57Fe NMR Chemical shifts and 57fe, 13C coupling constants in α-ferrocenyl carbocations. Direct metal participation in the stabilization of metallocenyl carbocations

The ¹³C{⁵⁷Fe} double resonance method has been used to investigate ⁵⁷Fe-enriched samples of ferrocene derivatives, α-ferrocenyl carbocations and carbonyl complexes with various σ- and π-hydrocarbon ligands. In the α-ferrocenyl carbocations the ⁵⁷Fe resonances span a 1200 ppm range, being a sensitive tool of direct iron participation in the stabilization. The ⁵⁷Fe resonances in the carbocations [FcCH₂][HSO₄] (I), [FcCHMe][HSO₄] (II), [FcCHPh][HSO₄] (III), [FcCHC₅H₄ Mn(CO)₃][CF₃CO₂] (IV), [(Fc)₂CH][BF₄] (V), [FcCHC₅H₄RuC₅Hs][BF₄] (VI) and [FcCMe₂][HSO₄] (VII), ?523.6, ?219.3, 221.0, 368.7, 699.0, 405.0 and 288.5 ppm, respectively, relative to ferrocene, are interpreted in terms of rehybridization of the iron non-bonding d orbitals (shielding effect and the electron withdrawing effect of the substituent in the cyclic ligand (deshielding effect). The role of rehybridization of non-bonding iron orbitals in the low-frequency shift of the ⁵⁷Fe resonances, in addition to that in the previously investigated complex [(C₅H₅)₂FeH][BF₃OH] (?1109.3 ppm), has been demonstrated for bridge-substituted [3]ferrocenophanes, whose ring tilting induces a low-frequency shift of up to 340 ppm relative to their unbridged analogues.The ¹³C NMR spectra of carbocations V and VI reveal a temperature dependence due to the rotation around the C(1)C_α exocyclic bonds. In carbocation VI the ruthenium atom effectively competes with the iron atom to bond with C_α whereas in carbocation V two equivalent metal atoms possess the same ability for such bonding; as a result, complex V has a more pronounced “carbenium ion” nature than IV and VI, as indicated by the relative positions of the ¹³C_α resonances in carbocations IV, V and VI: δ 122.4, 147.2 and 116.9 ppm, respectively.The values of ⁵⁷Fe, ¹³C coupling constants for α-ferrocenyl carbocations exclude Fe-C_α σ-bonding and support a structure in which the iron atom is π-bonded with six carbon atoms of a fulvenoid ligand. According to the data on ⁵⁷Fe resonances and ⁵⁷Fe, ¹³C coupling constants in α-ferrocenyl carbocations the strength of FeC_α bonding is markedly influenced by the electronic effect of the substituent at C_α, being even lower in carbocation I than that of Fe-cyclopentadienyl carbon atoms.     

On the net charges in cyclopentadienyl metal compounds

An attempt was made to estimate the net charges of a number of cyclopentadienyl metal compounds on the basis of ¹⁹F NMR data for p-fluorophenylcyclopentadienyl metal compounds. The investigated compounds can be clearly divided into four groups according to the polarity of metal-cyclopentadienyl bond: covalent compounds (derivatives of Fe, Ru, Os, Rh and Pd) with a net charge on the η-C₅H₅ ring in the range from ?0.19 to ?0.29, the so-called ionic compounds (derivatives of Li, Na and K) with a net charge on the ring ?0.64 ÷ ?0.72, and compounds with an intermediate character of the bond (derivatives of Cu, Mg and T1) with a net charge of ?0.44 ÷ ?0.46; the net charge on the rings of cyclopentadienyl manganese tricarbonyl and -rhenium tricarbonyl is near to zero. When the effective charge on the ring is near ?0.44 the cyclopentadienyl metal compounds are able to dissociate into ions in solution.     

Transition to Chaos in the Floating Half Zone Convection

The transition process from steady convection to chaos is experimentally studied in thermocapillary convections of floating half zone. The onset of temperature oscillations in the liquid bridge of floating half zone and further transitions of the temporal convective behaviour are detected by measuring the temperature in the liquid bridge. The fast Fourier transform reveals the frequency and amplitude characteristics of the flow transition. The experimental results indicate the existence of a sequence of period-doubling bifurcations that culminate in chaos. The measured Feigenbaum numbers are δ2 =4.69 and δ4 = 4.6, which are comparable with the theoretical asymptotic value δ=4.669.     

Delocalization of electron in biferrocenyl [fe(ii)fe(iii)] picrate

Conclusions Employing the -resonance spectroscopy method, it was shown that in biferrocenyl in the solid phase the exchange of an electron proceeds at a rate that is less than 10⁷ sec^–1.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimi-cheskaya, No. 1, pp. 132–134, January, 1973.     

Norbornadiene complexes of transition metals

Conclusions Correlations were established between the stereochemistry of 2-(-carbinol)norbornadiene complexes of rhodium and their mass spectra.This study is also communication 30 from the series Mass Spectrometry of Transition Metal- Complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2701–2703, December, 1982.     

Delocalization of charge by ferrocenyl and ruthenocenyl groups in α-metallocenyl carbocations

Conclusions The¹⁹F NMR chemical shifts of the ferrocenyl(p-fluorophenyl) and ruthenocenyl(p-fluorophenyl) carbocations testify to the greater effectiveness of the ruthenocenyl group over the ferrocenyl group in delocalizing the positive charge.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 711–712, March, 1984.The authors are grateful to M. V. Galakhov for assistance in obtaining the¹H and¹⁹F NMR spectra.     

P,C,P-Pincer complexes of ruthenium based on ruthenocene and pentamethylruthenocene

The first ruthenocene- and pentamethylruthenocene-based ruthenium pincer complexes, RuCl(CO)[{2,5-(Bu^t ₂PCH₂)₂C₅H₂}Ru(C₅H₅)] and RuCl(CO)[{2,5-(Bu^t ₂PCH₂)₂C₅H₂}Ru-(C₅Me₅)], were synthesized by cyclometallation of {1,3-(Bu^t ₂PCH₂)₂C₅H₂}Ru(C₅H₅) and {1,3-(Bu^t ₂PCH₂)₂C₅H₂}Ru(C₅Me₅), respectively, with RuCl₂(DMSO)₄ in 2-methoxyethanol and characterized by ¹H and ³¹P{¹H} NMR spectroscopy, and X-ray diffraction.     

Obliquely propagating ion-acoustic shock waves in a degenerate quantum plasma

A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars.