Kinetics of incorporation of copper(II) into meso-tetraphenylporphine in dimethylformamide-II. Effects of amines

Kinetics of incorporation of copper into meso-tetraphenylporphine (H₂TPP) in N,N-dimethylformamide at 30° were measured in the presence and in the absence of a variety of amines. The reaction was first order in both H₂TPP and Cu(II). The reaction was accelerated by the addition of butylamine or benzylamine, until at about [amine]/[Cu] = 12 it was almost twenty times faster than the reaction in the absence of the amines. At the ratio over 12, the rate was independent of the amine concentrations. With increasing concentrations of pyridine or imidazole, the rate increased, reached a maximum and, then, decreased slightly. The reaction was retarded by the addition of ethylenediamine or 2,2′-bipyridine. It is concluded that Cu(II) species coordinated by monoamines are more reactive than the solvated Cu(II), whereas species chelated by the bidentate ligands are inactive. The reaction was greatly accelerated by aniline or its derivatives with electron-donating substituents (An). The rate law was d[CuTPP]/dt = k[H₂TPP][Cu] + k_cat[H₂TPP][Cu][An] and k_cat was in the order p-anisidine > p-toluidine > aniline > m-toluidine > o-toluidine > 2,6-dimethylaniline. No appreciable catalysis was detectable for anilines substituted by an electron-withdrawing group. The results are interpreted in terms of the formation of a weak copper-aniline complex.