Odubo Favour E, Muthuramesh Snehashree, Zeller Matthias, Rosokha Sergiy V
Department of Chemistry, Ball State University, Muncie, Indiana 47306, USA.
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Phys Chem Chem Phys. 2024 Aug 7;26(31):21030-21039. doi: 10.1039/d4cp02573c.
The interaction of the tetracyanoethylene (TCNE) π-acceptor with oxo- and fluoro-anions (BF, PF, ClO, NO) led to the formation of anion-π complexes in which these polyatomic anions were located over the face of alkenes, with multiple contacts being shorter than the van der Waals separations. The anion-π associations of TCNE with halides were delimited by the electron-donor strengths and nucleophilicity of the anions. Specifically, while bromides formed persistent anion-π associations with TCNE in the solid state and in solutions, only transient anion-π complexes with iodides and chlorides were observed. In the case of iodide (strong 1e reducing agent), the formation of anion-π complexes was followed by the reduction of the π-acceptor to the TCNE˙ anion-radical. The interaction of TCNE with Cl (and F) anions (which are better nucleophiles in the aprotic solvents) led to the formation of 1,1,2,3,3-pentacyanoprop-2-en-1-ide anions. Thermodynamics, UV-Vis spectra, and structures, as well as contributions of electrostatics, orbital interactions, and dispersion to the interaction energies in the complexes of TCNE with various anions were closely related to the characteristics of the corresponding associations with the aromatic and -benzoquinone acceptors. This points out the general equivalence of the interactions in the anion-π complexes with different π-acceptors and the critical role of the nature of the anions in these bindings.
四氰基乙烯（TCNE）π受体与氧阴离子和氟阴离子（BF、PF、ClO、NO）的相互作用导致形成阴离子-π配合物，其中这些多原子阴离子位于烯烃表面，多个接触距离短于范德华间距。TCNE与卤化物的阴离子-π缔合受阴离子的电子供体强度和亲核性限制。具体而言，虽然溴化物在固态和溶液中与TCNE形成持久的阴离子-π缔合，但仅观察到与碘化物和氯化物的瞬态阴离子-π配合物。对于碘化物（强单电子还原剂），阴离子-π配合物形成后，π受体被还原为TCNE˙阴离子自由基。TCNE与Cl（和F）阴离子（在非质子溶剂中是更好的亲核试剂）的相互作用导致形成1,1,2,3,3-五氰基丙-2-烯-1-负离子。热力学、紫外-可见光谱和结构，以及静电、轨道相互作用和色散对TCNE与各种阴离子配合物中相互作用能的贡献，与相应的与芳香族和苯醌受体缔合的特征密切相关。这指出了阴离子-π配合物中不同π受体相互作用的一般等效性以及阴离子性质在这些键合中的关键作用。
