Homolysis of the Ln–N bond: Synthesis, characterization and catalytic activity of organolanthanide(II) complexes with furfuryl- and tetrahydrofurfuryl-functionalized indenyl ligands

Metal catalysts for ε-caprolactone polymerisation

“…The mechanism of formation was thought to involve a reductive elimination step that is not observed when reacting a Ln(III) starting material with an unsubstituted indenyl ligand. 47,48 When Ln ¼ Sm or Nd, the Ln(III) complexes 30 and 31 (Chart 7) were obtained from the same reaction rather than Ln(II) complexes; their formation pathway involved a silylamine elimination followed by a ligand redistribution. 49,50 The catalytic activity of these organolanthanide complexes depended strongly on the nature of the substituents on the indenyl moiety.…”

Developments in the Coordination Chemistry of Europium(II)

“…[12,78–80] With these catalysts, high activity is observed at high temperatures (0 to 30 °C for complexes 75 and 76 ; −30 to 60 °C for complex 74 ; 0 to 60 °C for complex 77 ; and 30 to 60 °C for complexes 78 and 79 ), and the activities of these complexes depend on the solvent. Complexes 77 – 79 have high activities when THF or toluene is the solvent; complex 74 exhibits high activity in dimethoxyethane, THF, and toluene, and 75 and 76 show good activity in toluene.…”

“…However, it is not clear what the role of the silyl substituent is in the polymerization process. [78] The use of more sterically bulky ligands in 79 relative to the ligands in 78 has been implicated to affect the chain propagation process, thus affecting the molecular weights of the polymers. [80] Wang and co-workers proposed that the polymerization of ε-caprolactone is initiated by the formation of Eu 3+ -containing alkoxyl radical species formed from the oxidation of the Eu 2+ metal center (Scheme 2).…”

“…Eu 2+ ‐containing complexes 74 – 79 , which contain indenyl, fluorenyl, and iminopyrrolyl ligands, showed catalytic activity in the ring‐opening polymerization of ϵ‐caprolactone 12,78–80. With these catalysts, high activity is observed at high temperatures (0 to 30 °C for complexes 75 and 76 ; –30 to 60 °C for complex 74 ; 0 to 60 °C for complex 77 ; and 30 to 60 °C for complexes 78 and 79 ), and the activities of these complexes depend on the solvent.…”

“…When the silyl substituent in the furfuryl‐ or tetrahydrofurfuryl‐functionalized indenyl ligands of complexes 75 and 76 was absent, the two complexes were not active. However, it is not clear what the role of the silyl substituent is in the polymerization process 78. The use of more sterically bulky ligands in 79 relative to the ligands in 78 has been implicated to affect the chain propagation process, thus affecting the molecular weights of the polymers 80.…”