The (Chloromethyl)dihalosilanes X₂HSiCH₂Cl (X = F, Cl, Br, I): Synthesis, Multinuclear NMR Spectroscopy and Rotational Isomerism Examined by Raman Spectroscopy

Abstract

(Chloromethyl)diphenylsilane Ph2HSiCH2Cl (1) was prepared from Ph2SiHCl and LiCH2Cl, in situ, and was then treated with CF3SO3H/LiCl and CF3SO3H/LiBr to give the (chloromethyl)dihalosilanes Cl2HSiCH2Cl (2) and Br2HSiCH2Cl (3). I2HSiCH2Cl (4) was formed quantitatively in a protodearylation reaction between liquid hydrogen iodide and 1. Fluorination of 4 with ZnF2 gave F2HSiCH2Cl (5), albeit in low yields. Compounds 1−5 were characterised by multinuclear NMR spectroscopy (29Si, 13C, 19F) and vibrational spectroscopy. The temperature‐dependent vibrational Raman spectra of 2, 3 and 4 prove that they are mixtures of gauche and anti rotamers in the liquid state. Enthalpy differences, ΔH (Hanti − Hgauche), were determined for the liquids by applying the van’t Hoff relation, with the gauche rotamer being lower in energy for 3 and 4, and the anti rotamer for 2. The vibrational spectra were assigned with the help of ab initio calculations of equilibrium geometries and harmonic fundamental frequencies. Harmonic symmetry force constants and potential energy distributions were calculated from the ab initio Hessian matrices. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)