Abstract
The interaction of pyridine with four tetrakis(arylisocyanide)cobalt(II) complexes, [Co(CNR)4(ClO4)2] R = 2,6-Me2C6H3 (A), 2,4,6-Me3C6H2 (B), 2,6-Et2C6H3 (C) and 2,6-iPr2C6H3 (D), have been studied in 2,2,2-trifluoroethanol medium. The kinetics of the reactions were investigated over the 293–318 K temperature range. The reaction profile exhibited two distinct processes, proposed to be an initial fast substitution followed by a slow reduction, for each of the reactions. The pseudo first-order rate constants for both processes increased with increasing concentration of pyridine with the reduction processes exhibiting saturation kinetics at high pyridine concentrations. Steric hindrance plays a significant role in the rates of the reactions, as the rates decrease in the order k(A) > k(B) > k(C) > k(D). The activation enthalpies, ΔH‡, increase from A to D while the activation entropies, ΔS‡, are relatively similar for the four reactions, indicating similar transition states and hence similar mechanisms. Complex B was first synthesized and characterized in this study.
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