Palladium(I1) acetate in acetic acid in the absence of acetate ion exists as the trimeric species Pd,(OAc),. The reaction of the trimer with NaOAc o r LiOAc at 25" was not instantaneous. Spectral studies on fully equilibrated systems indicated the first equilibria involved transformation of trimer to dimer . This rate expression is consistent with substitution processes suggesting the slow step of the reaction is the S N 2 attack of solvent or acetate on a Pd(I1)-acetate bond to break one of the acetate bridges.In the NaOAc system conversion of trimer to dimer was complete at 0.2 M NaOAc. Further addition of NaOAc caused the dimer to be converted to monomer. L'acetate de palladium(I1) dans I'acide acetique, en l'absence d'ions acetate, existe sous la forme d'un trimere Pd3(OAc)6. La reaction du trimere avec NaOAc ou LiOAc a 25" n'ktait pas instantanee. Des etudes spectrales sur des systemes completement equilibrts indiquaient que le premier equilibre impliquait la transformation du trimere en dimere. Dans le cas du systeme NaOAc, la conversion du trirnere en dimere etait complete a 0.2 M NaOAc. Une nouvelle addition de NaOAc provoquait la conversion du dirnere en monomere.KZl tgale 7.6 x M-' a 25 "C. [Traduit par le journal]Can. J. Chem., 52, 1241 (1974)

π-Complex equilibria between dimeric Pd(II) acetate and various olefins (ethylene, styrene, 3,3-dimethyl-1-butene, vinylic and allylic esters) in acetic acid solvent have been investigated by spectral means. The results indicate two π-complexes are formed. The first π-complex, which is formed rapidly, is a dimeric π-complex (ol = olefin ).[Formula: see text]The Benesi–Hildebrand plots for these complexes are linear for all olefins and thus values of Kπ22 can be readily evaluated. The values of the equilibrium coefficient, Kπ22, do not change with solution composition or [NaOAc]. The second π-complex is formed slowly. The data are consistent only with the equilibrium[Formula: see text]The data are inconsistent with the equilibrium[Formula: see text]which is analogous to that reported for the Na2Pd2Cl6 reaction with olefins in acetic acid. Furthermore, previous assumptions as to the equilibria between ethylene and Pd(II) in the all-acetate system have proved incorrect, and so the kinetics of oxidation of ethylene in this system must be reinterpreted in view of the present results.

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. Can. J. Chem. 53,2223Chem. 53, (1975. The kinetics of the palladium(I1) acetate catalyzed exchange of vinyl propionate with acetic acid solvent to give vinyl acetate has been studied in the sodium acetate concentration range from 0 to 1 M. The exchange rate first sharply increases as [NaOAc] increases, reaches a maximum at about 0.2 M and then gradually decreases as the sodium acetate concentration is increased to 1.0 M. Using previous results on the equilibrium between palladium(I1) acetate and sodium acetate in acetic acid it can be shown that the rate expression for exchange is: rate =, and kd = 0.089 M-' s-'. A monomeric palladium(I1) species, Na2Pd(OAc),, formed at high [NaOAc] is unreactive. Since the rate expression does not contain a term in [NaOAc], the sodium acetate serves only to convert one palladium(I1) species to another. The lack of a [NaOAc] term in the rate expression for the Na2Pd2(OA~)6 catalyzed reaction is believed to result from cancellation of an inhibitory term for x-complex formation by a catalytic term in [NaOAc] in the rate determining conversion of rr-complex to a-complex (acetoxv~alladation). Stereochemical studies indicate that acetox~~alladation is nonstereospecific. h i s result 'is expected since in the chloride free system a&te is both a ligand and a reactant. Thus it can attack from both inside and outside the coordination sphere of Pd(I1).