A pentacoordinate chlorotrimethylsilane derivative: a very polar snapshot of a Nucleophilic Substitution and its Influence on 29 Si Solid State NMR Properties

Abstract

The reaction of l-methyl-2-mercaptoimidazole (methimazole) with chloromethyldimethylchlorosilane (ClCH2)Si(CH3) 2Cl in the presence of triethylamine afforded the l-methylimidazol-2ylthiomethyl-substituted silane 1. The pentacoordinate silicon, atom of 1 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)°. The axial situation of the still Si-bound chlorine atom with its remarkably long Si-Cl separation of 2.5123(3) Å and a trani-situated imidazolyl nitrogen donor constitute a very polart molecule, the resulting intermolecular interactions of which in the solid state were investigated crystallographically and by 29Si CP/ MAS NMR spectroscopy. Single crystals of 1 revealed significantly lower susceptibility towards temperature changes along the crystallographic α-axis, which, is the axis along which chains of the polar molecules are aligned. Hence, the 29Si 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.