title: Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide.
abstract: Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h(-1) at 170 °C) at an initial CO2 pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides.
authors.affiliation: Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University, Tsushima, Okayama, 700-8530, Japan. cmaeda@okayama-u.ac.jp.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Maeda
authors.affiliation: Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University, Tsushima, Okayama, 700-8530, Japan.
authors.forename: Junta
authors.initials: J
authors.lastname: Shimonishi
authors.affiliation: Catalysis Research Center, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, 001-0021, Japan.
authors.forename: Ray
authors.initials: R
authors.lastname: Miyazaki
authors.affiliation: Catalysis Research Center, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, 001-0021, Japan. hasegawa@cat.hokudai.ac.jp.
authors.forename: Jun-Ya
authors.initials: JY
authors.lastname: Hasegawa
authors.affiliation: Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University, Tsushima, Okayama, 700-8530, Japan. ema@cc.okayama-u.ac.jp.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Ema
keywords: carbon dioxide fixation; cyclic carbonates; epoxides; homogeneous catalysts; porphyrinoids