A Pentacoordinate Chlorotrimethylsilane Derivative: A very Polar Snapshot of a Nucleophilic Substitution and its Influence on 29Si Solid State NMR Properties

The reaction of 1-methyl-2-mercaptoimidazole (methimazole) with chloromethyldimethylchlorositane (ClCH2)Si(CH3)(2)Cl in the presence of triethylamine afforded the 1-methylimidazol-2-ylthiomethyl-substituted silane 1. The pentacoordinate silicon atom of I is housed within an almost trigonal bipyramidal coordination sphere, i.e., the three equatorially situated C-Si-C angles sum up to 359.5(3)degrees. The axial situation of the still Si-bound chlorine atom with its remarkably long Si-Cl separation of 2.5123(3) angstrom and a trans-situated imidazolyl nitrogen donor constitute a very polar molecule, the resulting intermolecular interactions of which in the solid state were investigated crystallographically and by Si-29 CP/MAS NMR spectroscopy. Single crystals of I revealed significantly lower susceptibility towards temperature changes along the crystallographic a-axis, which is the axis along which chains of the polar molecules are aligned. Hence, the Si-29 NMR shielding tensor, experimentally determined by CP/MAS NMR spectroscopy, could only be simulated to a satisfactory extent when taking these intermolecular interactions into account.