M. S. Korobov

Synthesis, Molecular and Electronic Structures of Six-Coordinate Transition Metal (Mn, Fe, Co, Ni, Cu, and Zn) Complexes with Redox-Active 9-Hydroxyphenoxazin-1-one Ligands

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom.

Adducts of cobalt(ii) bis(salicylaldiminates) and redox-active phenoxazin-1-one: synthesis, structure, and magnetic properties

Adducts of cobalt(II) bis(salicylaldiminates) and 2,4,6,8-tetra-tert-butylphenoxazin-1-one were synthesized and their molecular and crystal structures were determined. According to the ESR and magnetochemical data, the metal atom is in the low-spin trivalent state (CoIII) due to the intramolecular electron transfer to the redox-active ligand. In the solid state, the mixedligand complexes are stable in air for several months, but in solution at elevated temperatures they dissociate to the starting components. Such a behavior detected by the temperature dependence of the effective magnetic moment is explained by the quantum chemical DFT calculations of the energy barriers of possible valence tautomeric dynamics, whose values were found to be higher than the enthalpy of dissociation.

Dehydration Rearrangements of Derivatives of Methylenedihydrobenzofuran - a New Path to Substituted Benzofurans

When heated with acidic agents derivatives of 3-amino-2-(hydroxydialkylmethyl)methylene-2,3-dihydrobenzofuran undergo rapid dehydration and rearrangement to substituted 2-alkenyl-3-aminobenzofurans.

Structural studies of 1,3-oxazolidine-containing spiropyrans

New 3’-(4-chlorophenyl)-5’,5’-dimethyl-2’-oxospiro[(2H)-chromene-2,4’-1,3-oxazolidine] was synthesized to study the donor influence of the chlorine atom at the N-phenyl substituent on the structure and photochromic properties of 1,3-oxazolidine-containing spiropyrans. Photochemical properties of synthesized 1,3-oxazolidine derivatives were studied at room temperature in toluene. The X-ray diffraction parameters for the new compound were compared with the data obtained earlier for similar spiropyrans.

Structure of the oxidative dimerization product of 4,6-di(tert-butyl)pyrogallol

The structure of the oxidation product of 4,6-di(tert-butyl)pyrogallol, viz., 6,10a-dihydroxy-3,4a, 7,9-tetra(tert-butyl)-1,2,4a,10a-tetrahydrodibenzo[b,e][1,4]dioxine-1,2-dione, was established by X-ray diffraction. Dimerization of intermediate 3-hydroxy-4,6-di(tert-butyl)-1,2-benzoquinone occurs by the mechanism of Diels—Alder heterocyclization.

New indoline spiropyrans containing azomethine fragment

The new spiropyran systems with an azomethine bridge were synthesized from a spiropyran containing aminogroup at 6′ position of the benzopyran fragment and substituted aromatic aldehydes. The chemical structure of compounds is confirmed by elemental analysis data, NMR (1H and 13C) and IR spectroscopy. Photochemical studies revealed the presence of photochromic properties at room temperature for one of the obtained spiropyrans.

Сyclization of 1-amino-2-hydrazinobenzimidazole treated with carbon disulfide. Synthesis of 9-amino-2,9-dihydro-3 Н -[1,2,4]triazolo[4,3- а ]benzimidazole-3-thione and its derivatives

Abstract1-Amino-2-hydrazinobenzimidazole when treated with carbon disulfide underwent a regioselective cyclization involving the hydrazino group to form 9-amino-2,9-dihydro-3Н-[1,2,4]triazolo[4,3-а]benzimidazole-3-thione. Being an N-amine this compound gives Schiff bases with aromatic aldehydes, and as thione in DMF at a temperature not exceeding 60°С it is successfully alkylated, particularly by functionalized alkylating agents, affording the corresponding sulfanylmethyl derivatives. In boiling DMF, as it is demonstrated by an example of benzyl chlorides, NNH2 group also undergoes alkylation that unexpectedly results in 4-benzylidenamino-3-benzylsulfanyltriazolobenzimidazoles.

Photo- and Thermochromic Spirans. 39. *Study of the Complexation of a New Crown-containing Benzoxazine Spiropyran with Metal Cations

A new benzoxazinone spiropyran containing a crown ether fragment have been synthesized. This compound was studied by both experimental and theoretical methods. In contrast to previously studied analogs, photoinduced coloration is not observed. By irradiating this crown-containing spiropyran, only an E-Z isomerization reaction proceeds. Complexation of the closed spiropyran form runs in a solution containing a calcium salt. A hypsochromic shift of the long-wavelength maximum in the absorption spectrum is observed.

Synthesis and stereochemical nonrigidity of isomeric Zn(ii)bis-[N-isopropyloxy(mercapto)naphthaldiminates]

Kinetics and reaction mechanisms governing inversion of the tetrahedral configuration at the metal center in the series ofbis-chelate Zn(II) complexes of 3,2-, 1,2-, and 2,1-oxy(mercapto)naphthaldimines, respectively4–6, have been studied with the use of dynamic1H NMR spectroscopy. A polytopal rearrangement of the diagonal twist type has been found to be an energetically preferable pathway of the inversion reaction for complexes4 and5 with a ZnN2O2 coordination site, whereas the inversion reaction for complexes with a ZnN2S2 coordination site occurs by an intramolecular dissociation-recombination pathway that involves cleavage of a Zn-N coordination bond. In the case of complexes6, the inversion reaction is governed mainly by intramolecular degenerate ligand exchange reactions.