Kinetics and Mechanism of Thermal Decomposition of Bis(η3-Allyl)Nickel Complexes

Kinetics and Catalysis - The kinetics of thermal decomposition of bis(η3-allyl) nickel complexes in various media is studied. The specific features of the mechanism are determined, including...     

Kinetics and Mechanism of Iridium(Ⅲ)-Catalyzed Oxidation of Ethanol Amine by Cerium(Ⅳ) in Sulfuric Acid Media

In this study, the kinetics and mechanism of the iridium(Ⅲ)-catalyzed oxidation of ethanol amine(EAN) by cerium(Ⅳ) in a sulfuric acid medium was investigated using titrimetric technique of redox in a temperature range of 298-313 K. It was found that the reaction is of first order with respect to Ce(Ⅳ) and Ir(Ⅲ), and a positive fractional order with respect to EAN. It was also found that the pseudo-first-order([EAN](》)[Ce(Ⅳ)]) rate constant kobs decreases with the increase of [H ] and [HSO-4]. Under the protection of nitrogen gas, the reaction system can initiate the polymerization of acrylonitrile, indicating the generation of free radicals. On the basis of the experimental results, a suitable mechanism was proposed. From the dependence of kobs on the concentration of hydrogen sulfate, Ce(SO4)2 was found to be the kinetically active species. The rate constants of the rate-determining step together with the activation parameters were evaluated.     

Iridium(III) Catalysts with an Amide-Pendant Cyclopentadienyl Ligand: Double Aromatic Homologation Reactions of Benzamides by Fourfold C−H Activation

The synthesis, characterization, and catalytic performance of iridium(III) catalysts that bear an amide-pendant cyclopentadienyl ligand ([Cp^AIrI₂]₂) is reported. These [Cp^AIrI₂]₂ catalysts were obtained from the complexation of a Cp^A ligand precursor with [Ir(cod)OAc]₂ followed by oxidation. Double aromatic homologation reactions of benzamides with alkynes by fourfold C−H activation proceeded in good to high yield with these [Cp^AIrI₂]₂ catalysts, demonstrating their superior catalytic performance in this challenging transformation.     

Thermal isomerization of η6-arene ferradicarbolllides. Experimental proof for isolobal relation between (η6-arene)Fe and (η5-cyclopentadienyl)Co cluster units

The heating of selected [1-(η(6)-arene)-closo-1,2,3-FeC(2)B(9)H(11)] complexes resulted in the thermal rearrangement and isolation of the corresponding 1,2,4-, 1,2,7-, and 1,2,8-cage isomers. Demonstrated here is a similar rearrangement and the NMR behaviour for isostructural [1-(η(5)-cyclopentadienyl)-closo-1,2,3-CoC(2)B(9)H(11)] compounds.     

Site- and Stereoselective C(sp3)−H Borylation of Strained (Hetero)Cycloalkanols Enabled by Iridium Catalysis

Transition metal-catalyzed site- and stereoselective C−H activation of strained (hetero)cycloalkanes remains a formidable challenge. We herein report a carbamate-directed iridium-catalyzed asymmetric β−C(sp³)−H borylation of cyclopropanol derivatives. A variety of densely functionalized cyclopropanols were obtained in good enantioselectivities via desymmetrization and kinetic resolution. In addition, site-selective C(sp³)−H borylation of methine groups furnished α-borylated (hetero)cycloalkanols in moderate to good yields. The synthetic utility of the method was further shown in a gram-scale synthesis and diverse downstream transformations of borylated products.     

Protonation of (μ-H)3Ru3(μ3-CR)(CO)9. Evidence for the formation of an agostic metalhydrogencarbon bond

Protonation of (μ-H)₃M₃(μ₃-CR)(CO)₉ (M = Ru, R = Et or M = Os, R = Me) by dissolution in HSO₃CF₃ yields H₃M₃(HCR)(CO)₉⁺, containing a MHC bridge. The products were characterized by ¹H and ¹³C NMR spectroscopy. Decompositions of other protonated methylidyne clusters from CH₃R and a variety of metal-containing products.     

Experimental (X-ray Diffraction,UV–Vis Spectroscopy) and DFT Studies of 1-Ethyl-3-methylquinoxaline-2-thione

Russian Journal of Physical Chemistry A - In this paper, we present the experimental and theoretical investigation of 1-ethyl-3-methylquinoxaline-2-thione, molecule exhibiting an important...     

Experimental and DFT studies of ethyl N′-3-(1H-imidazol-1-yl) propylcarbamoyl benzohydrazonate monohydrate

The Imidazole compound, Ethyl N′-3-(1H-imidazol-1-yl) propylcarbamoyl benzohydrazonate monohydrate, has been synthesized and characterized by IR, NMR, electronic spectroscopy, and X-ray single-crystal determination. Molecular geometry from X-ray experiment of the title compound in the ground state has been compared using the density functional method (B3LYP) with 6-31G+(d) basis set. To determine conformational flexibility, molecular energy profile of the title compound was obtained by DFT calculations with respect to two selected degrees of torsional freedom, which were varied from −180° to +180° in steps of 10°. Besides, molecular electrostatic potential (MEP), natural bond orbitals (NBO), frontier molecular orbitals (FMO), and thermodynamic properties were performed at B3LYP/6-31G+(d) level of theory.     

Molecular Structure,Electronic Properties,Homo–Lumo,MEP and NBO Analysis of (N-Isocyanimino) Triphenylphosphorane (Ph3PNNC): DFT Calculations

Journal of Structural Chemistry - N-isocyaniminotriphenylphosphorane (Ph3PNNC) is a type of iminophosphorane which is an important reagent in synthetic organic chemistry and a ligand in metallic...     

Mechanism on The Disproportionating Synthesis of Dichlorodimethyl- silane by ZSM-5(5 T)@γ-Al2O3 Series Core-Shell Catalysts

In view of the wide application of organosilicon bifunctional structure in industry, the most effective disproportionation solution is used by the new catalyst to prepare the largest and the most versatile organic silicon monomer dimethyldichlorosilane. However, there are still remaining doubts on the disproportionation mechanism of the catalyst. The Density Functional Theory (DFT) was used to theoretically calculate the disproportionation mechanism of 5 T clusters ZSM-5@γ-Al₂O₃ series catalysts at the B3LYP/6–311++G(3df, 2pd) level. The properties were verified and the catalytic effects of different active sites pre- and post- modified by AlCl₃ were calculated and compared. The active center of HZSM-5@γ-Al₂O₃ was proton, and that of AlCl₃/ZSM-5@γ-Al₂O₃ changed to lewis acidic center. The presence of the lewis acid center enhances the total activity of the catalyst to some extent. The catalytic activity of the 5 T cluster ZSM-5@γ-Al₂O₃ catalyst modified by AlCl₃ was higher, which was the same as the experimental results.     

Structure and Energetics of β-Diketonates. XII. Structure of Lanthanide tris-Dipivaloylmethanates for Er(thd)3 Used as an Example

A simultaneous electron diffraction and mass spectroscopic study of saturated vapors of erbium tris-dipivalylmethanate has revealed that at 136(5)°C, the vapor consists solely of Er(thd)₃ molecules. Electron diffraction data may be described by two alternative models (of C_3 and D_3 symmetry), for which r_a, r_g, and r structural parameters have been determined. D₃ symmetry is recognized to be preferable for free Er(thd)₃ molecules. The main structural parameters of the model are r (Er – O) 2.218(5), r (O – C) 1.279(5), r (C – C_r) 1.404(6), r (C – C_t) 1.512(3), r(C_t – C_m) 1.542(5), r (rm C_m– H) 1.804(4) , The ErO 75.0(0.4)°. The ErO₆ coordination polyhedron has a structure close to an antiprism. A rotational angle of the O–O–O trigonal face relative to the position in a regular prism is 20.7(0.8)°. Possible reasons for the differences in the structure of Er(thd)₃ molecules in the gas phase and crystal are discussed.     

A New Cd(Ⅱ) Coordination Polymer Constructed by 3-(2-Pyridyl)pyrazole and 5-Nitroisophthalic Acid:Synthesis,Crystal Structure and Theoretical Calculations

A new coordination polymer, [Cd_2(NIPH)(L)_2(H_2O)]n(1, HL = 3-(2-pyridyl)pyrazole and H_2NIPH = 5-nitroisophthalic acid), has been synthesized. The structure of complex 1 has been characterized by X-ray single-crystal diffraction, elemental analysis, IR spectrum analysis, thermogravimetric analysis and fluorescence spectrum analysis. Complex 1 belongs to the triclinic system, space group P1 with a = 8.9539(6), b = 11.6252(8), c = 12.2472(8) ?, α = 80.011(2), β = 80.3850(10), γ = 86.773(2)°, V = 1237.37(14) ?~3, Z = 2, D_c = 1.987 g/cm~3, μ = 1.780 mm~(-1), M_r = 740.25, F(000) = 724, the final R = 0.0295 and wR = 0.1015 with I 2σ(I). Two H_2NIPH as monodentate and bidentate ligands and two L ligands link four Cd(Ⅱ) ions to form a tetranuclear subunit. Each pair of the tetranuclear subunits is bridged by NIPH ligands to yield a one-dimensional double-chain structure. Furthermore, the 1D chains are linked into a 3D supramolecular framework with hydrogen bonds and π-π interactions. In addition, we analyzed Natural Bond Orbital(NBO) in using the PBE0/LANL2DZ method built in Gaussian 03 Program. The calculation results indicated the obvious covalent interaction between the coordinated atoms and Cd(Ⅱ) ion.     

Synthesis,Crystal Structure and Theoretical Calculations of a Manganese(Ⅱ) Coordination Polymer Assembled by 2,5-Thiophenedicarboxylic Acid and 3-(2-Pyridyl)pyrazole Ligands

A new Mn(Ⅱ) complex, [Mn_(0.5)(tdc)_(0.5)(L)]_(2n)(1, H2 tdc = 2,5-thiophenedicarboxylic acid, L = 3-(2-pyridyl)pyrazole), has been successfully synthesized under hydrothermal conditions. Its structure has been determined by single-crystal X-ray diffraction analysis, elemental analyses, IR, TG and UV spectrum. Single-crystal X-ray diffraction analysis reveals that complex 1 belongs to the orthorhombic system, space group Pnna with a = 11.5184(6), b = 16.8399(8), c = 11.7249(5) ?, V = 2274.26(19) ?3, Z = 4, D3c = 1.505 g/cm, μ = 0.715 mm-1, Mr = 515.41, F(000) = 1052, the final R = 0.0336 and w R = 0.0802 with I 2σ(I). It exhibits a one-dimensional zigzag-chain structure, which was stabilized through intermolecular C–H···O and intramolecular N–H···O hydrogen bonding interactions. Moreover, we analyzed Natural Bond Orbital(NBO) by using the PBE0/LANL2 DZ method built in Gaussian 09 Program. The calculation results showed obvious covalent interaction between the coordinated atoms and Mn(Ⅱ) ion.     

Which Stereoinductor Is Better for Asymmetric Functionalization of α-Amino Acids in a Nickel(II) Coordination Environment? Experimental and DFT Considerations

The results of extended comparative investigation of nickel(II) Schiff base complexes (containing various auxiliary chiral moieties) commonly used as a methodological platform for the asymmetric synthesis of tailor-made α-amino acids are provided. The following issues are addressed: 1) redox activity (determining the possibility for electrochemically induced reactions); 2) quantitative estimation of the reactivity of deprotonated complexes towards electrophiles; and 3) quantum-chemical estimation of noncovalent interactions in the metal coordination environment (which shed light on the origin of the stereochemical outcome observed for different stereoinductors). Possible mechanisms that determine the relationship between the stereochemical configuration of a molecule and its electronic structure are discussed. The DFT-calculated HOMO–LUMO energies and localization, as well as relative energies for the (S)- and (R)-alanine derivatives, that determine the stereoinduction efficiency in thermodynamically controlled reactions in nickel(II) coordination are provided. The computational data are supported by experimental results on the monobenzylation of glycine derivatives.     

Visible-Light-Driven Intermolecular Reductive Ene–Yne Coupling by Iridium/Cobalt Dual Catalysis for C(sp3)−C(sp2) Bond Formation

A new methodology to form C(sp³)−C(sp²) bonds by visible-light-driven intermolecular reductive ene–yne coupling has been successfully developed. The process relies on the ability of the Hantzsch ester to contribute in both SET and HAT processes through a unified cobalt and iridium catalytic system. This procedure avoids the use of stoichiometric amounts of reducing metallic reagents, which is translated into high functional-group tolerance and atom economy.     

Bis(sulfonylimide)ruthenium(VI) Porphyrins: X‐ray Crystal Structure and Mechanism of C?H Bond Amination by Density Functional Theory Calculations

The X‐ray crystal structure of [Ru^VI(NMs)₂(tmp)] (Ms=SO₂‐ p‐MeOC₆H₄; tmp=5,10,15,20‐tetramesitylporphyrinato(2?)), a metal sulfonylimide complex that can undergo alkene aziridination and C? H bond amination reactions, shows a Ru?N distance of 1.79(3) Å and Ru‐N‐S angle of 162.5(3)°. Density functional theory (DFT) calculations on the electronic structures of [Ru^VI(NMs)₂(tmp)] and model complex [Ru^VI(NMs)₂(por⁰)] (por⁰=unsubstituted porphyrinato(2?)) using the M06L functional gave results in agreement with experimental observations. For the amination of ethylbenzene by the singlet ground state of [Ru^VI(NMs)₂(por⁰)], DFT calculations using the M06L functional revealed an effectively concerted pathway involving rate‐limiting hydrogen atom abstraction without a distinct radical rebound step. The substituent effect on the amination reactivity of ethylbenzene by [Ru^VI(NX)₂(por⁰)] (X=SO₂‐p‐YC₆H₄ with Y=MeO, Me, H, Cl, NO₂) was examined. Electron‐withdrawing Y groups lower the energy of the LUMOs of [Ru^VI(NX)₂(por⁰)], thus facilitating their interaction with the low‐lying HOMO of the ethylbenzene C? H bond and hence increasing the reactivity of [Ru^VI(NX)₂(por⁰)]. DFT calculations on the amination/aziridination reactions of [Ru^VI(NSO₂C₆H₅)₂(por⁰)] with pent‐4‐enal, an aldehyde substrate bearing acyl, homoallylic, and allylic C? H bonds and a C?C bond, revealed a lower reaction barrier for the amination of the acyl C? H bond than for both the amination of the other C? H bonds and aziridination of the C?C bond in this substrate.     

Synthesis,Characterization and Real Molecule DFT Calculations for Neutral Organogallium(I) Aryl Dimers and Monomers: Weakness of Gallium?Gallium Bonds in Digallenes and Digallynes

Move closer : The gallium? gallium bond strength in terphenyl gallium(I) dimers [ArGaGaAr] (see figure) is similar to those in other molecules with closed shell interactions, implying that the Ga? Ga bond in doubly reduced Na₂[ArGaGaAr] is much closer to a single than a triple one.

     

Onset of Amorphous Structure in CaCO3: Geometric and Electronic Structures of (CaCO3) n (n?=?2–7) Clusters by Ab Initio Calculations

Electronic structures, vibrational analyses, stabilization energies and amorphicity were analyzed for the most stable configurations of the neutral gas phase clusters of calcium carbonate (CaCO₃) _n (n?=?2?C7). Minimum-energy structures were generated through simulated annealing using a mix of molecular dynamics/semiempirical optimization and then full optimization at the ab initio level (RHF/6-31G*). HF-level results are calibrated versus MP2/6-31G* results. Though many clusters are symmetric, the structural arrangements are not crystalline and resemble neither calcite nor aragonite. In general, greater symmetry means a lower stabilization energy. The BSSE- and zero point energy-corrected stabilization energies appear to plateau at about ?113?kcal/mol when n?=?7. Amorphous clusters start appearing when n?=?4 and the lowest-energy minima for n????5 are of C₁ symmetry. No solvent effect is necessary to induce amorphism.