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866 Organometallics 1984, 3, 866-87089397-83-1; Ag[(CH&CCSC(CH3)3], 89397-84-2;Ag[c6Hsc=CCBHJ, 89397-85-3; Au[CH3CECH], 89397-86-4; Au[CH3C=C-CHa], 89397-87-5; C U [ C ~ H ~ ] ~ ,5881-79-0; Cu[CH3C=CHI2,89397-88-6; Cu[(CH3)3CC=CH]2,89397-89-7; Cu[CF3C=CHI2,89397-90-0; CU [CH ~CE CCH ~]~ ,9397-91-1; Cu[ (CH3)3CC=C-C(CH& 2, 89397-92-2; Cu[C& CsCC&] 2, 89397-93-3;C u C H d H , 89397-62-6; CuCH=8CH3, 89397-63-7; CuCH=CCF3, 89397-64-8; CuCH=CC6Hs, 84074-16-8; AgCH=CH,89397-66-0; tr an ~- Ag cH =c C( CH ~) ~,9397-67-1;.AgCH=CCF,,89397-68-2; AgCH=CC6&, 84074-17-9; AuCH=CH, 84074-14-6;73373-74-7; AgCH=CCH3, 89397-65-9; ckAgCH=CC(CH3)3,

AuCHsCCH3, 89397-69-3; cis-AuCH=CC(CH,)B, 89397-70-6;tr~ns-AuCH=(k(CH~)~,9397-71-7;c~s-AuCH=CC~H~,4074-19-1;truns-AuCH=CC6H5,8407+18-0; uC[C(CHJ3]=&(CHJ3,89397-72-8; cis-CuC(C&,)=Cc6H5, 89397-73-9; truns-c uc-89397-75:l; ~~U~S-A~C[C(CH~)~]=CC(CH~)~,9397-76-2; AgC-(C6H5)=CC&,, 89397-77-3; AuC(CsH5)=CC6H5, 9397-7&4;cu,7440-50-8; Au, 7440-57-5; Ag, 7440-22-4; CH3C=CH, 74-99-7;(C&)=CC6H,, 89397-74-0; CZS-A~C[C(CH~)~]=CC(CH~

(CHJ3CC=CH, 917-92-0; CF~CSCH, 661-54-1; CH ~C EC CH ~,503-17-3;(CHJ3CC~CC(CH3)3,17530-24-4;F~CSCCF,, 692-50-2; C&C=CC&, 501-65-5; C2H2, 74-86-2.

Palladium(I 1)-Catalyzed Copolymerization of Carbon MonoxidewSth Ethylene. Direct Evidence for a Single Mode of ChainGrowth'Ta-Wang Lai and Ayusman Sen"

Chandlee Laboratory, Department of Chemistry, The Pennsylvania Sbte University,University Park, Pennsylvania 16802Received December 12, 1983

The series of cationic Pd(I1) compounds [Pd(PPh3),(CH3CN),,](BF,)2(n= 1-3), which may be syn-thesized in situ or separately, were found to catalyze the copolymerizationof CO and CzH4 at 25 "C andat a combined pressure of as low as 300 psi, in noncoordinating solvents suchas CHC13 and CH2C12. Higherreaction temperatures were required in coordinating solvents, in the presence of excess PPh,, or when morebasic tertiary phosphines were used instead of PPh3. The ethylene-carbon monoxide copolymer (E-COcopolymer) was a high melting solid having a regular structure with alternatingcarbon monoxide and ethyleneunits. The mechanism of the copolymerization is thought to involve a single mode of stepwise chain growthwith alternate insertions of carbon monoxide and ethylene into a preformed Pd-alkyl bond. The intermediacyof Pd(I1)-alkyl and -acyl species was supported by the observed catalytic activity of Pd(PPh,),(Me)(solv)+and Pd(PPh3)z(COMe)(solv)+. he use of alcoholsas solvents for the copolymerization reaction resultedin the synthesis of polyketo esters of the type RO(-COCH2CH2-),H. Schultz-Flory plots of the oligomericpolyketo esters formed resulted in straight lines, supporting a stepwise chain growth mechanism. Therate of termination was found to decrease with increasing steric size and decreasing nucleophilicity of thealcohol used. The v c p ~or the E-CO copolymer was abnormally low, and there was a monotonic decreasein v w ith increasing n for the solid oligomeric polyketo esters. This was tentatively ascribed to thepresence of intra- and intermolecular dipolar bonding between carbonyl groups.The formation of polyketones through the co-polymerization of CO with olefins is a reaction of signif-icant practical importance. Because of the relative re-activity of the carbonyl group, these polyketones are ex-pected to constitute a new class of photodegradable2 and,perhaps, biodegradable polymers. In addition, because ofthe ease with which the carbonyl group can be chemicallymodified, such polyketones should be excellent startingmaterials for other, new types of functional polymer^.^Prior to our initial communication,' three basic methods

for the copolymerization of CO with C2H4 were describedin the literature4+? nd their reaction conditions and the(1) Tnmition Metal Catalyzed Copolymerizationof Carbon Monoxidewi t h Olefins. 2. For part 1,see: Sen,A.; Lai, T.-W.J.Am . Chem. SOC.1982,104,3520.(2) (a) Heskins,M.; Guillet, J. E. Macromolecules 1970, 3, 224. (b)Hartley, G. H.; Guillet,J.E. Ibid. 1968,1,413. (c) Hartley, G. H.; Guillet,J. E. Ibid. 1968, 1, 165.(3 ) For chemical modifications of the E40 opolymer, see ref 4b and5a.(4 ) (a) Coffman, D. D.; Pinkney, P. S.; Wall, F. T.; Wood, W. H.;Young, H. S.J. Am. Chem. SOC.1952, 74, 3391. (b) Brubaker, M. M.;Coffman,D. D.; Hoehn, H. H. Ibid. 1952, 74,1509. (c) Brubaker,M. M.U.S. atent 2495286, 1950.(5) (a) Morishima, Y.;Takizawa, T.; Murahashi,S. Eur. Polym. J.1973, 9, 669. (b)Chatani, Y.;Takiiawa, T.; Murahashi,S.;Sakata, Y.;Nishimura,Y. J.Polym. Sci. 1961, 55, 811.

0276-733318412303-0866$01.50/0

Table Ifree radical 7-radiation palladiuminitiated4 induced' catalyzed6

reaction conditionstota l pressure, psi 200-15 000 2100-2800 800-1900temp, "C 120-165 25-90 95-135product propertiesCO/C,H, 0.8-0.1 - 1 b 1mp, "C

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Pd-Catalyzed Copolymerization of CO with CHzCH2 Organometallics, Vol. 3, No. 6, 1984 86 7Table I1

wt (mg) of additive/Pd( 11) total pressure, w t (mg) of[Pd(CH,C N)4](BF4),a additive molar ratio psi tem p, "C E-CO copo lym erC50 none 0 1000 25 050 PPh, 1 1000 25 75050 PPh, 2 1000 25 90050 PPh, 3 1000 25 60050 PPh, 4 1000 25 050 PPh, 4 400 60 840d50 PPh, 6 1000 25 050 PMePh, 2 1000 25 050 PMePh, 2 1000 60 9005 0 P-n-Bu, 2 1000 25 050 PCY 3 2 1000 25 050 P(OPh),50 NPh, 2 1000 2 5 0

2 1000 25 6702 1000 25 5400 AsPh,10 ml of CHCl, was used as solvent. b Pco/Pc,H4= 1, Reactions were run for 24 h except where noted , Reactionrun for 18 h .

novel and potentially useful reaction. In this paper, wereport that a series of cationic Pd(I1) complexes catalyzedthe copolymerization of CO and C2H4 under unusuallymild conditions (25 "C and total pressure of as ow as 30 0psi). In addition, we present direct evidence that thisreaction proceeded by a single mode of stepwise chaingrowth and we indicate a novel method for the control ofmolecular weight distribution in the ECCO copolymer. Ourstudies have also led to the first catalytic synthesis ofpolyketo esters of the type RO(-COCH2CHz-),H (R =alkyl; n > 2').

Results and DiscussionA. Catalyst Systems. The cationic Pd(I1) compound[Pd(CH3CN),](BF,),,8 1,was rapidly reduced to Pd metalby CO. However, the series of compounds [Pd(PPh3),-(CH3CN),,](BF4), ( n = 1-3) , containing the stabilizingligand PPh3, were found to catalyze the copolymerizationof CO and CzH4 at 25 "C and at a combined pressure ofas low as 300 psi (Pco/Pc,H = l ) , in noncoordinatingsolvents such as CHC13 and C!H2C12. At 60 OC, the mini-mum required combined pressure was 200 psi. Thisseriesof cationic Pd(I1) compounds were formed in situ by theaddition of appropriate equivalents of PPh3 to 1. Alter-natively, the compounds [Pd(PPh3),(CH3CN),]BF4)2,2,and [Pd(PPh3)3(CH3CN)](BF4)z,, were synthesized sep-arately and used as catalysts. The effect of the addedstabilizing ligand on the catalytic activity of 1 is shown inTable 11. Two trends are clearly evident. While theaddition of a stabilizing ligand wa s necessary for catalyticactivity, the addition of highly basic tertiary phosphinessuppressed this activity. It is possible that in the presenceof basic ligands, CO was bound too strongly to the Pd(I1)center , thus effectively poisoning the catalyst. Further-more, the addition of an excess of the stabilizing ligand

also suppressed catalytic activity presumably due to theblockage of all available coordination sites (see section C).B. Characterization of the E-CO Copolymer. TheECCO copolymer samples obtained were high melting (mp>200 OC) white solids. The elemental analysis of a co-polymer sample indicated a CO/CzH4 ratio of 1. Thestructure of the copolymers couldbe discerned from theirsolid-state 13CNMR spectra (Figure 1). There were tworesonances, at 38.3 and 211.8 ppm, respectively, with anapproximate intensity ratio of 2:l. The resonance at 211.8ppm was ascribed to the carbonyl carbons and was within(7) For a previous catalytic synthesis of n = 2 compound, see: Tsuji,(8) Schra", R. F.; Wayland, B. B. Chem. Commun. 1968,898.J.; Morikawa, M.; Kiji, J. Tetrahedron Let t . 1968, 1437.

+ROTOR( O E L R I N )

25 0 200 150 100 50 0 PPMFigure 1. 13C NMR pectrum (37.7 MHz) of solid EX0 co-polymer. The rotor (Delrin) consisted of -CH20- units.the range expected for a -CH2COCH2- unit.g The 38.3ppm absorbance was due to the a-methylene carbons. Theabsence of any resonance at -2 4 ppm (observed in caseof random E-CO copolymerslO) ndicated the absence of8-methylene carbons, leading to the conclusion that ourEX0 copolymer had a regular structure with alternatingcarbon monoxide and ethylene units.C. Mechanism of the Copolymerization Reaction.A rational mechanism for the formation of the E-CO co-polymer would involve the alternate insertions of CO andCzH4 into a preformed Pd-alkyl bond (Scheme I). Twopossible factors may favor the insertion of CO into a Pd-alkyl bond over the corresponding insertion of CzH4.Because of the greater binding ability of CO, the localconcentration of CO would be expected to be significantlyhigher than C2Hk In addition, there appears to be agreater inherent tendency for CO to insert into transitionmetal-alkyl bonds when compared to the correspondinginsertion of olefins.'l By contrast, while the insertion ofolefins into metal-acyl bonds isknown,12 he correspondinginsertion of CO has never been directly 0b~erved.l~ hus,

(9) Jackman, L. M.; Kelly, D. P. J. Chem. SOC. 1970,102.(10) Wu, T .-K.; Ovenall, D. W.; Hoehn, H. H. n "Applications ofPolymer Spectroecopy";Brauer,E. G., Ed.;Academic Press: New York,1978, p 19.(11) (a) Collman, J. P.; Hegedue, L. S. "Principles and Applicationsof Organotransition Metal Ch emistry"; University Science Books,MillValley , CA 1980; p 269. (b) For a specific comparison, see: Ivin, K. J.;Rooney, J. J.; Stewart, C. D.; Green, M. L. H.; ahtab, R. J . Chem. SOC.,Chem. Commun. 1978,604.(12) For specific examplea, we: Tsuji, J. "Organic Synthesis by M eansof Transition M etal Comp lexes"; Springer-Verlag: New York, 1976.

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868 Organometallics, Vol. 3, N o. 6, 1984Scheme I

Lat,and Sen0 MeOHI

-0

ICo0

m AI C 0

R O H RO

R OH R O b PFigure 2. Plots of log (W,/P) va.P or oligomeric polyketo eaters([Pd(PPh3)2(CH3CN)$+] 0.023M; initial pressure,PCO= Pc2&= 50 0 psi; reaction temperature, 70 "C). olvent: MeOH ( 0 ) ;EtOH (0).Table IIIa

00 0 ROH 0ROw 0

fthe proposed mechanism forces the alternate addition ofcarbon monoxide and ethylene units to the growing poly-mer chain. The slow step in the chain propogation isalmost certainly the insertion of C2H4 into the Pd-acylbond. This isbecause if the corresponding insertion of COinto he Pd-alkyl bond was slow, one should have observedproducts arising from a competing 8-hydrogen abstractionstep. In the absence of CO, the compounds [Pd(PPh3),-(CH3CN)4-n](BF4)2n= 1-3) were found to catalyze therapid dimerization of C2H4 (eq 1). The formation of C4H8clearly indicated that &hydrogen abstraction from Pd-alkyl species is fast compared to further insertions of C2H,.

' 4H8 (1)The intermediacy of cationic Pd(I1)-alkyl and -acylspecies in the copolymerization reaction was supportedbythe observation that the species generated by the reactionof AgBF, with Pd(PPh&(Me)(I), 4, and Pd(PPh3I2-(COMe)(Cl), 5 (presumably Pd(PPh3)2(Me)(solv)+ ndPd(PPh3)2(COMe)(solv)+,espe~tively'~)ere also activecatalysts for the copolymerization reaction under condi-tions identical with those used for [Pd(PPh3),-(CH3CN),,I(BF4), (n = 1-3). Most significantly, the

corresponding neutral compounds 4 and 5 as well as Pd-

Pd(PPhs).(CHsCN)~*+/(n=1-3)C2H4 25 OC, CHCls

(13) There are some reports in the literature on transition metal ca t-alyzed'double carbonylation"renctions,where the producta may poaeiblyarise from the insertion of CO into metal-acyl bonds, we: (a) Ozawa, F.;Soyama, H.; Yamamoto, T.;Yamamoto, A. Tetrahedron Lett . 1982,23,3383. (b) Kobayashi, T.; Tanaka, M. J. Organomet. Chem. 1982,233,C64. (c) Francahmi, F.; Foa, M. J . Electroanal. Chem. 1982,232,59. (d)Alper, H.; des Abbayes, H. J.Organomet. Chem. 1977,134, C11. How-ever, in a recent study, we have dem onstrated that theaereactiom do not,in fact, proceed through such a mechanistic step and, furthermore, themodel compound PdCO COPh (Cl)(PPh& spontaneouely decarbonylatedat 25 OC to PdCOPh(Cl)(PPh& and that the rata of decarbnylation WBBindependent of CO pressure of up to 700 pei. For detaih,we: Chen,J.-T.;Sen, A. J.Am. Chem. Soc. 1984,106, 1506.(14) Similar cationic P t(I1) species are known,me: (a) Clark, H. C.;Ruddick, J.D. Inorg. Chem. 1970,9,1226. (b) Kubota, M.; Rothrock, R.K. ; Geibel, J. J . Chem. SOC. , a lton Tram . 1973, 1267.

CY

so h from slope from interceptMeOH 0.33 0.31MeOD 0.38 0 .35EtOH 0.46 0.44

a [Pd(PPh,),(CH,CN),a+]= 0 . 0 2 3 M ; initial pressure,Pco = PCZH, 500 psi; reaction temp, 70 "C.(PPh3)2C12 nd Pd(PPh3)4were competely inactive underthese conditions, perhaps indicating of the crucial need foreasily accessible coordination sites. This was also sup-ported by the observation that although catalyst prepa-rations with PPh3/Pd2+ atios of 1-3 were active, thosewith ratios 4 and 6 were found to be inactive except atelevated temperatures (Table 11). Similarly, no co-polymerization was observed at 25 "C in coordinatingsolvents such as CH3CN and THF. Copolymerizationoccurred in THF, however, at 60 "C. A further reason forthe markedly enhanced catalytic activity of the cationicPd(I1) complexes when compared to their correspondingneutral analogues may be their reduced ability to stronglybind CO and C2H4, thus facilitating their transfer in theinsertion reactions.The origin of the initial Pd-alkyl species in aproticsolvents is uncertain but is almost certainly related to theobserved catalytic dimerization of C2H4 in the absence ofCO. The high molecular weight and th e very poor solu-bility of the E G O opolymer did not allow us to identifythe end groups.D. Copolymerization in Alcoholic Solvents. Directevidence for a mechanism involving a single mode of chaingrowth as depicted in Scheme I came from our studies onthe copolymerization reaction in alcoholic solvents. Themechanism, asoutlined in Scheme I, involves the forma-t ion of Pd-acyl species as ntermediates at every alternates t ep in the propagation sequence. Since the formation ofesters through the reactions of transition-metal acyls withalcohols is well pre~edent ed,'~t should be possible tointercept the propagation sequence if the copolymerizationwas carried out in the presence of alcohols (Le., eq 2).16

ROHPd(-COCH2CH2-),H RO(-COCH2CH2-),H (2 )(15) For specific examples, see ref 12.(16) Reppe had observed the formation of polyketo acids by the K2-[Ni(CN),] catalyzed cooligomerization of CO and CzH4 n water, see:Reppe, W. U.S. atent 2 577 208,1951. However, no mechanistic detailsare available for this system, and the limited data presented in the patentdid not allow us to construct Schultz-Flory p lots for the reaction prod-ucts.

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Pd- Catalyzed Copolymerizationof CO with CHzCHzTable IV

-compd VC=O (KBr) , cm-]MeO( -COCH,CH,- ) , H 1735MeO(-COCH,CH,-),H 1735,1715MeO(-COCH,CH,-) ,H 1735,1710MeO( COCH,CH,-),H 1735,1705MeO(-COCH,CH,-) ,H 1735,1700(-COCH,CH,-), 1695 (br )

Indeed, the formation of esters of the type RO(-COCH2CH2-),H was observed when the solvent for thecopolymerization reaction was RO H (R= Me, Et). Thepolyketo esters corresponding to n = 1-5 were separatedand quantified," and the results are presented in the formof Schultz-Flory plots18 in Figure 2. W , was the weightfraction (minus RO and H; R = Me, Et) of that oligomerwhose degree of polymerization was P . A straight line forsuch a plot indicated a single mode of stepwise chaingrowth. A quantity, a, qual to (rate of propagation)/(rateof propagation+ rate of termination) may be derived fromboth the slope and the point of intercept, and its valuesin three different solvents are given in Table III.l9 Thechange in a rom 0 .32 to 0.45 on going from MeOH toEtOH indicated that the rate of termination was 1.74 timesslower in EtOH than in MeOH (1 .21 , assuming that therates of termination were first order in alcohol and cor-recting for the concentration of alcohol). The above cal-culation was based on the assumption of identical propo-gation rates in MeOH and EtOH. This was checked in thefollowing way. Pd(PPh,),(COMe)(Cl) was refluxed witha mixture containing equal volumes of MeOH and EtOH.At the end of the reaction, the ratio of MeOCOCH, andEtOCOCH, was measured and found to be 1 .56 (1 .08 ,assuming hat the rates of formation of the esters were firstorder in alcohol and correcting for the concentration ofalcohol). The proximity of this value to that derivedpreviously indicates that the rate of propogation was vir-tually independent of the alcohol used. We ascribe theslower rate of termination in EtOH compared to MeOH,to the greater steric size of EtOH. In support of thisargument, only high molecular weight (n > 5) polyketoesters were obtained with t-BuOH as solvent. Further-more, only methyl esters were formed in 1 :l mixture (v/v)of MeOH and t-BuOH, indicating a substantially higherrate of termination with MeOH compared to that witht-BuOH. The termination rate was also dependent on therelative nucleophilicity of the alcohol employed, since onlythe higher polyketo esters (n > 5 ) were obtained whenCF,CH20H was used as solvent. The ratio of the rates oftermination in MeOH and MeOD wa s 1 .22 , indicating asmall but significant deuterium isotope effect.In principal, it should be possible to lowera (i.e., lowerthe rate of propogation compared to the rate of termina-tion) by lowering the Pco and PC2H,. Indeed,EtOCOCH,CH, was the only product observed, when thereaction was conducted in EtOH with an initial combinedpressure of 100 psi instead of 1000 psi ( P c o / P c , H ,= 1 ).It is clear that the rate of termination relative to the rateof propagation in the copolymerization of CO and CzH4is critically dependent on the nature of the alcohol and itsconcentration. This observation provides us with theunique opportunity t o control the molecular weight dis-

(17) We were unable to separate the higher hom ologs quantitatively.However, these were characterized by their 'H NMR and IR spectra.(18) Henrici-Olive, G .;Olive, S. Angew. Chem., Int. E d. Engl. 1976,15 , 136.(19) a s a function of Pco and Pc2= Therefore, ita values in differentsolvents are for comp arisons only.

Organometallics, Vol. 3, N o. 6, 1984 86 9tribution in the E-CO copolymer by a judicioius choice ofsolvent systems with an alcoholas one of the components.We are testing this possibility.E. IR Spectra of the E-CO Copolymer. Two re-markable features of the high molecular weight E-COcopolymer that was formed in chlorinated solvents wereits insolubility in common organic solvents and the ab-normally low pC4 ( - 1 6 9 5 cm-' (KBr)) of its carbonylgroups. We tentatively ascribe these phenomena to thepresence of the type of intra- and intermolecular dipolarbonding between carbonyl groups shown in I. In support0II

6IIJ\i\I

of this argument, we have observed a monotonic decreasein P~ with increasingn for the solid oligomeric polyketoesters MeO(-COCH,CH,-),H (Table IV). Such a dipolarinteraction is less likely in solution, and, indeed, while thecarbonyl groups in MeO(-COCH2CH2-)5H exhibited aP- = 1700 cm-' in the solid state, the Correspondingvaluein CHCIB olution was 1710 cm-l (broad).

Experimental SectionAnalytical Instrumentation. IR spectra were recorded ona Perkin-Elmer Model 580 spectrophotometer. 'H NMR spectrawere recorded on either a Varian EM360 spectrometer or BrukerWM360 and WP200 FT-NMR spectrometers. 31PNM R spectrawere recorded on a JEOL PS-100 FT-NMR spectrometer. Sol-id-state 3CNMR pectra were recorded by ProfessorJ.P. Facklerand Professor W. Ritchey at the Materials Research Laboratoryof Case Western Reserve University. Gas chromatography wasperformed on a Varian 3700 gas chromatograph equipment witha flame ionization detector.General Procedure. Reagent grade solvents were used.CHC13, CH2C12, nd CH3CN were dried by stirring over P2OS.THF was dried by stirring over Na/benzophenone. All solventswere deoxygenated either by vacuum distillation or by purgingwith N2 prior to their use. CO and C2H4 (C.P. grade) were usedas received. Pd(PPh3)2C12,20d(PPh3)4,21d(PPh3)n(Me)(I),224, and Pd(PPh3)2(COMe)(C1),22, were prepared by literatureprocedures.Preparation of [Pd(CH3CN)4](BF4)2,8. A 1.0-g sample ofPd sponge and 2.2 g of NOBF4 were stirred in 50 mL of CH3CNunder vacuum. NO generated in the course of the reaction wasremoved periodically. After being stirred for 12 h, the mixturewas filtered t o yield a yellow filtrate from which a pale yellowcompound was obtained by the additional of anhydrous ether.The compound was washed with anhydrous ether and dried undervacuum: 4.1 g, 98%; H NMR (CD3N02) 2.65 (9); IR (Nujol)DC=N 2335 cm-', BBF,- 1100-1000, 760 cm-'. Anal. Calcd forN, 12.3.Preparation of [Pd(PPh3)2(CH3CN)2](BF,)2,. A 0.25-gsampleof 1and 0.295g of Ph3P were stirred in 30mL of CH2C12for 1h. Following concentrationof the yellow solution undervacuum, a yellow solid was obtained by adding anhydrous ether.The compoundw as washedwith anhydrous ether and dried undervacuum (0.40 g, 80%): 'H N M R (CD3N02) 7.4-7.2 (30H, m ),1.85 (6 H, 8 ) ; ('HI NMR (CDC13, -50 O C ) 32.1 ppm (8 ) ; IR(Nujol)D * ~ 2335 cm-', PBF,- 1100-1000 cm-'.Preparation of [Pd(PPh3)3(CH3CN)](BF4)2,. A 0.20-gsample of 1 and 1.2 g of PPh3 were stirred in 30 mL of CH&

PdC8HiZNdB2F8: C, 21.7; H, 2.7; N, 12.6. Found: C, 21.8;H, 2.9;

(22) Fitton, P.;Johnson,M. P.; McK

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870 Organometallics, Vol. 3, No. 6 , 1984for 30min. A greenish yellow solution was obtained,and followingprecipitation by the addition of anhydrous ether, an air-stablegreenish yellow solid was isolated. The solid was washed withanhydrous ether and dried under vacuum (0.48 g, 97%): 31P 'H)NMR (CDCl,, -40 "C) 34.5 (1P, t, Jpp 11.7 Hz), 27.6 ppm (2P, d, Jpp 11.7 Hz); IR (Nujol) I-N 2335 cm-', Igp; 1100-1OOOcm-'.Copolymerization of CO and CzH4. In a typical reaction,50 mg of 1 and 59 mg of PP h3 (2 equiv relative to Pd) werecodissoved in 10mLof CHC1, and the solution placed in a 125-mLParr bomb under N2 atmosphere. The bomb was then pressurizedwith 500 psi of CO and further pressurized with 500 psi of CzH4,bringing the totalpressure to lo00 psi. The contents of the bombwere stirred magnetically at 25 "C for 24 h. At the end of thisperiod, the total pressure had dropped to 640 psi. After de-pressurization, 0.91 g of the solid E-CO copolymer was obtainedas a precipitate. The catalyst impurities present in the E-COcopolymer were removed by Soxhlet extraction with CHZClz,yielding a white polymer, mp 260 "C. Anal. Calcd for(COCHzCHz),: C, 64.3; H, 7.1. Found: C, 64.0; H, 7.1.The above procedure was used in other reactions where thetemperature, time, pressure, solvent, and the added ligand and/orthe Pd compound were varied.Preparation of RO(-COCHzCHz-),H. The experimentalprocedure was similar to that used for the synthesis of the highmolecular weight E-CO copolymer. In a typical reaction, 0.25g of 1 and 0.295 g of PPh3 (2 equiv relative to Pd) were codissolvedin 25mLof MeOH and the solution placed in a 125-mL Parr bombunder N2 atmosphere. The bomb was then pressurized up withCO (500 psi) and CzHl (500 psi), and the contents were stirredat 70 "C for 14 h. At the end of this period, he combined pressurehad dropped to 525 psi (a t 25 "C). The contents were filteredto remove the higher molecular weight (n> 6), methanol-insoluble,polyketo eaters (0.20 g, these were characterized separately). Thefiltrate yielded 2.10 g of the methanol-soluble polyketo estersMeO(-COCHzCH-),H (n= 1-6). These were separated eitheron a silica gel column or by gas chromatography using a 10%SP-2100 column. For samples separated by column chromatog-raphy, quantitative analysis was performed by using 'H NMRspectroscopy. For samples separated by gas chromatography,quantitative analysis was done by comparison with standardsamples. MeO(-COCHzCHz-),H: selected 'H NMR and IRspectral data. n = 1: 'H NMR (CDC13)S 3.60 (3 H, s, CH30),CH3CHzCOO); IR (KBr) I C ~ H ,735 cm-'. n = 2: 'H NMR(CDC13) 6 3.67 (3 H, s, CH308, 2.74 (2 H, t, J = 6.6 Hz,2.27 (2 H, q, = 7.2 Hz, CH,CHzCOO), 1.10 (3 H, t , J = 7.2 Hz,

CH30COCHZCHz), 2.59 (2 H, t , S 6.6 Hz, CH3OCOCHzCHz),

Lai and Sen2.49 (2 H, q, J = 7.2 Hz,OCHZCH,), 1.08 (3 H, t, J = 7.2 Hz,COCHzCH3); R (KBr) I C ~ H , 735 cm-', S C H ~ C ~ H ~715 cm-'.n = 3: 'H NMR (CDC1,) 6 3.67 (3 H, s, CH,O), 2.79 (2 H, t, JCH30COCHzCHz), .73 (4 H, m, COCHzCHzCO), .48 (2 H, q,(CDC13)6 3.67 (3 H, s,CHsO), 2.73 (