Stable Arylpalladium Iodides and Reactive Arylpalladium

Phillip J. Milner , Thomas J. Maimone , Mingjuan Su , Jiahao Chen , Peter ... The Asymmetric Intramolecular Heck Reaction in Natural Product Total Syn...
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Organometallics 1995,14, 207-213

207

Stable Arylpalladium Iodides and Reactive Arylpalladium Trifluoromethanesulfonates in the Intramolecular Heck Reaction John M. Brown*$+and Jesus J. Perez-Torrente Dyson Perrins Laboratory, South Parks Road, Oxford OX1 3QY, United Kingdom

Nathaniel W. Alcock and Howard J. Clase Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom Received July 28, 1994@ The reactions of l-iodo-2-(3-butenyl)benzene and of two side-chain ether analogs with [1,l'bis~diphenylphosphino)ferrocenel(q2-cyclooctatetraene)palladium gave the expected (+aryl)($-iodo)palldium adducts, the 2-oxa-3-butenyl complex being characterized by X-ray crystallography. The alkene does not interact directly with palladium. Restricted rotation about the aryl-palladium bond was observed on the NMR time scale in all cases, since the methylene groupb) of the side chain were diastereotopic. The complexes were stable, but on treatment with silver trifluoromethanesulfonate in acetone at low temperature an unstable species was identified by lH and 31PNMR in two of the three cases. Spectral observations were consistent with the formation and subsequent rearrangement of an intermediate along the Dathwav of an intramolecular Heck cvclisation with structure o-&H40C(CH3)(Pd[dppflOTfi. 1. Introduction

Among palladium-catalyzed C -C bond-forming reactions, the Heck synthesis enjoys considerable current popularity because of its versatility and tolerance of functiona1ity.l Recent developments include intramolecular examples leading to useful synthetic intermediates or targets,2 the coupling of Heck reactions in tandem with other catalytic proce~ses,~ and both interand intramolecular asymmetric s y n t h e s i ~ .Synthetic ~~~ application in this field has tended to run ahead of mechanistic under~tanding.~ The intention of the present work was to make an initial contribution to understanding the catalytic cycle by characterizing likely intermediates using heteronuclear NMR techniques; such approaches have proved successful in their application to Pd-catalyzed cross-coupline and other areas of homogeneous catalysis. Although the characterization of intermediates has not been completed at this stage, a general restricted rotation phenomenon has been delineated, underlining the tendency for arylpalladium complexes t o prefer an orthogonal relationship between the coordination plane and the aromatic ring. Further, an unstable intermediate derived from the initial alkene Reprint requests by E-mail: [email protected]. Abstract published in Advance ACS Abstracts, November 1, 1994. (1)Heck, R. F. Org. React. 1982,27,345. (2)Kondo, R;Sodeoka, M.; Mori, M.; Shibasaki, M. Synthesis 1993, 920. Ashimori, A,; Overman, L. E. J. Org. Chem. 1992,57, 45714572. (3) Burns, B.; Grigg, R.; Santhakumar, V.; Sridharan, V.; Stevenson, P.; Worakun, T. Tetrahedron 1992,48,7297. (4)Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T.; Nishioka, E.; Yanagi, K.; Moriguchi, K. Organometallics 1993,12,4188-4196. (5)For studies of acyl migration to coordinated alkenes: Daves, G. D., Jr.; Hallberg, A. Chem. Rev. 1989,89,1433-1445. Cf.: Ozawa, F.; Hayashi, T.; Koide, H.; Yamamoto, A. J. Chem. SOC.,Chem. Commun. 1991, 1469-1470. Dekker, G. P. C. M.; Elsevier, C. J.; Vrieze, K.; Van Leeuwen, P. W. N. M.; Roobeek, C. F. J. Organomet. Chem. 1992,430,357-372. (6)Brown, J . M.;Cooley, N. A. Organometallics 1990,9,353-359.

Scheme 1

' Y

SOpPh

d2

DMF, RT

S02Ph

Pd(OAC)2 ___)

P(otol),

MeCN. 60'C

MeCONMe, 71% e a

/-as base

66%e.e

J

@

insertion product by a /?-eliminationand Pd-H readdition process has been identified. 2. Results and Discussion

Synthesis of Complexes. At the outset, the intention of the present work was to define the structure of intermediates in the Heck synthesis and the pathways available for their interconversion. In order to simplify the problem, an intramolecular reaction was selected. There have been many examples of the synthesis of

0276-733319512314-0207$09.00/0 0 1995 American Chemical Society

+40-

Brown et al.

208 Organometallics, Vol. 14, No. 1, 1995

Chart 1

bI o -

1

2

3

CH3

4

5-ring heterocycles by the formal addition of an arylpalladium species to the double bond of an unsaturated ortho side chain.' When the alkene is three bonds removed from the aromatic ring, exocyclic ring closure occurs exclusively to give an indene or heterocyclic analog. Examples are shown in Scheme 1 which illustrates this point. It is significant to note that the initial product of reaction has an exocyclic double bond (as would be expected for formal Pd-Ar addition to the alkene) and that this is the sole product in the presence of silver carbonate as base, despite the fact that this is thermodynamically much less stable than the indole with an endocyclic double bond. The potential complexity of the reaction is indicated by the third example of Scheme 1, for which the preferred hand of product in an intramolecular Heck reaction depends on whether the base involved is Ag3PO4 or 1,2,2,6,6-pentamethylpiperidine. The range of precedents recorded made this an suitable starting point, and accordingly the three aryl iodide precursors 1,*and 39were synthesized. In previously reported studies of the mechanism of cross-coupling,6palladium complexes of 1,l'-biddipheny1phosphino)ferrocene have been successfully utilized. The putative first step in a catalytic Heck reaction is addition of the electrophile, normally an unsaturated iodide or trifluoromethanesulfonate, to a low-valent palladium species. Analogy with cross-coupling suggests that this is in the Pd(0) state. Zerovalent palladium complexes with a labile ligand and a cischelating diphosphine are difficult to isolate;1° hence, the +cyclooctatetraene complex 4 was prepared in solution in thf by reduction of the PzPdC12 precursor with dilithiocyclooctatetraene. The reaction of this alkene complex with alkenyl bromides gives first the direct alkene/alkene displacement product and subsequently the oxidative addition product derived from it; with alkenyl or aryl iodides only this $:+iodoalkyl complex is 0bserved.l' After preparation of complex 4 in situ as a 0.02 M solution in thf, the iodide 1 was added directly at -78 "C and warmed to ambient temperature, whereupon the (7)See, for example: Abramovitch, R. A.; Barton, D. H. R.; Finet, J.-P. Tetrahedron 1988,44,3039.Sakamoto, T.;Kondo, Y.; Uchiyama, M.; Yamanaka, H. J. Chem. Soc., Perkin Trans. 1 1993,1941. (8) Beckwith, A. L. J.; Gara, W. B. J. Chem. SOC.,Perkin Trans. 2 1975,795. (9)Negishi, E.;Nguyen, T.; OConnor, B.; Evans, J. M.; Silveira, A. Heterocycles 1989,28,55. (10)But see: Krause, J.; Bonrath, W.; Porschke, K. R. Organometallics 1992,11,1158.Hodgson, M.;Parker, D.; Taylor, R. J.; Ferguson, G. Organometallics 1988,7,1761. (11)Brown, J. M.; Guiry, P. J. Inorg. Chim. Acta 1994,220,249261.

b Figure 1. ORTEP representation of the molecular structure of complex 5a. The atomic coordinates and isotropic thermal parameters are collected in Table 1 and selected bond distances and angles in Table 2. color of the solution changed from dark red to orange. Workup gave a stable yellow solid in 81% yield which was recrystallized by slow diffusion of pentaneEt2O into its thf solution, giving red-orange blocks of 5a suitable for X-ray analysis. The structure obtained is shown in Figure 1and reveals a distorted-square-planar arrangement about the Pd atom; for example,the P-Pd-I angle is 171.3" and the P-Pd-C angle is 172.6" rather than the ideal 180". The ligand bite angle is 100.7", slightly larger than the typical value of 98" for the dppf ligand.12 This enhanced angle is created by staggering the two ferrocenyl rings, while the Fc-P bonds are coplanar with their rings. The side-chain double bond shows a high degree of libration, particularly in the region of C1 and C2, but is remote from Pd with no significant bonding interaction. The bound aryl group is close to orthogonality with the mean square plane, a common feature of structurally related metal aryls. In the present case, there is substantial steric hindrance t o positioning of the aryl group in the coordination plane, and this has consequences for the solution structures observed by NMR. Final atomic coordinates are given in Table 1and selected bond lengths and angles in Table 2. Restricted Pd-Aryl Rotation. Related complexes 6a and 7 were prepared by the same method used for complex 5a in 85% and 76% yields, respectively, and fully characterized. In all cases the lH NMR spectra were informative. Taking first the vinyl ether complex 5a in C&, the benzylic CH2 was diastereotopic as a sharp AB quartet at 5.25 and 5.49 ppm (Figure 21, despite the lack of stereogenicity in the structure; the 31P NMR in thf appeared as a single AX quartet at 7.9 and 25.9 ppm. If rotation about the Pd-C bond is slow on the NMR time scale, the aromatic ring possesses planar chirality, and the enantiomers are interconverted by that rotation process. This requires slow rotation of the aryl-palladium bond on the NMR time scale, since rotation about that bond interconverts the enantiomers (12)Hayashi, T.;Kumada, M.; Higuchi, T.; Hirotsu, K. J. Organomet. Chem. 1987,334,195.

Organometallics, Vol. 14,No. 1, 1995 209

Arylpalladium Iodides and Trifluoromethanesulfonates

~

Table 1. Atom Coordinates ( x 104) and Isotropic Thermal Parameters (A2 x 103) atom X Y Z U* 2380.9(4) 2777.7(4) 3866.5(8) 3255.1(14) 1925.1(13) 4380(9) 6452(18) 5661(17) 3789(9) 2418(8) 1919(14) 612(14) -175(14) 366(8) 1627(7) 3099(5) 4474(6) 5053(7) 4059(8) 2859(6) 3589(6) 484 l(6) 4667(6) 3319(7) 2643(6) 2288(6) 1145(6) 378(7) 733(9) 1837(9) 2638(8) 4851(6) 5647(7) 6925(9) 7278(10) 7278(10) 6493(10) 5286(9) 402(5) -195(6) -1312(7) -1798(7) - 124l(7) -153(6) 1758(6) 590(7) 514(8) 1536(10) 2686(9) 2778(7) 3563(22) 2309(28) 2258(33) 1533(26) 2458(36) 2112(35) 3830(33) 3334(60)

644.5(2) -506.9(2) 2723.0(4) 1250.0(7) 1533.9(7) -145(4) 284(10) 53(8) -50(4) -227(3) -658(5) -853(6) -612(5) -178(3) 120) 2222(3) 2148(3) 2798(4) 3283(4) 2949(3) 2161(3) 2487(3) 3204(3) 3332(3) 2692(3) 1239(3) 857(3) 884(4) 1282(4) 1659(5) 1647(4) 908(3) 761(4) 486(5) 358(5) 358(5) 493(5) 769(4) 1947(3) 1793(4) 2149(5) 2658(4) 2796(4) 2439(3) 1360(3) 1063(4) 908(5) 1030(5) 1302(5) 147l(4) 6890(13) 6703( 15) 6985(18) 7 3 7 315) 7864(21) 7552(19) 7569(19) 7030(36)

2114.4(2) 1495.9(2) 2110.9(4) 1266.5(7) 2766.0(7) 3983(3) 3653(11) 4107(8) 3344(3) 3282(3) 3722(5) 3612(7) 3094(7) 2668(4) 2770(3) 28 18(3) 2861(3) 2919(3) 2926(3) 2865(3) 1312(2) 1340(3) 13,69(3) 1363(3) 1318(3) 5W3) 426(3) -138(3) -63 l(3) -555(4) W3) 1131(3) 1678(4) 1643(6) 1023(7) 1023(7) 5W5) 552(4) 2506(3) 1917(3) 1701(4) 207 l(5) 2649(4) 2870(3) 3610(3) 3790(3) 4428(4) 4865(3) 4693(3) 4060(3) 117(12) 183(14) - 187(17) 159(13) 343(18) 664(18) 250(17) 622(32)

33(1)* 49(1)* 38(1)* 35(1)* 33(1)* 106(3)* 216(13)* 155(9)* 76(3)* 64(3)* 106(5)* 127(6)* 119(6)* 65(3)* 51(2)* 38(2)* 46(2)* 60(3)* 61(3)* 47(2)* 37(2)* 45(2)* 52(2)* 54(2)* 44w* 42(2)* 44(2)* 61(2)* 70(3)* 84(4)* 63(3)* 47(2)* 70(3)* 95(4)* 105(5)* 105(5)* 89(4)* 72(3)* 38(2)* 53(2)* 73(3)* 74(3)* 70(3)* 52(2)* 43(2)* 55(2)* 73(3)* 82(4)* 76(3)* 58(2)* 185(8) 5x71 71(8) 128(8) 83(10) 77(9) 79(9) 117(22)

"Values marked with an asterisk are equivalent isotropic U values, defined as one-third of the trace of the orthogonalized Uy tensor. Occupancy 0.5. Occupancy 0.25.

Of 5a. Recently,13a similar phenomenon was reported for the tmeda complex 8 in CDCl3, although in MeOH the same compound was dynamic between 20 and 60 "C through a process involving coordination of the hydroxyl group and ionic dissociation of bromide. A range of Pt-aryl complexes also demonstrate restricted rotation.l* In keeping with these observations, the same (13)Alster, P. L.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van Koten, G. Organometallics 1993,12,1639-1647. (14) Alcock, N. W.; Brown, J. M.; PBrez-Torrente, J. J. Tetrahedron Lett. 1992,33, 389-393; Organometallics, submitted for publication.

Table 2. Selected Bond Distances (A) and Angles (deg) Pd-I Pd-P(l) Pd-P(2) Pd-C(9) P( 1)-C( 15) P(2)-C(20) P( 1)-C(26) P(2)-C(10) P(2)-C(32) P(2)-C(38) I-Pd-P( 1) I-Pd-P(2) P( 1)-Pd-P(2) I-Pd-C(9) P( 1)-Pd-C(9) P(2)-Pd-C(9) C(2)-0-C(3) O-C(2)-C(l) O-C(3)-C(4) C(3)-C(4)-C(5)

2.647(1) 2.384(2) 2.287(2) 2.055(7) 1.810(6) 1.834(6) 1.821(7) 1.805(6) 1.812(6) 1.838(6) 88.0 171.2 100.7(1) 84.6(2) 172.5(2) 86.6(2) 117.8(9) 124.6(14) 112.8(7) 119.7(8)

1.381(19) 1.449(10) 1.387(28) 1.453(12) 1.383(13) 1.383(10) 1.403(20) 1.390(20) 1.387(16) 1.354(10) 120.0(7) 120.2(9) 117.2(10) 122.2(12) 118.6(12) 119.6(9) 119.9(5) 117.9(5) 122.2(7)

behavior was observed for both the butenyl complex 6a, where both the a-and @-methylenesare diastereotopic, and the allyloxy complex 7,the relevant regions of their lH NMR spectra being shown in Figure 2. A point of interest is that one of the two diastereotopic protons at the benzylic site in 7 exhibits a much stronger allylic coupling than the other, and also more pronounced homoallylic coupling, consistent with a well defined sidechain conformation in solution. As expected, the transPPh3 complex 9 exhibits a singlet for the benzylic CH2, since the symmetry plane orthogonal to the coordination plane renders the methylene hydrogens equivalent, irrespective of restricted rotation. The related l-butenylaryl complex 10 showed similar behavior. Platinum complexes 5b and 6b were prepared in 85% and 80% yields, respectively, from the stable v2-ethene complex 11, by refluxing in thf for 3 h, followed by recrystallization. lH NMR spectra very similar to those of their Pd analogs were obtained, with minor differences in chemical shift for the relevant diastereotopic proton pairs. Models for the Heck Reaction Pathway. The aryl iodide complexes Sa, 6a, and 7 were all thermally stable and in the absence of forcing conditions exhibited no tendency for cyclization or other involvement of the double bond. Given that many Heck reactions are promoted by silver salts,15 the effect on these model insertion step intermediates was investigated. Hence, reaction of complex Sa with AgOSOzCF3 in ds-acetone at -78 "C caused instant precipitation of AgI which was removed by low-temperature Celite filtration. The 31P NMR spectrum at -30 "C or below demonstrated complete conversion to a single AX species at this temperature: 6 31.1 and 15.3 ppm ( J = 51 Hz). Broadening of the signals was observed above that temperature, and on brief warming to ambient and recooling loss of signal intensity was observed. Insight into the structure of this new species was obtained from the lH NMR spectrum obtained at -20 "C. Two structures were anticipated from consideration of likely reaction pathways for a cationic complex produced in the Ag+-induced step, namely the coordinated alkene complex 12 and cyclization product 13,but the observed (15)Sato, Y.;Sodeoka, M.; Shibasaki, M. J . Org. Chem. 1989,54, 4738. Abelman, M.M.; Oh, T.; Overman, L. E. J. O g . Chem. 1987, 52,4130. Karabelas, K.;Hallberg, A. J . Org. Chem. 1986,51,5286.

Brown et al.

210 Organometallics, VoE. 14,No. 1, 1995 Chart 2

5 (a M = Pd) (b M = Pt)

6 (a M = Pd) (bM=Pt)

I

5.5

5.0

7

0

10

I

I

3.0

2.0

+-I

7

I

I

6.5

6.0 Figure 2. CH2 region of the lH NMR spectra of complexes 5a,6a,and 7,demonstrating magnetic inequivalence. spectrum is inconsistent with either of these. There is a inequivalent methylene group centered at 5.18 ppm (JAB= 19 Hz), with one of the pair partially obscured by a ferrocenyl signal, in which both protons possess two further couplings to phosphorus of 8 and 11Hz. The only high-field signal is methyl group at 1.40 ppm, possessing coupling of 10.5 and 11.5 Hz to the two phosphorus nuclei. Signals associated with the vinyl group of the original alkene are absent. It was established via a COSY experiment that there is no detectable coupling between the CH2 and CH3 groups a t 5.18 and 1.40 ppm; in the same experiment four contiguous aryl protons associated with the organic substrate were

Me'

9

11

identified, the ortho proton at 7.76 ppm possessing longrange coupling t o both protons of the CH2 group. Both the chemical shifts and the P couplings are consistent with one phosphorus trans to carbon and the other trans to a more electronegative group (OTf'),but the presence of an isolated methyl group requires an additional sequence of reactions not normally considered as a component of the catalytic cycle, as illustrated in Figure 3. The implication is that all the initial stages of this sequence are rapid and complete by the time that the first spectroscopic observations are made at -40 "C. Iodide ionization creates a vacant coordination site which is occupied by the alkene double bond in 12, followed by an exocyclic closure to give the primary alkyl complex 13, the expected intermediate. According to the usual view of the catalytic cycle, this would undergo P-hydride elimination to form Pd-hydride 14, which will then dissociate the alkene to form the observed Heck product, as shown. Evidently this dissociation is slower than Pd-H readdition to the alkene so that the more stable ql-benzyl complex 15 is the first observed intermediate. Structure 15 fits the available spectroscopic data. Its propensity for decomposition by P-elimination would explain why attempts to obtain a pure sample were unsuccessful. Furthermore, attempts to characterize organic decomposition products were equivocal. While structure 15 is the most probable structure for the unstable intermediate, minor variations are also consistent with the data-for example, the coordinated triflate could be replaced by an acetone solvent molecule in 16.16 The high reactivity of complex 12 toward Pd-C insertion may be due to a number of factors, including (16)Cf.: Seligson, A. L.;Trogler, W. C. J.Am. Chem. SOC.1991, 113, 2520.

Arylpalladium Iodides and Trifluoromethanesulfonates

Organometallics, Vol. 14, No. 1, 1995 211

Chart 3

5a AgOTf -78°C to -4O'C

P* = &PPh2 PdP2

16

I

;PdPp TfO

H 12

13

l

15

14

Figure 3. Reaction pathway from complex 5a to the unstable intermediate 15 on reaction with AgOTf'. the favorable formation of a five-membered ring. In addition, the insertion step can be viewed as an electrophilic carbodepalladation, the electrophile being the ether-stabilized carbocation formed by addition of palladium to the terminal carbon of the alkene. The stoichiometric addition of an alkenyl bromide to norbornene promoted by Pd(0) under mild conditions had been noted.6 Under the same reaction conditions, the butenylaryl complex 6a behaved similarly, although the purity and stability of the intermediate were both lower. Two coupled CH2 groups are observed at 6 2.85 and 1.55 ppm, with further complexity arising from coupling to phosphorus. A CH3 group with two equivalent phosphorus couplings is observed at 1.18 ppm. This new compound is assigned structure 17, the cyclization step again being fast in both cases and leading to an intermediate of similar structure. The allyloxy complex 7 did not follow the same reaction pathway, and it proved impossible to characterize anything in that case. Notably, the related intermediate 18 could decompose directly to 3,5-dimethylbenzofuran. For the truns-PPh3 complex 9, reaction with AgOS02CF3 was slow and incomplete below -20 "C and did not lead to a clean characterizable species. In addition, the Pt complex 5b did not yield useful information on treatment with AgOS02CF3 under the previously described conditions. The reaction occurred rapidly at -78 "C, but the first formed species was unstable and decomposed by multiple pathways. Significance of the Results. With normal reactants, and conventional catalysts, the rate of turnover in catalytic Heck reactions is quite slow, so that reactions are typically carried out at 80-100 "C.l Many attempts have been made to facilitate reactivity, including the addition of phase-transfer catalysts," conducting the reaction in water,18 and the use of silver or thallium (17) Jeffery, T.J. Chem. Soc., Chem. Commun. 1984,1287. (18) Bumagin, N.A.;More, P. G.; Beletskaya, I. P. J. Organomet. Chem. 1989,371,397.

17

PdP2

18

salts to promote the ionization of the Pd-I bond in the initial oxidative addition c0mp1ex.l~The use of aryl or vinyl triflates in place of halides as the electrophilic complex promises to permit the reaction to be conducted under milder condition^.^ In view of the general sluggishness of catalysis, the high reactivity of complexes 5a and 7 toward silver-ion promoted cyclization is surprising. It implies that the critical aryl-Pd insertion in the alkene is rapid at -40 "C and that the /?-elimination step is sufEciently facile for intramolecular loss and readdition of Pd-H, giving the benzylpalladium complex inaccessible by direct reaction. It remains to be seen whether this intermediate 15 can be cleanly broken down to the alkene product by base and whether the Pd(0) species thus generated can be quantitatively recycled. Summary and Conclusions. These experiments demonstrate that the pathway of the intramolecular Heck reaction can be simulated in a stoichiometric cycle, and in the absence of base (a normal component under catalytic conditions) an alkylpalladium complex 15 formed by eliminatiodreaddition of palladium hydride is observable at sub-ambient temperature. The initial alkene complex and the first Pd alkyl formed by PdAr addition to the coordinated alkene are evidently too transient to detect in this series. Access to a forward intermediate will permit further studies on the reaction mechanism to be carried out. Such studies will be the subject of future reports. 3. Experimental Section General Information. All solvents were freshly distilled from standard drying agents and degassed by three freeze1 thaw cycles before use. Organometallicreactions were carried out under dry argon by using Schlenk glassware and vacuum line techniques. Transfers were carried out with stainless steel cannulas under positive argon pressure. lH NMR spectra were recorded on a Varian Gemini 200 (200MHz), a Bruker WH-300 (300 MHz),or a Bruker AM-500 (500 MHz) spectrometer and are referenced to residual protic solvents with chemical shifts being reported as 6 (ppm) from TMS. 31PNMR spectra were recorded on a Bruker AM-250 spectrometer operating at 101.26 MHz using 85% H3P04 as external reference. Elemental analyses were performed by the Dyson Perrins LaboratoryAnalytical Service using a Carlo Erba 1106

elemental analyzer. The starting materials [1,1'-bis(diphenylphosphino)ferrocene]palladium dichloride,lg[1,l'-bis(diphenylphosphino)ferrocenel($-ethene)platinum (11),6 and tetrakis(tripheny1phosphine)palladium20were prepared by literature methods. Dilithium cyclooctatetraenide was prepared by the method of Katz and

Garratt.21 (19) Hayashi, T.;Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.; Hirotsu, K J.Am. Chem. Sac. 1984,106,158. (20) Coulson, D.R.Inorg. Synth. 1972,13,121. (21) Katz, T.J.; Garratt, P. J. J. Am. Chem. Sac. 1964,86, 4876.

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Brown et al.

[(dppDPd(I)(m-CHs(CsH4)-o-OCHzCH=CH2)1 (7).% Yield: Preparation of o-Iodobenzyl Vinyl Ether (1). The 76%. Anal. Calcd for C44H39FeIOP~Pd: C, 56.52; H, 4.20. compound was prepared from 2-iodobenzyl alcohol by following Found: C, 55.43; H, 4.73. lH NMR (300 MHz, de-toluene): a procedure similar to that given in the literature.s The crude 8.37 (m, 2H), 8.26 (m, 2H), 7.70 (m, 2H), 7.68-7.00 (m, 13H), product was distilled in a Kugelrohr apparatus: bp 80 "C, 0.3 mmHg (lit.9 bp 82-83"C, 0.8 mmHg). Yield: 70%. 6.90 (m, 2H), 6.75 (m, 2H) (ferrocenyl and aryl residues), 6.39 (d, l H , OCHz-), 6.20 (m, lH, -CH=CHz), 5.93 (m, l H , OCPreparation of l-Iodo-2-(3-butenyl)benzene (2). To a Hz-), 5.52 (dd, lH, J = 17, 1.8 Hz, -CH=CHz), 5.27 (dd, l H , stirred solution of 2-iodobenzyl bromide (5.0 g, 0.017 mol) J = 10, 1.8 Hz, -CH=CHz), 5.01 (8,lH), 4.35 (8,2H), 4.08 (s, (prepared by metathesis of the commercially available 2-iodobenzyl chloride with a large excess of NaBr) in THF (60 mL) lH), 4.00 (s, lH), 3.69 (s, 2H), 3.57 (s, 1H) (Cp), 1.97 (s, 3H, at -10 "C was added allylmagnesium bromide (18.5 mL, 1.0 -CH3). 31PNMR (250 MHz, thf7DzO): 26.6 (d), 8.2 (d) ( J p - P M, 0.018 mol) by syringe over a period of 10 min. A white = 31 Hz). precipitate was immediately formed. After 5 h of stirring at Synthesisof [(dppf)Pt(I)(o-(CsH4)CH20CH=CH2)1 (Sb). ambient temperature, saturated ammonium chloride solution To a solution of [(dppf)Pt(v2-ethene)](0.1 g, 0.128 mmol) in (10 mL) and water (20 mL) were added and the mixture was THF (10 mL) was added o-iodobenzyl vinyl ether (1;0.041 g, extracted with diethyl ether (2 x 20 mL). The ethereal layer 0.154 mmol). The mixture was refluxed for 3 h to give an was washed with water and brine, dried over anhydrous orange solution. The solvent was removed under vacuum, and MgS04, and concentrated under vacuum to give a yellow oil. then acetone (2 mL) was added. Slow addition of diethyl ether The product was obtained as a yellow liquid by Kugelrohr (5 mL) and pentane (10 mL) affords the complex as an orange distillation (100 "C at 0.3 mmHg); lit.8 130-132 "C, 19 mmHg. microcrystalline solid which was filtered, washed with pentane Yield: 92%. and dried in vacuo (0.109 g, 85%). Anal. Calcd for C43H37Preparation of 1-(Allyloxy)-2-iodo-4-methylbenzene FeIOPZPt: C, 51.15; H, 3.69. Found: C, 51.07; H, 3.86. 'H (3).9 The compound was synthesized from 2-iodo-4-methNMR (300 MHz, C&): 8.41 (m, 2H), 8.30 (m, 2H), 7.70 (m, ylphenolZ2and allyl bromide on an 0.076 mol scale by following 2H), 7.51 (m, lH), 7.30 (m, 4H), 7.26-6.85 (m, 9H), 6.78 (m, the literature procedure for the preparation of allyl aryl ethers: 4H) (ferrocenyl and aryl residues), 6.67 (dd, lH, -CH=CHz), 23 bp 125-127 "C, 0.3 mmHg. Yield: 89%. 'H NMR (200 MHz, 5.43 (2H, AB, 4, JAB= 12 Hz, -CHzO), 4.80 (s, lH, Cp), 4.74 CDC13): 7.63 (d, lH), 7.08 (dd, lH), 6.71 (d, 1H) (aryl), 6.08 (dd, lH, JH-H= 14, 1.4 Hz, -CH=CHz), 4.53 (s,lH, Cp), 4.19 (m, lH, -CH=CHz), 5.52 (dd, l H , J = 1 8 , 2 Hz, -CH=CHz), (dd, l H , J = 7, 1.4 Hz, -CH=CHz), 4.05 (s, lH), 4.02 (s, lH), 5.32 (dd, l H , JHH= 12, 2 Hz, -CH=CHz), 4.58 (br d, 2H, 3.72 (s, lH), 3.65 (s, 2H), 3.61 (s, lH), (Cp). 31P NMR (250 OCHz-), 2.23 (s,3H, -CH3). MHz, thUDz0): 13.6 (d, dd, J p t - p = 4163 Hz, J p - p = 16 Hz), Synthesis of the Complexes [(dppf)Pd(I)(R)]:R = 10.6 (d, dd, Jpt-p = 1746 Hz). o-(Cfi)CH20CH%H2 (Sa),O-(C~H~)CH&H~CH=CH~ (6a), Synthesis of [(~~~~)P~(I)(o-(C&)CHZCHZCH=CHZ)I m-CHs(C&)-o-OCHzCH=CH2 (7). A solution of dilithium cyclooctatetraenide (1.53 cm3, 0.26 M in diethyl ether, 0.41 (6b). The complex was prepared from [(dppf)Pt(v2-ethene)1 mmol) was added dropwise over a period of 5 min t o a stirred (2;0.026 (0.060 g, 0.077 mmol) and l-iodo-2-(3-butenyl)benzene suspension of [(dppf)PdClz](0.30 g, 0.41 mmol) in THF (20 mL) g, 0.1 mmol), by a procedure identical with that given for 6a, at -78 "C to give a dark red solution in 15 min. Then, the as an orange microcrystalline solid (0.062 g, 80%). Anal. appropriate o-iodoaryl species (1-3) (0.41 mmol) was added Calcd for C&sgFeIPzPt: C, 52.45; H, 3.90. Found: C, 52.40; and the mixture was warmed slowly to room temperature (3 H, 4.15. 'H NMR (300 MHz, C6D6): 8.43 (m, 2H), 8.26 (m, h) to give an orange solution. The solvent was removed under 2H), 7.93 (m, 2H), 7.65 (m, 1H) 7.35-6.76 (m, 13H), 6.66 (m, vacuum and the yellow residue extracted with toluene (15 mL) 4H) (ferrocenyl and aryl residues), 6.28 (m, l H , -CH=CHz), and then centrifugated in order to remove LiC1. Concentration 5.41 (d, lH, J = 17 Hz, -CH=CHz), 5.23 (d, lH, J = 10 Hz, of the clear orange solution under vacuum to ca. 2 mL and -CH=CHz), 5.12 (s, lH), 4.17 (s, lH), 4.05 (s, lH), 3.86 (s, slow addition of cold hexane (20 mL) gave the complexes Sa, lH), 3.73 ( 6 , lH), 3.64 (s, lH), 3.59 (9, lH), 3.57 (s, 1H) (Cp), 6a, and 7 as yellow solids which were collected by filtration, 3.52 (dt, lH, -CHzCHz-), 3.30 (m, l H , -CHzCHz-), 2.59 (dt, washed with cold hexane, and dried under vacuum. lH, -CHzCHz-), 2.35 (m, lH, -CHzCHz-). 31PNMR (250 [(dppf)Pd(I)(o-(C&)CH20CH=CH2)1 (Sa). Yield: 81%. MHz, thUDzO): 13.1 (d, dd, J p t - p = 4228 Hz, J p - p = 15 Hz), Anal. Calcd for C43H37FeIOP2Pd:C, 56.08; H, 4.05. Found: 10.0 (d, dd, J p t - p = 1716 Hz). C, 55.96; H, 4.13. 'H NMR (300 MHz, C6D6): 8.30 (m, 4H), Synthesis of [(PPh&Pd(I)(o-(CJ-&)CH20CH=CH2)1(9). 7.70 (m, 2H), 7.46 (m, lH), 7.30-6.91 (m, 9H), 6.88 (m, 4H), To a solution of [Pd(PPh3)4](0.2 g, 0.173 mmol) in THF (10 6.69 (m, 4H)u(ferrocenyl and aryl residues), 6.61 (dd, lH, mL) was added o-iodobenzylvinyl ether (1; 0.049 g, 0.19 mmol). -CH=CHz), 5.49, 5.25 (2H, AB q, J = 12 Hz, -CHzO), 4.81 The mixture was stirred for 2 h to give a pale yellow solution. (s,l H , Cp), 4.69 (dd, lH, J = 1.4, 1.5 Hz, -CH=CHz), 4.32 (6, Evaporation of the solvent under vacuum to ca. 1mL and slow lH, Cp), 4.14 (dd, lH, J = 7, 1.5 Hz, -CH=CHz), 4.03 (8,lH), addition of MeOH (10 mL) gave the complex as a yellow 3.94 (s, lH), 3.71 (s, lH), 3.63 (s, 2H), 3.55 (s, 1H) (Cp). 31P microcrystalline solid, which was filtered, washed with MeOH, NMR (250 MHz, thf7DzO): 25.9 (d), 7.9 (d) (Jp-p = 34 Hz). and vacuum-dried (0.140 g, 91%). Anal. Calcd for C45H39IOPz[(dppf)Pd(I)(o-(CJ&)CH2CH&H%H2)1 @a).Yield: 85%. Pd: C, 60.65; H, 4.41. Found: C, 60.50; H, 4.53. 'H NMR Anal. Calcd for CuH39FeIPzPd: C, 57.51; H, 4.27. Found: C, (300 MHz, CDC13): 7.47 (m, 12H), 7.35-7.20 (m, 18H) (PPh3 57.32; H, 4.25. 'H NMR (300 MHz, d8-toluene): 8.40 (m, 2H), ligands), 6.83 (d, lH), 6.49 (t, lH), 6.42 (d, lH), 6.25 (t, 1H) 8.20 (m, 2H), 7.93 (m, 2H), 7.53 (m, lH), 7.33-6.89 (m, lOH), (aryl ligand), 5.97 (dd, l H , -CH=CHz), 4.44 (s, 2H, -CHzO), 6.83 (m, 2H), 6.65 (m, 4H), 6.50 (m, 1H) (ferrocenyl and aryl 4.13 (dd, l H , J = 14, 1.7 Hz, -CH=CHz), 3.94 (dd, lH, J = 7, residues), 6.20 (m, lH, -CH=CHz), 5.37 (dd, lH, J = 17, 2 Hz, -CH=CHz), 5.20 (dd, lH, J = 11,2 Hz, -CH=CHz), 5.05 1.7 Hz, -CH=CHz). 31P NMR (250 MHz, thEIDz0): 23.5 (SI. (5, lH), 4.10 (9, 2H), 3.92 (8, lH), 3.75 (s, lH), 3.69 (s, lH), Synthesis of [(PP~~)~P~(I)(O-(C&)CH~CH~CH=C€€Z)I 3.64 (s, lH), 3.56 (s, 1H) (Cp), 3.66 (td, lH, Ar-CHz-1, 3.11 (10). The complex was synthesized from [Pd(PPh&l (0.1 g, (m, lH, -CHz-), 2.51 (td, lH, Ar-CHZ-1, 2.20 (m, lH, -C0.086 mmol) and 4-(o-iodophenyl)but-l-ene(IC;0.051 g, 0.2 Hz-). 31PNMR (250 MHz, thUDzO): 25.4 (d), 9.4 (d) ( J p - p = mmol); workup as above gave the compound as a yellow 35 Hz). microcrystalline solid (0.069 g, 90%). Anal. Calcd for C46H41IPzPt: C, 62.14; H, 4.64. Found: C, 61.81; H, 4.66. 'H NMR (22)Kometani, T.;Watt, D. S.; Ji, T.Tetrahedron Lett. 1985, 26, (300 MHz, CD2Cl2): 7.58-7.16 (m, 30H, PPh3 ligands), 6.88 2043. (d, lH), 6.51 (t, lH), 6.28 (t, lH), 6.22 (d, 1H) (aryl ligand), (23)White, W. N.;Gwynn, D.; Schlitt, R.; Girard, C.; Fife, W. J. 5.7 (m, lH, -CH=CH2), 4.97-4.90 (m, 2H, J = ca. 17, 10, 1.5 Am. Chem. SOC. 1958,80, 3271.

Organometallics, Vol. 14, No. 1, 1995 213

Arylpalladium Iodides and Trifluoromethanesulfonates Table 3. Crystallographic Data for Sa mol formula

Mr crys syst crys size (mm)

:pE b (A)

c (A) B (de@ v (A?

2

D,(g ~ m - ~ ) T (K) diffractometer radiation; A (A) P (cm-9 scan method 28(max) (deg) no. of unique rflns no. of obsd rflns criterium for observn no. of params refined S (goodness of fit) AJGll&X

R RW

residual electron density

Crystal Structure Determination. Suitable orange crys-

X-ray structure determination were obtained by slow C ~ ~ H ~ ~ O P ~ F ~ I . ' / ~ C ~ H I ~ Q ~ / ~ tals C ~ Hfor BO diffusion of a diethyl ether-pentane mixture into a saturated 951.5 solution of the complex in THF at -15 "C. Crystal data monoclinic collection parameters are summarized in Table 3. Data were 0.45 x 0.44 x 0.25 P21/c collected with a Nicolet P21 four-circle diffractometer in the 10.320(3) 0-28 mode. The maximum 28 was 50" with scan range +1.3" 19.499(5) (28) around the Kal-Kaz angles, scan speed 5-29' min-I, 21.150(5) depending on the intensity of a 2 s prescan; backgrounds were 94.61(2) at each end of the scan for 0.25 of the scan time. measured 4242(2) hkl ranges were: 0-12, 0-23, and -25 t o +25. Three 4 standard reflections were monitored every 200 reflections and 1.44 showed no change during data collection. Unit cell dimensions 290 and standard deviations were obtained by a least-squares fit Nicolet p21 Mo Ka; 0.710 69 to 15 reflections (25 < 20 < 27"). Intensity data were corretted 15.9 for absorption effects (by the Gaussian method); minimum and 0-20 maximum transmission factors were 0.66 and 0.78. 50 Heavy atoms were located by the Patterson interpretation 7510 section of SHELXTL and the light atoms then found on 5958 successive Fourier syntheses. One partially occupied disorI > 2u(z) dered solvent molecule was located; it was modeled as a 50: 474 50 mixture of the two ethers, sharing the same oxygen and 0.98 0.9 one carbon site, with a total occupancy of 0.5. All significant 0.042 residual peaks were in the vicinity of this solvent, indicating 0.050 that the description of the molecule was not perfect. Aniso1.U-0.4 tropic temperature factors were used for all non-H atoms,

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Hz, -CH=CHz), 2.51 (m, 2H, Ar-CHZ-1, 1.65 (m, 2H, -CH2-). 31P NMR (250 MHz, CHzC12/D20): 21.9 (8). Reaction of Sa and 6a with Silver Trifluoromethanesulfonate. Solid silver trifluoromethanesulfonate (0.044 g, 0.172 "01) was added to a solution of [(dppDPd(IXo-(C&)CHzOCH=CHz)] (Sa;0.184 g, 0.172 mmol) in a 1:lmixture of THF and acetone (6 mL) at -78 "C. The mixture was stirred for 1 h at this temperature and then filtered through Celite at -78 "C to give 9 clear orange solution containing complex 16. 31P NMR (250 MHz, thE/acetone/DzO, -40 "C): 31.1 (d), 15.3 (d) (Jp-p = 5.1 Hz). A sample for proton NMR was similarly obtained using d6-acetone as solvent. 'H NMR (500 MHz, d6acetone, -20 "C): 7.77 (m, 3H, dppf and aryl ligand), 7.687.48 (set of m, 14H, aryl), 7.34 (m, 3H, aryl), 7.03 (m, 1H, aryl), 6.78 (m, 2H, ferrocenyl), 6.59 (m, lH, aryl), 5.16 (m, 2H, -CHzO (see text)), 5.11 (s, lH), 4.80 (8, lH), 4.60 (s,2H), 4.34 ( 6 , 1H), 4.29 (8, 1H), 3.84 (s, 1H), 3.34 (9, 1H) (CP), 1.40 (dd, 3H, J H - p = 10.5, 11.7 Hz, -CH3). In a similar way, reaction of [(dppnPd(I)(o-(C6H4)CHzCHzCH=CHz)] (6a; 0.2 mmol scale) with AgOSOzCF3 gave an orange solution of complex 18. lH NMR (500 MHz, &-acetone, -20 "C): 7.85-7.10 (set of m, 20H, aryl residues), 7.05 (m, lH, aryl), 6.83 (m, 2H, dppf), 6.52 (m, l H , aryl), 5.03 (s, W, 4.74 (s, 1H), 4.70 (s, lH), 4.68 (s, lH), 4.33 (s, 1H), 4.30 (8, lH), 3.68 (8,lH), 3.47 (8,1H) (Cp), 2.85 (m, 2H, -CHz-), 1.53 (m, 2H, -CHz-), 1.18(t, 3H, J H - p = 11Hz, -CH3). 31PNMR (250 MHz, thf-acetoneDz0, -40 "C): 33.4 (d), 18.0 (d) ( J p - p = 56 Hz). (24) This compound was less pure than others in the series and did not analyze satisfactorily despite several attempts.

apart from solvent atoms. Hydrogen atoms were given fixed isotropic temperature factors; U = 0.07 k . Those defined by the molecular geometry were inserted at calculated positions and not refined (omitted on the solvent molecule). A weighting scheme of the form w = l/(a2(F) g F ) with g = 0.0043 was used and shown t o be satisfactory by a weight analysis. All calculations were performed on a DEC Microvax-I1computer using SHELXTL PLUSz5 Scattering factors in the analytical form and anomalous dispersion factors were taken from ref 26.

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Acknowledgment. We thank Johnson-Matthey for the loan of Pd and Pt salts and the Spanish Ministry of Education for a Fellowship (to J.J.P.-T). Supplementary Material Available: Text giving additional details on the X-ray structure determination and lists of anisotropic thermal parameters, H-atom coordinates, and bond lengths and angles (8 pages). Ordering information is given on any current masthead page. Additional data are available from the Cambridge Crystallographic Centre, comprising H-atom coordinates, thermal parameters, and all bond lengths and angles. OM940604+ (25) Sheldrick, G. M. SHELXTL User's Manual; Nicolet: Madison, WI, 1983, 1986. (26) International Tables for X-Ray Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV (present distributor Khwer Academic Publishers, Dordrecht, The Netherlands).