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#### Gas-phase molecular structures of bis(chloromethylsilyl)amine and bis(chloromethylsilyl)methylamine by electron diffraction and ab initio calculations; experimental support for n(N)–σ*(Si–Cl) hyperconjugation

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##### Citation

Fleischer, H., Brain, P. T., Rankin, D. W. H., Robertson, H. E., Bühl, M., & Thiel, W. (1998).
Gas-phase molecular structures of bis(chloromethylsilyl)amine and bis(chloromethylsilyl)methylamine by electron diffraction
and ab initio calculations; experimental support for n(N)–σ*(Si–Cl) hyperconjugation.* Journal of the
Chemical Society, Dalton Transactions,* (4), 593-600. doi:10.1039/A708219C.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0024-44C5-D

##### Abstract

The gas-phase molecular structures of NH(SiHMeCl)

_{2}1 and NMe(SiHMeCl)_{2}2 have been investigated by electron diffraction (ED) and by ab initio geometry optimisations at the MP2/6-31G* level. Ab initio calculations suggest six different conformers to be present for both compounds. They also predict that all conformers exhibit planar or nearly planar configurations at the N atom and that all the Si–Cl bonds are more or less orthogonal to the SiNSi plane, a feature that is supported by the ED refinement. Natural bond orbital analysis and an SCF deletion calculation showed an energy contribution of the n(N)–σ*(Si–Cl) hyperconjugative interaction of more than 80 kJ mol^{–1}, thus rationalising conformations that optimise an overlap of the two appropriate orbitals. The principal parameters (r_{a}) from electron diffraction for NH(SiHMeCl)_{2}(with estimated standard deviations given in parentheses and ab initio-calculated values for the lowest-energy conformer given in square brackets) are: r(Si–N) 171.2(2) [173.7], r(Si–Cl) 206.2(1) [207.7], r(Si–C) 184.5(3) [186.4] pm; Si–N–Si 128.8(12) [131.3], N–Si–Cl 112.9(4) [111.3], N–Si–C 115.7(9) [112.0] and Cl–Si–C 102.6(6) [107.3]°. For NMe(SiHMeCl)2: r(Si–N) 171.5(1) [173.7], r(Si–Cl) 207.1(1) [208.1], r(Si–C) 185.2(2) [186.8], r(N–C) 147.4(6) [148.1] pm; Si–N–Si 124.9(6) [123.7], N–Si–Cl 108.3(5) [110.4], N–Si–C 115.1(8) [112.4] and Cl–Si–C 107.3(7) [106.7]°.