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−)

Abstract

The reaction of the 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion [1,2-(1,2-C(2)B(10)H(10))Se(2)](2-) with dichloromethane (CH(2)Cl(2) or CD(2)Cl(2)) 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 ((1)H, (11)B, (13)C, and (77)Se). 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 ((1)H, (11)B, (13)C, and (77)Se).

A Spirocyclic Borate and a Dihydroborate Derived from the 1,2‐Diselenolato‐1,2‐dicarba‐closo‐dodecaborane(12) Dianion [1,2‐(1,2‐C2B10H10)Se2]2–: Structures, NMR Spectroscopy, and DFT Calculations

“…[14] Thus, we have studied the reaction of 4a with pyridine in CD 2 Cl 2 . There was no reaction of 4a with CD 2 Cl 2 .…”

“…The remaining oil at the bottom was dried in vacuo to leave an orange-red residue. After 2 d in CD 2 Cl 2 at room temp., the mixture contained 9c (90 %), 7 (R = H) (10 %), [14] and LiBH 4 . Crystal Structure Determination of Complexes 4e and 9e: Details pertinent to the crystal structure determinations are listed in Table 4.…”

“…After 24 h at room temp., volatile materials were removed in vacuo, the remaining mixture was dissolved in CD 2 Cl 2 (1 mL), and the liquid phase was separated by centrifugation. The mixture contained 9b (80 %), 7 (R = D) (20 %), [14] and LiBH 4 . Then 12-crown-4 (0.016 mL, 0.10 mmol) was added to this reaction mixture.…”

“…Since all relevant NMR spectroscopic data of 7 and 8 are known, [14] the analysis of this mixture was straightforward. Deboronation of one or both carborane cages in anion 4 -to give novel di-and trianions was not observed.…”

“…Indeed, the dianions of type 3 have proved to be valuable ligands in transition-metal chemistry, [4][5][6][7] and their main-group-element chemistry is also a developing and promising field. [8][9][10][11][12][13][14] The selenium derivative 3 is particularly attractive, since the 77 Se nucleus (natural abundance 7.58 %; I = ½) possesses favorable NMR spectroscopic properties, and thus 77 Se NMR spectroscopy is well suited to monitor reactions and characterize products, even in mixtures. [15] We have shown that it is advisable for many purposes to use 3 after careful isolation [10,12,14] instead of Scheme 1.…”