The thermodynamic properties of bis(η6-o-xylene)chromium(I) fulleride over the temperature range from T → 0 to 340 K

The temperature dependence of the heat capacity of bis(η⁶-o-xylene)chromium(I) fulleride, [(η⁶-(o-xylene))₂Cr]^+?[C₆₀]^??, over the temperature range 6–340 K was measured on an adiabatic vacuum calorimeter. The low-temperature (20 K ≤ T ≤ 50 K) heat capacity was subjected to multifractal processing; conclusions about the heterodynamic character of the structure were drawn. The experimental data were used to calculate the standard thermodynamic functions C _p ^° (T), H ^°(T)-H ^°(0), S ^°(T), and G ^°(T)-H ^°(0) over the temperature range from T → 0 to 340 K and estimate the standard entropy of fulleride formation from simple substances at 298.15 K. The standard thermodynamic characteristics of [(η⁶-(o-xylene))₂Cr]^+?[C₆₀]^?? were compared with those of the initial fullerene C₆₀.     

Isobaric specific heat capacity of {xH2O + (1 − x)NH3} with x = (0.0000, 0.1566, 0.1597, 0.3030, 0.3048, 0.4956, 0.7061, and 0.8489) at T = (280, 300, 320, and 360) K over the pressure range from (0.1 to 15) MPa

Measurements of the isobaric specific heat capacity of {xH₂O + (1 ? x)NH₃} with x = (0.0000, 0.1566, 0.1597, 0.3030, 0.3048, 0.4956, 0.7061, and 0.8489) were carried out by the calorimeter with the thermal relaxation method, which we have developed, at T = (280, 300, 320, and 360) K over the pressure range from (0.1 to 15) MPa. The comparison of the present c_p values with the literature data as well as the calculated c_p values by the equations of state (EoS) is presented. The behaviour of the present c_p values are correlated as a function of temperature, and mole fraction, at p = 5 MPa.     

Bis(arene)metal compounds: I. Nucleophilic substitution of bis(η6-chlorobenzo-trifluoride)chromium(0) with thiophenoxide

The ortho, meta and para complexes of bis(η⁶-chlorobenzotrifluoride)chromium(0) were made by metal-vapor synthesis. Nucleophilic substitutions by thiophenoxide of these complexes are compared to nucleophilic substitutions by thiophenoxide on the uncoordinated arenes. It was found that substitution at the chloro position is more facile on the complexes than on the free arenes. Substitution of the chloro on the meta-isomer sandwich was more facile than substitution of the chloro on the ortho-isomer sandwich, contrary to the observed reactivity pattern in the free arenes.     

Reactions of (η6-diphenylacetylene) chromiumtricarbonyl complexes with polynuclear carbonyls I. Synthesis of Cr(CO)3(η6-diphenylacetylene) complex and its reaction with Co2(CO)8. Crystal and molecular structure of Cr(CO)3(η6:η2-diphenylacetylene)Co2(CO)6

The reaction of Cr(CO)₃(NH₃)₃ with diphenylacetylene affords as a main product the complex with Cr(CO)₃ moiety bound to a phenyl ring of diphenylacetylene; Cr(CO)₃(η⁶-PhC₂Ph) (I). Complex I readily reacts with Co₂(CO)₈ yielding the mixed metal complex Cr(CO)₃(η⁶:η²-PhC₂Ph)Co₂(CO)₆ (II). The reaction proceeds with retention of the Cr(CO)₃ (η⁶-arene) structural unit, the Co₂(CO)₆ fragment being bound to the triple bond of diphenylacetylene in μ₂,η²-mode. The structure of II was determined by single crystal X-ray analysis. The complex crystallizes in space group P2₁/c with unit cell parameters a 8.666(3) Å, b 18.046(3) Å, c 15.155(6) Å. β 97.57(3)°, V 2349(2) ų, Z = 4, D_x = 1.70 g/cm³. The structure was solved by direct methods and refined by full-matrix least-squares technique to R and R_w values of 0.032 and 0.034, respectively, for 3655 observed reflections. The data obtained show that two structural units in II, Cr(CO)₃(η⁶-Ph-) and Co₂(CO)₆(μ₂,η²-CC), are distorted due to steric repulsion between these metal carbonyl moieties. The Cr(CO)₃ fragment is shifted from the centre of the phenyl ring and slightly tilted with respect to the phenyl ring plane. The Co₂C₂ tetrahedron in the Co₂(CO)₆(μ₂,η²-CC) moiety is distorted in such a way that two of the four Co_iC_j bonds are elongated.     

The thermodynamic properties of bis(η<Superscript>6</Superscript>-ethoxybenzene)chromium fulleride from <Emphasis Type="Italic">T</Emphasis> → 0 to 340 K

The temperature dependence of the heat capacity of crystalline bis-(η⁶-ethoxybenzene)chromium fulleride [(η⁶-(EtOPh))₂Cr]^·+[C₆₀]^·− was studied for the first time by adiabatic vacuum calorimetry over the temperature range 6–340 K with errors of ±0.2%. The temperature dependence of the EPR signal parameters of bis-(η⁶-ethoxybenzene)chromium fulleride was studied for the first time from 120 to 340 K. A reversible endothermic transformation was observed between 160 and 250 K during heating; it was caused by the dissociation of the [(C₆₀)₂]²⁻ dimer and the formation of the [(η⁶-(EtOPh))₂Cr]^·+[C₆₀]^·− fulleride; its standard thermodynamic characteristics were estimated and analyzed. The experimental data were used to calculate the standard thermodynamic functions, including the heat capacity, enthalpy, entropy, and Gibbs function of the fulleride dimer from T → 0 to 160 K and the [(η⁶-(EtOPh))₂Cr]^·+[C₆₀]^·− monomeric complex over the temperature range 250–340 K. The standard thermodynamic properties of the fulleride studied, fullerides studied earlier, and fullerite C₆₀ were compared.     

Synthesis and structure of tetra-p-tolylantimony complexes [(4-MeC6H4)4Sb] 2 + [Hg2I6]2−, [(4-MeC6H4)4Sb] 2 + [HgI4]2−, [(4-MeC6H4)4Sb] 3 + [Sb3I12]2−, and [(4-MeC6H4)4Sb]+[ReO4]−

Complexes [(4-MeC₆H₄)₄Sb] ₂ ⁺ [Hg₂I₆]^2? (I), [(4-MeC₆H₄)₄Sb] ₂ ⁺ [HgI₄]^2? (II), [(4-MeC₆H₄)₄Sb] ₃ ⁺ [Sb₃I₁₂]^2? (III), were synthesized by reactions of tetra-p-tolylantimony iodide with mercury iodide and antimony iodide, respectively. Tetra-p-tolylantimony perrhenate [(4-MeC₆H₄)₄Sb]⁺[ReO₄]^? (IV) was prepared from tetra-p-tolylantimony chloride and sodium perrhenate in acetone. Crystal structures of complexes I, II, and IV were determined by X-ray crystallography. Mercury and rhenium atoms have tetrahedral coordinations in these complexes. The Hg-I and Re-O distances in the structures of I, II, and IV vary within 2.7719(13)–2.7908(12)Å, 2.7028(3)–2.9163(3) Å, and 1.693(3)–1.744(3) Å, respectively. Antimony atoms in two crystallographically independent trinuclear centrosymmetric [Sb₃I₁₂]^2? anions of complex III have an octahedral environment. Each terminal SbI₃ fragment (Sb-I_t, 2.8265(9)–2.8333(10)Å) is bound to the central atom through tree bridging iodine atoms (Sb(2)-I_br, 3.2275(9)–3.3620(10)Å). The distances between the central Sb atom and bridging iodine atoms are much shorter (Sb(1)-I_br, 3.0153(6)–3.0316(6) Å; Sb(3)-I_br, 2.9926(6)–3.0074(6) Å).     

Near critical measurements of HmEandVmE for { xCO2 + (1 − x)SF6} and measurements made over the pressure range 2.5 to 10.0 MPa at the temperature T = 301.95 K

A flow mixing calorimeter, followed by a vibrating tube densimeter, has been used to measure excess molar enthalpies H_m^Eand excess molar volumesV_m^E of {xCO₂ +  (1  − x)SF₆}. Measurements over a range of mole fraction x have been made at the temperatures T =  302.15 K and T =  305.65 K at the pressures (3.76, 5.20, 6.20, and 7.38) MPa. The lowest pressure 3.76 MPa is close to thecritical pressure of SF₆ and the highest pressure 7.38 MPa is close to the critical pressure of CO ₂. Measurements atx =  0.5 have been made over the pressure range (2.5 to 10.0) MPa at the temperature 301.95 K. Some of the measurements are very close to the critical locus of the mixture. The measurements are compared with the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on {xCO₂ +  (1  − x)C₂H₆} and{xCO₂ +  (1  − x)C₂H₄} . The equation was used to calculate residual enthalpies and residual volumes for the pure components and for the mixture, and inspection of the way these combine to give excess enthalpies and volumes assisted the interpretation of the pressure scan measurements.     

Calorimetric study of poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K

For the first time, the heat capacity $ C_{\text{p}}^{^\circ } $ of poly(2-ethylhexyl acrylate) has been studied in an adiabatic vacuum calorimeter between 7 and 350 K, the standard thermodynamic functions: heat capacity $ C_{\text{p}}^{^\circ } $ (T), enthalpy H°(T) ? H°(0), entropy S°(T) ? S°(0), Gibbs function G°(T) ? H°(0) have been calculated from T → 0 to 350 K. The energy of combustion Δ_c U of the compound under study has been measured in a calorimeter with a stationary bomb and an isothermal shell. The standard enthalpy of combustion Δ_c H° and thermodynamic parameters of formation—enthalpy Δ_f H°, entropy Δ_f S°, Gibbs function Δ_f G°—at T = 298.15 K have been calculated. The results have been used to calculate the thermodynamic characteristics of 2-ethylhexyl acrylate bulk polymerization into poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K.     

Study of the origin of enantioselectivity in cyclopropanation reactions using the chiral iron carbene complex [(η5-C5H5)(CO)2FeCH[(η6-o-MeOC6H4)Cr(CO)3]]+

During our low temperature NMR studies we observed two rotational isomers of the carbene complex [(η⁵-C₅H₅)(CO)₂FeCH[(η⁶-o-MeOC₆H₄)Cr(CO)₃]]+ (3) with the O–Me group either anti or anti to the Fp moiety. While the Cr(CO)₃ group very effectively shields one face of the carbene complex from attack by the olefin, the presence of anti and anti isomers allows for the formation of both R and S configuration on C-1 of the cyclopropane through a backside or a frontside ring closure mechanism. The reaction of olefin with anti R-3 can result in R-configuration of the cyclopropane carbon C-1 through a frontside closure mechanism, or in S-configuration if backside closure takes place. In a similar manner, anti R-3 may produce S-configuration through frontside closure or R-configuration through backside closure. We previously have shown by crystallography that reaction the R-isomer of 3 with 2-methyl-propene induces predominantly a R-configuration at C-1 of the resulting cyclopropane (RR-(−)-2,2 dimethyl-1-o-methoxyphenyl(tricarbonyl chromium)cyclopropane, whereas the S-carbene results in the corresponding SS isomer. These findings are consistent with cyclopropane formation from the syn isomer through a frontside closure mechanism or from anti isomer through a backside closure mechanism. In the case of [(η⁵-C₅H₅)(CO)₂FeCH[(η⁶-o-MeC₆H₄)Cr(CO)₃]]+ (4), only anti isomer is observed and optical rotation data indicate that the methylcarbene exhibits the same asymmetric induction (i.e., R-carbene yields R-cyclopropane C-1 and S-carbene yields S-cyclopropane C-1) as the methoxy analogue, and the assumption of the anti isomer being the reactive one then implies that the reaction proceeds through a backside closure mechanism rather a frontside mechanism. It is very likely that this preference is also valid for the methoxy substituted complex 4. Our results on 4 indicate that the enantioselectivity of the cyclopropanation reaction is not determined by the relative abundance of the isomers. As the syn isomer is the more abundant one, the anti isomer has to be the more reactive one compared to the syn isomer. Interchange of syn and anti isomers occurs fast compared to the rate of reaction of the carbene with olefin. The fast rate of interchange of syn and anti isomers relative to the rate of reaction with olefin precludes the direct observation of any differential reactivity form a change in the syn to anti ratio in the NMR spectrum. However, the in general lower ee values observed for 3 compared with 4 are consistent with the fact that the reactive isomer is less abundant in this case. Our data thus show that enantioselectivity of cyclopropanation with “chiral at carbene” complexes is controlled by the higher reactivity of the anti isomer and occurs through a backside ring closure mechanism.