Zirconocene-Mediated Intramolecular Carbon−Carbon Bond Formation of Two Alkynyl Groups of Bis(alkynyl)silanes

Abstract

Treatment of bis(phenylethynyl)silane (PhC⋮C)2SiR2 (R = Me (2a), Et (2b) or Ph (2c)) with Cp2ZrEt2 (1) (Cp = cyclopentadienyl) and H2O/CuCl in this order afforded (1E,3E)-1,4-diphenyl-1,3-butadiene (3) in 56−88% yields after hydrolysis. On the other hand, hydrolysis of the reaction mixture of 2a−h with Cp2ZrEt2 gave silacyclobutene derivatives 4a−h in 61−87% yields. Zirconium-containing intermediate 7 was obtained as crystals suitable for X-ray analysis when t-BuC5H4 was used as the ligands of a zirconocene derivative. Structure of 7 showed that the intermediate contained the zirconacyclobutene−silacyclobutene fused ring system. Reaction of silacyclobutene 4a with CuCl selectively opened the silacyclobutene ring. The further treatment of the reaction mixture with PhI in the presence of a catalytic amount of Pd(PPh3)4 gave 1,3,4-triphenyl-1-silyl-1,3-butadiene compound 16. Zirconacyclopentadienes with an alkynylsilyl group at the α-position afforded zirconacyclohexadiene derivatives 19 in 82−98% yields. When t-BuC5H4 was used as the ligands instead of two Cp, the structure was determined by X-ray analysis. The structure clearly showed that 19 had the zirconacyclohexadiene−silacyclobutene fused ring system.