Thermodynamics and kinetics of the reaction of hafnium(IV) tetraphenylporphin dichloride with imidazole

摘要

The characteristics of step equilibria and the rates of forward and reverse reactions of hafnium(IV) tetraphenylporphin dichloride (CI2HfTPP) with imidazole (Im) in an inert solvent (toluene) have been determined. The stoichiometric mechanism of conversion includes several reversible and irreversible stages: (i) coordination of the Im molecule in the first coordination sphere (K-1 = 2.34 x 10(5) M-1) and slow irreversible displacement of one acid ligand (Cl-) from the mixed Cl-2(Im)HfTPP complex to the second coordination sphere (k(1) = 1.67 x 10(-3) s(-1)); (ii) replacement of one acid ligand (Cl-) from Cl-2(Im)HfTPP by the second Im molecule (K-2 1.44 x 10(4) M-1) and irreversible displacement of another acid ligand (Cl-) from the complex to the outer coordination sphere (k(2) = 1.21 x 10(-3) s(-1)); (iii) replacement of the acid ligand (Cl-) from the [CIIm(2)HfFPP](+). Cl- complex by the Im molecule (K-3 = 27.44 M-1). Mechanisms of the elementary events of ligand substitution are proposed, which are justified by the obtained kinetic data and the available results for the analogous complexes of other metals.