Benzimidazolylacetate metal complexes as catalysts for carbonylation reactions

Abstract

Eight metal–organic complexes were synthesized, characterized and evaluated as catalysts for the synthesis of phenylacetic acid. After tests on catalytic activity and catalyst recovery, two Co(II) complexes were proved to be good catalysts in the carbonylation reaction for their enhanced thermal stability and easy recovery from the reaction mixture. The novel catalysts show broad application prospects as they could be used in both homogeneous and two-phase catalytic systems. The catalytic stability of the complexes was also studied by performing consecutive batch runs with the same catalyst sample. The yield was reduced by 2 % first, then by 5 %. After the third batch, it was observed that the phenylacetic acid yield was reduced by less than 10 %, which indicated a high catalytic stability. Orthogonal tests were carried out to optimize experimental conditions. Moreover, the possible mechanism of the catalyzed carbonylation reaction was proposed. In the catalytic cycle, the cobalt complexes are first coordinated by carbon monoxide, and then are attacked by the electrophilic benzyl chloride, react with carbon monoxide afterwards, finally obtain the phenylacetic acid salt under alkaline conditions. During the catalytic cycle, the catalyzed carbonylation reaction has three transition states as carbonyl cobalt complexes, benzyl cobalt complexes and benzyl carbonyl cobalt complexes.