The base-catalyzed isomerization of trans-RCo(H2O)L2+ (L=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4, 11-diene)

摘要

The sec, rac-CH3Co(H2O)L2+ (L=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) was prepared successfully via meso-CH3Co(H2O)L2+ in aqueous solution. The isomerizations from meso-RCo(H2O)L2+ (R=CH3, C2H5 and C3H7) and sec, rac-CH3Co(H2O)L2+ to pri, rac-RCo(H2O)L2+ were both base catalyzed in aqueous solution. The kinetic results showed the reaction to be first order in both organocobalt complex and hydroxide ion with the reactivity order for the alkyl group being C3H7 similar to C2H5 much greater than CH3. However, the conversion from the most steric hindered isomer form of sec, rac- was slow. The ratio of the isomerization rate constants between meso-CH3Co(H2O)L2+ and sec, rac-CH3Co(H2O)L2+ to pri, rac-CH3Co(H2O)L2+ is almost a factor of 100. The thermodynamic activation parameters for these isomerization reactions were investigated. (C) 2003 Elsevier B.V. All rights reserved. [References: 24]