Asymmetric Induction From Ethyl Lactate in the Reduction of Acetophenone to Phenylethanol

Ethyl lactate was used for the first time as a solvent for acetophenone reduction to phenylethanol by borane and sodium tetrahydridoborate. Moderate enantiomeric excess was obtained with the pure reducing agents that could be improved up to 46% by employing stoichiometric amounts of the Lewis acid ZnCl₂. These are the highest e.e. values published for solvent‐induced chiral synthesis.     

KH添加对Na-Al-H配位氢化物可逆放氢性能的影响

以NaH粉和Al 粉为合成原料, 分别采用2% (摩尔分数, x) CeCl₃和2% CeCl₃/y% KH (y=0.02, 0.04)为催化添加剂, 在室温和3 MPa氢压下, 通过反应球磨(NaH/Al+CeCl₃)和(NaH/Al+CeCl₃/yKH) (y=0.02, 0.04)复合物成功制备出Na-Al-H 配位氢化物. 吸放氢性能测试结果表明, KH的加入能有效改善Na-Al-H 体系中第二步脱氢反应放氢动力学性能. (NaH/Al+CeCl₃/0.02KH)复合物170℃放氢时可在20 min内完成脱氢过程, 且在较低温度(100-140℃)下具有良好的可逆吸放氢性能. Kissenger 方法计算表明, 添加KH可降低Na-Al-H 体系第二步脱氢反应的表观活化能, 降低其放氢峰值温度. 相结构分析表明, KH的添加使Na-Al-H 体系中Na₃AlH₆的晶胞体积发生膨胀, 进而提高体系的第二步放氢动力学性能.     

Counterpoise correction is not useful for short and Van der Waals distances but may be useful at long range

This article investigates the errors in supermolecule calculations for the helium dimer. In a full CI calculation, there are two errors. One is the basis set superposition error (BSSE), the other is the basis set convergence error (BSCE). Both of the errors arise from the incompleteness of the basis set. These two errors make opposite contributions to the interaction energies. The BSCE is by far the largest error in the short range and larger than (but much closer to) BSSE around the Van der Waals minimum. Only at the long range, the BSSE becomes the larger error. The BSCE and BSSE largely cancel each other over the Van der Waals well. Accordingly, it may be recommended to not include the BSSE for the calculation of the potential energy curve from short distance till well beyond the Van der Waals minimum, but it may be recommended to include the BSSE correction if an accurate tail behavior is required. Only if the calculation has used a very large basis set, one can refrain from including the counterpoise correction in the full potential range. These results are based on full CI calculations with the aug-cc-pVXZ (X = D, T, Q, 5) basis sets.     

Synthesis and Structure of a Ruthenium（Ⅱ）-dithiocarbamate Complex [RuH（CO）（PPh_3）_2（4-ClPhNHCS_2）]·C_6H_（14）

The title complex [RuH(CO)(PPh3)2(4-ClPhNHCS2)]·C6H14 has been prepared and characterized by X-ray diffraction analysis.It crystallizes in the triclinic system,space group P1 with a = 11.0817(2),b = 14.3889(2),c = 15.2136(2) ,α = 71.018(1),β = 74.911(1),γ = 85.146(1)°,V = 2214.86(6) 3,Z = 2,Mr = 900.4,Dc = 1.350 g/cm3,Mr = 900.40,μ(MoKα) = 0.616 mm-1,F(000) = 926,S = 1.016,the final R = 0.0478 and wR = 0.0947 for 6828 observed reflections with I > 2σ(I) and 505 variables.The molecular structure of 1 consists of one neutral complex [RuH(CO)(PPh3)2(4-ClPhNHCS2)] and one hexane solvent molecule.The geometry around ruthenium is pseudo-octahedral with two trans-binding PPh3 ligands and one chelating bidentate 4-ClPhNHCS2- ligand via two sulfur atoms.The average Ru-S,Ru-P and Ru-H bond lengths are 2.4824(8),2.3495(8) and 1.71(2),respectively.The electrochemical properties of 1 have been studied in CH2Cl2 solution by cyclic voltammetry.     

Non-catalytic conversion of C-F bonds of gem-difluoromethylene derivatives to C-H bonds with lithium aluminum hydride under room temperature

An unexpected hydrodefluorination of unactivated aliphatic C-F bonds of CF₂ derivatives with LiAlH₄ at room temperature without any added metal catalyst was reported. Deuterium-labeling experiments suggested that the hydrogens introduced into the products originated from LiAlH₄.     

Role of O?H bonding in catalytic activity of Nb2O5 during the course of dehydrogenation of MgH2

The hydrogen desorption reaction of MgH₂, MgH₂ → Mg + H₂, is accelerated by the addition of metal oxide catalysts (e.g., Nb₂O₅). From our theoretical calculation of electronic structure, it was predicted that the catalytic activities of metal oxides are related closely to the O? H interaction operating at the interface between oxide catalyst and MgH₂. In this study, the O? H vibration on the Nb₂O₅‐catalyzed MgH₂ was investigated experimentally using FTIR spectroscopy. The broad absorption band due to the O? H stretching mode was observed in the region of 2,800–3,600 cm^?1 in the FTIR spectra of the specimens when hydrogen desorption reaction was in progress. The absorbance of the band decreased monotonously with decreasing hydrogen content in the specimen during the course of dehydrogenation of MgH₂. This experimental result was in agreement with our prediction for the existence of O? H interaction in the hydrogen desorption process. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Transition‐Metal‐Free Reductive Functionalization of Tertiary Carboxamides and Lactams for α‐Branched Amine Synthesis

A new method for the synthesis of α‐branched amines by reductive functionalization of tertiary carboxamides and lactams is described. The process relies on the efficient and controlled reduction of tertiary amides by a sodium hydride/sodium iodide composite, in situ treatment of the resulting anionic hemiaminal with trimethylsilyl chloride and subsequent coupling with nucleophilic reagents including Grignard reagents and tetrabutylammonium cyanide. The new method exhibits broad functional‐group compatibility, operates under transition‐metal‐free reaction conditions, and is suitable for various synthetic applications on both sub‐millimole and on multigram scales.     

Counterion Dependence of Dinitrogen Activation and Functionalization by a Diniobium Hydride Anion

We report the synthesis of anionic diniobium hydride complexes with a series of alkali metal cations (Li⁺, Na⁺, and K⁺) and the counterion dependence of their reactivity with N₂. Exposure of these complexes to N₂ initially produces the corresponding side‐on end‐on N₂ complexes, the fate of which depends on the nature of countercations. The lithium derivative undergoes stepwise migratory insertion of the hydride ligands onto the aryloxide units, yielding the end‐on bridging N₂ complex. For the potassium derivative, the N?N bond cleavage takes place along with H₂ elimination to form the nitride complex. Treatment of the side‐on end‐on N₂ complex with Me₃SiCl results in silylation of the terminal N atom and subsequent N?N bond cleavage along with H₂ elimination, giving the nitride‐imide‐bridged diniobium complex.     

Unexpected Vulnerability of DPEphos to C−O Activation in the Presence of Nucleophilic Metal Hydrides

C−O bond activation of DPEphos occurs upon mild heating in the presence of [Ru(NHC)₂(PPh₃)₂H₂] (NHC=N-heterocyclic carbene) to form phosphinophenolate products. When NHC=IEt₂Me₂, C−O activation is accompanied by C−N activation of an NHC ligand to yield a coordinated N-phosphino-functionalised carbene. DFT calculations define a nucleophilic mechanism in which a hydride ligand attacks the aryl carbon of the DPEphos C−O bond. This is promoted by the strongly donating NHC ligands which render a trans dihydride intermediate featuring highly nucleophilic hydride ligands accessible. C−O bond activation also occurs upon heating cis-[Ru(DPEphos)₂H₂]. DFT calculations suggest this reaction is promoted by the steric encumbrance associated with two bulky DPEphos ligands. Our observations that facile degradation of the DPEphos ligand via C−O bond activation is possible under relatively mild reaction conditions has potential ramifications for the use of this ligand in high-temperature catalysis.