Mechanism of CO oxidation by oxygen in the presence of palladium(ii) bromide complexes: a quantum chemical modeling

Abstract

Mechanisms of CO oxidation by oxygen in the PdBr2-LiBr-MeCN-H2O system in the absence and in the presence of iron(ii) phthalocyaninate (PcFe) as co-catalyst were studied within the framework of the density functional theory with the PBE functional. According to calculations, palladium(ii) bromide complexes most likely occur as Pd(AN)(CO)Br2 (AN is acetonitrile), Pd(CO)2Br2, and [Pd(CO)Br3]−. From the results of calculations it follows that neutral complexes Pd(AN)(CO)Br2 and Pd(CO)2Br2 can be highly catalytically active in the CO oxidation. Insertion of O2 into the Pd-H bond in the hydride complexes is the rate-limiting step of the CO oxidation reaction proceeding in the absence of PcFe as co-catalyst. Iron(ii) phthalocyaninate present in the reaction system causes a noticeable decrease in the activation energy of regeneration of the PdII complexes due to more efficient activation of O2. The oxidation of palladium hydride complexes by iron superoxophthalocyaninate can follow two routes that differ in the fashion of hydride transfer.