Oxidation of isomeric η6- and η5-fluorenylchromiumtricarbonyl anions

The oxidation of the carbon-centered [(⁶-C₁₃H₉)Cr(CO)₃]^– anion (1 ^–) results in formation of (-⁶:⁶-9,9-bifluorenyl)bis-chromiumtricarbonyl (3) due to coupling of the intermediate carbon-centered radical (1^.). The oxidation of the metal-centered anion [(⁵-C₁₃H₉)Cr(CO)₃]^– (2 ^–), which is isomeric to the 1^– anion, gives an equilibrium mixture of the chromium-centered radical {(⁵-C₁₃H₉)Cr(CO)₃}^. (2 ^.) and its dimer [(⁵-C₁₃H₉)Cr(CO)₃]₂ (6). Radical2 ^. readily reacts with MeI and the solvent (THF); the resulting derivatives, (⁵-C₁₃H₉)Cr(CO)₃R (R=Me (10); R=H (7)), undergo fast ricochet inter-ring ⁵⁶ rearrangements into (⁶-9R-C₁₃H₉)Cr(CO)₃ (R=CH₃ (9); R=H (4)).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1354–1358, July, 1995.The authors are grateful to D. V. Zagorevskii who recorded the mass spectra. This study was financially supported by the Russian Foundation for Basic Research (Grant No. 94-03-05209) and the International Science Foundation (Grant Nos. MQ 4000 and REV 000).     

Mass spectra of monohapto-cyclopentadienyl derivatives of group IVB elements

Dissociative ionisation of organometallic cyclopentadiene derivatives containing one, two or three M(CH₃)₃ groups (M  Si, Ge, Sn) has been studied.Among the monometallated compounds, C₅H₅Si(CH₃)₂Cl, C₅H₅Si(CH₃)₂OCH₃ and (C₅H₅)₄Sb have also been investigated. To verify fragmentation patterns, the spectra of deuterated compounds such as C₅D₅Si(CH₃)₃, C₅D₅Sn(CH₃)₃, C₅D₄Si₂(CH₃)₆ and C₅D₃Si₃)₉ have been measured. Dissociative ionisation of h¹-cyclopentadienyl derivatives has been shown to differ essentially from that of h⁵-compounds.     

Study of Redox-induced Reactions of Vinylidene and bis-Vinylidene Complexes of Manganese

Oxidative dehydrodimerization of some phenylvinylidene complexes of manganese is studied by cyclic voltammetry. In the case of (⁵-C₅H₅)(CO)₂Mn=C=C(H)Ph, the process occurs as the homolysis of the C–H bond in the radical cation of {(⁵-C₅H₅)(CO)₂Mn=C=C(H)Ph}^+· and the dimerization of intermediate -phenylethinyl cation [(⁵-C₅H₅)(CO)₂Mn–CC–Ph]⁺ to a binuclear dication of bis-carbine type (⁵-C₅H₅)(CO)₂Mn⁺C– C(Ph)=C(Ph)–CMn⁺(CO)₂(⁵-C₅H₅). The reduction of the latter leads to binuclear bis-vinylidene complex (⁵-C₅H₅)(CO)₂Mn=C=C(Ph)–C(Ph)=C=Mn(CO)₂(⁵-C₅H₅). Oxidative dehydrodimerization of complexes (⁵-C₅R₅)(CO)(L)Mn=C=C(H)Ph (R = H, L = PPh₃; R = Me, L = CO) occurs through the immediate C–C coupling of radical cations {(⁵-C₅R₅)(CO)(L)Mn=C=C(H)Ph}^+· and yields binuclear dication bis-carbine complexes (⁵-C₅R₅)(CO)(L)Mn⁺C–C(H)(Ph)–C(H)(Ph)–CMn⁺(CO)(L)(⁵-C₅R₅), whose reduction leads to neutral compounds (⁵-C₅H₅)(CO)₂Mn=C=C(Ph)–C(Ph)=C=Mn(CO)(L)(⁵-C₅H₅). Complex (⁵-C₅H₅)(CO)₂Mn=C=C(Ph)–C(Ph)=C=Mn(CO)₂(⁵-C₅H₅) undergoes the oxidation-induced nucleophilic addition of water, forming cyclic bis-carbene product with a bridge heterocyclic ligand (-3,4-diphenyl-2,5-dihydro-2,5-diylidene)-bis-(⁵-cyclopentadienyldicarbonyl manganese).     

Indenyl and fluorenyl transition metal complexes : V. Study of reversible isomerization of η6- and η5-fluorenylchromium tricarbonyl anions by IR and PMR spectroscopy

IR and PMR spectroscopy was used to study the reversible isomerization of η⁶- and η⁵-fluorenylchromium tricarbonyl anions (I and II, respectively) in solutions. Consideration was given to the dependence of the equilibrium position and nature of the resulting particles on the type of cation (Li⁺, Na⁺, K⁺, Ph₃PCH₃⁺, n-Bu₄N⁺), the solvent and the presence of solvating cation additives (dicyclohexyl-18-crown-6 (IV), DMSO). The η⁵-isomer exists in THF solution as an equilibrium mixture of solvent-separated and contact ion pairs (SSIP and CIP, respectively), the cation in the latter being located near the oxygen atom of one of the carbonyl groups. The existence of such an equilibrium is also shown for the salts of the C₅H₅(CO)₃Cr^? anion. The dependence of the equilibrium constants for I ? II on the above factors was determined. For the K salt in THF solution at 28°C both IR and PMR spectroscopy gave fairly coincident values of K_eq equal to 7.15 and 7.35, respectively. IR spectroscopy was applied to the kinetic studies of the reversible isomerization of K salts of I and II at 0—28°C with and without crown ether IV. The process is shown to be entropy controlled. The equilibrium position is governed by the type of cation, the degree of its solvation and the temperature. The factors promoting the formation of SSIP's lead to the equilibrium being shifted towards I.     

A CNDO/2 calculation of a rearrangement in cyclopentadienylsilane

The ground state geometry of cyclopentadienylsilane and the transition state geometry for SiH₃ group migration have been calculated by the CNDO technique, a semi-empirical version of the LCAO MO SCF approach.     

Synthesis and properties of 7,7-dichloro-3,4-benzobicyclo[4.1.0]heptane, its tricarbonylchromium complexes, and isomeric 7-chloro-3,4-benzobicyclo[4.1.0]heptanes

The reaction of Cr(CO)₆ with 7,7-dichloro-3,4-benzobicyclo[4.1.0]heptane gave the correspondingexo- andendo-chromium tricarbonyl complexes in a ratio of 4.5:1. The structures of the resulting compounds were established by NMR spectroscopy, mass spectrometry, and X-ray structural analysis. Reduction of dichlorobenzobicycloheptane and its chromium tricarbonyl complexes with LiAlH₄ affordedexo- andendo-7-chloro-3,4-benzobicyclo[4.1.0]heptanes in a 3.5:1 ratio. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 720–724, April, 1998.     

13C NMR spectra of metal σ-cyclopentadienyls

Proton decoupled ¹³C NMR spectra have been measured for the cyclopentadienyl compounds C₅H₅Si(CH₃)_nCl_3?n(n = 1, 2, 3), C₅H₅Ge(CH₃)₃, CH₃C₅H₄Ge(CH₃)₃, C₅H₅Sn(CH₃)₃, σ-C₅H₅Fe(CO)₂-π-C₅H₅ and C₅H₅HgCH₃. A fast metallotropic rearrangement occurring in the compounds causes the spectra to be temperature dependent for the Si, Ge, Sn and Fe derivatives. For the derivatives of silicon or germanium, the olefinic signals are unsymmetrically broadened by the 1,2-shift at lower migration rates. Line widths of the ring carbon signals have been measured to give an estimate for the activation parameters of the rearrangement in C₅H₅Ge(CH₃)₃ (E_a = 10·7 ± 0·9 kcal/mole, ΔG^? = 13·4 ± 0·9 kcal/mole) and C₅H₅Sn(CH₃)₃ (E_a = 6·8 ± 0·7 kcal/mole, ΔG^? = 7·1 ± 0·7 kcal/mole). At room temperature, the spectrum of C₅H₅HgCH₃ displays just one narrow signal responsible for the cyclopentadienyl ligand. The spectrum of CH₃C₅H₄Ge(CH₃)₃ at –30° demonstrates that two isomers containing methyl in the vinylic position are present, the ratio being ca. 2:1. The ¹³C spectra of the vinylic isomers have been analysed in the case of C₅H₅Si(CH₃)_nCl_3?n.     

Effect of σ,π conjugation on199Hg chemical shifts

Conclusions The¹⁹⁹Hg NMR spectra of compounds of the type HgCC=C and HgCC=0 have been studied and it has been shown that C-Hg/ conjugation produces a sharp increase in the shielding of the mercury nucleus.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1038–1042, May, 1982.