{nBuMg(OR)}2 und {Mg(OR)2}2 (R = 2, 4, 6‐tBu3C6H2) – sterisch überfrachtete Magnesiumalkoholate

Reaction of 2, 4, 6‐tri‐tert‐butylphenol ( 1 ) with di‐n‐butylmagnesium in the molar ratio 1:1 allows the synthesis of {(nBu)Mg(μ‐OR)₂Mg(nBu)} ( 2 ) (R = 2, 4, 6‐tBu₃C₆H₂), which reacts with excess 1 to give the homoleptic alcoholate complex {(RO)Mg(μ‐OR)₂Mg(OR)} ( 3 ) (R = 2, 4, 6‐tBu₃C₆H₂). The structures of 2 and 3 were determined by X‐ray crystallography.     

Dissociation constants of 2‐azidoethanamines in aqueous solution

Aqueous‐phase dissociation constants (K_a) for the conjugate acids of a series of 2‐azidoethanamine bases: R¹N(R²)CH₂CH₂N₃ ( 1 , R¹ = CH₃, R² = H; 2 , R¹ = CH₃, R² = CH₃; 3 , R¹ = CH₂CH₃, R² = CH₂CH₃; 4 , R¹/R² =  CH₂CH₂CH₂CH₂ ; 5 , R¹/R² =  CH₂CH₂OCH₂CH₂ ; 6 , R¹ = CH₂CH₃, R² = CH₂CH₂N₃) were measured and found to fall between those for analogous unfunctionalized and cyano‐functionalized ethanamines. To explore the possibility of a relationship existing between the constants and molecular geometry, a theoretically based study was conducted. In it, the Gibbs free energies of aqueous‐phase (equilibrium) conformers of the bases and their conjugate acids were determined via a density functional theory/polarizable continuum model method. The results indicate that an attractive interaction between the amine and azide groups that underlies the lowest‐energy gas‐phase conformer of 2 is negated in an aqueous environment by solvent–solute interactions. The magnitudes of the free energy changes of solvation and −TS (entropic) energies of the conformers of the 2‐azidoethanamines and their conjugate acids are observed to correlate with the magnitude of the separation between the conformers' amine and azide groups. However, those correlations are not by themselves sufficient to predict the relative free energies of a molecule's conformers in an aqueous environment. That insufficiency is due to the influence of the correlations being mitigated by three other parameters that arise within the thermodynamic framework employed to compute the observable. The nature of those parameters is discussed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A new Na/Mg inverse crown ether

A `missing' member of the inverse crown ether family, namely μ₄‐oxo‐tetrakis(μ‐2,2,6,6‐tetra­methyl­piperidinido)­di­mag­nes­ium­(II)­disodium(I), [Na₂Mg₂O(C₉H₁₈N)₄], has been synthesized by blocking the alternative aromatic metallation route via the use of sterically hindered 1,3,5‐mesityl­ene as a solvent. [Na₂Mg₂O(NR₂)₄] (NR₂ is 2,2,6,6‐tetra­methyl­piperidinide) is shown to form a cationic planar eight‐membered ring with alternating metal and N atoms, which captures at its core an oxide guest that lies on an inversion centre [principal dimensions: Na—O = 2.2405 (11) Å, Na—N = 2.445 (3) and 2.572 (3) Å, Mg—O = 1.8673 (9) Å, and Mg—N = 2.032 (2) and 2.063 (2) Å].     

The formation of grignard compounds—III : The influence of the solvent

The reaction of 6-bromo-1-hexene with Mg was studied in order to obtain information on the role of the solvent during the formation of Grignard reagents. The 5-hexenyl radical (R_nc^.) is known to cyclize rapidly and irreversibly to the cyclopentylmethyl radical (R_c^.). Changes in yields of the cyclized and non-cyclized Grignard compounds have been found on varying the solvent. Information on the radical pairs involved is obtained from the yields of the three possible coupling products (R_ncR_nc, R_ncR_c and R_cR_c). Results are correlated to the intensity of the CIDNP spectra of the Grignard compounds. It is found that basicity and viscosity of the solvents influence the reactions at the site of single electron transfer. Formation of Grignard compounds via radical pairs increases: (a) with decreasing basicity of the solvent, (b) with decreasing viscosity of the solvent, and (c) on dilution of THF with benzene. It is proposed that interaction between the radical and the π-electron rich solvent benzene plays a role in reactions run in Bz/THF mixtures.     

New Intermetallic Compounds Ln2Ni2Mg (Ln = Y,La–Nd,Sm, Gd–Tm) with Mo2FeB2 Structure

The title compounds were synthesized by reacting the elements in sealed tantalum tubes in a high‐frequency furnace. They crystallize with the Mo₂FeB₂ structure, a ternary ordered variant of the U₃Si₂ type, space group P4/mbm. All compounds were characterized through Guinier powder patterns and the lattice parameters were obtained from least‐squares fits. Four structures were refined from single crystal X‐ray data: a = 740.5(1) pm, c = 372.5(1) pm, wR2 = 0.0430, 247 F values, 13 variables for Y₂Ni_1.90Mg, a = 764.5(1) pm, c = 394.39(9) pm, wR2 = 0.0371, 310 F values, 12 variables for La₂Ni₂Mg, a = 754.4(1) pm, c = 385.20(9) pm, wR2 = 0.0460, 295 F values, 12 variables for Pr₂Ni₂Mg, and a = 752.53(8) pm, c = 382.33(5) pm, wR2 = 0.0183, 291 F values, and 12 variables for Nd₂Ni₂Mg. A refinement of the occupancy parameters indicated small defects on the nickel site of the yttrium compound, resulting in the composition Y₂Ni_1.90Mg for the investigated single crystal. The compounds with cerium, samarium, and gadolinium to thulium as rare earth component were characterized through their Guinier powder patterns. The cell colume of Ce₂Ni₂Mg is smaller than that of Pr₂Ni₂Mg, indicating intermediate‐valent cerium. The structures can be considered as an intergrowth of distored AlB₂ and CsCl related slabs of compositions LnNi₂ and LnMg. Chemical bonding in La₂Ni₂Mg and isotypic La₂Ni₂In is compared on the basis of extended Hückel calculations.     

Solvent‐Dependent Enantiodivergence in the Chlorocyclization of Unsaturated Carbamates

A remarkable solvent‐controlled enantiodivergence is seen in the hydroquinidine 1,4‐phthalazinediyl diether ((DHQD)₂PHAL)‐catalyzed chlorocyclization of unsaturated carbamates. Eyring plot analyses of this previously unreported reaction are used to probe and compare the R‐ and S‐selective pathways. In the CHCl₃/hexanes solvent system, the pro‐R process shows a surprising increase in selectivity with increasing temperature. These studies point to a strongly solvent‐dependent entropy–enthalpy balance between the pro‐R and pro‐S pathways.     

<!?tlsb=‐0.06pt>Zigzag polymer chains in catena‐poly[[[triaqua(isobutyrato‐κO)magnesium(II)]‐μ‐isobutyrato‐κ2O:O′] monohydrate]

The structure of the title compound, {[Mg(C₄H₇O₂)₂(H₂O)₃]·H₂O}_n, features one‐dimensional ...(μ₂‐ib)Mg(μ₂‐ib)Mg... zigzag chains (ib is isobutyrate) parallel to the c axis. The octahedral Mg environment is completed by three fac‐oriented terminal water ligands, as well as one further monodentate end‐on coordinated ib ligand. In the crystal structure, the hydrophobic ib groups are all oriented within one half of the coordination perimeter of each chain, whereas the water ligands, together with hydrogen‐bonded noncoordinated solvent water molecules, define the other half. Along the a axis, neighbouring strands are oriented so that both the hydrophilic and hydrophobic sides are adjacent to each other. This results in an extensive hydrogen‐bonding network within the hydrophilic areas, also involving an additional solvent water molecule per formula unit. There are van der Waals contacts between the aliphatic isopropyl groups of the hydrophobic areas.     

Isoequilibrium and free energy relationships in complex formation equilibria between Ag(I) and thiocarbonyl ligands in oxygenated solvent media

The standard enthalpy and entropy changes for the stepwise and overall complex formation homogeneous equilibria between Ag(I) and thiocarbonyl ligands or for the single reactions (series of reactions) in H₂O, CH₃OH (MeOH), C₂H₅OH (EtOH), C₃H₇OH (n-PrOH), CH₃CHOHCH₃ (Is-PrOH), and CH₃COCH₃ (Ac) are linearly correlated (corr. coeff. R > 0.9). The intercepts of the ?H????S regression straight lines ?H?=??H_res???τ ?S depend on both solvent and number of coordinated ligands (hereafter coordination level) in the coordination sphere of the substrate AgL_n. The slopes τ?=?d?H/d?S (hereafter susceptivities/sensitivities) depend only on solvent. Robust and sound hard solvent parameter scales, founded on solute–solute soft–soft interactions, can be set up on ?H_res and/or τ bases. At 25 °C, the transfer standard free energies for the overall complex formation reactions at the single coordination levels n = 1, 2, or 3 between the various solvents are uncorrelated. When considered as unique set with n = 1, 2, and 3, the results linearly correlated (0.85?≤?R?≤?0.97) with slope?≈?1 and intercepts depending on the actual couple of solvent media. The enthalpy(entropy) changes are uncorrelated.     

The hard-sphere model for linear and regular star polybutadienes

The dilute solution properties of linear, 18-arm, and 270-arm star polybutadienes have been studied in a theta solvent and in a good solvent. Values of the radius of gyration R_G, the second virial coefficient A₂, the intrinsic viscosity [η], and the diffusion coefficient D₀ have been measured for each polymer. The ratios R_T/R_G, R_V/R_G, and R_H/R_G for each type of polymer are used to compare the four dilute solution properties. R_T is termed the “thermodynamic radius.” It is the radius of the hard sphere with the same excluded volume as the polymer coil. R_T is calculated from A₂ by R_T = (3A₂M₂/16ηN_A)^1/3. R_V and R_H are equivalent hard spheres defined for the intrinsic viscosity and translational diffusion coefficient, respectively. R_T/R_G, R_V/R_G, and R_H/R_G increase from about 0.7 for linear polymer coils as the number of arms in the star increases. Values of the ratios for the 18-arm stars are less than the value for the hard-sphere, but the values of the ratios of the 270-arm stars are equal to the hard-sphere limit within experimental error.     

Synthesis,Crystal Structure Determination from X‐Ray Powder Diffractometry and Vibrational Spectroscopic Properties of Mg[N(CN)2]2 · 4 H2O

Magnesium dicyanamide tetrahydrate Mg[N(CN)₂]₂ · 4 H₂O was synthesized by aqueous ion exchange starting from Na[N(CN)₂] and Mg(NO₃)₂ · 6 H₂O. The crystal structure was solved and refined on the basis of powder X‐ray diffraction data (P2₁/c, Z = 2, a = 737.50(2), b = 732.17(1), c = 971.67(2) pm, β = 98.074(1)°, wR_p = 0.059, R_p = 0.046, R_F = 0.075). In the crystal there are neutral complexes [Mg[N(CN)₂]₂(H₂O)₄] which are only connected via hydrogen bonds. Above 40 °C the tetrahydrate decomposes into anhydrous Mg[N(CN)₂]₂.     

Geometric properties of micelles formed by triblock copolymers and solubilizates in dilute solutions

In this work we study the geometric properties of the triblock copolymer micelles with solubilized low-mass molecules in a selective solvent using the Monte Carlo technique on a cubic lattice. The triblock copolymers are of the ABA type, with the two insoluble blocks at the ends. The size of the micelles is characterized by the squared radius of gyration of the micellar core, R_g², while the shape is treated by the asphericity b and the acylindricity c, which are defined in terms of the principal moments of the radius of gyration tensor. The parameters varied are the amount of solubilizate molecules, the polymer concentration, the interaction parameters between A and B, A and solvent, solute and solvent, solute and B block, and the A and B block length. The micelle size, characterized by R_g², grows with increasing concentration of the solubilizates and/or the polymer, and stronger interactions between the incompatible species. The A block length is found not to modify R_g² monotonously, while an increase in B block length results in a decrease in R_g² at high concentrations. As the size expands, the micellar shape becomes less spherical but retains its cylindricity. In addition to an increase in the averaged R_g², the distribution of R_g² becomes broader and the system less homogeneous.     

Syntheses and crystal structures of two magnesium–tetrazole compounds in salt and polymeric forms

Two alkaline earth–tetrazole compounds, namely catena‐poly[[[triaquamagnesium(II)]‐μ‐5,5′‐(azanediyl)ditetrazolato‐κ³N¹,N^1′:N⁵] hemi{bis[μ‐5,5′‐(azanediyl)ditetrazolato‐κ³N¹,N^1′:N²]bis[triaquamagnesium(II)]} monohydrate], {[Mg(C₂HN₉)(H₂O)₃][Mg₂(C₂HN₉)₂(H₂O)₆]_0.5·H₂O}_n, (I), and bis[5‐(pyrazin‐2‐yl)tetrazolate] hexaaquamagnesium(II), (C₅H₃N₆)[Mg(H₂O)₆], (II), have been prepared under hydrothermal conditions. Compound (I) is a mixed dimer–polymer based on magnesium ion centres and can be regarded as the first example of a magnesium–tetrazolate polymer in the crystalline form. The structure shows a complex three‐dimensional hydrogen‐bonded network that involves magnesium–tetrazolate dimers, solvent water molecules and one‐dimensional magnesium–tetrazolate polymeric chains. The intrinsic cohesion in the polymer chains is ensured by N—H...N hydrogen bonds, which form R₂²(7) rings, thus reinforcing the propagation of the polymer chain along the a axis. The crystal structure of magnesium tetrazole salt (II) reveals a mixed ribbon of hydrogen‐bonded rings, of types R₂²(7), R₂²(9) and R₂⁴(10), running along the c axis, which are linked by R₂⁴(16) rings, generating a 4,8‐c flu net.     

Coordination of zwitterionic 8-quinolinol (oxine) to mixed oxinate-carboxylate complexes of divalent nickel,manganese, and magnesium

Three types of metal complexes containing coordinated zwitterionic 8-Quinolinol(oxine) are isolated from the reaction ofMOx ₂ (M=divalent Ni, Mn, or Mg; HO _x =oxine) and haloacetic acidsRCO₂H (R=CF₃, CCl₃, CHCl₂, or CH₂Cl) in benzene. These types are:M(O₂CR)Ox·HOx forM=Ni,R=CCl₃, CHCl₂, and CH₂Cl and forM=Mn,R=CHCl₂.MOx(HOx) (RCO₂)MOx·nH₂O forM=Ni, Mn, or Mg,R=CF₃ andn=1,1, and 4, respectively.MO _x (HOx) (RCO₂)₂ MOx forM=Mn andR=CCl₃. These types are compared with the simple mixed chelateMn(O₂CCH₂Cl)Ox. Interrelated reactions are suggested to explain the formation of these metal complexes and the contributing factors are discussed. The coordination of the zwitterion to the metal ion through its phenolate oxygen and the presence of the triatomic system⁺N–H...O in the three types of metal complexes are evidenced by typical infrared bands. Analytical and spectral data are in accordance with the suggested formulations.

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Koordination von zwitterionischem 8-Chinolinol (Oxin) an gemischten Oxinat-Carboxylat-Komplexen des divalenten Nickel, Mangan und Magnesium

Zusammenfassung Drei Typen von Metallkomplexen mit koordiniertem zwitterionischem 8-Chinolinol (Oxin) wurden aus der Reaktion vonMOx ₂ [M=Ni(II), Mn(II), Mg(II); HOx=Oxin] mit Halogen-essigsäurenRCOOH (R=CF₃, CCl₃, CHCl₂, CH₂Cl) in Benzol isoliert. Es werden Reaktionswege zur Bildung der Komplexe diskutiert. Die Koordination des Zwitterions über den phenolischen Sauerstoff und die Präsenz der Gruppierung⁺N–H...O in allen Typen der untersuchten Metallkomplexe wird auf Grund typischer IR-Banden nachgewiesen.

     

Phase separation in the (R4N)2[Nd(NO3)5]-hydrocarbon solvent-chloroform systems at various temperatures

Phase diagrams were studied for (R₄N)₂[Nd(NO₃)₅]-C _n H_{2n + 2}-chloroform liquid ternaries (where R₄N⁺ is trialkylbenzylammonium and n = 10, 12, 14, or 15) at T = 298.15−333.15 K. (R₄N)₂[Nd(NO₃)₅]-C _{n H2n + 2} binaries are two-phase liquid systems at all temperatures in this range. One phase (phase I) is an almost pure hydrocarbon solvent. The other (phase II) is enriched in (R₄N)₂[Nd(NO₃)₅]. The C _n H_{2n + 2} solubility in phase II decreases with increasing the alkyl chain length of the hydrocarbon solvent and increases with increasing temperature. The title liquid ternaries are characterized by a homogeneous solution field and a two-phase liquid solution field. One phase is enriched in (R₄N)₂[Nd(NO₃)₅] and chloroform; the other is enriched in the hydrocarbon solvent. Liquid-liquid phase separation fields enlarge with increasing C _n H_{2n + 2} alkyl chain length and slightly narrow with increasing temperature. Critical solution points at fixed temperatures depend on C _n H_{2n + 2}. Original Russian Text ? A.K. Pyartman, V.A. Keskinov, P.V. Zaitsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 531–534.     

Supported catalysts for stereospecific polymerization of propylene

Tetrabenzyltitanium (B₄Ti), tribenzyltitanium chloride (B₃TiCl), tetra(p-methylbenzyl)titanium (R₄Ti) and tri(p-methylbenzyl)titanium chloride (R₃TiCl) have been used as catalysts for ethylene and propylene polymerization activated by AlEt₂Cl. B₄Ti-AIEt₂Cl in solution polymerizes ethylene readily but its activity decays rapidly. B₄Ti was also supported on Cab-O-Sil, Alon C, and Mg(OH)Cl. The last support was found to give catalyst with longest lifetime with a rate of polymerization, R_p = 7.0 g/hr-mmole Ti-atm ethylene. ¹⁴CO counting techniques gave 1.13 × 10^?3 mole of propagating center per mole of B₄Ti; the rate constant of propagation, k_p = 540 l./mole-sec. None of the tetravalent titanium compounds polymerize propylene in solution. However, when supported on Mg(OH)Cl, Cab-O-Sil, Alon C, Cab-O-Ti, and charcoal, they all polymerize propylene. In this work the supports were characterized by various techniques, including the paramagnetic probe method, to determine the concentration and nature of surface hydroxyls. Those factors controlling the rate and stereospecificity of propylene polymerization were investigated. The system B₃TiCl–Mg(OH)Cl–AlEt₂Cl is the most active with R_p = 2.89 g/hr-mmole Ti-atm propylene. The concentration of propagation center is 0.9 × 10^?3 mole per mole of B₃TiCl; k_p = 32 l./mole-sec. This catalyst gave only about 70% stereoregular polymer. Diethyl ether is found to raise stereospecificity to 100%, but there is a concommittent tenfold decrease of activity. Other interesting catalyst systems are: (π-C₅H₅)TiMe₃–Mg(OH)Cl–AlEt₂Cl (1.56, 89.5); (π-C₅H₅)TiMe₂–Mg(OH)Cl–AlEt₂Cl (0.075, 94.5); and (π-C₅H₅)TiMe₃–Alon C–Al-Et₂Cl (0.08,97.2), where the first number in the parenthesis is R_p in g/mmole Ti-hr-atm and the second entry corresponds to percentage yield of stereoregular polypropylene. Hafnocene and titanocene supported on Mg(OH)Cl produce only oligomers of propylene.     

Geometry,basis set,and correlation energy dependence of computed protonation energies of imino bases

The nitrogen protonation energies of the imino bases HN?CHR, where R is H, CH₃, NH₂, OH, and F, have been evaluated to determine the dependence of absolute and relative protonation energies on geometry, basis set, and correlation effects. Reliable absolute protonation energies require a basis set larger than a split-valence plus polarization basis, the inclusion of correlation, and optimized geometries of at least Hartree–Fock 4-31G quality. Consistent relative protonation energies can be obtained at the Hartree–Fock level with smaller basis sets. Extending the split-valence basis set by the addition of polarization functions on all atoms decreases the computed absolute Hartree–Fock nitrogen protonation energies of the imino bases HN?CHR except when R is F, but increases the oxygen protonation energies of the carbonyl bases O?CHR.     

Generalized correlations for molecular weight and concentration dependence of zero-shear viscosity of high polymer solutions

Data are presented to show that two correlations of viscosity–concentration data are useful representations for data over wide ranges of molecular weight and up to at least moderately high concentrations for both good and fair solvents. Low molecular weight polymer solutions (below the critical entanglement molecular weight M_c) generally have higher viscosities than predicted by the correlations. One correlation is η_sp/c[η] versus k′[η], where η_sp is specific viscosity, c is polymer concentration, [η] is intrinsic viscosity, and k′ is the Huggins constant. A standard curve for good solvent systems has been defined up to k′[η]c ≈? 3. It can also be used for fair solvents up to k′[η]c ≈? 1.25· low estimates are obtained at higher values. A simpler and more useful correlation is η_R versus c[η], where η_R is relative viscosity. Fair solvent viscosities can be predicted from the good solvent curve up to c[η] ≈? 3, above which estimates are low. Poor solvent data can also be correlated as η_R versus c[η] for molecular weights below 1 to 2 × 10⁵.     

Catalytic synthesis and transformations of magnesacycloalkanes

Catalytic cyclometallation of bicyclo[2.2.1]hept-2-ene, spirocyclo[2.2.1]hept-2-ene-7.1'-cyclopropane andendo-tricyclo[5.2.1.0^2,6]deca-3,8-diene (dicyclopentadiene) with R₂Mg (R =n-Pr,n-Bu) leading to the formation of polycyclic magnesacyclopentanes (MC) has been studied. The yield of MC and the selectivity of the reaction have been shown to depend on the ratio of starting reagents, the solvent, and temperature. The most probable scheme of the transformation studied is proposed.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 165–169, January, 1993.     

Comparison of chromatographic parameters of heterocyclic bases and their N-oxides in liquid-liquid partition systems

Summary Relationships between R _M values and pH of aqueous stationary phase were determined for some heterocyclic bases and their N-oxides chromatographed in partition systems of the type: organic solvent (benzene, chloroform or mixture of chloroform with cyclohexane)—aqueous buffer solution. In view of large differences in pK _A values of the bases and their N-oxides, the R _Mr ^o (NNO) values (change of R _M during suppressed ionization, due to reaction) could only be estimated by graphical extrapolation of the chromatographic data. The R _Mr ^o values thus determined were in most cases in the range 2.2–2.7 R _M units.