Hydrogen bond assisted activation of a dinitrile towards nucleophilic attack

The possibility of tunable regioselective activation of a dinitrile towards nucleophilic attack was demonstrated. For that, a sulfo-arylhydrazone unit was introduced into malononitrile and the thus formed intramolecular hydrogen bond systems assisted specific nucleophilic attacks to the cyano moieties leading to a variety of amidines, carboxamides and iminoesters depending on the nucleophiles and conditions used.     

Pressure‐Assisted Hetero‐ and Homodialkylation of Sulfide in [Pt2(μ‐S)2(dppp)2]: One‐Pot Conversion of {Pt2(μ‐S)2} into {Pt2(SR)2} and {Pt2(SR)(SR′)}

Heterodialkylation of [Pt₂(μ‐S)₂(dppp)₂] (dppp=Ph₂P(CH₂)₃PPh₂) was achieved under high pressure (10 kbar). This enabled the synthesis of rare diplatinum complexes with structurally diverse thiolate bridges, such as [Pt₂(μ‐SC₅H₁₀CO₂CH₂CH₃)(μ‐SC₃H₇)‐(dppp)₂](PF₆)₂, which was crystallographically identified. Complete homodialkylation was also achieved under similar conditions (6 kbar at room temperature), thus permitting the isolation of [Pt₂(μ‐SC₂H₄CO₂CH₂CH₃)₂(dppp)₂]‐(PF₆)₂. The isolation of these complexes extends the applications of high‐pressure chemistry to thiolato homo‐ and heterobridged complexes that are otherwise not accessible.     

Competitive and selective Csp3-Br versus Csp2-Br bond activation in palladium-catalysed Suzuki cross-coupling: an experimental and theoretical study of the role of phosphine ligands

Phosphine ligands have been demonstrated to have an effect on reactivity and selectivity in the competitive intramolecular palladium-catalysed Suzuki-Miyaura coupling of dibromo sulfoxide 1a possessing two different hybridised electrophilic carbons. It was found that the bromine bond to the sp(3)-hybridised carbon is selectively replaced in the presence of unhindered phosphines such as PPh(3) or xantphos. The use of hindered phosphine ligands such as P(o-tol)(3) and P(1-naphthyl)(3) reversed the selectivity, conducting the cross-coupling at the Csp(2)-Br. Identical trends were observed in external competition experiments carried out with bromomethyl sulfoxide and different substituted bromoarenes. DFT and DFT/MM calculations showed that the selectivity observed is mainly due to the different facility of the ligands to dissociate. Bisphosphine catalysts favour coupling at the sp(3) carbon, whereas monophosphine catalysts prefer the sp(2) carbon.     

Front waves in the NO + NH3 reaction on Pt{100}

In the present work, we spatially extended a brand new kinetic mechanism of the NO + NH3 reaction on Pt{100} to simulate the experimentally observed spatiotemporal traveling waves. The kinetic mechanism developed by Irurzun, Mola, and Imbihl (IMI model) improves the former model developed by Lombardo, Fink, and Imbihl (LFI model) by replacing several elementary steps to take into account experimental evidence published since the LFI model appeared. The IMI model achieves a better agreement with the experimentally observed dependence of the oscillation period on temperature. In the present work, the IMI model is extended by considering Fickean diffusion and coupling via the gas phase. Traveling waves propagating across the surface are obtained at realistic values of temperature and partial pressure. A transition from amplitude to phase waves is observed, induced either by temperature or by the gas global coupling strength. The traveling waves simulated in the present work are not associated with fixed defects, in agreement with experimental evidence of spiral centers capable of moving on the surface. Also, the IMI model adequately predicts the presence of macroscopic oscillations in the partial pressures of the reactants coexisting with front wave patterns on the surface.     

A theoretical study of the vibrational structure in the \documentclass{article}\pagestyle{empty}\begin{document}$\tilde{A}^{2}A_{1} - \tilde{X}^{2}B_{1}$\end{document} transition of PH2

The potential energy curves of the bending mode of PH₂ in the ground ²B₁ and the excited ²A₁ states have been calculated using ab initio SCF -MO wave-functions. The radical is found, in agreement with experiment, to be bent in the two states. The calculated results clarify the interpretations of the anomalous behaviour of observed vibrational intervals, and offer an explanation of the ‘quasilinearity’; of the radical in the ²A₁ state.     

铂修饰的{001}面暴露的二氧化钛纳米片阵列的制备和光催化性能

采用有机溶剂热法在FTO衬底上制备{001}面暴露的单晶锐钛矿相TiO2纳米片阵列,通过FESEM和XRD研究样品的形貌和晶体结构. 与水热法制备的纳米片阵列相比,有机溶剂热法制备的样品取向性更好. 采用光沉积方法在纳米片阵列上沉积Pt,所得到的Pt纳米颗粒粒径更为均匀,并且更容易沉积在{001}面上. 所负载的Pt 纳米颗粒增强了TiO2纳米片的光吸收性能,同时大大减弱了光致发光强度. 在光催化性能测试中,具有最优负载量的样品催化性能提高了一倍. 与传统的Pt负载相比,{001}面的最优负载量显得相当小,这可能源于高活性{001}面的原子结构.     

Xanthate complexes of {Nb2S4}4+

Alkyl xanthate complexes [Nb₂S₄(S₂COR)₄] (R = Et (I), iso-Pr (II), n-Bu (III), and iso-Am (IV)) are synthesized by the ligand exchange reaction in solutions from (Et₄N)₄[Nb₂S₄(NCS)₈] and the corresponding potassium salts in satisfactory yields. The X-ray diffraction analyses are carried out for the isopropyl xanthate (II) and butyl xanthate (III) complexes. From the view point of mutual arrangement of chelate cycles, complexes II and III exist in crystals as ΛΔ isomers. The niobium-niobium distances are 2.8789(4) Å in complex II and 2.8856(3) Å in complex III. The first example for the formation of short S...S contacts between the disulfide ligands of the {Nb₂S₄}⁴⁺ fragments in the crystal structure of III is found (3.146 Å).     

Structural organization and thermal behavior of the heteropolynuclear complex [Au2{S2CN(CH3)2}4][ZnCl4] and the heterovalent complex ([Au{S2CN(CH3)2}2][AuCl2]) n obtained in the chemisorption system [Zn2{S2CN(CH3)2}4]-Au3+/2 M HCl

Reactions of freshly precipitated binuclear zinc dimethyldithiocarbamate with [AuCl₄]^? anions in 2 M HCl were studied. The heteropolynuclear complex [Au₂{S₂CN(CH₃)₂}₄][ZnCl₄] (I) and the polymeric heterovalent complex ([Au{S₂CN(CH₃)₂}₂][AuCl₂]) _n (II) were preparatively isolated from the chemisorption system [Zn₂{S₂CN(CH₃)₂}₄]-Au³⁺/2 M HCl. The products were characterized by ¹³C MAS NMR data and by X-ray diffraction determination of crystal and molecular structures. The principal structural units of compounds I and II are the tetragonal planar complex cations [Au{S₂CN(CH₃)₂}₂]⁺ (in which the complex-forming ion coordinates two MDtc ligands in the S,S′-bidentate mode) and the anions, namely, the distorted tetrahedral anion [ZnCl₄]^2? in I and the linear [AuCl₂]^? anion in II. The further structural self-organization of complexes at the supramoleular level occurs through relatively weak secondary bonds Au?S and Au?Cl. The chemisorption capacities of zinc dimethyldithiocarbamate calculated from gold(III)-binding reactions are 644.1 and 1288.2 mg of gold per gram of the sorbent. Simultaneous thermal analysis studies of the thermal behavior of I and II were used to elucidate the conditions of gold recovery.     

Effect of oxygen adsorption on the chiral Pt{531} surface

The adsorption of oxygen on the chiral Pt{531} surface was studied by high-resolution X-ray photoelectron spectroscopy (HRXPS) and low energy electron diffraction (LEED). After the surface is annealed in oxygen (3 x 10(-7) mbar), three O 1s peaks are observed in XPS. One peak, at 529.5 eV, is assigned to chemisorbed oxygen; it disappears after annealing in vacuo to temperatures above 900 K. The other two peaks at 530.8 and 532.3 eV are stable up to at least 1250 K. They are associated with oxide clusters on the surface. These clusters readily react with coadsorbed carbon monoxide at temperatures between 315 and 620 K.     

{AsW9O33}-{Mo3S4} based polyoxometalates including a metal-metal bond with Pd or Ni. Synthesis, structure and studies in solution

Heterometallic cuboidal clusters [Mo(3)S(4)M(H(2)O)(9)Cl](3+) M = Pd or Ni react with the trivacant [AsW(9)O(33)](9-) anion to give tetramodular complexes [(H(2)AsW(9)O(33))(4){Mo(3)S(4)M(H(2)O)(5)}(2)](20-) (M = Pd for anion 2 and M = Ni for anion 3) in good yield. Both anions crystallized as single crystals of potassium salts to give K-2 and K-3 salts which have been characterized structurally by X-ray diffraction. Both compounds are isomorphous and the anions 2 and 3 are described as two dimeric moeties, associated by internal hydrogen bonds, electrostatic interactions involving four outer potassium ion and coordination bonds within a central {M(2)S(2)} unit containing a M-M metallic bond. Studies in solution reveal that the dimeric association is maintained in solution in the 2 × 10(-4)-2 × 10(-3) mol L(-1) range. Conversely, in the presence of exogeneous ligands, such as iodide or pyridine the UV-vis data are consistent with the dissociation of the anion 2 into monomer through a Pd-L coordination bond (L = I(-) or Py). Furthermore, (183)W NMR spectrum of 2 shows that molecular structure of 2 is retained in solution. Elemental analysis and IR are also supplied. Electrochemical behavior of 2 and 3 are given and compared with the Pd or Ni free parent anion. The CVs are dominated mainly by irreversible reduction or oxidation processes, where the peak potentials appear dependent upon the ionic charge of the complex. However, the CV of the Pd-containing anion (2) is consistent with the deposition of Pd metal at the electrode, which gives rise to an oxidation process into palladium oxide.     

Adsorption dynamics of water on Pt{110}-(1 x 2)

The dynamics of H(2)O adsorption on Pt{110}-(1 x 2) is studied using supersonic molecular beam and temperature programed desorption techniques. The sticking probabilities are measured using the King and Wells method at a surface temperature of 165 K. The absolute initial sticking probability s(0) of H(2)O is 0.54+/-0.03 for an incident kinetic energy of 27 kJmol. However, an unusual molecular beam flux dependence on s(0) is also found. At low water coverage (theta<1), the sticking probability is independent of coverage due either to diffusion in an extrinsic precursor state formed above bilayer islands or to incorporation into the islands. We define theta=1 as the water coverage when the dissociative sticking probability of D(2) on a surface predosed with water has dropped to zero. The slow falling H(2)O sticking probability at theta>1 results from compression of the bilayer and the formation of multilayers. Temperature programed desorption of water shows fractional order kinetics consistent with hydrogen-bonded islands on the surface. A remarkable dependence of the initial sticking probability on the translational (1-27 kJ/mol) and internal energies of water is observed: s(0) is found to be essentially a step function of translational energy, increasing fivefold at a threshold energy of 5 kJ/mol. The threshold migrates to higher energies with increasing nozzle temperature (300-700 K). We conclude that both rotational state and rotational alignment of the water molecules in the seeded supersonic expansion are implicated in dictating the adsorption process.     

Density functional theory study of the structures and stabilities of CuO\documentclass{article}\pagestyle{empty}\begin{document}$_{3}^{-}$\end{document} and CuO3

Hybrid density functional theory calculations on the structures, vibrational frequencies, electron binding and dissociation energies, and bonding properties of CuO$_{3}^{-}$ and CuO₃ species have been carried out. Stable isomers containing an O₃ subunit and composed of O₂ bound to CuO have been located on the potential energy hypersurfaces of CuO$_{3}^{-}$ and CuO₃. The isomers formed by O₂ bonded to CuO in side‐on and end‐on coordination are more stable than those containing an O₃ subunit. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 162–168, 2001     

Strength of the PtCS2 bond in Pt(PPh3)2(CS2)

The enthalpy of the reaction: Pt(PPh₃)₂(CH₂CH₂)(cryst.) + CS₂(g) → Pt(PPh₃)₂(CS₂)(cryst.) + CH₂CH₂(g) has been determined as ΔH = ? 4.40 ± 2.2 kJ mol^?1 from solution calorimetry, and the bond dissociation energy D(PtCS₂) shown to be slightly greater than D(PtC₂H₄).     

Intramolecular general acid catalysis of phosphate transfer. nucleophilic attack by oxyanions on the PO3 2- group

Phosphate transfer from the 8-dimethylammonium-naphthyl-1-phosphate monoanion 4m to water and to a range of nucleophiles shows general acid catalysis by the neighboring NH(+) group, through the strong intramolecular hydrogen bond. Reactivity is insensitive to the charge on the nucleophile, so that fluoride and oxyanions displace dimethylaminonaphthol from the PO3(2-) group as effectively as do amines of the same basicity. Reactivity is (predictably) relatively insensitive to the basicity of the nucleophile and to the alpha-effect. A strong intramolecular hydrogen bond is present in the product, but also in the reactant, as evidenced by major perturbations in the pK(a)'s of the phosphate and dimethylamino groups, to 3.94 and 9.31, respectively, and by ab initio calculations. Rate accelerations are of the order of 10(6)-fold despite this stabilization: the strength of the hydrogen bond is evidently significantly enhanced in the transition state. The evidence suggests that it also depends remarkably strongly on the degree of ionization of the reacting phosphate group and will be significantly reduced for the neutral PO(OH)2 group. Thus, the hydrolysis of the substrate cation 4+ shows a correspondingly greater, >10(8)-fold acceleration.