Coupling Reaction of a Cyclopentadienyl Ligand with a Dienyl or Alkenyl Moiety on Titanocene

Abstract

Coupling reactions of a cyclopentadienyl (Cp) ligand with a dienyl or alkenyl ligand on dienyl- or alkenyltitanocenes proceeded to give dienylcyclopentadiene or alkenylcyclopentadiene derivatives in good to high yields. Dienyltitanocene derivatives were prepared by protonation of bis(cyclopentadienyl)titanacyclopentadienes with carboxylic acids. Chlorodienyltitanocene derivatives were formed by the reaction of titanacyclopentadienes with NCS. Alkenyltitanocene derivatives were prepared by the reaction of titanacyclopentene, which were prepared from Cp2TiEt2 and alkynes, with t-BuOH. The structure of the alkenyltitanocene (in the case of 1,2-diphenylethenyl) was determined by X-ray analysis of the single crystal. These dienyl-, chlorodienyl-, or alkenyltitanocenes were treated with azobenzene at 50 °C for 6 h, and the corresponding dienylcyclopentadienes, chlorodienylcyclopentadienes, and alkenylcyclopentadiene derivatives were obtained in good to high yields. This result supports the existence of the stepwise mechanism for the coupling reaction of a Cp ligand with a diene moiety of titanacyclopentadienes, giving indene derivatives in the presence of azobenzene.