Bifunctional Porphyrin Catalysts for the Synthesis of Cyclic Carbonates from Epoxides and CO: Structural Optimization and Mechanistic Study.
We prepared bifunctional Mg porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO. The activities of Id, lh, and li, which have Br , Cl, and I counteranions, respectively, increased in the order li < lh < Id. Catalysts Id and l j—m, which bear four tetraalkyl...
| Publicado en: | Journal of the American Chemical Society Vol. 136; no. 43; pp. 15270 - 15280 |
|---|---|
| Autores principales: | , , , , |
| Formato: | Artículo |
| Publicado: |
American Chemical Society
10/29/2014
|
| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=99619324&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 99619324 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 10/29/2014 vid: 136 iid: 43 pid: 997 pub: American Chemical Society artinfo: ui: 99619324 10.1021/ja507665a ppf: 15270 ppct: 10 formats: tig: atl: Bifunctional Porphyrin Catalysts for the Synthesis of Cyclic Carbonates from Epoxides and CO: Structural Optimization and Mechanistic Study. aug: au: Tadashi Ema Yuki Miyazaki Junta Shimonishi Chihiro Maeda Jun-ya Hasegawa affil: Division of Chemistry and Biotechnology, Graduate School of Natural Science and Technology, Okayama University, Tsushima, Okayama 700-8530, Japan Catalysis Research Center, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo 001-0021, Japan su: Bifunctional catalysis Catalysis Porphyrins Biological pigments Carbonates sug: subj: Bifunctional catalysis Catalysis Porphyrins Biological pigments Carbonates ab: We prepared bifunctional Mg porphyrin catalysts 1 for the solvent-free synthesis of cyclic carbonates from epoxides and CO. The activities of Id, lh, and li, which have Br , Cl, and I counteranions, respectively, increased in the order li < lh < Id. Catalysts Id and l j—m, which bear four tetraalkylammonium bromide groups with different alkyl chain lengths, showed comparable but slightly different activities. Based on the excellent catalyst Id, we synthesized Mg11 porphyrin lo with eight tetraalkylammonium bromide groups, which showed even higher catalytic activity (turnover number, 138,000; turnover frequency, 19,000 h”1). The catalytic mechanism was studied by using Id. The yields were nearly constant at initial CO pressures in the 1—6 MPa range, suggesting that CO was not involved in the rate-determining step in this pressure range. No reaction proceeded in supercritical CO, probably because the epoxide (into which the catalyst dissolved) dissolved in and was diluted by the supercritical CO. Experiments with lsO-labeled CO and D-labeled epoxide suggested that the catalytic cycle involved initial nucleophilic attack of Br on the less hindered side of the epoxide to generate an oxyanion, which underwent CO insertion to afford a CO2 adduct; subsequent intramolecular ring closure formed the cyclic carbonate and regenerated the catalyst. Density functional theory calculations gave results consistent with the experimental results, revealing that the quaternary ammonium cation underwent conformational changes that stabilized various anionic species generated during the catalytic cycle. The high activity of Id and lo was due to the cooperative action of the Mg and Br and a conformational change (induced-fit) of the quaternary ammonium cation. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2014 holdings: @attributes: islocal: N |
|---|