The Reaction Kinetics of Transition Metal Complexes with Gases in Solution

Abstract

The importance of the study of the reaction kinetics of transition metal complexes with gases in solution is discussed. Apparatus designed for following the kinetics of gas uptake, changes in absorption spectra and pH of the solution is described. Possible improvements are suggested. Four transition metal complex / gas systems were selected for kinetic studies on the grounds of their potential use as biological model systems or in the generation of industrially useful homogeneous catalysts. The uptake of oxygen by aqueous solutions containing 1, 2- diaminoethane and various cobalt (II) salts is shown to be rapid. The reagents interact in the stoicheiometric ratios of 1:5: 2 respectively to give [ (en)2CoμO2μen Co(en)2]4+ . This compound slowly equilibrates with [ (en)2CoμO2μOH Co(en)2]3+ while it may be oxidised to [ (en)2CoμO2μen Co(en)2]5+. These compounds were examined by physical techniques. Solutions of the μ -peroxo species were shown to react with gaseous carbon dioxide to yield [Co(en)2CO3]+. The reaction between oxygen and manganese (II) complexes of N, N' - disalicylaldehyde - 1, 3 - propanediimine was studied in various solvents. The reagent complexes and their various oxygen adducts were examined by physical techniques and are believed to be oligomeric or polymeric. The kinetics of the reduction of [RhIII (L)2Cl2]+ cations (where L is bipyridyl, phenanthroline or their substituted derivatives) in alkaline ethanolic solution at 60°C under a hydrogen atmosphere were investigated by following the rate of [ RhI(L)2]+ production spectrophotometrically and the rate of 1: 1 hydrogen uptake. An autocatalytic mechanism with hydrogen gas acting as reducing agent, is suggested. The rhodoxime (III) complexes H [RhIII(DMG)2C12] and [RhIII (DMG)2 P Ph3 Cl] and their reduction products were investigated by physical techniques. The kinetics of the reduction of H [ RhIII (DMG)2 C12 ] in alkaline ethanolic solution under a nitrogen atmosphere were investigated by following the rate of H [RhI (DMG)2] production spectrophotometrically. The reaction mechanism proved to be autocatalytic.