Реферат: Formation of palladium superoxo complexes in the reactions of palladium(II) acetate, propionate, trifluoroacetate, and bis(acetylacetonate) and palladium(O) tetrakis(triphenylphosphine) with hydrogen peroxide and potassium superoxide has been detected in solution by EPR. According to EPR parameters the superoxo complexes observed fall into two main types. The g factor of type I complexes is closer to an axial symmetrical one than that of type II complexes. For type I complexes, g1 = 2.08-2.1, g2 = 2.01, and g3 = 2.001-2.002, and for type II complexes, g1 = 2.075-2.085, g2 = 2.027-2.04, and g3 = 2.006-2.01. The EPR spectrum of type I complexes resulting from the interaction of H2O2 with Pd(OAc)2 in CHCl3 has a hyperfine structure indicating coupling to one Pd nucleus: A1 Pd = 6.7 G, A2 Pd = 3.0 G, and A3 Pd = 4.5 G. Type I superoxo complexes appear to be characteristic of trimeric Pd species, formed by palladium(II) acetate and palladium(II) propionate in poorly coordinating solvents (chloroform and benzene), while type II superoxo complexes are characteristic of monomeric Pd species, formed by palladium(II) acetate and palladium(II) propionate in well-coordinating solvents (acetonitrile, dimethyl sulfoxide) and by palladium(II) trifluoroacetate, palladium(II) acetylacetonate, and palladium(O) tetrakis(triphenylphosphine) in poorly coordinating solvents. When prepared via interaction with KO2 in the presence of 18-crown-6 ether, the type I superoxo complex initially formed in palladium(II) acetate and palladium(II) propionate systems rapidly transforms to the more stable type II complex, presumably due to the destruction of the trimeric Pd species by the 18-crown-6 ether. Type I superoxo complexes are more reactive than those of type II. Type I complexes formed by palladium(II) acetate and palladium(II) propionate easily oxidize simple olefins and CO, while type II complexes are inert with respect to these compounds. The type I superoxo complex of palladium(II) acetate oxidizes ethylene to ethylene oxide, 1 ± 0.1 mol of ethylene oxide being formed per 1 ± 0.3 mol of the superoxo complex decomposed. No other products have been detected with NMR for this reaction. The same superoxo complex oxidizes propylene to propylene oxide and acetone in a 1:2 ratio, again no other products being detected with NMR. The reaction rates demonstrate the first-order dependences on concentration of both the superoxo complexes and the olefins. The pseudo-first-order rate constants, determined for reactions of palladium(II) acetate type I complex with various alkenes at 300 K in CHCl3 with a large excess of the alkenes (0.3 M) over the superoxo complex (0.005 M), are as follows: 103k = 2.3 s-1 (CH2=CH2); 5.1 s-1 (MeCH=CH2); 5.1 s-1 (Me2C=CH2); 1.2 s-1 (Me2C=CMe2). For the oxidation of CO by the same complex, the pseudo-first-order rate constants determined with a large excess of CO (concentration about 0.01 M, determined by solubility of CO at 1 atm) over the superoxo complex (3 × 10-4 M) at various temperatures are as follows: 103k = 9 s-1 (266 K); 2 s-1 (258 K); 1 s-1 (238 K); 0.6 s-1 (226 K). Quantum-chemical calculations suggest that for the monomeric Pd(acac)O2 complex η2-coordination of the O2 - ligand is energetically more advantageous than η1-coordination. On this ground η2-coordination can be assumed for relatively stable superoxo complexes of type II. g values for more reactive palladium superoxo complexes of type I are similar to those of cobalt superoxo complexes, which, according to X-ray data, have η1-coordination. On this basis η1-ccordination of the O2 - ligand can be assumed for palladium superoxo complexes of type I.

Библиографическая ссылка: Talsi E.P. , Babenko V.P. , Shubin A.A. , Chinakov V.D. , Nekipelov V.M. , Zamaraev K.I.
Formation, Structure, and Reactivity of Palladium Superoxo Complexes
Inorganic Chemistry. 1987. V.26. N23. P.3871-3878. DOI: 10.1021/ic00270a012 WOS Scopus РИНЦ CAPlusCA OpenAlex

Даты:

Поступила в редакцию:	9 сент. 1986 г.
Опубликована в печати:	1 нояб. 1987 г.
Опубликована online:	1 мая 2002 г.

Идентификаторы БД:

Web of science:	WOS:A1987L012800012
Scopus:	2-s2.0-25944472779
РИНЦ:	31358564
Chemical Abstracts:	1987:627828
Chemical Abstracts (print):	107:227828
OpenAlex:	W2080619977

Цитирование в БД:

БД	Цитирований
Web of science	13
Scopus	15
РИНЦ	15
OpenAlex	14

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