Transition metal complexes of diazenes XXXIX: Stilbenylazobenzene derivatives by cobalt-catalysed addition of diphenylacetylene to 1,2-diaryldiazenes and their acid-catalysed rearrangement to N-anilinoindoles

Article abstract of DOI:10.1016/S0022-328X(97)00074-0

CoH₃(PPh₃)₃ catalyses the regioselective double and monoinsertion of tolan into the ortho-CH bonds of several 1,2-diaryldiazenes at room temperature. When halogenated azobenzene derivatives are involved, only the substituted phenyl ring is attacked. The structure of 2-(trans-stilbenyl)-3,5-dichloroazobenzene was determined by single crystal X-ray analysis. Depending on the substitution pattern the stilbenyl derivatives may isomerize to 2,3-dihydrocinnolines. These 1:1 adducts are identified as the intermediates previously postulated in the rhodium-catalysed synthesis of N-anilinoindoles from alkynes and 1,2-diaryldiazenes. The rearrangement of 2,3,4-triphenyl-2,3-dihydrocinnoline to N-anilino-2,3-diphenylindole was studied at 70-90 °C; it is catalysed by acetic acid and the rate law reveals reaction orders of 1.0 and 0.6 for the dihydrocinnoline and HOAc respectively. While the activation enthalpies of 56 ± 9 and 54 ± 3kJ mol^-1 are the same within experimental error, the activation entropy of the catalysed reaction, ΔS^?_298K = -136 ± 7 J K^-1 mol^-1, is more positive than the - 191 ± 14 J K^-1 mol^-1 value measured in the absence of HOAc.