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6592918 
Journal Article 
Iron Complexes for Cyclic Carbonate and Polycarbonate Formation: Selectivity Control from Ligand Design and Metal-Center Geometry 
Andrea, KA; Butler, ED; Brown, TR; Anderson, TS; Jagota, D; Rose, C; Lee, EM; Goulding, SD; Murphy, JN; Kerton, FM; Kozak, CM; , 
2019 
Yes 
Inorganic Chemistry
ISSN: 0020-1669
EISSN: 1520-510X 
AMER CHEMICAL SOC 
WASHINGTON 
58 
16 
11231-11240 
English 
31369254 
WOS:000482173300089 
A family of 17 iron(III) aminobis(phenolate) complexes possessing different phenolate substituents, coordination geometries, and donor arrangements were used as catalysts for the reaction of carbon dioxide (CO2) with epoxides. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of the iron complexes with a bis(triphenylphosphine)iminium chloride cocatalyst in negative mode revealed the formation of six-coordinate iron "ate" species. Under low catalyst loadings (0.025 mol % Fe and 0.1 mol % chloride cocatalyst), all complexes showed good-to-excellent activity for converting propylene oxide to propylene carbonate under 20 bar of CO2. The most active complex possessed electron-withdrawing dichlorophenolate groups and for a 2 h reaction time gave a turnover frequency of 1240 h-1. Epichlorohydrin, styrene oxide, phenyl glycidyl ether, and allyl glycidyl ether could also be transformed to their respective cyclic carbonates with good-to-excellent conversions. Selectivity for polycarbonate formation was observed using cyclohexene oxide, where the best activity was displayed by trigonal-bipyramidal iron(III) complexes having electron-rich phenolate groups and sterically unencumbering tertiary amino donors. Those containing bulky tertiary amino ligands or those with square-pyramidal geometries around iron showed no activity for polycarbonate formation. While the overall conversions declined with decreasing CO2 pressure, CO2 incorporation remained high, giving a completely alternating copolymer. The difference in the optimum catalyst reactivity for cyclic carbonate versus polycarbonate formation is particularly noteworthy; that is, electron-withdrawing-group-containing phenolates give the most active catalysts for propylene carbonate formation, whereas catalysts with electron-donating-group-containing phenolates are the most active for polycyclohexene carbonate formation. This study demonstrates that the highly modifiable aminophenolate ligands can be tailored to yield iron complexes for both CO2/epoxide coupling and ring-opening copolymerization activity.