R 3-Allyl palladium

Four-membered cycloalkenes, into r]3-allyl palladium complexes, 8, 363 Four-membered rings with G-G bonds, 3, 703... 

Catalytic conversion of esters through the C-0 bond cleavage has been developed. Pd-catalyzed carbonucleophilic substitution of naphthylmethyl and 1-naphthylethyl esters has been achieved as shown in Eq. 25 [65]. The ease of the naphthylalkyl-0 bond cleavage may be partly due to the stability of the naphthylmethyl entity that can form an r 3-allylic-palladium bond. 

Caution. (r)3-Allyl)(r)s-cyclopentadienyl)palladium is volatile and has an unpleasant odor. As the toxity is unknown, all manipulations should be carried out in an efficient hood. All solvents are dried over sodium metal and distilled under nitrogen. 

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. 

Allylic acetoxy groups can be substituted by amines in the presence of Pd(0) catalysts. At substituted cyclohexene derivatives the diastereoselectivity depends largely on the structure of the palladium catalyst. Polymer-bound palladium often leads to amination at the same face as the acetoxy leaving group with regioselective attack at the sterically less hindered site of the intermediate r 3-allyl complex (B.M. Trost, 1978). 

The selective synthesis of the 2-allyltetrazoles 55 by the three-component coupling reaction of the cyano compounds 54, allyl methyl carbonate 5b, and trimethylsilyl azide 42 was accomplished in the presence of Pd2(dba)3.CHCl3 and P(2-furyl)3 (Scheme 19) [55,56]. Most probably, the formation of (r)3-allyl)( ]5-tetrazoyl)-palladium complex 56 took place through [3 + 2] dipolar cycloaddition of 7r-allylpalladium azide 44 with the nitrile 54. The complex 56 thus formed would undergo reductive elimination to form the products 55. 

In addition to the ij3-allyl complexes of nickel, palladium, and platinum, we have also examined (i -allyl Rh and the (r)3-allyl)4M complexes of Zr, Mo, and W (70). The data for these complexes are collected in Table XI. 

The r)3-allylpalladium formate complex is considered as a model of the intermediate in a catalytic reductive cleavage of allylic formate or allylic acetate combined with formic acid to olefins. The r)3-allylpalladium formate was revealed to be decarboxylated to release olefins upon coupling of the produced palladium hydride with the r)3-allyl ligand (Eq. 7). 

Cleavage of the C-O bond in various allylic substrates by oxidative addition to M(0) species gives r 3-allylic complexes, which undergo nucleophilic attack to produce allylic compounds catalytically. A base is needed in most cases to remove HOX and to drive the catalytic cycle. There are a lot of synthetic reactions utilizing allylic oxygen bond cleavage catalyzed by palladium complexes [6, 7, 19-21]. 

The generally accepted mechanism for Pd-catalyzed allylic desulfonylations is illustrated in Scheme 1. The first step is coordination of the Pd(0) catalyst to the allylic sulfone. Oxidative addition or internal SN2-type nucleophilic attack of the electron-rich palladium at the allylic position generates a neutral Pd(II) r 3-allyl complex, which leads to a more reactive cationic complex that is finally reduced. The equilibrium between the neutral and the more reactive cationic complexes depends on the nature and concentration of the palladium ligands as well as the counter anions present in solution. 

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. 

On the other hand, when R = 3-allyl, the product [PdL2Cl2] is obtained, which i.r. studies show to contain an unco-ordinated olefinic group and unidentate bonding via the thiocarbonyl S. Also described is the synthesis of the new ligand H2(sacac)2(en), together with the preparation of the stable palladium complex... 

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... 

Palladium-catalyzed oxidation of 1,4-dienes has also been reported. Thus, Brown and Davidson28 obtained the 1,3-diacetate 25 from oxidation of 1,4-cyclohexadiene by ben-zoquinone in acetic acid with palladium acetate as the catalyst (Scheme 3). Presumably the reaction proceeds via acetoxypalladation-isomerization to give a rr-allyl intermediate, which subsequently undergoes nucleophilic attack by acetate. This principle, i.e. rearrangement of a (allyl)palladium complex, has been applied in nonoxidative palladium-catalyzed reactions of 1,4-dienes by Larock and coworkers29. Akermark and coworkers have demonstrated the stereochemistry of this process by the transformation of 1,4-cyclohexadiene to the ( r-allyl)palladium complex 26 by treatment... 

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