T 3-Allyl palladium

B. Akermark, B. Krakenberger, S. Hansson, Ligand Effects and Nucleophilic Addition to (T)3-Allyl)palladium Complexes. A Carbon-13 Nuclear Magnetic Resonance Study, Organometallics, 1987, 6, 620-628. 

A similar procedure with bis(t/3-allyl)palladium or bis(cycloocta-l,5-diene)palladium as catalyst leads to only slightly different product distributions of the tetramers. The absolute yield of the nonpolymeric products is lower in both cases.42... 

Similar solvent effects are observed in the stoichiometric formation of bridged (t/3-allyl)palladium trifluoroacetates40. A mixture of tetrahydrofuran and acetonitrile favors anti addition to yield the ra-adduct 19, whereas syn addition dominates in pure tetrahydrofuran. syn Attack of palladium(O) is much slower. The main effect of the polar coordinating solvent is to stabilize the transition state of the anti addition, in which charge separation is necessarily involved to a higher extent than for syn addition. The reaction conditions in the two reactions shown below represent feasible methods of preparing stable 7t-allylpalladium complexes 20. Palladium black will precipitate in the second reaction, if phenanthroline is not present. 

Nesmeyanov s laboratory (22) found that t/3-allyl palladium cyclopentadienyl reacted with iron pentacarbonyl to produce [CpFe(CO)2]2 and Cp2Fe. The fate of the palladium was not revealed. In a similar fashion, Cp(f/3-C3Hj)Pd reacted with FeCl2 in THF to produce [(r/3-C3H5)PdCl]2 and Cp2Fe. No conversions or yields were given. 

Mathew JP, Reinmuth A, MeUa J, Swords N, Risse W (1996) (t 3-Allyl)palladium(ll) and palladium(II) nitrile catalysts for the addition polymerization of norbomene derivatives with functional groups. Macromolecules 29 2755-2763... 

A series of (T 3-allyl) palladium complexes, such as (12), derived from insertion of conjugated dienes into the Pd-C bond of a cyclopalladated derivative of dimethylaminomethylferrocene has been prepared 32 and their conversion to N-heterocycles via... 

The carbonylation of (T 3.allyl) palladium(II) chloride dimer in the presence of an excess of ylide, such as Ph3PC(H)COR (R = Me, Ph) was shownl to occur with reduction of the palladium(n) complex to palladium metal and formation of the corresponding alkyl 3-butenoate in... 

Although t/3-allyl complexes of platinum(II) are not rare, their occurrence is not as frequent as for -alkene complexes. This situation is reversed for palladium(II) where r 3-allyl complexes are very common, and much of modern organopalladium chemistry is becoming dominated by the reactivity of j)3-allyl complexes. 

In an oxidative addition, Pd(0) complex 22 with BINAP as a ligand accepts alkenyl triflate It. The resulting Pd complex 23 is cationic, since the triflate anion is bound only loosely to the palladium and dissociates from the complex.1 Syn insertion of one of the two enantiotopic double bonds of the cyclopentadienc into the alkenyl-Pd bond of complex 23 leads firs to q -allyl-Pd complex 24. This is in rapid equilibrium with t 3-allyl-Pd complex 25. Neither 24 nor 25 contains a p-H atom in a yn relationship to palladium. Moreover, internal rotation is impossible in the con form a-tionaily fixed ring system. For this reason there is no possibility of a subsequent p-hydride elimination that would once again release the palladium catalyst. In a normal Heck reaction (see discussion) the catalytic cycle would be broken at this point. 

A wide variety of nucleophiles add to an -rf-allyl ligand. Desirable nucleophiles typically include stabilized carbanions such as CH(COOR)2 or 1° and II0 amines. Unstabilized nucleophiles such as MeMgBr or MeLi often attack the metal first and then combine with the n-allyl by reductive elimination. The Tsuji-Trost reaction, which is typified by the addition of stabilized carbanions to T 3—allyl ligands complexed to palladium followed by loss of the resulting substituted alk-ene, comprises an extremely useful method of constructing new C-C bonds, and many applications of this reaction have appeared in the literature.61 Equation 8.43 illustrates an example of a Pd-catalyzed addition of a stabilized enolate to an allyl acetate.62 The initial step in the catalytic cycle is oxidative addition of the allyl acetate to the Pd(0) complex, followed by nq1 to nq3—allyl isomerization, and then attack by the nucleophile to a terminal position of the T 3—allyl ligand. We will discuss the Tsuji-Trost reaction, especially in regard to its utility in chiral synthesis,63 more extensively in Chapter 12. 

In acyclic systems the 1,4-relative stereoselectivity was controlled by the stereochemistry of the diene. Thus, oxidation of (E,E)- and (E,Z)-2,4-hexadienes to their corresponding diacetates affords dl (>88% dl) and mesa (>95% me so) 2,5-diacetoxy-3-hexene, respectively. A mechanism involving a t vans-accto xy pal I adation of the conjugated diene to give an intermediate (rr-allyljpalladium complex, followed by either a cis or trans attack by acetate on the allyl group, has been suggested. The cis attack is explained by a cis migration from a (cr-allyl)palladium intermediate. The diacetoxylation reaction was applied to the preparation of a key intermediate for the synthesis of d/-shikimic acid, 3,... 

After the failure of the direct synthesis of the completely unsaturated heterocycle 34, an attempt was made to synthesize the partially saturated cyclopenta[t]-l, 2-diazcpine, which then could be dehydrogenated to the 5,6-diazaazulene 34. However, this approach by starting with a 1,2-diazepine ring 36 (made successfully by following published method) and its [3+2] palladium-catalyzed cycloaddition with allyl chlorosilane 35 to the bicyclic diazepine 37 failed (Scheme 8). 

Szabo, K. J. Effects of 3-Substituents and Ancillary Ligands on the Structure and Stability of (T -Allyl)palladium Complexes. Implications for the Regioselectivity in Nucleophilic Addition Reactions. J. Am. Chem. Soc. 1996, 118, 7818-7826. 

Szabo, K. J. Nature of the interaction between 3-substituents and the allyl moiety in (T -allyl)palladium complexes. Chem. Soc. Rev. 2001, 30, 136-143. 

In chapter 19 we discussed the uses of palladium allyl cation complexes as electrophiles. We established that Pd(0) adds to the opposite face of the allylic system to the leaving group232 to form an t 3 cation complex 233 and that the nucleophile attacks from the opposite face to the Pd so that the two inversions lead to retention. We established that regioselectivity and diastereoselectivity can be well controlled. If this seems unfamiliar we suggest you read the relevant section of chapter 19 before proceeding. 

Synthesis of All-t/a/is-Geranylgeraniol. The type of alkylation described above for the synthesis of bacillariolide III is widely used in the synthesis of natural products due to the mild reaction conditions and high stereospecificity. The formation of the C-C bond takes place when activated a-sulfonyl car-banions derived from (3-ketosul tones, a-sulfonyl sulfones or, less often, allylic sulfones react with the H-allyl palladium complex. In the synthesis of all-trans-geranylgeraniol, the a-sulfonyl carbanion adds to the Ti-allylpalladium complex of 2-(prop-l-en-2-yl)oxirane. Final reductive desulfonylation affords the desired compound, as depicted in Eq. 147.254... 

In 1968, van Helden and co-workers studied the corresponding carbopalladation reaction of 1,2-propadiene with the 7r-allylpaUadium species 5, affording ri -(2- 2 -alkenyl)allyl)palladium complex 6 (Scheme 3).f t Similar results were observed by Hughes and Powell. The rate-determining step for these insertion reactions is the actual insertion step, not the coordination of the 1,2-diene onto Pd. ... 

The reaction of [Cp2Ta(=CH2)CH3] with the palladium allyl complex [CpPd(T]3-C3H5)] afforded 23 [Cp2Ta(ll-CH2)2PdCpl with loss of one equivalent of propene. 

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