α-Cleavage of 2,2-Diazido-2,3-dihydroinden-1-one in Solution and Cryogenic Matrices.

The Norrish type I (α-cleavage) reaction is an excellent photochemical method for radical-pair formation in solution. However, in cryogenic matrices, the starting material typically re-forms before the radical pair diffuses apart. This study focused on N extrusion from an azido alkyl radical to prevent radical-pair recombination. Irradiation of 2,2-diazido-2,3-dihydroinden-1-one () in methanol mainly yielded methyl 2-cyanomethylbenzoate () and 2-cyanomethylbenzoic acid () via α-cleavage. Laser flash photolysis of in argon-saturated acetonitrile resulted in α-cleavage to form triplet biradical (λ ∼ 410 nm, τ ∼ 400 ns). In contrast, upon irradiation in glassy 2-methyltetrahydrofuran matrices, triplet alkylnitrene was directly detected using electron spin resonance (/ = 1.5646 cm, / = 0.00161 cm) and absorption spectroscopy (λ = 276 and 341 nm). Irradiation of in argon matrices generated , benzoyl azide , singlet benzoylnitrene , and isocyanide , as revealed by IR spectroscopy. The experimental results supported by density functional theory calculations [B3PW91/6-311++G(d,p)] suggest that irradiation of in matrices results in α-cleavage to form biradical , which extrudes N to yield . Rearrangement of into competes with cleavage of a N radical to form radical . The N/ radical pair combines to form , which upon irradiation yields and .