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The formation of compound (3) from salt ( 1 ) could be explained by a slow protonation and ring opening of the kinetically favored aziridine (2) followed by base catalyzed ring closure to nickel and loss of Ni-N bond. We demonstrated that ( 2 ) , in CHZCIZ/CH~NOZ (1: 1) solution, was quantitatively transformed into (3) (15 minutes, 25"C), confirming the required acid-base catalysis.The complex (3) was stable in inert solvents (T < 1W0C) but was quantitatively demetalated by acids into base ( 4 ) , as its corresponding salt (CF3COOH < 5 min; AcOH: 24 h).Reaction with ethanolic KOH gave tetraphenylporphinatonickel in loo"/, yield. When heated in solution (0.5% in xylene, 18 h under argon), compound (3) rearranged to the known homoporphinatonickel derivatives ( 5 ) and (6) (89 %; ratio 46: 54, as well as 10 % tetraphenylporphinatonickel).This reaction may occur via aziridine ( 2 ) , which was already known to yield (6) on heating at 80°C in solution['! The higher temperature (140°C) required to transform (3) into ( 5 ) and (6) explained the occurrence of both products, whose interconversion by ring inversion is rapid above 11O'C.-Reactions of the type described here could warrant attention for understanding the substrate binding in porphyrin and corrin coenzymes. N -Ethoxycarbonylmethylene-meso-tetraphenylporphinatonickel( 11) ( 3 )Triethylamine (35ml) and Na2S04 (3g) were added to a stirred solution of (I) (735mg) in CHzClz (40ml). After 3 days' stirring at 25°C the solution was filtered, the solvent evaporated and the residue chromatographed on silica gel. Toluene eluted the product which was crystallized from CH2C12/CH30H. Crystals suitable for the X-ray studies were obtained from CHC13/CH,0H. All physica data for (3) are compatible with the structure (IR, visible absorption, MS,

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