Frey Nathan C, Sarkar Samir Kumar, Dickie Diane A, Molino Andrew, Gilliard Robert J
Department of Chemistry, Massachusetts Institute of Technology 77 Massachusetts Avenue, Building 18-596 Cambridge MA 02139-4307 USA
Department of Chemistry, University of Virginia Charlottesville Virginia 22904 USA.
Chem Sci. 2025 May 12. doi: 10.1039/d5sc02000j.
Boron-phosphorus (B-P) frustrated Lewis pairs (FLPs) are an important class of compounds for activating various small molecules. Utilizing the ring expansion reactivity of 9-chloro-9-borafluorene, a borinine-based FLP was synthesized. Various five-membered main-group element heterocycles were obtained the reaction of the FLP with MeNO, S, and Se. Subsequent reduction of these species yielded the ring-expanded compounds, each featuring bridging B-E-B (E = O, S, Se) bonds. Similarly, halide abstraction from the FLP with AgNTf led to the formation of a cationic ring-expanded compound with a bridging B-Cl-B motif. This motif constitutes one of the first examples of a boron-stabilized chloronium ion, as verified using in-depth bonding analysis methods. Mechanistic pathways for the reduction- and halide abstraction-mediated ring expansion reactions are proposed with the aid of density functional theory. Electronic structure computations were performed to determine the best representation of bonding interactions in each compound, suggesting phosophorus(V)-chalcogen double bonding and chalcogen-boron(iii) dative interactions within the heterocycles.
硼 - 磷（B - P）受阻路易斯酸碱对（FLPs）是用于活化各种小分子的一类重要化合物。利用9 - 氯 - 9 - 硼芴的扩环反应活性，合成了一种基于硼氮烯的FLP。该FLP与MeNO、S和Se反应得到了各种五元主族元素杂环化合物。随后对这些物种进行还原得到了扩环化合物，每个化合物都具有桥连的B - E - B（E = O、S、Se）键。同样，用AgNTf从FLP中夺取卤化物导致形成具有桥连B - Cl - B基序的阳离子扩环化合物。如使用深入的键合分析方法所证实的，该基序构成了硼稳定的氯鎓离子的首批实例之一。借助密度泛函理论提出了还原和卤化物夺取介导的扩环反应的机理途径。进行了电子结构计算以确定每种化合物中键合相互作用的最佳表示形式，表明杂环内存在磷（V）- 硫族元素双键和硫族元素 - 硼（III）配位相互作用。
