The first metallacycles formed by oxidative addition of tin-sulfur, tin-selenium, tin-tellurium, and germanium-tellurium bonds to platinum(II) are reported. In particular, the ring compounds [(R2SnE)(3)], where R = Me, Ph and E = Se, Te, and the new compound [(Me2GeTe)(3)], react with [PtMe2(bu(2)bpy)] (bu(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine) to give the new organoplatinum(IV) metallacycles [PtMe2(R2SnE)(2)(bu(2)bpy)] and [PtMe2(Me-2-GeTe)(2)(bu(2)bpy)], respectively. The tin-containing metallacycles complexes can undergo exchange of either the R2Sn or the E groups by reaction with [(R-2'SnE)(3)] or [(R2SnE')(3)], respectively, to give the corresponding new metallacycles of general formula [PtMe2(R2SnE-R'2SnE)(bu(2)bpy)] or [PtMe2(R2SnE-R2SnE')(bu(2)bpy)]. The isostructural series of complexes [PtMe2(Ph2SnE)(2)(bu(2)bpy)] with E = S, Se, and Te have been characterized by X-ray structure determinations. It is shown that Sn-119 NMR is a useful method of structure determination for these metallacyclic compounds.