MECHANISTIC STUDIES OF THE DECOMPOSITION OF 2,3-DIAZABICYCLO(2.2.2)OCT-2-ENES

Abstract

Two bicyclic azoalkanes were prepared: 1-cyclopropyl-2,3-diazabicyclo 2.2.2 oct-2-ene (MCP) and 1,4-dicyclopropyl-2,3-diazabicyclo 2.2.2 oct-2-ene (DCP). Products derived from the photolysis of MCP and DCP were the typical bicyclo 2.2.0 hexanes and 1,5-hexadienes; however, the cyclopropylcarbinyl rearrangement was also influential in product formation especially in sensitized irradiations. A mechanism for product formation is presented in which a biradical spin correlation effect is invoked. A mechanism is present for excited state azoalkane decomposition through the ('1)(n,(pi)*) and ('3)(n,(pi)*) states without intersystem crossing (isc) between the two spin states. Maximum quantum yields for isc are calculated as 0.092 and 0.049 for MCP and DCP, respectively. Photophysical data and product ratios support the mechanism. Photolysis of MCP in CCl(,4) is rationalized by an electron transfer process from MCP to CCl(,4). Efforts to discover other electron acceptors which would undergo chemical reactions have failed; however, quenching of the fluorescence lifetime was observed and the data are presented