7r-Allylpalladium chloride

The most characteristic feature of the Pd—C bonds in these intermediates of both the stoichiometric and catalytic reactions is their reaction with nucleophiles, and Pd(0) is generated by accepting two electrons from the nucleophiles as exemplified for the first time by the reactions of 7r-allylpalladium chloride[2] or PdCl2-COD[3] complex with malonate and acetoacetate. It should be noted... 

Treatment of 7r-allylpalladium chloride with CO in EtOH affords ethyl 3-butenoate (321)[284]., 3, y-Unsaturated esters, obtained by the carbonylation of TT-allylpalladium complexes, are reactive compounds for 7r-allyl complex formation and undergo further facile transformation via 7r-allylpalladium complex formation. For example, ethyl 3-butenoate (321) is easily converted into 1-carboethoxy-TT-allylpalladium chloride (322) by the treatment with Na PdCL in ethanol. Then the repeated carbonylation of the complex 322 gives ethyl 2-... 

Fn some cases, r-allylpalladium complex formation by retention syn attack) has been observed. The reaction of the cyclic allyiic chloride 33 with Pd(0) affords the 7r-allylpalladium chlorides 34 and 35 by retention or inversion depending on the solvents and Pd species. For example, retention is observed in benzene, THF, or dichloromethane with Pd2(dba)3. However, the complex formation proceeds by inversion in these solvents with Pd(Ph3P)4, whereas in MeCN and DMSO it is always inversion[33]. The syn attack in this case may be due to coordination of Pd to chlorine in 33, because Pd is halophilic. The definite syn attack in complex formation has been observed using stereoche-mically biased substrates. The reaction of the cxoallylic diphenylphosphino-acetate 36 with phenylzinc proceeds smoothly to give 37. The reaction can be explained by complex formation by a syn mechanism[31]. However, these syn attacks are exceptional, and normally anti attack dominates. 

The reaction of isoprene with MeOH catalyzed by Pd(acac)2 and Ph3P is not regioselective, giving a mixture of isomers[37]. However, l-methoxy-2,6-dimethyl-2,7-octadiene (35), the head-to-tail dimer, was obtained in 80% yield, accompanied by the tail-to-tail dimer (15%) using 7r-allylpalladium chloride and BU3P. On heating, 35 was converted into 2.6-dimethyl-1,3,7-octatriene (36) by an elimination reaction[38]. 

The thiepin system 31 is formed quantitatively by ring expansion of the diazoacetate derivative 30 via carbene formation catalyzed by 7r-allylpalladium chloride and its intramolecular insertion[31], The 4-diazomethyl-4//-pyrane 32 is expanded to the oxepine 33 in quantitative yield with the same catalyst[32]. 

Others) with (+)-DIOP for asymmetric induction. The 7r-allylpalladium chloride dimer 118 was mixed with the hgand (ratio 1 2) in THF at the stated temperature, after which a solution of diethyl sodiomalonate in THF is added (Scheme 34). 119 was obtained with an optical purity of up to 20%. 

The stannylation and silylation of heteroaryl halides has also been studied. The stannylation of 4-iodo pyrimidine was conducted with hexamethyl and hexa-ra-butyl ditin in the presence of fluoride ion and Pd(PPh3)2(OAc)2 as catalyst. The stannylation of 5-bromopyrimidine occurred in the highest yields in the presence of the ligandless catalyst bis(7r-allylpalladium chloride).175 The silylation of bromopyridines, bromopyrimidines, and bromoquinolines also occurred after 96 h at 160 °C with Pd(PPh3)4 as catalyst in HMPT solvent.162... 

The main path of the palladium-catalyzed reaction of butadiene is the dimerization. However, the trimerization to form /j-1, 3,6,10-dodeca-tetraene takes place with certain palladium complexes in the absence of a phosphine ligand. Medema and van Helden observed, while studying the insertion reaction of butadiene to 7r-allylpalladium chloride and acetate (32, 37), that the reaction of butadiene in benzene solution at 50°C using 7r-allylpalladium acetate as a catalyst yielded w-1,3,6,10-dodecatetraene (27) with a selectivity of 79% at a conversion of 30% based on butadiene in 22 hours. 

Hydrosilanes react with butadiene by the catalysis of palladium compounds, but the nature of the reaction is somewhat different from that of the telomerization of other nucleophiles described before. Different products are obtained depending on both the structure of silanes and the reaction conditions. Trimethylsilane and other trialkylsilanes reacted with butadiene to give the 1 2 adduct, l-trialkylsilyl-2,6-octadienes (65), in high yield (98%) (62-64). Unlike other telomers which have the 1,6-octadienyl chain, the telomers of silanes have the 2,6-octadienyl chain. As catalysts, Pd(PPh3)2 (maleic anhydride), PdCl2(PhCN)2, PdCl2, and 7r-allylpalladium chloride were used. Methyldiethoxysilane behaved similarly to give the 1 2 adduct. 

Metal-Halogen Compounds. An unusual example of the addition of a metal halide to a conjugated diene has been reported. The complex formed from palladium chloride and butadiene has been shown to be a dimer of 1-chloromethyl-7r-allylpalladium chloride, (85). Whether this is a true insertion reaction or some type of ionic reaction has not been determined, but its close analogy with the olefin-palladium chloride insertion reaction mentioned above would suggest an insertion mechanism for the diene reaction also. 

Partial allyl compounds like 7r-allylpalladium chloride (15), or jr-allylcobalt tricarbonyl (7) had been discovered earlier by other authors not related to the author s institute. 

Asymmetric hydrosilylation of 1,3-dienes provides convenient access to optically active a-chiral allylsilanes.107 1073 1071 The combination of 7r-allylpalladium chloride dimer with axially chiral monophosphine ligand 17 realizes high catalytic activity and enantioselectivity in the reaction of cyclic 1,3-dienes with HSiCl3.108,108a The allyltrichlorosilanes obtained react with aldehydes in a syn-Se mode to give homoallyl alcohols with high diastereo-and enantioselectivity (Scheme 9). 

Bis(7r-allylpalladium chloride) (in which the 7r-allyl group occupies two coordination sites) reacts with donor reagents ... 

It has been shown that Fe(CO)s accumulates in solution (GLC and polarography), and it reacts considerably more slowly with 7r-allylpalladium chloride than does iron enneacarbonyl (155). 

The reaction products were isolated as stable phosphine derivatives. In the reaction with l,l,2-trimethyl-7r-allylpalladium chloride Heck isolated a compound whose structure probably resembles that of the intermediate in other allyl transfer reactions 159) ... 

The reaction is specific in that the allyl group retains its configuration in the course of transfer. Thus reactions of metallic mercury with an asymmetrically substituted 7r-allylpalladium chloride (for example, crotyl-palladium chloride) might equally afford both cis- and /raMr-2-butenyl-mercury chloride isomers, as well as the 1-butenyl compound. Hence generally three compounds could be expected in the reaction. However, it has been found 161) that essentially the reaction yields only trans-crotylmercury chloride (based on infrared spectra). In the case of 1-phenyl-77-allylpalladium chloride and l-acetyl-2-methyl-7r-allylpalladium chloride, again only the respective y-substituted /raw-allylmercury halides have been found. Since such conditions do not allow the allyl rearrangement 162), formation of the /ra r-allylmercury derivatives is evidence that the... 

The proton NMR spectra of many of these 7r-allyl-metal complexes are similar and exhibit three resonances with intensities in a 2 2 1 ratio. The two methylene peaks are equivalent, but the two hydrogen atoms on each methylene group are magnetically nonequivalent—two being nearer to the metal atom and two away from it. Several x-ray studies on dimeric 7r-allylpalladium chloride confirm the structures proposed on the basis of NMR and infrared spectra (157, 188, 189, 218, 218, 227). 

During the reaction, palladium metal precipitation was observed as would be expected in the vinylation reaction (Reaction 1). During product isolation, water is added to the reaction system. In most of the reactions run at 25°C. this addition resulted in further precipitation of palladium metal from the brown solution, probably owing to decomposition of the trace of 7r-olefin complex of palladium (II) present. However, the acetic acid solutions of products obtained from 100°C. reactions containing chloride were bright yellow and did not precipitate more palladium when water was added. This color is typical of 7r-allylpalladium chloride complexes and indeed di-/ix-chloro-di-7r-(methyl-3-ethylallyl) dipalladium (II) could be isolated from the reaction mixture. Formation of these complexes, 7r-olefin or 7r-allyl would, of course, result in decreased yields of vinylation products. 

In some preliminary studies on the eflFect of the metallic anion a series of reactions was run in which chloride in both the palladium and copper salts was replaced by other anions. When acetate was used, results similar to the chloride systems were obtained although product distribution was somewhat different see also Table 1). Both bromide and iodide were found to inhibit the reaction, and no products were isolated. For the oxyanions, nitrate, sulfate, and acetylacetonate, vinyla-tion products of these oxyanions in addition to the acetate vinylation products were found. Because of the increased complexity of these systems, they were not investigated further. All chloride-containing systems investigated—PdCl2, Na2PdCl4, (NH3)2PdCl2, and 7r-allylpalladium chloride—had similar reactivities and vinylation-product distributions. 

The combination of a bisfamide/phosphine) and 7r-allylpalladium chloride can be used to achieve asymmetric allylic alkylation " and deracemization of cyclic allyl esters. ... 

Silylstannation of the allenyl aldehyde 148 with 140 in THF at room temperature generated the allylstaimane 149, which attacked intramolecularly the formyl group to yield the cyclic homoallylic alcohol 150. Phosphine-free 7r-allylpalladium chloride was the most effective catalyst [48]. 

The distal bond cleavage occurs in hydroamination. Reaction of MCP 208 with dibenzylamine afforded the allylic amine 209 by using the combination of 7r-allylpalladium chloride with DPPP as a catalyst [61]. Similarly sulfonamide 211 was allylated with MCP 210 to produce the diallylated amide 212 using a complex mixture of Pd(0), Pd(II), and PPhs as a catalyst [62]. The use of Pd(0)-PPh3 in an appropriate ratio seems to be effective. 

The redox nature of palladium(ii) salts has been investigated, methods being described for the study of the rates of oxidation of olefins. The reduction of benzoquinone by 7r-allylpalladium chloride in aqueous hydrochloric acid solutions has also been reported. ... 

Formation of an enantiomerically pure, azide or amine containing, five or six membered ring by a pallidium catalyzed desymmetrization using a nitrogen nucleophile, where the palladium complex is derived from a chiral ligand and 7r-allylpalladium chloride ... 

PdClg heated 3 hrs. at 90° with 3-ethyl-2-pentene in 50%-acetic acid bis-(1,3-dimethyl-2-ethyl- 7r-allylpalladium chloride) (Y 98%) allowed to react with... 

The reaction of 7r-allylpalladium chloride with malonate and acetoacetate as soft carbon nucleophiles to give allytmalonate and allylacetoacetate, discovered by this author in 1965, is the first example of the carbon-carbon bond formation mediated by a Pd complex (Scheme In addition to the allylation of malonate, the reaction of cyclohexanone enamine with 7r-allylpalladium chloride gave 2-aUylcyclohexanone after hydrolysis. The discovery of the allylation of nucleohphiles with 7r-allylpalladium chloride means the birth of TT-allylpalladium chemistry, which has developed as a remarkably useful synthetic method. 

It was reported as early as 1980 " " that the reaction of the Li enolate of methyl cyclo-hexanecarboxylate with 7r-allylpalladium chloride can give either the expected a-allylated product or a-cyclopropyl derivative depending on the base and solvents used (Scheme 21). 

Asymmetric allylation of aldimine providing chiral homoallylamines is accomplished by using 5 mol % of 7r-allylpalladium chloride dimer derived from (75)-/3-(-)pinene (Scheme 29)P The pinene moiety serves not only as a chiral auxiliary but also as a dummy 7r-allyl group of unsymmetrical bis-7r-allylpalladium intermediate. The asym-metric induction is successful for aldimines derived from alkylamines (benzy-lamine, p-methoxybenzylamine, and isopropylamine) however, no asymmetric induction is observed for aldimines of aniline. 

Another interesting reaction of 7r-allylpalladium species is their reaction with carbon monoxide. 7r-Allylpalladium chloride, for instance, reacts with CO in EtOH to give car-bonylation products (Scheme 21). ... 

Cl bHi bC12Pc12, Bis(2-phenyl-7r-allylpalladium chloride), 34B, 444 ClbHiBCl2Pt, Dichloro(2,5-diphenyl-l,5-hexadiene)platinum(II), 46B, 846... 

Subsequent x-ray diffraction analysis proved the square planar configuration (Fig. 5-1) to be correct. Furthermore, it was revealed that the three chloride atoms are in the same plane as the platinum, while the ethylene molecule is perpendicular to the plane, as shown. A slight distortion of the basic square planar structure is noted since the platinum to chlorine bond length trans to ethylene is longer than those that are cis. A similar example of a square planar metal 7r-complex is seen in 7r-allylpalladium chloride [(tt-C3H5)PdCl]2(Fig.5-2). 

---