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# Mechanistic investigations of the reactions of nickel and iron complexes. Part I. Reactions of pyramidal Ni(Tim)-complexes. Part II. Reactions of aquapentacyanoferrate(II) and their importance to the environment

#### Abstract

With the intention of creating a five-coordinate nickel thiolate complex which could serve as a structural model for the Factor 430-coenzyme M complex, the synthesis of 2, 3, 9, 10-tetramethyl-1, 4, 8, 11-tertaaza-1, 3, 8, 10-cyclotetradecatetraene-nickel(II)-thiolate complexes have allowed for the discovery of an unusual deprotonation reaction leading to a novel macrocyclic product. Kinetic investigations of this reaction lead to a proposed mechanism implicating tautomerization in the rate determining step. A primary isotope effect of $\sim$6 is observed when the protons involved in tautomerization are substituted by deuterium. Labeling the positions involved in deprotonation also exhibits an effect on the reaction rates, however this effect is smaller and assigned to largely secondary isotope effects. The analysis of temperature dependence on the reaction rates gave activation parameters of: $\Delta$H$\ddagger$ = 47.1 kJ/mol, $\Delta$S$\ddagger$ = $-$197 J/mol, $\Delta$G$\ddagger$ = 105.7 kJ/mol. An unusual solvent dependence is observed and may be explained by the formation of solvent adducts. Support for this notion involves the serendipitous crystallization of a six-coordinate methanol adduct. The formation of solvent adducts is expected to affect the displacement of the metal out of the N$\sb4$-plane of the macrocycle. The degree of displacement may explain the solution state paramagnetism of the complexes, and is expected to influence the reaction rates. Kinetic studies of the decomposition of aquapentacyanoferrate(II), intending to probe the oxidation of this complex, have shown that the rate of oxidation to be accelerated by catalytic amounts of iron(II), manganese(II) and lead(II) ions. A synergistic effect on the reaction rate was noted for a mixture of Pb$\sp{+2}$ and Fe$\sp{+2}.$ By allowing the system to react under simulated environmental conditions, biphasic behavior was noted in the decomposition of the complex as a result of KFe$\sp{\rm (II)}$ (Fe$\sp{\rm (III)}$(CN)$\sb6\rbrack\cdot$xH$\sb2$O (Prussian Blue) formation. A speculative mechanism for the decomposition of aquapentacyanoferrate(II) is proposed, based on the results of this work. The release of cyanide as a consequence of the formation of Prussian Blue is discussed.

Chemistry

#### Recommended Citation

Figlar, James Neil, "Mechanistic investigations of the reactions of nickel and iron complexes. Part I. Reactions of pyramidal Ni(Tim)-complexes. Part II. Reactions of aquapentacyanoferrate(II) and their importance to the environment" (1998). Doctoral Dissertations Available from Proquest. AAI9823735.
https://scholarworks.umass.edu/dissertations/AAI9823735

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