Molecular design and catalytic performance evaluation of Rh(I)-2,2′-bipyridine-3,3′-dicarboxylic acid catalyst with asymmetric bidentate structure

Abstract

In this study, an electron-donating 2,2′-bipyridine-3,3′-dicarboxylic acid(H2bpdc) ligand through the theoretical study of the catalytic reaction has been designed, and then Rh(I)− 2,2′-bipyridine-3,3′-dicarboxylic acid (Rh(I)-H2bpdc) catalyst of methanol carbonylation has been synthesized as well. It was found that after H2bpdc replaced I of the industrial RhI catalyst, the Rh(I)-H2bpdc catalyst with an asymmetric double-serrate seven-membered ring coordination structure is formed. Because of the asymmetric structure of the catalyst consisting of the H2bpdc ligand with an electron-donating group and Rh atom, which are beneficial to reduce the energy barrier of the rate-determining step in the catalytic reaction and improve the catalytic activity. Rh atom forms an asymmetric seven-membered ring ligand with N and O, in which the stronger Rh-N always "grabs" Rh in the catalytic reaction to prevent Rh atom forming precipitate and deactivation and ensure the stability of the catalyst. Also, the weaker Rh-O bond cooperates with the configuration change of the catalyst during the reaction, which is significantly beneficial to reduce the reaction energy barrier and improving the activity. The catalyst performance evaluation indicates that the catalyst exhibited superior catalytic performance on 3.5 MPa, 200 ℃, 6 wt% water and 54 wt% acetic acid, at which the yield of acetic acid is 96.73 %, no by-products are produced, no precipitate is formed on the reactor wall, and the amount of water is reduced, which helps to save energy and reduce costs in the later stage. Thus the catalyst molecule design effectively improves the success rate of catalyst research.