Synthesis and Reactivity of 4,5-[1,2-Dicarba-closo-dodecaborano(12)]-1,3-diselenacyclopentane: Opening of the Icosahedron to Give a Zwitterionic Intermediate and Conversion into 7,8-Dicarba-nido-undecaborate(1−)

• Published in: Chemistry : a European journal 2011-03, Vol.17 (11), p.3238-3251
• Main Authors: Wrackmeyer, Bernd, Klimkina, Elena V., Milius, Wolfgang, Bauer, Tobias, Kempe, Rhett
• Format: Article
• Language: English
• Subjects: Anions; Anions - chemistry; Boranes - chemical synthesis; Boranes - chemistry; Borates - chemical synthesis; Borates - chemistry; Cage; carboranes; Cations; Chemistry; cluster compounds; Crystallography, X-Ray; Cyclopentanes - chemical synthesis; Cyclopentanes - chemistry; deboronation; Icosahedrons; Magnetic resonance; Methylene Chloride - chemistry; Molecular Conformation; NMR; NMR spectroscopy; Nuclear magnetic resonance; Pyridines; Pyridines - chemistry; Quaternary Ammonium Compounds - chemistry; selenium; Selenium Compounds - chemical synthesis; Selenium Compounds - chemistry; Spectrum analysis; Structural analysis; Temperature; X-rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201002277

The reaction of the 1,2‐diselenolato‐1,2‐dicarba‐closo‐dodecaborane(12) dianion [1,2‐(1,2‐C2B10H10)Se2]2− with dichloromethane (CH2Cl2 or CD2Cl2) in the presence of donor solvents gave 4,5‐[1,2‐dicarba‐closo‐dodecaborano(12)]‐1,3‐diselenacyclopentane, the title compound, which was characterized by X‐ray structural analysis and NMR spectroscopy (1H, 11B, 13C, and 77Se). In the presence of pyridine, opening of the icosahedron took place, and a zwitterionic intermediate was isolated and fully characterized in the solid state by X‐ray diffraction and in solution by multinuclear magnetic resonance techniques. Although such types of intermediates, prior to deboronation of the ortho‐carborane cage, have been proposed several times, this is first example for which the structure has been confirmed unambiguously. This intermediate possesses a nido structure and contains a 7,8‐dicarba‐nido‐undecaborate(1−) anion and a boronium cation, the latter with two pyridine rings linked to the boron atom, which has been extruded from the cage. It was shown that this process is reversible as long as the deboronation is not complete. The formation of the intermediate is accompanied by deboronation, which leads to the 7,8‐dicarba‐nido‐undecaborate(1−) anion. The latter was prepared independently by conventional routes from the title compound, isolated as crystalline material as the tetrabutyl ammonium salt, and characterized by X‐ray structural analysis and multinuclear magnetic resonance spectroscopy (1H, 11B, 13C, and 77Se). Open for business: 4,5‐[1,2‐Dicarba‐closo‐dodecaborano(12)]‐1,3‐diselenacyclopentane reacts reversibly with pyridine by the opening of the icosahedron to give a zwitterionic intermediate with a nido structure, followed by irreversible deboronation to afford the corresponding 7,8‐dicarba‐nido‐undecaborate(1−) anion (see figure).