No abstract

Photolysis of 1 in argon-saturated acetonitrile yields 2, whereas in oxygen-saturated acetonitrile small amounts of benzoic acid and benzamide are formed in addition to 2. Similarly, photolysis of 2 in argon-saturated acetonitrile results in 1 and a trace amount of 3, whereas in oxygen-saturated acetonitrile the major product is 1 in addition to the formation of small amounts of benzoic acid and benzamide. Laser flash photolysis of 1 results in an absorption due to triplet vinylnitrene 4 (broad absorption with λ(max) at 360 nm, τ = 1.8 μs, acetonitrile) that is formed with a rate constant of 1.2 × 10(7) s(-1) and decays with a rate constant of 5.6 × 10(5) s(-1). Laser flash photolysis of 2 in argon-saturated acetonitrile likewise results in the formation of triplet vinylnitrene 4 but also ylide 5 (λ(max) at 440 nm, τ = 13 μs). The rate constant for forming 4 in argon-saturated acetonitrile is 1.6 × 10(7) s(-1). In oxygen-saturated acetonitrile, vinylnitrene 4 reacts to form the peroxide radical 6 (λ(max) 360 nm, ~0.7 μs, acetonitrile) at a rate of 2 × 10(9) M(-1) s(-1). Density functional theory calculations were performed to aid in the characterization of vinylnitrene 4 and peroxide 6 and to support the proposed mechanism for the formation of these intermediates.

Photolysis of 3-methyl-2-phenyl-2H-azirine (1a) in argon-saturated acetonitrile does not yield any new products, whereas photolysis in oxygen-saturated acetonitrile yields benzaldehyde (2) by interception of vinylnitrene 5 with oxygen. Similarly, photolysis of 1a in the presence of bromoform allows the trapping of vinylnitrene 5, leading to the formation of 1-bromo-1-phenylpropan-2-one (4). Laser flash photolysis of 1a in argon-saturated acetonitrile (λ = 308 nm) results in a transient absorption with λ(max) at ~440 nm due to the formation of triplet vinylnitrene 5. Likewise, irradiation of 1a in cryogenic argon matrixes through a Pyrex filter results in the formation of ketene imine 11, presumably through vinylnitrene 5. In contrast, photolysis of 2-methyl-3-phenyl-2H-azirine (1b) in acetonitrile yields heterocycles 6 and 7. Laser flash photolysis of 1b in acetonitrile shows a transient absorption with a maximum at 320 nm due to the formation of ylide 8, which has a lifetime on the order of several milliseconds. Similarly, photolysis of 1b in cryogenic argon matrixes results in ylide 8. Density functional theory calculations were performed to support the proposed mechanism for the photoreactivity of 1a and 1b and to aid in the characterization of the intermediates formed upon irradiation.

The photolysis of 2-azido-1,4-naphthoquinone (1) in argon matrices at 8 K results in the corresponding triplet vinylnitrene (3)2, which was detected directly by IR spectroscopy. Vinylnitrene (3)2 is stable in argon matrices but forms 2-cyanoindane-1,3-dione (3) upon further irradiation. Similarly, the irradiation of azide 1 in 2-methyltetrahydrofuran (MTHF) matrices at 5 K resulted in the ESR spectrum of vinylnitrene (3)2, which is stable up to at least 100 K. The zero-field splitting parameters for nitrene (3)2, D/hc = 0.7292 cm(-1) and E/hc = 0.0048 cm(-1), verify that it has significant 1,3-biradical character. Vinylnitrene (3)2 (λmax ∼ 460 nm, τ = 22 μs) is also observed directly in solution at ambient temperature with laser flash photolysis of 1. Density functional theory (DFT) calculations support the characterization of vinylnitrene (3)2 and the proposed mechanism for its formation. Because vinylnitrene (3)2 is relatively stable, it has potential use as a building-block for high-spin assemblies.

Photolysis of vinylazide 1, which has a built-in acetophenone triplet sensitizer, in argon-saturated toluene results in azirine 2, whereas irradiation in oxygen-saturated toluene yields cyanide derivatives 3 and 4. Laser flash photolysis of azide 1 in argon-saturated acetonitrile shows formation of vinylnitrene 1c, which has a λmax at ∼300 nm and a lifetime of ∼1 ms. Vinylnitrene 1c is formed with a rate constant of 4.25 × 10(5) s(-1) from triplet 1,2-biradical 1b. Laser flash photolysis of 1 in oxygen-saturated acetonitrile results in 1c-O (λmax = 430 nm, τ ≈ 420 μs acetonitrile). Density functional theory (DFT) calculations were used to aid in the characterization of the intermediates formed upon irradiation of azide 1 and to validate the proposed mechanism for its photoreactivity.