Department of Chemistry, University of California Riverside, Riverside, California 92521, United States.
Inorg Chem. 2013 May 20;52(10):6223-9. doi: 10.1021/ic400786a. Epub 2013 May 7.
The chlorinated carba-closo-dodecaborate anion HCB11Cl11(-) is an exceptionally stable molecule and has previously been reported to be substitutionally inert at the B-Cl vertices. We present here the discovery of base induced cycloaddition reactions between this carborane anion and organic azides that leads to selective C and B functionalization of the cluster. A single crystal X-ray diffraction study reveals bond lengths in the heterocyclic portion of the ring that are shortened, which suggests electronic delocalization. Molecular orbital analysis of the ensuing heterocycles reveals that two of the bonding orbitals of these systems resemble two of the doubly occupied π-MOs of a simple 5-membered Hückel-aromatic, even though they are entangled in the carborane skeleton. Nucleus independent chemical shift analysis indicates that both the carborane cluster portion of the molecule and the carborane fused heterocyclic region display aromatic character. Computational methods indicate that the reaction likely follows a stepwise addition cyclization pathway.
氯代卡巴-closo-十二硼酸盐阴离子 HCB11Cl11(-) 是一种极其稳定的分子，以前曾报道其在 B-Cl 顶点处具有取代惰性。我们在此介绍了这种碳硼烷阴离子与有机叠氮化物之间的碱基诱导环加成反应的发现，该反应导致了簇的选择性 C 和 B 官能化。单晶 X 射线衍射研究揭示了环中环杂原子部分的键长缩短，这表明电子离域。对随后的杂环的分子轨道分析表明，这些体系的两个成键轨道类似于简单的 5 元 Hückel-芳香性的两个双占据 π-MOs，尽管它们纠缠在碳硼烷骨架中。核独立化学位移分析表明，分子的碳硼烷簇部分和碳硼烷稠合杂环区域都显示出芳香性。计算方法表明，该反应可能遵循逐步加成环化途径。
