Multinuclear NMR investigation on organometallic gold(III) pentafluorophenylarylazoimidazole complexes

Reaction of [Au(C₆F₅)(tht)₂Cl](OTf) with RaaiR′ in CH₂Cl₂ medium leads to [Au(C₆F₅)(RaaiR′)Cl](OTf) [RaaiR′ = p-R–C₆H₄–N=N–C₃H₂–NN-1-R′, (1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), tht is tetrahydrothiophen]. The maximum molecular peak of [Au(C₆F₅)(MeaaiMe)Cl] is observed at m/z 599.51 (100 %) in the FAB mass spectrum. Ir spectra of the complexes show –C=N– and –N=N– stretching near at 1590 and 1370 cm⁻¹ and near at 1510, 955, 800 cm⁻¹ due to the presence of pentafluorophenyl ring. The ¹H-NMR spectral measurements suggest methylene, –CH₂–, in RaaiEt gives a complex AB type multiplet while in RaaiCH₂Ph shows AB type quartets. ¹³C-NMR spectrum of complexes confirm the molecular skeleton. In the ¹H-¹H-COSY spectrum as well as contour peaks in the ¹H-¹³C HMQC spectrum for the present complexes, assign the solution structure and stereoretentive conformation. The electrochemistry gives the ligand reduction peaks.     

Organometallic gold(I)-pentafluorophenyl-P,O, As,S, TPA,dppm, dppe,dppa-coordinating-phosphines: synthesis and detailed spectroscopic characterisation

[Au(C₆F₅)(tht)], which on reaction with P, O, S-coordinating phosphines in CH₂Cl₂ medium leads to [Au(C₆F₅)(X)] [X = PPh₃ H, (1a), oMe, (1b), pMe, (1c), mMe, (1d), AsPh₃ (2), OPPh₃ (3), SPPh₃ (4), dppm, dppe, dppa = diphenylphosphino-methane,-ethane,-ammine(5, 6, 7), TPA = 135-tetraaza-7-phosphino adamentane(8), Py4H (9a), 4Bu (9b), 4Ac (9c), tht = tetrahydrothiophen, C₆F₅ is the pentafluorophenyl ring]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. I.r. spectra of the complexes show –C = C– and C₆F₅ stretching near at 1610 and 1510, 955, 800 cm⁻¹. The ¹H-n.m.r. spectra as well as ³¹P- (¹H)n.m.r. suggest solution stereochemistry, proton movement, phosphorus proton interaction. ¹³C-n.m.r. spectrum reflect the carbon skeleton in the molecule. In the ¹H–¹H COSY spectrum of the present complexes and contour peaks in the ¹H–¹³C-HMQC spectrum, assign the solution structure and stereoretentive conformation in each step.     

Synthesis and spectral properties of mixedmeso-metallocenylporphyrins

A series of mixed porphyrins with different numbers of metallocenyl (ferrocenyl and cymantrenyl) and aryl (Ph and C₆F₅) groups at themeso-positions was obtained and characterized by¹H NMR, electronic absorption, and mass spectra. The downfield shift of NH signals as well as the bathochromic shift ofQ-bands can be attributed to a distortion of the porphyrin macrocycle upon the introduction of bulkymeso-substituents. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1045–1049, May, 1998.     

Oxidation of ethers with dimethyldioxirane

Oxidation of a series of tert-butyl ethers Bu^tOR (R = Me, Et, CH₂CH₂Cl, Prⁱ, Buⁱ), diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, diisobutoxymethane, 1,4-dioxane, and tetrahydrofuran with dimethyldioxirane (DMDO) was studied. The reaction kinetics obeys the second-order equation w = k[DMDO][ether]. The rate constants in a range of 5–50 °C and the activation parameters of the reaction were determined. The solvent effect on the oxidation rate was studied. The oxidation products are the corresponding alcohols and carbonyl compounds. The competition between the nonradical (oxygen insertion) and radical mechanisms of the reaction is discussed. The reactions of the parent dioxirane and DMDO with a series of methyl ethers MeOr’ (r’ = Me, Et, CH₂CH₂F, Prⁱ) were studied by the density functional theory (DFT). The (U)B3LYP-6-311G(d,p) method was employed to calculate the geometry and energies of the reactants and transition states. The data obtained indicate a possible increase in the probability of oxidation via the radical route and an increase in the activation barrier for the substrates containing electron-withdrawing substituents. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2309–2318, October, 2005.     

Synthesis, structural investigation, and theoretical study of pentaf luoroethyl derivatives of [60]fullerene

Pentafluoroethyl derivatives of [60]fullerene C₆₀(C₂F₅)_n (n = 6, 8, and 10) were synthesized by the reaction of C₆₀ with C₂F₅I in glass ampoules at 380–440 °C. Isomers of composition C₆₀(C₂F₅)₆ (one isomer), C₆₀(C₂F₅)₈ (five isomers), and C₆₀(C₂F₅)10 (two isomers) were isolated by chromatographic separation. Their molecular structures were established by X-ray diffraction. The relative stabilities of isomers were compared by density functional theory calculations. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 881–887, May, 2007.     

Gold(I)-Gold(III)-4,4′-bpy-phosphine complexes: Synthesis and multinuclear NMR study

Silver assisted de-bromination gives [Au₂(dppm/dppe/dppa) (OTf)₂], which on reaction with 4,4′-bpy and gold(I) phosphines in CH₂Cl₂ medium, by the self assembly technique, leads to [(PPh₃)Au(4,4′-bpy)Au(PPh₃)], (1a–1d,2), [{Au₂(dppm/dppe/dppa)}{(4,4-bpy)Au(PPh₃)}₂](NO₃)₄, (3), [{Au₄(dppm/dppe/dppa)₂(4,4-bpy)₂}](OTf)_4, (4), [{(PPh₃)Au^I(4,4′-bpy)}₂Au^III(C₆F₅/Mes)](NO₃)₃, (5) [dppm/dppe/dppa =diphenyl phosphino-methane(a), –ethane(b), ammine(c), C₆F₅/Mes pentafluorophenyl/mesitylene]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. Ir spectra of the complexes show –C=C–, –C=N–, as well as phosphine, mesitylene and pentafluorophenyl stretching. The ¹H-NMR spectra as well as ³¹P(¹H)-NMR suggest solution stereochemistry, proton movement and phosphorus proton interaction. Considering all the moities there are a lot of carbon atoms in the molecule reflected by the ¹³C(H)-NMR spectrum. In the ¹H–¹H COSY spectrum of the present complexes and contour peaks in the ¹H–¹³C-HMQC spectrum, assign the solution structure and stereoretentive transformation in each step.     

One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications

Electron-transferable oxidants such as B(C₆F₅)₃/nBuLi, B(C₆F₅)₃/LiB(C₆F₅)₄, B(C₆F₅)₃/LiHBEt₃, Al(C₆F₅)₃/(o-RC₆H₄)AlH₂ (R=N(CMe₂CH₂)₂CH₂), B(C₆F₅)₃/AlEt₃, Al(C₆F₅)₃, Al(C₆F₅)₃/nBuLi, Al(C₆F₅)₃/AlMe₃, (CuC₆F₅)₄, and Ag₂SO₄, respectively were employed for reactions with (L)₂Si₂C₄(SiMe₃)₂(C₂SiMe₃)₂ (L=PhC(NtBu)₂, 1 ). The stable radical cation [ 1 ]^+. was formed and paired with the anions [nBuB(C₆F₅)₃]⁻ (in 2 ), [B(C₆F₅)₄]⁻ (in 3 ), [HB(C₆F₅)₃]⁻ (in 4 ), [EtB(C₆F₅)₃]⁻ (in 5 ), {[(C₆F₅)₃Al]₂(μ-F)]⁻ (in 6 ), [nBuAl(C₆F₅)₃]⁻ (in 7 ), and [Cu(C₆F₅)₂]⁻ (in 8 ), respectively. The stable dication [ 1 ]²⁺ was also generated with the anions [EtB(C₆F₅)₃]⁻ ( 9 ) and [MeAl(C₆F₅)₃]⁻ ( 10 ), respectively. In addition, the neutral compound [(L)₂Si₂C₄(SiMe₃)₂(C₂SiMe₃)₂][μ-O₂S(O)₂] ( 11 ) was obtained. Compounds 2 – 11 are characterized by UV-vis absorption spectroscopy, X-ray crystallography, and elemental analysis. Compounds 2 – 8 are analyzed by EPR spectroscopy and compounds 9 – 11 by NMR spectroscopy. The structure features are discussed on the central Si₂C₄-rings of 1 , [ 1 ]^+., [ 1 ]²⁺, and 11 , respectively.     

Cycloaddition of C60 fullerene to stable 2-RSO2-benzonitrile oxides

The interaction of stable 2-RSO₂-benzonitrile oxides1a−c (R=Ph, Bu^t, or PhMeN) with C₆₀ fullerene proceeds at the double (6,6)-bond of fullerene as the [3+2] cycloaddition to form the corresponding isoxazolines2a−c. The molecular structure of compound2b was established by X-ray structural analysis. The interaction of C₆₀ fullerene with 2-(5-methyl-4-nitrothiophene)carbonitrile sulfide, which was obtained by thermolysis of 5-(5′-methyl-4′-nitro-2′-thienyl)1,3,4-oxathiazol-2-one, affords only unstable products. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 118–126, January, 1997.     

Synthesis and structures of substituted tetramethylcyclopentadienyl dinuclear metal carbonyl compounds

Cyclopentadienes (C₅Me₄R) [R = Allyl (1), n-Butyl (2), Benzyl (3), and PhMe-2 (4)] reacted with Fe(CO)₅ in refluxing xylene to give new substituted tetramethylcyclopentadienyl dinuclear iron carbonyl complexes [(η ⁵-C₅Me₄R)Fe(CO)(μ-CO)]₂ [R = Allyl (5), n-Butyl (6), Benzyl (7), and PhMe-2 (8)], respectively. The four new complexes 5–8 were characterized by elemental analysis, IR, and ¹H NMR spectra. The crystal structures of complexes 5–7 were determined using single crystal X-ray diffraction. The crystal structure of complex 5 showed that allyl underwent isomerization to give the corresponding methyl-vinyl. A possible mechanism is discussed. The X-ray crystal structures of complexes 5, 6, and 7 confirm the structure with bridging and terminal CO groups. They show that the steric effects of substituents influence the Fe–Fe bond distances of the complexes.     

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

Structures of Rydberg transitions in the absorption spectra of methyl-substituted derivatives of bis(η6-benzene)chromium

The effect of methylation of ligands in bis(η⁶-benzene)chromium (1) on the structure of Rydberg transitions in absorption spectra has been studied. A detailed analysis and interpretation of all Rydberg elements of the vapor-phase spectra of bis(η⁶-benzene)chromium (2), bis(η⁶-o-xylene)chromium (3), bis(η⁶-m-xylene)chromium (4), and bis(η⁶-mesitylene)chromium (5) was carried out. The vapor-phase electronic absorption spectrum of bis(η⁶-p-xylene)chromium (6) was measured, and the assignment of the Rydberg bands was made for the first time. The first ionization potentials of complexes 2–5 were refined. The energy of detachment of the 3d_z ² electron and the parameters of the Rydberg excitations for molecule 6 were determined. The vibronic components of the 3d_z ²→R4p _x,y transition in the spectra of complexes 2 and 6 were assigned. The differences in the Rydberg structure of the spectra of compounds 2–6 were analyzed in terms of the selection rules for optical transitions in the corresponding symmetry groups. The vapor-phase spectra correspond to conformers with the symmetry groupsC _2v andC ₂ for complexes 2–4, with the symmetry groupsD _3h andD ₃ for compound 5, and with the symmetry groupD _2d for complex 6. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 897–903, May, 1998.     

Free radicals and their electron spin relaxation in cellobiose. X-band and W-band ESR and electron spin echo studies

By use of 9.7 GHz and 94 GHz ESR spectra and electron spin echo (ESE)-detected spectra the six radical centres produced by γ-irradiation of cellobiose were identified. The radicals are localized on different carbon atoms. Use of high-frequency ESR spectra with computer resolution enhancement methods enabled unique radical identification and determination of g-factors and proton hyperfine splitting, A, with high accuracy. For radiation doses below 20 kGy three radicals dominate: on C₁ with isotropic doublet A = 1.8 mT; on C₂, C₃ and C₄ with triplet A = 2.9 mT; and localized on CH₂ with anisotropic triplet. For doses above 100 kGy the radical on C₁ dominates, because of cleavage of the glycosidic bonds. Electron spin–lattice relaxation shows that radiation damage of the cellulose structure around the radical centres is significant and radical molecules do not participate in phonon dynamics of the host lattice. The relaxation is because of tunnelling motions of the ring or OH-groups, with tunnelling splitting 2.4 cm⁻¹. Electron spin echo dephasing results identify cellobiose ring torsions with activation energy 117 cm⁻¹.     

ESR study of radicals formed by the reduction of α-diketones C(O)C(O)CF3 (R=(CF3)2CF, C6F5, (CF3)3C) with several group I–III metals

The ESR spectra of radical anions formed by reduction of α-diketones RC(O)C(O)CF₃ (R=(CF₃)₂CF, C₆F₅, (CF₃)₃C) with metals (Li, Na, K, Mg, Cd, Zn, Hg, In, and TI) in THF were studied. For R=(CF₃)₂CF and C₆F₅, the radical anions are formed ascis-isomers, whereas for R=(CF₃)₃C,trans-isomers are obtained. Line broadening due to solvation and desolvation of the cation is observed in the latter case. The reduction of α-diketone (CF₃)₂CFC(O)C(O)CF₃ with Group II metals (Mg, Cd, Zn) results in the formation of radical pairs. Translated fromIzvestiya Akadmii Nauk. Seriya Khimicheskaya, No. 11, pp. 2228–2231, November, 1998.     

Ternatine, a new diterpene alkaloid fromDelphinium ternatum

A new alkaloid, ternatine (C₂₄H₃₃NO₅), was isolated from aerial parts of theDelphinium ternatum plant. According to the¹H,¹³C NMR, IR, and mass spectra of the base and its triacetate, ternative was assumed to have the structure of 4β-methyl-7α-isobutyryloxy-11α,15β,19β-trihydroxyhetisane. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 187–189, January, 1997.     

Hypercoordinate atoms of second-row elements in dodecahedrane endohedral complexes

The energy characteristics and geometric parameters of the dodecahedrane endohedral complexes X@C₂₀H₂₀ (X = C⁴⁻, N³⁻, O²⁻, F⁻, Ne) were studied by the density functional theory B3LYP method with the 6-311G(d,p), 6-311+G(d,p), and 6-311G(df,p)) basis sets. In all structures the central atoms X are characterized by a coordination number of 20. The energy of formation of the complexes decreases in the order X = C⁴⁻, N³⁻, O²⁻, F⁻, Ne. The coordination number of the central atom remains unchanged upon adding Li⁺ counterions to anionic systems. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 824–830, May, 2007.     

Kernresonanzspektroskopische Untersuchungen an Pentafluorphenylsubstituierten Silanen: II–Fernkopplungen und Through Space Effekte

Long range ⁵J(FH) and ⁶J(FH) couplings were observed for silanes of the type (C₆F₅)_nSiR_4-n (n = 1, 2, 3; R = alkyl, aryl) and disilanes C₆F₅[Si(CH₃)₂]₂R (R = CH₃, C₆F₅). A characteristic increase in line width for ¹⁹F-NMR spectra of (C₆F₅)_nSiR_4-n(n ≧ 2) is thought to be due to spin systems of the type ([AC]₂B)_n or ([AX]₂M)_n with intra-annular couplings between ortho-fluorine atoms of neighbouring ring systems.     

Synthesis and reactivity of trimethylsilyl substituted mono(cyclopentadienyl)titanium alkyl complexes

The preparation of a series of titanium half-sandwich compounds [Ti(η⁵-C₅H_5−x (SiMe₃) _x R₃] (x = 1–3, R = Cl, Me) and their reactivity for propene polymerization is reported. The compounds 1–3 polymerize propene, albeit in a much lower activity than the reported [Ti(η⁵-C₅Me₅Me₃]/B(C₆F₅)₃ catalyst. Unlike the reported [Ti(η⁵-C₅Me₅Me₃]/B(C₆F₅)₃ catalyst, the quasi living polymerization was not observed. Instead, we observe rather unusual temperature effects when the trityl salt [Ph₃C][B(C₆F₅)₄] was used as activator. The activity increases with increasing temperature, whereas when B(C₆F₅)₃ is used a decrease is observed The rather broad (>2) PDI indicates multisite catalysts, and ¹³C-NMR indicates predominantly atactic polypropene. The solid state structure of the hydrolysis product [{Ti(η⁵-C₅H₄(SiMe₃)Cl₂}O] (4) was determined.     

Reactions of salicylaldehyde with tris(pentaf luorophenyl)silanes and secondary amines

Reactions of tris(pentafluorophenyl)silanes RSi(C₆F₅)₃ with salicylaldehyde and secondary amines were studied. The reactions afforded α-pentafluorophenyl-substituted amines. Silanes RSi(C₆F₅)₃ (R = Me, Ph, C₆F₅, CH₂CH=CH₂, and CH=CH₂) were found to be efficient reagents for transfer of the C₆F₅ group to the iminium cation generated from salicylaldehyde and amine. However, tris(pentafluorophenyl)phenylethynyl-and tris(pentafluorophenyl)silanes were not able to serve as a source of a fluorinated substituent because of competitive transfer of acetylenide fragment or hydride. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 498–503, March, 2006.     

Kinetic and mechanism of alkene polymerization

Triphenylmethyl salts of the very weakly-coordinating borate anions [CN{B(C₆F₅)₃}₂]⁻ (1), [H₂N{(C₆F₅)₃}₂]⁻ and [M{CNB(C₆F₅)₃}₄]²⁻ (M = Ni, Pd) have been prepared in simple one-pot reactions. Mixtures of (SBI)ZrMe₂/1/AlBu ₃ ⁱ (SBI = rac-Me₂Si(Ind)₂) are 30–40 times more active in ethylene polymerizations at 60–100°C than (SBI)ZrCl₂/MAO. The quantification of anion effects on propene polymerization activity at 20°C gives the order [CN{B(C₆F₅)₃}₂]⁻ > [H₂N{(C₆F₅)₃}₂]⁻ ≈ B(C₆F₅) ₄ ⁻ ≫ [MeB(C₆F₅)₃]⁻. The highest productivities were of the order of ca. 3.0 × 10⁸ g PP (mol Zr)⁻¹ h⁻¹ [C₃H₆]⁻¹, about 1.3–1.5 times higher than with B(C₆F₅) ₄ ⁻ as the counter anion. The titanium system CGCTiMe₂/1/AlBu ₃ ⁱ gave activities that were very similar to the zirconocene catalyst. The concentration of active species [C*] as determined by quenched-flow kinetic techniques indicates typical values of around 10%, independent of the counter anion, for both the borate and MAO systems. Pulsed field-gradient spin echo and nuclear Overhauser effect NMR experiments on systems designed to be more realistic models for active species with longer polymeryl chains, (SBI)M(CH₂SiMe₃)(μ-Me)B(C₆F₅)₃ and [(SBI)MCH₂SiMe ₃ ⁺ ...B(C₆F₅) ₄ ⁻ ] (M = Zr, Hf), demonstrated the influence of bulky alkyl chains on the ion pair solution structures: while the MeB(C₆F₅)₃ compound exists as a simple inner-sphere ion-pair, the B(C₆F₅) ₄ ⁻ compound is an outer-sphere ion pair (OSIP), a consequence of the relegation of the anion into the second coordination sphere by the γ-agostic interaction with the alkyl ligand. The OSIP aggregates to ion hextuples (10 mM) or quadruples (2 mM). Implications for the polymerization mechanism are discussed; the process follows an associative interchange (I _a) pathway. The text was submitted by the authors in English.     

Investigation of the structure and energy of β-diketonates. XIV. Composition of overheated vapors and the molecular structure of monomeric yttrium tris-hexafluoroacetylacetonate Y(C5O2HF6)3

Simultaneous electron diffraction and mass spectrometry along with a quantum chemical (DFT/B3LYP) calculation are applied to study the molecular structure of yttrium tris-hexafluoroacetylacetonate Y(hfa)₃. The superheating of the vapor in a double two-temperature effusion cell shows that up to a temperature of ∼200°C ions containing from one to three metal atoms are formed, and the most intensive ion has the stoichiometry of (Y₂L₅)⁺ at a temperature below ∼120°C. The monomer starts to noticeably decompose at temperatures above 330°C.The electron diffraction patterns of monomers are obtained at T _exp = 208(5)°C. According to the results of theoretical and experimental investigations, Y(hfa)₃ molecule has D ₃-symmetry. The rotation angle of triangular O-O-O faces with respect to their position in the regular prism is equal to 14.4(1)°C. The values of internuclear distances and valence angles (r _h1-geometry) are: r(Y-O) = 2.259(6) Å, r(C-O) = 1.263(6) Å, r(C-C_r) = 1.413(4) Å, r(C-C_F) = 1.531(4) Å, r(C-F) = 1.344(3) Å, O-Y-O = 75.2(2)°, O-C-C_F = 113.8(2)°, C-C_F-F = 112.4(2)°. The results of quantum chemical calculations are well consistent with the experimental data. Original Russian Text Copyright ? 2007 by G. V. Girichev, V. V. Rybkin, N. V. Tverdova, S. A. Shlykov, N. P. Kuz’mina, and I. G. Zaitseva __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 5, pp. 871–879, September–October, 2007.