Bond-formation versuselectron transfer: C–C-coupling reactions of hydrocarbon dications with benzene

Abstract

The bimolecular reactions of several hydrocarbon dications C_mH_n²⁺ (m = 6–10, n = 4–9) with neutral benzene are investigated by tandem mass spectrometry using a multipole instrument. Not surprisingly, the major reaction of C_mH_n²⁺ with benzene corresponds to electron transfer from the neutral arene to the dication resulting in the pair of monocationic products C_mH_n⁺ + C₆H₆⁺. In addition, also dissociative electron transfer takes place, whereas proton transfer from the C_mH_n²⁺ dication to neutral benzene is almost negligible. Interestingly, the excess energy liberated upon electron transfer from the neutral arene to the C_mH_n²⁺ dication is not equally partitioned in the monocationic products in that the cations arising from the dicationic precursor have a higher internal energy content than the monocations formed from the neutral reaction partner. In addition to the reactions leading to monocationic product ions, bond-forming reactions with maintenance of the two-fold charge are observed, which lead to a condensation of the C_mH_n²⁺ dications with neutral benzene under formation of intermediate C_m+6H_n+6²⁺ species and then undergo subsequent losses of molecular hydrogen or neutral acetylene. This reaction complements a recently proposed dicationic route for the formation of polycyclic aromatic hydrocarbons under extreme conditions such as they exist in interstellar environments.