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.

Date of Award	1971
Original language	English