L. P. Yur'eva

The study of redox reactions of bisarenechromium complexes by the rotating disk electrode technique: I. Oxidation of bisarenechromium(O) complexes and reduction of bisarenechromium(I) cations

Abstract The redox properties of twenty bisarenechromium complexes have been studied by the rotating disk electrode technique in an aprotic solvent (DMSO). The half-wave potentials, E1/2, have been found to correlate well with the meta-substituent constants. The conclusion is drawn that the electronic effects of substituents are mainly transferred to the reaction centre (the metal atom) by the inductive mechanism. The conjugation of substituents with the coordinated ring is weaker in bisarenechromium complexes than in ferrocene derivatives.

Interaction of chromium vapour with benzonitrile and bromobenzene

Abstract Bis(benzonitrile)chromium was isolated from the reaction of benzonitrile with chromium vapour. The major process was accompanied by cyclotrimerization of benzonitrile to form 2,4,6-triphenyltriazine. Phenyl bromide reacted with chromium to give insignificant amounts of cationic bis(arene)chromium compounds containing bromobenzene, diphenyl and benzene as ligands.

Study of redox reactions of bis(arene) chromium complexes by the rotating disk electrode technique. IV: Electrochemical oxidation and ionization potentials of bis(arene) chromium complexes

Abstract The reversible electrochemical oxidation of a series of bis(arene)chromium com-plexes has been studied by use of the rotating disk electrode technique The half-wave potentials E 1/2 show an excellent correlation with the meta -substituent constants. The E 1/2 values were found to correlate well with the vertical ionization potentials ( IP ) of the same complexes in the gas phase determined from their He(I) photoelectronic spectra.

Electronic structure of bis-arene-chromium complexes

Abstract Dibenzenechromium derivatives of the type (C 6 H 5 R 1 )Cr(C 6 R 5 R 2 ) have been studied by He-I photoelectron spectroscopy. Substituent parameters have been found which allow the first and second ionization potentials of the bis-arene-chromium complexes to be determined using a very precise additive scheme. It has been shown that the change in the energy of the highest occupied MOs of the molecules is determined by the electrostatic field of ligands. The molecular electrostatic potentials of a number of species (C 6 H 5 R 1 )(C 6 H 5 R 2 ) have been calculated and the equation relating IP to ϕ( R ) has been found. A scheme for constructing the energy level diagram for dibenzenechromium and its derivatives is suggested.

The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring-disk electrode techniques : II. Electrochemical reduction of benzalacetophenone and bis(benzalacetophenone)chromium☆

Abstract The processes of electrochemical reduction of free benzalacetophenone and its symmetrical π-complex with chromium in DMSO show two ( e - + e - ) and three ( e - + e - + 2 e - ), respectively, cathodic waves on the polarization curves. π-Coordination with the chromium atom exerts little influence on the mechanism of the process in the region of the first cathodic wave potentials. In both cases reversible transfer of one electron is followed by dimerization of the primary products of the electrode reaction, i.e. anion-radicals (AR). AR and the products of their dimerization were detected directly by the rotating ring-disk electrode technique. The reactivity of bis(benzalacetophenone)chromium in the reaction is approximately an order of magnitude lower than that of free benzalacetophenone in a similar reaction: Accordingly, the half-wave potential of the former reaction is shifted towards a more negative value and the equilibrium constant decreases: log( K c / K L ) = -0.9 ± 0.3. The effect of coordination on the kinetics of AR dimerization is noticeably less. The rate constant of complex AR dimerization, k d C = (1.5 ± 0.7) × 10 4

Interaction of diphenylacetylene with chromium salts

Abstract The reaction of diphenylacetylene with chromium atoms results in the formation of bisarenechromium π-complexes containing diphenylacetylene and its cyclotrimer as ligands, viz., bis(η 6 -diphenylacetylene)chromium, (η 6 -diphenylacetylene)(η 6 -hexaphenylbenzene)chromium and bis(η 6 -hexaphenylbenzene)chromium. The other reaction products were found to be uncomplexed hexaphenylbenzene and 1,2,3,4-tetraphenylbutadiene-1,3.

The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring disk electrode techniques: III. Cathodic reduction of chromium(0) π-complexes and the corresponding arenes in dimethyl sulfoxide solutions☆

Abstract The rotating disk (RDE) and the rotating ring-disk (RRDE) electrode techniques have been employed to study the cathodic behavior of eight bisarenechromium complexes and seven corresponding arenes in DMSO solutions. In the first electrochemical step of the process reversible addition of one electron results in anion-radicals, whose formation has been demonstrated for certain arenes and chromium π-complexes by oxidation of these particles on the ring electrode. Substituents on different ligands of bisarenechromium complexes were found to exert pronounced mutual influences. The role of the chromium atom in transfer of electronic effects from one ligand to another is discussed. It was found that a linear correlation exists between the variations in the free energy of the equilibrium “initial compound anion-radical” (due to coordination of free arene with chromium which is displayed as a shift of the cathodic process half-wave potential ΔE 1 2 CL) and the half-wave potential of the oxidation of the corresponding Cr0 π-complex to a cation E 1 2 X ΔE 1 2 CL = a + αE 1 2 X At E 1 2 X 1 2 X > −0.3 V the process is facilitated.

Study of redox reactions of bis(arene)chromium complexes by use of the rotating disk and the rotating ring-disk electrodes: V. Cathodic processes involving nitriles; cyano derivatives of benzene and dibenzenechromium☆

Abstract The cathodic reduction in DMSO solutions of six aromatic nitriles of the benzene, and eight dibenzenechromium cyano derivatives have been studied by use of the rotating disk and rotating ring-disk electrodes. A substantial change in the character of the polarization curves of π-complexes in comparison with the same cathodic reduction curves of the benzene series is observed. This change manifests itself in the disappearance of the one-electron waves in the I , E -curves and the emergence of two-electron waves. The stepwise addition of two electrons (EEC-mechanism) for free aromatic nitriles, whose anion radicals (ARs) can be reduced, is replaced by the ECE-mechanism in the nitrile complexes: the reversible transfer of the first electron is followed by the chemical decomposition reaction of anion-radicals whose products are reduced at the potential that AR is formed. The reversibility of the addition of the first electron to the free and the complexed nitriles allows their reactivity to be compared directly under cathodic conditions.

35Cl NQR spectra of bis(chlorobenzene)chromium(0) and bis(chlorobenzene) chromium(I) iodide

ConclusionA study was carried out on the35Cl NQR spectra of bis(chlorobenzene)chromium(O) and bis(chlorobenzene)chromium(I) iodide. The coordination of chlorobenzene with the charged ClC6H6Cr+ fragment leads to a sharp decrease in electron density. This effect is significantly greater than that resulting from the coordination of chlorobenzene with the ClC6H5Cr group in neutral bis(chlorobenzene)chromium.

Synthesis and19F-NMR spectra of fluoro-substituted dibenzenechromium derivatives

Conclusions1.Simultaneous condensation of chromium vapors with the vapors of two substituted benzenes, one of which was fluorobenzene, gives substituted dibenzenechromium complexes of the type (C6H5F)Cr(C6H5X).2.The values of the19F chemical shifts correlate satisfactorily with the σm+ and σmp substituent constants.