Cyclotrimerization of Acetylene in Gas Phase V + (C 2 H 2 ) n Complexes:Detection of Intermediates and Products with Infrared Spectroscopy

Infrared laser spectroscopy and mass spectrometry were used to determine the structures of intermediates and products in the single-atom-catalyzed trimerization of acetylene to form benzene. Complexes of the form V+(C2H2)n were produced in the gas phase via laser ablation in a pulsed-nozzle source, size-selected with a mass spectrometer, and studied with infrared laser photodissociation spectroscopy. Density Functional Theory (DFT) calculations were performed in support of the experiments. Single- and double-acetylene complexes form VC2 metallacycle structures. Three-acetylene complexes exhibit a surprising dependence on the acetylene concentration, forming V(C2)3 and C2VC4 tri- and dimetallacycle ion structures at low concentration, and eventually V+(benzene) at higher concentrations. These observations reveal intermediates along the reaction path of acetylene cyclotrimerization to benzene.