Assessment of four rhodium(I) complexes bearing SNS ligands for the catalytic reaction of chemical CO2 conversion to obtain cyclic carbonates

Abstract

SNS pincer type ligands (L1-L4) were metallized with RhCl(PPh₃)₃, yielding new SNS type Rh(I) complexes. Different techniques, including ³¹P NMR, UV–Vis, XPS, mass, elemental analysis, molar conductivity, and FT-IR were used to analyze the synthesized compounds. According to the spectral data, the molecular structure of Rh(I) complexes has a four-coordinated square planar geometry around the metal center. The complexes’ lack of conductivity properties demonstrates their non-electrolyte nature in solution. The novel SNS-type Rh(I) complexes efficiently catalyzed the coupling of a variety of epoxides and CO₂ to create cyclic carbonates in the presence of DMAP as a Lewis base. Diverse cyclic carbonates were also synthesized under ideal conditions with good to perfect yields (2 h, 1.6 MPa, and 100 °C). Following the discovery of new SNS-type Rh(I) catalysts with outstanding catalytic performance, epoxide, the impact of the reaction time, base, CO₂ pressure, and temperature was examined for these catalysts. The complex L3-Rh and DMAP displayed the highest catalytic activity (89.6 %) and selectivity (99.4 %) for the coupling of CO₂ and ECH under optimum conditions (100 °C, 2 h, and 1.6 MPa).