Oxidation of Magnesium, Indium, and Thallium with Molybdenum and Cobalt Binuclear Carbonyl Complexes in Polar Solvents

Abstract

Oxidation of magnesium and thallium with bis (D 5 -cyclopentadienyltricarbonylmolybdenum) in dimethyl sulfoxide and of indium with octacarbonyldicobalt in tetrahydrofuran was studied. The formalkinetics relationships of the processes were revealed, and the intermediate and final products were identified. The apparent equilibrium constants, enthalpies and entropies of adsorption of reactants on the metal surface, and rate constants and activation energies of the reactions were determined. The reaction scheme was suggested.Redox insertion into the M3M bond in binuclear complexes (M is a main-group or transition metal) was studied in [133]. Thermal [1] or photochemical [4] activation weakens the M3M bond in compounds [Cp(CO) n M] 2 and promotes its dissociation with the formation of two 17-electron radicals [5]; this reaction is successfully used in the synthesis of polynuclear derivatives. According to [6], the rate of the reaction of [Cp(CO) 3 Cr] 2 with thallium in THF at 25oC is 250 times higher than the rate of thallium oxidation with [Cp(CO) 3 Mo] 2 under similar conditions. This relationship is consistent with the enthalpies of dissociation of the M3M bond in bis(h 5 -cyclopentadienyltricarbonylmetals) [7]: Compound [Cp(CO) 3 W] 2 [Cp(CO) 3 Mo] 2 [Cp(CO) 3 Cr] 2 I II III ,H M!M , 233.7 139.5 66.0 kJ mol !1Furthermore, in accordance with [5], the capability of metal-centered radicals generated by dissociation of binuclear complexes to abstract a halogen atom from halohydrocarbons decreases in the order h 5 -Cp(CO) 3 W > h 5 -Cp(CO) 3 Mo > h 5 -Cp(CO) 3 Cr > Co(CO) 4 . The bond energy in the corresponding dimer should vary in the opposite direction.Thus, certain success has been gained in studying the reactions under consideration and in choosing appropriate conditions to obtain the highest product yield. At the same time, some aspects of these reactions are still poorly understood. The kinetic relationships of the processes and the thermodynamic parameters of adsorption of the reactants on the metal surface are unknown. Moreover, there are no substantiated concepts concerning the reaction mechanism. It is also important to find how the reaction rate depends on the donor properties of the solvent used.The experimental results of this study show that the dependence of the rate of metal insertion into the M3M bond of a binuclear complex on the donor power of the solvent passes through a maximum, as in the case of metal oxidation with other oxidants [8]. The oxidation of magnesium and thallium is the fastest in DMSO. For the oxidation of indium, we used a solution of octacarbonyldicobalt IV in THF, since specifically in THF the dependence of the relative reaction rate on the solvent donor number DN(SbCl 5 )[9] has a maximum.The reaction of Mg with II in DMSO (C 0 0.125 M) was performed at a reactant ratio of 10 : 1 and 60oC; the mixture was stirred with a magnetic stirrer. After the reaction completion, the liquid phase was separated from the unchanged metal, and the major fraction of the solvent was removed un...

Oxidation of Indium with Triphenylbismuth in Polar Solvents

“…However, experimental determination of this dependence was unfeasible, because in the presence of commonly used inert diluents (toluene, p-xylene) [11] the reaction was extremely slow, and addition of n-heptane caused phase separation. It should be noted that a similar pattern was observed in oxidation of indium with dicobalt octacarbonyl [12] in THF in the presence of an inert diluent. The possible cause of the reaction cessation in the presence of an inert diluent (toluene, p-xylene) is competition of the solvent with the phenyl groups of (C 6 H 5 ) 3 Bi for the adsorption centers on the indium surface.…”