Binuclear Intermediate Research Articles

Slow substitution reaction of manganese(II) ion in dimethyl sulphoxide solution

The reaction between excess of MnII ion and 2,6-(2-pyridyl)pyridine (terpy) in dimethyl sulphoxide solution occurs in two stages; a rapid formation of a binuclear intermediate is followed by a very slow reaction attributed to final chelate ring closure.

Identification of inner- and outer-sphere paths in the reaction of chromium(II) with hexachloroiridate(IV), and the kinetics of the decomposition of the binuclear intermediate

The one-equivalent reaction of chromium(II) with hexachloroiridate(IV) has been studied at temperatures in the range 0–25°, µ= 1·0M(LiClO4). Part of the reaction is accounted for by an outer-sphere path: CrII(H2O)62++ IrIVCl62– [graphic omitted] CrIII(H2O)63++ IrIIICl63–. An inner-sphere mechanism is also effective and a binuclear intermediate [(H2O)5CrClIrCl5](peaks at 354 nm., Iµ 560; 400 nm., Iµ 400; and ca. 425, Iµ∼380) has been detected. This subsequently breaks down to give mononuclear products, Cr(H2O)5Cl2+ and IrCl5H2O2–: CrII(H2O)62++ IrIVCl62– [graphic omitted] [(H2O)5CrIIIClIrIIICl5] [graphic omitted] CrIII(H2O)5Cl2++ IrIIICl5H2O2 The rate of decomposition of the intermediate and the ratio of products [Cr(H2O)63+]:[Cr(H2O)5Cl2+] are independent of hydrogen-ion concentration over the range [H+]= 0·11 to 1·0M. At 25°k3= 4·23 × 10–2 sec.–1, ΔH3‡= 21·8 (±1·0) kcal. mole–1 and ΔS3‡= 8·4 (±3·0) e.u., and the rate constants k1 and k2 are > 106 l. mole–1 sec.–1. From the temperature dependence of the product ratio [Cr(H2O)62+]:[Cr(H2O)5Cl2+] the differences in activation parameters for the inner and outer-sphere paths are ΔH2‡–ΔH1‡= 5·7 (±0·7) kcal. mole–1 and ΔS2‡–ΔS1‡= 19·0 (±2·0) e.u. Possible implications of these values are considered.

The Reaction of the Copper(II) Chelate of Ethyl Acetoacetate with Bromine and the Reactions of the Copper(II) Chelates of Acetylacetone and Ethyl Acetoacetate with Dry Hydrogen Bromide

Abstract When the copper(II) chelate of ethyl acetoacetate reacts with bromine in dry dichloromethane, the chelate is broken, forming the α-bromoester and copper(I) or copper(II) bromide depending on the reactants’ mole ratio. However, in the reaction between bromine and the chelate at a mole ratio of 1 : 1 in dichloromethane saturated with water, copper-(I) bromide is not produced primarily; instead copper(II) hydroxide is formed, as is copper-(II) bromide. In the reactions of the copper(II) chelate of acetylacetone or ethyl acetoacetate with dry hydrogen bromide at the mole ratio of 1 : 1 or 1 : 1.5, more than 98% of the total copper precipitated as copper(I) bromide. Even when 2 mol. of hydrogen bromide was employed against 1 mol. of the chelate, more than 90% of the original copper changed to copper(I) bromide, in contrast with the results obtained in a similar reaction with bromine. The entire reaction pattern has been suggested employing a presumed intermediate binuclear complex containing a bromine double brigde.

Binuclear Intermediates in the Reaction between Uranium(VI) and Chromium(II)

It was found that at least one binuclear intermediate forms rapidly when Cr(II) and U(VI) are mixed in acid solutions near 0 deg . The spectrum of the intermediate indicated that it is a substituted Cr(III) species. The intermediate reacted with Tl(III) and V(IV) at rates which were first order in the intermediate concentration but zero order in the concentration of oxidizing agent. In the absence of other reactants the intermediate decomposed to give U(IV), U(VI), and Cr(III) with apparent half-times at 0 deg ranging between 4 and 8 min. Chemical, optical, and kinetic evidence were found for the presence of significant amounts of a second, more reactive, intermediate in the system.