Roles of Monomer Binding and Alkoxide Nucleophilicity in Aluminum-Catalyzed Polymerization of ε<b>-</b>Caprolactone
作者:Keying Ding、Maria O. Miranda、Beth Moscato-Goodpaster、Noureddine Ajellal、Laurie E. Breyfogle、Eric D. Hermes、Chris P. Schaller、Stephanie E. Roe、Christopher J. Cramer、Marc A. Hillmyer、William B. Tolman
DOI:10.1021/ma301130b
日期:2012.7.10
The kinetics of polymerization of epsilon-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, (L-R)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 (K-eq) and insertion (k(2)) events in the ring-opening polymerization process. Analysis of the effects of the substituent R as a function of temperature on both K-eq and k(2) yielded thermodynamic parameters for these steps. The rate constant k(2), related to alkoxide nucleophilicity, was strongly enhanced by electron-donating R substituents, but the binding parameter K-eq 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.
Electronic influence of ligand substituents on the rate of polymerization of ε-caprolactone by single-site aluminium alkoxide catalysts
作者:Luis M. Alcazar-Roman、Brendan J. O'Keefe、Marc A. Hillmyer、William B. Tolman
DOI:10.1039/b303760f
日期:——
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