Multielectron chemistry of zinc porphyrinogen: A ligand-based platform for two-electron mixed valency
Multielectron chemistry of zinc porphyrinogen: A ligand-based platform for two-electron mixed valency
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DOI：
10.1021/ja039617h
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发表时间：
2004-03-10
影响因子：
15
通讯作者：
Nocera, DG
中科院分区：
文献类型：
--
作者：
Bachmann, J;Nocera, DG
报道了一系列同系锌(II)卟啉化合物的合成、电子结构和氧化还原化学。以吡咯和丙酮为原料，分两步合成了该系列的完全还原成员[LZn](2-)。该化合物在+0.21和+0.63V对NHE进行连续的双电子、基于配体的氧化反应，生成[(LZn)-Zn-Delta]和[(LZn)-Zn-DeltaDelta](2+)，这两种化合物也是通过化学方法独立合成的。对氧化还原中间体[(LZn)-Zn-Delta]的X-射线衍射分析表明，部分氧化的大环是由亚甲基桥联的联吡咯与环丙烷桥联的两电子氧化联吡咯(L-Delta)组成的。两个空穴当量分子定位在卟啉原骨架的氧化侧，符合[(LZn)-Zn-Delta]物种的两电子混合价公式。电子结构计算和电子光谱支持这种形式主义。密度泛函理论计算确定HOMO定域在大环的还原部分，LUMO定域在其氧化部分。从能级图可以看出，[(LZn)-Zn-Delta]在吸收光谱中的最低能量跃迁表现出电荷转移特性。综上所述，这些结果证实了在设计多电子氧化还原方案时使用配体骨架作为两个和四个电子/空穴储存库的可行性。
The synthesis, electronic structure, and oxidation-reduction chemistry of a homologous series of Zn(II) porphyrinogens are presented. The fully reduced member of the series, [LZn](2-), was prepared in two steps from pyrrole and acetone. The compound undergoes consecutive two-electron, ligand-based, oxidations at +0.21 and +0.63 V vs NHE to yield [(LZn)-Zn-Delta] and [(LZn)-Zn-DeltaDelta](2+), which also have been independently prepared by chemical means. X-ray diffraction analysis of the redox intermediary, [(LZn)-Zn-Delta], shows that the partly oxidized macrocycle is composed of a methylene-bridged dipyrrole that is doubly strapped to a two-electron oxidized dipyrrole bridged by a cyclopropane ring (L-Delta). The localization of two hole equivalents on the oxidized side of the porphyrinogen framework is consistent with a two-electron mixed valency formulation for the [(LZn)-Zn-Delta] species. Electronic structure calculations and electronic spectroscopy support this formalism. Density functional theory computations identify the HOMO to be localized on the reduced half of the macrocycle and the LUMO to be localized on its oxidized half. As implicated by the energy level diagram, the lowest energy transition in the absorption spectrum of [(LZn)-Zn-Delta] exhibits charge-transfer character. Taken together, these results establish the viability of using a ligand framework as a two- and four-electron/hole reservoir in the design of multielectron redox schemes.