CO reduction with Re(i)-NHC compounds: driving selective catalysis with a silicon nanowire photoelectrode.

The CO-reduction activity of two Re(i)-NHC complexes is investigated employing a silicon nanowire photoelectrode to drive catalysis. Photovoltages greater than 440 mV are observed along with excellent selectivity towards CO over H formation. The observed selectivity towards CO production correlates with strong adsorption of the catalysts on the photoelectrode surface.

Mn-NHC Electrocatalysts: Increasing π Acidity Lowers the Reduction Potential and Increases the Turnover Frequency for CO Reduction.

A new manganese(I) N-heterocyclic carbene electrocatalyst containing a benzimidazole-pyrimidine-based ligand is reported for the two-electron conversion of CO. The increased π acidity of pyrimidine shifts the two-electron reduction to -1.77 V vs Fc/Fc, 70 mV more positive than that for MnBr(2,2'-bipyridine)(CO); increased catalytic current enhancement is also observed (5.

[18]Annulene put into a new perspective.

New insights into [18]annulene were gained by looking more closely at its X-ray structure, revealing a close face-to-face stacking of 3.16 Å in a herringbone-like crystal packing. Hexadehydro[18]annulene was co-crystalized in a benzene matrix, demonstrating the stabilizing role of intercalated solvent molecules in solid annulenes.

Re(I) NHC Complexes for Electrocatalytic Conversion of CO2.

The modular construction of ligands around an N-heterocyclic carbene building block represents a flexible synthetic strategy for tuning the electronic properties of metal complexes. Herein, methylbenzimidazolium-pyridine and methylbenzimidazolium-pyrimidine proligands are constructed in high yield using recently established transition-metal-free techniques. Subsequent chelation to ReCl(CO)5 furnishes ReCl(N-methyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3 and ReCl(N-methyl-N'-2-pyrimidylbenzimidazol-2-ylidine)(CO)3.

Electrocatalytic Reduction of Carbon Dioxide by Mn(CN)(2,2'-bipyridine)(CO)3: CN Coordination Alters Mechanism.

MnBr(2,2'-bipyridine)(CO)3 is an efficient and selective electrocatalyst for the conversion of CO2 to CO. Herein, substitution of the axial bromide for a pseudohalogen (CN) is investigated, yielding Mn(CN)(2,2'-bipyridine)(CO)3. This replacement shifts the first and second reductions to more negative potentials (-1.

Exploring the effect of axial ligand substitution (X = Br, NCS, CN) on the photodecomposition and electrochemical activity of [MnX(N-C)(CO)3] complexes.

The synthesis, electrochemical activity, and relative photodecomposition rate is reported for four new Mn(i) N-heterocyclic carbene complexes: [MnX(N-ethyl-N'-2-pyridylimidazol-2-ylidine)(CO)3] (X = Br, NCS, CN) and [MnCN(N-ethyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3]. All compounds display an electrocatalytic current enhancement under CO2 at the potential of the first reduction, which ranges from -1.53 V to -1.

NHC-containing manganese(I) electrocatalysts for the two-electron reduction of CO2.

The synthesis and characterization of the first catalytic manganese N-heterocyclic carbene complexes are reported: MnBr(N-methyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3 and MnBr(N-methyl-N'-2-pyridylimidazol-2-ylidine)(CO)3. Both new species mediate the reduction of CO2 to CO following two-electron reduction of the Mn(I) center, as observed with preparative scale electrolysis and verified with (13)CO2. The two-electron reduction of these species occurs at a single potential, rather than in two sequential steps separated by hundreds of millivolts, as is the case for previously reported MnBr(2,2'-bipyridine)(CO)3.

A concise synthesis of (+)-salvadione B.

The novel hexacyclic triterpene salvadione B was synthesized in seven steps from the chiral quinone shown. The insight gained from this synthesis permitted a two-step, one-pot sequence to introduce the three additional rings and seven chiral centers.

Diels-Alder reactions of 12-hydroxy-9(10®20)-5aH-abeo-abieta-1(10),8(9),12(13)-triene-11,14-dione.

12-Hydroxy-9(10-->20)-5aH-abeo-abieta-1(10),8(9),12(13)-triene-11,14-dione (quinone 2) served as the dienophile in numerous intermolecular Diels-Alder reactions. These cycloadditions were conducted either thermally (including microwave heating) or with Lewis acid activation. While most dienes reacted with quinone 2 in good chemical yield, others were incompatible under the experimental conditions used.

The taiwaniaquinoids: a review.

A comprehensive overview of the taiwaniaquinoid family of natural products is presented. A summary of the isolation, biosynthesis, and biological activity of these compounds is followed by a discussion of various synthetic strategies to the skeletal framework and a detailed discussion of 12 published syntheses of members of this family. This review covers the literature from the discovery of the first taiwaniaquinoid in 1995 until June 2009.

Total synthesis of (+)-19-deoxyicetexone, (-)-icetexone, and (+)-5-epi-icetexone.

The first asymmetric total syntheses of 19-deoxyicetexone, icetexone, and 5-epi-icetexone was achieved from epimeric tricyclic dienes.

Determination of capsinoids by HPLC-DAD in capsicum species.

Capsicum fruits contain a newly discovered phytochemical called capsinoids. Because little is known about the quantities of these compounds in both sweet and pungent pepper fruits, a high-performance liquid chromatography (HPLC) method was developed to identify and quantify the capsinoids (naturally present E-capsiate and dihydrocapsiate) utilizing fruit obtained from a variety of Capsicum spp. in the U.

Total synthesis of (-)-barbatusol, (+)-demethylsalvicanol, (-)-brussonol, and (+)-grandione.

The icetexane-based diterpenes (-)-barbatusol, (+)-demethylsalvicanol, and (-)-brussonol were synthesized. Synthetic demethylsalvicanol was dimerized to produce (+)-grandione using aqueous Diels-Alder conditions.

Total synthesis of (+)-komarovispirone.

(+)-Komaroviquinone photolytically rearranges to (+)-komarovispirone. A rationalization of this isomerization is presented.

Total synthesis of (-)-salviasperanol.

The achiral enynone shown cyclized to produce a tricyclic dienone that was converted in six steps to (-)-salviasperanol.

Poly(ethylene glycol) methacrylate/dimethacrylate hydrogels for controlled release of hydrophobic drugs.

Hydrogels have been successfully used to entrap hydrophilic drugs and release them in a controlled fashion; however, the entrapment and release of hydrophobic drugs has not been well studied. We report on the release characteristics of a model hydrophobic drug, the steroid hormone estradiol, entrapped in low (MW 360/MW 550) and high (MW 526/MW 1000) molecular weight poly(ethylene glycol) methacrylate (PEG-MA)/dimethacrylate (PEG-DMA) hydrogels. The cross-linking ratio, temperature, and pH ranged from 10:1 to 10:3, from 33 to 41 degrees C, and from 2 to 12, respectively.

A synthesis of (+)-salvadione-A.

[reaction: see text] The p-benzoquinone shown is converted to the novel hexacyclic triterpene salvadione-A in four steps.

Hydrogen abstraction and decomposition of bromopicrin and other trihalogenated disinfection byproducts by GC/MS.

Tribromonitromethane (bromopicrin), dibromochloronitromethane, bromodichloronitromethane, and trichloronitromethane (chloropicrin) have been identified as drinking water disinfection byproducts (DBPs). They are thermally unstable and decompose under commonly used injection port temperatures (200-250 degrees C) during gas chromatography (GC) or GC/mass spectrometry (GC/MS) analysis. The major decomposition products are haloforms (such as bromoform), which result from the abstraction of a hydrogen atom from the solvent bythermally generated trihalomethyl radicals.

Carbodiimide-Promoted Olefin Epoxidation with Aqueous Hydrogen Peroxide(,).

Commercially available carbodiimides in hydroxylic solvents containing hydrogen peroxide with mildly basic or acidic catalysts have been found to promote the epoxidation of olefins. A commercially available 30% aqueous solution of hydrogen peroxide serves as the oxidant for this process. The presumed reactive species is a peroxyisourea generated in situ by the addition of hydrogen peroxide to the carbodiimide.

Electrophilic Aromatic Bromination Using Bromodimethylsulfonium Bromide Generated in Situ.

It has been shown that bromodimethylsulfonium bromide, generated in situ by treating dimethyl sulfoxide with aqueous hydrobromic acid, is a milder and more selective reagent for electrophilic aromatic bromination than elemental bromine.

Use of Conjugated Dienones in Cyclialkylations: The Total Syntheses of (+/-)-Barbatusol, (+/-)-Pisiferin, (+/-)-Deoxofaveline, (+/-)-Xochitlolone, and (+/-)-Faveline.

Concise syntheses of five tricyclic diterpenoids are reported. The key reaction in each synthesis is a cyclialkylation of a functionalized arene with a Lewis acid-activated conjugated dienone to generate a 6,7,6-fused tricycle.