Hydrogen Peroxide:  A Poor Ligand to Gallium Tetraphenylporphyrin

2008-02-13T00:00:00Z (GMT) by Antonio G. DiPasquale James M. Mayer
As models for possible heme-iron-H<sub>2</sub>O<sub>2</sub> enzymatic intermediates, tetraphenylporphyrin (TPP)-gallium chemistry has been explored in CD<sub>2</sub>Cl<sub>2</sub>. (TPP)GaOTf (<b>1</b>) and (TPP)Ga(ClO<sub>4</sub>) (<b>2</b>) have been prepared from (TPP)GaCl and AgOTf or AgClO<sub>4</sub>. Trace water reacts with <b>2</b> to give [(TPP)Ga(OH<sub>2</sub>)](ClO<sub>4</sub>) (<b>5</b>) and with (TPP)GaOO<i><sup>t</sup></i><sup></sup>Bu to give (TPP)GaOH (<b>3</b>). These complexes were fully characterized including X-ray structures for <b>1</b>, <b>3</b>, the bis(aquo) analogue of <b>5</b>, and the methyl derivative (TPP)GaMe (<b>4</b>). A convenient procedure for preparing anhydrous dilute solutions of H<sub>2</sub>O<sub>2</sub> in methylene chloride is described. All of these gallium complexes, however, are unreactive with this anhydrous H<sub>2</sub>O<sub>2</sub> in CD<sub>2</sub>Cl<sub>2</sub>. H<sub>2</sub>O<sub>2</sub> does not displace even the weakly coordinating perchlorate or triflate anions, or coordinated water, indicating that H<sub>2</sub>O<sub>2</sub> is a very weak ligand.