NMR studies of pi molecular complexes in iron porphyrins

Abstract

Proton and carbon-13 NMR shifts and linewidths of a series of synthetic high-spin ferric porphyrin were investigated upon the addition of various aromatic pi acceptors and donors. The interactions are described by the formation of 1:1 adducts. Thermodynamics of the complex chloro(Tetraphenylporphyrin)-iron (3)/1,3,5-trinitrobenzene are indicative of pi-pi peripheral contact of the aromatic substrate with the porphyrin. Successful use of NMR was made to demonstrate the utility of intramolecular dipolar relaxation, induced at proton and carbon-13 of trinitrobenzene resonance by the ferric ion, in the determination of the solution structure of the pi molecular complex chloro(tetraphenylporphyrin) iron(3)/1,3,5-trinitrobenzene.