Vered Marks

Electrolyte Solutions with a Wide Electrochemical Window for Rechargeable Magnesium Batteries

Electrolyte solutions for rechargeable Mg batteries were developed, based on reaction products of phenyl magnesium chloride (PhMgCl) Lewis base and Alcl 3 Lewis acid in ethers. The transmetallation of these ligands forms solutions with Mg x Cl + y and AlCl 4-n Ph n - ions as the major ionic species, as analyzed by multinuclei nuclear magnetic resonance spectroscopy. Tetrahydrofuran (THF) solutions of (PhMgCl) 2 -Alcl 3 exhibit optimal properties: highly reversible Mg deposition (100% cycling efficiency) with low overvoltage: <0.2 V and electrochemical windows wider than 3 V. A specific conductivity of 2-5 X 10 -3 Ω -1 cm -1 could be measured between -10 and 30°C for these solutions, similar to that of standard electrolyte solutions for Li batteries. Mg ions intercalate reversibly with Chevrel phase (Mg x Mo 6 S 8 ) cathodes in these solutions. These systems exhibit high thermal stability. The solutions may enable the use of high voltage, high-capacity Mg insertion materials as cathodes and hence open the door for research and development of high-energy density, rechargeable Mg batteries.

Improved Electrolyte Solutions for Rechargeable Magnesium Batteries

Electrolyte solutions of magnesium organo-halo-aluminates in ethers are suitable for rechargeable magnesium batteries as they enable highly reversible electrodeposition for magnesium while they possess a wide electrochemical window (>2.2 V). Adding LiCI or tetrabutylammonium chloride to these solutions considerably improves their ionic conductivity, the kinetics of the Mg deposition-dissolution processes, and the intercalation behavior of Mg x MO 6 S 8 Chevrel cathodes. The dissolution of both salts in the electrolytic solutions involves acid-base reactions with complex species. Multinuclei nuclear magnetic resonance and Raman spectroscopy were used in conjunction with electrochemical techniques to study these systems. The nature of these reactions, their products, and the way they influence the various properties of these solutions, are discussed herein.

A sesquiterpene dimer from Xylopia aromatica

Abstract A new guaiane dimer has been isolated from the leaves of Xylopia aromatica. The natural product, whose IUPAC name is [11α,12β,13α,21β]-7-hydroxy-16-oxo-17-isopropylidene-1α,5,5,9β,14α,20-hexamethyl-6- oxaheptacyclo[10.9.1.02,10.04,7.012,21.013,19]docosa-2(10),3,19-triene, seems to have been formed by cycloaddition of two cyclopentadiene precursors, and contains an unusual hemiacetal oxetane ring. The structure was elucidated mainly by 1D and 2D NMR techniques; NOESY spectra were instrumental in the determination of stereochemistry.

CC bond formation using allylic organozirconium compounds. Nucleophilic additions on to isolated and in situ generated η5-pentadienyl-Fe(CO)3/Fe(CO)2PPh3(+1) cations

Abstract Two nucleophilic allylic organozirconium compounds 9 – 10 (R 5 : Me and t Bu) have been reacted with acyclic isolated η 5 -pentadienyl-Fe(CO) 3 /Fe(CO) 2 PPh 3 (+1) cations or with these intermediates generated in situ (Uemura-like conditions). Depending on reaction conditions, iron-complexed η 4 -dienyl-Fe(CO) 3 /Fe(CO) 2 PPh 3 and σ,η 3 -π-allyl-Fe(CO) 3 /Fe(CO) 2 PPh 3 condensation products have been selectively isolated and fully characterized.

Side-chain rotational processes in pentaethylated benzenes

Abstract The barriers for conformational exchange processes in pentaethylbenzenes C 6 Et 5 R (R = H, Br, COCH 3 , OCOCH 3 and OCOPh) were determined by NMR lineshape analysis; for the latter three substances these processes include both the stepwise rotation of the ethyl groups and the 180° reorientation of the side-chain R. The experimental barriers were compared to those calculated by molecular mechanics (MM3). These results have implications in the long-standing argument about the barrier of ethyl group rotation in hexaethylbenzene (R = Et) and some of its metal complexes.

1,1‐Diamino‐2,2‐dinitroethylenes are always zwitterions

The nitration of tetraiodoethylene (7) yields 1,1‐diiodo‐2,2‐dinitroethylene (8). The latter reacts with alkylamines 9 or alkyldiamines 11 to give the corresponding acyclic 1,1‐diamino‐2,2‐dinitroethylenes 10 or their cyclic analogs 12, respectively. On the basis of liquid and solid‐state 13C and 15N NMR data, x‐ray analysis and ab initio calculations, we suggest that the title compounds are always zwitterionic and that the CA–CN bond is not a true double bond. Copyright

The photosensitized oxidation of α-keto enols: A singlet oxygen approach to 2-oxasteroids

Abstract Fluoride ion catalyzed photosensitized singlet oxygenation of 2-hydroxycyclohexa-2,5-dien-1-ones 15a and b and the related steroidal α-keto enols 18a–g, generated the cyclohexenone lactols 16a–b and the corresponding steroidal analogs 19a–g generally in moderate to good yields (60–75%). Since the lactols can be conveniently reduced to the desired 2-oxasteroids in high yields, this 1O2 route presents itself as a synthetically acceptable alternative to the previously reported BCA approach for the preparation of 2-oxasteroids, especially in the case of base sensitive compounds.