Pentafluorophenyl Rings Research Articles

A new twist on an old molecule: a rotameric isomer of bis(pentafluorophenyl)mercury

Suspending crystals of bis(pentafluorophenyl)mercury [Hg(C6F5)2] (1a) in a saturated n-hexane solution for a prolonged period results in transformation into the new polymorph [Hg(C6F5)2] (1 b) monoclinic P21/n, a = 11.7060(3) Å, b = 7.8531(2) Å, c = 13.5429(4) Å, β = 107.247(3)°, V = 1189.00(6) Å3. The C-Hg-C angle in 1 b is 177.10(11)° and the pentafluorophenyl rings are rotated 74.6(1)° to each other in comparison to 1a, the form known for 50+ years, which has a rotation angle of 58.0(2)°. Polymorph 1 b could also be obtained by crystallization from chloroform, or a CHCl3/n-hexane (1:1) mixture at −20 °C, or by seeding with a crystal of 1 b. Theoretical calculations suggest that the barrier to rotation is low.

Synthesis, crystal structure and Hirshfeld surface analysis of (4-methyl-phen-yl)[1-(penta-fluoro-phen-yl)-5-(tri-fluoro-meth-yl)-1H-1,2,3-triazol-4-yl]methanone.

The title compound, C17H7F8N3O, was obtained via the reaction of 1-azido-2,3,4,5,6-penta-fluoro-benzene with 4,4,4-tri-fluoro-1-(p-tol-yl)butane-1,3-dione using tri-ethyl-amine as a base catalyst and solvent. The dihedral angles between the penta-fluoro-phenyl (A), triazole (B) and p-tolyl (C) rings are A/B = 62.3 (2), B/C = 43.9 (3) and A/C = 19.1 (3)°. In the crystal, the mol-ecules are linked by C-H⋯F and C-H⋯O hydrogen bonds as well as by aromatic π-π stacking inter-actions into a three-dimensional network. To further analyse the inter-molecular inter-actions, a Hirshfeld surface analysis was performed.

Crystal structure of 2,3-dimeth-oxy-meso-tetra-kis(penta-fluoro-phen-yl)morpholino-chlorin methyl-ene chloride 0.44-solvate.

The title morpholino-chlorin, C46H16F20N4O3, was crystallized from hexa-ne/methyl-ene chloride as its 0.44 methyl-ene chloride solvate, C46H16F20N4O3·0.44CH2Cl2. The morpholino-chlorin was synthesized by stepwise oxygen insertion into a porphyrin using a 'breaking and mending strategy': NaIO4-induced diol cleavage of the corresponding 2,3-di-hydroxy-chlorin with in situ methanol-induced, acid-catalyzed intra-molecular ring closure of the inter-mediate secochlorins bis-aldehyde. Formally, one of the pyrrolic building blocks was thus replaced by a 2,3-di-meth-oxy-morpholine moiety. Like other morpholino-chlorins, the macrocycle of the title compound adopts a ruffled conformation, and the modulation of the porphyrinic π-system chromophore induces a red-shift of its optical spectrum compared to its corresponding chlorin analog. Packing in the crystal is governed by inter-actions involving the fluorine atoms of the penta-fluoro-phenyl substituents, dominated by C-H⋯F inter-actions, and augmented by short fluorine⋯fluorine contacts, C-F⋯π inter-actions, and one severely slipped π-stacking inter-action between two penta-fluoro-phenyl rings. The solvate methyl-ene chloride mol-ecule is disordered over two independent positions around an inversion center with occupancies of two × 0.241 (5) and two × 0.199 (4), for a total site occupancy of 88%.

A Simple and Effective Method of Determining Lewis Acidity by Using Fluorescence

Summary The strength of a Lewis acid is an important parameter in establishing its utility for practical applications. Here, we report a universal fluorescence-based method for accurately determining the strength of a range of Lewis acids. Utilizing a fluorescent dithienophosphole oxide architecture, we are able to emulate the structural motif of the widely employed Gutmann-Beckett method. This allows us to precisely correlate the optical response to the strength of a Lewis acid. In comparison to commonly used methods that employ 31P NMR chemical shifts or quantum-chemical calculations, our method strongly suggests that using fluorescent Lewis acid-base adducts (FLAs) is more reliable. Moreover, our method provides a direct measure of the Lewis acidity of a given solution, independent of the Lewis base, with direct implications to the overall utility of a Lewis acid in practical applications.

Intramolecular π-π Interactions with a Chiral Auxiliary Ligand Control Diastereoselectivity in a Cyclometalated Ir(III) Complex.

The application of a chiral auxiliary ligand to control the diastereoselectivity in the synthesis of a cyclometalated iridium(III) complex is presented. The diastereomeric iridium(III) complexes 1a and 1b are reported, in which a phenoxyoxazoline auxiliary ligand incorporates a chiral center functionalized with a pendant pentafluorophenyl group. The diastereomers were readily separated, and their structural, electrochemical and photophysical properties are discussed. Solution-state NMR data and X-ray crystal structures establish that the pentafluorophenyl group engages in intramolecular π-π interactions. The X-ray analysis reveals that the two diastereomers display very different modes of intramolecular stacking. The variable-temperature 19F NMR data indicate that rotation of the pendant pentafluorophenyl rings in 1b and 1a is a temperature-dependent process and that there is a smaller energy barrier to rotation in 1b in comparison to 1a. This correlates with variable-temperature photoluminescence data, which show that upon heating the integrated emission intensity is reduced substantially more for 1b than for 1a, which is ascribed to the enhanced rotation in 1b, providing a more easily populated nonradiative pathway in comparison to 1a. These experimental data are supported by computational calculations. Phosphorescent organic light-emitting devices (PhOLEDs) using 1a as the dopant complex give blue-green emission with a high maximum external quantum efficiency (EQEmax) of 25.8% (at ca. 270 cd m-2) and with a low efficiency roll-off to 24.9% at 1000 cd m-2. Our results extend the scope of ligand design for cyclometalated iridium complexes which possess interesting structural and emission properties.

Catalytic activity of biomimetic model of cytochrome P450 in oxidation of dopamine

The introduction of electron-withdrawing group into porphyrin molecule as cytochrome P450 model can tune the energy level and have an effect on the electronic structure. In this work, linking with the strong electron-withdrawing fluorine atoms, a starburst dendritic molecule, 5,10,15,20-tetrakis(pentafluorophenyl)−21H,23H-porphyrin iron (III) chloride (FeTFPP), containing a saddle-shaped porphyrin as the central core and four pentafluorophenyl rings as the peripheral functional groups was successfully synthesized. Subsequently, the macrocyclic conjugate polymer film of FeTFPP was achieved via a low-cost electrochemical method and exploited as an efficient mimetic enzyme. Furthermore, a biomimetic sensor was constructed by the poly(FeTFPP) film and graphene (rGO) sheet (rGO-poly(FeTFPP)) for selective and sensitive detection of dopamine (DA). Here, the FeTFPP polymer performs three functions: electrochemical recognition (owing to the hydrogen bonding between the strongly electronegative fluorine atoms and DA), biomimetic microenvironment (owing to interaction between porphyrin core and DA), electrocatalysis (owing to remarkable catalytic ability of iron (III) ion). Under optimum conditions, the response to DA was linear in the concentration range between 0.05 to 300μM, and the detection limit was 0.023μM. In addition, we applied the rGO-poly(FeTFPP) film to detect DA in real samples and the results implied its feasibility for practical application. As a result, it is believed that the rGO-poly(FeTFPP) film is one of the promising biomimetic catalysts for electrocatalysis and relevant fields.

Intramolecular π-π Interactions in Flexibly Linked Partially Fluorinated Bisarenes in the Gas Phase.

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2 )3 and (CH2 )2 SiMe2 units were synthesized by hydrosilylation and C-C coupling reactions. Their solid-state structures are dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π-π interactions. For the silicon compounds, structures characterized by σ-π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6 H5 (CH2 )3 C6 F5 , in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations.

Further improvement of the macroscopic NLO coefficient and optical transparency of hyperbranched polymers by enhancing the degree of branching

In this paper, two new second-order nonlinear optical (NLO) hyperbranched polytriazoles (HP1 and HP2) containing nitro azobenzene as the chromophore were successfully prepared, through the AB4-type click polymerization under copper(I) catalysis. Thanks to the AB4-type branched monomer, the degree of branching (DB) of HP1 was improved to 0.691, much larger than that of its analogue, HPS1 (0.457), which was derived from an AB2-type monomer. The solubility, optical transparency and NLO coefficient of HP1 were all improved in comparison with those of HPS1, due to the better site-isolation effect. Furthermore, pentafluorophenyl rings were utilized as isolation groups to further enhance the NLO effect in HP2, and the d33 value and the d33(∞) value of HP2 were tested to be as high as 136 pm V−1 and 28 pm V−1, respectively.

Synthesis and Electroluminescence of Thieno-[3,4-b]-pyrazine-cored Molecule with Fluorinated Shell

A thieno-[3,4-b]-pyrazine-based molecule, F-DTP, was designed and synthesized for application as a red emitter in non-doped organic light-emitting diodes. F-DTP was designed with thieno-[3,4-b]-pyrazine as the luminescent core and pentaphenylphenylene (i.e. polyphenyl) groups as side arms. The peripheral phenyls on the polyphenyl arms were replaced by pentafluorophenyl rings to lower the lowest unoccupied molecular orbital level and thus enhance the electron-injecting feature of F-DTP. The photophysical, thermal, and electrochemical properties were investigated. F-DTP is characterized by a large Stokes shift of 113 nm. The bulky polyphenyl groups provide a site-isolating effect on the planar emissive core and thus effectively suppress unwanted intermolecular interactions. F-DTP was used as a non-doped emitter to fabricate an organic light-emitting diode by a vacuum evaporation technique. Red electroluminescence was obtained with a brightness of 1282 cd m–2 and a luminance efficiency of 0.7 cd A–1.

Formation of P–C Bond through Reductive Coupling between Bridging Phosphido and Benzoquinolinate Groups. Isolation of Complexes of the Pt(II)/Pt(IV)/Pt(II) Sequence

The rational synthesis of dinuclear asymmetric phosphanido derivatives of palladium and platinum(II), [NBu(4)][(R(F))(2)M(μ-PPh(2))(2)M'(κ(2),N,C-C(13)H(8)N)] (R(F) = C(6)F(5); M = M' = Pt, 1; M = Pt, M' = Pd, 2; M = Pd, M' = Pt, 3; M = M' = Pd, 4), is described. Addition of I(2) to 1-4 gives complexes [(R(F))(2)M(II)(μ-PPh(2))(μ-I)Pd(II){PPh(2)(C(13)H(8)N)}] (M = M' = Pt, 6; M = Pt, M' = Pd, 7; M = M' = Pd, 8; M = Pd, M' = Pt 10) which contain the aminophosphane PPh(2)(C(13)H(8)N) ligand formed through a Ph(2)P/C^N reductive coupling on the mixed valence M(II)-M'(IV) [NBu(4)][(R(F))(2)M(II)(μ-PPh(2))(2)M'(IV)(κ(2),N,C- C(13)H(8)N)I(2)] complexes, which were identified for M(II) = Pd, M'(IV) = Pt (9), and isolated for M(II) = Pt, M'(IV) = Pt (5). Complex 5 showed an unusual dynamic behavior consisting in the exchange of two phenyl groups bonded to different P atoms, as well as a "through space" spin-spin coupling between ortho-F atoms of the pentafluorophenyl rings.

Analysis of geometric parameters and packing considerations for triphenylboroxine derivatives, with tris(pentafluorophenyl)boroxine as an example

Molecules of the title compound [systematic name: 2,4,6-(pentafluorophenyl)-1,3,5,2,4,6-trioxatriborinane], C(18)B(3)F(15)O(3), are located on crystallographic twofold rotation axes which run through the boroxine and one of the pentafluorophenyl rings. The boroxine ring (r.m.s. deviation = 0.027 Å) and the pentafluorophenyl rings (r.m.s. deviations = 0.004 and 0.001 Å) are essentially planar. The dihedral angles between the boroxine and the two symmetry-independent benzene rings are 8.64 (10) and 8.74 (12)°. The two benzene rings are mutually coparallel [dihedral angle = 0.80 (11)°]. The packing shows planes of molecules parallel to ( ̅201), with an interplanar spacing of 2.99 Å. Within these planes, all the molecules are oriented in the same direction, whereas in neighbouring planes the direction is inverted. Short B···F contacts of 3.040 (2) and 3.1624 (12) Å occur between planes. The geometric parameters of the boroxine ring in the title compound agree well with those of comparable boroxine structures, while the packing reveals some striking similarities and differences.

Directional character of solvent- and anion-pentafluorophenyl supramolecular interactions

A thorough statistical analysis of the structures deposited in the Cambridge Structure Database reveals that both the lone-pair-π and anion-π interactions occur in a predictive and directional fashion, as evidenced by the careful examination of potential bonding contacts between some common solvent molecules or non-coordinating anions and the electron-rich phenyl or electron-deficient pentafluorophenyl rings. The general directional character of both the lone-pair-π and anion-π bonds is clearly observed in the solid state.

Single and Binary Self-Assembled Monolayers of Phenyl- and Pentafluorophenyl-Based Silane Species, and Their Phase Separation with Octadecyltrichlorosilane

In this paper, we first present the study of the formation of phenyltrichlorosilane film and self-assembled monolayers of phenylalkyltrichlorosilane (PATCl), pentafluoro-phenylalkyltrichlorosilane (PFATCl), and a mixture of the two, on silicon covered by its native oxide. These monolayers are shown to grow in two steps with characteristic time constants. The first step is characterized by a similar time constant of growth for all the studied trichlorosilane molecules and attributed to chemisorption. The second step corresponds to the arrangement between molecules, accelerated by the presence of the short alkyl chain (3-4 carbon atoms), and by mixing phenyl and pentafluoro-phenyl terminal moieties, which is accounted for by hydrogen bonding CH···FC and/or attractive quadrupolar interactions within a face-to-face phenyl/pentafluoro-phenyl alternating stack arrangement. Such results should allow improvement of intermolecular stacking within conjugated molecular domains, which is particularly important for molecular electronic devices. In the second part, we studied how PATCl, PFATCl, and their mixture phase separate with octadecyltrichlorosilane (OTS) molecules in various ratios. The way to improve phase separation was studied modifying aromatic ring to ring as well as aromatic-aliphatic interactions. OTS island size and coverage are shown to be smaller with the aromatic phase that involves stronger ring to ring interactions, i.e., attractive interactions between the phenyl species by mixing phenyl and pentafluoro-phenyl rings. The best phase separation is obtained with PFATCl as the aromatic molecule. If nanoislands of aromatic molecules could not be observed in these experiments, we show that they are attainable by mixing OTS and aromatic small organotriethoxysilanes whose grafting kinetics is slower. These results pave the way to the control improvement of the composition and nanostructuration of SAMs, essential for their further use within molecular devices.

Synthesis, post-modification and self-assembled thin films of pentafluorostyrene containing block copolymers

Block copolymers consisting of a pentafluorostyrene (PFS) block and a hydrophilic block were synthesized by RAFT polymerisation. The hydrophilic blocks consist of methacrylate derivatives, 4-hydroxystyrene or 4-vinylpyridine monomers. The block copolymers were obtained with narrow molecular weight distributions and the molecular weights were in good agreement with the theoretical values. In addition, a model thiol was reacted with the PFS moieties of the block copolymers. This polymer–analogous reaction was performed under ambient conditions in high yields resulting quantitatively in para-substitution of the pentafluorophenyl rings. Finally, thin films consisting of block copolymers that showed strong phase-segregation behaviour and ordered nanostructured surfaces consisting of both blocks were obtained.

Conformations of Silica-Bound (Pentafluorophenyl)propyl Groups Determined by Solid-State NMR Spectroscopy and Theoretical Calculations

The conformations of (pentafluorophenyl)propyl groups (-CH(2)-CH(2)-CH(2)-C(6)F(5), abbreviated as PFP), covalently bound to the surface of mesoporous silica nanoparticles (MSNs), were determined by solid-state NMR spectroscopy and further refined by theoretical modeling. Two types of PFP groups were described, including molecules in the prone position with the perfluorinated aromatic rings located above the siloxane bridges (PFP-p) and the PFP groups denoted as upright (PFP-u), whose aromatic rings do not interact with the silica surface. Two-dimensional (2D) (13)C-(1)H, (13)C-(19)F and (19)F-(29)Si heteronuclear correlation (HETCOR) spectra were obtained with high sensitivity on natural abundance samples using fast magic angle spinning (MAS), indirect detection of low-gamma nuclei and signal enhancement by Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence. 2D double-quantum (DQ) (19)F MAS NMR spectra and spin-echo measurements provided additional information about the structure and mobility of the pentafluorophenyl rings. Optimization of the PFP geometry, as well as calculations of the interaction energies and (19)F chemical shifts, proved very useful in refining the structural features of PFP-p and PFP-u functional groups on the silica surface. The prospects of using the PFP-functionalized surface to modify its properties (e.g., the interaction with solvents, especially water) and design new types of the heterogeneous catalytic system are discussed.

Synthesis and Characterization of Novel Perylenediimide-Cored Dendrimer with Fluorinated Shell

A perylenediimide-based dendrimer, PDI-F, was designed and synthesized for application as red host emitter in nondoped organic light-emitting diodes. PDI-F was designed with perylenediimide as the luminescence core and pentafluorophenyl rings as the surface groups. The dendrimer molecule constructed in this way is bulky and nonplanar. PDI-F exhibits good solubility in common organic solvents and is suitable for wet methods such as spin coating to make thin films. All new compounds of the intermediates and the target dendrimer were characterized by 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. In addition, the ultraviolet (UV) absorption and fluorescence (FL) of PDI-F were measured and discussed. To the best of our knowledge, this is the first report of dendrimer PDI-F.

Five-coordinate pentafluorobenzothiolate osmium(IV) complexes [Os(SC 6F 5) 4(P(C 6H 4X-4) 3)] (X = OCH 3, CH 3, F, Cl or CF 3): Solid and solution structural characterization

The reactions of OsO 4 with excess of HSC 6F 5 and P(C 6H 4X-4) 3 in ethanol afford the five-coordinate compounds [Os(SC 6F 5) 4(P(C 6H 4X-4) 3)] where X = OCH 3 1a and 1b, CH 3 2a and 2b, F 3a and 3b, Cl 4a and 4b or CF 3 5a and 5b. Single crystal X-ray diffraction studies of 1 to 5 exhibit a common pattern with an osmium center in a trigonal-bipyramidal coordination arrangement. The axial positions are occupied by mutually trans thiolate and phosphane ligands, while the remaining three equatorial positions are occupied by three thiolate ligands. The three pentafluorophenyl rings of the equatorial ligands are directed upwards, away from the axial phosphane ligand in the arrangement “3-up” (isomers a). On the other hand, 31P{ 1H} and 19F NMR studies at room temperature reveal the presence of two isomers in solution: The “3-up” isomer ( a) with the three C 6F 5-rings of the equatorial ligands directed towards the axial thiolate ligand, and the “2-up, 1-down” isomer ( b) with two C 6F 5-rings of the equatorial ligands directed towards the axial thiolate and the C 6F 5-ring of the third equatorial ligand directed towards the axial phosphane. Bidimensional 19F– 19F NMR studies encompass the two sub-spectra for the isomers a (“3-up”) and b (“2-up, 1-down”). Variable temperature 19F NMR experiments showed that these isomers are fluxional. Thus, the 19F NMR sub-spectra for the “2-up, 1-down” isomers ( b) at room temperature indicate that the two S-C 6F 5 ligands in the 2-up equatorial positions have restricted rotation about their C–S bonds, but this rotation becomes free as the temperature increases. Room temperature 19F NMR spectra of 3 and 5 also indicate restricted rotation around the Os–P bonds in the “2-up, 1-down” isomers ( b). In addition, as the temperature increases, the 19F NMR spectra tend to be consistent with an increased rate of the isomeric exchange. Variable temperature 31P{ 1H} NMR studies also confirm that, as the temperature is increased, the a and b isomeric exchange becomes fast on the NMR time scale.

Single and Mixed Self-Assembled Monolayers of Phenyl Species on SiO2 with Various Ring to Ring Interactions

AbstractWe studied the formation of phenylalkyltrichlorosilane self-assembled monolayers on native oxide covered silicon. After a first chemisorption step in the monolayer growth, the presence of the short alkyl chain (3-4 carbon atoms) is responsible for a second growth step which corresponds to the arrangement between molecules. We found that this packing step is accelerated by replacing phenyl by pentafluoro-phenyl rings, possibly due to quadrupolar interactions between fluorinated cycles. Furthermore we demonstrate that mixing phenyl and pentafluoro-phenyl molecules leads to an even faster packing step which is accounted for by hydrogen bonding CH...FC in a face to face phenyl/pentafluoro-phenyl arrangement. We believe these results allow improving charge delocalization over conjugated molecular domains. In a second part, we studied the phase separation between phenyl-alkyltrichlorosilane and octadecyltrichlorosilane (OTS) molecules. Improving the phase separation was studied using ring to ring interactions afore-analyzed. We show phase separation is improved and OTS islands are smaller with phenyl species that involve stronger ring to ring interactions. The best case is obtained with mixing phenyl and pentafluoro-phenyl rings using hydrogen bonds for packing together the aromatic species. These results demonstrate improved control of SAM composition and morphology essential to further use the obtained islands for building molecular devices.

Polyphenylene Dendrimers with Pentafluorophenyl Units: Synthesis and Self-Assembly

A series of polyphenylene dendrimers (PDs) incorporating additional pentafluorophenyl units have been synthesized. A key building block thereby is the tetrakis(pentafluorophenyl)cyclopentadienone, which serves as the end-capper for making the outer shells of the dendrimers. The variation of the peripheral pentafluorophenyl content was varied using desymmetrized tetraphenylmethane cores for the divergent construction of the dendrimers. The self-assembled nanostructures, prepared by drop-casting solutions of the second-generation species on highly oriented pyrolytic graphite (HOPG), have been investigated by tapping mode atomic force microscopy (AFM). Besides isotropic globular aggregates and percolated networks of nanometer size anisotropic objects, the herein presented dendrimers self-organize into micrometer long nanofibers. The formation of a certain morphology depends upon the amount of pentafluorophenyl rings at the periphery of the dendrimers. Furthermore, it has been observed that by the progressive blending of two dendrimers with different peripheral functionalities a certain control over the length of the formed nanofibers is possible.

The Synthesis, Molecular Structures, and Supramolecular Architecture of Amine Adducts of Bis(pentafluorophenyl)zinc

A series of eight adducts of the form (RR‘R‘ ‘N)2·Zn(C6F5)2 have been prepared through treatment of the Lewis acid Zn(C6F5)2 with 2 equiv of the corresponding amine (R = tBu or CH2Ph, R‘ = R‘ ‘ = H; R = R‘ = Me or CH2Ph, R‘ ‘ = H; R = Me, R‘ = CH2Ph, R‘ ‘ = H; RR‘ = cyclo-C4H8 or cyclo-C5H10, R‘ ‘ = H; R = R‘ = Me, R‘ ‘ = CH2Ph). The solid-state structures of all eight compounds have been elucidated by single-crystal X-ray diffraction. In each case the geometry about the zinc atom is essentially tetrahedral. However, there is considerable variation in the supramolecular architectures in the solid state. A number of types of noncovalent interactions are observed including phenyl−pentafluorophenyl stacking, X−H···F−C contacts, and offset face-to-face contacts between pentafluorophenyl rings, giving rise to one-, two-, and three-dimensional supramolecular structures. In our examples we find that no one intermolecular interaction predominates.