Catalytic decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide in dichloromethane by a discrete cobalt(II) alkoxide species generated in situ

Dimethyl pyrocarbonate (dmpc) [dimethyl mu-oxo-bis(dioxocarbonate)] and diethyl pyrocarbonate (depc) were catalytically decomposed to dimethyl and diethyl carbonate respectively and carbon dioxide in the presence of [CoL(OR)](+)[L = cis,cis-1,3,5-tris(E,E-cinnamylideneamino)cyclohexane, R = methyl or ethyl] which we propose to be generated in situ during reaction in dichloromethane. The activity of the catalyst is undiminished after 60000 turnovers. In both cases the catalytic rate enhancement for the decomposition is in excess of 10(7) dm(3) mol(-1) of catalyst. The catalytic process follows Michaelis-Menten type kinetics and k(obs) is 2.2(2) s(-1) for dmpc decomposition and 1.3(2) s(-1) for depc decomposition. Activation energies for the catalytic decomposition are E-dmpc = 113(5) and E-depc = 120(11) kJmol(-1). A mechanism involving cobalt-bound alkoxide attack on dialkyl pyrocarbonate is proposed. The crystal structure of [CoL(Cl)] BPh4 has been determined by single-crystal X-ray diffraction.