Department of Chemistry, University of Miami , Coral Gables, Florida 33124, United States.
Inorg Chem. 2013 Dec 16;52(24):13882-93. doi: 10.1021/ic401296f. Epub 2013 Nov 21.
In the current investigation, reactions of the "bow-tie" Ni(η(2)-TEMPO)2 complex with an assortment of donor ligands have been characterized experimentally and computationally. While the Ni(η(2)-TEMPO)2 complex has trans-disposed TEMPO ligands, proton transfer from the C-H bond of alkyne substrates (phenylacetylene, acetylene, trimethylsilyl acetylene, and 1,4-diethynylbenzene) produce cis-disposed ligands of the form Ni(η(2)-TEMPO)(κ(1)-TEMPOH)(κ(1)-R). In the case of 1,4-diethynylbenzene, a two-stage reaction occurs. The initial product Ni(η(2)-TEMPO)(κ(1)-TEMPOH)[κ(1)-CC(C6H4)CCH] is formed first but can react further with another equivalent of Ni(η(2)-TEMPO)2 to form the bridged complex Ni(η(2)-TEMPO)(κ(1)-TEMPOH)[κ(1)-κ(1)-CC(C6H4)CC]Ni(η(2)-TEMPO)(κ(1)-TEMPOH). The corresponding reaction with acetylene, which could conceivably also yield a bridging complex, does not occur. Via density functional theory (DFT), addition mechanisms are proposed in order to rationalize thermodynamic and kinetic selectivity. Computations have also been used to probe the relative thermodynamic stabilities of the cis and trans addition products and are in accord with experimental results. Based upon the computational results and the geometry of the experimentally observed product, a trans-cis isomerization must occur.
在当前的研究中，通过实验和计算的方法对“蝴蝶结”Ni(η(2)-TEMPO)2 配合物与各种供体配体的反应进行了研究。虽然 Ni(η(2)-TEMPO)2 配合物具有反式排布的 TEMPO 配体，但炔烃底物（苯乙炔、乙炔、三甲基硅基乙炔和 1,4-二乙炔基苯）的 C-H 键的质子转移会产生顺式排布的配体形式 Ni(η(2)-TEMPO)(κ(1)-TEMPOH)(κ(1)-R)。在 1,4-二乙炔基苯的情况下，发生了两阶段反应。首先形成初始产物 Ni(η(2)-TEMPO)(κ(1)-TEMPOH)[κ(1)-CC(C6H4)CCH]，但它可以进一步与另一个当量的 Ni(η(2)-TEMPO)2 反应，形成桥联配合物 Ni(η(2)-TEMPO)(κ(1)-TEMPOH)[κ(1)-κ(1)-CC(C6H4)CC]Ni(η(2)-TEMPO)(κ(1)-TEMPOH)。而与乙炔的相应反应，理论上也可以生成桥联配合物，但实际上并未发生。通过密度泛函理论（DFT），提出了加成机制，以合理说明热力学和动力学选择性。计算还用于探测顺式和反式加成产物的相对热力学稳定性，并且与实验结果一致。基于计算结果和实验观察到的产物的几何形状，必须发生反式-顺式异构化。
