Iron-catalyzed olefin cis-dihydroxylation by H2O2: electrophilic versus nucleophilic mechanisms

Previous studies have classified a series of nonheme iron catalysts for olefin cis-dihydroxylation by H2O2 into two groups. Complex 1, [(TPA)Fe(OTf)2], representative of Class A catalysts, forms a low-spin FeIII-OOH intermediate that gives rise to a high-valent FeV(=O)OH oxidant. The preference of this catalyst for electron-rich olefins demonstrates its electrophilic character. On the other hand, complex 2, [(6-Me3-TPA)Fe(OTf)2], representative of Class B catalysts, prefers instead to oxidize electron-deficient olefins, suggesting an oxidant with nucleophilic character. It is suggested that such a nucleophilic oxidant may be the high-spin FeIII-OOH intermediate derived from 2 or the FeIV(=O)(*OH) species derived therefrom.     

Vibrational Stark effect: Theoretical determination through the semiempirical AM1 method

The vibrational Stark effect of a series of small molecules has been calculated by means of the semiempirical AM1 method through addition of the electron–field interaction term in the one-electron Hamiltonian. Optimized geometrical parameters along with harmonic frequencies and line intensities are determined for different strengths of the applied uniform electric field. The perturbed spectra are compared with theoretical studies carried out at the ab initio level and with experimental results. The vibrational Stark effect of the retinal molecule is also computed, showing that this kind of study is feasible in systems of biochemical interest. © 1992 by John Wiley & Sons, Inc.     

Angle-resolved photoemission studies of C (2 × 2) oxygen overlayer on Ni (100)

We report angular-resolved photoemission experiments with 44 eV p-polarized radiation on a C (2 × 2) oxygen overlayer on Ni as a function of polar angle θ. A photoemission calculation using a single step model has been performed. We show that with our present expemental equipment, it is very difficult to discriminate the p_z and p_x,p_y states of oxygen, because of hybridization with Ni s-p levels, except at some high symmetry points for which partially polarized light may give a measurable distinction.     

The γ‐form of n‐eicosanol

In the crystal of the title compound, C₂₀H₄₂O, the mol­ecules are packed in layers parallel to the (100) plane. The alkyl chains are parallel to the [30] direction and these molecular chains are hydrogen‐bonded into chains parallel to the c axis. All C—C bonds of the alkyl chain show an antiperiplanar (trans) conformation, with a slight deviation from the ideal value (180°) in the C—C bonds close to the hydrogen bonds. The length of the alkyl chain is 27.92 (2) Å and the tilt angle is 59.7 (2)°.     

Vibrational and structural properties of glass and crystalline phases of TeO2

A wide-spread opinion regarding the paratellurite (-TeO₂) lattice as a parent structure of TeO₂ glass is questioned. Consequently, the Raman and infrared spectra of TeO₂ glass are contrasted with those of three crystalline lattices (, β, γ) of TeO₂ and their vibrational state density distribution functions. Additionally, the data on the crystallization of the liquid and glassy states of TeO₂ are considered. As a result, of the known crystalline phases of TeO₂, the γ-phase is proposed as the closest to TeO₂ glass.     

A site isolation-enabled organocatalytic approach to enantiopure γ-amino alcohol drugs

Solid support-enabled site isolation has previously allowed to use paraldehyde as an acetaldehyde surrogate in aldol reactions. However, only electron-poor aldehydes were tolerated by the system. Herein, we show that the temporary conversion of benzaldehyde into η⁶-benzaldehyde Cr(CO)₃ circumvents this limitation. Asymmetric synthesis of (R)-Phenoperidine, as well as formal syntheses of (R)-Fluoxetine and (R)-Atomoxetine, illustrate the benefits of this strategy.     

The nido‐Cage⋅⋅⋅π Bond: A Non‐covalent Interaction between Boron Clusters and Aromatic Rings and Its Applications

Non‐covalent interactions involving multicenter multielectron skeletons such as boron clusters are rare. Now, a non‐covalent interaction, the nido‐cage???π bond, is discovered based on the boron cluster C₂B₉H₁₂^? and an aromatic π system. The X‐ray diffraction studies indicate that the nido‐cage???π bonding presents parallel‐displaced or T‐shaped geometries. The contacting distance between cage and π ring varies with the type and the substituent of the aromatic ring. Theoretical calculations reveal that this nido‐cage???π bond shares a similar nature to the conventional anion???π or π???π bonds found in classical aromatic ring systems. This nido‐cage???π interaction induces variable photophysical properties such as aggregation‐induced emission and aggregation‐caused quenching in one molecule. This work offers an overall understanding towards the boron cluster‐based non‐covalent bond and opens a door to investigate its properties.     

Predictable Selectivity in Remote C−H Oxidation of Steroids: Analysis of Substrate Binding Mode

Predictability is a key requirement to encompass late-stage C−H functionalization in synthetic routes. However, prediction (and control) of reaction selectivity is usually challenging, especially for complex substrate structures and elusive transformations such as remote C(sp³)−H oxidation, as it requires distinguishing a specific C−H bond from many others with similar reactivity. Developed here is a strategy for predictable, remote C−H oxidation that entails substrate binding to a supramolecular Mn or Fe catalyst followed by elucidation of the conformation of the host-guest adduct by NMR analysis. These analyses indicate which remote C−H bonds are suitably oriented for the oxidation before carrying out the reaction, enabling prediction of site selectivity. This strategy was applied to late-stage C(sp³)−H oxidation of amino-steroids at C15 (or C16) positions, with a selectivity tunable by modification of catalyst chirality and metal.