Co(II)-N4 Catalysts for the Coupling of CO2 with Epoxides into Cyclic Carbonates: Catalytic Activity, Computational and Kinetic Studies

Bingyang Wang; Xuanyu Cao; Lixian Wang; Xiangyun Meng; Yong Wang; Wei Sun

doi:10.1021/acs.inorgchem.4c00461

Co(II)-N4 Catalysts for the Coupling of CO₂ with Epoxides into Cyclic Carbonates: Catalytic Activity, Computational and Kinetic Studies

Inorg Chem. 2024 May 7. doi: 10.1021/acs.inorgchem.4c00461. Online ahead of print.

Authors

Bingyang Wang¹, Xuanyu Cao², Lixian Wang¹, Xiangyun Meng¹, Yong Wang², Wei Sun¹

Affiliations

¹ State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China.
² Institute of Drug Discovery Technology, Ningbo University, Ningbo 315211, China.

PMID: 38713454
DOI: 10.1021/acs.inorgchem.4c00461

Abstract

In this study, we synthesized and characterized a series of cobalt(II) complexes bearing linear tetradentate N4 ligands. These Co(II)-N4 complexes proved to be efficient catalysts for the cycloaddition reaction between carbon dioxide and epoxides even at room temperature and 1 bar pressure of carbon dioxide without the need for solvents or cocatalysts. Furthermore, when combined with (triphenylphosphoranylidene)ammonium chloride (PPNCl) as a cocatalyst, the Co-N4 catalysts exhibited an impressive turnover frequency of up to 41,000 h^-1 for coupling of epichlorohydrin/CO₂. These Co(II)-N4 catalysts were found to have excellent stability and reusability, retaining their catalytic activity after they were recycled seven times. Density functional theory (DFT) calculations provided a comprehensive mechanism for the cycloaddition reaction, indicating that the rate-determining step is the epoxide ring opening, in both the presence and absence of PPNCl. Further kinetic studies allow us to determine the activation parameters (ΔH^‡, ΔS^‡, and ΔG^‡ at 25 °C) of the coupling reaction using the Eyring equation. The Gibbs free activation energy obtained from the kinetic studies was in close agreement with that of the DFT calculations. The substituent effect on the cycloaddition reaction of CO₂ with various substituted styrene oxides was also examined for the first time.