Intermediates and products of the hexachlorodisilane cleavage of group 14 element phosphanes and amines - Molecular structure of di-tert-butyl(trichlorosilyl)phosphane in the gas phase determined by electron diffraction and ab initio calculations

Reactions of dialkyl(trimethylsilyl)phosphanes RR'PSiMe3 (1: R, R' = tBu; 3 : R, R' = iPr; 5: R = iPr, R' = tBu) with Si2Cl6 provide stable trichlorosi lylphosphanes RR'PSiCl3 (2, 4, 6); the reactions of silyl- and stannylamine s of iPr(2)NMMe(3) (M = Si: 11; M = Sn: 12) with Si2Cl6, however, provide t he stable pentachlorodisilanylamine iPr(2)NSi(2)Cl(5) (13). Heating of 1 wi th the technical mixture Me-2(Cl)SiSiCl2Me/(MeCl2Si)2 yields the stable sil ylphosphane tBu(2)PSiMe(2)Cl (8) and the disilanylphosphane tBu(2)Psi(Me)(C l)Si(Me)Cl-2 (9). Methylation of 9 with MeLi gave tBu(2)PSi(2)Me(5) 10, whi ch was isolated in a pure state. Reactions of tBu(iPr)PSiMe3 (5) and of org anometal phosphanes tBu(iPr)PMR3 (14: M = Ge, R = Me; 17a-c: M = Sn; R = Me , Et, nBu) with Si,CI, were monitored by P-31, Si-29, and Sn-119 NMR. - In the first step of these reactions, new tBu(iPr)PSi2Cl5 (7) is formed. 7 is accompanied by increasing amounts of tBu(iPr)PSiCl3 (6) and Me3GeSiCl3 (15) /(Me3Ge)(2)Si(SiCl3)(2) (16) or traces of compounds R3SnSiCl3 (19a-c) that decompose providing (R3Sn)(2)Si(SiCl3)(2) (18a-c) and nBu(3)SnSi(SiCl3)(3) (20c). Subsequently, compounds 19a-c decompose providing increasing amounts of 18a-c. Stannylphosphane 17b is also cleaved by SiCl4 leading to 6 with liberation of Et3SnCl, whereas 17b is formed from the reaction of 5 with Et 3SnCl under liberation of Me3SiCl. The suggestion of an extra stabilisation of P-Si bonds of trichlorosilylphosphanes was subjected to direct evidence through the structure determination of the trichlorosilylphosphane tBu(2)P SiCl(3) (2) in the gas phase by electron diffraction. This crowded molecule has a "normal" P-Si bond length of 225.0(12) pm; its C-1 symmetric conform ation with both tBu groups and the SiCl3 group twisted about 17 degrees fro m the perfectly staggered positions, and with each of the three groups tilt ed about 6 degrees away from each other, allows to reduce steric strain.