Matrix infrared spectroscopic studies of a singlet heptafulvene carbene (C9H6) in solid neon

In this study, we generated and characterized two C3-benzene compounds through the reaction of a C3 carbon molecule with benzene at 4 K. These compounds were identified using infrared spectroscopy with D and 13C isotopic substitution of benzene reagents, as well as quantum chemical calculations. Upon sample deposition and annealing, a weakly interacting C3-benzene complex (labeled A) was observed. The predicted bond distance between the C3 unit and benzene is 3.260 Å, indicating a relatively weak interaction due to this extended separation. Under UV-light irradiation, a previously unconsidered singlet heptafulvene carbene (labeled B) was generated at the expense of species A. The overall C3-mediated C–C bond insertion reaction of benzene, leading to the formation of heptafulvene carbene (B), is predicted to be exothermic by 200 kJ mol−1. This novel singlet heptafulvene carbene compound has been produced and characterized experimentally for the first time in solid neon. In addition, the reaction pathway for fulvenallene formation in the reaction between a carbon atom and benzene is discussed in detail. The results presented herein provide new insights into understanding the reactivity of carbon molecules and the synthesis of novel carbene compounds.