title: CO2/ethylene oxide copolymerization and ligand variation for a highly active salen-cobalt(III) complex tethering 4 quaternary ammonium salts.
abstract: A cobalt(III) complex (1) of a salcy-type ligand tethering 4 quaternary ammonium salts, which is thought to act as a highly active catalyst for CO2/propylene oxide (PO) copolymerization, also shows high activity (TOF, 25,900 h(-1); TON, 518,000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO2/ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers (M(n), 200,000-300,000) that have strictly alternating repeating units. The related cobalt(III) complexes 11-14 were prepared through variations of the ligand framework of 1 by replacing the trans-1,2-diaminocyclohexane unit with 2,2-dimethyl-1,3-propanediamine, trans-1,2-diaminocyclopentane, or 1,1'-binaphthyl-2,2'-diamine or by replacing the aldimine bond with ketimine. These ligand frameworks are thought to favour the formation of the cis-β configuration in complexation, and the formation of the cis-β configuration in 11-14 was confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the quaternary ammonium salts. Complexes 11, 13, and 14, which adopt the cis-β configuration even in DMSO did not show any activity for CO2/PO copolymerization. Complex 12, which was constructed with trans-1,2-diaminocyclopentane and fluctuated in DMSO between the coordination and de-coordination of the acetate ligand as observed for 1, showed fairly high activity (TOF, 12,400 h(-1)). This fluctuating behaviour may play a role in polymerization. However, complex 12 did not compete with 1 in terms of activity, selectivity, and the catalyst cost.
authors.affiliation: Department of Molecular Science and Technology, Ajou University, Suwon 443-749, South Korea.
authors.forename: Jong Yeob
authors.initials: JY
authors.lastname: Jeon
authors.forename: Jung Jae
authors.initials: JJ
authors.lastname: Lee
authors.forename: Jobi Kodiyan
authors.initials: JK
authors.lastname: Varghese
authors.forename: Sung Jae
authors.initials: SJ
authors.lastname: Na
authors.forename: S
authors.initials: S
authors.lastname: Sujith
authors.forename: Min Jeong
authors.initials: MJ
authors.lastname: Go
authors.forename: Junseong
authors.initials: J
authors.lastname: Lee
authors.forename: Myung-Ahn
authors.initials: MA
authors.lastname: Ok
authors.forename: Bun Yeoul
authors.initials: BY
authors.lastname: Lee
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D005027:Ethylene Oxide / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D058105:Polymerization; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012492:Salts / Q000737:chemistry
chemical_list: D005029:Ethylenediamines; D008024:Ligands; D009942:Organometallic Compounds; D000644:Quaternary Ammonium Compounds; D012492:Salts; D002245:Carbon Dioxide; D003035:Cobalt; C011452:disalicylaldehyde ethylenediamine; D005027:Ethylene Oxide