Equilibria between Palladium(II) Acetate and Olefins in Acetic Acid containing Sodium Acetate

Abstract

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.

Selective and efficient oxidation of ethylene to ethylene glycol acetates with H2O2 catalyzed by Pd(OAc)2–di(2-pyridyl)ketone–di(2-pyridyl)methanesulfonate system

“…Altogether, these observations suggest that a possible reason for low activity of complexes 1, 2 and 3 in ethylene oxidation might be their relative kinetic inertness in ethylene coordination. Table 5 The ratio of the initial rates of the formation of glycol derivatives (V 0,EG ) and Wackertype products (V 0,W ) at various concentrations of Pd(OAc) 2 Based on these facts, we propose that both Wacker-type oxidation and glycol formation in our catalytically active systems (all entries in Table 3 except 1, 2 and 7) proceed via initial ethylene coordination to palladium acetate and acetoxypalladation to form a transient 10 (Scheme 5, steps i, ii), similar to the mechanism proposed for ethylene oxidation by Pd(OAc) 2 to produce vinyl acetate [2,43].…”

“…Detailed studies of these equilibria have previously been reported in the literature [2,43]. Modest broadening of the ethylene peak (half-width ca 2.5 Hz) was also observed in the absence of H 2 O 2 in solutions of the most catalytically active dpk-or dpk/Me-dpms-based systems listed in Table 3.…”

Palladium(II) Catalyzed Exchange Reactions. XI. Vinyl Propionate Exchange with Acetic Acid Catalyzed by Palladium(II) Acetate

“…The sources and methods of purification of most reagents, as well as preparation of stock solutions, has been described previously (2,3). The vinyl propionate (Aldrich Chemical Company) was distilled before use.…”

“…The interaction of olefins with the dimer, Na2Pd2(OAc),, has also been studied (3). In this case two equilibria were detected, one which attained equilibrium rapidly and a second slow equilibrium.…”

“…One problem in defining, this term is that no interaction between the trimer and vinyl propionate could be detected spectroscopically so equilibrium studies could not be carried out. This follows from the fact that vinyl esters are poor at complexing Pd(I1) as compared with allylic esters or ordinary monosubstituted olefins such as styrene (3). The reaction is zero-order [NaOAc] and requires an induction period to form a catalytically active species which is presumably an olefin n-com~lex.…”