Formation of novel tetrasulfido tin complexes and their ability to catalyze the cyclotrimerization of aryl isocyanates

Unusual cyclic tin tetrasulfido complexes {(CyNC(R)NCy)[N(SiMe3)2]}SnS4 (Cy = cyclohexyl; R = Me (3), tBu (4)) were prepared by the reaction of elemental sulfur with newly reported divalent tin starting materials [CyNC(R)NCy]Sn[N(SiMe3)2] (R = Me (1), tBu (2)). Compounds 3 and 4 were further converted to dimeric bridging sulfido complexes, ((CyNC(R)NCy)[N(SiMe3)2]Sn(μ-S)}2 (R = Me (5), tBu (6)), which can also be derived from the oxidative addition of sulfur atom sources (e.g., propylene sulfide) to 1 and 2, respectively. Single-crystal X-ray diffraction studies of 2,4, and 6 are presented. Compounds 3 and 4 are outstanding catalysts for the cyclotrimerization of aryl isocyanates to perhydro-1,3,5-triazine-2,4,6-triones (isocyanurates) at room temperature. The results of a single-crystal X-ray analysis of triphenylisocyanurate (7) are also reported.