The catalytic synthesis of thiacrowns from thiiranes by Group VI and VII transition metal carbonyl complexes

The synthesis of thiacrowns by the catalytic ring opening cyclooligomerization of thiirane has been investigated by using some Group VI and Group VII metal carbonyl complexes. The Group VI catalyst precursors were transition metal complexes of the form M(NCCH3)(PR3)x(CO)5−x (x=0, M=Cr, Mo and W; x=1, M=Cr, R=Ph; M=W, R=Ph, or OC6H4–p-Me). For Group VII, the manganese carbonyl cations: [Mn(NCCH3)(L)(CO)4]+, L=CO, PPh3, PMe2Ph, PEt3, PBu3 and P(OMe)3 were studied. The yields of the thiacrowns were significantly improved by the addition of dialkyl acetylenedicarboxylates to the reactions catalyzed by the Group VI complexes, but these had no beneficial effect for thiacrown formation for the manganese catalysts. The principal thiacrown products are 1,4,7,10-tetrathiacyclododecane (12S4), 1,4,7,10,13-pentathiacyclopentadecane (15S5) and 1,4,7,10,13,16-hexathiacyclohexadecane (18S6). Some of the manganese catalysts also yield the cyclic polydisulfides (SCH2CH2S)n (1–4) (where n=2–5), but the principal side product with the manganese catalysts is thiirane homopolymer. The phosphine-substituted catalysts give better yields of thiacrowns than the parent carbonyls in all cases.