title: Synthesis and characterization of new divalent lanthanide complexes supported by amine bis(phenolate) ligands and their applications in the ring opening polymerization of cyclic esters.
abstract: Treatment of an array of bis(phenol)s H2Lx {Lx = [(-OC6H2(2,4-R)(6-CH2))2 NCH2CH2X], where X = CH2NMe2, NMe2, NEt2, OMe and R = Bu(t), Pe(t) where Pe(t) = C(CH3)2Et} with [Ln(N(SiMe3)2)2(THF)2] (Ln = Yb, Sm) in a 1:1 molar ratio in hexanes afforded a multitude of new divalent lanthanide bis(phenolate) complexes: [L(2c)Yb]2 (X = NEt2, R = Bu(t)) 1, [L(2b)Yb]2 (X = CH2NMe2, R = Bu(t)) 2, [L(3a)Yb]2 (X = NMe2, R = Pe(t)) 3, [L(3b)Yb]2 (X = OMe, R = Pe(t)) 4, [L(2c)Sm] (X = NEt2, R = Bu(t)) 5, [L(3c)Yb] (X = NEt2, R = Pe(t)) 6, [L(3c)Sm] (X = NEt2, R = Pe(t)) 7. X-Ray crystallographic analyses of compounds 1 and 3 reveal dimeric, centrosymmetric structures with 5-coordinate ytterbium centers arising from bridging and terminal phenolate groups. A selection of divalent compounds (1, 3, 4, 5, 6 and 7) were tested as catalyst precursors in the polymerization of epsilon-caprolactone and/or L-lactide which resulted in high molecular weight polymers with PDIs of 1.11-2.81 and 1.13-1.56 for epsilon-caprolactone and L-lactide respectively. All polymerization studies were performed in either toluene or THF and at room temperature (epsilon-caprolactone) or 70 degrees C (L-lactide) at a variety of catalyst:monomer ratios (1:100-1:300). Kinetics analyses of the polymerization of L-lactide by compounds 1 and 5 indicated pseudo-first order response with respect to L-lactide.
authors.affiliation: Chemistry Department, University of North Dakota, Grand Forks, ND 58202, USA.
authors.forename: Divine T
authors.initials: DT
authors.lastname: Dugah
authors.forename: Brian W
authors.initials: BW
authors.lastname: Skelton
authors.forename: Ewan E
authors.initials: EE
authors.lastname: Delbridge
mesh_terms: D002413:Cations, Divalent; D004952:Esters / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*
chemical_list: D002413:Cations, Divalent; D004952:Esters; D028581:Lanthanoid Series Elements; D010636:Phenols; D011108:Polymers