Zhang Daoyang, Crawley Matthew R, Oldacre Amanda N, Kyle Lea J, MacMillan Samantha N, Cook Timothy R
Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260, United States.
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
Inorg Chem. 2023 Feb 6;62(5):1766-1775. doi: 10.1021/acs.inorgchem.2c01109. Epub 2022 Jun 14.
Cofacial porphyrin catalysts for the Oxygen Reduction Reaction (ORR) formed via coordination-driven self-assembly have so far been limited to designs with fourfold symmetry, where four molecular clips bridge two porphyrin sites. We have synthesized six PyPh (Py = pyridyl, Ph = phenyl) metalloporphyrin prisms (Co, Zn) bridged by molecular clips containing two Rh centers. Four of these structures are lower symmetry, with the PyPh and PyPh prisms containing three and two molecular clips, respectively. The Co species were evaluated for their ORR activity. Cyclic and hydrodynamic voltammetry studies of heterogeneous catalyst inks in aqueous media revealed marked differences in selectivity from ∼5% (PyPh) to ∼37% (PyPh) for the formation of HO. The single-crystal X-ray structure of the Zn PyPh prism shows an offset between the porphyrin faces. This structural feature may be responsible for the change in selectivity, consistent with previous studies of covalently tethered cofacial porphyrins that have shown that geometry is a critical determinant of two-electron/two-proton versus four-electron/four-proton pathways. Extraction of standard rate constants for the ORR revealed a cofacial enhancement of ∼2 orders of magnitude over mononuclear Co tetrapyridyl porphyrin. Even though all the prisms described here use the same molecular clip, the resultant structures, and thus the reactivity for the ORR, differ significantly based on the number and orientation of pyridyl donor groups on the porphyrins, highlighting how coordination-driven self-assembly can be used to rapidly tune dinuclear catalysts.
通过配位驱动自组装形成的用于氧还原反应（ORR）的共面卟啉催化剂，迄今为止仅限于具有四重对称性的设计，其中四个分子夹桥接两个卟啉位点。我们合成了六个由含有两个铑中心的分子夹桥接的PyPh（Py = 吡啶基，Ph = 苯基）金属卟啉棱柱（钴、锌）。其中四种结构具有较低的对称性，PyPh和PyPh棱柱分别包含三个和两个分子夹。对钴物种的ORR活性进行了评估。在水性介质中对非均相催化剂墨水进行的循环伏安法和流体动力学伏安法研究表明，对于HO的形成，选择性存在显著差异，从约5%（PyPh）到约37%（PyPh）。锌PyPh棱柱的单晶X射线结构显示卟啉面之间存在偏移。这一结构特征可能是选择性变化的原因，这与先前对共价连接的共面卟啉的研究一致，该研究表明几何形状是双电子/双质子与四电子/四质子途径的关键决定因素。ORR标准速率常数的提取表明，与单核钴四吡啶基卟啉相比，共面增强了约两个数量级。尽管这里描述的所有棱柱都使用相同的分子夹，但基于卟啉上吡啶基供体基团的数量和取向，所得结构以及因此对ORR的反应性存在显著差异，突出了配位驱动自组装如何可用于快速调节双核催化剂。
