Proton exchange and base-catalysed hydrolysis of some trans- and cis-dichloro(1,4,8,11-tetra-azacyclotetradecane) complexes of chromium(III), ruthenium(III), and rhodium(III)

Abstract

The ratio of the rate constants for the solvolysis (k₂) and reprotonation (k^–1) of the amido-conjugate base of trans-[M{RSSR-cyclam}Cl₂]⁺(M = Cr, Ru, or Rh) and cis-[M{RRRR(SSSS)-cyclam}Cl₂]⁺(M = Cr or Rh)(cyclam = 1,4,8,11-tetra-azacyclotetradecane) have been estimated from the proton exchange (k₁) and base hydrolysis (k_OH) rate constants. All complexes are considerably less reactive towards base hydrolysis than the analogous Co^III species. The lower reactivity of Cr^III is due to a lowering of k₁ and k₂/k_–1 by similar amounts, while that of Rh^III arises mainly from a large reduction of k₂/k_–1 in the cis isomer. A similar reduction of k₂/k₁ coupled with a big decrease in k₁ accounts for the extremely low reactivity of the trans isomer. The considerable reduction in k₂/k_–1 for the trans Ru^III complex is compensated by a large increase in k₁.