Reactions of Ta+ with Acetylene Studied with Infrared Photodissociation Spectroscopy and Theory

Tantalum cation complexes with up to four acetylene molecules are investigated using mass spectrometry and infrared photodissociation spectroscopy. The ion complexes are produced by laser ablation in an acetylene/argon molecular beam and analyzed using a time-of-flight mass spectrometer. After mass selection, infrared photodissociation spectra recorded in the C–H and C–C stretching region are compared with spectra predicted by DFT for different isomers. Ions of the form Ta+(C2H2) and Ta+(C2H2)n–H2 (n = 2–4) are observed, revealing efficient dehydrogenation and ligand coupling from the second acetylene molecule onward. Infrared spectroscopy enables the identification of these ligand-coupling products, revealing unexpected dehydrogenated metallacycle, acetylide, and metal hydride structures for n = 2 and 3. The third acetylene ligand completes the metal coordination sphere, resulting in an externally bound fourth acetylene ligand. Overall, this study demonstrates the remarkable efficiency of tantalum in promoting acetylene dehydrogenation and ligand coupling.