Determination of the gas-phase molecular structures of di-t-butyldichlorosilane and di-t-butylchlorosilane by electron diffraction and molecular mechanics calculations

Abstract The molecular structures of SiBu t 2 Cl 2 and SiBu t 2 ClH in the gas phase have been determined by a combination of electron diffraction and molecular mechanics. The advantage of using molecular mechanics as a guide to the structures is shown. In both structures the butyl groups adopt nearly staggered conformations with respect to opposite SiC bonds. In SiBu t 2 Cl 2 , assuming C 2 symmetry, the parameters ( r a ) are: r (SiCl)=206.9(1), r (SiC)=189.1(4), r [C(1)–C(2)]=154.8(2), r (CH)=113.5(2) pm, ∠ SiC(1)C(2)=108.7(2), ∠ CCH=112.6(9), ∠ CSiC=125.3(6), ∠ ClSiCl=102.7(5), o[C(14)SiC(1)C(2)]=167.1(1), o[SiC(1)C(2)H(3)]=145.9(18)°. In SiBu t 2 ClH, the geometric parameters are: r (SiCl)=208.7(2), r (SiC)=190.3(4), r [C(1)–C(2)]=154.1(1), r (CH)=113.1(3), r (SiH)=148.7 pm, ∠ SiC(1)C(2)=106.5(2), ∠ CCH=113.2(11), ∠ CSiC=125.2(5), ∠ ClSiH= 102.7(13), o[C(14)SiC(1)C(2)]=167.8(8), o[SiC(1)C(2)H(3)]=157.4(17)°.