Alkyne reagents have been applied as versatile ligands in organometallic chemistry. While alkynes readily form adducts with low-valent late transition metals, the early-transition-metal alkyne complexes are generally derived from reduction of a high-valent metal center in the presence of an alkyne. Herein, we introduce a facile, one-pot method to synthesize a series of tantalum alkyne complexes from a d0tantalum alkyl complex, where using strong reducing agent is avoided. Such synthetic method works on both terminal and internal alkynes bearing different functional groups.
Moreover, the reactivity of these tantalum alkyne complexes towards unsaturated molecules has been investigated. By treatment with carbon monoxide or isonitriles, these tantalum alkyne complexes produced nonplanar five-membered metallacycles. Interestingly, the chelation of a bidentate phosphine ligand could planarize the oxa five-membered ring and gave a six-electron metallafuran complex. On the other hand, direct reaction of the phosphine ligand with these terminal alkyne complexes afforded η2-vinyl complexes. The structures of these novel tantalum complexes have been unambiguously characterized by single crystal X-ray analyses.

Synthesis and Reactivity of Tantalum Alkyne Complexes Supported by Linked Cyclopentadienyl-Carboranyl Ligand

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