Convincing Catalytic Performance of Oxo-Tethered Ruthenium Complexes for Asymmetric Transfer Hydrogenation of Cyclic α-Halogenated Ketones through Dynamic Kinetic Resolution.

A highly efficient dynamic kinetic resolution of cyclic halohydrins was achieved by the asymmetric transfer hydrogenation of racemic α-haloketones. Bifunctional oxo-tethered Ru(II) catalysts could promote the reduction without deterioration of halogens. By structural tuning of the catalyst, chiral alcohols having halogen, ester, carboxamide, and sulfone functions were obtained variably with excellent diastereo- and enantioselectivities (up to >99:1 d.r. and >99.9 ee), which provided a concise synthetic approach to a dopamine D3 receptor ligand, (+)-PHNO.

Formal Deoxygenative Hydrogenation of Lactams Using PNHP-Pincer Ruthenium Complexes under Nonacidic Conditions.

A formal deoxygenative hydrogenation of amides to amines with RuCl2(NHC)(PNHP) (NHC = 1,3-dimethylimizadol-2-ylidene, PNHP = bis(2-diphenylphosphinoethyl)amine) is described. Various secondary amides, especially NH-lactams, are reduced with H2 (3.0-5.0 MPa) to amines at a temperature range of 120-150 °C with 1.0-2.0 mol % of PNHP-Ru catalysts in the presence of Cs2CO3. This process consists of (1) deaminative hydrogenation of secondary amides to generate primary amines and alcohols, (2) dehydrogenative coupling of the transient amines with alcohols to generate imines, and (3) hydrogenation of imines to give the formally deoxygenated secondary amine products.

Multiple Absolute Stereocontrol in Cascade Lactone Formation via Dynamic Kinetic Resolution Driven by the Asymmetric Transfer Hydrogenation of Keto Acids with Oxo-Tethered Ruthenium Catalysts.

A straightforward asymmetric construction of chiral fused γ- and δ-lactones containing multiple contiguous stereocenters was successfully developed by either (1) the dynamic kinetic resolution-asymmetric transfer hydrogenation (DKR-ATH) reaction using oxo-tethered Ru(II) complexes followed by syn-selective lactonization or (2) the tandem DKR-ATH/lactonization in combination with asymmetric hydrogenation catalyzed by Ru-chiral diphosphine complexes. The expedient protocol is applicable to the enantioselective synthesis of natural wine lactone and a biologically active benzo-fused lactone with an unprecedented level of diastereo- and enantioselectivity.

N-Monomethylation of Aromatic Amines with Methanol via PNHP-Pincer Ru Catalysts.

The use of methanol for the selective methylation of aromatic amines with RuHCl(CO)(PNHP) (PNHP = bis(2-diphenylphosphinoethyl)amine) is reported. Various aromatic amines were transformed into their corresponding monomethylated secondary amines in high yields at 150 °C with a very low catalyst loading (0.02-0.1 mol %) in the presence of KO tBu (20-60 mol %). The catalyst precursor, RuHCl(CO)(PNHP), was converted to [RuH(CO)2(PNHP)]+ under the catalytic conditions and also serves as a highly effective catalyst. The robustness of this catalyst contributes to its outstanding catalytic activity, even under reaction conditions, in which CO is liberated from methanol.

Atmospheric Hydrogenation of Esters Catalyzed by PNP-Ruthenium Complexes with an N-Heterocyclic Carbene Ligand.

New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup.

Efficient Access to Chiral Benzhydrols via Asymmetric Transfer Hydrogenation of Unsymmetrical Benzophenones with Bifunctional Oxo-Tethered Ruthenium Catalysts.

A concise asymmetric transfer hydrogenation of diaryl ketones, promoted by bifunctional Ru complexes with an etherial linkage between 1,2-diphenylethylenediamine (DPEN) and η(6)-arene ligands, was successfully developed. Because of the effective discrimination of substituents at the ortho position on the aryl group, unsymmetrical benzophenones were smoothly reduced in a 5:2 mixture of formic acid and triethylamine with an unprecedented level of excellent enantioselectivity. For the non-ortho-substituted benzophenones, the oxo-tethered catalyst electronically discerned biased substrates, resulting in attractive performance yielding chiral diarylmethanols with >99% ee.

Emissions of methane from offshore oil and gas platforms in Southeast Asia.

Methane is a substantial contributor to climate change. It also contributes to maintaining the background levels of tropospheric ozone. Among a variety of CH4 sources, current estimates suggest that CH4 emissions from oil and gas processes account for approximately 20% of worldwide anthropogenic emissions. Here, we report on observational evidence of CH4 emissions from offshore oil and gas platforms in Southeast Asia, detected by a highly time-resolved spectroscopic monitoring technique deployed onboard cargo ships of opportunity. We often encountered CH4 plumes originating from operational flaring/venting and fugitive emissions off the coast of the Malay Peninsula and Borneo. Using night-light imagery from satellites, we discovered more offshore platforms in this region than are accounted for in the emission inventory. Our results demonstrate that current knowledge regarding CH4 emissions from offshore platforms in Southeast Asia has considerable uncertainty and therefore, emission inventories used for modeling and assessment need to be re-examined.

Oxo-tethered ruthenium(II) complex as a bifunctional catalyst for asymmetric transfer hydrogenation and H2 hydrogenation.

Newly developed oxo-tethered Ru amido complexes (R,R)-1 and their HCl adducts (R,R)-2 exhibited excellent catalytic performance for both asymmetric transfer hydrogenation and the hydrogenation of ketonic substrates under neutral conditions without any cocatalysts to give chiral secondary alcohols with high levels of enantioselectivity.

Isotopomeric characterization of N2O produced, consumed, and emitted by automobiles.

Fossil fuel combustion is the second largest anthropogenic source of nitrous oxide (N2O) after agriculture. The estimated global N2O flux from combustion sources, as well as from other sources, still has a large uncertainty. Herein, we characterize automobile sources using N2O isotopomer ratios (nitrogen and oxygen isotope ratios and intramolecular site preference of 15N, SP) to assess their contributions to total global sources and to deconvolute complex production/consumption processes during combustion and subsequent catalytic treatments of exhaust. Car exhaust gases were sampled under running and idling state, and N2O isotopomer ratios were measured by mass spectrometry. The N2O directly emitted from an engine of a vehicle running at constant velocity had almost constant isotopomer ratios (delta15Nbulk = -28.7 +/- 1.2 per thousand, delta18O = 28.6 +/- 3.3 per thousand, and SP = 4.2 +/- 0.8 per thousand) irrespective of the velocity. After passing through catalytic converters, the isotopomer ratios showed an increase which varied with the temperature and the aging of the catalysts. The increase suggests that both production and consumption of N2O occur on the catalyst and that their rates can be comparable. It was noticed that in the idling state, the N2O emitted from a brand new car has higher isotopomer ratios than that from used cars, which indicate that technical improvements in catalytic converters can reduce the N2O from mobile combustion sources. On average, the isotopomeric signatures of N2O finally emitted from automobiles are not sensitive to running/idling states or to aging of the catalysts. Characteristic average isotopomer ratios of N2O from automobile sources are estimated at -4.9 +/- 8.2 per thousand, 43.5 +/- 13.9 per thousand, and 12.2 +/- 9.1 per thousand for delta15Nbulk, delta18O, and SP, respectively.

Development of two-dimensional gas chromatography/isotope ratio mass spectrometry for the stable carbon isotopic analysis of C(2)-C(5) non-methane hydrocarbons emitted from biomass burning.

A two-dimensional gas chromatography/combustion/isotope ratio mass spectrometry (2D-GC/C/IRMS) system was developed for stable carbon isotopic measurements of C(2)-C(5) non-methane hydrocarbons (NMHCs) in biomass burning smoke. The 2D-GC/C/IRMS system successfully improved the accuracy and precision for the measurements of C(4) and C(5) saturated compounds in a smoke sample by selective injection of target compounds into a combustion furnace and consequently allowed us to provide complete baseline separation for all individual NMHCs. The analytical precision of the delta(13)C of each compound was better than 0.5 per thousand for more than 500 pmolC injections and 2.1 per thousand for 30 pmolC injections, which was estimated from replicate analysis of standard gases. This system was applied to the analysis of NMHCs in smoke samples collected from laboratory biomass burning experiments. From the combustion of three fuel materials (rice straw, pine wood, and maize), we found that the isotopic fractionation between fuel material and individual NMHCs is almost independent of the fuel material and thus the delta(13)C values of the fuel materials are reflected in delta(13)C values of most of NMHCs. However, only i-butane emitted from maize combustion showed anomalous (13)C-depletion of -11.6 per thousand relative to the delta(13)C value of maize. Such a large (13)C depletion suggests the specific isotopic fractionation process which is attributed to the maize combustion itself or the chemical properties of i-butane during production from a radical recombination reaction.