Spectral, Electrochemical and Base-Binding Studies of Heterodinuclear Ruthenium-Cobalt Complexes of meso-α,α,α,α-Tetra(nicotinamidophenyl)porphine

Article abstract of DOI:10.1021/ja00303a015

The spectral, electrochemical, and ligand addition properties of metal complexes of the modified porphyrin (nic)4H2TPP have been examined.The porphyrin has the feature that two metal ions may be coordinated and held in close proxomity to each other, one ion in the porphyrin ring and the other coordinated to the pyridine-like nitrogens of the nicotinamide pickets.The results for the RuCl2(nic)4CoTPP complex studied indicate that the "neutral" fixed axial ligand Ru(II)Cl2 has very little effect on the electrochemistry and spectroscopy of the cobalt porphyrin when compared with simple CoTPP.However, oxidation of Ru(II) to Ru(III) greatly increases the Lewis acid strength of Co(II) relative to the strength of that center in CoTPP.The binding constant for the Ru(III)-Co(II) species with pyridine is found to be three orders of magnitude larger than that for Ru(II)-Co(II); the binding constant for Ru(III)-Co(III) with pyridine is seven orders of magnitude greater than that for Ru(III)-Co(II).In the presence of high concentrations of N-methylimidazole, the Ru(III)-Co(III) appears to form a bis-adduct, presumably by allowing partial entry of a 1-MeIm molecule into the porphyrin pocket.