Kepp Kasper P
DTU Chemistry, Technical University of Denmark , Building 206, 2800 Kongens Lyngby, Denmark.
Inorg Chem. 2016 Sep 19;55(18):9461-70. doi: 10.1021/acs.inorgchem.6b01702. Epub 2016 Aug 31.
Oxophilicity and thiophilicity are widely used concepts with no quantitative definition. In this paper, a simple, generic scale is developed that solves issues with reference states and system dependencies and captures empirically known tendencies toward oxygen. This enables a detailed analysis of the fundamental causes of oxophilicity. Notably, the notion that oxophilicity relates to Lewis acid hardness is invalid. Rather, oxophilicity correlates only modestly and inversely with absolute hardness and more strongly with electronegativity and effective nuclear charge. Since oxygen is highly electronegative, ionic bonding is stronger to metals of low electronegativity. Left-side d-block elements with low effective nuclear charges and electronegativities are thus highly oxophilic, and the f-block elements, not because of their hardness, which is normal, but as a result of the small ionization energies of their outermost valence electrons, can easily transfer electrons to fulfill the electron demands of oxygen. Consistent with empirical experience, the most oxophilic elements are found in the left part of the d block, the lanthanides, and the actinides. The d-block elements differ substantially in oxophilicity, quantifying their different uses in a wide range of chemical reactions; thus, the use of mixed oxo- and thiophilic (i.e., "mesophilic") surfaces and catalysts as a design principle can explain the success of many recent applications. The proposed scale may therefore help to rationalize and improve chemical reactions more effectively than current qualitative considerations of oxophilicity.
亲氧性和亲硫性是广泛使用的概念，但没有定量定义。在本文中，我们开发了一种简单通用的标度，它解决了参考态和系统依赖性问题，并捕捉了已知的对氧的经验趋势。这使得能够对亲氧性的根本原因进行详细分析。值得注意的是，亲氧性与路易斯酸硬度相关的观点是无效的。相反，亲氧性仅与绝对硬度呈适度的负相关，而与电负性和有效核电荷的相关性更强。由于氧具有很高的电负性，离子键对低电负性的金属更强。因此，具有低有效核电荷和电负性的左侧d区元素具有很高的亲氧性，而f区元素并非因为其正常的硬度，而是由于其最外层价电子的电离能小，能够容易地转移电子以满足氧的电子需求。与经验相符，亲氧性最强的元素出现在d区左侧、镧系和锕系。d区元素在亲氧性上有很大差异，这量化了它们在广泛化学反应中的不同用途；因此，使用混合的亲氧和亲硫（即“嗜中温”）表面和催化剂作为设计原则可以解释许多近期应用的成功。因此，与目前对亲氧性的定性考虑相比，所提出的标度可能有助于更有效地使化学反应合理化和改进。
