/: (j

Mechanismof ThermalDecomposition of Di-n-butylbis( triphenylphosphine ) platinum ( II )'

GeorgeM. Whitesides,*John F. Gaasch,2and Erwin R. StedronskyJ

Contributionfrom the Department of Chemistry, MassachusettsInstitute of Technology, Cambridge, Massachusetts 02139. ReceioedAugust 4, I97l

Abstract: The thermaldecomposition of di-n-butylbis(triphenylphosphine)platinum(Il)(l) in methylenechloride to n-butane,l-butene, and a complexof platinum(0)is proposedto takeplace by an intramolecularprocess involv- ing an initial dissociationof I equivof triphenylphosphinefrom 1 to yielda three-coordinateintermediate 5, elimi- nationof platinumhydride from one butyl groupof 5 with concomitanttransfer of the resultingl-butene to the vacantcoordination site, several cycles composed of rapidaddition of platinumhydride to thecoordinated butene and subsequentrapid reeliminationof platinumhydride from the resultingbutylplatinum complexes, and a final reductiveelimination of n-butanefrom an intermediatehaving both hydrideand butyl moietiesbonded to platinum. Three significantconclusions concerning the mechanismof thermal decompositionof t have emergedlrom this study. First a vacant coordinationsite on platinum is a prerequisitefor thermal decompositionunder the con- ditionsstudied. Second,the identity of therate-limiting step for the overalldecomposition reaction depends upon the concentrationof triphenylphosphineadded to the solution: in the absenceof addedtriphenyiphosphine, the rate-limitingstep is the dissociationof I to 5; in the presenceof ca. I equivof addedtriphenylphoiphine, the rate-limitingstep is the reductiveelimination of butane. Third, the olefinsparticipating in the platinum hydride addition-eliminationsequence are coordinatedin the intermediateplatinum Complexessufficiently firmly that they do not exchangewith 1-butenefree in solution.

f nformation concerning the mechanismsof thermal Mechanisms involving both the homolytic scission of r decomposition of alkyl derivatives of transition carbon-metal a bonds and the 6 elimination of metal metals is pertinent both to theoretical discussionsof hydrides have been proposed for these thermal de- the electronicstructure of carbon-metal c bonds and compositions;{'5 however, the latter course has been practical applications of transition metal organo- establishedas the more common for-n-alkyl derivatives metallic compounds in organic synthesisand catalysis. (4) M. S. Kharasch and O. Reinmuth. "Grignard Reactionsof Non- metallicSubstancEs," Prentice Hall, New York, N. Y., 1954,Chapter 5. (l) Supported'in part by The National ScienceFoundation, Grants (5) Reviews: (a) G. E. Coates, M. L. H. Creen, and K. Wadc, GP-7266and GP-142,17. "Organometallic Compounds," Vol. 2, 3rd ed, Methuen and Co., (?) National Institutes of Health Predoctoral Fellow, 1967-196g: London, 1968, Chapter 7; (b) G. W. Parshall and J. J. Mrowca, E. B. HerschbergFellow, 1966-1967. Adcan.Organometal. Chem.,7,157 (1968): (c) F. A. Cotton, Chem.Reo., (3) National Institutes of Health Predoctoral Fellow. 1967-1970, 52,557 (1955); (d) I. I. Kritskaya,Usp. Khim.,35, 167 (1966).

Journal ol'the Anterican Chemical Societ;' I 94:15 I Jult' 26, 1972 of platinum(Il),u rhodiur,n(I),7 and copper(I),E by ideniification of metal hydrides as products of the decompositions, and for derivatives of other metals by less direct techniques.s'e The nature of the factors determining both the rate of metal hydride elimination in the thermal decompositions of these classes of compoundsand the reversibilityof this elimination are unknown. The work reported in this paper dealswith an examinationof the mechanismof thermal decompo- sition of crs-di-n-butylbis(triphenylphosphine)plati- num(Il) (1), a representative alkyl derivative of a dE transition metal ion, whose physical properties make it amenable to detailed mechanistic examination. The purpose of this study was to substantiatea pathway for itreimat decomposition of 1 involving platinum hy- dride elimination and to provide detail to the steps surrounding this elimination. Results Preparation and Characterization of Alkylplatinum- (ID Compounds. Di-n-butylbis(triphenylphosphine)- platinum(II) and di'n-octylbis(triphenylphosphine)- platinum(ll) (2) were preparedby reactionof the corre- iponding n-alkyllithium reagentswith crs-dichlorobis- (triphenylphosphine)platinum(II)in ether-hexane at 0o, using proceduresdeveloped by Chatt and Shaw.t0' Deuterated derivativesof 1 were synthesizedby anal' PhrP\ PhrP\ \^ / ,,CHrCH-CH.,CHr -Dt/ -cDrcH,cH]cH, zl L\ -T-,-r-_I-rrl | | | ,rft-. -cH.,cH.,cH.,cHr ^r 'cD.,cH,,cH.,cH, | | Ph,P/ PhlP- I l-1,1-dt l" 5 loo oo5 (PPM) ogous proceduresusing as starting materials l-bromo- Figure l. Observed100-MHz deuterium-decouplednmr spectril cu. 0.25 rVlsolutions in methylenechloride of : (A) di-rr- butane-/,/-d,.rand l-bromobutane'2,2-d2which were takenof butyl-2,2-d,-[l, l'-bi s(d i phenylphosph i no )ferrocene]plati num( I I ) (3 ) ; (f); (C) PhJP. ,CH,,CDrCHjCH, (B) di-r-buryl-2,2-drbis(triphenylphosphine)platinum(lI) \prl calculatedspectrum of di-rr-buty"l-2,2-drbis(triphenylphosphine)- -/^ "\ -CH2CD:CH2CHi platinum(ll)(ref 14). Ph3P' l-2,2-d2 SchemeI. Synthesisof l-Bromobutane-2,2'dzand A\ Ph, (V)-P\ l-Bromobutane-l,l-dz /cr)cu)cHrcHl 'F?'l' T\, \tt( l. NsOEr,Dtorr Fe CHTCHzCCITCN+' CH'CHrCClzCOzEt I t \ 2. HrO. A/\ ,r^ a*F;,/(^ tHrcHrcHrcHt CH'CH:CDrCH'Br 3 CHTCHTCDzCO'Et ffi;;> -507,; 97%&,3% dt preparedfollowing the reactionsequences outlined in l' Li'\lDr SchemeI. rr Di-n-butyl' and di-n-butyl-2,2-d'rU,I'' cHrcHrcHzco:Et ' t cHrcHzcH:cD:Br 2. HBrll:-ior -50%; 98%dz,27i ttt (6) J. Chatt, R. S. Coffey,A. Gough, and D. T. Thompson,J. Chem. Soc.A, 190(1968), and referencescited therein. bis(diphenylphosphino)ferrocenelplatinum(II)(3 and (1968); also P. (7) R. Cramer, AccountsChem. Res., l, 186 see J. were prepared by reaction of thc Collman. ibid., 136(1968). 3-2,2-d2,respectively) (S) G. fvt. Whitcsidcs,E. R. Stredronskv,C. P. Casev,and J' San correspondinglithium reagentswith dichloro[1,1'-bis- Filippo, Jr.,J. Amer. Chem. 9oc.,92, 1426(19701. Seealso K. Wada, (diphenyl phosphino)ferrocenelplatinum(I I). t 3 lvLTamura. and J. I(ochi, ibid.,92,6656(1970). rH 1- (9) R. F. Heck, AccountsChem. Res.,2, l0 (1969); L. Reich and The deuterium-decoupled nmr spectrum of A. Schindler. "Polymerization by Organometatlic Compounds," 2,2-d!was examined to establishthe configuration of the 4; P' Candlin'K' A' Interscience.Nerv York, N' Y'' 1966,Chaptcr J' alkyl and phosphine groups. The group of lines be- Taylor, and D. T. Thompson, "Reactions of Transition-metalCom- plexes,"Elsevier, Amsterdam, 1967. tween -0.4 and 0.9 ppm in the spectrum shown in (10) (a) J. Chatt and B. L. Shaw,J. Chem.Soc., 705, 4020 (1959); Figure t can be assignedto the terminal ethyl groups 507,<(1962): (b) J. D. Ruddick and B. L. Shaw,J. Chem..Soc.,{, 2801 (1969). ( We found reductionof a-halo estersin a medium containing (13) J. J. Bishop,A. Davison,NI. L. Katcher,D. W. Lichtenberg, I I ) have (1971\' D:O to be a much more etficientmethod of introducingdeuterium c to R. E. Merrilt.and J. C. Smart,J. Organomerai.Chern.,27,24l platinum atoms the carbonyl group than the base-catalyzedexchange methods com- Thereis no evidenceof interactionbetwcen the iron and monly used.l2 in thesecompounds. We have used the ferrocene-l,l'-bis(diphenvi- preparcd (12) A. Murray and D. L. Williams, "Organic Synthesiswith Iso' phosphine)(fdpp)ligand in thesestudies because it is an easily topcs," Interscicnce,Nerv York. N. Y., 1958; M, Fctizon and J. Gra- bi.tenrate chelating phosphine whose dichloroplatinum(II) complcx main, Brrl1.Soc. Chint. Fr.,65l (1969). reactscleanly with n-butyllithium.

llthitesides, Gausclt, Stedronskl' ,t Di-n-butv'lbis(tiphenv'lplnspline)platinuntt I lt 5260 of the alkyl chains: the four.-linepattern at 1.04ppm DTNBO is entirely compatible with a mechanismfor and the one visible rerPtsatellite at 1.76ppm arise from thermolysis of I not involving free n-butyl radicals. the methylenegroups d to the platinumatom. Detailed However,the pertinenceof thesedata to discussionsof analysisof the a-methylene"quartet" indicatedthat the thermal behavior of I in the absenceof DTBNO two distinct PPTCH coupling constantswere required should be viewedwith some reservations,since DTBNO to simulatethe spectrumr{and confirmedthat I has forms complexeswith a number of metals16and since the cis configuration.expected by analogy with related a complex of 1 and DTBNO cannot be excludedas the organoplatinum compounds.r0 The spectrum of 3- species giving rise to the products obtained from 2.2-d2(Figure l) was not analyzedin detail; however, decompositionof 1 in the presenceof DTBNO on the its qualitativesimilarity to that of l-2,2-dt suggeststhat basisof presentlyavailable evidence. rT the PPIP and PPIC^F/coupling constants,and by in- In order to test explicitly the hypothesisthat the ferencethe correspondingbond angles,are similar for hydrogen atoms incorporated into the n-alkane por- thesetwo compounds. tion of the hydrocarbon productsoriginated exclusively Productsof the Thermal Decompositionof l. Heat- in the o-bonded n-alkyl groups of the starting organo- ing a 0.10 M solutionof I at 60ofor 24 hr in methylene metallic compound, and not in the solvent or the aryl chloride or benzeneresulted in completeconversion of groupsof the coordinatedtriphenylphosphine ligands, tt rr-butyl moieties to an equimolar mixture of n-butane the octane formed as a product of the thermal decom- and l-butene accompanied by transf,ormationof the position of 2 in methylene-d2chloride, and of di-n-

solution from its original pale yellow color to a dark C[)rC-l'r red color. The relativeyields of n-butaneand l-butene 2 --+ octane( 1.8% dt, 98.2% dr) + octene ti0". 20 lrr were independentof the extent of decompositionof 1. (< No lf each)crs-2-butene, trans-2-butene, or octane [(C6D;hP]:Pt(rr-ocryl), was observed as a decomposition product. Product # yields did not change when I was decomposedas a octane(0.3% dt,99.7% dn + octene suspensionin hexane or as the solid. Thermal de- octylbis(triphenylphosphine-d1;)platinum(II)in methyl- yielded . compositionof 2 under similarconditions 50% ene chloride. was isolated and its isotopic composi- n-octaneand 50[ l-octene. tion determined mass spectrometrically.te The low The observationthat octane is not formed in the Ievel of deuterium incorporation observed in these to excludethe decompositiono[ 1 is sufficientevidence experimentsestablishes that the n-alkyl groups of the possibilitythat butane and l-butene are formed by starting organoplatinum compounds are the only producedby disproportionationof freen-butyl radicals significant sources for the hydrogen found on the homolysisof the platinum-carbona bonds of 1. The hydrocarbon products. n-butyl is rate constant for the coupling of radicals Taken together, the foregoing observationsare in- a greater than that for their disproportionationby consistent with a free-radical mechanism for the vaporphase in factorof 4-6, both in the and solution.ts thermal decompositionof l. However,they are com- Moreover. were n-butyl radicals intermediatesin the patible with a mechanism for its decomposition, thermal decomposition. frce-radical abstraction of anticipatedby analogywith earlierstudies,6-8 involving chloride hydrogenor chlorineatoms from the methylene an initial elimination oI a platinum hydride with in a solventwould be expectedto be reflected difference concomitant formation of I equiv of butene,followed yields butene.in contrastto betrveenthe of butaneand by reduction of a carbon-platinum c bond in some yields. the observed equality in Indeed, decomposi- unspecifiedplatinum alkyl by this platinum hydride to good tion of a solutionoi I in 1,5-hexadiene,a hydrogen yield I equiv of butane. yield atom donor, resultedin a decreasein the of butane It was possibleto obtain direct evidencein support (uide relative to that of butene infra). of an intermediateplatinum hydride by examinationof the con- Additional qualitative evidencesupporting the productsarising from thermaldecomposition of 1 in not intermediates tention that free n-butyl radicalsare 1,5-hexadienesolution. Thermolysis of a 0.07 M 1 was provided in the thermal decomposition of solution of 1 in this solventresulted in formation of n- products observed when ther- by the distribution of butane (-457), l-butene (-557), l-hexene(10 :b was presenceof a fivefold molysis carried out in the 5%), and two additional compounds, tentatively (DTBNO). butyl- excessof dr-tert-butylnitroxyl The identified as crs- and tans-1.4-hexadiene(40 and 1507., conditionscon- derived products obtained under these respectively). Isotopic analysis of the hydrocarbons (467), (50%), with trace sist of butane l-butene only isolated from thermolysis of l'2,2-dz in 1,5'hexadiene (-l%) amounts of octane and lV,y'/-di'tert'butyl'O'n' established that approximately -87,, of one deu- butylhydroxylamine. The absence of a significant terium atom from a butyl group of the organoplatinum with yield of the product of coupling of butyl radicals compound was incorporated into solvent-derived

'Whitesides (l-11 6. N{. and J. F. Gaasch, J. Organometal. Chem.,33, (16) See C. !{. Whitesidcs and J. San Filippo, Jr., ibid.,92,6611 :-11 (1971). Spectral pilramcters obtained by matching of theoretical ( 1970). for reflerences. and expcrimental spectra were: 6cn, - 0.52,6cHrcuz :0.72, dca,pr: (17) Preliminary examination of the photol.v'ticdecomposition of I in - DTBNO appears to be compatible with the 1.04 ppm: /pptgtr (cisl : * 13,"/pp1gs (trans) - i 19,JPp' 21, JsH' the presence and absence of (see : 1.5,/p,s : 72,Js:'l'g1l, - 7.3 Hz. The accuracy of these phospho- production of tiee n-butyt radicals as intermediatcs the Experimental rous-hydrogen and hydrogcn-hydrogen coupling constants may not be Section for dctails). high; however, the value of ./pp' is in rcasonable agreement with values (18) For a revierv of reactions involving oxidative addition of aro- reportcd recent,ly by F. H. Allcn and S. N. Sze, J. Chem. Soc. A,2054 matic C-H boncls to metals, see C. W. Parshall, Accounts Chem, Res., 3, ,L97t\. 139(1970). (15) N. E. Morganrathand J. G. Calvert,J. Amer. Chem..Soc.,88, (19) Compound2 ratherthan I wasused for theseexperiments be- 5387(t966); A. P. Stefani,ibid.,90. 1694(1968); N. E. Morganrath causen-octane undergoes less fragmentation than n'butane at voltages anclJ. C. Crlvert,ibil., 88, 5387( 1966):R. A. Sheldonand J. K. Kochi, required for ionization and is, as a result, the more tractablesubject ibi(1.,92, -1395( 1970),and reltrcnccscrtcd in each. for accurateisotopic composition strrdies. Table I. MassSpectroscopicDeuterium Analysisof Products of the Thermal Decompositionof l-2,2-dzin 1,5-Hexadiene

Isotopic analysis, /o Compound Yield. 71" do dr dz l-Hexene l0*5b 86 l3 1.6 crs-1.4-Hexadiene 40 94 6.3 " t rans-1.4-Hexadiene"' r50 97 2.8 c .9 Yields are basedarbitrarily on the assumptionthat I mol of =60 " o productper mole of I correspondsto a yieldof 1007". bThe experi- CL E mentaluncertainty in this datum reflectsuncertainty concerning the o() quantityof residuall-hexene present as a contaminantin the 1,5- 370 hexadiene(see the ExperimentalSection). " trans-|,4r,tans'|,3', |. and cis-1,3-hexadieneall had identical retention times under the conditionsused for this glpc analysis. products (Table I).zo An intermediate platinum hy- dride would provide a plausible vehicle for the transfer of hydrogen from the butyl groups of l-2,2-d2to both the l-hexene and the isomerized hexadienes. o ' 5 6 The platinum originally present in 1 could be re- oi. t.l.,,l'tr coveredas a red solid of unknown compositionat the Figure2. Plotof percent decomposition of 1 us.time in methylene conclusionof thermal decompositionsin either methyl- chloridesolution at 60.0": (r) H : 0.280rVland (A) tll :0.0-i0 ene chloride or benzenesolution; thus, sincethe same rV,determined from butane-buteneareas; (O) Ul : 0.030rV, detcr- substanceis obtained from decompositionscarried out minedfrom concentrations of butane relative to a pentaneinternal in different solvents, it is presumed not to be derived standard. from reaction of some intermediate organoplatinum compound with solvent. The stoichiometry of the were not affectedby added triphenylphosphine; these decomposition suggests that ^ primary inorganic yields were not determinedfor decompositionscarried product might be l-butenebis(triphenylphosphine)-out in the presenceof methyl iodide. (4). platinum(0)or bis(triphenylphosphine)platinum(0) " Kinetics. The kineticsof thermaldecomposition ot- I (PhlP)3Pt(o) was examined by following thc _ pr,,p in methylene chloride \.- appearanceof 1-buteneusing glpc,after quenching t)#l (PhlJP)?Pt(0) samples with hydrochloric acid in methylenechloride. following the concen- PhlP\ 4 Points were obtained either by .zcH,Y tration of 1-butenerelative to that of an added internal standard or by using as a referencethe total concentra- Ph,P/Pt\I tion of buteneand butaneobserved following protonoll'- An analog of the former compound, ethylenebis(tri- sis. phenylphosphine)platinum(0),::dissociates readily in : 100 : solution to ethylene and 4.23 Both oi these com- fl decomposition [butene],/[butene]X pounds are yellow crystalline solids that decompose 2[butene],/([butane],f [butene]r)X l0() upon heating to a red melt.21'2r This last observation Typical data obtained by applicationof both methods suggeststhat the red product isolated from the ther- are shown in Figure 2. The slight discrepancy be- molysisof 1 might be a secondaryproduct derivedfrom tween the interceptsat / : 0 obtainedat the two con- 4. However, the ir spectrum of the red solid after centrations shown is a fair reflection ofl the precision decomposition of 1 does not agree with that of the of the data. Decompositionwas first order in 1, with decompositionof product of 4.2r a rate constantat 60o of k : 3.6 X l0-{ sec-l. Com- It was possibleto obtain indirect evidenceindicating parison of the rates of decompositionof 1 and l'2,2-d: that either 4 or some material of very similar reactivity that the thermolysis shows no significant was indeed an intermediate in the thermal decompo- established p-deuterium kinetic isotope effect'. krlkve,e-a,: 0.97 sition of 1 by isolating tris(triphenylphosphine)plati- * 0.05. num(0) and iodomethylbis(triphenylphosphine)plati- The observation that 1 and di-n-octylbis(triphen;"i- num(Il) when thermolysesof 1 were carried out in the (2) decomposeat very similar presenceof triphenylphosphineand methyl iodide as phosphine)platinum(Il) (krlk, : 1.ll :t 0.05) provides the basis for a trapping agents.23':{ The yields of butane and butene rates simple demonstration that the formal hydrogen trans- (20) The extent of deuterium iricorporation into C6 products pre- fer involved in conversionof the trvo alkyl groups of 1 sumably reflectsthe relative rates of hydride addition to coordinated buteneand displacementof buteneby 1,5-hexadiene.Neither of these to butene and butane proceedsby an intramolecuiar ratesis known. However,assuming that the extentof deuteriumscram- process. Decomposition of a solution containing a bling in the butyl groups under the circumstanccsof theseexperiments mixture of approximately equimolar amounts of l- compareswith that during thermal decompositionin the absenceof 1,5-lrexadiene(uide infra), the maximum exlent of deuteriumincorpora- 2,2-d2and 2 was carried out. the resulting octane iso- tion into C6 productsshould be -15%. lated, and its isotopic compositiondetermined by mass (21) R. Ugo, R. Cariati, and G. LaMonica, Chem. Commun.,868 analysis. Ii reduction of platinum- ( 1966). spectrometric (22) C. D. Cook and G. S. Jauhal, Inorg. Nucl. Chem.Lett., 3,31 carbon bonds were to occur by an intermolecular ( 1967). (23) J. P. Birk, J. Halpern, and A. L. Pickard,J. Amer. Chem.Soc., (24) Reviews: R. Ugo, Coord. Chent. Reu., 3' 319 (1968); J' 90,4491(1968); Inorg. Chem.,7,2672 (1968). Halpern, AccountsChem. Res., 3, 386( 1970).

IVhiteside:,Guasch, Stedronskv' I Di-n-burt'lhis(rriplrcn.t'lphosphine)p[atinunt\II t 5262 process, involving either qn intermediate platinum ( PhrP)zPtBu: -PPh, hydride or a direct hydrogen transfer from the alkyl ,//// I group of one molecule of organoplatinum compound 4+pph,- (PhrP)rPtBuz -PPhllltl products to that of a second, this octane would contain deu- +PPhr 6 {l terium originating in l-2,2-d2. In fact. the octanecon- Ph,PPtBu, tained no detectabledeuterium (solubility of 1 in pure methylene chloride solu- tion should be less than that in solutions containing 1(CaHrD2)2PtL,l added triphenylphosphine. However, if the added {+} C8Hr?D I tc*t{,,,1.P,L,) >< ./ triphenylphosphineinfluenced the rate by suppressing (c{H;D:XCsHr?)PtL: dissociation(1 = 5 + PPh'), and if the equilibrium constant for this dissociation lay far to the left, then The addition of triphenylphosphineto solutionsof 1 added triphenylphosphineshould have essentiallyno in methylene chloride strongly inhibits its thermal influence on the solubility of 1. Experimentally, decomposition, although decomposition continues to the solubilities of I in the presenceand absenceof follow approximately first-order kinetics. Thus, first- added triphenylphosphine are indistinguishable. order rate constantsfor thermolysisof 0.030M 1 in the Hence, the added triphenylphosphinemust affect the presence of concentrations of triphenylphosphine rate of thermal decompositionof I by affectinga dis' ranging tiom 0.043 to 0.202 I't appeared roughly sociatiueequilibrium (1 = 5) rather than an associative equal, centered around a value of 5.5 X 10-6 one (1 = 6). sec-r; uiz., a value approximately one-sixtiethof that This conclusion is a surprisingone, in that five-co- observedin the absenceof added triphenylphosphine. ordinate speciesof platinum(ll) are well established The limited solubility of triphenylphosphinein meth- both as discrete compoundst3':6- 're and as reaction ylene chloride precluded rate measurementsat higher intermediates,30while three-coordinatespecies of plati- concentrations. At concentrationsbelow ,- 0.04M, the num(ll) havenot commonlybeen impiicated.sla How- removalof triphenylphosphinefrom solutionby coordi- ever, both three- and two-coordinatecompounds of nation with the platinum(0)formed as a reactionproduct platinum(0) are well know'n.:{ and the usefulnessof resultsin significantchanges in the concentrationof tri- formal valence state terminologYin rationalizing the phenylphosphineduring the course of a kineticrun. Un- behavior of organometalliccompounds is debatable, der thesecircumstances any kinetic data obtainedwould since the strongly c-donating alkyl or aryl ligands are be uselesswithout extensive corrections requiring a capable of imposing a considerablyhigher charge knowledge of the equilibrium constants for dissocia- density on the metal atom to rvhich they are bonded tion of platinum-ligand bonds; these data are not than that usually encounteredin coordinationchem- available. istry involvingless basic ligands.stb Nonetheless,the qualitative observation of rate de- The influenceof chelatingdiphosphine ligands on the pressionon additionof triphenylphosphineto solutions stability of di-n-butyl derivatives of platinum(lI) of 1 could in principle reflect one o[ two types of equi- qualitatively confirms the requirementfor dissociation libria taking place during the thermal decomposition of a phosphine ligand during the thermal decompo- process: one involving dissociationof triphenylphos- sition. Heating methylenechloride solutions of either phine from 1 at some point before or during the rate- di-n-butylIbis(diphenylphosphino)ferrocene]platinum(I I ) determiningstep for the reaction: or a secondrequiring (3) or di-n-butyl(diphos)platinum(II)at 60o for 24 a preequilibrium or rate-limiting associationof tri- hr resultedin decompositiononly to the extentof l-4f, phenylphosphine. These two possibilitiesare exempli- in contrast to the completedecomposition experienced fied by limiting casesinvolving preequilibrium forma- by 1 under these conditions. The qualitative close tion of discretethree- or five-coordinateplatinum com- similarity in the CHrPt regionsof the nmr spectraof I plexes (5 and 6). Equilibria involving addition of and 3 (Figure l) suggeststhat this differencein thermal triphenylphosphineto 1 could be excluded unambigu- stability is not the result oi differencesin the geometry ously by measuringthe solubility of 1 in the presence Stol- of excesstriphenylphosphine. If the rate suppression (26) R. D. Cramer, R. V. Lindse.'-,Jr., C. T. Prervitt,and U. G. berg,-/. Amer. Chem.Soc., 87, 658 ( 1965). observed in the presence of triphenylphosphine re- (27) J. P. Fackler,Jr., W. C. Scidel,and J. A. Fetchin,ibid',90,2707 flectedthe operation of a parasitic equilibrium 1 = 6, (1968); C. M. Harris, R. S. Nyholm,and D. J. Phillips,J.Chem' Soc', 4379(1960): C. NI. Harris and R' S. Nvholm.ibid.,4375 (1956)' (1964)' (25) The evidencc presented later that the deutcrium and hydrogen (28) L. lVI.Venarrzj, Angew' Chem., Int. Ec!.Eng1.,3,453 "\lechanisms Inorganic atoms of intermediate platinum hydride derived from l-2,2-dr would be Qg\ F. Basolo ancl R. G. Pc'arSon' of Y', 1967, 5. extensively scramblcd during this experimcnt in no way vimtes this Reactions."2ncl cd, !Viley',Nerv York, N. Chapter "Ligandsubstitution Processes," conclusion. Approximately l5 % of the deutcrium present in one butyl- (30) c. H. Langtbrdand H. B. Gre1,, P. Haake and r/: moicty of l-2,2-d: (i.e., -0.3 deuterium atoms per CrHrD: group) is W.,q.. Benjamin.Nerv York, N. \'., 1965,Chaptr.'r 2; (1969). transferrcd to thc second in forming butane (cide infra, Table II). R. M. Pfeiffer,Chem. Commun., l3i0 platinumrll) in which one coordina- Thus. since the rates of decomposition of l,l-2,2-d!, and 2 are very simi- (31) (a) Four-coordinate specics displacedsolvent molecule havc lar, the octane isolated from the mixed decomposition of l-2,2-dt andZ tio'n site is looselyoccupied by an easily ibid.,957(1971)' rvould be expected to be composed of -15'Z dr and 857, do material, beeniclentilied: cf. H.C. Clark and H. Kurosawa, from these solubility provided that thc dculerium kinctic isotopc efect for the rates of re' The "three-coordinate" intermecjiate inferrcd solventmOlecule. (b) i.rction betwcen platinum hydride (deutcridc) and the carbon-metal cxpcrlmcnrsmay conrain ir rvcekir-coordirrattng tl4, (19i2). bonds of octy[- and butylplatinum complexcs were equal. W. H. Riggs,Anal. Chem., 810 or electronic character of the metal-lieand bonds of TableII. lsotopicComposition of l-Butenefrom Thermal chelating and nonchelating phosphinei; hence, the Decompositionof Di-rr-butyl-2,2-dr and Di-rr-butyl-/, /-dr-bis(triphenylphosphine)plati num( II) most direct explanation of this differenceis that the chelatingphosphines exercise their stabilizinginfluence Isotopic compn. 7o"- on the di-n-butylplatinum(II) moiety by inhibiting Compd do dt dt dt loss of one coordinated phosphine group during the l' I ,l'dzb 2 3l 66 rate-determinings.tep for the decomposition.s2 l-2,24rb," J 29 67 I In a brief effort to determinethe rate of interchange l-2,2-d,,t I 27 7l of triphenylphosphinefree in solution with triphenyl- . Precision is estimated to be ll'n. b Decomposition was car- phosphine coordinated with 1, the deuterium-de- ried out in methylenechloride solution at 60". " The isotopiccom- coupled, tH nmr spectra of solutions containing 1- position was establishedto be independentof conversion of L-2.2-tl: l-butene (see the Experimental Section). d wrth- were examined as a to Decomposed 2,2-d2and triphenylphosphine func- out solventat -160'. tion of temperature. At the highest temperatures reached (-60o), there was no evidence of collapse of the pattern of the CHzPt protons due to PPTCHspin- an isotope effect kslko ) I would decreasethis prob- spin coupling. In related experiments,the spectrum ability.16 Sincethis probabilityis ^-0.3 experimentally of a solution containing a mixture of L-2,2-d:and di- (Table II), the implication is that the distribution oi' phos was examinedat 30o as a function of time. Slow deuterium atoms along the butyl chain is not quite replacementof the coordinated triphenylphosphineby statistical. diphos was readily evident, with the reaction being An unexceptional,reversible elimination and addi- complete after several hours. No effort was made to tion of platinum hydride is almostcertainly responsible establishthe kinetic order of this process. Thus, al- for the deuterium scramblingobserved in 1-/,/ -dt ancl though these experiments permit no quantitative con- l-2,2-d.r(Scheme I[;.rs However, at least one un- they do that ligand exchangeis clusion, demonstrate SchemeII. Platinum(ll)Hydride Elimination-Addition slow on the nmr time scaleand that substitutionof one Mechanismfor DeuteriumScrambling coordinatedphosphine in 1 by another is possiblewith- CDC"H. out the destructionof the carbon-platinum bonds. qr-il DeuteriumLabeling and ScramblingExperiments. In cHD {.H.D I order to establishthe extent to which the platinum hy- _-. D dride elimination responsible [or the formation of -Y I -/ ]c$,o, butene from 1 is reversible,a study was carried out of cDc:H1 the deuteriumdistribution in products of thermal de- -i* PtCH.CDrC.H, Bt-ll - PICDC"H. composition of L-l,I-d2 and l-2,2-dt, both in the cH, presenceand absence oI added triphenylphosphine. t-2,2-dr I I D cH2D n The resultsof this study combine with those described I previouslyto provide a detailed picture of the reaction tltt profile for the thermal decompositionof l. etc. Comparison of the isotopic compositionsof 1-bu- expectedconclusion concerningthis platinum hydricir: tene isolated from thermal decomposition of l-2,2-d,: and readdition sequenceemerges from the and l-/,l-d.: in methylenechloride solution established elimination data in Table II: r'i2..the observationthat no appreci- that a deuteriumoriginating at the I or 2 position of able quantity of 1-butene-dris formed during thesc the butyl groups would be lost with equal probability reactions indicates that the butene which is coordi- in formation of 1-butene(Table II) and thus demon- nated to platinum in the intermediaterepresented in stratedthat complete scramblingof deuterium between the I and 2 positions of the butyl groups occursduring Scheme II does not exchangewith l-butene free in the thermaldecomposition. To what extentscrambling solution (e.9., 7=#8). I[ exchangedid occur, co- extendsbeyond the I and 2 positions to the 3 and 4 ordination of l-butene-dt to a platinum(Il) deuteride positions is not clear from these data. If deuterium center, followed by deuterideaddition and platinum scramblingalong the butyl chain were completeduring hydride elimination,would providean efficientroute to the thermal decomposition,and ii there were no deu- l-butene-dr, and this substanceis not observed as a terium kinetic isotope effect on the reaction sequence : leadingto butene,the probability that the butenewould (36) The data of Chatt, er a/., suggestan isotopeeffect of ksike ethylenefrom while the - 1.5-2.0 for loss of [(C:Hr)rP]:PtBrCDrCHr,6 be formed by loss of deuterium would be 219 0.22; isotopeeffccts for loss of copperhy"dride frorn [CHTCHTCHDCHzCUP- (n-Bu)3J^&p.lko - 4.'7)37and of lithium hydridefrom n-butyllithium (32) The exceptional thermal stability of other chelatedtransition (kgl ko: 3J)s are larger. How'ever,these data are not directly itp- metai organometallic compounds (e.9., diisopropylcyclooctatetraene- plicableto considerationsof the probablemagnitudes of isotopeerfccts platinum(II),tr diethyldipyridylnickel(II),3rand alkyI cobaloximes)]s in the data of Table II, sincethe stepexpected, on the basisof the mcch' and the enhanced stability of many phosphine-coordinatedorgano- anism of Figure 5, to determinean isotopeeffect would be reductirc metallic compounds in the solid state both probably have a similar eliminationof butane from a L:BuPtH(D) fragment. mechanisticexplanation. These observationssuggest that isolation of (37) E. R. Stedronsky, Ph.D. Thesis, lvlassachusettsInstitute ot' othcr, presentlyunknown, organometallicspccies susceptible to metal Technology,Cambridge, Mass., 1970. hvdride elimination may be possiblcby appropriatechoice of chelating (3S)R. A. Finneganand H. w. Kutta,J. Org.Chem',30,4138 (196-it. ligands. (39) For reviervsof evidencepertinent to metalhydride addition and (33) J. Miiller and P. Gijser, Angew. Chem.,Inr. Ed. Eng|.,6,364 eliminationto olefins,see F. R. Hartlev,Chem. Reu.,69,799 (1969), attd ( 1967). ref 6 and 7. Note that prior coordinationof olefin to the metallic (3.1)T. Saito, Y. Uchida. A. Misono, A. Yamamoto, K. Morifuji, centerctnnot be assumedto be a prerequisitefor addition of a metel and S.Ikeda,f . Amer.Chem. Soc., 88, 5198(1966); A. Yamamoto and hydride to the olefin, since such coordinationis almost certainly not 3- S. Ikcda, ibid., 89,5989 ( 1967): T. Yamamoto, A. Yamamoto, and S. involveclin at least one instance: udz.,the addition of IHCo(CN)'] Ikeda,ibid.. 93,3350, 3360 ( l97l ). to otefins. Cf. J.Halpern and L. Wong, I' Amer. Chem. Soc., 90. (35) G. N. Schrauzer,Accounts Chem. Res., l, 97 ( 1968). 6665( r968).

lVhitesides,Guasclt, Stedronsk.r* I Di-n-burvlbis(rriplrcnv'lphosphine)platinunt(llt 5264 mass spectrum examined at low ionizing voltages. C"ll"Or8r'l 1 6 C.Hp.Bre c"t.o.B'i/ Examination of the mass spectra of l-bromobutane- |c.qqa/' n n n n ffH n n I,l-d2 and l-bromobutane'2,2'dt demonstrated that relatively little positional scrambling of cleuterium occurs in the molecular ion prior to its fragmentation by loss of ethyl radical (Figure 3, Table III): oiz., only

,-M+ ---

Figure3. Massspectra of deuteratedl-bromobutanes showing the " Thenominal value of theionizing voltage was l1 eV. Isotopic - compositionsare corrected for contributionsfrom r3C; precision molecularion regionand M 29ion region: A, rr-butyl-drbromide b after I half-life in the presence added tri- is estimatedto be +1%. l-Bromobutanewas obtainedfrom derived from 1-2.2-dz of (O.3 phenylphosphine;B, rr-butyl-r/.rbromide derived from 1-2,2-dzatter partialthermal decomposition of l-2,2-dz M in CHrClr). I half-lifein the absenceof addedtriphenylphosphine; C, n-butyl- " l-Bromobutanewas obtained from partial thermal decomposition 2,2-chbromide; D, rr-butyl-l,l-dt bromide. Eachregion is normal- of l-2,2-dz(0.3 M in CH:Clr)in the presenceof addedtriphenyl- ized independently.The isotopic doublet for CrHrDrTeBrand phosphine(0.3 lvl). CrHzDrErBr(for M+) and for C.rHrD.rTeBrand CrHrDzEtBr(for M - 29)" is indicatedabove each trace. ca. 13-161" of one deuterium atom is lost from the C1 and C: positionsin the fragmentationof the molecular significant reaction product. {0 Thus, the rate of ion of l-bromobutane-/,/-d': or -2,2-dzunder the con- addition of the platinum hydride moieties, which are ditions used in obtaining these spectra. Thus, com- presumeci to be intermediates in the scrambling pro- parison of the isotope compositionsof the M+ and cess, to coordinated molecules of l-butene, and the (M - Et)+ peaksin the spectraof samplesof l-bromo- rate of the subsequent reductive elimination of butane butane obtained from partially decomposedsamples from these intermediates, must be considerably more of L-2,2-dzprovides a measureof the manner in which rapid than the rate of exchange of coordinated l- the deuterium present in the molecule is divided be- butene with [-butene free in solution. tween the first two and last two carbon atoms of the Having established that the deuterium present in the butyl group. The data in Table tII indicate that l- l-butene produced on thermal decomposition of bromobutane-d'tderived from partial thermal decom- l-l,l-d! and I-2,2-d.2 is extensively scrambled, we position of L-2,2-d'zin methylene chloride shows the turned our attention to the complementary problem of same mass spectral isotopic distribution as l-bromo- determining the extent to which deuterium in the butane-2,2-dt. Hence, thermal decomposition of 1- starting material is scrambled during thermolysis. 2,2-d,rin the absence of added triphenylphosphine The procedures used to effect this analysis are outlined apparentlydoes not take place with significantscram- Scheme III. Samples of L-dt were heated at 60o for bling of deuteriumalong the alkyl chain in undecom- SchemeIII. Determinationof the Extentof Deuterium posedstarting material. Scramblingin l-l,l-dz and l-2,2-dzRecovered Following In contrast,comparison of the isotopic composition PartialThermolysis of M+ and (M Et)+ for l-bromobutane obtained to ca. half-life Ph,P\orlc{H7Dz tntt-o*/t' from a sample of l-2.2-dt thermolyzed I e- 2C,HrD.Br ..,-' in a solution containing added triphenylphosphine "\c,H,D,, PhrP/^'-8, Ph,rP/ electron indicates that extensive deuterium scrambling has occurred under these conditions. If two deuterium atoms are distributed entirely randomly along an n- butyl chain, the relative probabilities that the Ct,C, ethylenemoiety will contain two, one, and zero deu- IC.HrD2Br]+' c{H?D2CN terium atoms are 17:56:28, respectively.nt Approxi- mate corrections to these probabilities for the slight ["".n,.*. deuterium loss observed (Table III) from the Ct,C, CHrcN f,,,,.. I ethylene moiety of l-bromobutane-d: on fragmenta- tion suggestthat a statisticaldistribution of deuterium c3H?-nD^CH?CN along the chain of l-bromobutane-2,2-d2would lf*'4. lead to a distribution of isotopic compositionsfor the ca. I half-life of the thermal decompositionreaction and (M Et)* fragment of do:d1:d.2:35 :50: 15. Thus. qualita- then cooled and treated with molecular bromine. the observeddistribution, 24 49:26. indicates The 1-bromobutane-d:produced was isolated and its tively that thermolysis of l-2,2-dt in a solution con- taining added triphenylphosphineis accompaniedby product (40) Chatt, et al., apptrently did not observeethylene-dr as a almost complete scrambling of the deuterium in the of thermal decomposition of solid ethyl-l,l-dz-bromobis(triphenyl- phosphine)platinum(ll).6 This observationleads to conclusionscon- butyl groups of undecomposedstarting material. cerning the relative ratcs of exchangeof free and coordinated ethylene and platinum hydride addition to coordinated ethylenein the solid (.11)H. Margenauand G. M. Murphy, "The Mathematicsof Physics stateor melt that are similar to thosediscussed here. and Chemistry," Van Nostrand, Princeton,N. J., pp 4lt ff. The isotopic composition data in Table III demon- strate that thermal decomposition of l-2,2-d2 in a solution containing no added triphenylphosphinedoes not result in interchangebetween deuterium at Cz and hydrogen at Cr or Cr; they do not permit any conclu- sions to be drawn concerning scrambling between C1 and C:. The extent of this scramblingwas determined explicitly by converting the 1-bromobutane-d:obtained from recovered dibutyl-d:-bis(triphenylphosphine)- platinum(tI) to valeronitrile, washing out any deu- terium in the position a to the nitrile group by treat- ment with base,and comparing the isotopic composi- tion of the resulting exchangedvaleronitrile with that of the l-bromobutane from which it was made.{2 The l-bromobutane had isotopic composition do, 07o; dt, 27n; dt, 98%; while that of the valeronitrile was do, 6/o; dr, l9%; d2, 75%. Thus, ca. l3/o of the deuteriumoriginally presentin the bromobutanecan be exchangedfollowing conversion to valeronitrile; this 3"o r"o number provides a direct measure of the extent of 3;i' scrambling of deuterium onto Cr during the thermal (A) decompositionof L-2,2-d':. Figure4. 60-MHznmr spectra in carbontetrachloride of: l- bromobutane-c/:derived from l-l,l-.1)after partial thermolysis in The conclusions drawn from these mass spectro- theabsence of triphenylphosphine;(B) l-bromobutane-r/: denved metric studies were confirmed independently by froml-2.1-rl: after partial thermol)'sis in the presence of triphenrl- complementarynmr studies. Integration of the spec- phosphine;(C) l-bromobutane-c/,r. trum of 1-bromobutane-dr obtained from L-I ,l -dl atier incomplete thermolysis in methy'lenechloride sitioncontaining platinum(0), are formed in a first-order. solution containing no added triphenylphosphine intramolecularprocess. No 2-buteneis formed. indicatedthat the area of the CH,-nDnBr peak at 3.15 (2) The rate of decompositionin methylenechloridc ppm correspondedto 0.24 * 0.I protons (Figure .1). solution is decreasedby adding triphenylphosphinett'r This estimateof transt'erof ca.0.2-t protons from C: to the solutionand by coordinationof the dialkylplatinunr- C1during thermal decompositionof 1-l,l-dr is in satis- (ll) moiety to a chelatingbidentate phosphine. Solrr- factory qualitative agreement with the estimate, bilitv experimentsdemonstrate that the effect of thc obtained by exchange and mass spectrometry,of addedtriphenyiphosphine is that of inhibitingdissocia- transferof 0.13 deuteronsfrom C1 to C1 during ther- tion of a phosphineligand from l. molysis oI L-2,2-d). Similarly, integration of the (3) Deuteriumpresent at Cr or C2of 1 is extensively' spectrum of l-bromobutane-d,:obtaineC from I-2,2-d2 scrambled in the i-butene product. The degree t)l after incomplete thermolysis in meth!'lene chloride scrambling aDpearsto be independentof the extent solutioncontaining 0.3 M triphenylphosphineindicated of decompositionof the sample. qualitativelythat the deuteriumoriginally localized at (1) During the platinum hydride elimination and C: of the butyl group was statisticallydistributed along addition reactions responsible for this deuterirrm thealkyl chain. The errot in this measurementis signifi- scrambling.there is no exchangebetween l-butene free cant: however,within its limits oi precision,it also in solutionand 1- or 2-butenecoordinated to platinunl. points to approximately the same deuterium dis- (5) Deuterium presentat Cr or C2of the butyl groups tribution as that inferred from the massspectrometric at the otltset of decompositioncarried out in solutions studies. containing no added triphenylphosphineis found to be In summary, these labeling experiments establish onty slightly scrambled in startin-ematerial recovered that deuterium scrambling in recoveredstarting ma- after I hali-life. deuterium presentat C: is extensively' terial is restrictedto a small (-13 of one hydrogen) % scrambled in starting material recoveredafter t haii- interchangebetween C1 and Cx, for thermal decompo- life in solutionscontaining added triphenylphosphine. sition of 1 carried to I half-liie in solutionscontainin-e (6) There is no observable d-deuterium isotope no addedtriphenylphosphine; scramblins of deuterium effecton the rate of thermal decompositionof 1 carried during thermal decompositionsof 1 carried to I hali- out in solutions containing no added triphenyiphos- liie in solutions containing 0.3 r14triphenylphosphine phine. is essentiailycomplete between all four carbon atoms The most important featuresof the reaction profile of the n-butyl moiety. characterizingthe thermal decompositionof 1 in soltr- Discussion tions containing no added triphenylphosphineare defined by three of these observations. First, tire Six lines of evidence are directly pertinent to the scramblingof deuteriumin the l-buteneformed durinc mechanismof thermai decompositionoi 1. decomposition of l-l.l-d': and 1-2,2-d)indicates that (l) The products of the thermal decomposition,l- the eliminationof platinum hydride from butyl groups butene,butane, and a compound of unknown compo- and its readdition to coordinated 1-buteneare botir more ranid reactionsthan the reductiveelimination of .''aleronitrile-2,2

lVhitesirles.Gtutsclt, Stetlronsl;)' Di-n-bur,,'lhis(rripitt'nvlphosphine)platinunu I ll existenceof LPtBur 8S6r discrete intermediate along the Dlrsociotion * t1 reaction coordinate and certainly no evidencecon- cerning its stability relative to that of the intermediates respon-siblefor scrambling. In principle.extrusion of the olefin into the coordination site occupieclby the :1 leaving phosphine ligand could be concerted with phosp-hine-platinum bond breaking' However, the that there is no p-cleuteriumisotope effect Dccomp obseivation decompositionof I in the ab- fl Yinout on the rate of thermal ( l-) suggeststhat p c-H '* cxcs!3 L senceof added triphenylphosphine f I '-//t ,a bond breaking is not important in the dissociation [uPtBu.J rH'Bu Decornp step.{{ Third, the Structure and relative energiesof wilh the intermediatesresponsible for deuteriumscrambling, H. A- cxc€s3L the magnitudes of the barriers separatingthese ,rh PI'Bu ancl (y, L/ species,are not known. The deuterium scrambling data suggestthat exchangebetween cr and cz is more -/.. ,t that between Cx and Cr. Evidencetaken ")") Pr'8, rapid tfiin LBU ( irom other studiessuggests that complexesof 2'butene with platinum(Il) should be lessstable than analogous Figure _<. Schematic representation of the reaction coordtnate compiexesof 1-butene.7'3e'{;These observations,al- be- dcicribing the thermal decomposition of l. The separation though helpful in estimating qualitative stabilitiesfor ts arbitrary, Sinceone representsGibbs ttee energy tween two curves the intermediates involved in the deuterium scram- 6 for a :;olutron containing no added pliosphine while the second provide suftrcientinformation to estimate representsc l'or a solution containing added triphenylphosphine. bling, do not L representstriphenr lphosphine. relativeconcentrations' \\'e assumethat the intermediatefrom which reduc- tive elimination of butane takes place has hydride observationthat the scramblingof deuteriumdoes not ancl alkyl groups cis{6and that the reductiveelimina- exrend to unclecomposedstarting material establishes tion step is concerteci.'; that the starting nlaterial and those intermediatesin This study. in establishingthe basicmechanism for which deuteriuntScrambling occurs are Separatedby a the thermal deconrpositionoi 1. points out certain barrier lrigher than that for the reductive elimination principlesrvhich shouid be applicablein practiceto the step. Finally, since the highest barrier for thermal synthesisof organometalliccompounds of platinum. decompositioncarried out in the absenceo[ added and presumably of orher transition metals. hal'ing triphenylphosphineappears to be that separating high thermal stabiiiry. Thus. in particular, alkyl srarringmareiial from the hydrido- and sec-butylplati- scram- Cr num intermediatesresponsible for deuterium (43t Thc obscrvation of I small ilmounl of scrambling between and sincethe overall rate o[ the decomposition anci C, i11lccevcrcd starrirrgmutcrial in thc ]bscnce of addcd L suggcsts blins, of L from l, that rhc cnerglcs of thc transition stltes lceciipg to loss by either the presenceof triphenylphos- -l kcalimol' is dicreased and to rcductivc climinltion of butanc, in lnct ditfcr by on the to give a dvc- phine in solution or by chelating phosphines t.l-tt .4.norhcrirlterrlrtrVe, inl'olving cxtrusion of olcrin Occurring platinum atom. the rate-determininest€p in.the ab- coorciinarc irrtcrrnccii;.ttecomplcx iirr a prcequiliL'rium step i.n.. oi acicledtriphenylphosphine can be assignedto -,-^ LrPt(n'Bu ): a srep involving dissociationof 1 into I equiv of tri- a three-coordinate phenylphosphini and 1 equiv of -** L'PIH(n'Bul(l'butene' LPtHBu(l'butene) platinum complex. presumably having the composi- iion phrppt(n-eu),(S). A reaction coordinatewhich determrning +t accommodatesthese observations is represented in n'BuX sec'Bu ) Fieure5. L,Ptt this diagram. and of the is also form- i number of features of be.l'oreethanol. studiedto date, since metal hydride elimination rather potassium tetrachloroplatinite according to the method of Jensen.56had mp 305" dec (lit.56mp than homolytic carbon-metal bond scissionseems to 308' dec). provide the lowest energy pathway for thermal de- cis-Dichlorobis(triphenylphosphine-t/r;)platinum(II)was prepared composition available for alkyl derivatives of those using triphenylphosphine-c/r;having mass spectralisotopic analysis: metalscapable of forming strong bonds to hydrogen.{e 90/, dr 9'Z ,lrr, l\ d1x.57Recrystallization from CHrCh-heptane gave having mp 305" dec. high stability associatedwith methyl, neopentyl, material The Dichloro[,1'-bis(diphenylphosphino)ferrocene]platinum(II). A and aryl derivativesof thesemetals is thus attributable solurion of 2.0 C (-1.8mmol) of potassiumtetrachloroplatinite in 30 to the absenceof 6 hydrogenswhich can be eliminated ml of \rater was treated rvith 1.0 g (10 mmol) of diethyl sulfide' as metal hydride. The reaction mixture was stirred for 3 hr and extractedwith two was added to a For compoundsof the dS-dr0 metals in which metal 20-ml portions of methylenechloride.58 The extract of 3 g (:1.8mmol) of l.l'-bis(drphenylphosphino)ferro- has beenblocked as a pathwayfor solution hydrideelimination cener3se in 80 mtot methylenechloride.After the reactionmixture thermaldecomposition. it is not obviouswhat reaction was stirred for I hr. 75 ml of [eptane rvasadded. and the resulting type will emerge as preferred for decomposition. s6lution was slorvly'concentrated at room temperatureby stirring Mechanismsinvolving homolytic scissionof carbon- using reduceclpressure ( 100Torr)to crt.70 ml. The resultingsolid The brrght yellow powder had metal bonds provide one possibility;;0 bimolecular rvasfiltercd and drred at 0.01 Torr. mp 335' dec (lit.rr mp > 315' dec)and rveighed3.8 g (907"): ir decompositions,or reactions occurring between or- (KBr) 3050w, l-130sp, l160 mb. ll00 mb.750 sb,650 w, 500 b ganicligands on a common metalcenteror on thesurface cm- I. of a metalatom cluster,provide a second.i't If radical mechanismsdo intervene.increasingly the polarity of the carbon-metal bond should increasethe stability (5-l) ivlclting points rvcrc dctcrmirled using a Thomas-Hoover capil- in tubcs scalcd utrdcr rcduced pressurc (8() and lary mclting point apparltus of the compound toward thermal decomposition, Torr) and are uncorrcctcd. Boiling points arc uncorrected. Infrarcd the stability of organometallicderivatives of fluoro- spcctri.r\vcre- takcn in sodium chloridc cclls or potassium bromide pcllets carbons,t: metal acetylides,and the recently reported as notc

lVlitesielas.Gttasch, Stedronsk)' ,' Di-n-butt'lbis(triphcnvlplnsphine)platinunt(Ill 5268 (!lu.\(),). cis-Di-l-buty lhis(tripheny I phosphine)platinum( I I) ( I ). To a stirred tions of I .l/ sodrum bicarbonate. drted and distilled suspensionof 2.0 g (2.5 mmol) ot' crs-dichlorobis(triphenylphos- carefullr using a 40-cm Tctlon sprnntng-bandcolrrrnn. Analysis by phinetplatinum(ll)in 20 ml of dry ether at 0'was added4 ml(6.2 glpc (column G) showed that early-distrllatton 'rircrrons contained mmol) of a 1.6 rfl solution oI r-butyllithium in hexane. The reac- erlryl 2-chlorobuty-rate.derivecl from a small qrrirrrttryof 2-chloro- tion mixture was allorvedto tvarm to 25'over 30 min and l0 ml of butyronitrile in the starting materia[. The ethyl ].2-tlichlorobuty- warer was added. The resultingsolid was collectedand washed in rate(140 5.76:,;l obtainedhad bp 75-76'(llJ'l'orr)[lit.cl bp 7i' successionwith 5-ml portions of water. ethanol. and ether. After ( l6 Torr tl. (2Ul drying at 100 Torr. the product weighed 2.0 g t95 \) and had mp l-Butanol-2.1-rl:. Porvdered zinc metal v) wfls activated b' '). 125' dec ( lit.m mp I 32- lJ.l Precipitationof the sample from ca. rvashing rvrth 100 ml of 5 [ hydrochlorrc acid lirlftrwedby three ?0 ml of methylenechloride by adding an equal volume of heprane 100-ml portions of ',vater. The actrvated porvrler rvascollected br- and removing mcthylenechlorrde at reducedpressure[20'( l00mm)1, fi[tration and placed in a three-necked2'1. liask cquipped wirh u follorved by recrystallization lrom methylene chloride. yielded a mechanical stirrer and Dean-Stark trap. Bcnzcnc ridO ml) was colorlesscrystalline analytical sample (90'a), having ir (KBr) 3050 added anrl the nrixture was refluxed unttl all wirtcr was removed. m, 2950sh, 2920s, 2860sh, l480sp, l.l-l0sp,I 190m, I 160m, ll00s. \lost of the benzenewas removed by distillati()nrnd 250 ml of 1.2- 740 vs, 700 vs. 5.10sh, 515 vs, 500 sh,.l20 cm-r, and nmr (CD1CI:) dimetho.ryethane ( D!l E). freshly distilled I'rotn benzophenone 60.5-1.3 (m, l8)and 7.1-7.7 (m. 30). sodium dianion. was added. A rellux condcnscr and dropping Anal. Calcd for CrrH,'rP:Pt: C. 63.37. funnel rvere fittcd to the flask. The dropping lirrrnclwas charged Found: C, 63.I I ; H. 5.85: P,7.29. with 145g (0.8 mol) of ethyl 2.2-dichlorobutyrrtt..u0 e (4 mol) of The complexes t, 2. and 3 were microcrystalline powders when deuterium oxide 09.57; dr). and 300 ml o[ dry l)i\lE. This two- precipitatedlrom methylenechloride by hcptane. When recrystal- phase mixture was agitated while being addcrl ovcr 2 hr to the lized slowly fiom a singlesolvent, thel' rverem'-lcrocrystalline solids. stirred.refluxing suspension of zinc in DiVlE.6r Al'tcran additional These materials are stable when solid toward tvater and oxygen. 8 hr at reflux temperature no dichloro ()r morrochloro ester re- stablein solution towirrd rvatcr,slightly ox) gen-sensitivein solution. mained. as determined by glpc (column G). z\l'tcr cooling, the and somewhatlight sensitive both wherrsolid and in solution. Thev solids rvere tiltcred and rvashedvv'ith two 150-nrl'ortions of drr are insoluble in saturated hydrocarbon solventsand water, slightly ether. The combirred filtrates wcrc addcd slowlv irver l2 hr to a solublein ethy'letherand ethantrl,and moderatelysoluble in methyl- ntirtureof 80g (2 mol)ol'lithiumaluminum hvrlrrrlc rn 250mlof drr cnechloride and toluene. erhcrin the sameapparatus. On conrplctiorttll tlrcreduction. cau- cis-Di-rr-octylbis(triphenl'lphosphine)platinum(lI)(2). To a rrous arldition ol'll0 ml tti satttrrttedsodium :ull:rtesolution pro- stirred suspensionoi 1.6 g (2 mnrol) of cis-dicirlorotris(triphenyl- duced a scmisolid maJSthi.lt lvas extroctecllirtrr trrncswith 100-ml phosphine)platinunr(ll)in 20 ml of ether at 0 rvasadded 3 ml t6 porriousol'ether. The dried ( NlgS()')extract w;rs tlistilled using a nrnrol)ol'a 2 rll solution ot'r-octyllithiunr in hexane. After the sl)tnnlng-irantlcolLrrnrl to ) icltl ll g (7l ",'t Telltrl '. of l-butant-ll- acldition.the reaction nrixture rvasallorved to rvarm to room tem- :.:-d!. havirrgbP I l6 pcrature over J0 min and I nrl ot'methunttl r,vasadded. The solu- l_llutan0l_/.1-(/jwlts prcpurct! [rr rcr.luctit)nol illcth] Lr-butyratc llr)n was corrccntratcd under reduccclllrcssurc. arrd the resulting usrrrg lithiuntaluminttrn dcutcrtdc. strlid p:rtitione'J lrctrvcena mirture ot'20-ml each of water and l-[fromobutlnc-/. lf'D,.:Oand ctlrll dichltlrobtltt'rlltc lrdtlcd to l''e zrrrqsusocnsion rverc (60) B. A. l\{orrorr, Cutt.J. Chem.,48.:l9l (1970). roughlv proportiorrute, despitc' tlte hete rogcltct)..i n,rrurcotl the mixturc. t 6l ) Compotrnd 3 includes solvent rtf crvsrallization tenaciously. (6-i) O. I(lmm and C. S. iVlarvcl,"Organic S. ttllrcscs,"Collect. Vol. This analy-ticalsantple \r'.rsprcparcd by Dr. Tcrry Ncrvirth. I, Wilct', N*v Y-ork, N. \'., l9'll, p I's. t6l) l,l-Dichlorobut)'rorrirrile rvas ob(;.rincdas a gift from thc Dorv t66) Diphos w(Is prep.tred frtlm triphc'nylphc'rpltttrchv the procedure Ciremical Co. ol'J. Cltutt ltrtdF. A, H.rrt,J' Chen. Soc.,llTi'l'tr,ttl.

Jtturnul ttl tlte ,'ltnaricurt Clrtnricul Sr;r'rt,/t. t 9,1;t5 I Jult' 26. 197) 5268 (NIgSOr), cis-Di-n-butylbis(triphenylphosphine)platinum(lI)( l). To a stirred tions of I r,l"/sodium bicarbonate.dried and distilled suspensionof 2.0 g (2.5 mmol) cif cis-dichlorobis(triphenylphos- carefullyusing a 40-cm Tetlon spinnrng-bandcolumn. Analysis by phine)platinum(ll) in 20 ml of dry ether at 0' was added 4 ml(6.2 glpc (column G) showed that early-drstillation fractions contained quantity mmol) of a 1.6 Il solution of l-butyllithrum in hexane. The reac- etiryl 2-chloroburyrare.derived from a small of 2-chloro- material, The ethyl 2,2-dtchlorobuty'- tron mixture was allowed to tvarm to 25" over 30 min and l0 ml of buryronitrilein the starting '75-76'(18 rvater was added. The resulting solid was collected and washed in rate(140 c,76%) obtainedhad bp Torr) [lit'crbp 7l' successionrvith 5-ml portions o[ rvater. ethanol. and ether. After ( l6 Torr)1. (200 g) was activated drying at 100 Torr. the product rveighed 2.0 g (gS\) and had mp l-Butanol-2..?-rlr. Porvdered zinc metal by 125" dec (lit.m mp 132-l'3.1'). Precipitationof tlresample from cn. rvashingwith 200 ml of 5T hydrochloric acid followed by three 20 ml of methylenechloride by adding an equal volume of heptane 200-ml portions of water. Tlte acttvated powder was collected by and removing methylenechloride at reducedpressure[20'( 100 mm )], filtration and placeclin a three-necked2-1. flask equipped with a followed by recrystallization from metlry'lene chloride, yielded a nrechanicalstirrer and Dean-Stark trap. Benzene (200 ml) wa.s colorfesscrystalline analy'tical sample (90%), having ir (KBr) 3050 added and the mixture was refluxed until all water was removed. m. 2950sh, 2920s. 2860sh. 1480sp, l4-10sp, I 190m, I 160m, I 100s. \lost of the benzenewas removed by distrllationand 250 ml of 1.2- 7.10vs. 700 vs, 540 sh. 515 vs. 500 sh. -120cm-r, and nmr (CDrCl:) climethoxyethane( DNI E), freshly distilled lrom benzophenone ,i0.5-1.3 (m. l8) and 7.1-7.7(m, 301. sodium dianion. rvas added. A reflux condenser and dropping Anal, Calcd for CrrHrsP..,Pt: C, 63.37, H. 5.80: P, 7.43. funnel were fitted to the flask. T[e dropping funnel was charged C, 63.1I H, 5.85; P, 7.29. with 145 (0.8 mol) of ethvl 2,2-dichlorobutv'rate,80g (4 mol) ot- Found: ; c ,99.5% The complexes 1. 2. and 3 were microcrystallinepowders when deuterium oxide c/:).and 300 ml oidry DME. This two- precipitated from methylene chloride by heptane. When recrystal- pfiase mixrure rvas agitated while being added over 2 hr to the lized slowl.vfrom a single solvent. they rverem:rcrocrystalline solids. itirred. refluxingsuspension of zinc rn DiVlE.6{ After an additional These materials are stable when solid toward lvater and oxygen. 8 hr at reflux temperature no dichloro or monochloro ester re- stablein solution toward lvater.slightly ox)'gen-sensitivein solution. maineci.as determined b-v glpc (coltrmn G). After cooling, thc and somewhatlight sensitiveboth ''vhensolid anclin solution. Thev solids rverefiltered and rvashedrvith tlvo l-iO-ml portions ot' dry are insolublein saturatedhydrocar['lon solvents ancl water, slightty' cther. The com[iped hltrates wcrc added slowly over l2 hr to a solublein ethyl ether and ethanol,and moderate[-v'solublein methyl- nrixrureoi 80 g ( I mol) ot'litIium altrmtt'tttmhydride in 250 ml of dr1 enechlorrde and toluene. erher in thc santeapparatLls. On ctlntl;lctionof the reduction, caLl- ci.r-f)i-rr-octylbis(triphenylphosphine)platinum(II)(2). To a trous acldition of 80 rnl tlf satttrltcii stldium sulfate solution pro- stirred suspensionof L6 g (2 mnrol) of c'i.s-dichlorobis(triphenyl- ciucerla semisclid mass tltat wlls extrllctedlbur times with l0()-ml phosphine)platinum(ll)in lC ml ot'cther at 0" rvasadded 3 mt l6 porrions ol' ether. The drie.l ( IlgS() r) extract was distilled using lr mmol) ol'a 2 rl/ solution ol'r-octyllitlritrnrin hexane. After tlre Tctiorr spinnirrg-bitntlcolutnrl to yrclelJl S Q3%) of l'butantr[- addition. the reaction nrixture rvasallorved to rvarm to room tem- -'.1-,/.r.having bP I l6'. pcrature over 30 min and I nrl of metltanol rv'asaddcd. The solu- l-8uten6l-1./-rl: rvaspreparcc! [11 retluctitll oI methyl rt-trutyrltc tion rvas concentrated uncler reduccd pressurc.and the resulting using lititruntaluntinttm dcuteridc. solid prrtrtionei lrenvecna mixture ol']0-ml cach of water and l-ilrrrmobutane-/.l-,1: ',nd 1-lrr0mobutlne-l.l

Jrturtttrl,tl tlt,: .lrnaricurt Clttttrtt'ul Sttt'iety I 91.15 I July 26. 197: 5269

or trans-2-buteneor octane. Products were identified by com- l-butene. internal standard. and solvent there were three peaks re- ptnson of glpc retentlon times and mass spectra with those of spectrvely'assignedto l-hexene(0.8 mg.0.0l mmol. l0 -+-5[ bascd authentrcsamples ( !latheson ). on the assumption that productron of I cquiv of l-hexenefrom ther- An rnorgrnrcproduct was isolatedby heatinga saturated(at 60') mal decomposrtion of I equiv oi I would constitute lO0%). crs-l.J- \olurronot'l in benzeneor methylenechloridelor ca.3 hr. allowing hexadiene(\tructure assignedby comparison of glpa retention trmc rhe ruLrero s(and at room temperatureovernight, collecting by fil- and mass spectrum wrth that of an authentic sample).and a com- irarron. washrng thc resulting red solid with hexane, and drying. pound rvhoseretention tlme correspondedwith those of trans-1.4-. From 0.i0 g oi I rn I mlo[benzene was obtained0.21 g of material. cis-1.3-. and trans-1,3-hexadiene. Samples of l-hexene used for mp lJ]' dec (wrth cftangein lbrm at 139'); from 0.3 g of I in 0.5 isotopic analysistbllowing thermal decomposirionof l-2,2-dzin I.5- nrl oi m:tht'lene chloride was obtained0 22 g of material.mp 2.10' hexadienervere collected from glpc(column E). tlc'crrvrrh change rn form at 139'): ir (KBr) 3050mb. 1480-1470s Reaction of I with Hydrochloric ,\cid. [nto a flame-dried cenrri- tjoublet. l-l-.10sp, 1380mb. I 120wsh, 1095s. 735s, 685 vs cm-r. fuge tube rvasrv'eighed 50 mg (0.017mmol) of 1' A no-air stopper .-tnot. Found: C. 55.20; H, 3.95: P. 9.3l. ',vasfitted to the tube and the solid dissolvedat 0o in I ml oI merhy'l- \\'e were not successfulin identifying this subsrance(ride supra). ene chloride containing pentanc as internal standard. At 0'. I ml Tris(triphenylphosphine)platinum(O)was prepared according to oIconcentrated aqueous hydrochloric acid rvasadded and the tube rhe method of Ugo, et al., by reduction of potassiumtetrachloro- was shaken for 5 min. The product mixture was centrifuged and platrnite in ethanol in the presenceof triphenylphosphine.6?The the methylene chloride layer rv'asanalyzed by' glpc using columns ,A, tellow solid obtainedhad mp (in airt 120-125'ili1.0r(in air) 125- and B. The:"ield of butane was 100%; no ((lf) buteneor oc- 135'1,mp ( I mm) 192-198" (red liquid) [ir.67mp ( I mm) 205-206' tane was formed. The upper aqueous iayer was discarded and 5 nrl tre'Jlrqurd)]. Recrystallizationunder nitrogen liom acetone6Tgave of pentane added to the remaining mixture. The solid was coi- pale 1'ellow plateletswhich darkened instantl,vto a bronze color lected,washed with pentane.and dried to give 50 mg of dichloroLrrs- uoon exposureto air. Er,'enin a nitrogen-fillcdglove bag the color ltnphenylphosphine)platinumtll), mp 303' dec,mmp 303' dec. changeCslightly during transterto a melting poinr capillary: mp Kinetics Studies. General \lethods. Solutions of I useJ lbr rlmm)195-200'; ir(KBrl l4l0vs. l175vs.ll50mn, 1075vs,1020 kinericsstudies \\ere prepared Lrvrveighing I into a volumetric flask s.990 s. 710vs. 700vs cm-r. and adding drt' methylene chlorrde that had been distilleC and lodomethylbis(triphent'lphosphine)pl:rtinum( II) rvas prepared ac- stored over 5A Linde i\lolecular Sieves. Aliquots (0.25 ml) of rhi' cording ro the method of Chattr0" by relction of tris(triphenyl- solution were transferred to P-rrex tubes (8 mm) that had ltcen phosphrnetpletrnum(0) and methyl iodide. After recrystallization w'ashedwlth dilute hydrochlorrc acici. rinsed rvith distilleo warcr. l'rom benzene.the materialhad mp 272-275'(lir.d7mp 270-27J'l: soaked in dilute ammonia solutron.end drieC in a vacuum ovcn: rr (KBr) -i0i0 rv, 2950 rv, l-180sp, lJ.l0 sp, ll00 sb, 715 sb, 690 r's the tubes rvere degassedat 0.05 Torr and seeled. The tubes rverc r. cm- intmerscd in a 6{) + 0.1" oil ltath (cxcept as noted), removed ut The solubility of di-rr-hut1'lbis(tripheny'lphosphine)platinum(II)in intervals.and stored at liquicl nrtrogentcmperature until quenchcd. rvas rvith methylenechloride detcrmined and lvithour 0.1 II trr- Quenching w'as carried out by opening the tube at 0o, adding crr. pheny'lphosphincpresent. A mixturc of cxcesssolid platinum ().1ml ol'concentratedhydrochlortc acrd. fitting a no-air stopperrtr conrplcx and mcthy'lencchkrridc or of exccssconrplex and a solu- the tube. arrd mixing the two lercrs l;l shaking. All samplesrvcrc tron of triphcnl.lphosphincin nreth_'-lencchloride'uvas stirred at :l' qucnchedat the sametime ancl:trtrerl ltt -20'during glpc analrscs. l'ttr l0 nrrn and tilteredinto a l-ml volumetric flask.and the solvent As a control. one tubc in each sct \vitsn()t heated but was otherrvisc !r'asremoved under vacuum to constant rveight. The solubilitres treated in the sarne manner ls the thermoly'zedsamples. Anall'sr' 'i weredctcrmrned to be ll8 mg ol'complexper mrlliliter of methylene ol'this tube showed no olehn t .

lVlitesiclas. Grru:;clr, Srtlrttnskt' Di-n-bur',lt:i.srrrinht'n.rlplto.soltine)platinuntt ll t 5270 t- r--

constantfor decompositionwas determinedto be 1.9 X l0-{ sec-t medium-pressuremercury lamp. The resultingyellowish solution at 120* 2'. was analyzedby glpc usingcolumns A (butaneand butene)and B Deuterium Labeling Studies. General l\lethods. Solutions of (octane). The yield of butanewas 5.1%, of butenewas 3 f, andot deuterated platinum complexes were prepared and thermolyzed octanewascl[. following proceduresoutlined in the Kineticssection; exceptwhere Thermolysisand Photolysisof SolutionContaining cls-Di-rr-butyl- noted solutions were heated for ca. 6 half-lives. In purifying mate- bis(triphenylphosphine)platinum(lI)and Di-rerr-butylNitroxide in rial by glpc fiordeuterium analyses.care lvas taken to collect as much i\lethyleneChloride. A solutionof 70.8mg (0.085mmol) of 1 and of the peak as possible to avoid isotopic lractionation.$ Hydro- 68.3mg (0.47mmol) of di-rerr-butylnitroxide60 was dissolved in 4.0 carbons were collected.atliquid nitrogen temperature(column A) ml of methylenechlorrde containing pentane and undecaneas tn- and their isotopiccomposition determinedusing a nonrinalionizing ternalstandards. A portion of thissolution was heated to 80oand voltageof l0 eV.68 Resultsof thesestudies are givenin the text. held at that temperaturefor I hr. Anotherporrion was irradiated Preparation and Nlass Spectral .\nalysis of l-Bromobutane from for 8 hr in a Pyrex cell with 3500-Alamps in a Rayonetreactor. Di-r-buty l-2,2-rlr-bis(tripheny l phosphine) pla tin um(I I ) Recovered Fol- Analysis for butane and butene was carried out by glpc using lowing Partial Thermal Decomposition. A solution of 250 mg column A. Analy'sis for N.N-d i- terr-butyl-O-n- butylhydroxylami ne of the platinum compound in 2 mI of methylenechloride contained (DTBNO-n-butyl) and octane was carried out using column B. in an 8-mm Pyre.x tube was degassedat 0.001 Torr, sealed, and The productyields observedin theseexperiments are summarized heated at 60.0" for 20 min. The tube was opened, the volatiles in TableIV. were swept off rvith a stream of nitrogen, and the resulting solid was evacuatedto 0.05 Torr for 30 min. After 2 hr. 2 ml of chloroben- zene was added and the resulting red mixture was stirred at room TableIV. HydrocarbonProducts from Thermolysis temperature',vhile being treated with an excessof bromine which was and Photolysisof 1 in the Presenceof DTBNO swept slowly over the mixture in a stream of nitrogen. The solid product was separated by centrifugation and the l-bromobutane Products(yields. 7,Y-- was collected by glpc from the supernatantsolution (column C); DTBNO --50%. the yield of bromide rvas The mass spectrum of this sub- Butane l-Butene Octane rr-butyl stanceat I I eV rvasexamined for the isotopic compositions of the .16 -l molecularion (iVI') and oi(M - Er)": iV[*,0'\ dr,97'Z dz,37" 4, Thermo[1srs 50 -l t'l A' 0"; dr; (M - Et)', 0% r/,.83 7id,, 16Tl rl,, l'\Jo. Photoly'sis 2 13 qz A similar analvsiswas perlormed on l-bromobutane from a solu- tion originall-vcontaining 250 mg of the l-l.l-rlr and 80 mg of tri- phenllphosphinein I ml of methylenechloridc: M*, 0% &,987; d,,,2*o d,, 0'' :./,. ( Nl - Et )-. 0.6\ d t, 26",',I t. J9''u r/1,21'Z d,,. A solution of crr. 50 mg of di-rr-butllbis(triphenylphosphinet- Conversionof l-Bromobutlne to Valeronitrile. A micromagnetic platrnum(ll) and c'a.30 mg ot'di-rerr-butylnitroxide in methylene strrringbar rvassealcd into a small bulb tbsironed from S-mm tubing chloride atier standing at room tcmpcrarure5 daysshows ir absorp- together rvith a mrxture of ca. 2 nrg ol' I-lrromobutane. 50 mg ol' tions at 1670.ll00-1100. and 970 cm-t in additionto bandschar- sodium cy'anide.and 0.15 ml of dry digl-r'nre. The reactionmixture acteristicol'the trv'o starting materials. rvasheated at 65' for t2 hr rvith stirring. Thc tube rvascooled and rV.rV-Di-rerr-butyl-O-n-butvlhl'droxy'lamine.To a flame-dried opened: valcronrtrilc 1-70'T yield) rvas collccted using glpc 50-ml round-bottomed tlask equipped rvith a side arm. condenser. (column B). magneticstirnng bar. and nitrogen inlet tube were added 3.6 g (ZS Exchange of a H-'"drogensof Valeronitrile. The exchange of mmol) of di-rerr-butylnitroxyl. -.10ml of dry dimethoxyethane,and hy'drogenlbr deuterium uv'ascarried out in a solution of NaCH:CN l.l g tlarge excess)of sodium metal. The mixture was allowed to in acetonitrrleprepared by cautiously adding l0 ml of acetonitrilc reflux under nitrogen, with stirrrng.overnrght. The resultingcolor- (distilledfrom PrO;) to crr.0.2 g ot'sodium amide (iVlathesonCole- lesssolution was transferredby cannula to a ciry 5Gml round-bot- man and Bell) at 0', stirring for 30 min at room temperature.and tomed flask.equipped with a magneticstir bar and relluxcondenser. separatinginsoluble material by centril'ugatron. The supernatant containing -1.6g (25 mmol) ol' l-iociobutane. The solution was liquid had a yellowish color that disappearedupon exposure ro allorvedto stir for f hr under nitrogenand wasquenched with water. water. Only' samplesdispiaying this ."'ellorvcolor were considered the aclueousla1'er was saturatedwrth sodium chloride.the organic to containactive base. layer rvas separated, and the aqueous phase e.rtractedseveral times Valeronitrile!vas ccllected from glpc directlf into a flame-dried rvith ether. The combined ether phase rvas washed with water. l-mm Pyrextube cooledto -78'. Onc end ot'thetube was sealed. dilute hydrochloric acid. water. saturatedsalt solution, dried (Nlg- the other end rvasclosed rvith a no-uir stopper.and the valeronitrile SO,). and concentrated. Unreacted l-iodobutane was separated rvasforceC into the sealedend of the tube by centrifugation. The lrom the product by distrllatron. The resultingpale orange oil was tube was tlushedrvith dry nitrogen.and cn. 150pI of the acetonitrile passedthrough a silicagel G column (l I X I cm)eluting with cyclo- solution of NaCH:CN was added using a syringe. The tube was hexaneto give 0.95 g ( 19tr1 of n-bun'l-di-tcrr-butylhydroxylamine: sealed.completely'immersed in a 70'orl bath for l2 hr. thencooled. ir (CCl,) 3000. 2970.2930.:875. l-500.1485. 1470. 1460, 1370,1250. and opened. Valeronitrile was purified by glpc (column C) for 1205.1075, l0-i0. 1025 cm-i: nmr (CCl.)d 3.65(t.2 H), 1.15(t, l8 isotopic analysis( l5-eV nominrl ionizing voltage). After valerno- H). l.l(m.7H). nrtnle that had been preparedfrom l-bromobutane-l,l-dzO87i d!) Arrctl. Calcd for Cr:H:rNO: mol rvt. 201.209. Found: mol rvassubjected to this exchangeand analvsisprocedure. its isotopic wr. 201.208. composrrion was lbund to be 0.77; d!. d1,96.6\f, 2.7"i do. After Acknorvledgments.We wish to thank Dr. David J. valeronitrrlethat had been preparedfrom l-bromobutane obtaineci from 1-1.?-cl.rafrer parrial thermol.vsis rvithout added triphenl,l- Boschetto for assistancein obtaining nmr spectra. phosphineas describedabove rvassu['rjected to this procedure.its i\{atthey Bishop. Inc., for loans of potassiumtetra- ''i, isotopecomposition \!'asfound to be 75 d.:.197" d,,67i do. chloroplatinite.and the Dow ChemicaiCo. for a gift ot Photoll'sis of cis-Di-l-but1' lhis(triphenv I phosphine)platinum(II). 2.2-dichlorobutyronitrile.\Ve are indebted to Professor A degassed0.021 .t/ solution oi 1 in merhylenechloride containing pentane and undecane as internal standards rvas irradiated in a Klaus Biemannand C. Hieniteior hish-resolutionmass Prrex cell lor 8 hr at room temperatureusinrl a 3600-A Hanovia spectra.

(69) A. I(. Hoffman, A. !t. Fcldman, E. Gelblum, and W. G. Hodg- (68) For dctails of the collection and analysis proccdure, see J. F. son,.,/.Amer. Chenr. Soc.. 86, 639 t196.{t; A. R. Forrester,J. M. Hat', Gaasch, Ph.D. Thes,is,^\[assachusetts Insrirutc of Technology, Cam- and R. H. Thompson, "Organic Chemistrl' of Stable Free Radicals," bridgc, Ntass.,1970. Academic Press, Nerv York, \. Y., 1968.

Jtturnul ttl tlte .ltrtertcun Cltemiculsrrcicrr 9.1:I5 I July 26. 1972