On the intermediacy of chlorinated alkylcobalt complexes in the reductive dehalogenation of chloroalkenes.: A first-principles molecular dynamics study

According to constrained Car - Parrinello molecular dynamics (CPMD) simulations and thermodynamic integration, the free energy for protonation of a reduced cobaloxime PCE complex, [Co(Hgly)(2)(PCE)](-)(Hgly = glyoximato, PCE = tetrachloroethylene), to form the chlorinated ethylcobalt species Co(Hgly)(2)(CCL2CCL2H)(H2O) is at least - 10 kcal/mol in aqueous solution (employing the BP86 density functional), with an upper limit of ca. 18 kcal/mol for the free-energy barrier of this process. Because this activation barrier is lower than those computed previously for chloride elimination from PCE complexes (affording chlorinated vinylcobalt species), and because it had been shown computationally that chlorinated ethylcobalt complexes may decompose under formation of dechlorinated olefins (Pratt, D. A.; van der Donk, W. A. Chem. Commun. 2006, 558), chlorinated ethylcobalt complexes are indeed viable and likely intermediates in the reductive dehalogenation of chlorinated olefins, as it is catalyzed, for example, by vitamin B-12.