Formation of nitrile ylides in the addition of singlet carbene to nitrile compounds - laser flash photolysis of (biphenyl-4-yl)chlorodiazirine in thepresence of nitrile compounds

Formation of a nitrile ylide (NY) by addition of a singlet carbene to a nit rile compound was studied by laser flash photolysis (LFP) of (biphenyl-4-yl )chlorodiazirine (BCD) in the presence of nitrile compounds. Although the g enerated (biphenyl-4-yl)chlorocarbene (BCC) forms a NY by addition to a nit rile compound in an equilibrium reaction, the absorption spectrum of the NY can be measured only in the LFP of BCD in the presence of 2,4,6-trimethoxy benzonitrile. The equilibrium constants for the NY formation iii the additi on of BCC to propiononitrile or pivalonitrile were determined to be 0.45 an d 0.37 M-1 at 295 K, respectively The reactivity of NY towards olefins seem s to be substantially lower than those of BCC. The reaction of BCC with 2,3 -dimethylbut-2-ene was carried out in 2,2,4-trimethylpentane and propionitr ile in the temperature range of ca. 170 to 300 K. In both solvents, the rat e constants increased with decreasing temperature and the maximum value app eared at around 210 K. Using the difference in the rate constants, the free energy difference for the equilibrium constant was also estimated to be ca . 4.2 kJ mol(-1).