Mechanistic aspects of the chemistry of mononuclear CrIII complexes with pendant-arm macrocyclic ligands and formation of discrete CrIII/FeII and CrIII/FeII/CoIII cyano-bridged mixed valence compounds

Abstract

The kinetics and mechanism of the redox reaction between [Fe II (CN) 6 ] 4-and the macrocyclic ligand complex [CrClL 15 ] 2+ (L 15 = 6-methyl-1,4,8,12-tetraazacyclopentadecane-6-amine) 4 ] 2+ has been prepared following the same procedures and the results are comparable. The final complex has the same Class II mixed valence character and its electronic spectrum shows the characteristics of both the Fe II -to-Cr III and Fe II -to-Co III CT bands. The study allows the application of the redox and/or substitutionally driven methodology, already described and kinetically designed, for the preparation of discrete mixed valence complexes of inert centres, so avoiding the unpredictable nature of other approaches seen in the past.

Copper(II) Complexes of a Hexadentate Mixed‐Donor N3S3 Macrobicyclic Cage: Facile Rearrangements and Interconversions

“…[25] In less constrained macromonocyclic Co III complexes, equilibrium and mechanistic information has been obtained identifying both ligand substitution plus amine and thioether inversion reactions. [26,27] The copper(II) chemistry of cage ligands is distinct from other transition metals due to its extreme lability and unusual coordination geometries. The d 9 Cu II metal ion in a six-coordinate environment undergoes a spontaneous distortion from octahedral or trigonal symmetry due to the JahnTeller effect.…”

Outer‐Sphere Redox Reactions Leading to the Formation of Discrete CoIII/FeII Pyrazine‐Bridged Mixed‐Valence Compounds

“…[25] Here we present the kinetic and mechanistic study of the reaction of compounds [ [23,24,28] To ascertain the redox-coupled or direct (redox-absent) substitutional nature of the general process being monitored, the reactions with [Co III X(NH 3 ) 5 ] n+ were also monitored in the presence and absence of added ethylenediaminetetraacetic acid (EDTA; [EDTA]/[Co] = 1-2). In the absence of this sequestering agent, an immediate precipitate is formed, as found in other systems, [29][30][31] [6][7][8] For the reactions of complexes with encapsulating macrocycles, [9,10,17,18] the relative stability of the {Co II L} resulting reduced species, as well as the substitution/inner-sphere redox processes that follow the outer-sphere redox reaction ({Co II 4-result in similar outcomes. [9] The nature of the final species formed for the Co III macrocyclic complexes (Scheme 3) was checked by electrochemistry, ion chromatography and 1 H NMR spectrometry experiments.…”

“…[13][14][15] We have been involved in the kinetic and mechanistic study of the outer-sphere redox processes between [Fe II -(CN) 6 ] 4-(Scheme 1, Red 2 ) and Co III or Cr III complexes of pentadentate macrocyclic (N) 5 ligands (Scheme 1, Oxd 1 ). [10,[16][17][18] In these studies the careful tuning of both the reactants and reaction conditions has been possible, and the characterization of a large family of molecular di-, triand tetranuclear discrete mixed-valence (electron donor-acceptor) cyano-bridged Co III /Fe II and Cr III /Fe II has been accomplished. The compounds include species with acceptor metal ions in different environments and protonation states.…”

“…[23,25,33] These undesired photodecomposition reactions have also been observed in cyanide-bridged Cr III analogous compounds described elsewhere. [18] All of the observed pseudo-first-order rate constants, k obs , measured for the Fe II to Co III redox processes studied as a function of the complex concentrations, temperature and pressure are collected in Table S1 (Supporting Information). The decomposition/dimerization process of the reductant, [Fe II (CN) 5 (pz)] 3-, was also kinetically monitored under control conditions, given the similarity of the rates expected both for this decomposition and the redox reactions that were monitored.…”

The Fe-catalyzed oxidation of aroyl hydrazones to aroyl hydrazines: mechanistic insight to a remarkable reaction

“…Observed rate constants were derived from the absorbance versus time traces at wavelengths where a maximum increase and/or decrease of absorbance was observed without interference from other absorbing species [13]. The general kinetic technique is that previously described [14][15][16]. The observed rate constants were determined by analyses performed with Specfit [17].…”