Matrix-IR spectroscopic investigations of the thermolysis and photolysis of diazoamides.

Matrix photolysis of N,N-dialkyldiazoacetamides 1a-d at 7-10 K results in either the formation of C-H insertion products (in case of N,N-dimethyl and N,N-diethyl diazoamides) or almost exclusive Wolff rearrangement to ketenes (in the case of the cyclic diazoamides N-(diazoacetyl)azetidine and N-(diazoacetyl)pyrrolidine). This can be ascribed to higher activation barriers for the approach of the singlet carbene p orbital in 5 (or of the diazo carbon in an excited state of 1) to the stronger and "tied back" nature of the C-H bonds in the cyclic substituents. In contrast, flash vacuum thermolysis (FVT) of diazoamides 1a-d, in which reactions of excited states are excluded, gives rise to clean C-H insertion with only minor Wolff rearrangement to ketenes.

Linear ketenimines. Variable structures of C,C-dicyanoketenimines and C,C-bis-sulfonylketenimines.

C,C-dicyanoketenimines 10a-c were generated by flash vacuum thermolysis of ketene N,S-acetals 9a-c or by thermal or photochemical decomposition of alpha-azido-beta-cyanocinnamonitrile 11. In the latter reaction, 3,3-dicyano-2-phenyl-1-azirine 12 is also formed. IR spectroscopy of the keteniminines isolated in Ar matrixes or as neat films, NMR spectroscopy of 10c, and theoretical calculations (B3LYP/6-31G) demonstrate that these ketenimines have variable geometry, being essentially linear along the CCN-R framework in polar media (neat films and solution), but in the gas phase or Ar matrix they are bent, as is usual for ketenimines.