Novel routes for the modification of iron porphyrins

The effects of unconventional modifications of iron tetraarylporphyrins on their electronic structure and chemical properties were examined. The alter ations included the beta(meso)-substitution or an oxygen atom insertion int o an iron-nitrogen bond. The profound transformation of porphyrin to 2-pyri diniumylporphyrin, isoporphyrin or porphodimethene occurred in reactions in volving iron porphyrin in highly-oxidized states and pyridine. Addition of 2,4,6-collidine generated iron porphyrin N-oxides. The 2-hydroxy substitute d tetraphenylporphyrin (a hybrid-type ligand) coordinates using a tetranitr ogen macrocyclic center and an ionized hydroxy group of the periphery to fo rm the cyclic trimer [(2-O-TPP)Fe(III)](3). The seven pyrrole protons of (2 -X-TPP)Fe(III)Cl and [(2-X-TPP)Fe(III)(CN)(2)] provided the direct probe of the spin density distribution around the porphyrin macrocycle as determine d by H-1-NMR. Studies on the controlled modification of the tetraarylporphy rin periphery also included a symmetrical modification of a single pyrrole ring to obtain iron(III) quinoxalinoporphyrin characterized by the less com mon (d(xz)d(yz))(4)(d(xy))(1) low-spin ground electronic state of the bis-c yanide derivative [(QTPP)Fe(III)(CN)(2)](-). (C) 1999 Elsevier Science S.A. All rights reserved.