Ring Expansion and Contraction in Reactions of an Alkyne with Stannylplatinum(IV) Metallacycles:  Formation of an Alkyl(alkenyl)(alkynyl)platinum(IV) Complex

The five-membered stannylplatinum(IV) metallacycles [PtMe2{SnMe2ESnMe2E}(bu2bpy)], E = S, Se, Te, bu2bpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine, undergo facile ring expansion by insertion of the electrophilic alkyne RCCR, R = CO2Me, into the PtE−Sn bond to yield the corresponding seven-membered metallacycles [PtMe2{SnMe2ESnMe2CRCRE}(bu2bpy)]. The seven-membered metallacycles slowly eliminate “Me2SnE” to give new five-membered metallacycles [PtMe2{SnMe2CRCRE}(bu2bpy)]. When E = Se, reaction with excess RCCR gives the complex [PtMe2(CRCRH)(CCR)(bu2bpy)], which contains alkyl, alkenyl, and alkynyl functionalities in the same molecule. In the presence of excess RCCR and [(Me2SnSe)3], the products Se(Z-CRCHR)2 and the selenole Se(CRCRCRCR) are formed catalytically.