Factors Affecting Hydrogen Atom Transfer Reactivity of Metal-Oxo Porphyrinoid Complexes.
Factors Affecting Hydrogen Atom Transfer Reactivity of Metal-Oxo Porphyrinoid Complexes.
复制标题
DOI：
10.1021/acs.accounts.8b00414
复制
发表时间：
2018-11-20
影响因子：
18.3
通讯作者：
Goldberg DP
中科院分区：
文献类型：
--
作者：
Sacramento JJD;Goldberg DP
金属/氧物种介导的氢原子转移(HAT)反应因其在金属酶功能和合成催化剂中的核心作用而备受关注。本文重点介绍了我们在合成高价金属氧基和金属羟基卟啉类化合物以及测定它们在一系列HAT过程中的反应活性方面的进展。在这些研究中，我们使用了腐拉津和Corole配体，这是一种环收缩的卟啉类化合物，旨在稳定高价金属络合物。高价锰络合物MnV(O)-(TbP8Cz)(TbP8Cz=八(4-叔丁基苯基)腐拉津)提供了一个很好的低电势氧化剂的早期例子，它表现出氧化还原电位，表明它是一个相对较弱的氧化剂，但仍然可以有效地从20个特定的C−H/O−H键中提取H原子。用四方图方法对MNV(O)络合物及其相关物种的HAT反应的热力学进行了近似，其中HAT可形式地分离为质子(PKA)和电子转移(E°)，表明与质子的亲和力(即碱度)是促进HAT的关键因素。阴离子轴向配体对MNV(O)(TBP8Cz)的HAT反应活性有很大影响，支持碱度是决定反应活性的关键参数的结论。考察了Lewis酸对MNV(O)(TBP8Cz)的影响，结果表明，HAT的电子结构和反应活性都发生了显著的变化。合成了高价的Cr(O)、Re(O)和Fe(O)腐蚀性氮化物，并研究了它们与HAT的一系列反应。铬和锰配合物在相同的配体环境中形成了一对罕见的结构表征的CrV(O)和MNV(O)物种，允许直接比较它们的HAT反应活性。虽然从氧化还原电位来看，CrV(O)是更好的氧化剂，但MNV(O)在HAT氧化反应中明显更具活性，再次表明碱性是HAT反应活性的关键决定因素。铁配合物FeIV(O)(TBP8Cz+·)是血红素酶化合物I中间体的类似物，被发现对从C-H键上提取H原子有温和的反应。相反，Rev(O)(TbP8Cz)对HAT是惰性的，尽管单电子氧化为Rev(O)(TbP8Cz+·)导致了一些有趣的反应，仅由π-自由基-阳离子配体介导。其他配体的修饰，包括外围取代以及Cz核上新的中位位置的烷基化，都被考察了它们对HAT的影响。用空间位阻较高的三(2，4，6-三苯基苯基)钴(Ttppc)分离和表征了类卟啉环境中的第一个MnIV(OH)配合物：MnIV(OH)(Ttppc)。该配合物在HAT与O-H底物的反应中具有很高的活性，并且被发现比其更高氧化态的对应化合物MNV(O)(Ttppc)的活性要高得多，这提供了重要的机理见解。这些研究为高价M(O)和M(OH)模型中血红素酶活性的结构和功能之间的关系提供了基础知识。
There has been considerable interest in hydrogen atom transfer (HAT) reactions mediated by metal/oxygen species because of their central role in metalloenzyme function as well as synthetic catalysts. This Account focuses on our progress in synthesizing high-valent metal–oxo and metal–hydroxo porphyrinoid complexes and determining their reactivities in a range of HAT processes. For these studies we have utilized corrolazine and corrole ligands, which are a ring-contracted subclass of porphyr inoid compounds designed to stabilize high-valent metal complexes. The high-valent manganese complex MnV(O)-(TBP8Cz) (TBP8Cz = octakis(4-tert-butylphenyl)corrolazine) provided an early example of a well-characterized low-potential oxidant that exhibits a redox potential indicating it to be a relatively weak oxidant yet can still be effective at abstracting H atoms from 20 certain C−H/O−H bonds. Approximating the thermodynamics of the HAT reactivity of the MnV(O) complex and related species with the help of a square scheme approach in which HAT can be formally separated into proton (pKa) and electron transfers (E°) indicates that affinity for the proton (i.e., the basicity) is a key factor in promoting HAT. Anionic axial ligands have a profound influence on the HAT reactivity of MnV(O)(TBP8Cz), supporting the conclusion that basicity is a critical parameter in determining the reactivity. The influence of Lewis acids on MnV(O)(TBP8Cz) was examined, and it was shown that both the electronic structure and reactivity toward HAT were significantly altered. High-valent Cr(O), Re(O), and Fe(O) corrolazines were prepared, and a range of HAT reactions were studied with these complexes. The chromium and manganese complexes form a rare pair of structurally characterized CrV(O) and MnV(O) species in identical ligand environments, allowing for a direct comparison of their HAT reactivities. Although CrV(O) was the better oxidant as measured by redox potentials, MnV(O) was significantly more reactive in HAT oxidations, pointing again to basicity as a key determinant of HAT reactivity. The iron complex, FeIV(O)(TBP8Cz+•), is an analogue of the heme enzyme Compound I intermediate and was found to be mildly reactive toward H atom abstraction from C–H bonds. In contrast, ReV(O)(TBP8Cz) was inert toward HAT, although one-electron oxidation to ReV(O)(TBP8Cz+•) led to some interesting reactivity mediated by the π-radical-cation ligand alone. Other ligand modifications, including peripheral substitution as well as novel alkylation of the meso position on the Cz core, were examined for their influence on HAT. A highly sterically encumbered corrole, tris(2,4,6-triphenylphenyl)corrole (ttppc), was employed for the isolation and structural characterization of the first MnIV(OH) complex in a porphyrinoid environment, MnIV(OH)(ttppc). This complex was highly reactive in HAT with O–H substrates and was found to be much more reactive than its higher-oxidation-state counterpart MnV(O)(ttppc), providing important mechanistic insights. These studies provided fundamental knowledge on the relationship between structure and function in high-valent M(O) and M(OH) models of heme enzyme reactivity.
登录
查看更多内容
影响因子：
15
作者：
Mandimutsira, BS;Ramdhanie, B;Goldberg, DP
通讯作者：
Goldberg, DP
影响因子：
15
作者：
Leeladee, Pannee;Baglia, Regina A.;Goldberg, David P.
通讯作者：
Goldberg, David P.
DOI：
10.1073/pnas.0709471104
发表时间：
2007-12-04
影响因子：
11.1
作者：
Sastri, Chivukula V.;Lee, Jimin;Nam, Wonwoo
通讯作者：
Nam, Wonwoo
影响因子：
56.9
作者：
Rittle, Jonathan;Green, Michael T.
通讯作者：
Green, Michael T.
影响因子：
4.6
作者：
Joslin, Evan E.;Zaragoza, Jan Paulo T.;Goldberg, David P.
通讯作者：
Goldberg, David P.