Metal cluster catalysis: A kinetic and mechanistic study of the carbonylation of methanol to give methyl formate as catalyzed by [Et4N](2)[Fe-3(CO)(9)E] (E = S, Be, Te)

摘要

The cluster compounds [Et4N](2)[Fe-3(CO)(9)E] (E = S, Se, Te) catalyze the homogeneous carbonylation of methanol to form methyl formate under moderate CO pressures (6001200 psi) between 50 and 90 degreesC. A detailed kinetic analysis of this system shows that the reaction is first order with respect to cluster concentration and quasi-second order with respect to the pressure of CO. All three cluster compounds show similar behavior. The reaction appears to be almost independent of the [CH3O-](total) at values of [CH3O-]total less than or equal to 3 x 10(-3) M, but at higher concentrations it appears to be first-order dependent on [CH3O-](total).This system affords the opportunity to compare the effects of different main group heteroatoms in a homologous series. The rates of the reaction were found to lie in the following order: Te (6 x 10(-4) M(.)min(-1)) > S (4 x 10(-4) M(.)min(-1)) > Se (2 x 10(-4) M(.)min(-1)) at 1200 psi and 90 degreesC. The activation energies were found to be 43 +/- 11 kJ.mol(-1) (E = S), 76 8 kJ.mol(-1) (E = Se), and 72 +/- 7 kJ.mol(-1) (E = Te). The rate dependence upon CO pressure suggests a mechanism in which metal-metal bond opening is important. [References: 66]