Competing kinetic pathways in the bromine addition to allylic ethers in 1,2‐dichloroethane: Opposite temperature effects

The kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2‐dichloroethane, has been investigated. Two of them followed a prevalent second‐order pathway, while the third one exhibited a classical, clean third order. The second‐order pathway in the first two olefins is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. In the molecular bromination of 2,4‐cis‐dimethyl‐8‐oxabicyclo[3.2.1]‐6‐octen‐3‐cis‐ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second‐order reaction was explained by the lesser stability of the bromiranium–bromide ionic intermediate, compared to the bromiranium–tribromide in the third‐order profile. © 2007 Wiley Periodicals, Inc. 39: 197–203, 2007     

Synthesis,characterization and coordination chemistry of the new tetraazamacrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt

A new potentially hexadentate tetraazamacrocycle based on the cyclen skeleton has been synthesized and fully characterized. The macrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt (Me2DO2PME) contains mutually trans monoethyl ester phosphonate acid substituents on two nitrogen atoms, and trans methyl substituents on the other two nitrogen atoms. The protonation constants of this macrocycle and the stability constants of its complexes with Cu2+, Zn2+, Gd3+ and Ca2+ ions have been determined by pH potentiometric titrations. The protonation sequence of the macrocycle has been studied by 1H, 31P[1H] and 13C[1H] NMR spectroscopy: the first and second protonation steps take place at the methyl-substituted nitrogen atoms, while the third protonation involves one oxygen from a phosphonate group. Upon protonation, all the CH2 ring protons become magnetically inequivalent on the NMR time scale due to a slow conformational rearrangement, most likely occasioned by the formation of multiple hydrogen bonds within the macrocyclic ring. Me2DOPM forms neutral, mononuclear complexes with all the metals investigated. The presence of hydroxo complexes was observed for Ca2+ and Zn2+ at high pH values. Structural information on the neutral complex [Cu(Me2DO2PME)] has been obtained by a solution X-Band EPR study. It is proposed that Me2DO2PME binds Cu2+ in a distorted octahedral structure using all of its donor atoms, i.e. the four nitrogen atoms and the two phosphonate oxygen atoms. The redox chemistry of [Cu(Me2DO2PME)] in dimethyl sulfoxide and water has been studied by electrochemical measurements. Cyclic voltammetry in DMSO shows the complex to undergo a quasireversible one-electron reduction step leading to an unstable CuI species.     

Structures of new secofriedelane and friedelane acids from Calophyllum inophyllum of French Polynesia

Three new friedelane-type triterpenoids, 3,4-secofriedelan-3,28-dioic acid (1), 27-hydroxyacetate canophyllic acid (2) and 3-oxo-27-hydroxyacetate friedelan-28-oic acid (3), were isolated from the leaves of Calophyllum inophyllum (Clusiaceae) grown in French Polynesia. Their structures were established by the concerted application of 2D NMR techniques including gs-COSY, gs-HMQC and gs-HMBC.     

Low density polyethylene by tandem catalysis with single site Ti(IV)/Co(II) catalysts

A variety of branched polyethylenes (PE), ranging from semicrystalline linear low density polyethylene to completely amorphous low density polyethylene and rubbery PE, can be produced from ethylene alone by tandem catalysis using as oligomerization catalysts the (imino)pyridyl Co(II) complexes N^BTCoCl₂ (1) ({6-(benzo[b]thiophen-2-yl)-2-(imine)pyridyl)}CoCl₂), N^ETCoCl₂ (2) ({6-(4-ethylthiophen-2-yl)-2-(imine)pyridyl)}CoCl₂), or N^PhCoCl₂ (3) ({6-(phenyl)-2-(imine)pyridyl)}CoCl₂) and as a copolymerization catalyst [η⁵-C₅Me₄)SiMe₂(t-BuN)]TiCl₂ (4). The catalytic activity of the systems 1/4/MAO, 2/4/MAO, and 3/4/MAO has been evaluated under comparable experimental conditions (T = 30°C, [ethylene] = 0.35 mol/l), varying the molar fraction of the cobalt precursors. A positive comonomer effect was observed for all the systems investigated. The maximum productivity (4570 kg PE (mol Ti)⁻¹ h⁻¹) was obtained for the benzothiophenyl-substituted cobalt complex. An effective control of the branching in the polymer backbone was achieved by varying either the oligomerization catalyst or its molar fraction. Completely amorphous materials with T _g as low as-60°C could be obtained. The text was submitted by the authors in English.     

Reactivity of the tetrahydroborate copper(I) complexes [(PR3)2Cu(η2-BH4)] (R = Ph,Cy) toward CO2, COS,and SCNPh

CO₂, COS, and SCNPh react under very mild conditions with the copper(I)-tetrahydroborate complexes [(PR₃)₂Cu(η²-BH₄)] (R = Ph, Cy); CO₂ and COS give the complexes [(PR₃)₂Cu(η²-O₂CH)] and [(PR₃)₂Cu(η²-OSCH)] respectively, whereas SCNPh gives the η²-dithiocarbamate complexes [(PR₃)₂Cu-(η²-S₂CNHPh)]. Addition of PPh₃ under CO₂ to solutions of [(PPh₃)₂Cu-(η²-BH₄)] gives [(PPh₃)₃Cu(η¹-O₂CH)] while addition of PPh₃ and NBu₄ClO₄ under CO₂ gives [(PPh₃)₃Cu(η-O₂CH)Cu(PPh₃)₃] ClO₄.     

1H- and 2H-T1 relaxation behavior of the rhodium dihydrogen complex [(triphos)Rh(eta 2-H2)H2]+

Protonation of the classical trihydride [(triphos)RhH3] (2) at 210 K in either THF or CH2Cl2 by either HBF4.OMe2 or CF3SO2OH gives the nonclassical eta 2-H2 complex [(triphos)Rh(eta 2-H2)H2]+ (1) [triphos = MeC(CH2PPh2)3]. Complex 1 is thermally unstable and highly fluxional in solution. In THF above 230 K, 1 transforms into the solvento dihydride complex [(triphos)Rh(eta 1-THF-d8)H2]+ (5) that, at room temperature, quickly converts to the stable dimer trans-[[(triphos)RhH]2(mu-H)2]2+ (trans-6). In CH2Cl2, 1 is stable up to 240 K. Above this temperature, the eta 2-H2 complex begins to convert into a mixture of trans- and cis-6, which, in turn, transform into the bridging-chloride dimers trans- and cis-[[(triphos)RhH]2(mu-Cl)2]2+ at room temperature. Complex 1 contains a fast-spinning H2 ligand with a T1min of 38.9 ms in CD2Cl2 (220 K, 400 MHz). An NMR analysis of the bis-deuterated isotopomer [(triphos)RhH2D2]+ (1-d2) did not provide a J(HD) value. At 190 K, the perdeuterated isotopomers [(triphos)RhD3] (2-d3) and 1-d4 show T1min values of 16.5 and 32.6 ms (76.753 MHz), respectively, for the rapidly exchanging deuterides. An analogous 2-fold elongation of T1min is also observed on going from [(triphos)IrD3] to [(triphos)Ir(eta 2-D2)D2]+. A rationale for the elongation of T1min in nonclassical polyhydrides is proposed on the basis of both the results obtained and recent literature reports.     

Dioxomolybdenum(VI) Complexes with New Enantiomerically Pure Amino Diol Ligands

(R)-Phenylglycinol is shown to be an efficient building block for the synthesis of chiral amino diols in pure diastereomeric form by epoxide ring-opening reactions. The reaction with rac-trans-stilbene oxide gives [HOCH(2)-(R)-PhCH]NH[(S)-PhCH-(R)-PhCHOH] [2(R)-3(R)-4(S)-HNO(2)H(2)] in 32% yield, which can be methylated at nitrogen to give enantiomerically pure [HOCH(2)-(R)-PhCH]NCH(3)[(S)-PhCH-(R)-PhCHOH] [2(R)-3(R)-4(S)-MeNO(2)H(2)]. These amino diol ligands have been used to prepare chiral dioxomolybdenyl complexes of the formula N(R)-2(R)-3(R)-4(S)-(HNO(2))MoO(2) (1) and N(R)-2(R)-3(R)-4(S)-(MeNO(2))MoO(2) (2). The absolute configuration at each stereocenter in the Mo(VI) complexes has been established by (1)H NOESY spectroscopy. The configuration determined for 1 has been confirmed by an X-ray analysis. Crystal data: orthorhombic P2(1)2(1)2(1), a =7.620(3), b = 13.589(2), c = 20.339(3) ?, Z = 4, R = 0.0336. The structure consists of a polymeric chain of N(R)-2(R)-3(R)-4(S)-(HNO(2))MoO(2) molecules connected through unsymmetrical Mo=O --> Mo bridges. Each metal center is coordinated in a distorted octahedral geometry by a cis dioxo unit and by two trans alkoxo atoms. The coordination polyhedron is completed by a nitrogen atom and by a bridging oxo oxygen atom from an adjacent molecule. Compound 2 catalyzes the oxidation of PPh(3) to OPPh(3) by DMSO through a mechanism that involves the intermediacy of a Mo(IV) species.     

SBV REGULARITY OF GENUINELY NONLINEAR HYPERBOLIC SYSTEMS OF CONSERVATION LAWS IN ONE SPACE DIMENSION

The problem of the presence of Cantor part in the derivative of a solution to a hyperbolic system of conservation laws is considered.An overview of the techniques involved in the proof is given,and a c...     

Active Sites of Dermatan Sulfate for Heparin Cofactor II. Isolation of a Nonasaccharide Fragment Containing Four Disaccharide Sequences [α-l-Iduronic Acid 2-O-Sulfate (1,3)-β-d-N-Acetylgalactosamine 4-Sulfate]

Abstract

The active site of dermatan sulfate (DS) for heparin cofactor II (HCII) was isolated in a fragment obtained by periodate oxidation, borohydride reduction, mild acid hydrolysis, and SE- and SAX-chromatography of beef mucosal and pig skin DS preparations. Characterization by mass spectrometry, one- and two-dimensional NMR spectroscopy, and HPLC analysis of disaccharides, obtained by exhaustive digestion with chondroitinase-ABC, indicates that the fragment has the prevalent structure 1, GalNAc-4SO₃-[IdoA-2SO₃-GalNAc-4SO₃]₄-R, where R is CH(CH₂OH)CH(COO^?)-OH. 1, is the largest DS fragment thus far isolated containing IdoA2SO₃ as the only uronic acid. Its lower activity (30%) with respect to the parent polymeric DS is explainable by Tollefsen model, requiring longer polyanionic chains for formation of ternary complex with thrombin.     

Single versus poly-crystalline layered oxide cathode materials for solid-state battery applications - a short review article

The recent developments in the application of single-crystalline (SC) cathode materials in solid-state batteries are discussed in this mini-review. The characteristics of SC and poly-crystalline (PC) cathode materials are explored, with emphasis on the kinetic and mechanical properties. The critical factors influencing their performance in liquid electrolyte and solid-state battery cells are investigated. Finally, the advantages and disadvantages of both morphologies are discussed and considerations to ensure a fair comparison between SC and PC cathodes in different systems are raised.