XAS STUDIES OF HIGH-VALENT FE MODEL COMPLEXES RELEVANT TO METHANE MONOOXYGENASE

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 在甲烷单加氧酶(MMO)和核糖核苷酸还原酶(RNR)中，高价铁中间体都是活性氧化物种。在MMO中，中间体Q被认为由一个将甲烷转化为甲醇的FeIV(Mu-O)2FeIV核心组成。而在氧桥联FeIFeIV物种RNR中，中间体X是核苷酸还原的活性物种。这些反应的重要性和合成类似物在仿生均相催化中的潜在用途推动了合成类似物的努力。我们实验室最近的工作集中在以强烈的pi和sigma给体酚类和t-胺为给体合成和表征双核Fe-oxo配合物。生成的[LFe(MU2-O)FeL]络合物(1)可被氧化成正离子[LFe(MU2-O)FeL](1)和阳离子[LFe(MU2-O)FeL]2(12)。EPR数据为1表明是氧桥联FeIIIFeIV配方。然而，比较1和2与单核类似物的UV-Vis数据表明，这两个配合物都发生了以配体为中心的氧化，形成了1的二铁苯氧基和12的二铁二苯氧基。相对于单阴离子物种来说，阳离子的稳定性更高被认为是由于前者(12)中铁氧键的对称加强，而不是后者(1)中产生的不对称情况。由于这些物种只能在低温溶液中生成，XAS为表征这些络合物的电子结构和局部几何结构提供了理想的手段。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. High-valent iron intermediates are invoked as the active oxidizing species in both methane monooxygenase (MMO) and ribonucleotide reductase (RNR). In MMO, intermediate Q is thought to consist of an FeIV(mu-O)2FeIV core which converts methane to methanol. Whereas in RNR, an oxo-bridged FeIIIFeIV species, intermediate X is the active species in ribonucleotide reduction. The importance of these reactions and the potential utility of synthetic analogues in biomimetic homogeneous catalysis have driven efforts to synthesize analogues. Recent work in our laboratory has focused on the synthesis and characterization of dinuclear Fe-oxo complexes utilizing strongly pi- and sigma- donating phenolates and t-amines as donors. The resultant [LFe(mu2-O)FeL] complex (1) can be oxidized to the monocation [LFe(mu2-O)FeL]+ (1+) and to the dication [LFe(mu2-O)FeL]2+ (12+). EPR data of 1+ suggests an oxo-bridged-FeIIIFeIV formulation. However comparison of UV-vis data for 1+ and 2+ to mononuclear analogues suggests a ligand-centered oxidation occurs in both complexes, forming a diferric phenoxyl radical in 1+ and a diferric diphenoxyl radical in 12+. The greater stability of the dication relative to the monoanionic species is thought to result from a symmetric strengthening of the Fe-oxo bonds in the former (12+), as opposed to the asymmetric situation which is generated in the later (1+). As these species can only be generated at low temperature in solution, XAS provides an ideal means for characterizing the electronic structure and local geometric structure of these complexes.