Electron-withdrawing Trifluoromethyl Group Research Articles

Synthesis and Properties of Novel Fluorinated Polyamides Based on Noncoplanar Sulfoxide Containing Aromatic Bis(ether amine)

A novel sulfoxide containing bis(ether amine) monomer, 2,2′-sulfoxide-bis[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (M2), was synthesized from the halogen displacement of 2-chloro-5-nitrobenzotrifluoride with dibenzosulfoxide (DH) in the presence of potassium carbonate, followed by catalytic reduction of bis(ether nitro) intermediate with Zinc/Ammonium chloride. A series of organic-soluble poly(ether amide)s (PA1–7) bearing sulfoxide and electronwithdrawing trifluoromethyl group were synthesized from bis(ether amine) with various aromatic diacids (1–7) via a direct polycondensation with triphenyl phosphite and pyridine. The resulting polymers had inherent viscosities ranging from 0.35 to 0.90 dL g−1 at a concentration of 0.5 g/dL in N,N-dimethylacetamide (DMAc) solvent at 25 °C. All the polymers showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents (e.g., N-methyl-2-pyrrolidone (NMP), DMAc, and N,N-dimethylformamide) and even dissolved in less polar solvents (e.g., pyridine, and tetrahydrofuran). Also these polymers could be cast into flexible and tough films from DMAc solutions. The glass-transition temperatures of these poly(sulfoxide ether amide)s were recorded between 160–220 °C. 10% weight loss temperatures were recorded in the range of 400–505 °C in nitrogen and 380–480 °C in air atmosphere.

Electronic Structure Studies on Deprotonation of Dithiophosphinic Acids in Water Clusters

We report herein a computational study of proton transfer reactions between dithiophosphinic acids (HAs) and water clusters using B3LYP and MP2 methods. The ground-state and transition-state structures of HA-(H(2)O)(n) (n = 1, 2, 3) cluster complexes have been calculated. The influence of water molecules on energy barrier heights of proton transfer reactions has been examined in the gas phase and solution for bis[o-(trifluoromethyl)phenyl]- and bis(2,4,4-trimethylpentyl)dithiophosphinic acids (HA1 and HA2, respectively). Gas-phase calculations indicate that electron-withdrawing substituents and trifluoromethyl groups in the ortho position favor deprotonation of HA1 when three water molecules are included in the cluster. This suggests that at least three water molecules are necessary to solvate the abstracted proton in the presence of the anion. In the case of HA2, the electron-donating groups favor the reverse proton transfer reaction, namely, protonation of dithiophosphinate anion. Bulk solvent effects have been modeled for aqueous and organic media with the CPCM model. The calculated results show that polar solvents can lower the activation energy for less energetically stable transition states that have more localized charges.

Two novel mono-organoimido functionalized polyoxometalate clusters: Convenient synthesis, crystal structure and bioactivity of [( n-C 4H 9) 4N] 2[Mo 6O 18(NAr)] (Ar = o-CF 3C 6H 4, p-OCF 3C 6H 4)

The hexamolybdate cluster has been functionalized with fluorine-containing aromatic amine by the DCC ( N, N′-dicyclohexylcarbodiimide) dehydrating protocol and two novel mono-functionalized arylimido derivatives of hexamolybdates bearing the electron-withdrawing trifluoromethyl group and trifluoromethoxy group, (Bu 4N) 2[Mo 6O 18(≡NAr)] (Ar = o-CF 3C 6H 4) 1 and (Bu 4N) 2[Mo 6O 18(≡NAr)] (Ar = p-OCF 3C 6H 4) 2 have been synthesized by improved method. Complete assignments were achieved for the title compounds by elemental analysis, IR, 1H NMR, UV/visible and single-crystal X-ray diffraction analyses. The preliminary herbicidal activity test indicated that they have some herbicidal activities.

Reduction of 2,2,2-trifluoro-1-arylethanones with alkyl phosphines

In the presence of alkyl phosphines, reduction of 2,2,2-trifluoro-1-arylethanones proceeded smoothly to give the corresponding reduction products in moderate to high yields at room temperature. The possible mechanism was discussed on the basis of deuterium labeling and control experiments, indicating that one hydrogen transfer took place from alkyl phosphine to the carbonyl group activated by a strongly electron-withdrawing trifluoromethyl group.

Synthesis of Aqueous Polyethylene Dispersions with Electron-Deficient Neutral Nickel(II) Catalysts with Enolatoimine Ligands

A series of new, electron-poor neutral κ2-N,O chelated Ni(II) complexes were studied for ethylene polymerization in aqueous emulsion. Complexes based on enolatoimine ligands bearing electron-withdrawing trifluoromethyl and trifluoroacetyl groups [κ2-N,O-{2,6-R2C6H3NC(H)C(COCF3)C(O)CF3}]Ni(L)Me (4a, R = iPr, L = pyridine; 4b, R = 3,5-(CF3)2C6H3, L = pyridine; 5b, R = 3,5-(CF3)2C6H3, L = PPh3) were prepared. The complexes are very active in aqueous emulsions, with 1.4 × 104 TO h-1 for 4a (50 °C) and 1.9 × 104 TO h-1 for 4b (70 °C), affording stable polyethylene dispersions. The phosphine complex 5b is active in the absence of a phosphine scavenger, with similar activities as 4b. Polyethylenes of typically Mw 3 × 104 g mol-1 (Mw/Mn 2.0−2.5) with 25−50 branches per 1000 carbon atoms and Tm 94−112 °C are obtained.

Synthesis of the First Chiral Bidendate Bis(trifluoromethyl)phosphane Ligand through Stabilization of the Bis(trifluoromethyl)phosphanide Anion in the Presence of Acetone

Lewis acid/Lewis base adduct formation of the P(CF3)2- ion and acetone leads to a reduced negative hyperconjugation and, therefore, limits the C--F bond activation. The resulting increased thermal stability of the P(CF3)2- ion in the presence of acetone allows selective substitutions and enables the synthesis of the first example of a chiral, bidentate bis(trifluoromethyl)phosphane ligand: a DIOP derivative, [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis(methylene)]bis(diphenylphosphane), in which the phenyl groups at the phosphorus atoms are replaced by strong electron-withdrawing trifluoromethyl groups. The resulting high electron-acceptor strength of the synthesized bidentate (CF3)2P ligand is demonstrated by a structural and vibrational study of the corresponding tetracarbonyl-molybdenum complex. The stabilization of the P(CF3)2- ion in the presence of acetone is based on the formation of a dynamic Lewis acid/Lewis base couple, (CF3)2PC(CH3)2O-. Although there is no spectroscopic evidence for the formation of the formulated alcoholate ion, the intermediate formation of (CF3)2PC(CH3)2O- could be proved through the reaction with (CF3)2PP(CF3)2, which yields the novel phosphane-phosphinite ligand (CF3)2PC(CH3)2OP(CF3)2. This ligand readily forms square-planar Pt(II) complexes upon treatment with solid PtCl2.

Synthesis, Characterization, and Ethylene Polymerization Activities of Neutral Nickel(II) Complexes Derived from Anilino-Substituted Enone Ligands Bearing Trifluoromethyl and Trifluoroacetyl Substituents

A series of neutral Ni(II) complexes derived from anilino-substituted enone ligands bearing electron-withdrawing trifluoromethyl and trifluoroacetyl groups have been synthesized and characterized: [η2-ArNC(R1)CC(R2)C(O)CF3]Ni(PPh3)Ph (3a, Ar = 3,5-i-Pr2C6H3, R1 = H, R2 = COCF3; 3b, Ar = 3,5-i-Pr2C6H3, R1 = Me, R2 = COCF3; 3c, Ar = 3,5-i-Pr2C6H3, R1 = Me, R2 = H; 3d, Ar = 3,5-Me2C6H3, R1 = Me, R2 = COCF3). When they are activated with either Ni(COD)2 or B(C6F5)3, these complexes are active for the polymerization of ethylene to branched polyethylenes. Complex 3a is especially active and long-lived, with a turnover frequency of 5 × 105 at 60 °C and 200 psig of ethylene, a half-life exceeding 15 h at 35 °C, and a total turnover number exceeding 106 at 35 °C and 200 psig. Molecular weights and degrees of branching of polyethylenes obtained from 3a are reported as a function of reaction temperature and ethylene pressure.

A trifluoromethyl substituted organoimido derivative of the hexametalate cluster: Synthesis, crystal structure and bioactivity of [Mo 6O 17(NAr) 2] 2− (Ar = o-CF 3C 6H 4)

The hexamolybdate cluster has been functionalized with fluorine-containing aromatic amine by the DCC ( N, N′-dicyclohexylcarbodiimide) dehydrating protocol and a novel bifunctionalized arylimido derivative of hexamolybdate bearing the electron-withdrawing trifluoromethyl group, (Bu 4N) 2[Mo 6O 17(NAr) 2] (Ar = o-CF 3C 6H 4), has been prepared. Complete assignments were achieved for the title compound by elemental analysis, IR, 1H NMR, UV/visible and single-crystal X-ray diffraction analyses. The preliminary agricultural biological activity test indicated that it has some herbicidal and insecticidal activities.

Novel Poly(p-phenylenevinylene)s Derivatives with CF3-Phenyl Substituent for Light-Emitting Diodes

New PPV derivatives which contain electron-withdrawing trifluoromethyl (CF 3 ) group, poly[2-(2-ethylhexyl-oxy)-5-(4-trifluoro methylphenyl)-1,4-phenylenevinylene] (EHCF 3 P-PPV), and poly[2-(2-ethylhexyloxy)-5-(3,5-bis(trifluoromethyl)-phenyl)-l,4-phenylenevinylene] (EHBCF 3 P-PPV), have been synthesized by GILCH polymerization. As the result of the introduction of the electron-withdrawing CF 3 group to the phenyl substituent, the LUMO and HOMO energy levels of EHCF 3 P-PPV (2.8, 5.1 eV) and EHBCF 3 P-PPV (3.0, 5.3 eV) were lower than those of known poly[2-(2-ethylhexyloxy)-5-phenyl-1,4-phenylenevinylene] (EHP-PPV) (2.6, 4.9 eV). These polymers have been used as the electroluminescent (EL) layers in double layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). EHCF 3 P-PPV, and EHBCF 3 P-PPV show maximum photoluminescence (PL) peaks at λ m a x = 550, 539 nm, and maximum EL peak at λ m a x = 545, 540 nm, respectively. The current-voltage-luminance (I-V-L) characteristics of the polymers show that turn-on voltages of EHCF 3 P-PPV and EHBCF 3 P-PPV are around 4.0 and 3.5 V, respectively.

W(CO) 6-Mediated desulfuroligomerization of bis-dithioacetals. New synthesis of substituted oligo(phenylene–vinylenes)

Treatment of bisdithioacetals of 1,4-diaroylbenzenes ( 4) with W(CO) 6 in refluxing chlorobenzene afforded the corresponding substituted oligophenylenevinylenes (OPVs) ( 5). Average molecular weights determined by GPC indicate that OPVs 5 have 5–13 repetitive substituted phenylenevinylene units with narrow polydispersities. Emission in the blue–green to green region was observed for these OPVs depending on the nature of the substituent. The electron-donating alkoxy substituent shifted the emission to the longer wavelength whereas the electron-withdrawing trifluoromethyl group caused a blue shift in the fluorescence spectra.

Rational Design of Benzyl-Type Protecting Groups Allows Sequential Deprotection of Hydroxyl Groups by Catalytic Hydrogenolysis

Benzyl protection of a hydroxyl group is one of the most frequently used procedures in synthesis because of the mild conditions involved in its removal by catalytic hydrogenolysis.1-3 The synthesis of polyhydroxylated compounds often requires orthogonal protecting strategies to distinguish between hydroxyl groups. It would be highly desirable to develop a range of benzyl-type protecting groups with different reactivities that can be sequentially removed via catalytic hydrogenolysis. This requires a detailed understanding of the mechanism of the cleavage of the benzyl oxygen bond by the palladium hydrogen species. Recently, we have determined the amphipolar nature of the palladium hydrogen bond (modes a, Mδ+ Hδ-, or b, MδHδ+) in both homogeneous4 and heterogeneous5 hydrogenation of alkenes. This has led us to test whether the electronic properties of the aromatic group can influence the rate of cleavage, which should in turn guide the development of hydroxyl protecting groups with different reactivities. The results in Table 1 show that the rate of debenzylation can be dramatically affected by the electronic properties of the aromatic ring. The substitution of the electron-withdrawing trifluoromethyl group onto the aromatic ring severely retards debenzylation under 1 atm of hydrogen. In contrast, there is considerable acceleration by electrondonating substituents, which suggests that the benzylic carbon bears a partial positive charge in the transition state. The hydrogenolysis of benzyl alcohols carried out in acetic acid has shown that protonation of the hydroxyl group is essential for the cleavage of the carbon-oxygen bond.6 Under the neutral conditions in our study, the reaction may occur by protonation of the benzyl oxygen atom, through the operation of mode b, MδHδ+, to give a positively charged benzylic carbon. Alternativly, it is possible that palladium could act as a Lewis acid and coordinate to the benzyl oxygen atom to promote the same electron-deficient transition state (mode a, Mδ+ Hδ-). The large difference in reactivity within this range of substituted benzyl groups suggests that they can be sequentially deprotected, therefore proving useful in multistep synthesis. To test the synthetic application of these groups, competition experiments were conducted on model systems with two differently substituted benzyl groups attached to ethanediol (Scheme 1a). Surprisingly, the benzyl group was cleaved first in competition with any of the substituted benzyl groups. This phenomenon has been observed with the 4-methoxybenzyl group (PMB); however, no explanation was proposed.7,8 The results with the linker experiments (Scheme 1a) seem to contradict those obtained when only one benzyl group is involved (Table 1). Surface scientists have determined that the aromatic ring lies flat on the metal surface for optimal coordination.9,10 It is possible that substitution on the aromatic ring could have an adverse steric effect that would interfere with the planar geometry required for effective binding and thus reduce its affinity for the metal surface. The linker experiments show that the limited number of active sites on the palladium surface could lead to a competition for adsorption sites between substituted and unsubstituted benzyl groups. This may explain why the least substituted benzyl group, although not electronically favored, can still be preferentially cleaved. It is clear that for the rational design of selective benzyl type protecting groups both electronic factors and adsorption must be taken into account. For synthetic purposes, it would be desirable to find a more labile group than the benzyl group for protection of the hydroxyl functionality. We anticipated that the 2-naphthylmethyl (NAP) group would fulfill these criteria: it is electron rich and should have a (1) Greene, T. W.; Wuts, P. G. M. In Protective Groups in Organic Synthesis; John Wiley & Sons, Inc.: New York, 1991. (2) (a) Czernecki, S.; Georgoulis, C.; Provelenghiou, C. Tetrahedron Lett. 1976, 3535. (b) Iverson T.; Bundle K. R. J. Chem. Soc., Chem. Commun., 1981, 1240. (3) Czech, B. P.; Bartsch, R. A. J. Org. Chem. 1984, 49, 4076. (4) Yu, J.; Spencer, J. B. J. Am. Chem. Soc. 1997, 119, 5257. (5) Yu, J.; Spencer, J. B. J. Org. Chem. 1997, 62, 8618. (6) Kieboom, A. P. G.; De Kreuk, J. F.; Van Berkum, H. J. Catal. 1971, 20, 58. (7) Srikrishna, A.; Viswajanani, J. A.; Sattigeri, J. A.; Vijaykumar, D. J. Org. Chem. 1995, 60, 5961. (8) Sajiki, H.; Kuno, H.; Hirota, K. Tetrahedron Lett. 1997, 38, 399. (9) Lin, R. F.; Koestner, R. J.; Van Hove, M. A.; Somorjai, G. A. Surf. Sci. 1983, 161. (10) Held, G.; Bessent, M. P.; Titmuss, S.; King, D. A. J. Chem. Phys. 1996, 11305. Table 1a

Exalted Resonance Effect in the Aryl-Assisted Solvolyses of 2-Aryl-2-(trifluoromethyl)ethyl m-Nitrobenzenesulfonates

Abstract The substituent effects on solvolysis of 2-aryl-2-(trifluoromethyl)ethyl m-nitrobenzenesulfonates, in acetic acid and in 80% aqueous trifluoroethanol, were analyzed by Yukawa-Tsuno equation. The resonance demands (r = 0.77 in acetic acid) were larger than that of standard aryl-assisted solvolysis by 0.2. This enlargement should depend on a destabilization of aryl-assisted transition-state by an electron-withdrawing trifluoromethyl group.

Dramatic Change of Carbonyl Oxide Reactivity by the Potent Electron-Withdrawing Trifluoromethyl Group.

alpha,alpha,alpha-Trifluoroacetophenone oxide, generated by (1)O(2) oxidation of Ph(CF(3))CN(2), reacted electrophilically with sulfoxides (rho = -0.74 vs sigma; r = 0.95) affording sulfides as the major product. The intermediacy of persulfoxides formed via cyclic peroxidic sulfuranes in the novel deoxygenation was evidenced by an (18)O-tracer study and by the formation of benzaldehyde in the reaction with benzyl phenyl sulfoxide. Olefins were oxidized to epoxides during the photooxidation of Ph(CF(3))CN(2). From the fact that the epoxidation proceeded almost stereospecifically and the substituent effect on styrenes resulted in the negative rho-value of -1.66 vs sigma (r = 0.97), a dioxirane was proposed as the second intermediate which might be formed by the isomerization of carbonyl oxide. Trapping experiments with styrenes and sulfoxides suggested that the cyclization of carbonyl oxide is competitive with the reaction with sulfoxides. In contrast to the known nucleophilic nature of carbonyl oxides, the present oxide is shown to have an electrophilic character, indicating that the reactivity of carbonyl oxides could be controlled by substituents.

New CF 3-substituted PPV-type oligomers and polymers for use as hole blocking layers in LEDs

New CF 3-substituted PPV derivatives have been synthesised by Wittig-Horner polycondensation. To obtain a better understanding of the relationship between absorption and luminescence properties and structure a single crystal X-ray analysis of a model oligomer has been performed. The effect of electron withdrawing trifluoromethyl groups at vinylidene linkages in PPVs on absorption, luminescence, hole blocking and electron injecting properties has been investigated.

Direct synthesis of 3,4-dihydro-2 H-pyrido[1,2- a]pyrimidines, by addition reactions with 2-aminopyridines

Reaction of 2-aminopyridines with formaldehyde and electron rich alkenes permits synthesis of pyridopyrimidines by formation of imines and subsequent addition to the alkenes in a formal aza Diels Alder reaction. The structure of the cyclic amidine products is confirmed by single crystal X-ray analysis on a neutral amidine isolated from an aminopyridine substituted with an electron withdrawing trifluoromethyl group and of a trifluoroacetate salt of an amidine obtained from 2-aminopyridine, formaldehyde and indene. These structural studies permit the regio- and stereo-chemical outcome of these additions to be defined and compared with related processes.

Trifluoroalanine N-Carboxy Anhydride: A Reactive Intermediate for the Synthesis of Low Surface Energy Polypeptides

D,L-Trifluoroalanine N-carboxy anhydride (D,L-TFANCA) was synthesized by phosgenation of 3,3,3-D,L-trifluoroalanine in tetrahydrofuran. ^1H nuclear magnetic resonance and infrared spectra indicate that the electron withdrawing trifluoromethyl group in the a position increases the acidity of the amide proton and the electrophilicity of the carbonyl groups of the anhydride. D,L-TFANCA was polymerized with aniline, thiophenol, or triethylamine as initiator. Time of flight matrix assisted laser desorption mass spectrometry was used to determine the absolute molecular weights and molecular weight distributions of the resulting polypeptides. Knowledge of the exact molecular weight confirmed the structural integrity of the products and gave insight into the mechanism of polymerization. D,L-TFANCA was also copolymerized with γ-benzyl L-glutamate NCA. Incorporation of 20 mol % D,L-trifluorodanine into poly(γ-benzyl L-glutamate) leads to a marked decrease in the surface energy of the polymer, as determined by contact angle measurements.

Iron(III) porphyrins substituted with highly electron-withdrawing trifluoromethyl groups: electronic absorption, MCD, and EPR spectral study

Iron(III) porphyrins substituted with highly electron-withdrawing trifluoromethyl groups: electronic absorption, MCD, and EPR spectral study

Synthesis of fluorinated retinal: A C6-C7 s-trans fixed retinal containing a trifluoromethyl group at the terminal position of the conjugated system.

For the study of retinal-binding proteins by using fluorine-modified retinals, the all-trans bicyclic trifluororetinal (1), whose C6-C7 bond is fixed in the s-trans form by an ethano bridge, was synthesized. Introduction of a trifluoromethyl group was carried out in 70% yield by photochemical trifluoromethylation of the dienol ether compound (2) with trifluoromethyl iodide. From a comparison of the absorption maximum of 1 with that of the bicyclic retinal (12), it is clear that the electron-withdrawing trifluoromethyl group induces a notable hypsochromic shift (18 nm) of 1.

Chemistry of trifluoromethyl compounds. 2. Synthesis and characterization of bis(pyridine)bis(trifluoromethyl)zinc

Reported here are the results of the isolation of bis(pyrdine)bis(trifluoromethyl)zinc from the reaction of dimethylzinc and bis(trifluoromethyl)mercury in pyridine. The stability of the resulting compound is due to the pyridine, which, as a result of its electron-withdrawing trifluoromethyl groups evidently satisfies the electronic properties of zinc. IR and NMR spectra were measured, as were thermal stability, solubility, and chemical properties. 1 figure.