text: Metal porphyrin complexes are almost always prepared by direct reaction of a metal halide with the free porphyrin, abbreviated here as HP:
  :MCl  +  HP  →   M(P)Cl  +  2HCl
  Two pyrrole protons are lost.  The porphyrin dianion is an LX ligand.
  These syntheses require somewhat forcing conditions, consistent with the tight fit of the metal in the N "pocket."  In nature, the insertion is mediated by chelatase enzymes.  The insertion of a metal proceeds by the intermediacy of a "sitting atop complex" (SAC), whereby the entering metal interacts with only one or a few of the nitrogen centers.
  In contrast to natural porphyrins, synthetic porphyrin ligands are typically symmetrical (i.e., their dianionic conjugate bases). Two major varieties are well studied, those with substituents at the meso positions, the premier example being tetraphenylporphyrin.  These ligands are easy to prepare in one-pot procedures.  A large number of aryl groups can be deployed aside from phenyl.
  A second class of synthetic porphyrins have hydrogen at the meso positions.  Octaethylporphyrin (HOEP) is the subject of many such studies. It is more expensive than tetraphenylporphyrin.
  Protoporphyrin IX, which occurs naturally, can be modified by removal of the vinyl groups and esterification of the carboxylic acid groups to gives deuteroporphyin IX dimethyl ester.