Photoequilibration of 1-Naphthylcarbene and 4,5-Benzobicyclo[4.1.0]hepta-2,4,6-triene

Irradiation (λ > 300 nm) of 1-naphthyldiazomethane ( 11 ) or 1-naphthyldiazirine ( 12 ) isolated in an argon matrix at 10 K produces 4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene ( 2 ) and a small amount of triplet 1-naphthylcarbene ( 1 ). Cyclopropene 2 is characterized by infrared and UV/visible spectroscopy while triplet 1-naphthylcarbene ( 1 ) is characterized by infrared, UV/visible, and ESR spectroscopy. Experimental and computed (B3LYP/6-31G*) IR spectra display good agreement. Carbene 1 and cyclopropene 2 are thermally stable in the matrix at 10 K, although they may be interconverted photochemically. Further irradiation of the matrix under a number of conditions (λ > 300, λ = 342 ± 10, λ > 497, or λ = 544 ± 10 nm) causes disappearance of carbene 1 and exclusive growth of cyclopropene 2 . Shorter wavelength photolysis (λ = 290 ± 10 nm) triggers reversion of 2 back to 1 . Conversion of either compound to 4,5-benzocyclohepta-1,2,4,6-tetraene ( 6 ), 2-naphthylcarbene ( 8 ), or 2,3-benzobicyclo-[4.1.0]hepta-2,4,6-triene ( 9 ) was not observed under any of our experimental conditions. Matrix isolated cyclobuta[ de ]naphthalene ( 4 ) disappears slowly upon prolonged UV irradiation (λ > 200 nm), affording a trace of triplet 1-naphthylcarbene ( 1 ).