Álvarez-Ruiz Elena, Sancho Ignacio, Navarro Marta, Fernández Israel, Santamaría Cristina, Hernán-Gómez Alberto
Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación Química "Andrés M. del Río" (IQAR), Universidad de Alcalá, Campus Universitario, Alcalá de Henares, Madrid E-28805, Spain.
Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Ciudad Real 13071, Spain.
Inorg Chem. 2024 May 13;63(19):8642-8653. doi: 10.1021/acs.inorgchem.4c00149. Epub 2024 May 1.
The synthesis, structure, and catalytic activity of a Ti(II)/Ti(III) inverted sandwich compound are presented in this study. Synthesis of the arene-bridged dititanium compound begins with the preparation of the titanium(IV) precursor [TiCl(PDA)(thf)] (PDA = ,'-bis(2,4,6-trimethylphenyl)--phenylenediamide) (). The reduction of with sodium metal results in species [{Ti(PDA)(thf)}(μ-Cl){Na}] () in oxidation state III. To achieve the lower oxidation state II, undergoes reduction through alkylation with lithium cyclopentyl. This alkylation approach triggers a cascade of reactions, including β-hydride abstraction/elimination, hydrogen evolution, and chemical reduction, to generate the Ti(II)/Ti(III) compound [Li(thf)][(TiPDA)(μ-η: η-CH)] (). X-ray and EPR characterization confirms the mixed-valence states of the titanium species. Compound catalyzes a mild, efficient, and regiospecific cyclotrimerization of alkynes to form 1,3,5-substituted arenes. Kinetic data support a mechanism involving a binuclear titanium arene compound, similar to compound , as the resting state. The active catalyst promotes the oxidative coupling of two alkynes in the rate-limiting step, followed by a rapid [4 + 2] cycloaddition to form the arene product. Computational analysis of the resting state for the cycloaddition of trimethylsilylacetylene indicates a thermodynamic preference for stabilizing the 1,3,5-arene within the space between the two [TiPDA] fragments, consistent with the observed regioselectivity.
本研究介绍了一种Ti(II)/Ti(III)反夹心化合物的合成、结构和催化活性。芳烃桥连二钛化合物的合成始于钛(IV)前体[TiCl(PDA)(thf)]（PDA = ，'-双(2,4,6-三甲基苯基)--苯二胺）（）的制备。用金属钠还原得到氧化态为III的物种[{Ti(PDA)(thf)}(μ-Cl){Na}]（）。为了达到较低的氧化态II，通过用环戊基锂进行烷基化反应对进行还原。这种烷基化方法引发了一系列反应，包括β-氢化物的提取/消除、氢气释放和化学还原，以生成Ti(II)/Ti(III)化合物[Li(thf)][(TiPDA)(μ-η: η-CH)]（）。X射线和电子顺磁共振表征证实了钛物种的混合价态。化合物催化炔烃进行温和、高效且区域选择性的环三聚反应，形成1,3,5-取代芳烃。动力学数据支持一种机制，该机制涉及一种双核钛芳烃化合物，类似于化合物，作为静止状态。活性催化剂在限速步骤中促进两个炔烃的氧化偶联，随后快速进行[4 + 2]环加成反应以形成芳烃产物。对三甲基硅基乙炔环加成静止状态的计算分析表明，在两个[TiPDA]片段之间的空间内稳定1,3,5-芳烃具有热力学偏好，这与观察到的区域选择性一致。
