Kinetics and Thermodynamics of the Template Synthesis and of an Acidic Decomposition of the Clathrochelate Iron(II) Tris-Cyclohexanedion-1,2-Dioximate (Nioximate) Formed by a Cross-Linking with Methylboronic Acid

• Published in: Russian journal of inorganic chemistry 2020-10, Vol.65 (10), p.1503-1512
• Main Authors: Pomadchik, A. L., Belov, A. S., Lebed, E. G., Voloshin, Ya. Z.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Chemistry of Macrocyclic and Metallocyclic Compounds; Crosslinking; Decomposition; Inorganic Chemistry; Iron; Kinetics; Rate constants; Synthesis
• ISSN: 0036-0236; 1531-8613
• DOI: 10.1134/S0036023620100162

— The title complex is formed in a quantitative yield in diluted solutions and the kinetics of its template synthesis and its acidic decomposition were photometricaly studied. The effective synthesis rate constants were determined as the pseudo-first-order rate constants with respect to the concentration of Fe 2+ ions. The orders with respect to those of nioxime, CH 3 B(OH) 2 and H + ions are equal to 3, 1 and –1, respectively. The plausible pathway of its assembly includes a reversible formation of the protonated pseudooctahedral iron(II) tris-nioximate, followed by its monodeprotonation and addition of CH 3 B(OH) 2 . Thus obtained pseudooctahedral intermediate undergoes a rate-determining stage of double cyclization with elimination of two molecules of water and structural rearrangement as well, thus giving the trigonal-prismatic iron(II) semiclathrochelate monocation. The latter complex easily undergoes a cross-linking with CH 3 B(OH) 2 , resulted in elimination of H + ion and in formation of the title clathrochelate. Its acidic decomposition rate constants were also obtained as the pseudo-first-order rate constants, but with respect to the concentration of this complex. This rate substantially increases with increase in activity of H + ions and decreases in the presence of CH 3 B(OH) 2 .