Synthesis of Organotantalum Alkyne Complexes [{η5:σ-Me2C(C5H4)(C2B10H10)}TaMe(η2‑R1CCR2)] and Their Reactions with Unsaturated Molecules

Hydrogenolysis of tantalum methyl complex [Ta­(L)­Me3] (1, L = [η5:σ-Me2C­(C5H4)­(C2B10H10)]) in the presence of terminal or internal alkynes R1CCR2 gave the corresponding π-alkyne complexes [TaL­(η2-R1CCR2)­Me] (2a–2g) in 71–93% yields. Their reactions with various kinds of unsaturated molecules were investigated. Complex 2b reacted with trimethylsilyl acetylene to give an η3-butadienyl complex 3. Complexes 2a–2c reacted with XylNC to give aza-η3-butadienyl complexes 5a–5c via the η2-iminoacyl η2-alkyne intermediates 4a–4c. Treatment of 2f with CO in the presence of 1,2-bis­(dimethylphosphino)­ethane (dmpe) afforded a tantallafuran complex 6. The reaction of 2a with PhNCO produced an oxo N-alkenyl η2-iminoacyl complex 7, whereas 2b reacted with PhNCO to generate a metallacyclic complex 8. The structures of these complexes have been confirmed by single-crystal X-ray analyses.