Influence\nof Curvature on the Physical Properties\nand Reactivity of Triplet Corannulene Nitrene

Although\nnitrene chemistry is promising for the light-induced modification\nof organic compounds, the reactivity of large polycyclic aromatic\ncompounds and the effects of their curvature remain unexplored. Irradiation\nof azidocorannulene (<b>1</b>) in methanol/acetonitrile followed\nby HCl addition produced diastereomers <b>5</b> and <b>5′</b>. Azirine <b>2</b> is apparently trapped by methanol to form\ndiastereomeric acetal derivatives that are hydrolyzed with HCl to\nyield <b>5</b> and <b>5</b>’. ESR spectroscopy\nin a glassy matrix at 77 K showed that irradiation of <b>1</b> yields corannulene nitrene <sup>3</sup><b>1N</b>, which has\nsignificant 1,3-biradical character. Irradiation of <b>1</b> in a glassy matrix resulted in a new absorption band in the region\nof 360–440 nm, with λ<sub>max</sub> at 360 and 410 nm,\nattributed to <sup>3</sup><b>1N</b>, as supported by time-dependent\ndensity function theory calculations, which placed the major electronic\ntransitions of <sup>3</sup><b>1N</b> at 367 nm (<i>f</i> = 0.0407) and 440 nm (<i>f</i> = 0.0353). Laser flash\nphotolysis of <b>1</b> revealed a similar absorption spectrum.\nNitrene <sup>3</sup><b>1N</b> had a lifetime of only a few hundred\nnanoseconds and was efficiently quenched by oxygen, because of its\n1,3-biradical character. CASPT2(12,11)/6-311G** calculations revealed\nsmall energy gap (7.2 kcal/mol) between singlet and triplet configurations,\nsuggesting that <sup>3</sup><b>1N</b> is formed by intersystem\ncrossing of <sup>1</sup><b>1N</b> to <sup>3</sup><b>1N</b>. Spin-density, nucleus-independent chemical shift, and anisotropy\nof the induced current density calculations verified that <sup>3</sup><b>1N</b> is a triplet vinylnitrene with unpaired electrons\nlocalized on the CC–N moiety; decaying by intersystem\ncrossing to <b>2</b>, which is more stable owing to its aromaticity,\nas supported by calculations (SA-CASSCF/QD-NEVPT2/CBS).