Oxygen-Containing Multi-dentate Ligand-based Rare Earth Complexes And Their Catalytic Toward The Ring-Opening Polymerization

The reaction between sodium salt of 2,2'-ethylidene-bis(4,6-di-tert-butylphenol)(EDBPH₂) and lanthanide borohydride performed smoothly to give discrete ion-paircomplexes [Ln(EDBP)₂(DME)Na(DME)₃] [Ln=Er, Yb, Sm]. These complexes werecharacterized by elemental analysis and FT-IR, and the bonding model was confirmedby X-ray single crystal diffraction for complex Er. It was found that four O atoms intwo biphenol ligands as well as two O atoms in one molecule of ethylene glycoldimethyl ether (DME) connect to the central rare earth metal while sodium exists ascounterpart cation to balance the charge. [Ln(EDBP)₂(DME)Na(DME)₃] can all beused as single component initiators for polymerization ofε-CL and DTC.The ratio of [monomer]/[Ln], temperature and time effect were also investigated. Itwas found that larger metal radius favored the polymerization which could beattributed to stronger coordination capability of the monomer to the rare earth center,resulting in relative higher polymerization efficiency (Yb＜Er＜Sm). When complexSm was employed as initiator, at the some condition(65℃, [CL]/[Sm]=400, 4h), theMn of PCL is 3.8×10⁴ with conversation of 61% , while for that of PDTC was8.1×10⁴ and 89%. The polymers were characterized by FT-IR, DSC and GPC, and theT_m of PCL was at 58℃and PDTC was at 116℃. ¹H-NMR suggested that thepolymerization ofε-CL underwent acyl-oxygen cleavage mechanism and no CO₂elimination was found in the polymerization of DTC. The polymerization ofε-CLshowed some characteristic of living polymerization.A new 6,6'-methylenebis(4-chloro-2-isopropyl-5-methylphenol) (MCIMPH₂) basedytterbium complex [Yb(MCIMP)₂(DME)Na(DME)₃] was also synthesized, whichshowed no activity for polymerization of 8-CL. Besides, two kinds of schiff base,[6,6'-(1E, 1 'E)-(1,2-phenylenebis(azan-1 -yl-1 -ylidene))bis(methan-1 -yl-1 -ylidene)bis(2,4-di-tert-butylphenol)],[6,6'-(1E, 1'E)-(cyclohexane-1,2-diylbis(azan-1 -yl-1 -ylidene))bis(methan-1-yl-1-ylidene)bis(2,4-di-tert-butylphenol)] were tried to prepare tworare-earth complexes which showed no activities toward polymerization.