Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
Nat Chem. 2011 Jan;3(1):19-27. doi: 10.1038/nchem.943. Epub 2010 Dec 15.
Reactivity principles based on orbital overlap and bonding/antibonding interactions are well established to describe the reactivity of organic species, and atomic structures are typically predicted by Hund's rules to have maximum single-electron occupancy of degenerate orbitals in the ground state. Here, we extend the role of exchange to transition states and discuss how, for reactions and kinetics of bioinorganic species, the analogue of Hund's rules is exchange-controlled reactivity. Pathways that increase the number of unpaired and spin-identical electrons on a metal centre will be favoured by exchange stabilization. Such exchange-enhanced reactivity endows transition states with a stereochemistry different from that observed in cases that are not exchange-enhanced, and is in good agreement with the reactivity observed for iron-based enzymes and synthetic analogues. We discuss the interplay between orbital- and exchange-controlled principles, and how this depends on the identity of the transition metal, its oxidation number and its coordination sphere.
基于轨道重叠和成键/反键相互作用的反应性原理已被广泛用于描述有机物种的反应性，原子结构通常根据洪德规则预测，即在基态下具有简并轨道的最大单电子占据。在这里，我们将交换作用扩展到过渡态，并讨论对于生物无机物种的反应和动力学，洪德规则的类似物是交换控制的反应性。增加金属中心上不成对和自旋相同电子数量的途径将受到交换稳定化的青睐。这种交换增强的反应性赋予过渡态与非交换增强情况下观察到的立体化学不同的性质，并且与基于铁的酶和合成类似物的反应性很好地一致。我们讨论了轨道和交换控制原理之间的相互作用，以及这种相互作用如何取决于过渡金属的身份、其氧化数和其配位球。
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