Chen Xi, Yang Yin, Wang Hao, Mo Zhenbo
State Key Laboratory and Institute of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, College of Chemistry, Nankai University, Tianjin 300071, China.
J Am Chem Soc. 2023 Mar 29;145(12):7011-7020. doi: 10.1021/jacs.3c00949. Epub 2023 Mar 20.
Metal-ligand cooperativity has emerged as an important strategy to tune the reactivity of transition-metal complexes for the catalysis and activation of small molecules. Studies of main-group compounds, however, are scarce. Here, we report the synthesis, structural characterization, and reactivity of a geometrically constrained (silylene)-stabilized borylene. The one-pot reaction of [(SiNSi)Li(OEt)] (SiNSi = 4,5-(silylene)-2,7,9,9-tetramethyl-9-acridin-10-ide) with 1 equiv of [BBr(SMe)] in toluene at room temperature followed by reduction with 2 equiv of potassium graphite (KC) leads to borylene [(SiNSi)B] (), isolated as blue crystals in 45% yield. X-ray crystallography shows that borylene () has a tricoordinate boron center with a distorted T-shaped geometry. Computational studies reveal that the HOMO of represents the lone pair orbital on the boron center and is delocalized over the Si-B-Si unit, while the geometric perturbation significantly increases its energy. Borylene () shows single electron transfer reactivity toward tris(pentafluorophenyl)borane (B(CF)), forming a frustrated radical pair [(SiNSi)B][B(CF)], which can be trapped by its reaction with PhSSPh, affording an ion pair [(SiNSi)BSPh][PhSB(CF)] (). Remarkably, the cooperation between borylene and silylene allows the facile cleavage of the N-H bond of aniline, the P-P bond in white phosphorus, and the C═O bond in ketones and carbon dioxide, thus representing a new type of main-group element-ligand cooperativity for the activation of small molecules. In addition, is a strikingly effective catalyst for carbon dioxide reduction. Computational studies reveal that the cooperation between borylene and silylene plays a key role in the catalytic chemical bond activation process.
金属-配体协同作用已成为调节过渡金属配合物反应活性以催化和活化小分子的重要策略。然而，关于主族化合物的研究却很少。在此，我们报告了一种几何受限的（硅烯）稳定硼烯的合成、结构表征及反应活性。[(SiNSi)Li(OEt)]（SiNSi = 4,5 -（硅烯）- 2,7,9,9 - 四甲基 - 9 - 吖啶 - 10 - 亚胺）与1当量的[BBr(SMe)]在甲苯中于室温下进行一锅反应，随后用2当量的石墨化钾（KC）还原，得到硼烯[(SiNSi)B]（ ），以蓝色晶体形式分离得到，产率为45%。X射线晶体学表明硼烯（ ）具有一个三配位硼中心，呈扭曲的T形几何结构。计算研究表明， 的最高占据分子轨道（HOMO）代表硼中心上的孤对轨道，并在Si - B - Si单元上离域，而几何扰动显著提高了其能量。硼烯（ ）对三（五氟苯基）硼烷（B(CF)）表现出单电子转移反应活性，形成一个受阻自由基对[(SiNSi)B][B(CF)]，该自由基对可通过与PhSSPh反应被捕获，得到离子对[(SiNSi)BSPh][PhSB(CF)]（ ）。值得注意的是，硼烯与硅烯之间的协同作用使得能够轻松裂解苯胺的N - H键、白磷中的P - P键以及酮和二氧化碳中的C═O键，从而代表了一种用于活化小分子的新型主族元素 - 配体协同作用。此外， 是一种非常有效的二氧化碳还原催化剂。计算研究表明，硼烯与硅烯之间的协同作用在催化化学键活化过程中起关键作用。
