FORMATION AND REACTIONS OF STANNANETHIONES AND STANNANESELONES

Two approaches for the formation of stannanethiones and stannaneselones were examined, i.e., (i) the thermal retrocycloaddition of trichalcogenastannolanes 1 and (ii) the dechalcogenation of tetrachalcogenastannolanes 2 and 3. Novel heterocycles containing tin and chalcogen atoms, 1,2,4,3-trichalcogenastannolanes Tb(Tip)SnY3CPh2 [1a,b (Y = S, Se; Tb = 2,4,6-tris[bis-trimethylsilyl)methyl]phenyl; Tip = 2,4,6-triisopropylphenyl)], have been synthesized by the thermal reaction of 1,2,3,4,5-tetrachalcogenastannolanes Tb(Tip)SnY4 (3) with diphenyldiazomethane followed by dechalcogenation with hexamethylphosphoric triamide. Thermal decomposition of trichalcogenastannolanes 1 in the presence of dimethyl acetylenedicarboxylate (DMAD) afforded thiastannete 8 and selenastannete 14 as novel tin-containing heterocycles. The formation of 8 and 14 was explained in terms of a [2 + 2]cycloaddition of intermediary stannanethione 18a and stannaneselone 18b with DMAD. Dechalcogenation of tetrachalcogenastannolanes 2 and 3 with trivalent phosphorus compounds in the absence of trapping agents gave dichalcogenadistannetanes whose formation was explained in terms of dimerization of stannanethione 18a or stannaneselone 18b, except for the reaction of more crowded triisopropylphenyl-substituted 3a which gave a monomeric product 28 at room temperature on account of a slower rate of dimerization. The desulfurization of 3a with triphenylphosphine in the presence of an excess amount of 2,3-dimethyl-1,3-butadiene provided [4 + 2]cycloadduct 32 as the first example of [4 + 2]cycloaddition of a stannanethione. The structures of 26, 27, 31, 8, and 14 were definitely determined by X-ray diffraction analysis. The central four-membered rings of trans-dichalcogenadistannetanes 26 and 31 were almost completely planar, while those of cis-27 had unprecedentedly large fold angles due to the steric repulsion between two Tb groups. Both 8 and 14 were found to have distorted trapezoid skeletons reflecting the coexistence of long tin-chalcogen bonds and short carbon-carbon double bonds.