Formation of O⁻ Centers by Homolytic Decomposition of OH⁻ Groups on Magnesium Oxide

Abstract

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,

Recrystallization effect during the dehydration of magnesium hydroxide

“…This process repeats itself rhythmically until the reaction front reaches the core of the Mg(OH)z crystallites and all the origin substance is used up. If well-annealed, fine grained MgO is only superficially hydroxylated or deuteroxylated by exposure to 26 mbar water vapor pressure at 80 ~ [1 ], the irregularities in the dehydration curve become even more marked than for bulk Mg(OH)~ as shown in the last Fig. 3.…”

“…In case A a step mode with 25 ~ intervals and 7 min. isothermal heating periods was used [1 ] whilst in case B a linear heating rate of 2~ [2] was used. The gas evolution from the sample was monitored by a memory-free, all platinum Omegatron mass spectrometer [3].…”

“…However, we have repeatedly observed [1,2] that the dehydration of microgram quantities of magnesium hydroxide under ultrahigh vacuum conditions, as measured mass-spectroscopically by the gas evolution rate, does not result in a smooth curve.…”