C–C Bond Rupture in the Oxidation of Lower (C2–C6) Alcohols with Hydrogen Peroxide Mediated by Iron-Containing Compounds

C–C bond rupture upon the oxidation of alcohols in the Fe(ClO₄)₃+ H₂O₂system in aqueous acetonitrile at room temperature is found. The relative yield of the products of C–C bond rupture is 20–30% under standard conditions for C₂and C₃alcohols and decreases in the series C₂> C₃> C₄> C₆. The alkyl radical and carboxylic acid are the products of C–C bond rupture in alcohol oxidation. Cyclohexane is a competitive inhibiting agent for C–H bond oxidation in 1-propanol, and it does not affect the yield of the products of C–C bond rupture. When H₂O₂is replaced by tert-BuOOH, the fraction of the products of C–C bond rupture decreases by an order of magnitude. Our data suggest that a non-radical intermediate, likely Fe(III) hydroperoxo complex, is responsible for C–C bond rupture in alcohol under the reaction conditions.     

Functionalization of the Methyl C(sp3)–H Bond of 2,3-Dimethylquinoxaline with 5-Arylfuran-2,3-diones

Russian Journal of Organic Chemistry - 5-Arylfuran-2,3-diones reacted with 2,3-dimethylquinoxaline to give mono- and bis-C-acylation products,...     

B(C6F5)3-Catalyzed Hydroboration of Alkenes with N-Heterocyclic Carbene Boranes via B—H Bond Activation

In this work,a novel mode for the activation of N-heterocyclic carbene boranes (NHC-boranes) was developed by generating the highly reactive zwitterion species ...     

Temperature Dependence of the Ratios of C—H (C—D) Bond Breaking Rates in Reactions of Cycloalkanes C5H10, C6H12, C6D12 with Adamantyl Carbocations in Sulfuric Acid

We have determined the differences in the parameters log A and E of the Arrhenius equations for the kinetic isotope effect (KIE) (c-C₆H₁₂/c-C₆D₁₂) and the 5/6 effect (c-C₅H₁₀/c-C₆H₁₂) in reactions of the C—H bonds of cycloalkanes with adamantyl (Ad⁺) carbocations (1-adamantanol in 92.8% H₂SO₄, 40-97 °C). We have established the compensation relations between log A and E for the kinetic isotope effect and the 5/6 effect for anthracene (AH⁺), hydroxymethyl (CH₂OH⁺), Ad⁺ carbocations and the hypothetical "infinitely strong reagent," supporting a hydride transfer mechanism in such reactions.     

Ruthenium (II) Catalyzed C(sp2)−H Bond Alkenylation of 2-Arylbenzo[d]oxazole and 2-Arylbenzo[d]thiazole with Unactivated Olefins

Functionalization of the bio-relevant heterocycles 2-arylbenzo[d]oxazole and 2-arylbenzo[d]thiazole has been achieved through Ru(II)-catalyzed alkenylation with unactivated olefins leading to selective formation of the mono-alkenylated products. This approach has a broad substrate scope with respect to the coupling partners, affords high yields, and works for gram scale synthesis using a readily available Ru-based catalyst. Mechanistic studies reveal a C−H activation pathway for the dehydrogenative coupling leading to the alkenylation. However, the results of the ESI-MS-guided deuterium kinetic isotope effect studies indicate that the C−H activation stage may not be the rate-determining step of the reaction. The use of a radical scavenging agent such as TEMPO did not show any detrimental effect on the reaction outcome, eliminating the possibility of the involvement of a free-radical pathway.     

Unconventional Pathway in the Gas-Phase Synthesis of 9H-Fluorene (C13H10) via the Radical–Radical Reaction of Benzyl (C7H7) with Phenyl (C6H5)

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five-membered ring—9H-fluorene (C₁₃H₁₀)—is produced isomer-specifically in the gas phase by reacting benzyl (C₇H₇⋅) with phenyl (C₆H₅⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1-(6-methylenecyclohexa-2,4-dienyl)benzene intermediates (C₁₃H₁₂) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical-radical reactions are initiated through recombination at their radical centers. The structure of 9H-fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings.     

1H, 13C and 31P NMR studies of some (C6H5)3−nPRn and (C6H5)3−nPRn Cr(CO)5 (n = 0–3; R  H,CH3, C2H5, i-C3H7, t-C4H9) derivatives

The ³¹P chemical shift of the (C₆H₅)_3−nPR_n and (C₆H₅)_3−nPR_nCr(CO)₅ (n = 0–3; R  H, CH₃, C₂H₅, i-C₃H₇, t-C₄H₉) derivatives is dominated by the steric effect. A small inductive effect is also operative but there are no indications of notable (d_Cr→d_P)π back-bonding. The ¹³C chemical shift of the phenyl carbon atoms indicates that (p_ring-d_P)π electron delocalization is unimportant.The ¹³C chemical shift of the carbonyl carbon atoms, which is mainly governed by the mean excitation energy, confirms the conclusion that there are no notable changes in (d_Cr→d_P)π back-bonding in this series of compounds.     

Reaction of Mo(CO)6 with Alkoxide: Synthesis and Structure of the Mo(0)-OR Complex [Et4N]3[Mo2(CO)6(μ-OC6H4OCH2C6H5)3]

The reaction of molybdenum hexacarbonyl with C6H5CH2OC6H4ONa and Et4NBr in CH3CN at 60 ℃ afforded the di-nuclear Mo(0) compound [Et4N]3[Mo2(CO)6(μ-OC6H4OCH2- C6H5)3] 1. 1 crystallizes in monoclinic, space group P21/c with a=15.359(2), b=18.378(3), c=24.952(2)(A), β=102.268(4)°, V=6882.3(16) (A)3, Mr=1348.34, Z=4, Dc=1.301 g/cm3, F(000)=2832 and μ= 0.424 mm-1. The final R=0.0606 and wR=0.1552 for 9396 observed reflections (Ⅰ ＞ 2σ(Ⅰ)). 1 contains a [Mo2O3]3- core in triangular bi-pyramidal configuration and each Mo atom adopts a distorted octahedral geometry with three carbon atoms from carbonyls and three μ-O atoms from C6H5CH2OC6H4O- bridging ligands. The Mo…Mo distance is 3.30(8) (A), indicating no metalmetal bonding. A formation pathway via forming a di-molybdenum(0) di-bridging OR compound [Mo2(μ-OR)2(CO)8]2- has been figured out and the reaction of Mo(CO)6 with alkoxide has also been discussed.     

Comparison of CRDS to ICL-PAS and phase-shift CRDS spectroscopies for the absolute intensities of C–H (ΔvCH=6) overtone absorptions

Cavity ring-down spectroscopy (CRDS) has been used to obtain the visible overtone spectra (Δv_CH=6) of neo-pentane, C(CH₃)₄, propane, C₃H₈, and n-butane, C₄H₁₀, yielding absolute f-values for the transitions to better than 3%. For the neo-pentane overtone intensity, comparison with a recent measurement using intra-cavity laser photoacoustic spectroscopy (ICL-PAS) provides favourable agreement, with improved precision. Being absolute this value may be used as a standard for relative intensity measurements obtained by ICL-PAS. The measured propane and n-butane overtone intensities, when compared to recent work using phase-shift CRDS, indicate a lack of agreement to quoted uncertainties.     

How Do G–Se Nonbonded and Y–Se Through π -Bond Interactions Determine the Structures of 8-G-1-( p-YC6H4Se)C10H6?

Abstract

Structures of 8-G-1-( p-YC ₆ H ₄ Se)C ₁₀ H ₆ (G = H (1), SeMe (2), Cl (3), and Br (4)) bearing various Y are determined by the X-ray crystallographic analysis. While Y dependence in the structures originates from the through π interaction between n _p (Se) and n _p (Y), G dependence is based on the nonbonded n _p (G)…σ*(Se–C) 3c–4e interaction. QC calculations reveal that the specific stability appears when the π 2c–4e is distorted (Möbius type stability).     

Differentiable Formation of Chiroptical Lanthanide Heterometallic LnnLn’4-n(L6) (n=0–4) Tetrahedra with C2-Symmetrical Bis(tridentate) Ligands

Construction of lanthanide heterometallic complex is important for engineering multifunction molecular containers. However, it remains a challenge because of the similar ionic radii of lanthanides. Herein we attempt to prepare chiral lanthanide heterometallic tetrahedra. Upon crystallization with a mixture of [Eu₂ L ₃] and [Ln₂ L ₃] (Ln=Gd, Tb and Dy) helicates, a mixture of heterometallic Eu_nLn’_4-n( L ₆) (n=0–4) tetrahedra was prepared. Selective formation of heterometallic tetrahedron was observed as MS deconvolution results deviated from statistical results. The formation of heterometallic tetrahedron was found to be sensitive to ionic radii as well as the ratio of the two helicates used in the crystallization.     

An e.p.r. study of tetradentate Schiff base copper complexes with an N–(CH2)n–N,n = 3–6 backbone

Cu^II complexes of Schiff-base ligands with a general formulation o-HOC₆H₄CH=N–(CH₂) _n –N=CHC₆H₄OH-o, where n = 3–6 have been prepared and their e.p.r. spectra investigated in order to determine the effect of the flexible methylene backbone length on the structure. The room temperature and 77 K e.p.r. spectra of the compounds, n = 3 and 4, are typical of the axially symmetric ground state with g > g . When n = 5, on the other hand, the complex gives an isotropic spectrum at room temperature. For n = 6, g appears to be greater than g . The g _iso value increases gradually from n = 3 to n = 6 indicating deviation from planarity. Simulation of the 77 K spectrum for n = 6 shows the presence of two distinct Cu²⁺ sites of equal probability. The Q-band spectrum of this compound exhibits a narrowed g signal indicative of exchange coupling. The spectrum is a consequence of intermolecular electron exchange giving a pseudo d² _z state.     

Can Aromaticity Coexist with Diradical Character? An Ab Initio Valence Bond Study of S2N2 and Related 6π‐Electron Four‐Membered Rings E2N2 and E42+ (E=S,Se, Te)

A series of 6π‐electron 4‐center species, E₂N₂ and E₄²⁺ (E=S, Se, Te) is studied by means of ab initio valence bond methods with the aims of settling some controversies on 1) the diradical character of these molecules and 2) the radical sites, E or N, of the preferred diradical structure. It was found that for all molecules, the cumulated weights of the two possible diradical structures are always important and close to 50 %, making these molecules comparable to ozone in terms of diradical character. While the two diradical structures are degenerate in the E₄²⁺ dications, they have on the contrary strongly unequal weights in the E₂N₂ neutral molecules. In these three molecules, the electronic structure is dominated by one diradical structure, in which the radical sites are the two nitrogen atoms, while the other diradical structure is much less important. The ordering of the various VB structures in terms of their calculated weights is confirmed by the relative energies of individual VB structures. In all cases, the major diradical structure (or both diradical structures when they are degenerate) is (are) the lowest one(s), while the covalent VB structures lie higher in energy. The vertical resonance energies are considerable in S₂N₂ and S₄²⁺, about 80 % of the estimated value for benzene, and diminish as one goes down the periodic table (S→Se→Te). This confirms the aromatic character of these species, as already demonstrated for S₂N₂ on the basis of magnetic criteria. This and the high weights and stabilities of one or both diradical structures in all systems indicates that aromaticity and diradical character do not exclude each other, contrary to what is usually claimed. Furthermore, it is shown that the diradical structures find their place in a collective electron flow responsible for the ring currents in the π system of these species.     

Theoretical Investigation on the Interaction of C2H Radical with Small Gold Clusters Au n 0/− (n = 1–4)

A density-functional theory investigation on the interactions between C₂H radical and small gold clusters Au _n ^0/? (n = 1–4) has been performed. The calculated results predict that C₂H radical inclines to interact with small gold clusters Au _n ^0/? (n = 1–4) as an integrity in the most stable structures of C₂HAu _n ^0/? (n = 1–4). The Au _n ^0/? (n = 1–4) clusters retain their structural integrity as units in the ground states of C₂HAu _n ^0/? (n = 1–4). The stretching vibrational frequencies of C≡C and C–H in the ground states of C₂HAu _n ^? (n = 1–4) are decreased compared with those of the C₂H radical due to the interaction between the Au _n ^0/? clusters and C₂H radical. Smaller red shifts in the C≡C and C–H stretching bands of C₂HAu _n ^? occur with an increase in n. The photoelectron spectra of the most stable structures of C₂HAu _n ^? (n = 1–4) have been simulated to aid their future experimental characterizations. The current study provides further insight into the interaction between C₂H radicals and gold clusters, which may lead to exploitation of the high activity of gold nanocrystals.     

Layered Lanthanum Complex with 3-Nitrophthalic Acid Assembled via Hydrogen Bonds-Synthesis, Structure and Characterization of [LaL(HL)(H2O)3]2·2H2O (H2L = 3-NO2C6H3(CO2H)2)

A new dinuclear centrosymmetric complex [LaL(HL)(H2O)3]2(2H2O (H2L = 3-nitrophthalic acid, NPA) was synthesized in water/ethanol solution and characterized by X-ray diffraction, IR spectrum and TGA-DTA. The complex crystallizes in triclinic system, space group P-1 with a = 8.1549(16), b = 8.8856(18), c = 15.277(3)(A),α= 100.93(3),α= 90.81(3), γ= 104.56(3)°, V = 1049.8(4)(A)3, Z = 1,μ= 2.125 mm-1, Dc＝1.994 g/cm3, R = 0.0259 and wR = 0.0679. Two 3-nitrophthalates(2-) coordinate with the La3 ions in a bridging mode, and two monohydrogen- 3-nitrophthates(1-) and three waters in terminal ways, respectively. Each La3 ion is nine-coordinated to exhibit a distorted tricapped trigonal prism coordination polyhedron. Both the coordinated and crystal waters are involved in the inter- and intramolecular hydrogen bonds. The dinuclear units are linked into a 2D network structure in the ab plane via intermolecular hydrogen bonds along the axes a and b. Two crystal waters fill each rhombic pore of the network. The networks are further packed along the c axis forming a layered supramolecular structure through the C-H…O weak forces between the adjacent sheets. TGA analysis shows the complex undergoes the loss of waters of crystallization and coordination and the decomposition of ligands sequentially.     

C—H…Cl Hydrogen Bond and π-π Interaction Based Two 3D Supramolecular Architectures of Cu(II) and Co(II) Complexes with Chiral 1,2-Bis(benzimidazol-2-yl) ethane Ligand Containing 2D Grids

合成了两个新的配合物CuLCl₂•2EtOH(1) 和CoLCl₂ (2) [L是( S , S )－1,2－二N－甲基苯并咪唑－1,2－二甲氧基－乙烷],并通过单晶X衍射确定它们的结构。配合物1中,L作为三齿[N, N, O]配体,而配合物2 中,L作为二齿[N, N]配体。这两个配合物共同的结构特点都是通过分子内氢键形成2维的格子结构,然后通过分子间的C－H···Cl型氢键和π–π堆积作用形成3维结构。     

rα Structures of partially oriented pentafluorobenzenes C6F5X (X = H, Cl, I) as determined from 19F NMR spectra with 13C satellites

The (19)F spectra with natural-abundance carbon-13 satellites of C(6)F(5)X (X = H, Cl or I) in ZLI 1695 liquid crystal were analysed. Excluding fluorine-fluorine dipolar coupling constants from the fitting, the vibrationally corrected structures of these molecules were derived and compared with those calculated at DFT/B3LYP level of theory with the aug-cc-pVTZ basis set. The results show that pentafluorobenzene did not exhibit noticeable distortion of the aromatic ring, while chloropentafluorobenzene and iodopentafluorobenzene molecules showed some deformations in their determined structures. Relative anisotropies of F-F couplings have been deduced with accuracy for C(6)F(5)H molecule. Due to uncertainties in structure determination of C(6)F(5)Cl and C(6)F(5)I molecules, it was not possible to obtain precise values for all the corresponding anisotropies. In addition, it was found that the orientation of these molecules in the solvent used can be qualitatively explained in terms of dispersion forces.     

Unexpected Carbon–Carbon Bond Cleavage in the Reactions of the Pentagonal Bipyramidal Cluster Fe3(CO)6(μ-CO)2[μ3-η4-{RCC(Et)C(Et)CR}] with Styrene. Synthesis and X-ray Structure of Fe3(CO)6[μ3-η4-{EtC2CR}]2 (R = CH3(=CH2))

The thermal reactions of 2-methyl-1-hexen-3-yne [CH₃CH₂C≡CC(=CH₂)CH₃, metey] with Fe₃(CO)₁₂ have been studied: cluster opening or fragmentation and alkyne dimerization occur. Main products are the open triangular isomers [Fe₃(CO)₆(μ-CO)₂{CH₃(=CH₂)CC(Et)C(Et)C(=CH₂)CH₃}] (complex 3a) and [Fe₃(CO)₆(μ-CO)₂{C(Et)CCH₃(=CH₂)C(Et)CCH₃(=CH₂)}] (complex 3b). The structure and isomerism of the complexes has been confirmed by X-ray studies. The minor products of the reaction have been characterized by spectroscopic techniques. An attempt at exploiting the reactivity of the “free” C=C bonds of the coordinated ene-yne was made: complex 3a was reacted with styrene under thermal conditions. Unexpectedly considerable yields of the closed triangular cluster [Fe₃(CO)₆{EtC₂C(=CH₂)CH₃}₂] (complex 5) have been obtained. This behaviour had not been previously observed. The unprecedented structure of complex 5 has been confirmed with an X-ray study.     

3-(diallylamino)propanenitrile ((C3H5)2NC2H4CN, L) π-complexes with copper(I) ionic salts. Syntheses and crystal structures of compounds [Cu(H+L)ClO4]ClO4 · H2O, [Cu(H+L)BF4]BF4 · H2O, and [Cu(H+L)(H2O)]SiF6 · H2O

Qualitative single crystals of ??-complexes Cu(H⁺L)(ClO₄)]ClO₄ · H₂O (I), Cu(H⁺L)(BF₄)]BF₄ · H₂O (II), and [Cu(H⁺L)(H₂O)]SiF₆ · H₂O (III) are synthesized from solutions of 3-(diallylamino)propanenitrile (L) in propanol, ethanol, and methanol-water acidified with the corresponding acid to pH 3.5?C5 and from the copper(II) salts (Cu(ClO₄)₂ · 6H₂O, Cu(BF₄)₂ · 6H₂O, and CuSiF₆ · 4H₂O) using the alternating-current electrochemical method on copper wire electrodes. The crystal structures of the complexes are determined. All compounds crystallize in the monoclinic crystal system: complexes I and II are isostructural, space group P2₁/n, Z = 4. For compound III, space group P2₁/c, Z = 8. Unit cell parameters: for I a =7.8153(3), b = 16.7824(7), c = 12.4426(5) ?, ?? = 93.410(2)°, V = 1629.1(1) ?³; for II, a = 7.6755(4), b = 16.7119(7), c = 12.3784(6) ?, ?? = 94.354(2)°, V = 1583.2(1); and for III a = 9.826(2), b = 24.009(3), c = 12.061(2) ?, ?? = 91.820(6)°, V = 2843.9(7) ?³. The trigonal pyramidal coordination of the copper atom in complexes I-III is formed by two C=C bonds of the allyl groups of H⁺L, the nitrile N atom of the adjacent cation of the ligand, and the O or F atom of the ClO ₄ ^? or BF ₄ ^? anions. In structure III, the apical position of the pyramid is occupied by the O atom of the water molecule, since the SiF ₆ ^2? anion is considerably remote from the copper(I) atom. However, this anion is bound to the organic cation by hydrogen bonds F??H (2.05?C2.51 ?).