Vanadium Pentafulvene Complexes: Synthon for Unprecedented VanadoceneIII Derivatives.

The benzene ligand at CpV(η6 -C6 H6 ) (1) is exchanged for pentafulvenes. Using sterically demanding pentafulvenes gives a clean exchange reaction, yielding vanadium pentafulvene (2 a and 2 b) and benzofulvene complexes (3 a and 3 b). The molecular structures of the target compounds suggest a π-η5 :σ-η1 coordination mode with a vanadiumIII center. With the sterically low demanding 6,6-dimethylpentafulvene, a C-H activation at the leaving ligand is observed, yielding the ring-substituted vanadoceneII 4. The reactivity of the pentafulvene complexes was investigated. A series of unprecedented vanadoceneIII compounds were synthesized: Under mild conditions, E-H splitting of 4-tert-butylphenol, diphenylamine, and 2,6-diisopropylaniline yield well characterized examples of rare vanadoceneIII phenolate and amide complexes. Insertion reactions into the V-Cexo bond of the pentafulvene complexes by multiple bond containing substrates were found for acetone, 4-chlorobenzonitril and N,N'-dicyclohexylcarbodiimide.