Exchange of organic radicals with organo-cobalt complexes formed in the living radical polymerization of vinyl acetate
Journal
Journal of the American Chemical Society
Journal Volume
130
Journal Issue
40
Pages
13373-13381
Date Issued
2008
Author(s)
Abstract
Exchange of organic radicals between solution and organo-cobalt complexes is experimentally observed and the reaction pathway is probed through DFT calculations. Cyanoisopropyl radicals from AIBN (2,2?? azobisisobutyronitrile) enter solutions of cobalt(II) tetramesityl porphyrin ((TMP)CoII,? 1) and vinyl acetate (VAc) in benzene and react to produce transient hydride (TMP)Co-H and radicals (?CH(OAc)CH 2C(CH3)2CN (R1?)) that proceed on to form organo-cobalt complexes (TMP)CO-CH(OAC)CH3 (4, Co-R 2) and (TMP)Co-CH(OAc)CH2C(CH3)2CN (3, Co-R1), respectively. Rate constants for cyanoisopropyl radical addition with vinyl acetate and hydrogen atom transfer to (TMP)Co II? are reported through kinetic studies for the formation and transformation of organo-cobalt species in this system. Rate constants for near-degenerate exchanges of radicals in solution with organo-cobalt complexes are deduced from 1H NMR studies and kinetic modeling. DFT computations revealed formation of an unsymmetrical adduct of (TMP)CO-CH(OAC)CH3 (4) with ?CH(OAc)CH3 (R 2?) and support an associative pathway for radical interchange through a three-centered three-electron transition state [R?CO?R]. Associative radical interchange of the latent radical groups in organo-cobalt porphyrin complexes with freely diffusing radicals in solution that is observed in this system provides a pathway for mediation of living radical polymerization of vinyl acetate. ? 2008 American Chemical Society.
Other Subjects
ABS resins;Chemical reactions;Cobalt;Free radical polymerization;Living polymerization;Monomers;Polymers;Polyvinyl acetates;Porphyrins;Sulfur compounds;Transition metals;Azo-bis-isobutyronitrile;Cobalt complexes;DFT calculations;Living radical polymerization;Organic radicals;Reaction pathways;Vinyl acetate;Solutions;azo compound;benzene;cobalt complex;hydrogen;nitrile;organic compound;porphyrin derivative;radical;vinyl acetate;article;atom transfer radical polymerization;chemical reaction kinetics;complex formation;density functional theory;diffusion;electron transport;polymerization;reaction analysis
Type
journal article