| Abstract
| - m-Phenylene-coupled carbenonitrenes [(3-nitrenophenyl)methylene (2-H), (3-nitrenophenyl)fluoromethylene (2-F), (3-nitrenophenyl)chloromethylene (2-Cl), (3-nitrenophenyl)bromomethylene (2-Br)] have been investigated computationally (with B3LYP, MCSCF, CASPT2, ROMP2, andQCISD(T) methods) and experimentally (with IR, UV, and ESR spectroscopy). For each species,five electronic states were considered. At the highest level of theory explored, the parent compound(2-H) has a quintet ground state, but its halogen derivatives (2-X, X = F, Cl, and Br) have tripletground states. A linear relationship between the Q−T energy gap of 2-X and the T−S gap of thecorresponding phenylcarbenes 8-X is found, which can be helpful in rationalizing and predictingground-state multiplicities in m-phenylene-linked carbenonitrenes and similar species. Precursorsfor the photochemical generation of 2-X (X = H, F, Cl, and Br) were synthesized and photolyzed inmatrixes (Ar, triacetin) at low temperatures. IR (Ar, 13 K) and ESR (triacetin, 77 K) data arecompatible with the generation of triplet halocarbenonitrenes 2-X, (X = F, Cl, and Br). All fourcompounds upon further irradiation undergo isomerization to substituted cyclopropenes 5-X (X =H, F, Cl, and Br), as suggested by their IR spectra.
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