Matrix isolation, time-resolved IR, and computational study of the photochemistry of benzoyl azideDedicated to Professor Dr Z. R. Grabowski and Professor Dr J. Wirz on the occasions of their 75th and 60th birthdays.Electronic supplementary information (ESI) available: Cartesian coordinates and details of the CASSCF/CASPT2 calculations, details of the excited-state calculations on formylnitrene, the full IR spectra, additional results from the TRIR experiments and two tables with results from CASPT2 calculations with different level shifts. See http://www.rsc.org/suppdata/cp/b2/b209775c/

Abstract

It was shown recently on the basis of DFT calculations (N. P. Gritsan and E. A. Pritchina, Mendeleev Commun., 2001, 11, 94) that the singlet states of aroylnitrenes undergo tremendous stabilization due to an extra N–O bonding interaction. To test experimentally the multiplicity and the structure of the lowest state of benzoylnitrenes we performed a study of their photochemistry in Ar matrices at 12 K. Formation of two species was observed on irradiation of benzoyl azide (1b) and its 4-acetyl derivative (1c). One of these species has an IR spectrum, which is consistent with that of isocyanate (2b,c). The IR and UV spectra of the second intermediate are in very good agreement with the calculated spectra of the singlet species (3b,c), whose structure is intermediate between that of a carbonylnitrene and an oxazirene. We further examined the photochemistry of benzoyl azide in solution at ambient temperatures by nanosecond time-resolved IR methods and obtained additional evidence for the singlet ground state of benzoylnitrene as well as insight into its reactivity in acetonitrile, cyclohexane, and dichloromethane. The above experiments were accompanied by quantum chemical calculations which included also a thorough investigation of the parent species, formylnitrene, at different levels of theory.