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Hydrogen Peroxide:  A Poor Ligand to Gallium Tetraphenylporphyrin

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posted on 13.02.2008, 00:00 authored by Antonio G. DiPasquale, James M. Mayer
As models for possible heme-iron-H2O2 enzymatic intermediates, tetraphenylporphyrin (TPP)-gallium chemistry has been explored in CD2Cl2. (TPP)GaOTf (1) and (TPP)Ga(ClO4) (2) have been prepared from (TPP)GaCl and AgOTf or AgClO4. Trace water reacts with 2 to give [(TPP)Ga(OH2)](ClO4) (5) and with (TPP)GaOOtBu to give (TPP)GaOH (3). These complexes were fully characterized including X-ray structures for 1, 3, the bis(aquo) analogue of 5, and the methyl derivative (TPP)GaMe (4). A convenient procedure for preparing anhydrous dilute solutions of H2O2 in methylene chloride is described. All of these gallium complexes, however, are unreactive with this anhydrous H2O2 in CD2Cl2. H2O2 does not displace even the weakly coordinating perchlorate or triflate anions, or coordinated water, indicating that H2O2 is a very weak ligand.