Oleg M. Nikitin

Application of reductive amination reaction for preparation of ferrocene-modified porphyrins

Porphyrin-modified ferrocenes were synthesized via the reductive amination reaction of ferrocenylpyrazolecarboxaldehydes and tetraphenylporphyrinamine. The steric hindrance of ferrocene moiety was found to play the key role in this reaction.

Solvent switchable CuII complexes

A new tetranuclear complex Cu4, [Cu2L(OH)]2·2CH3OH·H2O (1), with the functionalized Schiff base ligand 2,6-bis((2-(acetylamino)phenylimino)methyl)-4-tert-butylphenol (H3L) has been obtained and characterized in the solid state by X-ray diffraction. The formation of the tetranuclear species is solvent dependent, the presence of water being a determinant in its isolation. Based on the mass-spectrometric evidence, the behaviour of the H3L–CuII system in the presence of water was investigated. Namely, water can switch the nuclearity of the CuII cluster from dinuclear to tetranuclear. The redox behaviour of this species in DMSO solution, showing two cathodic metal-centred peaks at EP = −0.80 and −1.35 V and an irreversible ligand-centred anodic peak at EP = 1.03 V, was found to be similar to that of a pristine dinuclear complex. The tetranuclear species was also characterized in the solid state by magnetic measurements, showing a dominating bulk antiferromagnetic behaviour, with a singlet ground state at approximately 2 K. DFT calculations permitted us to estimate the strong intradimer antiferromagnetic exchange interaction (J1 = −440 cm−1), together with two weak interdimer ferromagnetic exchange interactions (J2 = +0.5 and J3 = +1.7 cm−1).

Pyrrolizidine and cyclobutane bridged double-caged fullerene derivatives

Novel types of double-caged [60]fullerene derivatives containing adjacent pyrrolizidine and cyclobutane bridges have been synthesized and characterized by MALDI MS, UV/VIS, 1H and 13C NMR spectroscopy, and cyclic voltammetry.

Polymer biquinolyl-containing complexes of Pd(II) as efficient catalysts for cyanation of aryl and vinyl halides with K4Fe(CN)6

A catalytic system for cyanation of aryl and vinyl halides with K4Fe(CN)6 based on a structurally tunable and nontoxic polymer backbone of polyamic type with biquinolyl fragments in the polymer chain capable of coordination to PdII ions is developed. The catalyst is eligible for thermal and microwave activation; in the latter case the reaction time is dramatically decreased. Cyanation of vinyl bromides occurs stereoselectively, and the configuration of the starting alkene is retained; even for Z-isomers the impact of configuration inversion is less than 5%. The polymer-based Pd catalyst is applicable for one-pot multi-step synthesis of the precursors of mesogenic structures of biphenyl type. Consecutive cross-coupling and cyanation reactions can be performed in the presence of the same portion of catalyst, in the same solvent, without isolation of intermediate products.

Electrocatalytic dehalogenation of α-bromoketones in the presence of Cp2TiCl2

Processes of direct and electrocatalytic (in the presence of electrochemically reduced Cp2TiCl2) reduction of three α-bromoketones containing the C(sp3)-Br or C(sp2)-Br bond, viz., 2-bromo-and 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-ones and α-bromo-acetophenone, were studied by cyclic voltammetry and preparative electrolysis. In all cases, the dissociative electron transfer proceeds via the concerted mechanism. Preparative electrolysis of these α-bromoketones in the presence of Cp2TiCl2 affords the reductive debromination products in 40–80% yield at low cathodic potentials (−0.85 V vs. Ag/AgCl/KCl). In the case of 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-one in the potentiostatic regime, only one bromine atom can be eliminated selectively.

Synthesis and electrochemical properties of ruthenium(II) complexes with biquinoline-containing polyamic acids—Polybenzoxazinone prepolymers

New polyamic acids with biquinoline units in the backbone, which are prepolymers of polybenzoxazinones, as well as their metal-polymer complexes containing [Ru(bpy)2]2+, were prepared. The electronic structure of these polymers was studied with the use of cyclic voltammetry, electronic absorption spectroscopy, and quantum-chemical calculations, and the location sites of electronic changes upon electrochemical reduction and oxidation were determined.

Polymeric 2,2′-biquinolyl-containing NiII complexes as catalysts for the Suzuki reaction

The Suzuki reaction with polymeric Ni catalysts based on the biquinolyl-containing polyamic acids can be carried out under conditions close to the conditions used for the catalytic transformations in the presence of PdII complexes with the same polymeric ligands. However, the yields of the cross-coupling products on the Ni catalysts are somewhat lower than those obtained in the presence of palladium complexes. The yield of the cross-coupling product increases with the increase in the conformational mobility of the polymeric ligand. Unlike catalysis by palladium complexes, in catalytic transformations by nickel complexes activation of the catalyst is required. Such an activation can be carried out either by addition of chemical reducing agents or by applying the corresponding cathodic potential (−0.8 V relative to Ag/AgCl/KCl). The electrochemical activation was shown to lead to higher yields of the cross-coupling product than the use of chemical reducing agents.

Electroactive Composite Pd–Polypyrrole and Its Catalytic Properties in the Reaction of Styryl Bromide Cyanation

A composite material in the form of powder is synthesized by a redox reaction in mixed aqueous solution of Pd(NH3)4Cl2 + pyrrole. The composite consists of polypyrrole globules with palladium nanoparticles uniformly distributed inside the latter. Being applied as a film on the electrode surface, both components of this material exhibit redox activity. Palladium particles inside the composite exhibit catalytic properties in cyanation of styryl bromides, a reaction widely used in fine organic synthesis.

The synthesis of ferrocenyl- and ferrocenoylpyrimidines

New derivatives of pyrimidine were synthesized from ferrocenyl ketones by the reactions of [3+1+1+1]annulation and intermolecular cyclization. The electrochemical behavior of the obtained compounds was studied by the method of cyclic voltammetry. All the compounds may be characterized with the signal, corresponding to the reversible one-electron transfer in ferrocene-ferrecinium and lowering of the redox potential with respect to ferrocene.

Electrochemical Formation of the Redox-Active Metal-Containing Polymers for Catalytic and Electrocatalytic Applications

A convenient electrochemical approach to new redox-active Cu, Pd, Ni -containing polymers of polyamic type with biquinoline (biQ) fragments was elaborated. The comparative analysis of the data obtained revealed the main factors which influence the type of metal coordination unit formed in the polymer: the nature of metal, the number of biQ fragments and conformational rigidity of the polymer backbone as well as the electrolysis conditions. Voltammetric investigation of metal-polymers allows distinguishing the types and relative amounts of metalcoordination units formed. The comparison of the electrochemical data with the results of catalytic tests revealed the guidelines for electrochemical synthesis of efficient catalytic systems.