Five-coordinate iron(II) porphyrins derived from meso-α,β,γ,δ tetraphenylporphin: synthesis, characterization, and coordinating properties

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Abstract
Meso-.alpha.,.beta.,.gamma.,.delta.-tetraphenylporphin derivatives bearing acrylic (cis and trans isomers) and propionic side chains with a terminal imidazole group were synthesized. Intermediate compounds obtained during their preparation were characterized by visible spectroscopy and NMR. In non-coordinating solvents (benzene or toluene), Fe(III) complexes of these compounds did not show intramolecular coordination of the terminal base on the metal ion. Reduced forms of the compounds were obtained from ferric forms by heterogeneous reduction with aqueous dithionite and exhibit optical spectra characteristic of 5 coordinate ferrous complexes. The nitrogenous bases and CO affinities of the latter were measured and the trans influence exerted by the terminal imidazole apparently does not depend greatly on the nature and the structure of the covalent side chain. The stability of the 5-coordinate compounds depends on the side chain (trans acrylic < propionic < cis acrylic) as suggested by the values reported for the replacement constants of the terminal imidazole by 4-cyanopyridine in unsymmetrical 6-coordinate derivatives. Stability of these compounds towards oxidation is also reported.