Aerobic oxidation of methyl p-tolyl sulfide catalyzed by a remarkably labile heteroscorpionate RuII-aqua complex,fac-[RuII(H2O)(dpp)(tppm)]2+

fac-[RuII(Cl)(dpp)(L3)]+ (L3 = tris(pyrid-2-yl)methoxymethane (tpmm) = [1A]+ and tris(pyrid-2-yl)pentoxymethane (tppm) = [1B]+ and dpp = di(pyrazol-1-yl)propane) rapidly undergo ligand substitution with water to form fac-[RuII(H2O)(dpp)(L3)]2+ (L3 = tpmm = [2A]2+ and tppm = [2B]2+). In the structure of [2A]2+, the distorted octahedral arrangement of ligands around Ru is evident by a long Ru(1)-O(40) of 2.172(3) A and a large angle O(40)-Ru(1)-N(51) of 96.95(14) degrees . The remarkably short distance between O(40) of H2O and H(45a) of dpp confirms the heteroscorpionate ligand effect of dpp on H2O. [2B]2+ aerobically catalyzes methyl p-tolyl sulfide to methyl p-tolyl sulfoxide in 1,2-dichlorobenzene at 25.0 +/- 0.1 degrees C under 11.4 psi of O2. Experimental facts in support of this aerobic sulfide oxidation are the absence of H2O2 and the oxidative reactivity of the putative Ru(IV)-oxo intermediate toward methyl p-tolyl sulfide, 2-propanol, and allyl alcohol. This study provides the first documented example of aerobic-sulfide oxidation catalyzed by the remarkably labile heteroscorpionate Ru(II)-aqua complex without the formation of a highly reactive peroxide as an intermediate.     

The remarkable reactivity of high oxidation state ruthenium and osmium polypyridyl complexes

There is a remarkable redox chemistry of higher oxidation state M(IV)-M(VI) polypyridyl complexes of Ru and Os. They are accessible by proton loss and formation of oxo or nitrido ligands, examples being cis-[RuIV(bpy)2(py)(O)]2+ (RuIV=O2+, bpy=2,2'-bipyridine, and py=pyridine) and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy=2,2':6',2' '-terpyridine). Metal-oxo or metal-nitrido multiple bonding stabilizes the higher oxidation states and greatly influences reactivity. O-atom transfer, hydride transfer, epoxidation, C-H insertion, and proton-coupled electron-transfer mechanisms have been identified in the oxidation of organics by RuIV=O2+. The Ru-O multiple bond inhibits electron transfer and promotes complex mechanisms. Both O atoms can be used for O-atom transfer by trans-[RuVI(tpy)(O)2(S)]2+ (S=CH3CN or H2O). Four-electron, four-proton oxidation of cis,cis-[(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+ occurs to give cis,cis-[(bpy)2(O)RuV-O-RuV(O)(bpy)2]4+ which rapidly evolves O2. Oxidation of NH3 in trans-[OsII(tpy)(Cl)2(NH3)] gives trans-[OsVI(tpy)(Cl)2(N)]+ through a series of one-electron intermediates. It and related nitrido complexes undergo formal N- transfer analogous to O-atom transfer by RuIV=O2+. With secondary amines, the products are the hydrazido complexes, cis- and trans-[OsV(L3)(Cl)2(NNR2)]+ (L3=tpy or tpm and NR2-=morpholide, piperidide, or diethylamide). Reactions with aryl thiols and secondary phosphines give the analogous adducts cis- and trans-[OsIV(tpy)(Cl)2(NS(H)(C6H4Me))]+ and fac-[OsIV(Tp)(Cl)2(NP(H)(Et2))]. In dry CH3CN, all have an extensive multiple oxidation state chemistry based on couples from Os(VI/V) to Os(III/II). In acidic solution, the OsIV adducts are protonated, e.g., trans-[OsIV(tpy)(Cl)2(N(H)N(CH2)4O)]+, and undergo proton-coupled electron transfer to quinone to give OsV, e.g., trans-[OsV(tpy)(Cl)2(NN(CH2)4O)]+ and hydroquinone. These reactions occur with giant H/D kinetic isotope effects of up to 421 based on O-H, N-H, S-H, or P-H bonds. Reaction with azide ion has provided the first example of the terminal N4(2-) ligand in mer-[OsIV(bpy)(Cl)3(NalphaNbetaNgammaNdelta)]-. With CN-, the adduct mer-[OsIV(bpy)(Cl)3(NCN)]- has an extensive, reversible redox chemistry and undergoes NCN(2-) transfer to PPh3 and olefins. Coordination to Os also promotes ligand-based reactivity. The sulfoximido complex trans-[OsIV(tpy)(Cl)2(NS(O)-p-C6H4Me)] undergoes loss of O2 with added acid and O-atom transfer to trans-stilbene and PPh3. There is a reversible two-electron/two-proton, ligand-based acetonitrilo/imino couple in cis-[OsIV(tpy)(NCCH3)(Cl)(p-NSC6H4Me)]+. It undergoes reversible reactions with aldehydes and ketones to give the corresponding alcohols.     

Thermal decomposition of methyl butanoate: ab initio study of a biodiesel fuel surrogate

In this paper, we report a detailed analysis of the breakdown kinetic mechanism for methyl butanoate (MB) using theoretical approaches. Electronic structures and structure-related molecular properties of reactants, intermediates, products, and transition states were explored at the BH&HLYP/cc-pVTZ level of theory. Rate constants for the unimolecular and bimolecular reactions in the temperature range of 300-2500 K were calculated using Rice-Ramsperger-Kassel-Marcus and transition state theories, respectively. Thirteen pathways were identified leading to the formation of small compounds such as CH(3), C(2)H(3), CO, CO(2), and H(2)CO. For the initial formation of MB radicals, H, CH(3), and OH were considered as reactive radicals participating in hydrogen abstraction reactions. Kinetic simulation results for a high temperature pyrolysis environment show that MB radicals are mainly produced through hydrogen abstraction reactions by H atoms. In addition, the C(O)OCH(3) = CO + CH(3)O reaction is found to be the main source of CO formation. The newly computed kinetic sub-model for MB breakdown is recommended as a core component to study the combustion of oxygenated species.     

The Scent of Maibowle – π Electron Localization in Coumarin from Its Microwave-Determined Structure

The microwave spectra of the natural substance coumarin, a planar aromatic molecule with the specific scent of maibowle, a popular fruit punch served in spring and early summer, were recorded using a molecular jet Fourier transform microwave spectrometer working in the frequency range from 4.0 to 26.5 GHz. The rotational constants and centrifugal distortion constants were determined with high precision, reproducing the spectra to experimental accuracy. The spectra of all singly-substituted ¹³C and ¹⁸O isotopologues were observed in their natural abundances to determine the experimental heavy atom substitution r_s and semi-experimental equilibrium r_e^SE structures. The experimental bond lengths and bond angles were compared to those obtained from quantum chemical calculations and those of related molecules reported in the literature with benzene as the prototype. The alternation of the C−C bond lengths to the value of 1.39 Å found for benzene reflects the localization of π electrons in coumarin, where the benzene ring and the lactone-like chain −CH=CH−(C=O)−O− are fused. The large, negative inertial defect of coumarin is consistent with out-of-plane vibrations of the fused rings.     

Halide Anion Triggered Reactions of Michael Acceptors with Tropylium Ion

Tropylium bromide undergoes noncatalyzed, regioselective additions to a large variety of Michael acceptors. In this way, acrylic esters are converted into β-bromo-α-cycloheptatrienylpropionic esters. The reactions are interpreted as nucleophilic attack of bromide ions at the electron-deficient olefins and the approach of the tropylium ion to the incipient carbanion. Quantum chemical calculations were performed to elucidate the analogy to the amine- or phosphine-catalyzed Rauhut–Currier reactions. Subsequent synthetic transformations of the bromo-cycloheptatrienylated adducts are reported.     

Molecularly engineering polymeric membranes for H2/CO2 separation at 100–300 °C

Over the last two decades, polymers with superior H₂/CO₂ separation properties at 100–300 °C have gathered significant interest for H₂ purification and CO₂ capture. This timely review presents various strategies adopted to molecularly engineer polymers for this application. We first elucidate the Robeson's upper bound at elevated temperatures for H₂/CO₂ separation and the advantages of high-temperature operation (such as improved solubility selectivity and absence of CO₂ plasticization), compared with conventional membrane gas separations at ~35 °C. Second, we describe commercially relevant membranes for the separation and highlight materials with free volumes tuned to discriminate H₂ and CO₂, including functional polymers (such as polybenzimidazole) and engineered polymers by cross-linking, blending, thermal treatment, thermal rearrangement, and carbonization. Third, we succinctly discuss mixed matrix materials containing size-sieving or H₂-sorptive nanofillers with attractive H₂/CO₂ separation properties.     

Analysis of trace elements in the fingernails of breast cancer patients using instrumental neutron activation analysis

Journal of Radioanalytical and Nuclear Chemistry - The aim of this study was to find trace elements that increase risk of breast cancer based on the deviation of the concentration of trace elements...     

The [4Fe-4S](2+) cluster in reconstituted biotin synthase binds S-adenosyl-L-methionine

The combination of resonance Raman, electron paramagnetic resonance and M?ssbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes.     

Dissolution of ionisable groups and lignocellulosic components during low-temperature kraft pulping of pinus radiata

A wide range of kraft pulps from radiata pine produced by low-temperature kraft pulping in flow-through reactors was assessed for carboxyl and hexenuronic acid (HexA) contents using the conductometric titrations and UV spectrophotometer, respectively. The Kappa number of pulps varied from 20.8 to 84.7 when using a cooking liquor of 1 M effective alkali as Na₂O, 25% sulfidity, and cooking time of 100–250 min. The experimental results showed that the carboxyl groups (including HexA) and HexA groups dissolved and their residual values in the pulp samples correlate linearly with Kappa number and pulp yield. The dissolving rate of all carboxyl groups is much faster than the loss of HexA. The HexA/lignin ratio decreased non-linearly with Kappa number.     

Isolation and crystallographic characterization of solvate- and anion-stabilized PCP pincer complexes of palladium(II)

Pincer PCP-Pd(II) complex [PdCl(PCP)] (1) (PCP = ^?CH(CH₂CH₂PPh₂)₂) reacts with AgNO₃ to give [Pd(NO₃)(PCP)] (2). Similar reaction with AgBF₄ gives the aqua complex [Pd(OH₂)(PCP)][BF₄] (3) and the dinuclear complex [{Pd(PCP)}₂(μ-Cl)][BF₄] (4) with singly bridging chloro ligand. All new complexes were characterized by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Complex 1 and the triflate complex [Pd(OTf)(PCP)] (5) are active towards Suzuki–Miyaura coupling between aryl bromides and phenyl boronic acid.