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)Me-3] (1, L = [eta(5):sigma-Me2C(C5H4)(C2B10H10)]) in the presence of terminal or internal alkynes (RC)-C-1 equivalent to CR2 gave the corresponding pi-alkyne complexes [TaL(eta(2)-(RC)-C-1 equivalent to 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 eta(3)-butadienyl complex 3. Complexes 2a-2c reacted with XylNC to give aza-eta(3)-butadienyl complexes 5a-5c via the eta(2)-iminoacyl eta(2)-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 eta(2)-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.