Catalytic Formation of Five-Membered Zirconacycloallenoids and Their Reaction with Carbon Dioxide

Hydrozirconation of phenylacetylene
followed by a reaction with
((trimethylsilyl)­ethynyl)lithium gave the respective (σ-alkenyl)­(σ-alkynyl)­zirconocene
complex 6a. Its treatment with a catalytic amount of
B­(C6F5)3 (2 mol %) at room temperature
resulted in efficient σ-ligand coupling with the formation of
the isomeric five-membered zirconacycloallenoid complex 9a. Two similar examples with different substituents R1 (SiMe3, tBu) were also investigated.
All three new zirconacycloallenoids (9a–c) were characterized by X-ray diffraction. The addition reaction
of carbon dioxide to the zirconacycloallenoid complex 9c and two related examples from the literature were studied. The carbon
dioxide addition products were also characterized by X-ray crystal
structure analysis.