CO2 adducts of N-heterocyclic carbenes: Thermal stability and catalytic activity toward the coupling of CO2 with epoxides
Release Time:2019-03-10 Hits:
Indexed by: Journal Article
Date of Publication: 2008-10-17
Journal: JOURNAL OF ORGANIC CHEMISTRY
Included Journals: Scopus、ESI高被引论文、PubMed、EI、SCIE
Volume: 73
Issue: 20
Page Number: 8039-8044
ISSN: 0022-3263
Abstract: Thermal stability Of CO2 adducts of N-heterocyclic carbenes (NHCs) was studied by means of in situ FTIR method with monitoring of the v(CO2) region of the infrared spectra under various conditions. 1,3-Bis(2,6-diisopropylphenyl)imidazolinium-2-carboxylate(SIPr-CO2) shows higher thermal stability compared with 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (IPr-CO2) The presence of free CO2 can significantly inhibit the decomposition of NHC-CO2 adducts, while the addition of an epoxide such as propylene oxide has a negative effect on stabilizing these adducts. As zwitterionic compounds, NHC-CO2 adducts were also proved to be effective organic catalysts for the coupling reaction of CO2 and epoxides to afford cyclic carbonates, for which a possible mechanism was proposed. Among these NHC-CO2 adducts, the relatively unstable IPr-CO2 exhibits the highest catalytic activity. The presence of an electrophile such as SalenAIEt could greatly improve the catalytic activity of IPr-CO2 due to intermolecular cooperative catalysis of the binary components.