Silicon–Phosphorus and Silicon–Arsenic Cage Compounds with Bicyclo[2.2.1]heptane, Bicyclo[3.2.1]octane and Tricyclo[3.3.3.1.03,7]nonane Backbones

The reaction of tris(chlorodimethylsilyl)methylsilane (1) and 1,1,2,2-tetrakis(chlorodimethylsilyl)-1,2-dimethyldisilane (2) with sodium/potassium arsenide Na3As/K3As afforded decamethyl-2,3,5,6,7-pentasila-1,4-diarsabicyclo[2.2.1]heptane (3)and dodecamethyl-2,3,4,6,7,8,9-heptasila-1,5-diarsatricyclo[3.3.1.03,7]nonane (4). Compounds 3 and 4 were isolated from the reaction mixture by fractional crystallization and structurally characterized by single-crystal X-ray crystallography. The reaction of 1 with an excess amount of sodium/potassium phosphide (Na3P/K3P) afforded the cage-shaped anionsodium hexamethyl-2,4,6,7-tetrasila-1-phosphanido-3,5-diphosphabicyclo[3.2.1]octane (5), which reacts with chlorotrimethylsilane to form trimethylsilyl-substituted derivative 6. The molecular structures of 5 and 6 were established by X-ray crystallography. Cages 3–6 were also characterized by 29Si- and 31P NMR spectroscopy. Owing to indirect spin–spin coupling between the 29Si and 31P nuclei, the resonances of the 29Si nuclei in the spectra of 5 and 6 are only of first order approximately. To account for the observed preferences of the cage structures in these reactions, extensive B3LYP/6-31G* quantum chemical calculations of relative energies of bicyclo[2.2.2] and bicyclo[3.2.1] isomers of Si8H14, PSi7H13, P2Si6H12 and P3Si5H11 were conducted. On the basis of the computed charge distributions, the concept of topological charge stabilization was used to predict the relative stabilities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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