Photochemistry of matrix-isolated 4-diazo-4H-imidazole: IR-spectroscopic identification of 4H-imidazol-4-ylidene

Irradiation of 4-diazo-4H-imidazole (1) in an argon matrix at 10 K at a wav elength of lambda = 313 nm leads to rapid loss of nitrogen and the formatio n of 4H-imidazol-4-ylidene (2). Upon photoexcitation of 4N-imidazol-4-ylide ne (2) at wavelengths longer than 570 nm, the ring-opened carbene S-6 can b e detected. S-6 can be photochemically converted (lambda > 310 nm) to 2-cya no-2H-azirene (5). In CO-doped argon matrices, 2 is trapped and 4H-imidazol -4-ylidene ketene (7) can be observed.