A high-frequency and high-field EPR study of new azide and fluoride mononuclear Mn(III) complexes

The isolation, structural characterization and electronic properties of three new six-coordinated Mn(III) complexes, [Mn(bpea)(F)(3)] (1), [Mn(bpea)(N(3))(3)] (2), and [Mn(terpy)(F)(3)] (3) are reported (bpea = N,N-bis(2-pyridylmethyl)-ethylamine; terpy = 2,2':6',2' '-terpyridine). As for [Mn(terpy)(N(3))(3)] (4) (previously described by Limburg J.; Vrettos J. S.; Crabtree R. H.; Brudvig G. W.; de Paula J. C.; Hassan A.; Barra A-L.; Duboc-Toia C.; Collomb M-N. Inorg. Chem. 2001, 40, 1698), all these complexes exhibit a Jahn-Teller distortion of the octahedron characteristic of high-spin Mn(III) (S = 2). The analysis of the crystallographic data shows an elongation along the tetragonal axis of the octahedron for complexes 1 and 3, while complex 2 presents an unexpected compression. The electronic properties were investigated using a high-field and high-frequency EPR study performed between 5 and 15 K (190-575 GHz). The spin Hamiltonian parameters determined in solid state are in agreement with the geometry of the complexes observed in the crystal structures. A negative D value found for 1 and 3 is related to the elongated tetragonal distortion, whereas the positive D value determined for 2 is in accordance with a compressed octahedron. The high E/D values, in the range of 0.103 to 0.230 for all complexes, are correlated with the highly distorted geometry present around the Mn(III) ion. HF-EPR experiments were also performed on complex 1 in solution and show that the D value is the only spin Hamiltonian parameter which is slightly modified compared to the solid state (D = -3.67 cm(-1) in solid state; D = -3.95 cm(-1) in solution).     

Apparent Molar Volume, Heat Capacity, and Conductance of Lithium Bis(trifluoromethylsulfone)imide in Glymes and Other Aprotic Solvents

Lithium bis(trifluoromethylsulfone)imide (LiTFSI) is a promising electrolyte for high-energy lithium batteries due to its high solubility in most solvents and electrochemical stability. To characterize this electrolyte in solution, its conductance and apparent molar volume and heat capacity were measured over a wide range of concentration in glymes, tetraethylsulfamide (TESA), acetonitrile, -butyrolactone, and propylene carbonate at 25°C and were compared with those of LiClO₄ in the same solvents. The glymes or n(ethylene glycol) dimethyl ethers (nEGDME), which have the chemical structure CH₃–O–(CH₂–CH₂–O) _n –CH₃ for n = 1 to 4, are particularly interesting since they are electrochemically stable, have a good redox window, and are analogs of the polyethylene oxides used in polymer-electrolyte batteries. TESA is a good plasticizer for polymer-electrolyte batteries. Whenever required, the following properties of the pure solvents were measured: compressibilities, expansibilities, temperature and pressure dependences of the dielectric constant, acceptor number, and donor number. These data were used in particular to calculate the limiting Debye-Hückel parameters for volumes and heat capacities. The infinite dilution properties of LiTFSI are quite similar to those of other lithium salts. At low concentrations, LiTFSI is strongly associated in the glymes and moderately associated in TESA. At intermediate concentrations, the thermodynamic data suggests that a stable solvate of LiTFSI in EGDME exists in the solution state. At high concentrations, the thermodynamic properties of the two lithium salts approach those of the molten salts. These salts have a reasonably high specific conductivity in most of the solvents. This suggests that the conductance of ions at high concentration in solvents of low dielectric constant is due to a charge transfer process rather than to the migration of free ions.     

Correlation of the volumes and heat capacities of solutions with their solid-liquid phase diagrams

Liquid systems which have strong non-idealities, as seen from their thermodynamic properties, often show evidence of these interactions in the solid-liquid phase diagrams. This suggests that some of the structures present in the solid state can persist in the solution state, on a time average, up to temperatures much higher than the melting point. Volumes and heat capacities of typical systems were either taken from the literature or measured to illustrate this correlation with the phase diagrams. With mixtures of aprotic solvents which show nearly-ideal simple eutectic phase diagrams, the properties of the solutions are also nearly ideal. Examples of systems investigated which show strong non-idealities are ionic surfactant solutions, alcohol-water mixtures, chloroform-triethylamine mixtures and lithium salts in aprotic solvents.Paper written in the honor of Loren Hepler on the occasion of his retirement.     

Stereochimie de l'action des organomagnesiens et des organolithiens sur les dimethyl-1,2 alcoxy-1 silacyclobutanes

The reaction of organomagnesium organolithium compounds (alkyl, aryl, allyl and benzyl derivatives) with 1,2-dimethyl-1-alkoxy-l-silacyclobutanes proceeds with retention of configuration at the silicon atom. Stereochemical results are discussed in terms of the S_N2Si mechanism. The proposed configurations are supported by ¹H and ¹³C NMR data.     

A new catalytic method for the synthesis of selectively substituted biphenyls containing an oxoalkyl chain

A novel reaction sequence leading to the synthesis of substituted biphenyls containing a carbonyl group in an aliphatic chain has been achieved in one-pot reaction starting from iodoarenes and allylic alcohols under the catalytic action of palladium and norbornene. The latter is temporarily incorporated into a palladacycle, which directs the reaction towards the selective formation of an arylaryl bond. Norbornene spontaneously deinserts to allow the biphenylylpalladium bond thus formed to react in its turn with the allylic alcohol.     

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.     

Réactions de germylènes avec divers oxirannes et le thiiranne. Mise en évidence de germanones et germathiones intermédiaires. Communication préliminaire

Complexed dialkylgermylenes R₂GeNR₃ or R₂GePy react with oxiranes or thiirane and lead to dialkylgermanone and germathione via germaoxetanes or germathiacyclobutane. The formation of germadioxolanes or germadithiolane finally observed arises from condensation of dialkylgermanone (or germathione) on oxiranes (or thiirane).     

Syntheses of Diamino-dideoxylyxose Derivatives using Acylnitroso Dienophiles

N-Acylnitroso derivatives 6 which were prepared by in-situ oxidation of the corresponding hydroxamic acids 5 reacted instantaneously and in high yields with dihydropyridine 4 . The Diels-Alder adducts 8 were formed regiospecifically with the acylnitroso dienophiles 6a–c , whereas the dienophiles 6d–f gave mixtures of both regioisomers 7 and 8 . These and some other results [2] were best explained by the FMO theory. The Diels-Alder adducts 7 and 8 gave the corresponding ‘anti’-cis-glycols when reacted with OsO₄/N-methylmorpholine N-oxide. Hydrogenolysis of the N–O bond followed by peracetylation led to the expected aminolyxose derivatives 14 and 16 . A similar sequence, using 4 and the hydroxamic-acid derivative 18 of (+)-D-mandelic acid led, with a poor asymmetric induction, to a mixture of the expected optically active aminolyxose compounds 19A / 19B .