Configurational effects in the reaction of cobalt(I) Schiff-base complexes with alkyl bromides

Abstract

Electrogenerated diasteroisomeric cobalt(I) chelate complexes of quadridentate Schiff bases derived from substituted ethylenediamines and salicylaldehyde react with PrⁿBr, BuⁿBr, and Bu^tBr at different rates. The difference in the second-order rate constant can be attributed to the various distortions of the cobalt(I) complex in different configurations. The rate-limiting step is independent of the formation of the cobalt–carbon bond and it is proposed that the reaction occurs via an inner-sphere alkyl-bridged electron transfer, with a [Co^I(chelate)]^–⋯ R⁺⋯ X^– transition state. The reaction is sensitive to purely stereochemical perturbations of the co-ordination sphere of the metal atom.