Theoretical modeling of the oxidation of hydrazine by iron(II) phthalocyanine in the gas phase. Influence of the metal character.

The hydrazine oxidation by iron(II) phthalocyanine (Fe(II)Pc) has been studied using an energy profile framework through quantum chemistry theoretical models calculated in the gas phase at the density functional theory B3LYP/LACVP(d) level. We applied two models of charge-transfer mechanisms previously reported (J. Phys. Chem. A 2005, 109, 1196) for the hydrazine oxidation mediated by Co(II)Pc. Model 1 consists of an alternated loss of one electron and one proton, involving anionic and neutral species. Model 2 considers an alternated loss of two electrons and two protons and includes anionic, neutral, and cationic species. Both applied models describe how the charge-transfer process occurs. In contrast with the obtained results for Co(II)Pc, we found that the hydrazine oxidation mediated by Fe(II)Pc is a fully through-bond charge-transfer mechanism. On the other hand, the use of different charge-transfer descriptors (spin density, electronic population, condensed Fukui function) showed a major contribution of the iron atom in comparison with the cobalt atom in the above-mentioned process. These results could explain the higher catalytic activity observed experimentally for Fe(II)Pc in comparison with Co(II)Pc. The applied theoretical models are a good starting point to rationalize the charge-transfer process of hydrazine oxidation mediated by Fe(II)Pc.