Palladium acetate-tertiary phosphine

Dimerization(46,47) with a palladium acetate/tertiary phosphine complex (di-ace tate-bis--[ tri-phenyl phosphine] palladium) in the absence of air gives primarily the desired linear dimer with smaller amount of branched, cyclic, and heavy product (Equation 13.). The reaction product is a complex mixture of cis and trans geometric isomers which makes analysis difficult. In order to simplify this problem, the product analysis is made after hydrogenation over 5% palladium on carbon. 

The use of palladium and ruthenium as halogen-free carbonylation catalysts has been studied intensively by Shell. The catalysts were principally designed for the carbonylation of olefins in the presence of alcohols in order to yield carboxylic esters [26], but work also well for the synthesis of carboxylic acids or anhydrides. The latter are formed when the reaction is conducted in an acid as a solvent [27]. The palladium systems typically consist of palladium acetate, tertiary phosphines, and strong acids such as mineral acids or acids with weak or noncoordinating anions such as p-toluenesulfonic acid. Remarkable activities are achieved when aromatic phosphines that carry pyridines as substituents are... 

Palladium(II) acetate-tertiary phosphine-carbon monoxide. 

Ligands of similar size but increasing basicity, for a given series of palladium acetate tertiary monodentate phosphines solubilized in isoquinoline, lead to improved nondi-enoate ester yields in the order ... 

Palladium(II) acetate - tertiary phosphine - carhon monoxide. 

In high polarity solvents, such as acetonitrile, dimethyl sulfoxide, methyl acetate, and methanol, the branched dimer, 4-methyl azelate precursor, is formed in high yield. In methanol, a methoxy dimer (CH302CCgH] 4(0013)0020113) is also formed in moderate yield. Heavies contain both an acyclic methyl, 4-pentadienoate trimeric product and high molecular weight methyl, 4-pentadienoate homopolymer. Polymerization in the absence of air(48) appears to be catalyzed by traces of the tertiary phosphine which is used to prepare the palladium dimerization catalyst. 

Under optimum reaction conditions (See Table IV.), selectivity to linear dimer is controlled by the choice of temperature, solvent and tertiary phosphine. Toluene and tetrahydrofuran are the best solvents. Temperatures between 25 to 60 C with a triphenyl or tributylphosphine/palladium acetate catalyst give linear dimer selectivities in the 80 s. At 25 C in toluene, a palladium acetate/tributylphosphine catalyst gave 98.7% conversion and 89.6% linear, 4.7% branched, 1.9% cyclic, and 3.8% heavies selectivity. The linear dimerization reaction was second order in diene with a 3.6 Kcal/mole activation energy. 

The reaction is catalyzed by a group VIII metal species, particularly that of rhodium or palladium. The initial metal species may be any variety of complexes (e.g., PdCl2 Pd acetate, etc.). A source of halide is necessary iodide is especially effective. The most convenient source is methyl iodide, since it is likely a reaction intermediate. In addition, an organic promoter must be included for catalytic activity. These promoters are generally tertiary phosphines or amines. Also, chromium complexes were found to have an important promotional effect. 

Vinyl iodides are considerably more reactive than bromides in the vinylations. It may be presumed that chlorides are not generally useful, with one exception noted below, since they have not been employed in the reaction. The bromides are usually reacted with a palladium acetate-triphenyl- or tri-o-tolyl-phos-phine catalyst at about 100 C. The reaction will occur without the phosphine if a secondary amine is present. Vinyl iodides will react in the absence of a phosphine even with only a tertiary amine present.48 37 The iodides are so reactive, in fact, that reactions occur even at room temperature if potassium carbonate is the base and tetra-zi-butylammonium chloride is used as phase transfer agent in DMF solution when palladium acetate is the catalyst.88... 

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