NDLI: Exceptionally high lactide polymerization activity of zirconium complexes with bridged diketiminate ligands

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Schaper, Frank El-zoghbi, Ibrahim Whitehorne, Todd J. J.
Description	Author Affiliation: El-Zoghbi I ( Département de chimie, Université de Montréal, Montréal, Québec H3C 3J7, Canada.)
Abstract	A cyclohexanediyl-bridged, bis(N-xylyl) diketiminate ligand , $(±)-C_{6}H_{10}(nacnac^{Xyl}H)_{2},$ $LH_{2}$ (Xyl = 2,6-dimethylphenyl), was obtained from the reaction of [(2,6-dimethylphenyl)amino]-pent-3-en-2-one first with Meerwein's salt, then with (±)-cyclohexanediamine . The reaction of the ligand with $Zr(NMe_{2})_{4}$ yielded $LZr(NMe_{2})_{2}.$ Protonation of the remaining diamide ligands with EtOH or $[H_{2}NMe_{2}]Cl$ yielded $LZr(OEt)_{2}$ and $LZrCl_{2},$ respectively. The latter complex was also obtained by the reaction of $LH_{2}$ first with nBuLi and then with $ZrCl_{4}(THF)_{2}.$ The dichloride complex yielded $LZr(OEt)_{2}$ and $LZrMe_{2}$ upon reaction with NaOEt or MeLi / AlMe $_{3}$ , respectively. X-ray diffraction studies showed a trans-configuration of the ancillary ligands in $LZrCl_{2}$ and $LZrMe_{2},$ and a cis-configuration in $LZr(NMe_{2})_{2}$ and $LZr(OEt)_{2}.$ $LZr(OEt)_{2}$ was tested as a catalyst for the polymerization of rac- lactide . Kinetic investigations yielded a rate law first order in catalyst and monomer and a rate constant k = 14(1) L $mol^{−1}$ $s^{−1},$ the latter being orders of magnitude higher than typical activities for group 4 complexes in lactide polymerization . Analyses of the obtained polymer revealed an atactic polymer and broad polymer molecular weight distributions with sizeable fractions of cyclic oligomers. The influence of contaminants on the polymerization activity was examined: while lactic acid deactivates the catalyst , addition of up to 1 equiv. of water or para-toluenesulfonic acid revitalized catalysts not showing maximum activity.
ISSN	14779226
Issue Number	25
Volume Number	42
e-ISSN	13645447
Journal	Dalton Trans.
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2013-07-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Dioxanes Chemistry Imines Nitriles Organometallic Compounds Zirconium Catalysis Kinetics Ligands Models, Molecular Molecular Structure Chemical Synthesis Polymerization Journal Article Research Support, Non-U.S. Gov't
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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