Condensation of ethyl diazoacetate with cobalt porphyrins

Condensation of ethyl diazoacetate with various cobalt complexes of octaethylporphyrin causes insertion of ethoxycarbonylcarbene into a cobalt–nitrogen bond to give a salt (VI) of the cobalt(III) adduct. Reduction of the salt (VI) with chromium(II) salts causes the formation of neutral halogenocobalt(II) complexes of N-ethoxy-carbonylmethyloctaethylporphyrin, e.g.(XIII). The action of acid under oxidative conditions on (VI) yields first a halogenocobalt(II)N-ethoxycarbonylhalogenomethyloctaethylporphyrin (XI), and then, after removal of the metal, 21,22-ethoxycarbonylmethyleneoctaethylporphyrin, the first example of a cis-21,22-bridged porphyrin. The parent 21,22-methyleneoctaethylporphyrin is obtained by condensation of di-iodomethane with octaethylporphyrin.