Nickel-Catalyzed Coupling of Carbon Dioxide with Cyclohexene Oxide by Well-Characterized Bis(N-Heterocyclic Carbene) Carbazolide Complexes

Ting Yu Lee, Yi Jen Lin, Yuan Zhen Chang, Li Shin Huang, Bao Tsan Ko, Jui Hsien Huang

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The facile synthesis, structural characterization, and catalytic studies for CO2/epoxide coupling of nickel acetates based on carbazolide-bis(NHC) (NHC = N-heterocyclic carbene) were reported. Treatment of 3,6-di-tert-butyl-1,8-bis(3-alkylimidazolium-1-yl)carbazole salt proligands (bis(R-Im-X)Cz, R = benzyl (Bn), n-butyl (nBu), methyl (Me), X = Br or I) with nickel acetate tetrahydrate in the presence of excess triethylamine generated monomeric four-coordinate nickel complexes [(bis(R-Im)Cz)Ni(OAc)] (R = Bn (3), R = nBu (4), and R = Me (5)). Single-crystal X-ray diffraction of Ni complexes 4 and 5 indicates that the bis(NHC)-carbazolide fragment behaves as a CNC-tridentate pincer ligand to coordinate the metal center, and the ancillary acetate group assumes a terminal acetate bonding mode. Catalysis for coupling of carbon dioxide with cyclohexene oxide (CHO) by these carbazolide-bis(NHC)-ligated Ni complexes was systematically examined. Experimental results displayed that cycloaddition of CHO and CO2 catalyzed with complex 4 could give cyclohexene carbonate (CHC) with >99% cis-isomer selectivity on using low catalyst concentrations and high reaction temperature, whereas catalyst 3 was able to copolymerize CHO and CO2 to afford a narrowly dispersed and perfectly alternating poly(cyclohexene carbonate) (PCHC) as the major product at the higher catalyst loadings and lower copolymerization temperature. This is the first time that the air-stable bis(NHC)-carbazolide nickel(II) acetate is an effective and versatile catalyst for the formation of either biodegradable PCHCs or cis-CHCs.

Original languageEnglish
Pages (from-to)291-297
Number of pages7
JournalOrganometallics
Volume36
Issue number2
DOIs
Publication statusPublished - 2017 Jan 23

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All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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