New iron nitrosyl complexes containing strong electron donating carbaporphyrins

Abstract

A serious of new iron nitrosyl complexes containing carbaporphyrins as the macrocyclic ligand has been synthesized. Two methods have been developed to introduce the axial nitric oxide, either through nitrite reduction or through direct reaction with nitric oxide gas. In the case of nitrite reduction, the formation of the reduced {Fe (NO)}7 complex or the oxidized {Fe (NO)}6 can be controlled through the stoichiometry of the nitrite anion used as the reactant. Both oxidized and reduced carbaporphyrin iron nitrosyl complexes exhibit a 3N1C coordination environment for iron metal center to bind with the carbaporphyrin with which containing an inverted pyrrole ring to give an inner carbon atom in the coordination sphere. The linear and bent bond angles for {Fe (NO)}6 and {Fe (NO)}7, respectively, as well as the NO stretching frequencies in IR spectroscopy resemble regular iron porphyrin nitrosyl complexes. On the other hand, unique chemistry has been observed using the inner carbon methylated carbaporphyrin as the ligand. It is found that the iron oxidation and the nitric oxide coordination synchronized a C–H activation on the inner methyl group to give an unusual {Fe (NO)}6 iron nitrosyl complex. The conformation confirmed by the single crystal X-ray structure suggests a non-planar porphyrinic core with a strong pi-donating from the inner alkene to the iron center. The strong backbonding also resulted a small Fe–N–O angle at 148 degree. The unusual spectroscopies, electronic structures, and reactions of these carbaporphyrin complexes will be discussed.