Chufán Eduardo E, Mondal Biplab, Gandhi Thirumanavelan, Kim Eunsuk, Rubie Nick D, Moënne-Loccoz Pierre, Karlin Kenneth D
Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA.
Inorg Chem. 2007 Aug 6;46(16):6382-94. doi: 10.1021/ic700363k. Epub 2007 Jul 6.
Heme-Cu/O2 adducts are of interest in the elucidation of the fundamental metal-O2 chemistry occurring in heme-Cu enzymes which effect reductive O-O cleavage of dioxygen to water. In this report, the chemistry of four heme-peroxo-copper [FeIII-(O22-)-CuII]+ complexes (1-4), varying in their ligand architecture, copper-ligand denticity, or both and thus their structures and physical properties are compared in their reactivity toward CO, PPh3, acids, cobaltocene, and phenols. In 1 and 2, the copper(II) ligand is N4-tetradentate, and the peroxo unit is bound side-on to iron(III) and end-on to the copper(II). In contrast, 3 and 4 contain a N3-tridentate copper(II) ligand, and the peroxo unit is bound side-on to both metal ions. CO "displaces" the peroxo ligand from 2-4 to form reduced CO-FeII and CO-CuI species. PPh3 reacts with 3 and 4 displacing the peroxide ligand from copper, forming (porphyrinate)FeIII-superoxide plus CuI-PPh3 species. Complex 2 does not react with PPh3, and surprisingly, 1 reacts neither with PPh3 nor CO, exhibiting remarkable stability toward these reagents. The behavior of 1 and 2 compared to that of 3 and 4 correlates with the different denticity of the copper ligand (tetra vs tridentate). Complexes 1-4 react with HCl releasing H2O2, demonstrating the basic character of the peroxide ligand. Cobaltocene causes the two-electron reduction of 1-4 giving the corresponding micro-oxo [FeIII-(O2-)-CuII]+ complexes, in contrast to the findings for other heme-peroxo-copper species of different design. With t-butyl-substituted phenols, no reaction occurs with 1-4. The results described here emphasize how ligand design and variations influence and control not only the structure and physical properties but also the reactivity patterns for heme-Cu/O2 adducts. Implications for future investigations of protonated heme/Cu-peroxo complexes, low-spin analogues, and ultimately O-O cleavage chemistry are discussed.
血红素 - 铜/O₂加合物对于阐明血红素 - 铜酶中发生的基本金属 - O₂化学过程具有重要意义，这些酶能将双氧进行还原O - O裂解生成水。在本报告中，研究了四种血红素 - 过氧 - 铜[FeIII-(O₂²⁻)-CuII]+配合物（1 - 4）的化学性质，它们在配体结构、铜 - 配体齿合度或两者方面存在差异，因此比较了它们在与CO、PPh₃、酸、二茂钴和酚类反应时的结构和物理性质。在1和2中，铜（II）配体为N₄四齿配体，过氧单元以侧基方式与铁（III）结合，以端基方式与铜（II）结合。相比之下，3和4含有N₃三齿铜（II）配体，过氧单元以侧基方式与两个金属离子结合。CO从2 - 4中“取代”过氧配体，形成还原态的CO - FeII和CO - CuI物种。PPh₃与3和4反应，从铜上取代过氧化物配体，形成（卟啉）FeIII - 超氧化物加CuI - PPh₃物种。配合物2不与PPh₃反应，令人惊讶的是，1既不与PPh₃反应也不与CO反应，对这些试剂表现出显著的稳定性。1和2与3和4的行为差异与铜配体的不同齿合度（四齿对三齿）相关。配合物1 - 4与HCl反应释放出H₂O₂，表明过氧化物配体具有碱性。二茂钴使1 - 4发生双电子还原，生成相应的微氧[FeIII-(O₂⁻)-CuII]+配合物，这与其他不同设计的血红素 - 过氧 - 铜物种的研究结果不同。对于叔丁基取代的酚类，1 - 4不发生反应。这里描述的结果强调了配体设计和变化不仅如何影响和控制血红素 - 铜/O₂加合物的结构和物理性质，还影响其反应模式。讨论了对未来质子化血红素/Cu - 过氧配合物、低自旋类似物以及最终O - O裂解化学研究的启示。
