ZIRCONOCENE-MEDIATED INTRAMOLECULAR CARBON-CARBON BOND FORMATION OF 2ALKYNYL GROUPS OF BIS(ALKYNYL)SILANES

Treatment of bis(phenylethynyl)silane (PhC=C)(2)SiR2 (R = Me (2a), Et (2b) or Ph (2c)) with Cp2ZrEt2 (1) (Cp = cyclopentadienyl) and H2O/CuC l 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 reac tion 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 in termediate contained the zirconacyclobutene-silacyclobutene fused ring system. Reaction of silacyclobutene 4a with CuCl selectively opened t he 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. Zirconacyclopentadien es with an alkynylsilyl group at the alpha-position afforded zirconacy clohexadiene derivatives 19 in 82-98% yields. When t-BuC5H4 was used a s the ligands instead of two Cp, the structure was determined by X-ray analysis. The structure clearly showed that 19 had the zirconacyclohe xadiene-silacyclobutene fused ring system.