摘要:

1979 939q-Allylmetal Chemistry. Part 7.l Allylic Alkylation catalysed by PlatinumComplexes. Isolation of Rigid (a-Allyl)( pentane-2,4-dionato)platinum( 11)Corn pl exesBy Hideo Kurosawa, Department of Petroleum Chemistry, Osaka University, Suita, Osaka 565, JapanReactions of b-diketo-anions with q3-allylbis(triphenyIphosphine)platinum(ii) complexes or ally1 acetates in thepresence of triphenylphosphineplatinum complexes afford high yields of allylic alkylation products. Alkylation ofthe corresponding -q3-but-2-enylplatinum(ll) complex gives a larger amount of the product of coupling at thesecondary carbon than of that at the primary carbon, while the reversed selectivity is found in the reaction of theq3-but-2-enylpalladium(ii) complex. Reactions of q3-allylmono(triphenylphosphine)platinum(i~) complexes withthallium(i) pentane-2,4-dionate give stereochemically rigid, thermally stable, (a-allyl) (pentane-2,4-dionato) -platinum(l1) complexes.ALLYLIC alkylation by means of reactions between q3-allylpalladium( 11) complexes and carbanions derived fromp-diketo-compounds has received much attention inrecent yearsJ2 but there is no report on the correspondingreaction of analogous q3-allylplatinum(11) complexes.In continuation of work on q-allylplatinum(I1) chemistry,lI have undertaken a comparative study of allylicalkylation using q3-allyl-platinum (11) and -palladium(II)complexes.The study on the platinum complexesappeared to be of particular interest in that organo-platinum intermediates involved in the reaction areexpected to be more stable than the analogous organo-palladium intermediates, and this would shed some lighton the mechanistic aspects of the reaction.The presentpaper describes the isolation and/or spectroscopicidentification of reaction intermediates in the allylicalkylation with q3-allylplatinum(~~) complexes, including(o-allyl)(pentane-2,4-dionato)platinum(11), a class of themost rigid o-allylplatinum (11) complexes.RESULTS AKD DISCUSSIONAlthough it is generally accepted that organoplatinum-(11) complexes are much more reluctant to undergooxidative cleavage of metal-carbon bonds than theanalogous organopalladium (11) complexes, I have founda very rapid quantitative reaction between q3-allyl-platinum( 11) complexes and p-diketo-anions [equation(l)].The initial product in this alkylation reactionmay well be [Pt(olefin)(PPh,),] (see later), which mightR’C(O)CHC(O)Me + [Pt (~3-011yl) (PPh3)z]CIR 3 ,COR’( 1 1COMeR’= Me or OMc ; R2, R3, R4=H or Mebe capable of undergoing oxidative-addition reactions.Moreover, since I have separately confirmed that the q3-allylplatinum(I1) complexes can be prepared easily by thereaction between [Pt(PPh,),] and allyl acetates [equation(2)], it may also be expected that the reaction betweenOzCMe[Pt(PPh,),] + R*1R = H or Meallyl acetates and the p-diketo-anions occurs in thepresence of a catalytic amount of phosphineplatinumcomplexes to give the same products as in equation (1).This was indeed found to be the case with [Pt(PPh,),],cata I yst 11 R - Me or OMc; R Z , R 3 , I?‘= H or Me!Pt(~3-allyl)(PPh,)2]C1 (allyl = CH,CH=CH,, CH2CH=CHMe, or CH,CMe=CH,), or [PtH(Cl)(PPh,),] as theeffective catalyst [equation (3)].A similar catalyticfunction of [Pd(PPh,),] was reported in the alkylationof allyl acetates2 In this reaction, as well as in therelated palladium-catalysed exchange of allyl groupsbetween esters, ethers, and a r n i n e ~ , ~ the formationof q3-allylpalladium(~~) intermediates from palladium(0)complexes and allyl carboxylates has been postulated940 J.C.S. Daltonfavour metal to olefin x donation,66 the combined effectof the electronic and steric factors should result in agreater difference between the stabilities of (1) and (2)for M = Pt than for M = Pd.The energy of thetransition state on the way to (1; M = Pt) may wellbe sufficiently lower than that to (2; M = Pt) to yield alarger amount of CH,=CHCH (Me) R’. * The difference inthe energy of the transition state is possibly less im-portant in the reaction of the palladium complex, and thealkylation in this case could be controlled by the ease ofapproach of the nucleophile to the opposite side of theq3-but-2-enyl plane with respect to the palladium atom,,affording the primary coupling product in higher yield.but never confirmed. In any case, reaction (2) as well asits palladium analogue must be, more or less, reversible,and the irreversibility in the C-C bond-formation stepmay be important in driving the palladium- andplatinum-catalysed alkylation of ally1 acetates to com-ple t ion.Of further interest in equations (1) and (3) is the factthat the alkylation of [Pt (q3-CH,CH=CHMe)C1( PPh,),] orMeCH=CHCH,O,CMe and CH,=CHCH(Me)O,CMe in thepresence of the platinum catalysts gave a larger amountof CH,=CHCH(Me)R‘ [R‘ = CH(COR)(COMe)J, a pro-duct of coupling at the secondary carbon, than MeCH=CHCH,R’ (see Table 1).This result may be contrastedTABLE 1Alkylation of q3-but-2-enylmetal complexes or but-2-enyl acetate[MeCH=CHCH,CH(COR) (COMe)]:Nucleophile Reagent Catalyst [CH,=CHCH(Me)CH(COR) (COMe) JTl[CH (COMe) , J Pt 0.59R’0,CMe Pt 0.67Pd 2.23R’0,CMe Pd 2.03Tl[CH(CO,Me) (COMe)] Pt 0.59R’0,CMe Pt 0.64Pd 8.04R’0,CMe Pd 1.50Pt = [Pt(v3:CH2CH=CHMe)C1(PPh3),], Pd = [Pd(q3-CH,CH=CHMe)C1(PPh3),], R‘ = MeCHKHCH,.An almost identicalresult was obtained with CH,=CHCH(Me)O,CMe.with the observation that the alkylation of [Pd-($-CH,CH=CHMe)C1(PPh3),J or both MeCH=CHCH,-0,CMe and CH,=CHCH(Me)O,CMe in the presence ofthe palladium catalyst gave a larger amount of theproduct of coupling at the primary carbon (Table 1).In addition, it was reported previously * that treatment of[Pd(q3-CH,CH=CHMe) (acac)] (acac = MeCOCHCOMe)with carbon monoxide in benzene affords MeCH=CHCH,CH(COMe), and CH,=CHCH(Me)CH(COMe), ina 6 : 1 ratio. However, the alkylation of PhCH=CHCH,O,CMe using both the platinum and palladiumcatalysts resulted in almost preferential formation ofPhCH=CHCH,R‘.Factors which affect the regioselectivity in the allylicalkylation are difficult to explain sati~factorily,~ but itis relevant to consider the stability of the initial products,[M(olefin)(PPh,),] (1) and (2), of which (1; M = Pt) wasactually detected by lH n.m.r.spectroscopy (see Experi-mental section). For both the platinum and palladiumcomplexes, steric repulsions may destabilise the metal-olefin interaction in (2) relative to that in (1). Withregard to electronic effects, it was proposed previouslythat the order of x backbonding from the metal to theolefin in [M(CH,=CH,)(PPh,),] is Pt > Pd.h Since lessalkyl substitution at the olefinic carbon is expected toIsolation of (a-Allyl) (pentane-2,4-dionato)platinum( 11)Complexes.-It was pointed out previously that 2 molof tertiary phosphine ligand per Pd atom are preferablefor a clean alkylation reaction to occur between [Pd-(q3-allyl)C1] and the 8-diketo-nucleophiles.In view ofthis fact, it seems particularly interesting that (a-ally1)-(pentane-2,4-dionato)platinum(11) complexes, (3), can beisolated from reaction (4) by employing a 1 : 1 ratio ofRY- RtIMe( 3 a R’= R ~ = H( 3 b ) R’= Me, R2= H( 3 ~ ) R = H , R * = M ~ 1PPh, to Pt. Complexes (3) are stable in the solid state,and in hot benzene or tetrahydrofuran solution. Addi-tion of 1 mol of PPh, to a chloroform solution of (3)In view of the greater tendency of +allylplatinum(~~)complexes to form a-ally1 species compared to the palladium(I1)analogues,’ a greater degree of bond distortion in the q3-but-2-enylplatinum(I1) than in the corresponding palladium(I1) com-plex is an attractive alternative explanation for the differentregioselectivity in the two metal systems, although we could notconfirm such a difference in bond distortion spectroscopically1979 941caused an immediate coupling to occur to give thealkylation products.However, only a small amount ofthese products could be obtained from slow decom-position of (3) in the same solution at higher tem-perature, in the absence of the phosphine, although themajor products in this case remain to be identified.Complexes of the type [M(q3-allyl)(acac)] (M = Pd orPt) having a chelated pentane-2,4-dionate ligand arealso stable in solution.s These facts suggest that therole of the two molecules of phosphine in the allylicalkylation can be attributed, in part, to their ability toinhibit the chelation of the p-diketo-anions to the metal,thereby promoting ionic dissociation of these anion^.^Nucleophilic attack of the anions at the q3-allyl plane incationic complexes has been suggested to be a readyprocess.1°coupling - .Pt -,? 11 CH(COMeI2R3P'The synthesis, lH n.1n.r.spectra, and crystal structureof a-allyl-palladium( 11) and -platinum( 11) complexeshave received much attention in the last few years,1*11912in view of the role of these species as intermediates inreactions of q3-allylmetal complexes. I believe thatcomplexes (3) represent one of the most rigid types ofa-ally1 complex of these metals in solution, as will bedescribed below.The chelate co-ordination of the acacligand appears so tight that the lH n.m.r. spectra of (3)at room temperature can be satisfactorily interpreted interms of rigid a-allyl-platinum bonding (see Table 2).An alternative form of bonding might involve a non-as the average of those (<20, 82 Hz) of [Pt(q3-CH,CH=CH,) (O,CCF,) (PPh,)] (see Experimental section).H2 H'0' 0'HS0Most aspects of the lH n.m.r. spectra of (3) in benzeneor 1,2-dichlorobenzene did not change significantly onheating except that two non-equivalent acac methylresonances coalesced into singlets [coalescence tem-peratures: 90 (3a), 85 (3b), and 65 "C (3c)l. At thesetemperatures the coupling between 3lP and the CH,protons is still observable and the chemical shifts of theallylic as well as the ligand proton resonances are almostthe same as those at room temperature, indicating thatthe predominant species a t the higher temperatures isstill the a-ally1 form without dissociation of the phos-phine.The order of the coalescence temperatures aboveis the reverse of that of the tendency for the a-allyl-platinum(I1) form to be converted into the q3-allyl form,lCH,CH=CH, 21 CH,CH=CHMe < CH,CMe=CH,. Theseresults may suggest that the coalescence of the methyl-proton resonances in the acac ligand in (3) proceeds viaq3-allyl complex as an intermediate or the transitionstate. The existence of (3) predominantly as the a-ally1form, even at high temperature, is in marked contrastto the ready dissociation of PPh, from trans-[Pt-(a-CH,CH=CHR)(C,HCl,)(PPh,),] (R = H or Me) at90 "C to form the q3-allyl comp1exes.lTABLE 2Hydrogen-1 n.1n.r.data u for [€%(a-allyl) (acac) (PPh,)] complexes (3)Ally1 acac-7 ~.--- .-A-Complex -CH,- -CH= Me Me -CH=(3a) 2.33 (dd) 5.91 (ddt) 4.7-4.2 (m) 1.55 (s) 5.28 (s)7-1.92 (s) g3) ";:.5J (H) 8.0J(H") 9.85.7 (m) 4.79 (dq) 1.41 (d) 1.52 ( s ) 5.20 (s)jgy;(3c) d i.($2(:;(3b) C 2.43 (dd)1.91 (s) J(W 6J(Pt) 20J ( H ) 6J(H') 154.56 (br) 2.14 (s) 1.47 (s) 5.20 (s)4.76 (br) 1.85 (s)c In C,H,Cl,-1,2.J ( H ) 8.0J(P) 4.0J(P) 4.0JW 94Chemical shifts (6) in p.p.in., ,I in Hz. Q In CDC1,. In C,H,.rigid q3-allyl structure, e.g. as shown below.However, EXPERIMENTALthis possibility can be readily eliminated since the Hydrogen-l n.m.r. spectra were recorded on a J~~~~~,J(Pt-CH,) values of (3) are much larger than the Electron Optics JNM-PS-100 spectrometer with Sihfe,average of J(Pt-H) for the syn (41.5 Hz) and anti as internal standard. The complexes [Pt(q3-ally1)Cl-protons (92 Hz) of [Pt(q3-CH2CH=CH,)(acac)] as well (PPh,),] l2*l3 and [Pt(q3-allyl)CI(PPh,)] l2 (ally1 = CH,CHJ.C.S. DaltonCH,, CH,CH=CHMe, or CH,CMe=CH,) were preparedaccording to the reported methods. The complex [Pd-(q3-CH2CH=CHMe)C1(PPh3),] was prepared in situ bymixing a dichloromethane solution of [{ Pd (q3-CH,CH=CHMe)Cl},] with 2 equivalents of PPh,, and this solutionwas used, without isolating the complex, for catalytic aswell as stoicheiometric alkylation reactions.The saltsTl[CH(COR)(COMe)] (R = Me or OMe) were prepared bytreating thallium(1) ethoxide with the appropriate p-diketone in ethanol.Allylic A 1kylation.-Identification of the alkylation pro-ducts was based on comparison of g.l.c., and of 1H n.m.r.spectra, with those of authentic samples prepared by thereaction of sodium salts of the p-diketo-compounds with theappropriate allyl chlorides. Total yields of the alkylationproducts always exceeded 90%. The isomer ratio,[MeCH=CHCH,CH(COMe),] : [CH,=CHCH(Me)CH (COMe) ,]was determined by lH n.m.r. spectroscopy on the basis ofthe peak areas due to -CH%H- (6 5.2-5.8), CH,=C<(4.9-5.1), as well as MeCH=C- [1.61, J(H) 6.01 and-1MeCH- [0.98 p.p.m., J(H) 6.7 Hz]. The ratio [MeCH=CHCH,CH(CO,Me) (COMe)] : [CH,=CHCH(Me)CH(CO,Me)-(COMe)] was determined similarly.The compound MeCH=CHCH,R' [R' = CH(COR)(COMe)] always contained asmall amount of the 2 isomer, but its exact amount was notdetermined.Stoicheiometric aZkylation. In a typical experiment,Tl[CH(COMe),] (91 mg, 0.30 mmol) was added to a stirredsolution of [Pt(q3-CH,CH=CHMe)Cl(PPh3)J (243 mg, 0.30mmol) in dichloromethane ( 2 cm3) under nitrogen at roomtemperature. Precipitation of TlCl occurred immediately,and the solution became reddish brown. After 30 minCCI,=CCl, (50 mg, 0.30 mmol) was added, and the solutionwas filtered. The solvents were removed in vacuo, and theresidual mixtiire was subjected to g.1.c. and lH n.m.r.analyses.The lH n.m.r. spectrum of the reaction mixturebefore adding CCl,=CCl, showed that the amount ofMeCH=CHCH,CH (COMe), l4 present was almost identicalwith that in Table 1 , but the resonances due to CH,=CHCH(Me)CH(COMe), l4 were very weak. Instead, aslightly broadened doublet [0.51 p.p.m., J(H) 6.4 Hz] andtwo singlets (1.90, 2.03 p.p.m.) were observed, all of whichdisappeared completely on adding CCl,=CCl, or PPh,, andwere replaced by the resonances due to CH,=CHCH(Me)CH-(COMe),.Similarly, the spectrum of the reaction mixture from[Pt(q3-CH,CH=CHMe)C1(PPh3),] and Tl[CH(CO,Me) (COMe)]before adding CCl,=CCl, showed, besides the resonances ofMeCH=CHCH,CH(CO,Me)(COMe) [1.62 (d), J(H) 5.9 Hz,3 H ; 2.19 (s), 3H; 2.52 (br), 2 H; 3.68 (s) p.p.m., 3 H), apair of doublets [0.50, J(H) 6.5; 0.62 p.p.m., J(H) 6.5 Hz]and two pairs of singlets (1.96, 1.99; 3.55, 3.61 p.p.m.), allof equal intensity, which again disappeared completely onadding CCl,=CCl,.In this case the two doublets werereplaced by those El.02, J(H) 6.7; 1.06 p.p.m., J(H) 6.7 Hz]of CH,=CHCH(Me)CH(CO,Me) (COMe), The sets of reson-ances which disappear on treatment with CC1,=CCl2 orPPh, are assigned to those of [ l ; M = Pt, R' = CH(COMe),or CH(C0,Me) (COMe)], although the olefinic proton reson-ances of these complexes could not be detected, possiblyowing to their broadness and superimposition with moreintense absorptions. In these experiments, the addition ofmore than a five-fold excess of PPh, t o the reaction mixturecaused precipitation of yellow crystalline [Pt(PPh,),J.No1H n.m.r. evidence for the palladium analogues (1) or ( 2 )(M = Pd) could be obtained in the analogous reactionmixture from [Pd (q3-CH,CH=CHMe)C1 (PPh,) ,I.Catalytic alkylation. In a typical experiment, to astirred dichloromethane solution (5 cm3) containing allylacetate (100 mg, 1.00 mmol) and 0.05 mmol of the catalystwas added Tl[CH(COMe),J (303 mg, 1.00 mmol) undernitrogen. The solution was stirred vigorously for 30 min.After filtration, the solvent was evaporated i n vacuo, andthe residue when examined by g.1.c. and by 1H n.m.r.spectroscopy showed almost quantitative formation ofCH,=CHCH,CH(COMe),.Reaction of Ally1 Acetate with [Pt(PPh,),].-To a dichloro-methane solution (10 cm3) of [Pt(PPh,),] (196 mg, 0.20mmol) was added allyl acetate (50 mg, 0.50 mmol) undernitrogen.The initial yellow colour of the solution paledgradually. A slight excess of Na[ClO,] was then addedand the solvent was removed i n vacuo. The resulting solidwas recrystallised from CH,Cl,-n-hexane to give 103 mg(60%) of [Pt(q3-allyl) (PPh,),][C104].15 The complex [Pt-(q3-CH,CH=CHMe) (PPh,) ,] [ClO,] l5 was obtained similarly.Preparation of (o-Allyl) (pentane-2,4-dionato) (triphenyl-phosphine)platinum(rr) .-A benzene solution (10 cm3)containing [Pt(q3-allyl)Cl(PPh,)] (160 mg, 0.30 mmol) andTl[CH(COMe),] (91 mg, 0.30 mmol) was stirred vigorouslyfor 2 h. The precipitate of TlCl was filtered off, and thevolume of the solution reduced to ca.3 cm3 in zracuo.n-Hexane (ca. 5 cm3) was added and the solution was keptin a refrigerator overnight, to give 80 mg (45%) of finecrystalline [Pt(o-CH,CH=CH,) (acac) (PPh,)] (3a), m.p. 145-146 "C (decomp.) (Found: C, 52.4; H, 4.6. Calc. forC,,H,,O,PPt: C, 52.2; H, 4.5%); i.r. spectrum in Nujol1615 [v(C=C)], 1580 and 1517 cm-l (acac). Complexes(3b), m.p. 155 "C (decomp.) (Found: C, 52.5; H, 4.7. Calc.for C,,H,,O,PPt: C, 53.0; H, 4.8%) and (3c), m.p. 118-120 OC (decomp.) (Found: C, 53.0; H, 4.8. Calc.: C, 53.0;H, 4.8%) were obtained similarly. Infrared spectrum inNujol: (3c), 1625 cm-l [v(C=C)].Preparation of ( 1-3-q-Allyl) (trifluoroacetato) (triphenyl-phosphine)pZatinum(II) .-To a dichloromethane solution ( 5cm3) of [Pt(q3-CH2CH=CH,)Cl(PPh3)] (220 mg, 0.41 mmol)was added Ag[O,CCF,] (90 mg, 0.41 mmol) in methanol( 2 cm3).The solution was stirred for 3 h at room tem-perature, filtered, the filtrate evaporated to dryness, andthe residue recrys tallised from acetone-n-hexane to give150 mg (60%) of a colourless crystalline solid, m.p. 155-160 "C (decomp.) (Found: C, 45.0; H, 3.3. Calc. forC,,H,,F,O,PPt: C, 45.2; H, 3.3%); i.r. spectrum inNujol 1680 cm-l [v(CO)]. Hydrogen-1 n.m.r. spectrum inCDCI,: 2.20 (br d), J(H) 12, J(Pt) 82 Hz; 2.94 (vbr), widtha t half-height ca. 15 Hz; 3.39 (dd), J(H) 13.5, J(P) 9 ,J(Pt) 30 Hz; and 4.6-5.2 (m) p.p.m.[8/773 Received, 26th Apvil, 19781{ [Pt(?"allYl)C1(PPh,)~], [PtH(C1) (PPh3)2], Or [Pt(PPh3),]}REFERENCESChem., 1977, 16, 1737.1 Part 6, S.Numata, R. Okawara, and H. Kurosawa, Inovg.2 For a review, see B. M. Trost, Tetrahedron, 1977, 33, 2616.3 G . Hata, K. Takahashi, and A. Miyake, Chem. Comm., 1970,1392; K. E. Atkins, W. E. Walker, and R. M. Manyik, Tetva-hedron Letters, 1970, 3821.4 Y. Takahashi, K. Tsukiyama, S. Sakai, and Y. Ishii,Tetrahedron Letters, 1970, 1913.6 B. M. Trost and P. E. Strege, J. Amer. Chem. Soc., 1975, 97,2534; B. M. Trost and T. R. Verhoeven, J. Org. Chem., 1976, 41,321519796 (a) C. A. Tolman, W. C. Seidel, and D. H. Gerlach, J . Amer.Chem. Soc., 1972, 94, 2669; (b) W. Partenheimer, ibid., 1976, 98,2779.B. M. Trost and T. J. Fullerton, J . Amer. Chem. SOC., 1973,95, 292.8 B. L. Shaw and G. Shaw, J. Chem. SOC. ( A ) , 1969,602; B. E.Mann, B. L. Shaw, and G. Shaw, ibid., 1971, 3536.S . Okeya, Y. Onuki, Y. Nakamura, and S. Kawaguchi,Chem. Letters, 1977, 1305.lo B. Akermark, M. Almemark, J. Almlof, J . E. Backvall, B.Ross, and A. Stsgard, J . Amer. Chem. Soc., 1977, 99, 4617.l1 G. Carturan, A. Scrivanti, U. Belluco, and F. Morandini,Inorg. Chim. Acta, 1978, 2'7, 37; J. C. Huffman, M. P. Laurent,and J. K. Kochi, Inorg. Chem., 1977, 18, 2639; N. M. Boag, M.Green, J. L. Spencer, and F. G. A. Stone, J . Organometallic Chem.,1977, 127, C61; J. A. Kaduk and J. A. Ibers, ibid., 139, 199;H. C. Clark and C. R. Jablonski, Inorg. Chem., 1975, 14, 1518.H. Kurosawa and G. Yoshida, J . Organometallic Chem., 1976,120, 297.l3 H. C. Volger and K. Vrieze, J . Organometallic Chem., 1967, 9,527.l4 K. Takahashi, A. Miyake, and G. Hata, Bull. Chem. SOC.Japan, 1972, 4!5, 1183.H. Kurosawa, Inorg. Chem., 1975, 14, 2148

ISSN:1477-9226    

DOI:10.1039/DT9790000939

出版商:RSC    

年代:1979

数据来源: RSC