Inter- and intramolecular ligand exchange reactions of ruthenium(II) carbonyl porphine complexes with nitrogen bases

Abstract

To investigate both inter- and intramolecular site exchange in coordinated nitrogenous bases the complexes of tetra( p-isopropylphenyl)porphinato ruthenium carbonyl with4-tert-butylpyridine, 2-methylpyridine, 3,5-dimethylpyrazole, 4,5-dimethylpyridazine, and 3,6-dimethylpyridazine have been studied by total line shape analysis of the variable temperature PMR spectra. Both types of exchange mechanisms have been found in these complexes. All of the complexes undergo intermolecular ligand exchange at rates ranging from ∼0.09 sec −1 (Δ G ≠ ∼ 19 kcal/mol) to 2 × 10 4 sec − (Δ G ≠ ∼ 12 kcal/mol) at 25° for the various complexes, independent of the concentration of excess ligand. Thus the rate determining step is dissociation. The two pyridazine complexes provide the first examples of intramolecular ligand exchange with coordinated nitrogenous bases. The rates at 25° for intramolecular site exchange (∼10 6 and 66 sec −1) are 20–85 times faster than the rates for intramolecular ligand exchange in the same complexes. Within experimental uncertainty there is no intramolecular ligand site exchange in the 3,5-dimethylphyrazole complex. Full kinetic and mechanistic details are discussed.