Versatile Behavior of Conjugated Diynes with Zirconocene Reactive Species

Thermal decomposition of Cp2ZrPh2 in the presence of the buta-1,3-diynes RCCCCR (R = Ph, SiMe3) can lead to seven- or five-membered metallacycles. In both cases a stable benzo-fused seven-membered zirconacyclocumulene arising from a 2-fold insertion of the triple bonds of the dialkyne in the in situ generated zirconocene benzyne is formed. In the case of Me3SiCCCCSiMe3 a second minor complex is isolated: a 3-alkynyl-substituted zirconaindene arising from a β monoinsertion of one acetylenic function of the conjugated diyne in the zirconocene benzyne. No stable 2-alkynyl-substituted zirconacycle was isolated. This α monoinsertion complex is an intermediate in the exchange of the metalated moiety with a main-group atom (e.g., antimony) in a zirconacyclocumulene, explaining the formation of a 2-alkynyl-substituted stibaindene. In the thermal decomposition of Cp2Zr(Me)SCH2R4 (R4 = Ph, p-MeOC6H4) in the presence of PhCCCCPh, only the α monoinsertion of one triple bond of the diacetylenic reagent in the transient zirconathiirane is observed. The 2-alkynyl-substituted five-membered zirconathiolane is isolated as a bis-sulfonium zirconocene-ate dimer. X-ray diffraction studies corroborate the molecular structure of all these zirconacyclic complexes and stibacycle.