The interaction of pyridine with four tetraki(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, DH , increase from A to D while the activation
entropies, DS , 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.