Reactions of Titanocene and Zirconocene Complexes with ­Bis(tert‐butoxy)acetylene – Coordination and C–O Bond Cleavage

Abstract

Abstract The reactivity of the bis‐oxygen substituted alkyne bis(tert‐butoxy)acetylene (3) towards titanocene‐ and zirconocene complexes of btmsa [btmsa = bis(trimethylsilyl)acetylene] was investigated. Those metallocenes with unsubstituted Cp ligands (Cp = η5‐cyclopentadienyl) afforded metallacyclopropenes by alkyne replacement, but only in low yields. The metallocenes bearing the sterically more demanding Cp* ligands (Cp* = η5‐pentamethylcyclopentadienyl) do not engage in replacement reactions with the alkyne 3. If titanocene monochloride is present in the reaction mixture of Cp2Ti(η2‐btmsa) with the alkyne 3, a rather unusual Calkyne–O bond cleavage occurs. The so‐formed acetylide moiety bridges two titanocene centres with an end‐on σ coordination to one of them and a π‐side‐on one to the other. This complex was investigated by X‐ray crystallography and temperature dependent NMR spectroscopy, revealing an unusual behavior.