Mechanism and steric course of octahedral aquation. Part IX. The stereoretentive aquation, anation, and base hydrolysis of the trans-dichloro(1,4,8,11-tetra-azacyclotetradecane)cobalt(III) cation and its solvento-derivatives

Abstract

The aquation equilibria and kinetics of trans-[Co cyclam Cl₂]⁺(cyclam = 1,4,8,11-tetra-azacyclotetradecane) have been studied over a range of temperature. The anation of trans-[Co cyclam H₂O Cl]²⁺ by thiocyanate and chloride ions is reported and SCN^– is shown to be a much more effective reagent than Cl^–. The base hydrolysis of trans-[Co cyclam Cl₂]⁺ is a fast, two-stage reaction and has been studied in buffer solutions. In the pH region 6·2 to 7·4 the first stage, which has a first-order rate dependence on [OH^–], is rate-determining but at higher pH the second stage, whose rate is independent of pH, becomes distinguishible and eventually rate-determining. This stage is identified as the aquation of trans-[Co cyclam OH Cl]⁺ and the assignment confirmed by studies on the independently prepared hydroxochloro-cation. All the reactions reported proceed with complete retention of configuration. The behaviour of the cyclam complexes is compared with that of the corresponding bisethylene-diamine species.