Asymmetric organocatalysis of the addition of acetone to 2-nitrostyrene using N-diphenylphosphinyl-1,2-diphenylethane-1,2-diamine (PODPEN)

The highly enantioselective addition of acetone to 2-nitrostyrene, using N-diphenylphosphinyl-trans-1,2-diphenylethane-1,2-diamine (PODPEN) as a catalyst, is described.     

Surprising selectivity in the transformation of dimethoxy azaindoles

Transformation of 4,7-dimethoxy-6-azaindole into 4-hydroxy-7-methoxy-6-azaindole or 7-hydroxy-4-methoxy-6-azaindole can be readily controlled by careful selection of a reagent. Treatment with concentrated HCl results in hydrolysis at the 4-position exclusively, while TMS-I provides demethylation at the 7-position only. Products were unambiguously identified by single crystal X-ray crystallography.     

Conversion of methanol to 2,2,3-trimethylbutane (triptane) over indium(III) iodide

InI3 is able to catalyze the conversion of methanol to a mixture of hydrocarbons at 200 degrees C with one highly branched alkane, 2,2,3-trimethylbutane (triptane), being obtained in high selectivity. The mechanism for InI3-catalyzed reactions appears to be basically the same as that proposed for the previously studied ZnI2-catalyzed system in which sequential methylation of olefins is followed by competing reactions of the resulting carbocation: proton loss to give the next olefin vs hydride transfer to give the corresponding alkane. Although the reaction conditions and typical triptane yields achievable with ZnI2 and InI3 are quite similar, the two systems behave rather differently in a number of important particulars, including significant differences between the detailed product distributions. Most of the differences in behavior can be ascribed to the stronger Lewis acidity of InI3, including the ability to activate some alkanes, the higher activity for methylation of arenes, and the fact that methanol conversion can be observed at somewhat lower temperatures with InI3 than with ZnI2.     

A General Method for Extracting Individual Coupling Constants from Crowded 1H NMR Spectra

Couplings between protons, whether scalar or dipolar, provide a wealth of structural information. Unfortunately, the high number of ¹H‐¹H couplings gives rise to complex multiplets and severe overlap in crowded spectra, greatly complicating their measurement. Many different methods exist for disentangling couplings, but none approaches optimum resolution. Here, we present a general new 2D J‐resolved method, PSYCHEDELIC, in which all homonuclear couplings are suppressed in F₂, and only the couplings to chosen spins appear, as simple doublets, in F₁. This approaches the theoretical limit for resolving ¹H‐¹H couplings, with close to natural linewidths and with only chemical shifts in F₂. With the same high sensitivity and spectral purity as the parent PSYCHE pure shift experiment, PSYCHEDELIC offers a robust method for chemists seeking to exploit couplings for structural, conformational, or stereochemical analyses.     

Si<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing

The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O₂ ⁺ over an energy range of 0.25–2.5 keV were used to probe the interface between Si_0.73Ge_0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS.

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Systematic studies of early actinide complexes: thorium(IV) fluoroketimides

Reaction of (C5Me5)2Th(CH3)2 with 2 equiv of NC-ArF gives the corresponding fluorinated thorium(IV) bis(ketimide) complexes (C5Me5)2Th[-N=C(CH3)(ArF)]2 (where ArF = 3-F-C6H4 (4), 4-F-C6H4 (5), 2-F-C6H4 (6), 3,5-F2-C6H3 (7), 3,4,5-F3-C6H2 (8), 2,6-F2-C6H3 (9), 2,4,6-F3-C6H2 (10), and C6F5 (11)). The complexes have been characterized by a combination of single-crystal X-ray diffraction, cyclic voltammetry and NMR, and UV-visible absorption and low-temperature luminescence spectroscopies. Density functional theory (DFT) and time-dependent DFT (TD-DFT) results are reported for complexes 5, 11, and (C5Me5)2Th[-N=C(Ph)2]2 (1) for comparison with experimental data and to guide in the interpretation of the spectroscopic results. The most significant structural perturbation imparted by the fluorine substitution in these complexes is a rotation of the fluorophenyl group (ArF) out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 9-11 when the ArF group possesses two ortho fluorine atoms. Excellent agreement is obtained between the optimized ground state DFT calculated structures and crystal structures for 11, which displays the distortion, as well as 5, which does not. In complexes 9-11, the out-of-plane rotation results in large interplanar angles (phi) between the planes formed by ketimide atoms N=C(CMe)(Cipso) and the ketimide aryl groups in the range phi = 49.1-88.8 degrees , while in complexes 5, 7, and 8, phi = 5.7-34.9 degrees . The large distortions in 9-11 are a consequence of an unfavorable steric interaction between one of the two ortho fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. Excellent agreement is also observed between the experimental electronic spectroscopic data and the TD-DFT predictions that the two lowest lying singlet states are principally of nonbonding nitrogen p orbital to antibonding C=N pi* orbital (pN-->pi*C=N or npi*) character, giving rise to moderately intense transitions in the mid-visible spectral region that are separated in energy by less than 0.1 eV. Low-temperature (77 K) luminescence from both singlet and triplet excited states are also observed for these complexes. Emission lifetime data at 77 K for the triplet states are in the range 50-400 mus. These emission spectral data also exhibit vibronic structure indicative of a small Franck-Condon distortion in the ketimide M-N=C(R1)(R2) linkage. Consistent with this vibronic structure, resonance enhanced Raman vibrational scattering is also observed for (C5Me5)2Th[-N=C(Ph)(CH2Ph)]2 (2) when exciting into the visible excited states. These systems represent rare examples of Th(IV) complexes that engender luminescence and resonance Raman spectral signatures.     

Trifluoromethylation of alkenyl bromides and iodides (including 5-iodouracils) with (CF3)2Hg and Cu ("trifluoromethylcopper")

Bromo- and iodoalkenes undergo trifluoromethylation efficiently in DMA with "CF3Cu" generated from (CF3)2Hg and Cu. Variable stereochemical inversion is observed with substrates having a gem-carbonyl group. Substrates having gem-hydrogen, -alkyl, or -alkenyl groups give products with stereochemical retention.     

High‐Pressure Raman and Calorimetry Studies of Vanadium(III) Alkyl Hydrides for Kubas‐Type Hydrogen Storage

Reversible hydrogen storage under ambient conditions has been identified as a major bottleneck in enabling a future hydrogen economy. Herein, we report an amorphous vanadium(III) alkyl hydride gel that binds hydrogen through the Kubas interaction. The material possesses a gravimetric adsorption capacity of 5.42 wt % H₂ at 120 bar and 298 K reversibly at saturation with no loss of capacity after ten cycles. This corresponds to a volumetric capacity of 75.4 kgH₂ m^?3. Raman experiments at 100 bar confirm that Kubas binding is involved in the adsorption mechanism. The material possesses an enthalpy of H₂ adsorption of +0.52 kJ mol^?1 H₂, as measured directly by calorimetry, and this is practical for use in a vehicles without a complex heat management system.     

Amphiphilic treelike rods at interfaces: layered stems and circular aggregation

Amphiphilic dendron-rod molecules with three hydrophilic poly(ethylene oxide) (PEO) branches attached to a hydrophobic octa-p-phenylene rod stem were investigated for their ability to form two-dimensional micellar structures on a solid surface. A treelike shape of the molecules was reported to be a major factor in the formation of nonplanar micellar structures in solution and in the bulk state (cylindrical and spherical). We observed that in these treelike amphiphilic molecules the hydrophilic terminated dendron branches assemble themselves in surface monolayers with the formation of two-dimensional layered or circular micellar structures. We suggested the formation of the planar ribbon-like structures with interdigitated layering within the loosely packed monolayers and circular, ringlike structures (2D circular aggregates) in the precollapsed state.