Iron porphyrin complexes ("hemes") are the dominant metalloporphyrin complexes in nature.  Consequently, synthetic iron porphyrin complexes are well investigated.  Common derivatives are those of Fe(III) and Fe(II).  Complexes of the type Fe(P)Cl are square-pyramidal and high spin with idealized C symmetry.  Base hydrolysis affords the "mu-oxo dimers" with the formula [Fe(P)]O.  These complexes have been widely investigated as oxidation catalysts.  Typical stoichiometries of ferrous porphyrins are Fe(P)L where L is a neutral ligand such as pyridine and imidazole. Cobalt(II) porphyrins behave similarly to the ferrous derivatives.  They bind O to form dioxygen complexes.