Hydroxoundecahydro-closo-dodecaborate(2−) as a Nucleophile. Preparation and Structural Characterization of O-Alkyl and O-Acyl Derivatives of Hydroxoundecahydro-closo-dodecaborate(2−)

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Abstract
The syntheses, solid state structures, and spectral properties of O-alkyl and O-acyl derivatives of hydroxoundecahydro-closo-dodecaborate(2−), 1, are described. Alkylation of 1 with ethyl iodide was achieved in dimethyl sulfoxide using potassium hydroxide as a base, leading to [N(n-C4H9)4]2[CH3CH2O−B12H11(2−)], 2, bis(tetrabutylammonium) ethoxyundecahydro-closo-dodecaborate(2−) [monoclinic P21/n, a = 1192.4(9) pm, b = 1253.9(4) pm, c = 3049.1(10) pm, β = 92.69(4)°, Z = 4, R1 = 0.0693, wR2 = 0.1517]. Alkylation with 1,5-dibromopentane afforded the cyclic oxonium salt [PPN][C5H10O−B12H11(1−)], 3, (μ-nitrido)bis(triphenylphosphorus)(1+) tetrahydropyrane−undecahydro-closo-dodecaborate(1−) [monoclinic P21/c, a = 1938.1(2) pm, b = 1329.7(10) pm, c = 1944.0(2) pm, β = 108.82(10)°, Z = 4, R1 = 0.0484, wR2 = 0.0833]. Acylation of 1 in acetonitrile with acyl chlorides in the presence of pyridine yielded [N(n-C4H9)4]2[C6H5CO2-B12H11(2−)], 4, bis(tetrabutylammonium) undecahydrobenzoyl-closo-dodecaborate(2−) [monoclinic P21/c, a = 1812.0(4) pm, b = 1711.9(3) pm, c = 1685.0(3) pm, β = 114.03(3)°, Z = 4, R1 = 0.0915, wR2 = 0.2093], and [N(n-C4H9)4]2[CH3CO2-B12H11(2−)], 5, bis(tetrabutylammonium) acetoxyundecahydro-closo-dodecaborate(2−) [monoclinic P21/n, a = 1190.5(2) pm, b = 1243.0(10) pm, c = 3078.4(4) pm, β = 92.76(10)°, Z = 4, R1 = 0.0642, wR2 = 0.1462]. All crystal structures showed distortion of the pseudoicosahedral geometry of the boron cluster. The boron−oxygen distances varied from 144.2(5) pm for 2, 148.5(3) pm for 5, 149.4(12) pm for 4, to 152.8(4) pm for 3. The 3-fold coordinated oxygen of oxonium salt 3 is nearly planar.

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