Hydrogen Peroxide: A Poor Ligand to Gallium Tetraphenylporphyrin

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.

为了构建可能的血红素铁-过氧化氢酶中间体模型，研究者已在二氯二苯基（CD2Cl2）中探讨了四苯基卟啉（TPP）-镓化学。从（TPP）GaCl与AgOTf或AgClO4反应制备了（TPP）GaOTf（1）和（TPP）Ga(ClO4)（2）。微量的水分与2反应生成[(TPP)Ga(OH2)](ClO4)（5），并与（TPP）GaOOtBu反应生成（TPP）GaOH（3）。这些配合物均经过了全面表征，包括1、3、5的双水合类似物以及甲基衍生物（TPP）GaMe（4）的X射线晶体结构。描述了一种简便的制备无水稀过氧化氢氯仿溶液的方法。然而，这些镓配合物在CD2Cl2中与无水过氧化氢均不发生反应。过氧化氢甚至不能取代弱配位的过氯酸或三氟甲磺酸根阴离子，或配位的水分子，这表明过氧化氢是一个非常弱的配体。