Stereochemistry and Mechanism of Chloropalladation of Acetylenes

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Organometallics 1995,14, 4242-4246

4242

Stereochemistry and Mechanism of Chloropalladation of Acetylenes Jan-E. Backvall,* Ylva I. M. Nilsson, and Roberto G. P. Gatti Department of Organic Chemistry, University of Uppsala, Box 531, S-75121 Uppsala, Sweden Received April 11, 1995@ The stereochemistry of chloropalladation of acetylenes has been studied. Chloropalladation adducts from terminal acetylenes were trapped in situ by reaction with either allyl chloride or 1,3-cyclohexadiene. It was found that the stereochemistry of the chloropalladation reaction was deDendent on the chloride ion concentration. At a low chloride concentration cis chlorophladation predominates, whereas at a high chloride concentration there is a preference for trans chloropalladation. Scheme 1

Vinylpalladium complexes are versatile reactive intermediates in a number of catalytic rea~tions.l-~ In these reactions, such as vinyl couplings,l carbonylations,2 and Heck reaction^,^ the vinylpalladium species is generated by oxidative addition of a vinyl halide or triflate to palladium(0). Another way of generating a vinylpalladium complex is by the addition of a nucleophile (coordinated or free) t o an (acety1ene)palladium(11) complex. Although the latter approach has had limited applications in catalytic reaction^,^ recently the use of hydr~palladation~ and chl~ropalladation~~~ of an acetylene has been used to generate vinylpalladium in palladium(I1)-catalyzed reactions. In one of the latter reactions, developed in our l a b ~ r a t o r y dienyne ,~ 1 afforded product 2 in a palladium(I1)-catalyzed oxidation reaction (eq 1). The reaction was suggested to proceed E

1

E

u

0

chloride attack, i.e., trans chlorpalladation, we were intrigued by the observation that acetylenes seem to undergo both cis and trans chl~ropalladation.~~~J~J~ We therefore decided to study the stereochemistry and mechanism of chloropalladation of acetylenes.

cat. Pd(ll) LiCl benzoquinone 2 65% (>98% 1 ,Csyn-add)

via a chloropalladation of the acetylene followed by insertion of one of the double bonds of the conjugated diene in the vinyl-palladium bond (Scheme 1). The n-allyl complex formed is subsequently attacked by a chloride anion to give product 2. In the reaction given in eq 1the product is a mixture of double bond isomers indicating that the chloropalladation is nonstereospecific. Since chloropalladation of olefins,8 diene^,^ and viny1cyclopropaneslOis known to take place by external @Abstractpublished in Advance ACS Abstracts, July 15, 1995. (1)(a) Negishi, E. Acc. Chem. Res. 1982,15, 340. (b) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986,25,508. (c) Miyaura, N.; Maeda, K.; Suginome, H.; Suzuki, A. J. Org. Chem. 1982,47,2117. (2)Schoenberg, A.; Heck, R. F. J . Org. Chem. 1974,39,3327. (b) Heck, (3)(a)Cabri, W.; Candiani, I. Acc. Chem. Res. 1995,28,2. R. F. Org. React. 1982,27,345. (4)(a) Kaneda, K.; Uchiyama, T.; Fujiwara, Y.; Imanaka, T.; Teranishi, S. J. Org. Chem. 1979,44,55. (b) Lambert, C.; Utimoto IC; Nozaki, H. Tetrahedron Lett. 1984,25,5323.(c) Kosugi, M.; Sakaya, T.; Ogawa, S.; Migita, T. Bull. Chem. Soc. Jpn. 1993,66, 3058. (d) Larock, R. C.; Riefling, B. Tetrahedron Lett. 1976,4661. (5) Trost, B. M. Acc. Chem. Res. 1990,23,34. (6)(a) Ma, S; Lu, X. J. Org. Chem. 1991,56,5120.(b) Ma, S.;Lu, X. J. Org. Chem. 1993,58, 1245. (7)Backvall, J. E.; Nilsson, Y. I. M; Andersson, P. G.; Gatti, R. G. P.; Wu, J. Tetrahedron Lett. 1994,35,5713.

Results and Discussion Chloropalladation of Alkynes. In the work by Kaneda4*only cis chloropalladation was observed with substituted acetylenes. This is in contrast to the work by us7 and others,6where the results indicate competing trans and cis chloropalladation with substituted acetylenes. In fact, in some cases trans chloropalladation predominated over the cis chloropalladation. In the present study the chloropalladation of a few substituted acetylenes have been studied under different reaction conditions. Two different methods to trap the vinylpalladium species from chloropalladation was used. The first method, which has previously been used (8) (a) Wipke, W. T.; Goeke, G. L. J. Am. Chem. SOC.1974,96,4244. (b) Wiger, G.; Albelo, G.; Rettig, M. F. J . Chem. SOC.,Dalton Trans. 1974. 2242. --I

(9) Backvall, J. E. Unpublished results. (10)(a) Backvall, J. E.; Bjorkman, E. E. J . Chem. Soc., Chem. Commun. 1982,693 (b) Backvall, J. E.; Wilhelm, D.; Nordberg, R. E.; Norin, T. Organometallics 1985,4,1296. (11)(a)Mann, B. E.; Bailey, P. M.; Maitlis, P. M. J.A m . Chem. SOC. 1975.97,1275.(b) Yukawa, T. T.; Tsutsumi, S. Inorg. Chem. 1968, 7, 1458. (12)Maitlis, P.M.; Espinet, P.; Rusell, M. J. H. In Comprehensive Organometallic Chemistly;Wilkinson, G., Stone, F. G. A,, Abel, E. W.,

Eds.; Pergamon Press: London, 1982; Vol. 6, p 455.

0276-7333/95/2314-4242$09.00/0 0 1995 American Chemical Society

Chloropalladation of Acetylenes

Organometallics, Vol. 14, No. 9, 1995 4243

Table 2. Chloropalladation of Substituted Alkynes: Trapping with l-Chloro-2-propenea

Scheme 2 1

Z:Ee entry substrateb [C1-Itotc(M) Droductd (cis-add:trans add) 1 3a 0.08 4a 98:2 2 2.0 31:69 3 3b 0.08 4b 1oo:o 4 2.0 1oo:o 5 3c 0.08 4c 98:2 6 2.0 71:29 7 5 0.08 6 54:46 8 2.0 62:38 ~~

R-

c

Table 1. Chloropalladationof 1-Hexyne: Trapping with l-Chloro-2-propenea entry 1 2

3 4 5 6 7

[ C l - l b ~(Mj ,~ 0.08 0.2 0.53 1.0 1.0 2.0 2.0

[l-hexynel (M) 0.03 0.2 0.2

0.2 0.03 0.2 0.03

Z-4a93-4ac (cis-add:trans addp 98:2 93:7 80:20 64:36 58:42 49:51 31:69

The reactions were performed in acetone-acetic acid (4:l) with PdClz and added LiCl in the presence of excess 1-chloro-2-propene. was 0.3:l:lO. The ratio of [PdCl~l:[l-hexynel:[l-chloro-2-propenel * The [C1-Itot.refers to the total amount of C1- including that on PdC12. The yield of 4a (based on 1-hexyne) was in the range of 70-80%. The stereochemistry was determined by IH NMR. Refers to the chloropalladation across the triple bond.

in several instances,4acJ3 involves trapping by allyl chloride (eq 2). The second method utilizes 1,3-cyclo-

hexadiene as the trapping molecule. The latter method was employed because of the uncertainty that the first method, i.e. palladium-catalyzed reaction between an acetylene and allyl halide, may involve an alternative pathway via a (n-a1lyl)palladium intermediate.14 A. Trapping with Allyl Chloride. The acetylene (3) was allowed to react with palladium chloride at low temperature in acetone-acetic acid (4:l) in the presence of allyl chloride which led to the formation of (E)-and (274 (Scheme 2). The concentrations of the C1- (as LiC1) and the substrate were varied. Reaction of 1-hexyne (3a) with PdC12-LiC1 at a low chloride concentration afforded mainly isomer (2)-4a ((2)-4a:(E)-4a= 98:2) consistent with a pathway via 98% cis chloropalladation (Table 1,entry 1). An increased chloride concentration increased the relative amount of trans chloropalladation as indicated by the increase of (E)-4a. At a total chloride concentration, [C1-]tot.,15of 2 M there was a slight preference for (E)-4a. The stereochemical outcome was slightly dependent on the substrate concen(13)Liebeskind, L. S.;Bombrun, A. J . Org. Chem. 1994,59, 1149. (14)Formation of a n-allyl complex from the allyl chloride followed by insertion of the acetylene and subsequent reductive elimination was

considered as an alternative pathway. In fact in one s t u d 9 this pathway is likely since Pd(0) intermediates were present. In another the n-allyl pathway was ruled out on the basis of the regiochemical outcome of the reaction.

a The reactions were performed in acetone-acetic acid (4:l) with PdClz and added LiCl in the presence of excess 1-chloro-2-propene. The ratio of [PdCl~l:[substratel:[l-chloro-2-propenel was 0.3:l: 10. The concentration of the substrate was 0.03 M in all cases. The [C1-]tOt.refers to the total amount of C1- including that on PdC12. The yields were in the range of 60-80% except in entry 4 where the yield was -20%. e The stereochemistry was determined by lH NMR.

tration. Thus, a t 2 M [Cl-ltot.the ratio (2)-4a:(E)-4aat substrate concentration 0.2 and 0.03 M was 4951 and 31:69, respectively (entries 6 and 7). A similar effect by the substrate concentration was observed at 1 M [C1-ltot,(entries 4 and 5 ) . Some other acetylenes were also studied in order to determine the effect of the substituent on the stereochemical outcome. The sterically hindered tert-butylacetylene (3b) (Table 2, entries 3 and 4) was dramatically different from 1-hexyne (entries 1and 2) and gave only (2)-4bfrom cis chloropalladation (100% cis addition) under all chloride concentrations studied. Phenylacetylene (3c)showed a chloride concentration dependence but weaker than that of 1-hexyne (3a), and at [C1-ltot. concentrations of 0.03 and 2 M 3c gave (2)-4c and (E1-4~in ratios of 98:2 and 71:29, respectively (entries 5 and 6). A disubstituted acetylene 5 was also studied (eq 3). Acetylene 5 afforded a mixture of (2)-and (E)-6in ratios of 54:46 and 62:38 at low and high chloride concentrations, respectively (Table 2, entries 7 and 8).

B. Trapping with 1,3-Cyclohexadiene. In an alternative trapping method 1,3-cyclohexadiene was used as trapping molecule. It is known that vinylpalladium species add to conjugated dienes to give (n-allyl)palladium intermediates in catalytic Heck type reactions.16-18 Thus, 1,4-functionalizations of conjugated dienes via vinylpalladation followed by nucleophilic (15) The [C1-ltOt.refers to the total amount of C1- including those on palladium(II), and therefore the concentration of chloride ions in solution will be lower than the [C1-Itot. given. At high chloride concentration and low palladium(I1) salt concentrations, however, the chloride ion concentration in solution is approximatelyequal to [Cl-]t,t.. (16)Backvall, J. E. In Advances in Metal-Organic Chemistry; Liebeskind,L. S.,Ed.; JAI Press: Greenwich,CT, 1989;Vol. 1,pp 135175. (17) (a) Heck, R. F. Acc. Chem. Res. 1979,12, 146.(b) Patel, B. A.; Kao, L. C.; Cortese, N. A.; Minkievics,J. V.; Heck, R. F. J . Org. Chem. 1979,44,918. ( c ) Connor J. M.; Stallman, B. J.;Clark, W. G.; Shu, A. Y. L.; Spada R. E.; Stevenson, T. M.; Dieck, H. A. J . Org. Chem. 1983, 48, 807. (d) Shi, L.; Narula, C. K.; Mak, K. T.; Kao, L.; Xu, Y.; Heck, R. F. J . Org. Chem. 1983,48, 3894. (18) Larock, R.C.; Harrison, L. W.; Hsu, M. H. J . Org. Chem. 1984, 49. 3664.

4244 Organometallics, Vol. 14, No. 9, 1995

Backuall et al.

Table 4. Chloropalladation of Substituted Alkynes: Trapping with l,3-Cyclohexadienea

Scheme 3

R-

E (4-7

PdCU2

PdCU2

(E)-7

Table 3. Chloropalladation of 1-Hexyne: Trapping with 1,3-CyclohexadieneU entry 1

2 3 4 5 6

[C1-Itot.b(M) 0.06 0.12 0.81 3.0 1.5 2.0

[l-hexynel (M) 0.03 0.03 0.2 0.2 0.03 0.03

Z-7a3-7ac (cis-add:trans addy 98:2 86:14 72:28 50:50 41:59 33:67

a The reactions were performed in acetone-acetic acid (4:l)with PdClz and added LiCl (no added LiCl in entry 1)in the presence of excess cyclohexadiene. The ratio of [PdC1~l:[l-hexynel:[cyclohexadiene] was 1:l:lO. The [Cl-l~t.refers to the total amount of C1- including that on PdC12. The yield of 7a (based on 1-hexyne) was in the range of 70-80%. The stereochemistry was determined by lH NMR. Refers to the chloropalladation across the triple bond.

attack on the n-allyl intermediate have been reported.17J8 In our trapping of the vinylpalladium intermediate the (n-ally1)palladium complexes were isolated and characterized (Scheme 3). The double bond stereochemistry of (2)-and (E)-7was established by lH NMR NOE measurements. Reaction of 3a with equimolar amounts of PdClz in the presence of 10 equiv of 1,3-cyclohexadieneproduced (n-al1yl)palladiumcomplexes (2)-7aand (E)-7ain a ratio of 98:2 indicating that mainly cis chloropalladation takes place (Table 3, entry 1). An increase of the chloride concentration increased the relative amount of (E)-7a. At 0.12, 1.5, and 2 M [C1-lbt, and substrate was 86: concentrations of 0.03 M, the ratio (2)-7a:(E)-7a 14,4159, and 33:67, respectively, indicating a predominance of trans chloropalladation at higher chloride concentrations (entries 2 , 5 , and 6). The results are in accordance with those obtained from the trapping with allyl chloride. Also for the 1,3-cyclohexadienetrapping the stereochemical outcome was dependent on the concentration of the substrate (Table 3). Acetylenes 3b,c were also studied with 1,3-cyclohexadiene as the trapping molecule. The results obtained (Table 4) are in accordance with the results in Table 2, where allyl chloride was employed as a trapping molecule. C. Attempts To Isolate the Intermediate Chloropalladation Adduct. The reaction between 3a and LizPdC4 was followed by lH NMR at low temperature (-60 to 0 "C) in acetoned6-acetic acidd4 (4:l). The acetylene was slowly consumed, but it was not possible to observe any significant amount of the expected vinylpalladium complex from chloropalladation. It appears that the chloropalladation adducts cis and trans-A are in equilibrium with the n-acetylene complex (Scheme 4).

Z:Ee entry substrateb [C1-lbtc (M) productd (cis-add:trans add) 1 3a 0.06 7a 98:2 2 2.0 33:67 3 3b 0.06 7b 1oo:o 4 2.0 1oo:o 5 3c 0.06 7c 1oo:o 6 2.0 45:55 The reactions were performed in acetone-acetic acid (4:l)with PdClz and added LiCl (no added LiCl in entries 1,3, and 5) in the presence of excess cyclohexadiene. The ratio of [PdClz]:[substrate]: [cyclohexadiene] was 1:l:lO. The concentration of the substrate was 0.03 M in all cases. The [Cl-lht, refers to the total amount of C1- including that on PdC12. The yields were in the range of 50-70%. e The stereochemistry was determined by 'H NMR.

Scheme 4 I .

I

I

n

I

J

cis-A

Pd-CI

L

J

fransA

CI

Since the trapping of cis- and trans-A may occur with slightly different rates (kzc differs from k d , the results from the trapping experiments do not necessarily reflect the relative amounts between cis- and trans-A in an equilibrium situation. However, with a large excess and high concentration of the trapping molecule, the trapping reaction may become faster than the retro-chloropalladation, e.g. kz,[cis-AI[trapping molecule] =- k-&isAI. This would explain the difference between the experiments carried out at different concentrations (e.g. entry 4 versus entry 5 and entry 6 versus entry 7 in Table 1;cf. also entries 4 and 5, Table 3). Since a ratio of 1 : l O between the acetylene and the trapping molecule was maintained in all cases, the concentration of trapping molecule was 0.3 and 2 M at the two different concentrations. There is also an example in the literature where the chloropalladation adduct from an acetylene has been isolated (eq 4).llb In this reaction the trans-chloropal-

M

N

T

Me

3

+

LbPdCI4

-2LiCI

Me

*

e d-ci I'

(4)

2

8 9

ladation adduct 9 obtained from 8 is stabilized by intramolecular coordination. Also in this case it is possible that a kinetic cis chloropalladation occurs, but due to the nitrogen coordination the thermodynamic product will be 9, which also can be isolated. We have prepared 9 and confirmed its structure.1g The dimer 9, which occurs as a 1:1.5 mixture of its cisoid and transoid dimeric forms, was transformed to the monomer 10. Irradiation of the vinylic proton gave an NOE (19)In the original study the stereochemistry of 9 was not explicitly proven but proposed on the analogy of the corresponding oxy adducts previously reported by Cope: Cope, A. C.; Klieman, J. M.; Friedrich, E. C. J. J. Am. Chem. SOC.1965, 87, 3272.

Organometallics, Vol. 14, No. 9, 1995 4245

Chloropalladation of Acetylenes

9

pyridine

10

on the a protons of the pyridine ring of 8.3% but no detectable NOE on any of the methyl groups. Furthermore, there was no NOE between the pyridine protons and any of the methyl groups. Further confirmation of the structure of complex 10 was given by the 3JC,H coupling constant of 6.7 Hz between the vinylic proton and the allylic carbon. The magnitude of the coupling constant requires that the proton and carbon are trans t o one another.20

Experimental Section General Methods. NMR spectra were recorded for CDC13 solutions with a Varian 400 spectrometer, 'H a t 400 MHz and 13Ca t 100.5 MHz, using chloroform-dl (7.26 ppm, 'H, 77.0 ppm, I3C) as internal standard. Commercial acetone (99.5%),acetic acid, lithium chloride (99%),propiolic acid (98%),1-hexyne (3a) (98%),phenylacetylene (3c)(98%),3,3-dimethyl-l-butyne (3b) (98%), and 1,3-cyclohexadiene (97%) were purchased from Aldrich and used without further purification. Allyl chloride was purchased from BDH laboratory reagents and was used without further purification. PdCl2 was obtained from Johnson Matthey. Pd(PhCN)2C12was prepared according to a literature procedure.21 Compound 8 was prepared according t o ref 22. Merck silica gel 60 (240-400 mesh) was used for flash chromatography.

General Procedure for the Chloropalladation of Acetylenes: Trapping with Allyl Chloride. To PdCl2 (0.032 g, 0.18 mmol) and the appropriate amount of LiCl(0-39.6 mmol) in acetone-acetic acid (4:l) (2.5 or 20 mL) at -78 "C was added the acetylene (0.61 mmol) followed by 1-chloro-2-propene (0.466 g, 6.09 mmol). The reaction was stirred at -78 "C for 30 min and then allowed to warm up over night. Water (10 mL) was added, and the mixture was extracted with ether (3 x 15 mL). The combined organic layers were washed with 2 M NaOH (until the water layer was neutralized) followed by brine (10 mL). All aqueous washings were back-extracted with ether. The combined organic layers were dried (MgSOd), and the solvent was removed on a rotary evaporator. The crude product was purified by flash chromatography (pentane).

General Procedure for the Chloropalladation of Acetylenes: Trapping with 1,3-Cyclohexadiene. To PdCl2 (0.108 g, 0.61 mmol) and the appropriate amount of LiCl(038.8 mmol) in acetone-acetic acid (4:l) (2.5 mL or 20 mL) a t -78 "C was added the acetylene (0.61 mmol) followed by cyclohexadiene (0.488 g, 6.09 mmol). The reaction was stirred a t -78 "C for 30 min and then allowed to warm up over night. Water (10 mL) was added, and the mixture was extracted with CHzC12 (3 x 15 mL). The combined organic layers were washed with water (until the water layer was neutralized) followed by brine (10 mL). All aqueous washings were backextracted with CHzC12. The combined organic layers were dried (MgSOd), and the solvent was removed on a rotary evaporator. The crude product was purified by flash chromatography (pentane:CHCls, 1:U. (Z)-S-Chloro-l,4-nonadiene ((Z)-4a):4a'H NMR 6 5.855.70 (m, 1 H, HC=CHz), 5.47 (dt, J = 6.7, 1.0 Hz, 1 H, ClC=CH), 5.08-4.98 (m, 2 H, HC=CH2), 2.92 (tm, J = 6.7 Hz, 2 H, C=CHCHzCH=C), 2.35-2.30 (m, 1H, C=CCH2CHd, (20) Vogeli, U.;von Philipsborn, W. Org. Mugn. Reson. 1975,7,617. (21) Kharasch, M.S.;Seyler, R. C.; Mayo, F. R. J.Am. Chem. SOC. 1938,60, 882. (22)Hennon, G.F.;Nelson, K. W. J.Am. Chem. SOC.1957,79,2142.

1.57-1.49 (m, 2 H, CHZCH~CH~), 1.37-1.27 (m, 2 H, CH2CH31, NMR 6 135.9, 135.4,122.3, 0.906 (t,J = 7.2 Hz, 3 H, CH,); 115.2,39.2,32.8,29.5,21.7,13.8. NOE difference experiments gave a significant NOE between the vinyl proton on the trisubstituted olefin and the CH2 in the butyl group. (E)-Ei-Chloro-l,I-nonadiene ((E)-4a):'H NMR 6 5.855.70 (m, 1H, HC=CH2), 5.61 (t,J = 7.7 Hz, 1H, ClC=CH), 5.08-4.98 (m, 2 H, HC==CH2),2.78 (m, 1H, C=CHCHzCH=C), 2.35-2.30 (m, 1H, C=CCHzCH2), 1.57-1.49 (m, 2 H, CH2CH2CH2), 1.37-1.27 (m, 2 H, CHZCH~), 0.914 (t, J = 7.2 Hz, 3 H, CH3). NOE difference experiments gave a significant NOE between the bis-allylic CH2 and the CH2 in the butyl group. (Z)-S-Chloro-6,6-dimethyl-1,4-heptadiene ((2)-4b): 'H NMR 6 5.86-5.75 (m, 1 H, HC=CH2), 5.52 (t, J = 8.0 Hz, 1 H, ClC=CH), 5.05 (dm, J = 17 Hz, 1 H, HC=CHH (trans)), 4.99 (dm, J = 10 Hz, 1 H, HC-CHH (cis)), 2.92 (tm, J = 6.2 Hz, 2 H, C=CHCH&H=CH2), 1.18 ( s , 3 H, CH3); I3C NMR 6 145.9, 135.6, 119.2, 115.1, 38.6, 33.0, 28.9. NOE difference experiments gave a significant NOE between the vinyl proton on the trisubstituted olefin and the CH3 protons in the tertbutyl group. (Z)-l-Chloro-l-phenyl-l,4pentadiene ((zl-4~):~" 'H NMR 6 7.65-7.55 (m, 2 H, -Ph), 7.45-7.3 (m, 3 H, -Ph), 6.17 (t, J = 7.6 Hz, 1 H, ClC=CH), 6.0-5.85 (m, 1 H, HC=CHz), 5.18 (dq, J = 12, 1.7 Hz, 1H, HC=CHH (trans)),5.10 (dq, J = 10, 1.7 Hz, 1 H, HC=CHH (cis)), 3.18 (m, 2 H, CHd; I3C NMR 6 138.1,134.8, i33.7,i28.4,12a.2,i26.4,i24.9,ii5.8,33.8. NOE difference experiments gave a significant NOE between the vinyl proton on the trisubstituted olefin and the ortho-protons in the phenyl group. (E)-l-Chloro-l-phenyl-l,4-pentadiene ((E)-4c):'H NMR 6 resolved peaks 6.03 (t,J = 7.8 Hz, 1 H, ClC=CH), 2.86 (ddt, J = 7.8, 6.0, 1.6 Hz, 2 H, CH2). (Z)-1-Chloro-2-methyl-l-phenyl-l,4-pentadiene ((22-6):

4a1HNMR67.36-7.20(m,5H,Ph),5.73(ddt,J=17.0,10.0, 6.2 Hz, 1H, HC=CH2), 5.05 (dm, J = 17.0 Hz, 1H, HC=CHH (trans)), 5.01 (dm, J = 10.0 Hz, 1H, HC=CHH (cis)),3.17 (dm, J = 6.2 Hz, 2 H, CH2), 2.27 (t,J = 0.6 Hz, 3 H, CH3); I3C NMR 6 141.5, 134.3, 134.1, 128.5, 128.0, 127.2, 126.9, 116.0, 39.4, 22.9. NOE difference experiments gave a significant NOE between the methyl protons and the ortho-protons in the phenyl group. Anal. Calcd for C12H13C1: C, 74.80, H, 6.80. Found: C, 74.54, H, 6.86. (E)-l-Chloro-2-methyl-l-phenyl-l,4-pentadiene ((E)-6): 'H NMR 6 7.38-7.28 (m, 5 H, Ph), 5.76 (ddt, J = 16.9, 10.0, 6.2 Hz, 1 H, HC=CHz), 5.08 (dq, J = 10.0, 1.5 Hz, 1 H, HC=CHH (cis)), 5.03 (dq, J = 16.9, 1.6 Hz, 1 H, HC=CHH (trans)),2.79 (dt, J = 6.2, 1.5 Hz, 2 H, CHd, 1.98 (s, 3 H, CH3); 13c NMR 6 139.1, 135.3, 132.2, 128.9, 128.2, 128.0, 127.4, 116.5,39.6, 19.7. NOE difference experiments gave a significant NOE between the bis-allylic CH2 and the ortho-protons in the phenyl group. [4-{(Z)-2-Chloro-l-hexen-l-yl}-~3-cyclohexen-3-yllpalladium Chloro Dimer ((Z)-7a):'H NMR 6 5.81 (d, J = 8.5 Hz, 1 H, C=CH), 5.47 (dd, J = 7, 6.5 Hz, 1 H, CH-central r3allyl), 5.11-5.06 (m, 1 H, CH2CH-q3-allyl),4.81 (dm, J = 6.5 Hz, 1 H, CHCH-q3-allyl), 2.38 (m, 1 H, CHCH=), 2.34 (t, J = 7.5 Hz, 2 H, C=CC1CH2), 2.31-2.23 (m, 1H, CH&HzCHCH=), 2.05-1.97 (m, 1 H, CH&H2CHCH=), 1.69-1.60 (m, 1 H, CH2CH2CHCH=), 1.54 (quint, J = 7.5 Hz, 2 H, CH&H&H2), 1.26-1.16 (m, 1H, CH21.32 (sext, J = 7.5 Hz, 2 H, CHZCH~), CHZCHCH=), 0.91 (t,J = 7.5 Hz, 3 H, CH3); I3C NMR 6 135.3, i27.4,io0.9,ai.6,80.5,39.0,37.i, 29.7,29.4,26.4,21.7,13.8. NOE difference experiments gave a significant NOE between the vinyl proton and the CHZin the butyl group. [4-{(E)-2-Chloro-l-hexen-l-yl}-~3-cyclohexen-3-yllpalladium Chloro Dimer ((E)-7a):'H NMR 6 resolved peaks 5.97 (dm, J = 10 Hz, 1 H, C=CH), 4.74 (dm, J = 6.2 Hz, 1H, CHCH-q3-allyl). [4-{(Z)-2-Chloro-3,3-dimethyl-l-buten-l-yl~-~s-cyclohexen-3-yllpalladiumChloro Dimer ((Z)-7b): 'H NMR 6 5.92 (d, J = 8.4 Hz, 1 H, C=CH), 5.47 (t, J = 6.6 Hz, 1 H,

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Organometallics, Vol. 14, No. 9, 1995

CH-central v3-allyl),5.13-5.08 (m, 1H, CH2CH-v3-allyl),4.83 (dm, J = 6.6 Hz, 1 H, CHCH-q3-allyl), 2.44-2.36 (m, 1 H, CHCH-), 2.30-2.16 (m, 1H, CH&HzCHCH=), 2.06-1.96 (m, lH, CHzCHzCHCH=), 1.71-1.58 (m, 1 H, CHzCH2CHCH=), 1.30-1.20 (m, 1 H, CHzCHzCHCH;=),1.20 ( s , 9 H, 3 x CH3); 13CNMR6 145.2,124.6, 101.0,81.7,80.5,38.7,37.2,29.3,22.8, 26.4. NOE difference experiments gave a significant NOE between the vinyl proton and the CH3 protons in the tert-butyl group. Anal. Calcd for C24H3&14Pd2: C, 42.44; H, 5.34. Found: C, 42.17; H, 5.16.

[4-{(2)-2-Chloro-2-phenyl-ethenl-yl}-q3-cyclohexen-3yllpalladium Chloro Dimer ((2)-7c):lH NMR 6 7.70-7.64 (m, 2 H, Ph), 7.37-7.28 (m, 3 H, Ph), 6.59 (d, J = 8.9 Hz, 1H, C=CH), 5.51 (app t, J = 6.8 Hz, 1 H, CH-central q3-allyl),

Backvall et al.

Complex 9. This complex was prepared from 822according t o Yukawa and Tsutsumi.llb It was found to consist of two dimeric forms, one transoid dimer and one cisoid dimer. The ratio between the diasteromeric dimers was 1:1.4 (it is not possible to assign which is the major isomer). 'H NMR 6 5.87, 5.82 (two s, l H , vinylic proton, 42% integral on 5.871, 2.74, 2.73 (two s, 6H, NMez), 1.42(s, 6H, CMe2). 13C NMR: 6 (signals in each bracket correspond to one carbon) 1132.41, [131.7, 130.31, [76.3, 76.21 L46.9, 46.61, 123.71. Complex 10. To 18.2 mg of 4 (0.032 mmol) in CDC13 (0.5 mL) in an NMR tube was added 5.0 mg of pyridine (0.063 mmol). The tube was shaken, and NMR spectra were recorded. Only one isomer was observed: 'H NMR d 8.74-8.71 (m, 2H, a-pyridine protons), 7.78-7.73 (m, H, y-pyridine proton), 7.33-7.29 (m, 2H, ,&pyridine protons), 5.79 (s, lH, vinyl), 2.87 (s, 6H, Me& 1.43 (s, 6H, Mez); 13C NMR 6 153.3, 137.7, 137.4, 133.9, 125.0, 76.3, 46.7, 23.9. Irradiation of the vinylic proton gave a n NOE on the a protons of the pyridine , ~ constant ring of 8.3%. Furthermore, there was a 3 J ~coupling of 6.7 Hz between the vinylic proton and the allylic carbon.

5.18-5.11 (m, 1H, CH2CH-v3-allyl),4.97-4.90 (m, 1H, CHCHv3-allyl), 2.71-2.58 (m, 1 H, CHCH=), 2.41-2.25 (m, 1 H, CH&HzCHCH=), 2.11-1.98 (m, 1H, CH&H&HCH-), 1.801.66 (m, 1 H, CHZCH~CHCH=),1.38-1.23 (m, 1H, CHzCHzCHCH=); 13C NMR 6 137.5, 132.9, 129.3, 128.5, 128.2, 126.5, 101.1,80.6,37.9,29.0,26.3. NOE difference experiments gave a significant NOE between the vinyl proton and the orthoprotons in the phenyl group. Anal. Calcd for C Z E H ~ E C ~ ~ P ~ ~ : Acknowledgment. We are grateful to the Swedish C, 46.76; H, 3.92. Found: C, 46.87; H, 3.94. [4-{(E)-2-Chloro-2-phenyl-ethenl-yl}-q3-cyclohexen-3- Natural Science Research Council for financial support and to Johnson Matthey for a loan of PdC12. We thank yllpalladium Chloro Dimer ((E)-7c):lH NMR 6 resolved Dr. Adolf Gogoll for help concerning NMR problems. peaks 6.34 (d, J = 9.2 Hz, 1H, C=CH), 5.44 (app t, J = 6.7 Hz, CH-central v3-allyl),5.09-5.00 (m, 1H, CHzCH-v3-allyl), OM950261V 4.81-4.75 (m, 1 H, CHCH-v3-allyl).