Radical copolymerization of 2,2,2-trifluoroethyl methacrylate with cyano compounds for dielectric materials: Synthesis and characterization

The copolymerization of cyano (nitrile) monomers and a fluoroalkylmethacrylate is used to develop new dielectric polymers containing C-CN and C-F substituents. Methacrylonitrile (MAN), acrylonitrile (AN) and methylvinylidene cyanide (MVCN) were chosen as cyano monomers. 2,2,2-Trifluoroethyl methacrylate (MATRIF) was used as a fluorinated comonomer. The copolymers based on cyano monomers such as AN, MAN or MVCN, and MATRIF comonomers were synthesized by radical process initiated by AIBN. The yields of the copolymerizations were ranging between 40 and 60%. These copolymers were characterized by ¹H, ¹³C, ¹⁹F NMR and IR spectroscopy which showed that the percentages of incorporation of AN and MAN in the copolymers were 45%. However, only 5% of MVCN was incorporated into poly(MVCN-co-MATRIF) copolymer. Thermogravimetric analyses showed that the thermal decomposition occurred from 200, 230 or 240 °C for copolymers of MVCN, MAN or AN, respectively, and indicated that the process of degradation depends on the nature of cyano monomer.     

2π + 2π cycloaddition kinetics of some fluoro olefins and fluoro vinyl ethers

The second order 2π + 2π homo- and co-dimerization between various classes of fluorinated olefins has been investigated. The fluorinated olefins examined in this study were: (1) R_fOCFCF₂ (perfluorinated vinyl ethers); (2) R_fCFCF₂ (perfluorinated terminal olefins); (3) RCH₂CFCF₂; (4) PhOCFCF₂ (aryl perfluorinated vinyl ethers).Homo-dimerizations between vinyl ethers have an E_a between 20 and 24 kcal mol⁻¹ while homo-dimerizations between terminal olefins have an average E_a between 35 and 40 kcal mol⁻¹; vinyl groups have a second order cyclodimerization rate constant of formation between 1 × 10⁻⁷ and 1 × 10⁻⁴ M⁻¹ S⁻¹ while vinyl ethers have a second order cyclodimerization rate constant of formation = 1 × 10⁻¹ M⁻¹ s⁻¹. If there is a CH₂ group α to the terminal olefin, the E_a of cyclodimerization is about 7 kcal mol⁻¹) lower with respect to those olefins with a CF₂ α to the instauration. At 270 °C co-dimerizations have an average ΔS^≠ = −45 cal K⁻¹ mol⁻¹ and a second order rate constant of cyclodimerization ranging between 0.1 × 10⁻⁴ M⁻¹ S⁻¹ and 16 × 10⁻⁴ M⁻¹ S⁻¹ while homo-dimerizations have an average ΔS^≠ = −17 cal K⁻¹ mol⁻¹ and a second order rate constant which can span from 7 × 10⁻⁷ M⁻¹ S⁻¹ to as much as 1 × 10⁻¹ M⁻¹ S⁻¹ depending on the electronic nature of the perfluorinated terminal olefin.A good correlation between the electronegativity χ and the activation energy E_a demonstrates that “polarizing” groups, O, PhO, α to the olefin play an important role in the formation and stabilization of the cyclodimerization biradical intermediate.     

Selective anodic fluorination of electrophilic alkenes

Anodic fluorination of some electrophilic alkenes (conjugated with electron-withdrawn groups), ethyl cinnamates, RC₆H₄CHCHCO₂Et (R = H, CH₃, CH₃O, F and CF₃), cinnamonitrile, C₆H₄CHCHCN, phenyl stryryl ketone, and t-butyl styryl ketone using ammonium fluorides as the fluorine source and supporting electrolyte, in CH₂Cl₂ as electrolytic solvent yields the expected vicinal difluoro compounds, as mixture of erythro and threo isomers. The anodic fluorination of phenyl 3,5-di-t-butyl-4-hydroxystyryl ketone yields two monofluoro compounds. A possible reaction mechanism is discussed.     

Synthesis of novel highly heat-resistant fluorinated silane coupling agents

Novel fluorinated silane coupling agents with a biphenyl structure, C_nF_2n+1(C₆H₄)₂CH₂CH₂Si(OCH₃)₃ (n = 4, 6, and 8), were synthesized with the aim to improve the heat-resistance, oxidation-resistance, and acid-resistance of the surface modified with a common fluorinated silane coupling agent. Alcohols, Rf(C₆H₄)₂CH(OH)CH₃, were obtained by reducing the intermediates, Rf(C₆H₄)₂COCH₃, the products of the reaction of 4-acetyl-4′-bromobiphenyl with perfluoroalkyl iodides in the presence of copper powder. The reaction of the alcohols with phosphorus tribromide gave olefins, Rf(C₆H₄)₂CHCH₂, which were then allowed to react with tetramethoxysilane in the presence of hexachloroplatinate(IV) catalyst to yield novel fluorinated silane coupling agents with a biphenyl structure. The coupling agents with four and six carbon atoms in their fluorocarbon chains were obtained as a colorless liquid while that with 8 carbon atoms was a white gel. Evaluations were made of the coupling agents using surfaces modified with them in terms of water contact angles, heat-resistance, oxidation-resistance, and acid-resistance. The agents behaved similarly to the conventional fluorinated silane coupling agents with respect to water contact angles, oxidation-resistance, and acid-resistance, whereas the former showed an extremely higher heat-resistance (up to 350 °C). In addition, C₆H₅C₆H₄CH₂CH₂Si(OCH₃)₃ and CH₃(C₆H₄)₂CH₂CH₂Si(OCH₃)₃ with no fluoroalkyl group were synthesized and the heat-resistance of glass surfaces modified with these compounds was examined.     

Preparation of soluble functional polymers by modification of nanosized polyacetylene

The reaction of electrophilic reagents such as halogens, nitric and sulfuric acids, and sulfur dioxide with nanosized stereoregular polyacetylene was studied. Polymers with chlorine content as much as 65% were obtained and the MW properties of the polymers were found to depend on the structure of pristine polyacetylene prepared under various conditions. The reaction between nitric acid and stereoregular polyacetylene occurred to give first [CH(NO₂)CHCHCH(OH)]_n while the totally nitrated product [CH(NO₂)CH(ONO₂)]_n was obtained with nitrogen content of 18.3% after complete nitration. GPC, NMR- and IR-spectroscopy were used for structural and MWD analysis of the original polyacetylene and obtained products. The mechanism of the reaction between electrophilic reagents and polyacetylene is discussed on the basis of the experimental and literature data.     

Luminescent rhenium(I)-gold(I) hetero organometallics linked by ethynylphenanthrolines

The first luminescent rhenium(I)-gold(I) hetero organometallics, Re{phenAu(PPh₃)}(CO)₃Cl (3) and Re{(PPh₃)AuphenAu(PPh₃)}(CO)₃Cl (4), have been prepared using the gold(I) complex AuCl(PPh₃) (PPh₃ = triphenylphosphine) and the novel rhenium(I) complexes Re(phenH)(CO)₃Cl (5) (phenH = 3-ethynyl-1,10-phenanthroline) or Re(HphenH)(CO)₃Cl (6) (HphenH = 3,8-bis(ethynyl)-1,10-phenanthroline). All the present rhenium(I) complexes 3-6 were revealed to possess a facial configuration (fac-isomer) with respect to the three carbonyl ligands. The main frameworks for these new gold(I) organometallics were constructed by the Au-C σ-bonding (with the η¹-type coordination) between the ethynylphenanthrolines and the Au(I) phosphine unit. Re(I)-Au(I) heterometallics 3 and 4 have shown single phosphorescence from the ³MLCT excited state and this observation can be interpreted in terms of the efficient intramolecular energy transfer from the Au(I) unit to the Re(I) unit.     

Synthesis, crystal structure, and magnetic properties of two 3d-4f heterometallic coordination polymers

Two new 4f-3d heterometallic coordination polymers, [Gd₂^IIICo^II(pydc)₃(ox)(H₂O)₄)·2H₂O] (1) and [Dy^IIICu^II(pydc)₂(ox)_1/2(H₂O)₂·H₂O] (2) (pydc = pyridine-2,5-dicarboxylate anion, ox = oxalate dianion) were successfully synthesized under hydrothermal condition. Structure and magnetism of the two coordination polymers were characterized by single crystal X-ray diffraction and Quantum Design (MPMS) SQUID magnetometer. In both compounds, metal centers were connected by double ligand bridges. In 1 the gadolinium ions were linked in sheets by OCO ligand bridges and these sheets were connected by separated cobalt coordination spheres to generate the overall 2-D structure. In 2 the dysprosium centers were constructed into one dimensional chain by OCO bridges from pydc ligand bridges and these chains were linked by oxalate bridges to form sheets and different sheets were connected by copper coordination planes. The copper centers in 2 were linked in chain by elongated OCO brides and the chains were connected by hydrogen bond to generate 3-D structure. Magnetic properties of the two complexes were investigated by variable temperature magnetic susceptibility. The magnetic data suggest that overall antiferromagnetic interactions are present in the two compounds.     

Synthesis, structure and benzannulation of chalcogen-tethered Fischer carbene complexes

Addition of PhSH-NEt₃ or PhSeNa to PhCCC(OC₂H₅)M(CO)₅ [M = Cr or W] afforded stable, β-chalcogenide tethered conjugated carbene complexes 3-6 as a mixture of E,Z-isomers. The Z-configuration was ascribed to those isomers that readily yield cyclometallated complexes. Aminolysis with methylamine yielded corresponding amino carbene complexes as mixtures of E,Z-isomers. Alkylation by methyl iodide afforded separable E,Z-isomers of dimethylamino complexes. One-step aminolysis of ethoxy carbene complexes with dimethylamine furnished only the Z-isomer of the dimethylamino complex. The Z-isomer of dimethylamino carbene complexes yielded cyclometallated products on warming. Representative crystal structures of these complexes confirm isomer assignments. Only E-isomers of the S or Se-tethered ethoxy complexes undergo benzannulation reaction with alkynes, with loss of chalcogenide atom.     

Correlation between MO eigenvectors and enthalpies of formation for alkanes

A new model for the calculation of enthalpies of formation of alkanes (up to C₈) is presented. An additive bond energy scheme, using the experimental methane and diamond values for the CH and CC bond energies, respectively, is supplemented by correction for the CC π antibonding character of the highest occupied molecular orbitals (HOMOs), effectively adjusting the CC bond energies. The effect is calculated by the summation of products of appropriate eigenvectors from semiempirical PM3 or HF/STO-3G calculations, after orthogonal transformation. The enthalpy of formation can then be expressed in terms of only one adjustable parameter. With HF/STO-3G eigenvectors, the mean discrepancy between experimental and calculated enthalpies of formation, after a one-parameter correction for 1,4 steric interactions, is 2.2 kJ mol⁻¹, comparable with more highly parameterized models. The results using PM3 eigenvectors are less satisfactory, probably on account of the neglect of overlap in the semiempirical scheme.     

Reactivity of [CpRh(η-C6H3NH2-2,6-i-Pr2)](OTf)2 toward phosphines and alkynes

The cationic aniline complex [Cp^∗Rh(η⁶-2,6-(Me₂CH)₂C₆H₃NH₂)](OTf)₂ (1) was prepared from either [Cp^∗Rh(η²-NO₃)(η¹-OTf)] or [Cp^∗Rh(OH₂)₃](OTf)₂ and 2,6-diisopropylaniline. Complex 1 underwent substitution with phosphines or phosphites, indicating the labile character of the η⁶-aniline ligand. Complex 1 mediated cycloaddition reactions of several alkynes in refluxing ethanol: the [2 + 2] dimerization for PhCCPh and the [2 + 2 + 1] trimerization for PhCCH and CH₃C₆H₄CCH. The unexpected cyclobutadiene complex [Cp^∗Rh(η⁴-C₄(C(O)CH₃)₂H(SiMe₃))] was obtained from complex 1 and Me₃SiCCCCSiMe₃ and structurally characterized by X-ray diffraction.     

Argon matrix effect on the geometry and infrared spectrum of H2CMH2 (M = Ti, Zr, Hf): A theoretical study

Within the framework of polarizable continuum model with integral equation formalism (IEF-PCM), an argon matrix effect on the geometry and infrared frequencies of the agostic H₂CMH₂ (M = Ti, Zr, Hf) methylidene complexes was investigated at B3LYP level of theory with the 6-311++G(3df,3pd) basis set for C, H, and Ti atoms and Stuttgart/Dresden ECPs MWB28 and MWB60 for the Zr and Hf atoms. At the B3LYP/IEF-PCM level of theory, H₂CTiH₂ was optimized to an energy minimum having a pyramidal structure. The calculated dipole moment of this structure is 3.06 D. The B3LYP/IEF-PCM simulations gave the three complexes’ agostic angle ∠HCM (°), distance r(H?M) (Å), and CM bond length r(CM) (Å) as follows: ∠HCTi = 87.4, r(H?Ti) = 2.079, r(CTi) = 1.803; ∠HCZr = 89.3, r(H?Zr) = 2.243, r(CZr) = 1.956; ∠HCHf = 94.7, r(H?Hf) = 2.343, r(CHf) = 1.972. As a comparison, the B3LYP simulations gave the values as follows: ∠HCTi = 91.5, r(H?Ti) = 2.150, r(CTi) = 1.811; ∠HCZr = 92.9, r(H?Zr) = 2.299, r(CZr) = 1.955; ∠HCHf = 95.6, r(H?Hf) = 2.352, r(CHf) = 1.967. As far as the MH₂ symmetric and asymmetric stretching and CH₂ wagging frequencies are concerned, the IEF-PCM calculated values are in better agreement with the experimental argon matrix ones than those calculated based on a gas phase model.     

Iron(II) and iron(III) complexes containing ethynyl thiophene fragments

The synthesis of the new complexes Cp*(dppe)FeCC2,5-C₄H₂SR (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; 2a, R = CCH; 2b, R = CCSi(CH₃)₃; 2c, R = CCSi(CH(CH₃)₂)₃; 3a, R = CC2,5-C₄H₂SCCH; 3c, R = CC2,5-C₄H₂SCCSi(CH(CH₃)₂)₃) is described. The ¹³C NMR and FTIR spectroscopic data indicate that the π-back donation from the metal to the carbon rich ligand increases with the size of the organic π-electron systems. The new complexes were also analyzed by CV and the chemical oxidation of 2a and 3c was carried out using 1 equiv of [Cp₂Fe][PF₆]. The corresponding complexes 2a[PF₆] and 3c[PF₆] are thermally stable, but 2a[PF₆] was too reactive to be isolated as a pure compound. The spectroscopic data revealed that the coordination of large organic π-electron systems to the iron nucleus produces only a weak increase of the carbon character of the SOMO for these new organoiron(III) derivatives.