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

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 高价铁中间体在甲烷单加氧酶（MMO）和核糖核苷酸还原酶（RNR）中都被称为活性氧化物种。在MMO中，中间体Q被认为由将甲烷转化为甲醇的FeIV（mu-O）2FeIV核组成。 而在RNR中，氧桥FeIIIFeIV物种，中间体X是核糖核苷酸还原中的活性物种。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效用推动了合成类似物的努力。我们实验室最近的工作集中在利用强π-和σ-供体酚盐和叔胺作为供体的双核Fe-氧代配合物的合成和表征。生成的[LFe（μ 2-O）FeL]络合物（1）可被氧化成一价阳离子[LFe（μ 2-O）FeL]+（1+）和二价阳离子[LFe（μ 2-O）FeL]2+（12+）。1+的EPR数据表明氧桥-FeIIIFeIV制剂。然而，1+和2+单核类似物的紫外-可见光数据的比较表明，在这两个复合物中发生配体为中心的氧化，形成二铁苯氧基自由基的1+和二铁二苯氧基自由基的12+。相对于单阴离子物种，二价阳离子的更大稳定性被认为是由于前者（12+）中Fe-氧代键的对称加强，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下在溶液中产生，XAS提供了一个理想的手段来表征这些配合物的电子结构和局部几何结构。

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.