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(SiMe 3 ) 2 ]}SnS 4 (Cy = cyclohexyl; R = Me ( 3 ), t Bu ( 4 )) were prepared by the reaction of elemental sulfur with newly reported divalent tin starting materials [CyNC(R)NCy]Sn[N(SiMe 3 ) 2 ] (R = Me ( 1 ), t Bu ( 2 )). Compounds 3 and 4 were further converted to dimeric bridging sulfido complexes, {(CyNC(R)NCy)[N(SiMe 3 ) 2 ]Sn(μ-S)} 2 (R = Me ( 5 ), t Bu ( 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.