The course of hydrogenation of nickel(II)β-alkylated 1,19-dimethyltetradehydrocorrin salts

Abstract

The course of hydrogenation of nickel and cobalt tetradehydrocorrin salts is profoundly affected by the β-alkyl. substitution pattern. In the absence of alkyl substituents at C-2 and C-18, the hydrogenation products vary according to the experimental conditions. At room temperature, rings A and D are hydrogenated with the formation of the nickel BC-didehydrocorrin salt whereas at 100° the isomeric nickel AD-didehydrocorrin salt is obtained. Further hydrogenation of these products yields the amorphous nickel corrin salts often accompanied by the corresponding 4,5-dihydrocorrin salts. Vigorous hydrogenation of nickel(II) tetradehydrocorrin salts bearing alkyl groups at positions 1, 2, 18, and 19 can yield either an isocorrin salt or its 17,18-dehydro-derivative and their formation is a consequence of the steric crowding of the alkyl substituents around the direct AD linkage. Easy dehydrogenation at certain specified positions in the hydrogenated nickel salts has been observed in the mass spectrometer and the results have been correlated with the postulated structures.