O. V. Kuznetsova

Transition metal NMR chemical shifts and polarizability effect in organometallic complexes

The literature data on substituent influence on the 51V, 55Mn, 57Fe, 59Co, 61Ni, 95Mo, 103Rh, 183W, 187Os and 195Pt NMR chemical shifts (δ) and on J (M, P; M = Mn, Fe, Mo, Rh, W, Os) coupling constants have been analyzed for 30 series of the organometallic complexes. It has been established for the first time that the δ and J values depend on the inductive, resonance and polarizability effects of substituents. The polarizability effect is caused by the partial charge on the central M atom. The contribution of this effect ranges from 3 to 86%. Copyright

Electron affinity and substituent effects in radical anions

The first vertical electron affinities EA of 13 series of molecules and free radicals D(Xi)n are related to the inductive (σI), resonance (σR−), and polarization (σα) parameters of substituents Xi by the dependences EA = EAH + aΣσI + bΣσR/− + cΣσα: In radical anions D+·(Xi)n, compared to radical cations D+·(Xi)n, the polarization interaction is weaker or similar in magnitude but has an opposite sign. The previously unknown resonance parameters σR− of substituents SiMe3 and CH2SiMe3 bound to the radical anion center H2C=CH−· were calculated.

Substituent effects in donor-acceptor complexes with D→A coordination bonds (D = N, O, S; A = B, Al, Ga, Sn, Sb) and related systems

The effect of substituent on the enthalpy ΔH0 and free energy ΔG0 of complexation, on the dipole moments of complexes μC and coordination bonds μDA, and on the degree of charge transfer Δq was analyzed for 20 series of complexes with D→A coordination bonds (D = N, O, S; A = B, Al, Ga, Sn, Sb), hydrogen bonds, and charge transfer. It was found that ΔH0, ΔG0, μC, μDA, and Δq depend not only on the inductive and resonance effects, but also on the polarization effect of substituents; its contribution varies in a wide range and can exceed 50%.

NQR parameters of complexes and polarizability effect.

The literature data on substituent influence on the nuclear quadrupole resonance frequencies (ν), quadrupole coupling constants (e2Qq ⋅ h− 1), and asymmetry parameters (η) for 36 series of the H‐complexes, charge–transfer complexes, transition metal complexes and other donor–acceptor complexes have been considered, using the correlation analysis. Generally the ν, e2Qq ⋅ h− 1, and η values were first established to depend on the inductive, resonance, polarizability, and steric effects of substituents. The presence or otherwise of certain effects as well as relation between their contributions are determined by the type of series. The polarizability effect owes its existence to the appearance of an excess charge on the indicator centre as a result of the complexation. The contribution of this effect ranges up to 75%. Copyright

EPR parameters of radical ions and polarizability effect

The literature data on substituent influence on the g factors, hyperfine coupling (hfc) constants (a) of the EPR signals and the spin densities (ρ) have been analyzed for 25 series of the organic radical cations and radical anions as well as of the transition metal complexes. The g, a, and ρ values were first established to depend not only on the inductive and resonance effects but also on the polarizability of substituents which can be characterized by the σα constants. The polarizability effect is caused by the partial charge on the radical center. This effect consists in an electrostatic attraction between the charge and the dipole moments induced by this charge in the substituents. The polarizability contribution ranges up to 92%. Copyright

Electrochemical Reduction of Organic and Organometallic Compounds. Polarization Effect in Radical Anions

Half-wave potentials of electrochemical reduction and electron affinities of X-B-RC compounds belonging to 23 reaction series depend not only on the inductive and resonance effects but also on the polarization effect of the X substituent, which was not taken into account previously. In some cases, the contribution of the polarization effect reaches 50% of the overall substituent effect. The main factors responsible for the magnitude of polarization effect in X-B-RC∸ radical anions are the natures of reaction center RC and bridging moiety B and the distance between the substituent X and reaction center RC.

Electrochemical oxidation of organic, organometallic, and coordination compounds. Polarization effect in radical cations

Half-wave potentials of electrochemical oxidation of 24 reaction series X-B-RC depend on the inductive, resonance, and polarization effects of substituents X. The polarization effect was not taken into account previously. In X-B-RC·+ radical cations, the contribution of the polarization effect increases with decreasing size of bridge B linking X with the reaction center RC and can reach 30%.

Quinone complexes of aluminum: Synthesis and structures

Reactions of aluminum metal with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in various solvents gave aluminum tris-o-semiquinolate and catecholate. The metal catecholate underwent partial hydrolysis in the presence of water. The dimeric complex [(Cat)Al(OH)Bipy]2 × 4C2H4Cl2 (Cat is the 3,6-Q dianion and Bipy is 2,2-bipyridyne) with bridging OH groups was isolated and characterized by X-ray diffraction. A reaction of aluminum with o-quinone in the presence of molecular iodine yielded the dimeric catecholate iodide [(Cat)2Al(Et2O)2]AlI2. The structure of the latter was confirmed by X-ray diffraction. An aluminum catecholato-o-semiquinolate complex was obtained by an exchange reaction between [(Cat)2Al(Et2O)2]AlI2 and thallium o-semiquinolate.

Tin(IV) complexes based on 2-hydroxy-3,6-di-tert-butyl-para-benzoquinone: Syntheses, structures, and electrochemical behavior in solution

A series of new tin(IV) complexes based on 2-hydroxy-3,6-di-tert-butyl-para-benzoquinone (LH) of the general formula L2SnR2 (R = Me (I), Et (II), Bun (III), Ph (IV)) and LSnMe3 (V) were synthesized. The obtained compounds were characterized by IR and 1H, 13C and 119Sn NMR spectroscopy and elemental analysis. The X-ray diffraction analysis was carried out for complexes L2Sn(Bun)2 (III) and LSnMe3 (V). The low-frequency region of the IR spectra, which has not earlier been studied in detail, was interpreted for compounds I–V and previously described complex LSnPh3 (VI). The electrochemical properties of LH and related tin complexes I–VI were studied. The nature of the hydrocarbon groups at the metal atom affects the stability of the intermediates formed in the electrochemical reactions.

NMR spectroscopy on heavy nuclei of transition metal complexes. The role of polarization effect

Chemical shifts (δ) and spin-spin coupling constants (J) in the NMR spectra on heavy nuclei M (51V, 55Mn, 57Fe, 95Mo, 103Rh, 187Os, 195Pt) for 27 series of transition metal complexes have been analyzed. In general case in the absence of steric factors the values of δ and J depend on three effects of substituents X: inductive, resonance, and polarization. The latter effect increases with the decrease in the distance between M and X and with growing charge on atom M. The contribution of the polarization effect varies from 0 to 80% depending on the type of the series.