Mass-selected copper-acetylene and vanadium-acetylene cation complexes of the form Cu(C2H2)n+ and V(C2H2)n+ are produced by laser ablation and studied via infrared laser photodissociation spectroscopy in the C-H stretching region. Spectra for larger species are measured via ligand elimination, whereas argon tagging is employed to enhance dissociation yields in smaller complexes. The number of infrared active bands, their frequency positions and their relative intensities provide insight into the structure, bonding and reactivity of these ions. Density functional theory calculations are carried out in support of this work. For Cu(C2H2)n+, the combined data show that cation-π bonds are formed for the n = 1−3 species, resulting in red-shifted C-H stretches on the acetylene ligands. Three acetylene ligands complete the coordination of the copper cation. Additional ligands (n = 4−6) solvate the n = 3 core by forming CH-π bonds. Distinctive vibrational patterns are exhibited for coordinated vs. solvent ligands. For V(C2H2)n+, the combined data provides evidence for the metal-catalyzed trimerization of acetylene to form benzene, as well as the formation of exotic metallacycles for larger complexes.

Structural trends and reactivity of first-row transition metal cation-acetylene complexes revealed by probing their C-H stretching fundamentals

253rd National Meeting (2017)

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