- Roles of monomer binding and alkoxide nucleophilicity in aluminum-catalyzed polymerization of ε - Caprolactone
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The kinetics of polymerization of ε-caprolactone (CL) initiated by aluminum-alkoxide complexes supported by the dianionic forms of N,N-bis[methyl-(2-hydroxy-3-tert-butyl-5-R-phenyl)]-N,N- dimethylethylenediamines, (LR)Al(Oi-Pr) (R = OMe, Br, NO2) were studied. The ligands are sterically similar but have variable electron donating characteristics due to the differing remote (para) ligand substituents R. Saturation kinetics were observed using [CL]0 = 2-2.6 M and [complex]0 = 7 mM, enabling independent determination of the substrate coordination (Keq) and insertion (k2) events in the ring-opening polymerization process. Analysis of the effects of the substituent R as a function of temperature on both Keq and k 2 yielded thermodynamic parameters for these steps. The rate constant k2, related to alkoxide nucleophilicity, was strongly enhanced by electron-donating R substituents, but the binding parameter Keq is invariant as a function of ligand electronic properties. Density functional calculations provide atomic-level detail for the structures of key reaction intermediates and their associated thermochemistries.
- Ding, Keying,Miranda, Maria O.,Moscato-Goodpaster, Beth,Ajellal, Noureddine,Breyfogle, Laurie E.,Hermes, Eric D.,Schaller, Chris P.,Roe, Stephanie E.,Cramer, Christopher J.,Hillmyer, Marc A.,Tolman, William B.
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experimental part
p. 5387 - 5396
(2012/09/22)
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- Electronic influence of ligand substituents on the rate of polymerization of ε-caprolactone by single-site aluminium alkoxide catalysts
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A series of novel five-coordinate aluminium mono alkoxide complexes supported by R1,R2BPBA (bis-3-R1-5-R2- phenoxymethyl-bisamine) ligands were synthesized to probe the effect of electronic variation in the supporting ligand on the rate of ε-caprolactone polymerization. Substitution on the aromatic position para to the phenoxide donor oxygen by tert-butyl, methoxy and bromo substituents furnished aluminium complexes that catalyzed the polymerization of ε-caprolactone at different rates. We propose that a subtle interplay between complex Lewis acidity and alkoxide nucleophilicity determines the overall rate of polymerization in these systems. The Royal Society of Chemistry 2003.
- Alcazar-Roman, Luis M.,O'Keefe, Brendan J.,Hillmyer, Marc A.,Tolman, William B.
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p. 3082 - 3087
(2007/10/03)
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