Effect of the axial ligands on the structure and reactivity of tin verdoheme in the ring opening process

The effect of axial ligands on the reactivity and structure of tin(IV) verdoheme in hydrolysis reaction has been investigated using the B3LYP method. In the saturated six coordinate tin(IV) verdoheme complexes, tin has no coordination role and the nucleophilic reactions are initiated by direct addition of hydroxide to the positive oxo-carbon centers followed by formation of a hydroxy intermediate. For tin(IV) hydroxyl imidazole verdoheme, conversion of this intermediate to opened chain macrocycle is favorable thermodynamically but not kinetically. So, the former intermediate is the final product of reaction. In this complex, ring opening is prevented through a ligand centered mechanism. Whereas, in some other cases, formation of opened chain macrocycles are favorable from both thermodynamics and kinetics point of views.