Synthesis, molecular structure and reactivity of the dimethyl sulfide adduct of a 1,3,2-diselenaborolane with an annelated dicarba-closo-dodecaborane(12) unit

Oxidative addition of elemental selenium to 1,4,2,5-diazadiborinine

A heavier analogue of dibora-peroxide 4 involving a B–Se–Se–B unit has been synthesized and fully characterized.

Closely related yet different: a borylene and its dimer are non-interconvertible but connected through reactivity

The self-stabilizing, tetrameric cyanoborylene [(cAAC)B(CN)]4 (I, cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and its diborene relative, [(cAAC)(CN)B[double bond, length as m-dash]B(CN)(cAAC)] (II), both react with disulfides and diselenides to yield the corresponding cAAC-supported cyanoboron bis(chalcogenides). Furthermore, reactions of I or II with elemental sulfur and selenium in various stoichiometries provided access to a variety of cAAC-stabilized cyanoboron-chalcogen heterocycles, including a unique dithiaborirane, a diboraselenirane, 1,3-dichalcogena-2,4-diboretanes, 1,3,4-trichalcogena-2,5-diborolanes and a rare six-membered 1,2,4,5-tetrathia-3,6-diborinane. Stepwise addition reactions and solution stability studies provided insights into the mechanism of these reactions and the subtle differences in reactivity observed between I and II.

Reactivity of alkynylsilanes towards B-halogeno-1,3,2-diselenaborolanes with an annelated dicarba-closo-dodecaborane(12) unit

The C≡C bond of alkynylsilanes undergoes 1,2-haloboration with 2-halogeno-1,3,2-diselenaborolano-4,5-[1,2-dicarba-closo-dodecaborane(12)], in competition with reversible insertion into one of the B–Se bonds (selenoboration) to afford a seven-membered ring and finally, by elimination of Me3Si–X (X = Cl, Br, I), the corresponding B-alkynyl derivatives. The reactions were monitored by NMR spectroscopy (11B, 13C, 29Si and 77Se NMR). The proposed solution-state structures are also supported by DFT calculations of single molecule geometries and NMR parameters [B3LYP/6-311 + G(d,p) level of theory].

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-)

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).