CO2/ethylene oxide copolymerization and ligand variation for a highly active salencobalt(iii) complex tethering 4 quaternary ammonium saltsCCDC 894114, 894115 and 894116. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt31854g

• Main Authors: Jeon, Jong Yeob, Lee, Jung Jae, Varghese, Jobi Kodiyan, Na, Sung Jae, Sujith, S, Go, Min Jeong, Lee, Junseong, Ok, Myung-Ahn, Lee, Bun Yeoul
• Format: Journal Article
• Language: English
• Published: 04.06.2013
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c2dt31854g

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 CO 2 /propylene oxide (PO) copolymerization, also shows high activity (TOF, 25900 h 1 ; TON, 518000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO 2 /ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers ( M n , 200000300000) that have strictly alternating repeating units. The related cobalt( iii ) complexes 1114 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 - configuration in complexation, and the formation of the cis - configuration in 1114 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 - configuration even in DMSO did not show any activity for CO 2 /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, 12400 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. A highly active catalyst for CO 2 /propylene oxide copolymerization also shows high activity for CO 2 /ethylene oxide copolymerization and its derivatives were prepared through variations of the ligand framework.