May Trifluoromethylation and Polymerization of Styrene Occur from a Perfluorinated Persistent Radical (PPFR)?

The radical polymerization of styrene (St) initiated by a trifluoromethyl radical generated from a perfluorinated highly branched persistent radical (PPFR) is presented with an isolated yield above 70 %. The release of . CF3 radical occurred from a temperature above 85 °C. Deeper 1 H and 19 F NMR spectroscopies of the resulting fluorinated polystyrenes (CF3 -PSts) evidenced the presence of both CF3 end-group of the PSt chain and the trifluoromethylation of the phenyl ring (in meta-position mainly). [PPFR]0 /[St]0 initial molar ratios of 3:1, 3:10 and 3:100 led to various molar masses ranging from 1750 to 5400 g mol-1 in 70-86 % yields. MALDI-TOF spectrometry of such CF3 -PSts highlighted polymeric distributions which evidenced differences between m/z fragments of 104 and 172 corresponding to styrene and trifluoromethyl styrene units, respectively. Such CF3 -PSt polymers were also compared to conventional PSts produced from the radical polymerization of St initiated by a peroxydicarbonate initiator. A mechanism of the polymerization is presented showing the formation of a trifluoromethyl styrene first, followed by its radical (co)polymerization with styrene. The thermal properties (thermal stability and glass transition temperature, Tg ) of these polymers were also compared and revealed a much better thermal stability of the CF3 -PSt (10 % weight loss at 356-376 °C) and a Tg of around 70 °C.

Reactions of Bifunctional Perfluoroarylsilanes with Activated C-F Bonds in Perfluorinated Arenes.

Reactions of bifunctional perfluoroarylsilanes, p- and m-C6F4(SiMe3)2 as well as o-BrC6F4SiMe3, with substituted perfluoroarenes having electron-withdrawing groups were investigated using NMR and density functional theory calculation techniques. The C-F bond in perfluoroarenes was activated by the para-position of an electron-withdrawing group, such as CF3, C6F5, CN, and NO2. The reaction of C6F4(SiMe3)2 mainly occurred at the para-position of the perfluoroarenes and also occurred at the ortho-position of C6F5CN and C6F5NO2. Two equivalent reactions of perfluoroarenes with bifunctional p- and m-C6F4(SiMe3)2 provided disubstituted perfluoroarenes, along with a small amount of protonated monosubstituted perfluoroarenes. The reaction of o-BrC6F4SiMe3 with the CF3- and CN-substituted pentafluorobenzenes provided unexpected coupling products between C-Br and C-F bonds, in addition to the coupling products between C-SiMe3 and C-F bonds.

Origin of attraction in p-benzoquinone complexes with benzene and p-hydroquinone.

The origin of the attraction in charge-transfer complexes (a p-hydroquinone-p-benzoquinone complex and benzene complexes with benzoquinone, tetracyanoethylene and Br2) was analyzed using distributed multipole analysis and symmetry-adapted perturbation theory. Both methods show that the dispersion interactions are the primary source of the attraction in these charge-transfer complexes followed by the electrostatic interactions. The natures of the intermolecular interactions in these complexes are close to the π/π interactions of neutral aromatic molecules. The electrostatic interactions play important roles in determining the magnitude of the attraction. The contribution of charge-transfer interactions to the attraction is not large compared with the dispersion interactions in these complexes.

Magnitude and Directionality of Halogen Bond of Benzene with C6F5X, C6H5X, and CF3X (X = I, Br, Cl, and F).

Geometries of benzene complexes with C6F5X, C6H5X, and CF3X (X is I, Br, Cl, and F) were optimized, and their interaction energies were evaluated. The CCSD(T) interaction energies at the basis set limit (Eint) of C6F5X (X is I, Br, Cl, and F) with benzene were -3.24, -2.88, -2.31, and -0.92 kcal mol(-1). Eint of C6H5X (X is I, Br, and Cl) with benzene were -2.31, -1.97, and -1.48 kcal mol(-1). The fluorination of halobenzenes slightly enhances the attraction. Eint of CF3X (X is I, Br, Cl, and F) with benzene (-3.11, -2.74, -2.22, and -0.71 kcal mol(-1)) were very close to Eint of corresponding C6F5X with benzene. In contrast to the halogen bond of iodine and bromine with pyridine (n-type halogen bond acceptor) where the main cause of the attraction is the electrostatic interactions, that of halogen bond with benzene (p-type acceptor) is dispersion interaction. In the halogen bonds with p-type acceptors (halogen-π interactions), the electrostatic interactions and induction interactions are small. The overall orbital-orbital interactions are repulsive. The directionality of halogen bonds with p-type acceptors is very weak, owing to the weak electrostatic interactions, in contrast to the strong directionality of the halogen bonds with n-type acceptors and hydrogen bonds.

Introducing a new radical trifluoromethylation reagent.

Perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (PPFR) is a persistent radical stable at room temperature, but easily decomposes at 90 °C to produce a CF3 radical which is able to react with a variety of aromatic compounds to afford the corresponding trifluoromethyl derivatives, usually as mixtures of regioisomers in good to excellent overall yields.

Substituent-controlled preference of carbonyl group-metal coordination in d8 metal complexes with non-symmetric pentadentate ligands. Structural and stereochemical aspects.

Chirally switchable Ni(II) and Pd(II) complexes were synthesized and fully characterized by X-ray crystallography and additionally by spectroscopic means (NMR and MS). The syntheses and characterization of their ligands are also reported. It was found that control of the stereochemical preference between (S*,S*) and (S*,R*) diastereomers by substituent modification of the ligand sidearms was possible in the solid state with the preferred atomic coordinations of the sidearms consistent with expectations based on the electron-withdrawing properties of the substituent -o-CF3 group. The dilemma arising in terms of assigning the absolute configuration descriptors resulting from selecting between strictly following only the covalent bonds of the ligand and disregarding the nature of the bonds altogether and thus bringing the coordinate bonds into consideration to determine the stereochemical priority sequence is hereby resolved by declaring that the latter option is to be preferred. The results obtained here provide a clear indication that sidearm substitution of the Ni(II) and Pd(II) complexes need not disturb macromolecular stereochemical arrangements leading to quasidiastereomeric relationships. This permits the design of molecular systems sensitive to external stimuli with predictable macromolecular structure.

Optical purifications via self-disproportionation of enantiomers by achiral chromatography: case study of a series of α-CF3-containing secondary alcohols.

This work demonstrates that self-disproportionation of enantiomers via achiral chromatography can be recommended as inexpensive and general method for optical purification of enantiomerically enriched compounds. In particular, the advantage of this approach over conventional recrystallization is that it can be used for both crystalline as well as liquid compounds.

CCSD(T) level interaction energy for halogen bond between pyridine and substituted iodobenzenes: origin and additivity of substituent effects.

The CCSD(T) level interaction energies at the basis set limit (E(int)) were calculated for 33 halogen bonded pyridine complexes with substituted iodobenzenes. The CCSD(T) level electron correlation correction substantially decreases the magnitude of attraction in comparison with the MP2. The E(int) for the pyridine complexes with mono substituted iodobenzenes varies from -3.14 to -4.42 kcal mol(-1), depending on the substituent. The electron-withdrawing substituents such as NO2 enhance the attraction, while the effects of electron-donating substituents reduce. The additivity of the substituent effects is observed for the E(int) of the pyridine complexes with multiple substituted iodobenzenes. The electrostatic interactions are mainly responsible for the substituent effects on the magnitude of the attraction in the halogen-bonded complexes. The electrostatic energy depends significantly on the substituent. They have a strong correlation with the E(int). On the other hand the effects of the substituent on the dispersion energy are small, however the dispersion does contribute greatly to the attraction.

Novel source of trifluoromethyl radical as efficient initiator for the polymerization of vinylidene fluoride.

A persistent perfluoroalkyl radical (PPFR), perfluoro-3-ethyl-2,4-dimethyl-3-pentyl, is shown to be a good source of •CF(3) radicals and a useful radical capable of initiating the polymerization of vinylidene fluoride (VDF). NMR characterizations of the resulting PVDF homopolymers showed that polymerization of VDF was exclusively initiated by •CF(3) radicals. The addition of •CF(3) radical onto VDF was regioselective leading to CF(3) -CH(2) -CF(2) -PVDF and the CF(3) end-group acted as an efficient label to assess the molecular weights by (19) F NMR spectroscopy. Various [PPFR](0) /[VDF](0) initial molar ratios lead to CF(3) -PVDF-CF(3) of different molecular weights. When that ratio decreased, both the molecular weights and the thermostability of these PVDFs increased, showing less defects of chaining and higher crystallinity.

Magnitude and origin of the attraction and directionality of the halogen bonds of the complexes of C6F5X and C6H5X (X = I, Br, Cl and F) with pyridine.

The geometries and interaction energies of complexes of pyridine with C(6)F(5)X, C(6)H(5)X (X = I, Br, Cl, F and H) and R(F)I (R(F) = CF(3), C(2)F(5) and C(3)F(7)) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (E(int)) for the C(6)F(5)X-pyridine (X = I, Br, Cl, F and H) complexes at the basis set limit were estimated to be -5.59, -4.06, -2.78, -0.19 and -4.37 kcal mol(-1) , respectively, whereas the E(int) values for the C(6)H(5)X-pyridine (X = I, Br, Cl and H) complexes were estimated to be -3.27, -2.17, -1.23 and -1.78 kcal mol(-1), respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C(6)F(5)X. The values of E(int) estimated for the R(F)I-pyridine (R(F) = CF(3), C(2)F(5) and C(3)F(7)) complexes (-5.14, -5.38 and -5.44 kcal mol(-1), respectively) are close to that for the C(6)F(5)I-pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short-range (charge-transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C(6)F(5)I- and C(2)F(5)I-pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water-formaldehyde complex. The calculations suggest that the C-I and C-Br halogen bonds play an important role in controlling the structures of molecular assemblies, that the C-Cl bonds play a less important role and that C-F bonds have a negligible impact.

Innovative Trifluoromethyl Radical from Persistent Radical as Efficient Initiator for the Radical Copolymerization of Vinylidene Fluoride with tert-Butyl α-Trifluoromethacrylate.

A persistent perfluoroalkyl branched radical (PPFR), perfluoro-3-ethyl-2,4-dimethyl-3-pentyl, was shown to be a good source of •CF3 radicals able to initiate the radical copolymerization of vinylidene fluoride (VDF) with tert-butyl α-trifluoromethacrylate (MAF-TBE). NMR characterizations of the resulting poly(VDF-co-MAF-TBE) copolymers showed that copolymerization was exclusively initiated by •CF3 radicals, as evidenced by the thermal decomposition of PPFR above 80 °C. The addition of •CF3 radical onto VDF/MAF-TBE system was regioselective leading to CF3-CH2-CF2• radical that further cross propagated onto MAF-TBE unit and the α,ω-trifluoromethyl group acted as an efficient label to assess the molecular weights of the resulting copolymers by 19F NMR spectroscopy. Three [PPFR]0/([VDF]0 + [MAF-TBE]0) initial molar ratios (2.0, 1.0, and 0.5%) led to various molecular weights ranging from 21300 to about 105000 g·mol-1. When that ratio decreased, both the molecular weights and the thermostability of these original poly(VDF-co-MAF-TBE) copolymers increased.

Ridge-tile-like chiral topology: synthesis, resolution, and complete chiroptical characterization of enantiomers of edge-sharing binuclear square planar complexes of Ni(II) bearing achiral ligands.

Binuclear square planar Ni(II) complexes are described, formed by two tridentate ligands with two imine-nitrogens coordinating two nickel atoms. Such complexes are synthetically readily available with great structural variety and present new types of ridge-tile-like chiral compounds that are reasonably stable in the appropriate "bent" conformation. Enantiomerically pure samples of these compounds have been obtained for the first time using HPLC with a chiral stationary phase. Absolute configurations and chiroptical properties are fully characterized by ECD, VCD, ORD spectroscopy, and theoretical calculations. These new compounds with ridge-tile-like chiral topology are configurationally reasonably stable [DeltaG(double dagger) = 121.4 kJ mol(-1), t(1/2) = 14.9 h (78 degrees C, ethanol)], and therefore their chemistry, physical properties, and applications can be systematically studied.

Noninvasive in vivo electron paramagnetic resonance study to estimate pulmonary reducing ability in mice exposed to NiO or C60 nanoparticles.

PURPOSE: To develop new methods that can estimate the influences of manufactured nanomaterials on biological systems, the in vivo pulmonary reducing ability of mice that had received inhalation exposures to NiO or C60 nanoparticles was investigated using a 700 MHz electron paramagnetic resonance (EPR) spectrometer. MATERIALS AND METHODS: NiO or C60 suspensions were atomized and mice in exposure chambers inhaled the resulting aerosol particles for 3 hours. The exposure conditions, number-based geometric average diameters, and the average number concentration were precisely controlled at almost the same levels for both NiO and C60 nanoparticles. Two days or 2 weeks after exposure, an EPR study was conducted noninvasively. Temporal changes in EPR signal intensity at the target area (ie, lung field) were obtained by the region-selected intensity determination (RSID) method. RESULTS: NiO nanoparticles significantly suppressed pulmonary reducing ability 2 days and 2 weeks after exposure, but C60 nanoparticles had no such effect. CONCLUSION: This is the first in vivo estimation of the reducing ability in experimental animals exposed to manufactured nanoparticles.

Resolution/deracemization of chiral alpha-amino acids using resolving reagents with flexible stereogenic centers.

This work has demonstrated that a previously unexplored approach to separation of enantiomers via formation of diastereomeric derivatives with three stereogenic centers has obvious practical potential and deserves further systematic study. The design reported here is based on the unusual application of a configurationally unstable stereogenic nitrogen, which plays a key role in setting up the stereochemical match between the three stereogenic centers in the corresponding products.

DFT-GIAO calculations of 19F NMR chemical shifts for perfluoro compounds.

The (19)F NMR shieldings for 53 kinds of perfluoro compounds were calculated by the B3LYP-GIAO method using the 6-31G(d), 6-31+G(d), 6-31G(d,p), 6-31++G(d,p), 6-311G(d,p), 6-311++G(d,p), 6-311G(2d,2p), 6-311++G(2d,2p), 6-311++G(2df,2p), 6-311++G(3d,2p), and 6-311++G(3df,2p) basis sets. The diffuse functions markedly reduce the difference between the calculated and experimental chemical shifts. The calculations using the 6-31++G(d,p) basis set give the chemical shifts within 10 ppm deviations from experimental values except for the fluorine nuclei attached to an oxygen atom, a four- and a six-coordinated sulfur atom, and FC(CF(3))(2) attached to a sulfur atom.

Convenient asymmetric synthesis of beta-substituted alpha,alpha-difluoro-beta-amino acids via Reformatsky reaction between Davis' N-sulfinylimines and ethyl bromodifluoroacetate.

The enantiopure Davis' N-sulfinylimines were found to be efficient as chiral imine equivalents in the high-temperature Reformatsky-type additions with BrZnCF(2)COOEt affording an efficient approach to the enantiomerically pure alpha,alpha-difluoro-beta-amino acids. High chemical and stereochemical yields (drs > 9:1, and as high as 99:1) render this method immediately useful for preparing the target amino acids.

Biomimetic Reductive Amination of Fluoro Aldehydes and Ketones via [1,3]-Proton Shift Reaction.(1) Scope and Limitations.

A systematic study of azomethine-azomethine isomerizations of the N-benzylimines 2, derived from fluorinated aldehydes or ketones and benzylamine, has been made. The results reveal that, in sharp contrast to hydrocarbon analogs, fluorinated imines of 2 in triethylamine solution undergo isomerizations to give the corresponding N-benzylidene derivatives 5 (for 5/2 K > 32) in good isolated yields. The rates of the isomerizations depend on the starting imine structures and increase in the following order: aryl perfluoroalkyl ketimine 2m, per(poly)fluoroalkyl aldimine 2a,d-g, perfluoroaryl aldimine 2h, alkyl perfluoroalkyl ketimine 2i,j. The presence of chlorine or bromine atoms in the alpha-position to the C=N double bond of the starting imine favors a dehydrohalogenation reaction, giving rise to unsaturated products 6-9. The azomethine-azomethine isomerization was studied and proven to proceed essentially (>98%) intramolecularly with isotope exchange experiments. High chemical yields, the simplicity of the experimental procedure, and the low cost of all reagents employed make this biomimetic transamination of fluorocarbonyl compounds a practical method for preparing fluorine-containing amines of biological interest.