reactions of [Co,(CO),] with organichalides of the form RCX, result in the formation of a19 M.D. Carr, V. V. Kane, and M. C. Whiting, Proc. Chem. Soc.,1964,408.20 M. J. Piper and P. L. Timms, J.C.S. Chern. Comm., 1972.50.21 N . L. Bauld, Tetrahedron Letters, 1963, 18411976 1709series of novel cobalt clusters based on the [CO,C(CO)~]unit.,, It is possible therefore that the reactionspresented in this section could lead to similar rutheniumclusters.Although it would be unwise to try and comparecategorically the reactions of iron and rutheniumcarbonyls on the basis of their organic products, sincein the case of ruthenium some of these ‘products’could still remain co-ordinated to the metal, it doesappear that the use of [RU,(CO)~~ rather than [Fe,(CO),,]does not lead to a distinctively different and moreactive system.Tetracarbonylironnzerc~ry.--The use of [Fe,( CO) 12] asa chlorine abstracting reagent under reflux conditionsleads readily to the formation of [Fe(CO),].Thetoxicity of this species together with its undesirablehere have appeared during the course of this work.Thus [Ni(CO),] is also capable of converting a CCl,group into a CHC1, group,29 whilst Petrova andFreidlina 30 were able to effect a similar transformationusing [Fe(CO),] and a thiol, the latter giving an organicdisulphide. However, a mechanistic dilemma stillexists amongst the various research groups and sig-nificantly a recently published extensive review of thearea deals only superficially with the role of the metalcarbonyl.,l Whilst some research groups believe thatreactions of metal carbonyls with organochlorine com-pounds involve co-ordination r n e ~ h a n i s m s , ~ ~ - ~ ~ , ~ ~ othersare firmly convinced of free-radical Barn-ford favours a route in which radicals are produced by aco-ordination rnechani~m,~~ whereas Webb and Bor-cherdt 35 suggested that the coupling of allylic halidesTABLE 2[Ru3(CO) 12] + chloroethane ___t organic products + organorutheniuni complexes“-C,H,,re0ux1,1,1,2-Tetrachloroethane Hexachloroethane 1,1, 1-TrichloroethaneOrganic productsL r >Mixture of isomeric heptenes (moderate mixture of isomeric heptenes (major1,l-Dichloroethylene (major product) tetrachloroethylene (major product) 1,l-dichloroethane (moderate yield)cis-1,2-Dichloroethylene (trace)mixture of isomeric heptenes (moderateyield) yield) product)1,1,2-Trichloroethane (second highest1-, 2-, 3-, and 4-Chloroheptane (small yield)yield)1-, 2-, 3-, and 4-chloroheptane (trace) 1-, 2-, 3-, and 4-chloroheptane (trace)effect on g.1.c.detectors makes it necessary to either devisesuitable methods for its removal or to use alternativereagents. For this reason an investigation of someanalogous reactions of [FeHg(CO),] 23 was undertaken.In the case of, for example, 1,1,1,2-tetrachloroethane,using n-octane rather than n-heptane as solvent, themajor product was trichloroethylene (ie. dehydro-chlorination) in high yield (70%) together with a traceamount of 1, 1-dichloroethylene (i.e.1,2-dechlorination).This reagent therefore significantly contrasts with[Fe,(CO),,] and [Ru,(CO),,], but a number of reagentsparticularly FeC1, or AlC1, 24-26 are equally efficient andmore readily available dehydrochlorinating reagents.No carbonyl-stretching frequencies were observed in thei.r. spectrum of the solid residue, but the formation ofFeCl, and metallic mercury suggested that the [FeHg-(CO),] had been converted into [Fe(CO),(HgCl),] 27which decomposed under the reaction con&tions.z8Possible Mechanisms.-A number of papers describingreactions somewhat similar to some of those presentedR. R. Penfold and B. H. Robinson, Accoztnts Chem. Res.,23 H.Hock and H. Stuhlmann, Chenz. Ber., 1929, B62, 431.24 N. I<. Taikova, A. E. Kulikova, and E. N. Zil’berman, J . Ovg.25 A. E. Kulikova, E. N. Zil’berman, N. K. Taikova, and N. M.26 E. N. Zil’berman, A. E. Kulikova, and E. G. Pomerantseva,27 H. Hock and H. Stuhlmann, Chem. Ber., 1928, B61, 2097.1973, 6, 73.Chewz. (U.S.S.R.), 1968,4, 1814.Pinchuk, .J. Ovg. Chem. (U.S.S.R.), 1968, 4, 1834.J . Org. Chtm. (U.S.S.R.), 1967, 3, 1158.Gmelins Handbuch der anorganischen Chemie, Berlin, 1932,T. Kunieda, T. Tamura, and T. Takizawa, J.C.S. Chem.vol. 59b, p. 501.Comm., 1972, 885.by [Ni(CO),] could proceed through either type ofmechanism but consider the free-radical route to be themost plausible.H H HRH H R’Fe(COIL H - FelCG), -+ coSCHEME 3Similar arguments apply equally well to the reactionsdiscussed herein. Thus, the addition of various types ofstandard free-radical inhibitors to some of the reactionsof [Fe,(CO),,] with chloroethanes does not in generalalter the product distribution and yield.However,this observation should be interpreted with care since(a) the free-radical inhibitors may co-ordinate to theiron carbonyl units; and (b) very ‘ hot ’ free radicals like30 R. G. Petrova and R. K. Freidlina, Izvest. Akad. NaukS.S.S.R., Ser. khim., 1970, 1574.31 R. K. Freidlina and E. C . Chukovskaya, Synthesis, 1974, 477.32 R. F. Heck and C. R. Boss, J . Amer. Chenz. Soc., 1964, 86,33 B. L. Booth and B. L. Shaw, 1. Ov~anometallic Chewz., 1972,2580.- -43, 369.34 C.H. Bamford. G. C . Eastmond, and D. Whittle, .J. Ovgam- - -metallic Chem., 1969, 17, P33.73, 2654.35 I. D. Webb and G. T. Borcherdt, J . Amer. Chew.. Soc.. 19511710 J.C.S. DaltonIC I I1 RCH CH CHRI2 1C I Fe(CO), 11 RCH CH~CH~R’ R C H2C H2CH C L R ’IC i Fe (CO),RCHCKH ,c H ~ R ’SCHEME 4 (i), Decomposition to alkene, RCH,CH=CHR’;(ii) , decomposition to alkene, RCH=CHCH,R’c1IR LIRLR3 R’\C=C< i- FeC12 + 3 C ORL’ R *IIR LR3C-R5.1FeCLZf 3 C O +R 3 R’ R’ R3I I I IRL- C-C-C-C - RLSCHEME 5 Route (b) is regarded as less likely since it involvesan iron(1v) intermediat1976 1711C1- are not easily quenched.38 Precedent wouldsuggest ,18937338 however, that alkene isomerism is likelyto involve a co-ordination mechanism in which an(7-allyl) t ricarbonylhydrido-iron (or -ruthenium) inter-mediate is formed, the trans internal isomers beingpreferentially produced purely on steric grounds sincethey will be the most unreactive (Scheme 3).Theobserved isomerization of the alkyl halides is probablythe result of a similar type of mechanism; one suchpossibility (Scheme 4) also provides an alternative routeto heptene formation and isomerism.The mechanism whereby a CCl, group exchanges withhydrogen atoms of the alkane to give the correspondingCHC1, group and the monochloroalkane is probably freeradical. This is because : (a) the monochloroalkanesare formed in minute traces in the absence of any metalcarbonyl and the [M(CO)J unit (M = Fe or Ru) is liableto be involved in the initial formation of radicals; 31(b) the isomer distribution of monochloroalkanes issimilar to that observed in the liquid-phase elementalchlorination of alkane~.3~ This proposed free-radicalhydrogen-chlorine exchange could be accomplishedaccording to equations (8)-(10).RCCl, + [Fe(CO)J + [Fe(CO),Cl] + RCCl,.(8)RCCl,* + C,HiB+ RCC1,H + C7H15.The dimerization or 1,Z-abstraction of chlorine atomsin chloroet hanes, using iron and ruthenium carbonyls,could proceed along co-ordination routes somewhatsimilar to those proposed by Alper 40 (Scheme 5). How-ever, the experimental results are not completely con-sistent with such a mechanism since it could be expectedthat this should also lead to ketone formation.l3-15Moreover, it might be expected that by such a mechan-ism the nature and distribution of organic productsshould change dramatically as the metal is changed.Thus, consistent with the reported ease of dechlorin-ation of radicals like -CCl2CC1,H, the following free-radical mechanism could effect the experimentallyobserved transformations.RCC1, + [Fe(CO),] +RCCl,* + [Fe(CO),ClJ (8)2RCC1,- _.t RC12CCC1,R (11)RCl,CCCI,R + [Fe(CO),J _.+[Fe(CO),Cl] + RC12C&1R (12) I (b) RCI,CcClR + RCGCClR + C1- (13)RC1,CtCIR + [Fe(CO),Cl] --+RClC=CClR + FeCl, + 4CO (14) i As a result of this chloroethane study, it could beinferred that Coffey's proposal (b), and particularly of a* 1 eV E 1.60 x 10'ls J.36 C.Walling, ' Free Radicals in Solution,' J.Wiley, London,1957.37 W. Strohmeier, R. Fleischmann, and W. Rehder-Stirnweiss,1. Oreanonzetallic Chem.. 1973. 47. C37.carbene intermediate in the formation of tetraphenyl-ethylene from dichlorodiphenylmethane and [Fe(CO),] ,was incorrect.l6 It would be expected that the inter-mediate 1,2-dichloro-1,1,2,2-tetraphenylethane could beisolated from this reaction and indeed, in the case of1,1,1-trichloroethane and [Fe,(CO),J , 2,2,3,3-tetrachloro-butane was isolated and shown to be an intermediate inthe formation of cis- and trans-2,3-dichlorobut-2-ene.In conclusion therefore it appears that the reactionsof chloroethanes with iron and ruthenium carbonyls arehighly complex and it is necessary to rationalize themany products by a number of mechanisms.However,the results suggest that monochloroalkanes can beactivated by such metal carbonyls and this is, at thevery least, not unfavourable towards us achieving ourgoal of alkane activation by metal complexes. Indeedit cannot be unequivocally stated that chloroheptaneformation is not the result of metal carbonyl inter-actions, and this suggests that a study of the alkanesthemselves with metal carbonyls is appr~priate.~~EXPERIMENTALThe complexes [Fe, (CO) ,42 [Ru, (CO) 12], 43 [FeHg (CO) 4]and [Fe(C0)4(HgC1)2] 23*27,44 were prepared by the literaturemethods. Whilst hexachloroethane was purified by sub-limation and recrystallization (hexane), the other chloro-ethanes were fractionally distilled using a heated vacuum-jacketed distillation column (3 ft, glass beads).G.1.c. onthe middle fractions showed 100% purity for all of thecompounds except 1 1,l-trichloroethane which contained1 yo 1,2-dichloroethane as impurity. Alkanes were purifiedby stirring over concentrated sulphuric acid for 24 h,treating with sodium hydrogencarbonate solution and water,and then degassing with nitrogen followed by distillationover calcium hydride through a Vigreux column. G.1.c.confirmed the complete absence of alkenes. All reactionswere carred out under dry oxygen-free nitrogen.Infrared spectra were recorded as solutions in 0.5 niniNaCl cells using a Perkin-Elmer 257 spectrometer withpolystyrene as calibrant. Mass spectra were obtainedusing an A.E.I. M.S.12 instrument operating a t 70 eVionizing potential.* G.1.c.spectra were recorded on aPerkin-Elmer F11 FI machine (analytical) and an F.M.machine (preparative) using 0.125- and 0.25-in diametercolumns respectively. lH N.m.r. spectra were recorded at100 MHz on a Varian Associates HA 100 spectrometer.Synthesis of authentic samples of some of the organicproducts was achieved using adaptations of literatureroutes. Thus, 2,2,3,3-tetrachlorobutane was prepared bythe chlorination of but-2-yne using SbCl, as a catalyst.451-Chlorohexane and chloroheptane were prepared by heat-ing n-hexanol or n-heptanol under reflux with thionyl38 R. Fields, G. L. Godwin, and R. N. Haszeldine, J . Organo-metallic Chem., 1971, 26, C70.3s N. Colebourne and E. S. Stern, J . Chem. SOL, 1965, 3599.40 H.Alper and E. C . H. ICeung, J . Org. Chem., 1972, 3'9, 2566.41 C. R. Eady, B. F. G. Johnson, and J. Lewis, J.C.S. Dalton,42 R. B. King and F. G. A. Stone, Inorg. Syntk., 1963, 7, 193.43 M. I. Bruce and F. G. A. Stone, J . Chem. SOC. ( A ) , 1967,1238.44 J. Lewis and S. B. Wild, J . C h e w SOC. ( A ) , 1966, 69.45 T. T. Verbanc and G. F. Hennion. r. Amer. Chem. Soc.. 1938,in the press1712 J.C.S. DaltonThe remaining isomers could not be preparedby this method and the triphenylphosphine-carbon tetra-chloride reagent was used instead.47~48Typical Reaction of a Chloroethane with [Fe,(CO),,] in12-Heptane.-This is well illustrated by the 1,1, l-trichloro-ethane reaction. The complex [Fe,(CO),,] (6.3 g, 0.012mol) was heated under reflux in n-heptane (35 cm3) with1,1,l-trichloroethane (5.0 g, 0.037 mol) for 24 h.Thereaction mixture was regularly monitored by i.r. spectro-scopy [v(CO)] and this showed the slow decomposition of[Fe3(C0),,] into [Fe(CO),]; no other bands could beobserved in the carbonyl-stretching region (1 800-2 200cm-1). The reaction mixture was then partially separatedby a bulb to bulb distillation to give a light brown solid anda yellow liquid. The solid residue showed no bands in thecarbonyl-stretching region but gave qualitative analysistests consistent with the presence of both Fez’ and C1-.The yellow colouration in the liquid fraction was due to[Fe(CO),] and, whereas conventional oxidants such asammonium cerium(1v) sulphate, bromine, or iodine werenot capable of selectively removing this metal carbonyl,treatment with water (10 cm3) and mercury(I1) chloride( 5 g) removed the [Fe(CO),] as [Fe(CO),(HgCl),]; formationof the latter species takes place selectively in the waterlayer in which only [Fe(CO),] and HgC1, are soluble.G.1.c. was the only technique available for the separationof the resulting dry n-heptane layer.Three differentstationary phases were used : tricresyl phosphate, M.S. 550,and LAC 1R 296, of which the latter proved to be the mostsuccessful particularly for preparative work (oven tem-perature 70 “C). The complete characterization of thevarious compounds isolated from the reactions of chloro-ethanes with metal carbonyls depended on published dataon mass spectro~copy,4~-51 n.m.r.spectros~opy,~~ andg.1.c. (retention times) .63-55 In particular, the monochloro-heptanes did not show molecular ions in their mass spectrabut in the case of 1-chloroheptane a F’r group was ejected togive a five-membered ring containing a chlorine heteroatom,whilst 2-chloroheptane gave a small amount of the methyl-substituted ring with corresponding ejection of an E t group.Instead of ring formation, 3- and 4-chloroheptane gave ionscorresponding to loss of HC1.Typical Reaction of a Chloroethane with [Ru3(CO),,] inn-Heptane.-This is well illustrated by the hexachloro-46 A. I. Vogel, ‘A Text-book of Practical Organic Chemistry,’3rd edn., Longmans, London, 1959, p. 274.47 I. M. Downie, J. B. Holmes, and J. B. Lee, Chem.and Ind.,1966, 900.48 J. B. Lee, J . Auner. Chem. Soc., 1966, 88, 3440.48 F. W. McLafferty, Analyt. Chem., 1962, 34, 2.50 H. Budzikiewicz, C. Djerassi, and D. H. Williams, ‘ Inter-pretation of Mass Spectra of Organic Compounds,’ Holden-Day,San Francisco, 1964, p. 125.ethane reaction. The complex [Ru,(CO),J (0.53 g, 0.83mmol) was heated under reflux in n-heptane (6 cm3) withhexachloroethane (0.59 g, 2.5 mmol) for 24 h during whichtime the solution gradually changed from orange to reddishbrown. After a bulb to bulb distillation, the solid residuewas chromatographed using thin-layer silica plates (2%ethyl acetate-cyclohexane as eluant) whilst the liquidfraction was analysed by g.1.c. as previously described.Reaction of [FeHg(CO),] with 1,1,1,2-Tetrachloroethane inn-Octane.-The complex [FeHg(CO),] (3.6 g, 0.01 mol) washeated under reflux with 1,1, lJ2-tetrachloroethane (5.0 g,0.03 mol) and n-octane (50 cm3) for 24 h.The yellowcolour of [FeHg(CO),] was slowly replaced by the light greyof metallic mercury. The mixture was centrifuged andthe heptane layer separated off and analyzed by g.1.c.Gaseous Products.-The use of a bladder to maintain aninert atmosphere permitted a convenient analysis ofgaseous products. The complete absence in all cases ofhydrogen chloride was confirmed, but this result must betreated with caution since i t has been reported that[Fe(CO),] will react thermally or photochemically withhydrogen halides to give dimeric halogen-bridged ironcarbonyls which can then decompose to FeC12.56Yields of Reactions.-The major difficulty associated withthis study of metal carbonyls and chloroalkanes was itscomplexity. G.1.c. was the only technique which couldseparate the large number of organic products and eventhen not completely satisfactorily. Collection methods wereused which gave only small amounts of pure material andunfortunately they were not suitable for the calculation ofquantitative yields. In most cases therefore only relativeyields are given but some indication of quantitative yieldscan be derived from Tables 1 and 2 and the Figure.We thank Johnson, Matthey and Co. Ltd. for theirgenerous loan of RuCl,, I.C.I. (Mond Division) for providingthe chloroethanes, and The Salters’ Company and TrinityHall, Cambridge, for the award of Fellowships (to C. R. E.).[5/1602 Received, 14th August, 1975161 H. Budzikiewicz, C. Djerassi, and D. H. Williams, ‘MassSpectrometry of Organic Compounds,’ Holden-Day, San Fran-cisco, 1967, p. 432.52 J. W. Emsley, J. Feeney, and L. H. Sutcliffe, ‘ Fgh Resolu-tion Nuclear Magnetic Resonance Spectroscopy, Pergamon,London, 1966, vol. 2, p. 722.53 G. F. Harrison, ‘ Vapor Phase Chromatography,’ Butter-worths, London, 1957, p. 332.64 D. A. Tourres, J . Gas Chi(omatografihy, 1967, 35.5c R. A. Hively and R. E. Hinton, J . Gas Chrornntografilzy,1968, 203.56 E. Koerner von Gustorf, J. C. Hogan, and R. Wagner, 2.Naturfursch., 1972, B27, 140
ISSN:1477-9226
DOI:10.1039/DT9760001706
出版商:RSC
年代:1976
数据来源: RSC