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Issue 12, 1976
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Kinetics of hydrolysis of trans-dichloro- and trans-dibromo-(n-meso-5,12- dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11 -diene)cobalt(III) cations

Abstract

The kinetics of hydrolysis of the title cations trans-[CoX2(N-meso-L4)]+(X = Cl or Br; L4= 5,12-dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11 -diene) have been studied at I= 0.1 mol dm–3 over the range pH 3.0–4.5. Hydrolysis of the first halogen ligand obeys a rate expression of the form kobs.=kOH2+k1OH[OH], where kobs. is the observed first-order rate constant at constant pH. The values of k1OH are 8.5 × 107(X = Cl)and ca.1 × 109 dm3 mol–1 s–1(X = Br) at 25 °C. The base-hydrolysis rates are the highest yet reported for halogenocobalt(III) complexes of the [CoX2(N4)]2+ type. Ths pH-independent process is represented by kOH2= 5.4 × 10–3 s–1 for the chloro-complex. Hydrolysis of the second halogen ligand proceeds more slowly and in this case kobs.=k2OH[OH] with k2OH= 5.9 × 106(X = Cl) and 1.2 × 107 dm3 mol–1 s–1(X = Br) at 25 °C. The thermodynamic activation parameters for the hydrolysis of the second halogen ligand are ΔH= 57 kJ mol–1 and ΔS298= 75 J K–1 mol–1(X = Cl) and ΔH= 56 kJ mol–1 and ΔS= 80 J K–1 mol–1(X = Br). These values may indicate rate-determining deprotonation of the substrate in the base-hydrolysis reactions.

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Article type: Paper
DOI: 10.1039/DT9760001086
Citation: J. Chem. Soc., Dalton Trans., 1976,0, 1086-1089
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    Kinetics of hydrolysis of trans-dichloro- and trans-dibromo-(n-meso-5,12- dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11 -diene)cobalt(III) cations

    R. W. Hay and G. A. Lawrance, J. Chem. Soc., Dalton Trans., 1976, 0, 1086
    DOI: 10.1039/DT9760001086

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