Nitrogen , iron complexes

The reduction electrochemistry of ECP porphyrin films furthermore responds to added axial ligands in the expected ways. We have tested this (2,6) for the ECP form of the iron complex of tetra(o-amino)phenyl)porphyrin by adding chloride and various nitrogeneous bases to the contacting solutions, observing the Fe(III/II) wave shift to expected potentials based on the monomer behavior in solution. This is additional evidence that the essential porphyrin structure is preserved during the oxidation of the monomer and its incorporation into a polymeric film. 

In summary, the fragmentary evidence at hand suggests that sulfur was the primordial iron complexing material and that this ligand system was selectively modified by stepwise transition to a mixed sulfur-nitrogen and sulfur-oxygen and, finally, to an all-oxygen type of coordination. 

Figure 6.4 Example of a two-coordInate iron complex, [Fe N(SiMePh2)2 2]- ° Iron and nitrogen atoms are shown as black spheres, silicon atoms are grey and carbon atoms are white. Selected bond lengths and an angle Fe-NI 1.90, Fe-N2 1.91 N-Fe-N 172. F ...

At the same time the bond angles (C—N—C) at the N7 position vary from 112 (-fp3 as expected for an amine ligand) in the manganese complex (where repulsion is least) up to a maximum value of 120 in the iron complex with maximum repulsions. The tertiary amine nitrogen atom (N7) corresponds to a three-ribbed umbrella that has been inverted by the wind (the handle is the lone pair directed at the metal). As the a, and If levels fill, the repulsions increase, the metal-nitrogen distance increases, and the umbrella begins to flatten ... 

Several porphyrin analogues with the pyrrolic nitrogens substituted by heteroatoms have been synthesized, but only the oxa analogues (23 X = O, Y = NH) are reported to form stable metal complexes (Figure 8). 60 Formation of a Zn complex of the thia analogue (23 X = S, Y = NH) requires the presence of a large excess of Zn" ion. An iron complex of dithiaporphyrin (23 X = Y = S) is also known. 

The apparently anomalous behavior of the iron tetracarbonyl halides in terms of the inverse stability gradation iodide > bromide > chloride—the latter is labile above 0° C—which is the reverse sequence to that found with the nitrogen-base complexes L4FeX2 (L = NH3, pyridine, etc.), caused us... 

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