Steric effects upon chelate ring-opening and ring-closure substitution reactions of (o-dimethylaminophenyldimethylarsine)rhodium(III) complexes

Abstract

The kinetics of the reversible reaction (i) have been studied in methanol [amine = NH₃, NMeH₂, NEtH₂, NPrⁿH₂, trans-[RhL₂Cl₂]⁺+ amine ⇌mer-[RhL(L′)(amine)Cl₂]⁺(i) NBuⁿH₂, N(CH₂Ph)H₂, NPrⁱH₂, NBuⁱH₂, NBu^sH₂, or N(CH₂Bu^t)H₂; L and L′=o-dimethylaminophenyldimethyl-arsine-NAs and -As respectively]. The pseudo-first-order rate constant of the approach to equilibrium exhibits the form k_obs. =k_(t→m)[amine]+k_(m→t). The rate constant of the forward reaction (i) is scarcely affected by the nature of the entering primary amine. On the other hand, the rate constant of the reverse reaction is strongly dependent on the leaving amine, the change of reactivity being satisfactorily rationalized in terms of changes of the amine steric hindrance, in agreement with a dissociative mode of activation.