title: Synthesis of γ-amidine-functionalized dianionic β-diketiminato lanthanide amides and trianionic β-diketiminato Na/Sm heterobimetallic complexes and their reactivity in polymerization of L-lactide.
abstract: The readily accessible dianionic β-diketiminato lanthanide amido complexes LnLN(SiMe3)2(THF) (L = {(2,6-(i)Pr2C6H3)NC(CH2)CHC(CH3)N(2,6-(i)Pr2C6H3)}(2-)) show an unprecedented reactivity toward carbodiimides. The reaction with N,N'-dicyclohexylcarbodiimide (DCC) led via [4 + 2] cycloaddition to γ-amidine-functionalized dianionic β-diketiminato lanthanide amido complexes, LnL(1)N(SiMe3)2 (L(1) = {[(NHC6H11)(NC6H11)C]HC[C(CH2)N(2,6-(i)Pr2C6H3)]2}(2-), Ln = Sm(1), Yb(2), Y(3), Gd(4)). Conversion of a mixture of SmLN(SiMe3)2(THF) and NaN(SiMe3)2 with carbodiimide furnished the heterobimetallic complexes of Sm/Na with a novel amidinate-functionalized trianionic β-diketiminate ligand, [Na(DME)2](μ-L(2))[SmN(SiMe3)2] (L(2) = {[C(N(i)Pr)2]HC[C(CH2)N(2,6-(i)Pr2C6H3)]2}(3-), DME = dimethoxyethane) (5) for N,N'-diisopropylcarbodiimide (DIC) and [Na(DME)3](+)[SmL(3)N(SiMe3)2](-) (L(3) = {[C(NCy)2]HC[C(CH2)N(2,6-(i)Pr2C6H3)]2}(3-)) (6) for DCC. Molecular structures of complexes 1-6 were determined by an X-ray single crystal structure analysis. Complexes 1-4 were found to be highly active initiators of the ring-opening polymerization (ROP) of L-lactide (L-LA). The activity depended on the central metal with the increasing sequence of Yb < Y < Gd < Sm. Notably, the binary 1/BnOH (benzyl alcohol) system exhibited an "immortal" nature and proved able to convert 2000 equivalents of L-LA with up to 100 equivalents of BnOH per initiator. All the polylactides (PLAs) obtained showed monomodal, narrow molar mass distributions (M(w)/M(n) = 1.08-1.13) with the M(n) (average number molar mass) decreasing with increasing amount of BnOH proportionally.
authors.affiliation: Key Laboratory of Organic Synthesis of Jiangsu Province, Department of Chemistry and Chemical Engineering, Dushu Lake Campus, Soochow University, Suzhou 215123, People's Republic of China. qshen@suda.edu.cn.
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.forename: Hongxia
authors.initials: H
authors.lastname: Chen
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Mingqiang
authors.initials: M
authors.lastname: Xue
authors.forename: Yingming
authors.initials: Y
authors.lastname: Yao
authors.forename: Qi
authors.initials: Q
authors.lastname: Shen