Abstract

Rhenacyclobutadiene complexes supported by carbonyl ligands were reported to react with electron-rich internal alkynes to give η5-cyclopentadienyl complexes.1 In this work, we report reactions of rhenacyclobutadiene with terminal alkynes. Low valent rhenacyclobutadienes 1 did not react with 4-ethynylanisole (2) at room temperature, but reacted at 60 °C to give the η5-cyclopentadienyl complexes 3, which is similar to previously reported reactions with internal alkynes. The reactions of rhenacyclobutadienes 1 with 4-ethynyl-N,N-dimethylaniline (4) gave unexpected results. This reaction proceeded at room temperature and gave a mixture of two products:
η5-cyclopentadienyl complexes 5 and the rearrangement products 6. The new
η5-cyclopentadienyl complexes, with a substitution pattern (of the groups R, CO2Et, OEt) different from that in 1, are believed to be formed via rhena-dewar-benzene intermediates. The interesting observations are reported in the presentation.

Reference

(1) Plantevin, V.; Wojcicki, A. J. Organomet. Chem. 2004, 689, 2000–2024.