TRANSITION-METAL COMPLEXES OF DIAZENES .34. 2,6-DI(TRANS-STILBENYL)AZOBENZENES AND 2,3-DIHYDROCINNOLINES BY COBALT-CATALYZED DOUBLE ADDITION OF TOLAN TO AZOBENZENE DERIVATIVES

Addition of CoH(N-2)(PPh(3))(3) or CoH3(PPh(3))(3) to a melt of diphenylacetylene and an azobenzene derivative at 85 degrees C in dependence on the substitution pattern affords 2,6-di(trans-stilbenyl)azobenzenes and 2,3-dihydrocineolines. The reaction is catalytic and regioselective. When 3,5-dihalogenazobenzenes are employed, the product structure suggests that the intermediate ortho-metalation occurs via nucleophilic attack of the cobalt-centre. The dark-red 2,3-dihydrocinnolines are photochromic as indicated by short irradiation of their diluted solutions which induces ring-opening to give 2,6-di(trans-stilbenyl)azobenzenes. These cyclize back to the 2,3-dihydrocinnolines upon standing in the dark for some minutes at room temperature. The structures of all new compounds were determined by X-ray analysis.