Synthesis and crystal structures of two 1,3-di(alk-yloxy)-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borates

Two salts were prepared by methyl-ation of the respective imidazoline-2-thione at the sulfur atom, using Meerwein's salt (tri-methyl-oxonium tetra-fluorido-borate) in CH₂Cl₂. 1,3-Dimeth-oxy-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borate (1), C₆H₁₁N₂O₂S⁺·BF₄ ^-, displays a syn conformation of its two meth-oxy groups relative to each other whereas the two benz-yloxy groups present in 1,3-dibenz-yloxy-2-(methyl-sulfan-yl)imidazolium tetra-fluorido-borate (2), C₁₈H₁₉N₂O₂S⁺·BF₄ ^-, adopt an anti conformation. In the mol-ecules of 1 and 2, the methyl-sulfanyl group is rotated out of the plane of the respective heterocyclic ring. In both crystal structures, inter-molecular inter-actions are dominated by C-H⋯F-B contacts, leading to three-dimensional networks. The tetra-fluorido-borate counter-ion of 2 is disordered over three orientations (occupancy ratio 0.42:0.34:0.24), which are related by rotation about one of the B-F bonds.