A Series of Room-Temperature Thermally Stable Bromostannylenes Bearing the Bulky Rind Group: Synthesis, Characterization, and Crystal Structures

A series of bromostannylenes, (Rind)­BrSn: (1; Rind = EMind (a, R¹ = Et, R² = Me), Eind (b, R¹ = R² = Et), MPind (c, R¹ = Me, R² = ⁿPr)), have been obtained as room-temperature thermally stable crystalline materials incorporating the fused-ring bulky Rind groups (Rind = 1,1,7,7-tetra-R¹-3,3,5,5-tetra-R²-s-hydrindacen-4-yl). The bulky Eind- and the bulkier MPind-based bromostannylenes (1b,c) have been synthesized by the reaction of SnBr₂·(dioxane) with 1 equiv of (Rind)Li in THF. In contrast, the less bulky EMind-based halostannylenes (EMind)­XSn: (X = Br (1a), Cl (2a)) have been prepared by a ligand redistribution reaction between the diarylstannylene (EMind)₂Sn: (3a) and SnX₂·(dioxane) (X = Br, Cl), in toluene. The crystal structures of (EMind)­BrSn: (1a), (Eind)­BrSn: (1b), and (MPind)­BrSn: (1c) have been determined by X-ray diffraction methods along with that of (EMind)­ClSn: (2a). While the bulkier MPind-based 1c has a monomeric structure with a bent two-coordinate Sn­(II) center, a coordination dimer was found for the Eind-based 1b in which two Sn atoms are asymmetrically bridged by two Br atoms. The less bulky EMind-based 1a and 2a show a unique one-dimensional (1-D) polymeric structure in their crystals with alternating Sn and Br or Cl atoms supported by the perpendicularly oriented EMind groups. The halostannylenes 1a–c and 2a all exist as monomers in solution on the basis of their spectroscopic data, and their electronic properties have been experimentally and theoretically characterized.