Importance of Nonclassical σ-Hole Interactions for the Reactivity λ3-Iodane Complexes
Importance of Nonclassical σ-Hole Interactions for the Reactivity λ3-Iodane Complexes
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DOI：
10.1021/acs.joc.7b01716
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发表时间：
2017-11-17
影响因子：
3.6
通讯作者：
Luthi, Hans Peter
中科院分区：
文献类型：
--
作者：
de Magalhaes, Halua Pinto;Togni, Antonio;Luthi, Hans Peter
观察到的反应活性的关键是涉及碘原子和两个线性排列的配体的 3 中心 4 电子键的特性，λ(3)-碘是选择性地将官能团转移到亲核试剂的强大试剂。该键还参与 lambda(3)-碘与亲核试剂（可以是溶剂分子或反应物）之间初始络合物的形成。这种复合物中的键合可以通过西格玛-空穴相互作用来描述。在卤素化合物中，西格玛-空穴相互作用被认为是晶体堆积或超分子链形成中的力。最近，西格玛-空穴相互作用也被证明会影响碘基高价试剂的反应性。相对于它们的单价对应物，西格玛孔位于西格玛键的延伸部分，在超价物质中，我们的 DFT 计算揭示了具有一个甚至两个最大值的非经典西格玛孔区域的形成。以此观察计算。 SAPT 分析表明 lambda(3)-碘和亲核试剂之间的西格玛空穴键不一定具有纯静电性质，但也可能包含重要的共价成分。该共价组分可以通过还原消除或其他机制促进化合物的化学转化，因此是其反应性的指示剂。在这里，我们还表明，西格玛孔的形状、位置和强度可以通过配体的选择和碘试剂的布朗斯台德活化等措施来调节。在极限情况下，调节将非经典西格玛孔区域转变为配位位点，这使我们能够控制亲核试剂如何与碘结合和反应。
Key for the observed reactivity lambda(3)-iodanes, powerful reagents for the selective transfer of functional groups to nucleophiles, are the properties of the 3-center-4-electron bond involving the iodine atom and the two linearly arranged ligands. This bond is also involved in the formation of the initial complex between the lambda(3)-iodane and a nucleophile, which can be a solvent molecule or a reactant. The bonding in such complexes can be described by means of sigma-hole interactions. In halogen compounds, sigma-hole interaction was identified as a force in, crystal packing or in the formation of supramolecular chains. More recently, sigma-hole interactions were also shown to affect the reactivity of the iodine-based-hypervalent reagents. Relative to their monovalent counterparts, where the sigma-hole is located on the extension of the sigma-bond, in the hypervalent species our DFT calculations, re-veal the formation of a nonclassical sigma-hole region with one or even two maxima. This observation calculations. The SAPT analysis shows that the sigma-hole bond between the lambda(3)-iodane and the nucleophile is not necessarily of purely electrostatic nature but may also contain a significant covalent component. This covalent component may facilitate chemical transformation of the compound by means of reductive elimination or other mechanisms and is therefore an indicator for its reactivity. Here, we also show that the shape, location, and strength of the sigma-holes can be tuned by the choice of ligands and measures such as Bronsted activation of the iodane reagent. At the limit, the tuning transforms the nonclassical sigma-hole regions into coordination sites, which allows us to control how a nucleophile will bind and react with the iodane.