Perfluoroaryl Groups Research Articles

Perfluoroaryl⋯aryl interaction: The most important subset of π -hole⋯ π bonding

The perfluoroaryl⋯aryl interaction, the most important subset of π-hole⋯π bonding, refers to the attractive stacking interaction between a perfluoroaryl group and an aryl group. In contrast to the aryl⋯aryl interaction with the same size, the much stronger perfluoroaryl⋯aryl interaction has its own characteristics and applications. A brief history of the development of the perfluoroaryl⋯aryl interaction was given first in this review, followed by an overview of the state-of-the-art of the nature of the perfluoroaryl⋯aryl interaction. Much attention was paid to the application of the perfluoroaryl⋯aryl interaction both in the traditional research fields such as crystal engineering and organic luminescent materials and in the hot research fields such as photovoltaics materials and biological engineering. It is believed that this timely and comprehensive review provides a foundation and guide for the future development and application of the perfluoroaryl⋯aryl interaction.

Exciton-Scissoring Perfluoroarenes Trigger Photomultiplication in Full Color Organic Image Sensors.

We report an unprecedented but useful functionality of perfluoroarenes to enable exciton scissoring in photomultiplication-type organic photodiodes (PM-OPDs). Perfluoroarenes that are covalently connected to polymer donors via photochemical reaction enable us to demonstrate high external quantum efficiency and B-/G-/R-selective PM-OPDs without the use of conventional acceptor molecules. We investigated the operation mechanism of the suggested perfluoroarene-driven PM-OPDs, "How can covalently bonded polymer donor:perfluoroarene PM-OPDs perform as effectively as polymer donor:fullerene blend-based PM-OPDs?". By employing a series of arenes and conducting steady-state/time-resolved photoluminescence and transient absorption spectroscopy analyses, we find that interfacial band bending between the perfluoroaryl group and polymer donor is responsible for exciton scissoring and subsequent electron trapping, which induces photomultiplication. Owing to the acceptor-free and covalently interconnected photoactive layer in the suggested PM-OPDs, superior operational and thermal stabilities were observed. Finally, we demonstrated finely patterned B-/G-/R-selective PM-OPD arrays that enable the construction of highly sensitive passive matrix-type organic image sensors. This article is protected by copyright. All rights reserved.

5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin as a Functional Platform for Peptide Stapling and Multicyclisation.

Polyfluorinated aromatic reagents readily react with thiolates via nucleophilic aromatic substitution (SN Ar) and provide excellent scaffolds for peptide cyclisation. Here we report a robust and versatile platform for peptide stapling and multicyclisation templated by 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, opening the door to the next generation of functional scaffolds for 3D peptide architectures. We demonstrate that stapling and multicyclisation occurs with a range of non-protected peptides under peptide-compatible conditions, exhibiting chemoselectivity and wide-applicability. Peptides containing two cysteine residues are readily stapled, and the remaining perfluoroaryl groups permit the introduction of a second peptide in a modular fashion to access bicyclic peptides. Similarly, peptides with more than two cysteine residues can afford multicyclic products containing up to three peptide 'loops'. Finally, we demonstrate that a porphyrin-templated stapled peptide containing the Skin Penetrating and Cell Entering (SPACE) peptide affords a skin cell penetrating conjugate with intrinsic fluorescence.

Synthesis of perfluoroaryl sulfides at electron-poor arenes via an SNAr step with an unexpected mechanism

Perfluoroaryl groups are a recurring motif in materials and pharmaceutical chemistry. Here, we report a method to couple perfluoroarenes and thiols to yield perfluoroaryl sulfides via a nucleophilic aromatic substitution (SNAr) step. The discussed synthesis strategy can be applied at ambient conditions or conducted as industrial processes with either ball mill or flow techniques. In addition, it tolerates a large variety of functional groups, thus allowing it to be used for late-stage functionalization. The nature of the proposed reaction is a nucleophilic attack of a thiol group at an electron-poor aromatic ring, which is expected to feature a stepwise mechanism involving a “Meisenheimer complex” as an intermediate. However, computational simulations predict a concerted mechanism for the process. The preference for a concerted or stepwise SNAr pathway is rationalized through a Marcus-type argument considering the relative stability of the reactant, intermediate, and product species.

Novel fluorescent nanofibrous polyether template developed by SNAr polymerization of fluoroaryl-containing 1, 3, 4-oxadiazole: Photophysical properties, mesogenic phases and self-assembly

Supramolecular organogels that respond to external stimuli have been extensively investigated; however, assembling a liquid crystal-based fluorescent gel with an efficient thermoreversible activity is a difficult challenge. Various pentafluorobenzene-containing aromatic adducts have been synthesized via nucleophilic aromatic substitution (SNAr), which is highly regio-selective to para positions. In order to prepare calamitic liquid crystals, those pentafluorobenzene-functionalized 1, 3, 4-oxadiazole aromatic adducts are a perfect choice. Novel fluoroaryl(FA)-containing 1, 3, 4-oxadiazole (Ox) main-chain polyether (PE) (FAOx@PE) were synthesized employing in situ SNAr as a practical technique for the synthesis of fluorescent liquid crystals with perfluoroaryl groups and ether bonds. The perfluoroaryl group was inserted into the 1, 3, 4-oxadiazole compound by the reaction of potassium pentafluorobenzoate and tetrazole-containing biphenyl using a DCC-assisted decarboxylating coupling. Using 1H/13C/19F NMR and FTIR spectroscopic techniques, the chemical structure of FAOx@PE was determined. Differential scan calorimeter (DSC), X-ray diffraction (XRD) and polarization microscope (POM) were utilized to examine the liquid crystal mesophases. The absorption and emission spectral patterns were detected in the ultraviolet–visible range demonstrating solvatochromic activity. Scanning electron microscope (SEM) was employed to inspect the nanofibrous morphology of FAOx@PE organogel.

Pentafluorophenylphosphonic Acid as a New Building Block for Molecular Crystal Fabrication

Molecular crystals have been prepared from pentafluorophenylphosphonic acid (4). These include 2C6F5PO3H2·H2O (4·4·H2O), [(C6F5PO3H–)(H3O+)]·C6F5PO3H2 (4·4–·H3O+), [(C6F5PO3H–)(NH4+)]·C6F5PO3H2 (4·4–·NH4+), [(C6F5PO3H–)(Me2NH2+)] (4–·DMA+), [(C6F5PO3H–)(Me2NH2+)]·H2O (4–·DMA+·H2O), [(C6F5PO3H–)(Me2NH2+)]·C6F5PO3H2 (4·4–·DMA+), [(C6F5PO3H–)(Me2NH2+)0.5(NH4+)0.5] (4–·DMA+·NH4+), and [(C6F5PO3H–)(+H3NCH2CO2H)] (4–·Gly+), where DMA+ = dimethylammonium and Gly+ = glycinium. All of the assemblies incorporate an ammonium cation, a water molecule, or a hydronium ion in their structure, and these included species act as adhesive agents. They interact via O/N–H···O hydrogen bonds and C–H···O contacts with PO3H2 or PO3H– moieties located in polar sheets, forcing the building blocks to assemble with a 2D layered arrangement. The robustness of this arrangement is reminiscent of that observed in metal arylphosphonates and guanidinium sulfonates, yet the architectures described herein differ significantly from the second family of compounds in two aspects: the lack of puckering of the layers and the absence of void spaces to accommodate solvent molecules. Interestingly, however, just as in guanidinium sulfonates, two structural types have been recognized depending on the size of the included species: a single-layer stacking motif and a bilayer stacking motif. Even though hydrogen bonding is the prevailing interaction in these systems, the use of perfluoroaryl groups is also central, as these moieties bring about weak C–F···π, π···π, C–F···F–C, C–F···H–C, and O/N–H···F–C interactions that help to increase the cohesion of the nonpolar regions. As a result, new architectures are created that significantly differ in some cases from those prepared from phenylphosphonic acid. However, the weakness of perfluoroaryl-based interactions is also their strength, as these interactions are sufficiently flexible to allow changes in the organization of the aromatic groups in response to changes (ionization) occurring in the polar regions, as observed in the structures of 4·4·H2O and 4·4–·H3O+. This situation is quite unusual and may be regarded as some kind of acidity-modulated polymorphism. The work presented here broadens the knowledge on molecular crystal formation with arylphosphonic acids, a research area largely dominated by carboxylic and sulfonic acids. Also, the computational evaluation of 4·4·H2O and 4·4–·H3O+ described in this report suggests that this family of fluorinated compounds may show interesting prospects as molecular semiconductors, a research area that is currently receiving increased attention.

Evaluating the Impact of Fluorination on the Electro-optical Properties of Cross-Conjugated Benzobisoxazoles.

Six 2,4,6,8-tetrarylbenzo[1,2- d:4,5- d']bisoxazoles (BBOs) were synthesized: three bearing phenyl substituents at the 2- and 6-positions and three bearing perfluorophenyl groups at those positions. The influence of perfluoro-aryl group substitution on the physical, optical, and electronic properties of 2,4,6,8-tetrarylbenzo[1,2- d:4,5- d']bisoxazoles (BBO) was evaluated using both experimental and theoretical methods. The density functional theory (DFT) model was found to be well-matched to the experimental optical data, as evidenced by the UV-vis spectra. Both cyclic voltammetry (CV) and ultraviolet photoelectron spectroscopy (UPS) were used to determine the position of the HOMO with varying results. The values obtained by CV were deeper than those obtained via UPS and correlated well with the theoretical calculations. However, the UPS values were more consistent with the expected outcomes for a system with segregated frontier molecular orbitals (FMOs). The UPS results are also supported by the electrostatic potential maps, which indicate that the electron density within the LUMO and HOMO is nearly completely localized along the 2,6- or 4,8-axis, respectively. The summation of the results indicates that strongly electron-withdrawing groups can be used to selectively tune the LUMO level with minor perturbation of the HOMO, something that is challenging to accomplish in typical donor-acceptor systems.

Click and Multicomponent Reactions Work Together for Polymer Chemistry

AbstractThis article investigates the current combinations of click and multicomponent reactions (MCRs) to produce complex macromolecular structures through polymer–polymer conjugation or hetero‐functionalization of polymers. The click and MCRs display similar features covering the equimolarity, fast time scale, high yields, stable compounds, modular, orthogonal and single reaction trajectory. Of classical click reactions, CuAAC, Diels–Alder, thiol‐ene (‐yne), and nucleophilic substitution on perfluoroaryl groups reactions are combined with MCRs, namely, Passerini, Ugi, or Biginelli reactions. It should be noted that these combinations can afford the target polymer structures, which are not attainable by employing one of these reactions alone.

On the ambiguity of 1,3,2-benzodiazaboroles as donor/acceptor functionalities in luminescent molecules

A series of 1,3-bis(perfluoroaryl)-2-(hetero)aryl-1,3,2-benzodiazaboroles, 1,3-(F)Ar2-2-Ar-1,3,2-N2BC6H4 (Ar = Ph, (F)Ar = C6F5 5; Ar = Ph, (F)Ar = 4-C5F4N 6; Ar = Ph, (F)Ar = 4-NCC6F4 7; Ar = 2-C4H3S, (F)Ar = C6F5 8; Ar = 2-C4H3S, (F)Ar = 4-C5F4N 9; Ar = 2-C4H3S, (F)Ar = 4-NCC6F4 10), were synthesised by cyclocondensation of the adducts PhBBr2·PPh3 or 2-thienylBBr2·PPh3 with N,N'-bis(perfluoroaryl)-o-phenylenediamines in the presence of 2,2,6,6-tetramethylpiperidine. Similar treatments of the PPh3 adducts of 4-(1',3'-diethyl-1',3',2'-benzodiazaborolyl)-phenyldibromoborane with the corresponding diamines gave rise to the push-pull compounds, C6H4(NEt)2B-1,4-C6H4-B(N(F)Ar)2C6H4 ((F)Ar = C6F5 11; 4-C5F4N 12) and C6H4(NEt)2B-2,5-C4H2S-B(N(F)Ar)2C6H4 ((F)Ar = C6F5 13; 4-C5F4N 14). The X-ray structures of 8, 11, 12 and 13 were determined. Electronic structure calculations reveal that the LUMOs are located at the perfluoroaryl groups in 5-14; thus the fluorinated benzodiazaborolyl groups are considered as electron-withdrawing moieties. These moieties differ from alkylated benzodiazaborolyl groups which are regarded as donors. The emission spectra for 5-14 show charge transfer bands with significant solvatochromism and large Stokes shifts (6100-12,500 cm(-1) in cyclohexane and 8900-15,900 cm(-1) in CH2Cl2). The emissions of the benzodiazaboroles, 5-10, arise from a different charge transfer (CT) process to the local charge transfer (LCT) process typically found in many fluorescent benzodiazaboroles. This novel remote charge transfer (RCT) process involving the perfluoroaryl groups is supported by CAM-B3LYP computations. The push-pull systems 11-14 here give fluorescent emissions with moderate to high fluorescence quantum yields (65-97%) that arise from the usual LCT process only.

Investigations of the Tautomeric Equilibria between Phosphane Oxides and Their Corresponding Phosphinous Acids Bearing Electron‐Withdrawing Perfluoroaryl Groups

AbstractThe unusual form of a phosphinous acid can be stabilized by strongly electron‐withdrawing substituents such as trifluoromethyl and pentafluoroethyl groups. The less electron‐withdrawing pentafluorophenyl group favors the phosphane oxide tautomer (Rf)2P(O)H in the solid state, whereas in solution a solvent‐dependent equilibrium with the phosphinous acid tautomer (Rf)2POH is observed. The increasing donating ability of the solvent leads to an increasing amount of the corresponding phosphinous acid tautomer. In accord with quantum chemical calculations, the electron‐withdrawing effects of the p‐tetrafluoropyridyl and 2,4‐bis(trifluoromethyl)phenyl groups exceed the pentafluorophenyl group and should therefore be ideally suited to stabilize the corresponding phosphinous acid tautomer (Rf)2POH. The syntheses of bis(tetrafluoropyridyl)‐ and bis[2,4‐bis(trifluoromethyl)phenyl]phosphane oxide enabled the investigation of the solvent‐dependent tautomerism by NMR spectroscopy. Introduction of the tetrafluoropyridyl group shifts the tautomeric equilibrium significantly towards the phosphinous acid. Surprisingly, the comparably electron‐withdrawing but more bulky 2,4‐bis(trifluoromethyl)phenyl group favors the oxide tautomer. The experimental results have been confirmed by DFT calculations. In summary, electron‐withdrawing substituents stabilize the phosphinous acid tautomer, whereas it is destabilized by space‐demanding groups by an increased C–P–C angle.

Use of perfluoro groups in nucleophilic 18F‐fluorination

AbstractSubstrates with leaving groups that contained perfluoro moieties were investigated in labelling chemistry in order to exploit their properties to improve reactivity and purification. [18F](Fluoromethyl)benzene was used as the model target compound. Precursors containing perfluoroalkyl and perfluoroaryl sulfonate moieties were subjected to nucleophilic 18F‐fluorination, and the impact of perfluoro groups on the substitution reaction and product purification was investigated. [18F]Fluoride interacted with perfluoroalkyl chains, precluding nucleophilic substitution. When perfluoroaryl groups were used, the substitution proceeded, and the separation of product was explored. The radiolabelled product was obtained in 32% analytical yield and the radiochemical purity was increased to approximately 77% using fluorous solid phase extraction purification. Copyright © 2009 John Wiley & Sons, Ltd.

Some transition metal complexes derived from mono- and di-ethynyl perfluorobenzenes

Transition metal alkynyl complexes containing perfluoroaryl groups have been prepared directly from trimethylsilyl-protected mono- and di-ethynyl perfluoroarenes by simple desilylation/metallation reaction sequences. Reactions between Me(3)SiC[triple bond, length as m-dash]CC(6)F(5) and RuCl(dppe)Cp' [Cp' = Cp, Cp*] in the presence of KF in MeOH give the monoruthenium complexes Ru(C[triple bond, length as m-dash]CC(6)F(5))(dppe)Cp' [Cp' = Cp (); Cp* ()], which are related to the known compound Ru(C[triple bond, length as m-dash]CC(6)F(5))(PPh(3))(2)Cp (). Treatment of Me(3)SiC[triple bond, length as m-dash]CC(6)F(5) with Pt(2)(mu-dppm)(2)Cl(2) in the presence of NaOMe in MeOH gave the bis(alkynyl) complex Pt(2)(mu-dppm)(2)(C[triple bond, length as m-dash]CC(6)F(5))(2) (). The Pd(0)/Cu(i)-catalysed reactions between Au(C[triple bond, length as m-dash]CC(6)F(5))(PPh(3)) and Mo( identical withCBr)(CO)(2)Tp* [Tp* = hydridotris(3.5-dimethylpyrazoyl)borate], Co(3)(mu(3)-CBr)(mu-dppm)(CO)(7) or IC[triple bond, length as m-dash]CFc [Fc = (eta(5)-C(5)H(4))FeCp] afford Mo( identical withCC[triple bond, length as m-dash]CC(6)F(5))(CO)(2)Tp* (), Co(3)(mu(3)-CC[triple bond, length as m-dash]CC(6)F(5))(mu-dppm)(CO)(7) () and FcC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC(6)F(5) (), respectively. The diruthenium complexes 1,4-{Cp'(PP)RuC[triple bond, length as m-dash]C}(2)C(6)F(4) [(PP)Cp' = (PPh(3))(2)Cp (); (dppe)Cp (); (dppe)Cp* ()] are prepared from 1,4-(Me(3)SiC[triple bond, length as m-dash]C)(2)C(6)F(4) in a manner similar to that described for the monoruthenium complexes -. The non-fluorinated complexes 1,4-{Cp'(PP)RuC[triple bond, length as m-dash]C}(2)C(6)H(4) [(PP)Cp' = (PPh(3))(2)Cp (); (dppe)Cp (); (dppe)Cp* ()], prepared for comparison, are obtained from 1,4-(Me(3)SiC[triple bond, length as m-dash]C)(2)C(6)H(4). Spectro-electrochemical studies of the ruthenium aryl and arylene alkynyl complexes - and -, together with DFT-based computational studies on suitable model systems, indicate that perfluorination of the aromatic ring has little effect on the electronic structures of these compounds, and that the frontier orbitals have appreciable diethynylphenylene character. Molecular structure determinations are reported for the fluoroaromatic complexes , , , and .

Polyfluorinated arylnitrosamines

N-Methyl-, N-n-butyl-, N-t-butylperfluoroarylamines undergo nitrosation with nitrous acid to give the corresponding N-nitroso derivatives. Perfluoroaryl groups were selected from the benzene, indane, biphenyl, naphthalene and pyridine series. According to 1H and 19F NMR spectra, N-nitroso-N-methyl derivatives of polyfluoroarenes consist of E and Z isomers with the former prevailing. The more bulky n-butyl group promotes an increase in the formation of Z isomers. Only Z isomers have been obtained from N-t-butyl derivatives of perfluorinated 4-toluidine and 4-aminopyridine. The structure of the Z isomer of N-nitroso-N-methylperfluoro-4-toluidine is confirmed by X-ray data.

Highly Lewis Acidic Bifunctional Organoboranes

Chelating Lewis acids have not been developed to the same degree as multidentate Lewis bases. Nonetheless, such compounds have attracted interest due to their potential for the enhanced activation of basic substrates and the selective binding of anions. Organodiboryl compounds form a class of bidentate Lewis acids which have a long, but relatively underdeveloped history. Many examples exist where donor groups on boron serve to stabilize the Lewis acid centers. More recently, advances in the chemistry of diboryls with highly Lewis acidic boron centers substituted with perfluoroaryl groups have been made. In particular, compounds of general formula (F5C6)2B−linker−B(C6F5)2 have been prepared and their chemistry examined. In this Microreview, we survey the classes of bifunctional boron Lewis acids known, including their synthesis, properties and anion binding chemistry. Particular emphasis is placed on the role these Lewis acids play in olefin polymerization catalyst generation from simple metallocene precursors.

Arylation of polyamines by perfluoroarenes

The conditions of selective mono- and diarylation of diamines, and di- and triarylation of triamines by perfluoroarenes are described. The introduction of four perfluoroaryl groups in cyclam and two groups in dioxocyclam has been carried out.

Nucleophiles useful for the transfer of fluorinated moieties to organic and inorganic substrates

The reactions of R fSi(CH 3) 3 (Rf = CF 3, C 2F 5, C 3F 7) with a variety of fluorinated organic and inorganic substrates containing a sulfur- or carbon-oxygen double bond have received some attention [1,2]. In order to extend our work, we have synthesized several interesting new as well as previously reported perfluoroalkyl and perfluoroaryl silanes. These reactive materials can be used effectively to replace directly active fluorine atoms bound to carbon with a number of fluorinated moieties, e.g., polyfluorinated polynitrogen compounds containing perfluoroaryl groups are prepared simply by using these silyl reagents. This powerful technique provides a direct route to previously known compounds, thus making them readily available for further study, as well as to a variety of heretofore unknown compounds. The reaction chemistry of these silanes with carbon-fluorine bonds will be discussed, and characterization of selected products will be presented.

Condensation of αβ-unsaturated amines with perfluoroarenes

Condensation of αβ-unsaturated amines (enamines, keten ON-acetals, ynamines) with perfluoroarenes (perfluorobenzene, perfluorotoluene, bromopentafluorobenzene, perfluoropyridine) leads to the formation of ketones, esters, and amines α-substituted by a perfluoroaryl group. In the case of enamines, C-arylation can be followed by intramolecular N-arylation, giving fluorinated tetrahydrocarbazoles which can then be dehydrogenated by chloranil to give fluorinated carbazoles.