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