Photodecomposition of Thienylsulfonyl Azides: Generation and Spectroscopic Characterization of Triplet Thienylsulfonyl Nitrenes and 3-Thienylnitrene.

The photochemistry of 2-thienylsulfonyl azide () and 3-thienylsulfonyl azide () has been disclosed by combining matrix-isolation spectroscopy with quantum chemical calculations. Two novel heteroaryl sulfonyl nitrenes, 2-thienylsulfonyl nitrene () and 3-thienylsulfonyl nitrene (), have been generated during the 266 nm laser photolysis of and , respectively. Both nitrenes in the triplet ground state have been characterized with matrix-isolation IR (N-labeling) in solid Ar (10.0 K), N (10.0 K), and Ne (2.8 K) matrixes and EPR spectroscopy (, |/| = 1.452 cm and |/| = 0.0058 cm; , |/| = 1.492 cm and |/| = 0.0060 cm) in solid toluene at 5.0 K. Upon subsequent UV-light irradiation (365 nm), no Curtius rearrangement but decomposition of occurs by SO-elimination and the concurrent formation of ring-opening product ()-4-thioxo-2-butenenitrile () via the intermediacy of the putative 2-thienylnitrene (). In contrast, violet-light irradiation (400 ± 20 nm) of causes SO-elimination to yield triplet 3-thienylnitrene (), for which the IR spectroscopic identification is supported by quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level. 3-Thienylnitrene is highly reactive, since it not only combines with SO to furnish 3-thienyl--sulfonylamine () but also undergoes ring-opening to (-)-4-thioxo-2-butenenitrile () under the UV-light irradiation (365 nm).