Synthesis of trithiolanes and tetrathianes from thiiranes catalyzed by ruthenium salen nitrosyl complexes

The compound [Ru(salen)(NO)(H₂O)](SbF₆) (1) (salen = N, N′-ethylene-bis-salicylidene aminate) reacts catalytically with thiiranes and converts them to olefins and 1,2,3,4-tetrathianes or 1,2,3-trithiolanes. The monosubstituted thiiranes styrene sulfide and propylene sulfide reacted to form the corresponding olefin and the 4-substituted 1,2,3-trithiolane in a 2:1 ratio in isolated yields in excess of 90%. The disubstituted thiirane cis-stilbene sulfide was converted to cis-stilbene and 5,6-trans-1,2,3,4-diphenyltetrathiane in a 3:1 ratio in the presence of a catalytic amount of 1 in CD₃NO₂. Coordination of cis-stilbene sulfide to the salen complex in a ligand substitution reaction was established by isolation of [Ru(salen)(NO)(cis-stilbene sulfide)]-(SbF₆) (6). ¹H NMR studies performed on 6 indicated that the salen macrocycle had rearranged upon thiirane coordination. A similar rearrangement was found to be stabilized by other ligands including tetramethylethylene sulfide, tetrahydrothiophene, and d₃-acetonitrile. The α-deuterio-cis-stilbene sulfide catalyst adduct (d-6) reacted with unlabeled cis-stilbene sulfide to form deuterium-labeled trans-diphenyl-tetrathiane and unlabeled cis-stilbene as shown by GCMS and ¹H NMR. Thus, the solution thiirane behaves as a sulfur donor and forms olefin, whereas the coordinated thiirane becomes the cyclic polysulfide. β-cis-Deuteriostyrene sulfide was used to show that ring closure to form cyclic polysulfide incorporated inversion of stereochemistry versus starting thiirane. A mechanism for catalysis consistent with experimental data is presented that requires coordination of thiirane to the metal complex followed by bimolecular attack of free thiirane on the coordinated thiirane.