Abstract
(η4-Butadiene)(η5-cyclopentadienyl)tantalum dichloride (6), synthesized by treatment of CpTaCl4 (5) with (butadiene)magnesium (7), was treated with 2 molar equiv of sodium cyclopentadienide to yield Cp3Ta(butadiene) (9). The spectroscopic analysis revealed the (η5-Cp)2(η1-Cp)(η2-C4H6)Ta structure of 9. Treatment of 9 with 1 molar equiv of the salt [(Cp2Zr−CH3)+(CH3B(C6F5)3)-] (11) resulted in the clean transfer of a cyclopentadienide ligand from tantalum to zirconium with formation of the neutral zirconium compound Cp3Zr−CH3 (12) and the cation Cp2Ta(butadiene)+ (10; with CH3B(C6F5)3- counteranion). The spectroscopic characterization and an X-ray crystal structure analysis has revealed that 10 is a cationic (s-trans-η4-butadiene)bis(η5-cyclopentadienyl)tantalum complex. It reacts cleanly with a variety of ketones at 60 °C to form the respective 7,7-disubstituted tetrahydrotantalaoxepines 13. These cationic seven-membered metallacyclic σ-allyl complexes undergo a rapid topomerization process on the NMR tim...
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