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The oxidation of benzene, fluorobenzene, chlorobenzene, and phenol in the presence of O2 and N2O on HZSM-5 type zeolite with Si/Al = 24 was studied by EPR spectroscopy. It was shown that the thermal decomposition of nitrous oxide on zeolite forms molecular and chemisorbed atomic oxygen. It was found that the catalytic oxidation of benzene, fluorobenzene, chlorobenzene, and phenol under the action of О2 and N2O proceeds at Lewis acid sites and leads to the formation of phenoxyl radical cations with characteristic g factors and hyperfine structure of the EPR spectrum.

The pressure dependence of the solubility of hydrophobic solutes in aqueous solutions is equivalent to volume changes upon hydrophobic hydration. This phenomenon has been attributed to the packing effects induced by the van der Waals volume difference between the solute and water. However, the volume changes may also be related to the chemical properties of the solute. In this study, we investigated hydrophobic hydration using a series of halogenated benzenes. Solution density measurements revealed negative volume changes for benzene, fluorobenzene, and chlorobenzene, whereas those for bromobenzene and iodobenzene were positive. Subsequent volumetric analyses demonstrated that the relationship between the excess particle number for hydration water and the van der Waals volume for bromobenzene and iodobenzene significantly deviated from the universal line for hydrophobic solutes. This behavior suggests that the volume changes are due to factors other than the packing effect with bromo and iodine functional groups acting as modulators of the hydration structure, resulting in enhanced water depletion.

International audience; The photochemical activation of dimagnesium(I) compounds, and subsequent high yielding, regioselective reactions with inert arenes are reported. Irradiating benzene solutions of [{((Ar)Nacnac)Mg}(2)] ((Ar)Nacnac=[HC(MeCNAr)(2)](-); Ar=2,6-diisopropylphenyl (Dip) or 2,4,6-tricyclohexylphenyl (TCHP)) with blue or UV light, leads to double reduction of benzene and formation of the "Birch-like" cyclohexadienediyl bridged compounds, [{((Ar)Nacnac)Mg}(2)(mu-C6H6)]. Irradiation of [{((Dip)Nacnac)Mg}(2)] in toluene, and each of the three isomers of xylene, promoted completely regio- and chemo-selective C-H bond activations, and formation of [((Dip)Nacnac)Mg(Ar ')] (Ar '=meta-tolyl; 2,3-, 3,5- or 2,5-dimethylphenyl), and [{((Dip)Nacnac)Mg(mu-H)}(2)]. Fluorobenzene was cleanly defluorinated by photoactivated [{((Dip)Nacnac)Mg}(2)], leading to biphenyl and [{((Dip)Nacnac)Mg(mu-F)}(2)]. Computational studies suggest all reactions proceed via photochemically generated magnesium(I) radicals, which reduce the arene substrate, before C-H or C-F bond activation processes occur.

By the example of 4-fluorobenzene-1-thiolate (p-FTP) films on Au(111), we show that a long-term post-preparation storage can improve significantly the quality of fluorinated aromatic self-assembled...

Quinoxaline (Qx) has an easily modifiable structure, which allows for fine-tuning its properties through optimizing the length of side chains and the kinds of aromatic rings in conjugated side chains. Qx based polymer PBDTT-ffQx with alkoxy substituted fluorobenzene side chains shows a power conversion efficiency (PCE) of 8.47% in nonfullerene solar cells. In this work, we change the alkoxy substituted fluorobenzene side chains to alkyl substituted fluorothiophene in the Qx unit and employ the benzodithiophene (BDT) unit with different lengths of alkyl thiophene side chains to obtain two new Qx based polymers, named TTFQx-T1 and TTFQx-T2, respectively. The TTFQx-T1:ITIC blend film has clear nanoscale phase separation and a suitable domain size, and the device with the TTFQx-T1:ITIC blend film shows lower geminate recombination and higher charge mobility than those with TTFQx-T2:ITIC. Therefore, the TTFQx-T1:ITIC based device exhibits a higher PCE of 10.52% than that based on the TTFQx-T2:ITIC blend with a moderate PCE of 7.22%. The inverted devices from TTFQx-T1:ITIC blends with a larger active area of 16 mm2 than the conventional device (4.5 mm2) show a good PCE of 9.21%. The results highlight that the alkyl lengths and the kinds of aromatic rings in side chains are significant for the development of high performance photovoltaic polymers. Optimizing the conjugated side chains of Qx based polymers is an efficient way to improve photovoltaic properties, and Qx based polymers are potential candidates for fabricating highly efficient polymer solar cells.

The radiolytic oxidation of aromatic compounds in dilute aqueous solution is due to the electrophilic strength of the •OH that results from the radiolysis of water. This radical is preferentially added to the electron-rich centers in aromatic rings. Therefore, studies of the charge distribution of the hydroxycyclohexadienyl radicals produced by the addition of the •OH to the aromatics can provide information about their charge distribution. In the present work, the radiolytic oxidation reaction of fluorobenzene, chlorobenzene, bromobenzene, and iodobenzene with the •OH in diluted aqueous solutions was studied. The identification and quantification of the radiolytic products thus formed were carried out utilizing HPLC. The yields found for fluorobenzene, chlorobenzene, bromobenzene, and iodobenzene were 0.609, 0.527, 0.508, and 0.501 μmol/J, respectively. The electron density distribution in fluorobenzene, chlorobenzene, and bromobenzene was in the following order: for para > ortho > meta » ipso; however, in iodobenzene, there is a higher electron density in the "ortho" position than in the "para" position. From the total reaction rates for the halobenzenes with the •OH, the partial rate constants were obtained for the reaction of the •OH with each of the positions in the halobenzenes.

In this paper, a non-fullerene electron acceptor, SF(DPPFB)4, which owns a spirobifluorene core and four diketopyrrolopyrrole (DPP) arms end capped by 4-fluorobenzene, is designed and synthesized for solution-processable organic solar cells (OSCs). SF(DPPFB)4 shows similar absorption bands as those of its non-fluorinated parent compound, SF(DPPB)4. However, the terminal fluorine atoms reduce the energy levels of SF(DPPFB)4, especially, its lowest unoccupied molecular orbital level decreases by 0.04 eV than that of SF(DPPB)4, which enlarges the energy offset between the electron donor and acceptor, favorable for the dissociation of excitons in OSCs. Moreover, the fluorination improves the electron mobility of SF(DPPFB)4. Thus, the OSCs with poly(3-hexylthiophene) as the electron donor and SF(DPPFB)4 as the electron acceptor can provide a maximum power conversion efficiency of 4.42%, with a lifted short-circuit current (Jsc) of 8.48 mA cm−2.

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAACMe] (cAACMe=:C(CMe2)2(CH2)NAr, Ar=2,6-iPr2C6H3) with H2SiI2 in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAACMe)2Si:.]+I− (1), which features a cationic cAAC–silicon(I) radical, and [cAACMe−H]+I−. In addition, the reaction of the NHC–iodosilicon(I) dimer [IAr(I)Si:]2 (IAr=:C{N(Ar)CH}2) with 4 equiv of IMe (:C{N(Me)CMe}2), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(IMe)2SiH]+I− (2) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the CAr−H bond activation product [1-F-2-IMe-C6H4]+I− (3). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1. Compounds 1–3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography.

Methylaluminoxane (MAO) is a key activator for olefin polymerization catalysts, making its chemistry of ongoing interest. Neutral donors such as octamethyltrisiloxane (OMTS) are effective abstractors of the dimethylaluminum cation, [Me2Al]+, from methylaluminoxane (MAO), and this process can be readily investigated using electrospray ionization mass spectrometry (ESI-MS) in fluorobenzene (PhF) solution. Complementary studies employing 1D and 2D 1H NMR spectroscopic studies in bromobenzene-d5 solution provide details on the extent of ionization vs. donor-acceptor complex formation. DFT studies employing different neutral model precursors and mono- vs. bi-dentate donors shed light on possible mechanisms for ion-pair formation.

Analytical Chemistry, 91 (16), ISSN:1520-6882, ISSN:0003-2700

Rotational spectra for the normal isotopic species and for six additional isotopologues of the 1,2-difluorobenzene⋯acetylene (C6H4F2⋯HCCH) weakly bound dimer have been assigned in the 6–18 GHz region using chirped-pulse Fourier-transform microwave spectroscopy. This is the third complex in a series of fluorinated benzene⋯acetylene dimers. In 1,2-difluorobenzene⋯HCCH, the H⋯π distance (2.725(28) A) is longer by about 0.23 A, and the estimated binding energy (EB = 2.3(6) kJ mol−1) is weaker by about 1.8 kJ mol−1, than in the previously studied fluorobenzene⋯HCCH complex. In addition, in 1,2-difluorobenzene⋯acetylene, HCCH tips ∼46(3)° away from perpendicular to the aromatic ring, with the H nearest the ring moving away from the fluorine atoms along the C2 axis of the monomer, while in the fluorobenzene and benzene complexes HCCH is perpendicular (benzene⋯HCCH) or nearly perpendicular (fluorobenzene⋯HCCH, ∼7° tilt) to the ring plane. Results from ab initio and DFT calculations will be compared to an experimental structure determined from rotational constants for the DCCD and five unique 13C substituted isotopologues.

In a preceding work with dopant assisted-atmospheric pressure photoionization (DA-APPI), an abundant ion at [M + 77](+) was observed in the spectra of pyridine and quinoline with chlorobenzene dopant. This contribution aims to reveal the identity and route of formation of this species, and to systematically investigate structurally related analytes and dopants. Compounds containing N-, O-, and S-lone pairs were investigated with APPI in the presence of fluoro-, chloro-, bromo-, and iodobenzene dopants. Computational calculations on a density functional theory (DFT) level were carried out to study the reaction mechanism for pyridine and the different halobenzenes. The experimental and computational results indicated that the [M + 77](+) ion was formed by nucleophilic aromatic ipso-substitution between the halobenzene radical cation and nucleophilic analytes. The reaction was most efficient for N-heteroaromatic compounds, and it was weakened by sterical effects and enhanced by resonance stabilization. The reaction was most efficient with chloro-, bromo-, and iodobenzenes, whereas with fluorobenzene the reaction was scarcely observed. The calculated Gibbs free energies for the reaction between pyridine and the halobenzenes were shown to increase in the order I < Br < Cl < F. The reaction was found endergonic for fluorobenzene due to the strong C-F bonding, and exergonic for the other halobenzenes. For fluoro- and chlorobenzenes the reaction was shown to proceed through an intermediate state corresponding to [M + dopant](+), which was highly stable for fluorobenzene. For the bulkier bromine and iodine, this intermediate did not exist, but the halogens were shown to detach already during the approach by the nucleophile.

The cationic rhodium complex [Rh(PcPr3)2(η6-PhF)]+[B{3,5-(CF3)2C6H3}4]− (PcPr3 = triscyclopropylphosphine, PhF = fluorobenzene) was used as a catalyst for the hydrogenation of the charge-tagged alkyne [Ph3P(CH2)4C2H]+[PF6]−. Pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS) was used to monitor reaction progress. Experiments revealed that the reaction is first order in catalyst and first order in hydrogen, so under conditions of excess hydrogen the reaction is pseudo-zero order. Alkyne hydrogenation was 40 times faster than alkene hydrogenation. The turnover-limiting step is proposed to be oxidative addition of hydrogen to the alkyne (or alkene)-bound complex. Addition of triethylamine caused a dramatic reduction in rate, suggesting a deprotonation pathway was not operative.

A range of cationic rhodium bisphosphine η6-fluorobenzene (fluorobenzenes = C6H6−nFn, n = 1–3) and related complexes have been synthesized and characterized. These complexes act as useful organometallic precursors for catalysis or further synthetic elaboration. The relative binding affinity of the arene ligands has been investigated using Electrospray Ionisation Mass Spectrometry (ESI–MS) and two different collision-induced dissociation (CID) techniques. The influence of arene fluorination upon arene binding affinity is discussed as well as the comparison of different bis–phosphine ligands with regard to bite angle and phosphine substitution. We show that this simple technique allows fast and easy comparison of the binding affinity of arene ligands to cationic organometallic fragments.

Halogen bonding (XB) non-covalent interactions can be observed in compounds containing chlorine, bromine, or iodine which can form directed close contacts of the type R1-XY-R2, where the halogen X acts as a Lewis acid and Y can be any electron donor moiety including electron lone pairs on hetero atoms such as O and N, or π electrons in olefin double bonds and aromatic conjugated systems. In this work, we present the first evidence for the formation of ionic halogen bonds (IXBs) in the hydration of bromobenzene and iodobenzene radical cations in the gas phase. We present a combined thermochemical investigation using the mass-selected ion mobility (MSIM) technique and density functional theory (DFT) calculations of the stepwise hydration of the fluoro, chloro, bromo, and iodobenzene radical cations. The binding energy associated with the formation of an IXB in the hydration of the iodobenzene cation (11.2 kcal mol-1) is about 20% higher than the typical unconventional ionic hydrogen bond (IHB) of the CHδ+OH2 interaction. The formation of an IXB in the hydration of the iodobenzene cation involves a significant entropy loss (29 cal mol-1 K-1) resulting from the formation of a more ordered structure and a highly directional interaction between the oxygen lone pair of electrons of water and the electropositive region around the iodine atom of the iodobenzene cation. In comparison, the hydration of the fluorobenzene and chlorobenzene cations where IHBs are formed, -ΔS° = 18-21 cal mol-1 K-1 consistent with the formation of less ordered structures and loose interactions. The electrostatic potentials on the lowest energy structures of the hydrated halogenated benzene radical cations show clearly that the formation of an IXB is driven by a positively charged σ-hole on the external side of the halogen atom X along the C-X bond axis. The size of the σ-hole increases significantly in bromobenzene and iodobenzene radical cations which results in strong interaction potentials with the electron lone pairs of the oxygen atom of the water molecules and thus IXBs provide the most stable hydrated structures of the bromobenzene and iodobenzene radical cations. The results clearly distinguish the hydration behaviors resulting from the ionic hydrogen and halogen bonding interactions of fluorobenzene and iodobenzene cations, respectively, and establish the different bonding and structural features of the two interactions.

With 4-fluoro-N,N-dimethylaniline (DMA4F), only a single fluorescence from a locally excited (LE) state is observed, irrespective of solvent polarity, temperature, and excitation wavelength. The relatively small excited state dipole moment mu(e) = 7.3 D confirms the identification as LE. The single exponential fluorescence decays in the nonpolar n-hexane (2.04 ns) and in the strongly polar acetonitrile (5.73 ns) are a further support. Similar results are obtained with 4chloro-N,N-dimethylaniline (DMA4C1), having a chlorobenzene subgroup, a somewhat better electron acceptor than the fluorobenzene moiety in DMA4F. The absence of intra-molecular charge transfer (ICT) with DMA4F is in accord with its large energy gap Delta E(S-1,S-2) of 8300 cm-(1) in n-hexane between the two lowest singlet excited states, which is even larger than that (6300 cm(-1)) of N,N-dirnethylaniline (DMA), for which an LE -> ICT, reaction likewise does not occur. The results with DMA4F are in contradiction with a publication by Fujiwara et al. (Chem. Phys. Lett. 2013, 586, 70), in which the appearance of dual LE + ICT emission is reported for DMA4F in n-hexane and MeCN at room temperature. The ICT/LE fluorescence quantum yield ratio Phi/(ICT)/Phi(LE) reached a maximum value of similar to 2in- n-hexane and surprisingly also in MeCN, as the excitation wavelength approaches the red-edge of the absorption spectrum. These, in our opinion, erroneous observations were supported by time-dependent density functional theory (TDDFT) calculations, which compute a perpendicularly twisted lowest ICT state (TICT) state. This is a further example of the general tendency, of computations to find a TICT conformation for the lowest excited singlet state of electron donor/acceptor molecules such as p-substituted anilines.

Atmospheric transport is the major route for global distribution of semi-volatile compounds such as halogenated aromatics as well as their major exposure route for humans. Their major atmospheric removal process is oxidation by hydroxyl radicals. There is very little information on the reaction mechanism or reaction-path dynamics of atmospheric degradation of halogenated benzenes. Furthermore, the measured reaction rate constants are missing for the range of environmentally relevant temperatures, i.e. 230-330 K. A series of recent theoretical studies have provided those valuable missing information for fluorobenzene, chlorobenzene, hexafluorobenzene and hexachlorobenzene. Their comparative analysis has provided additional and more general insight into the mechanism of those important tropospheric degradation processes as well as into the mobility, transport and atmospheric fate of halogenated aromatic systems. It was demonstrated for the first time that the addition of hydroxyl radicals to monohalogenated as well as to perhalogenated benzenes proceeds indirectly, via a prereaction complex and its formation and dynamics have been characterized including the respective transition-state. However, in fluorobenzene and chlorobenzene reactions hydroxyl radical hydrogen is pointing approximately to the center of the aromatic ring while in the case of hexafluorobenzene and hexachlorobenzene, unexpectedly, the oxygen is directed towards the center of the aromatic ring. The reliable rate constants are now available for all environmentally relevant temperatures for the tropospheric oxidation of fluorobenzene, chlorobenzene, hexafluorobenzene and hexachlorobenzene while pentachlorophenol, a well-known organic micropollutant, seems to be a major stable product of tropospheric oxidation of hexachlorobenzene. Their calculated tropospheric lifetimes show that fluorobenzene and chlorobenzene are easily removed from the atmosphere and do not have long-range transport potential while hexafluorobenzene seems to be a potential POP chemical and hexachlorobenzene is clearly a typical persistent organic pollutant.

Two series of fluorine-substituted benzoate ester type rod-shaped liquid crystals incorporating the azobenzene as side arm linked with terminal double bonds as polymerizable functional groups were synthesized and characterized by polarized-light optical microscopy (POM), differential scanning calorimetry (DSC) and UV–visible spectroscopy investigations. Thus, rod-shaped monomers, namely 4a and 4b having odd and even number of carbon in the terminal group exhibited nematic phase and SmA type phase was found at lower temperature. Compound 5 showed nematic phase whereas compound 6 showed SmA phase. These rod-shaped molecules exhibit strong photoisomerization behaviour in solution. The photoswitching properties of the compounds showed trans to cis isomerization in about 10 s, whereas the reverse process takes place about 120 min in solutions. Proposed materials may have potential to use it in optical storage devices.

Reaction of triphenylmethylium tetrakis(pentafluorophenyl)borate, [Ph3C][B(C6F5)4], with excess neat triethylsilane affords triethylsilylium(triethylsilane) tetrakis(pentafluorophenyl)borate, [(Et3Si)2(μ-H)][B(C6F5)4] (1), identified by X-ray crystallography. In chlorobenzene and fluorobenzene, 1 is observed in solution. When 1 is dissolved in benzene or toluene, the evolved gas was shown to be hydrogen. Isotope labeling experiments demonstrate that the hydrogen arises from the reaction of Et3SiH with the silylium complex of the arene solvent.

The luminescent tungsten-alkylidyne metalloligand [WCl(≡C-4,4'-C6H4CC-py)(dppe)2] (1; dppe=1,2-bis(diphenylphosphino)ethane) and the zinc-tetraarylporphyrins ZnTPP and ZnTP(Cl)P (TPP=tetraphenylporphyrin, TP(Cl)P=tetra(p-chlorophenyl)porphyrin) self-assemble in fluorobenzene solution to form the dyads ZnTPP(1) and ZnTP(Cl)P(1), in which the metalloligand is axially coordinated to the porphyrin. Excitation of the porphyrin-centered S1 excited states of these dyads initiates intramolecular energy-transfer (ZnPor→1) and electron-transfer (1→ZnPor) processes, which together efficiently quench the S1 state (~90%). Transient-absorption spectroscopy and an associated kinetic analysis reveal that the net product of the energy-transfer process is the (3)[dπ*] state of coordinated 1, which is formed by S1→(1)[dπ*] singlet-singlet (Förster) energy transfer followed by (1)[dπ*]→(3)[dπ*] intersystem crossing. The data also demonstrate that coordinated 1 reductively quenches the porphyrin S1 state to produce the [ZnPor(-)][1(+)] charge-separated state. This is a rare example of the reductive quenching of zinc porphyrin chromophores. The presence in the [ZnPor(-)][1(+)] charge-separated states of powerfully reducing zinc-porphyrin radical anions, which are capable of sensitizing a wide range of reductive electrocatalysts, and the 1(+) ion, which can initiate the oxidation of H2, produces an integrated photochemical system with the thermodynamic capability of driving photoredox processes that result in the transfer of renewable reducing equivalents instead of the consumption of conventional sacrificial donors.

Here, we report the first experimental and computational study of the noncovalent binding energies and structures of ionized benzenes containing electron-withdrawing substituents solvated by one to four HCN molecules. Measured by ion mobility mass spectrometric equilibrium studies, the bond dissociation enthalpies of the first HCN molecule to the fluorobenzene (C6H5F(•+)), 1,4-difluorobenzene (C6H4F2(•+)), and benzonitrile (C6H5CN(•+)) ions (11.2, 11.2, and 9.2 kcal/mol, respectively) are similar to those of HCN with the benzene (C6H6(•+)) and phenyacetylene (C6H5CCH(•+)) radical cations (9.2 and 10.5 kcal/mol, respectively). DFT calculations at the B3LYP/6-311++G(d,p) level show that HCN can form in-plane hydrogen bonds to ring hydrogens, or bind electrostatically to positively charged carbon centers in the ring. The electron-withdrawing substituents increase the bond energy by increasing the partial positive charge on the ring hydrogens that form CH(δ+)---NCH bonds, and by creating a π hole, as evidenced by positive charge centers on the fluorinated ring carbons for electrostatically bonded isomers. In the complexes of benzonitrile(•+), similar to benzene(•+), hydrogen bonded planar isomers have the lowest energy. In the complexes of (fluorinated benzene)(•+), the lowest energy isomers are electrostatically bonded where HCN is perpendicular to the ring and its dipole points to a positively charged ring carbon. However, in all cases the planar hydrogen-bonded and vertical electrostatic isomers have similar binding energies within 1 kcal/mol, although HCN interacts with different sites of the ionized benzenes in these isomers, suggesting that the observed cluster populations are mixtures of the planar and vertical isomers. Further HCN molecules can bind directly to unoccupied ring CH hydrogens or bind to the first-shell HCN molecules to form linear HCN---HCN--- hydrogen bonded chains. The binding energies decrease stepwise to about 6-7 kcal/mol by 4 HCN molecules, approaching the macroscopic enthalpy of vaporization of liquid HCN (6.0 kcal/mol).

The photocatalytic fluorination of benzene occurs under photoirradiation of an oxygen-saturated acetonitrile (MeCN) of the 3-cyano-1-methylquinolinium ion (QuCN(+)) containing benzene and tetraethylammonium fluoride tetrahydrofluoride (TEAF·4HF) with a xenon lamp (500 W) attached to a colored-glass filter (λ < 290 nm) to yield fluorobenzene and hydrogen peroxide. The quantum yield of formation of fluorobenzene was 6%. Nanosecond laser flash photolysis measurements were performed to elucidate the mechanistic details for photocatalytic fluorination. Transient absorption spectra taken after the nanosecond laser excitation at 355 nm of a degassed MeCN solution of QuCN(+) and benzene exhibited absorption bands due to QuCN(•) (λmax = 500 nm) and the benzene dimer radical cation (λmax = 900 nm), which were generated by photoinduced electron transfer from benzene to the singlet excited state of QuCN(+). The decay rate of the transient absorption band due to the benzene dimer radical cation was accelerated by the addition of TEAF·4HF. The observed rate constant increased with increasing concentration of TEAF·4HF. The rate constant of the electrophilic addition of fluoride to the benzene radical cation was determined to be 9.4 × 10(9) M(-1) s(-1). Thus, the photocatalytic reaction is initiated by intermolecular photoinduced electron transfer from benzene to the single excited state of QuCN(+). The benzene radical cation formed by photoinduced electron transfer reacts with the fluoride anion to yield the F-adducted radical. However, QuCN(•) can reduce O2 to O2(•-), and this is followed by the protonation of O2(•-) to afford HO2(•). The hydrogen abstraction of HO2(•) from the F-adduct radical affords fluorobenzene and H2O2 as the final products.

This manuscript explores new chemistry that can be related to the unobserved 14-electron [(FPNP)Pt]+ transient (FPNP = (4-F-2-(iPr2P)C6H3)2N). Its reactivity can be accessed via abstraction of triflate from (FPNP)PtOTf (1) with K[B(C6F5)4] in various solvents serving as substrates. With benzene, toluene and fluorobenzene, net heterolytic splitting of an aromatic C–H bond across the N–Pt bond is observed, without any detectable intermediates, leading to the [(FPN(H)P)Pt–Ar]+ products (Ar = Ph, 3a; Ar = C6H4Me, 3b (ortho), 3c (meta), 3d (para); Ar = o-C6H4F, 3e). The latter can be alternatively prepared by protonation of the neutral (FPNP)Pt–Ar compounds. Compounds 3a–3e do not release free arene under thermolysis at 80 °C, and compounds 3b/c/d do not interconvert under ambient temperature. With chlorobenzene and bromobenzene, the kinetic product is the κ1-Cl or κ1-Br adduct [(FPNP)Pt–Cl–Ph]+ (4) or [(FPNP)Pt–Br–Ph]+ (10). Compound 4 rearranges into a C–H splitting product [(FPN(H)P)Pt–C6H4Cl]+ (3f), while 10 slowly reacts by formal transfer of Br atom to Pt. An analogous Cl atom transfer to Pt is observed upon the reaction of 1 with K[B(C6F5)4] in dichloromethane, producing [(FPNP)PtCl][B(C6F5)4] (9a) which features an oxidized FPNP ligand framework. X-Ray diffractometry established structures of [(FPN(H)P)Pt–C6H4F-o][B(C6F5)4] (3e, disordered rotamers), [(FPN(H)P)Pt–C6H4Me][B(C6F5)4] (disordered meta- and para-isomers 3c/d), and [(FPNP)PtCl][HCB11Cl11] (9b). DFT calculations at the PBE0 and M06-L levels on the free [(FPNP)Pt]+ cation predict a relatively small (10–12 kcal mol−1) separation between the singlet and the triplet states. The relatively low triplet energy is probably related to the viability of the unexpected halogen atom abstraction reactions.

The Balz–Schiemann is the method of synthesizing fluorobenzene, which is complex and involves several hazardous chemicals, such as hydrofluoric acid, hydrochloride, sodium nitrite and so on, confronted with a high risk of intoxication and explosion. A comparison study of the thermal safety of preparing fluorobenzene using the Balz–Schiemann and fluorodenitration schemes is made by the density functional theory (DFT) method at the B3LYP/6-31G(D) level. The thermal safety is analyzed with reaction rate and statistic thermodynamic functions of reactants (R), products (P), intermediates (IM) and transition states (TS). The pathways of both the two reactions are also calculated without any assumption. According to calculation results, the reaction rate constant of fluorodenitration reaction is tens orders of magnitude less than that of the Balz–Schiemann reaction. Computational results also suggest that fluorodenitration is a milder exothermic reaction with higher thermal safety, which have great significance in inherently safety design during chemical process.

A cobalt(II) fluoride complex, [LtBuCo(μ-F)]2 [LtBu = 2,2,6,6-tetramethyl-3,5-bis(2,6-diisopropylphenylimido)hept-4-yl], was synthesized from LtBuCo using Me3SnF via homolytic cleavage of the Sn–F bond. LtBuCo also performed the overall binuclear oxidative addition of fluorinated arenes to give [LtBuCo(μ-F)]2 and a cobalt(II) aryl complex of the corresponding fluorobenzene substrate in a 1:2 molar ratio. The C–F activation reaction has a first-order rate dependence on both cobalt and fluorobenzene concentrations. The rate is increased by meta-fluoride substituents, and slowed by ortho-fluoride substituents, suggesting electronic and steric influences on the transition state, respectively. The data are most consistent with a mechanism beginning with rate-limiting oxidative addition of the aryl fluoride to cobalt(I), followed by rapid reduction of the cobalt(III) aryl fluoride intermediate by a second molecule of LtBuCo. [LtBuCo(μ-F)]2 also reacts with Et3SiH to give the hydride complex [LtBuCo(μ-H)]2. This...

Site-selective Sonogashira cross-coupling reactions of 1,4-dibromo-2-(trifluoromethyl)benzene have been performed, affording a variety of functionalized alkynyl-substituted (trifluoromethyl)benzenes. The site selectivity, in favor of position C-4, was confirmed by 13C NMR and 1H–13C HMBC NMR measurements, X-ray crystal structure analysis as well as DFT calculations. Furthermore, the mesomorphic properties and optical textures were examined by differential scanning calorimetry and polarized optical microscopy. Several dialkynyl-substituted (trifluoromethyl)benzenes showed nematic liquid-crystalline properties over a long phase range. The influence of terminal and lateral substituents on the formation and stability of the molecular network within the liquid-crystalline phase is explained by the results of DFT calculations. Additionally, the absorption and fluorescence properties were analyzed in detail. The intramolecular influence of electron-donating or electron-withdrawing groups and also of solvatochromatism are considered. In this context, time-dependent B3LYP/6-31G* (TD-B3LYP) calculations were carried out to characterize the main absorption bands.

Activation of the B-H sigma-bond of amine-boranes on the chromium(0) center of arene chromium tricarbonyl complexes (eta(6)-arene) Cr(CO)(3) (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia-borane (H3N center dot BH3, AB) and tert-butylamine-borane ((BuH2N)-Bu-t center dot BH3, TBAB) resulted in H-2 evolution and precipitation of a BNHx polymer. On the other hand, photolysis in the presence of trimethylamine-borane (Me3N center dot BH3, TMAB) resulted in the formation of a sigma-borane complex (2) along with Cr(CO)(5)(eta(1)-HBH2 center dot NMe3) (3). The sigma-borane complexes (eta(6)-arene) Cr-( CO)(2)(eta(1)-HBH2 center dot NMe3) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by H-1, B-11, and C-13 NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable sigma-borane moiety in this series of complexes. (C) 2011 Elsevier B.V. All rights reserved.

The chemical reactivity and reaction mechanism of fluorobenzene formation by dehydrogenation of fluorocyclohexenes was investigated. 1-Fluorocyclohexene reacted with oxidants such as nitrobenzene and oxygen to give fluorobenzene in good yields under moderate conditions in the presence of a Pd catalyst. A detailed comparison of oxidative dehydrogenation with non-oxidative dehydrogenation proved that the oxidants effectively suppressed isomerization and disproportionation, and offered a selective synthesis of fluorobenzene.

The reactions of the bis(solvento) complexes [OsCp(MeCN)2(PiPr3)]PF6 (1; Cp = cyclopentadienyl) and [OsTp(κ1-OCMe2)2(PiPr3)]BF4 (1a; Tp = hydridotris(pyrazolyl)borate) with allenes have been investigated. Complex 1 reacts with 1-methyl-1-(trimethylsilyl)allene and 1,1-dimethylallene to give the π-allene derivatives [OsCp(η2-CH2═C═CRMe)(MeCN)(PiPr3)]PF6 (R = SiMe3 (2), Me (3)). In fluorobenzene at 80 °C, complexes 2 and 3 are moderately stable and evolve into the isopropenyldiisopropylphosphine derivative [OsCp{κ3P,C,C-PiPr2[C(Me)═CH2]}(MeCN)]PF6 (4) by hydrogen transfer from an isopropyl substituent of the phosphine to the coordinated double bond of the allene. Under an ethylene atmosphere the acetonitrile ligand of 4 is displaced by the olefin. The resulting π-ethylene derivative [OsCp(η2-CH2═CH2){κ3P,C,C-PiPr2[C(Me)═CH2]}]PF6 (5) is obtained through a one-pot synthesis procedure by the stirring of 3 in fluorobenzene at 80 °C under 2 atm of ethylene. Treatment of 2 and 3 with dimethyl acetylenedicarboxylate gives [OsCp{η2-CH(CO2Me)═CH(CO2Me)}{κ3P,C,C-PiPr2[C(Me)═CH2]PF6 (6). The reaction of 1a with 1,1-dimethylallene leads to [OsTp(η2-CH2═C═CMe2)(κ1-OCMe2)(PiPr3)]BF4 (7). In contrast to its Cp counterpart, complex 7 evolves into the hydride−alkenylcarbyne derivative [OsHTp(≡CCH═CMe2)(PiPr3)]BF4 (8), by means of a double migration of the hydrogen atoms of the terminal CH2 group of the allene. One of them migrates to the central carbon atom of the allene, and the other one goes to the metal center. The alkenylcarbyne group of 8 is selectively deprotonated in the presence of the hydride ligand to afford the hydride−alkenylvinylidene OsHTp{═C═CHC(Me)═CH2}(PiPr3) (9). The X-ray structures of 2, 5, 8, and 9 are also reported., Financial support from the Spanish MICINN(ProjectsCTQ2008-00810 and Consolider Ingenio 2010 (CSD2007-00006)), theDiputación General deAragón (E35) and the European Social Fund is acknowledged.

Aryl fluoride has attracted much attention as a resist component for extreme ultraviolet (EUV) lithography, because of the high absorption cross section of fluorine for EUV photons; however, less is known about electron attachment to fluorobenzene (FBz) and the stability of the reduced state. Picosecond and nanosecond pulse radiolysis of tetrahydrofuran solutions of FBz from mono-, di-, tri-, tetra-, penta-, and hexafluorobenzene was performed, and the effects of isomeric structure and number of fluorine atoms were examined. Scavenging of solvated electrons was found to correlate with the electron affinity obtained by density functional theory in the gas phase, whereas the decay of FBz radical anions was dominated by the activation energy of fluorine anion dissociation calculated using a polarized continuum model (PCM). A sharp contrast in the lifetimes of ortho-, meta-, and para-position difluorobenzene was observed, which could provide information on the molecular design of functional materials.

Van der Waals heterodimers of p-difluorobenzene (DFB) with other molecules, prepared in a supersonic jet beam expansion, were studied by resonant two-photon ionization (R2PI) through their S1 ← S0 transition. The functional molecule in these systems is DFB. The partners-molecules are: p-difluorobenzene (homodimer), fluorobenzene, 1,3,5-trifluorobenzene, furan, N-methylpyrrole, ethanol and propargyl alcohol. In each case, the recorded spectra are relatively broad as the result of at least two structures present in the molecular beam. Using hexafluorobenzene or pyrrole as partners of DFB, the S1 ← S0 transition of the respective heterodimer was not detected. Intracluster ion-molecule reactions have been observed in the cases of p-difluorobenzene with ethanol and propargyl alcohol.

The electrode processes of chlorobenzene (CB) and fluorobenzene (FB) on polycrystalline platinum (Pt-pc) electrode in sulfuric acid were studied by differential electrochemical mass spectrometry (DEMS). Contrary to the oxidation of adsorbed benzene on Pt surface, the oxidation of adsorbed CB and FB in the oxygen adsorption region does not provide solely CO2 as the final product. At negative polarization potentials CB and FB were desorbed under dehalogenation. While in the case of FB only benzene was detected, CB gave intermediates besides benzene. The final product of stepwise hydrogenation of these species was cyclohexane.

The neopentylidene-neopentyl complex (PNP)Ti═CHtBu(CH2tBu) (1; (PNP− = N[2-P(CHMe2)2-4-methylphenyl]2) extrudes neopentane in neat fluorobenzene under mild conditions (25 °C) to generate the transient titanium alkylidyne (PNP)Ti≡CtBu (A), which subsequently undergoes regioselective 1,2-CH bond addition of a fluorobenzene across the Ti≡C linkage to generate (PNP)Ti═CHtBu(o-FC6H4) (2). Kinetic and mechanistic studies suggest that the C−H activation process is pseudo-first-order in titanium, with the α-hydrogen abstraction being the rate-determining step and the post-rate-determining step being the C−H bond activation of fluorobenzene. At 100 °C complex 2 does not equilibrate back to A and the preference for C−H activation in benzene versus fluorobenzene is 2:3, respectively. Compound 1 also reacts readily, and in most cases cleanly, with a series of hydrofluoroarenes (HArF), to form a family of alkylidene-arylfluoride derivatives of the type (PNP)Ti═CHtBu(ArF). Thermolysis of the latter compounds generates ...

Dimethylamine-borane (DMAB) acid/base properties, its dihydrogen-bonded (DHB) complexes and proton transfer reaction in nonaqueous media were investigated both experimentally (IR, UV/vis, NMR, and X-ray) and theoretically (DFT, NBO, QTAIM, and NCI). The effects of DMAB concentration, solvents polarity and temperature on the degree of DMAB self-association are shown and the enthalpy of association is determined experimentally for the first time (-ΔH°assoc = 1.5-2.3 kcal/mol). The first case of "improper" (blue-shifting) NH···F hydrogen bonds was observed in fluorobenzene and perfluorobenzene solutions. It was shown that hydrogen-bonded complexes are the intermediates of proton transfer from alcohols and phenols to DMAB. The reaction mechanism was examined computationally taking into account the coordinating properties of the reaction media. The values of the rate constants of proton transfer from HFIP to DMAB in acetone were determined experimentally [(7.9 ± 0.1) × 10(-4) to (1.6 ± 0.1) × 10(-3) mol(-1)·s(-1)] at 270-310 K. Computed activation barrier of this reaction ΔG(‡theor)298 K(acetone) = 23.8 kcal/mol is in good agreement with the experimental value of the activation free energy ΔG(‡exp)270 K = 21.1 kcal/mol.

2-, 3- and 4-substituted fluorobenzenes and 5-substituted 1,3-difluorobenzenes were metalated with sec-butyllithium (LIS) and with lithium 2,2,6,6-tetramethylpiperidide (LiTMP) under irreversible conditions in order to determine the rates of reaction relative to the unsubstituted parent compounds (fluorobenzene and 1,3- difluorobenzene). In addition, the pairs of resulting aryllithiums were subjected to acid-base equilibration to furnish the thermodynamic stabilities (or: basicities) of these species again relative to the parent compounds. Not surprisingly, the effect diminishes with the distance of a given substituent to the lithiation center (ortho > meta > para) and it reaches its maximum at the ground state equilibration of the organometallic intermediate whereas it fades away at transition states, in particular reactant-like ones. Fluorine, the most powerful activator in the entire series if located at an ortho position, increases the rates of LIS- and LiTMP-promoted metalations by respectively 2 and 3 powers of ten, but by 7 to 8 powers of ten the aryllithium equilibrium stability.

The rate determining steps of isomeric ortho, meta and para nitrations of fluorobenzene and chlorobenzene have been theoretically investigated at the B3LYP/6-311G** level. Stationary points of the step involving reactant, transition state and intermediate complexes were successfully located and characterized without any restriction on the internal coordinates. Their molecular geometries, electronic structures, IR spectra, and the FMO symmetries of two initial aromatic compounds and the NO 2 + suggest that the halogens are ortho-para directive, and also activating substituents in the gas phase. The blue shift of the C-N stretching vibration and the red shift of the tetrahedral C-H stretching vibration from transition state to Wheland intermediate demonstrate that the formation of the C-N and the cleavage of the C-H are not concerted but stepwise at the rate determining step. This provides theoretical evidence for the experimental fact of the absence of primary kinetic isotopic effect in most aromatic nitration reactions. The fully optimized geometries of nitro-chlorobenzene complexes show that the C-Cl bond in nitro-chlorobenzene complexes become much shorter than in chlorobenzene molecules and appears as a double bond. On the contrary, the C-F bond in nitro-fluorobenzene complexes is still a single bond, and even lengthens slightly as the NO 2 + moves toward the fluorobenzene. This reveals that there is a special interaction, namely inductomeric effect, between the chlorine and nitro group in nitro-chlorobenzene complexes. The inductomeric effect may cause a marked increase in the percentage of ortho product for the nitration of chlorobenzene.

Protonated fluorobenzene ions (C6H6F+) are produced by chemical ionization of C6H5F in the cell of a FT-ICR mass spectrometer using either CH5+ or C2H5+. The resulting protonation sites are probed by IR multiphoton dissociation (IRMPD) spectroscopy in the 600-1700 cm-1 fingerprint range employing the free electron laser at CLIO (Centre Laser Infrarouge Orsay). Comparison with quantum chemical calculations reveals that the IRMPD spectra are consistent with protonation in para and/or ortho position, which are the thermodynamically favored protonation sites. The lack of observation of protonation at the F substituent, when CH5+ is used as protonating agent, is attributed to the low-pressure conditions in the ICR cell where the ions are produced. Comparison of the C6H6F+ spectrum with IR spectra of C6H5F and C6H7+ reveals the effects of both protonation and H F substitution on the structural properties of these fundamental aromatic molecules.

Time-resolved optical Kerr effect spectroscopy has been used to probe the molecular environment afforded by the hydrophobic core of oil-in-water microemulsions. This was achieved by measuring the ultrafast dynamics of a series of benzene derivatives (benzonitrile, nitrobenzene, fluorobenzene, styrene, and toluene) incorporated as the oil phase within oil-in-water microemulsions and comparing them to the dynamics in neat liquid and the liquid diluted in nonpolar solvent. Polar and strongly interacting liquids (benzonitrile and nitrobenzene) showed dynamics in the microemulsion that are similar to those in the solution phase, while weakly interacting and mildly polar liquids (fluorobenzene, styrene and toluene) reveal dynamics more similar to those of the neat liquid. This suggests stabilization of the polar dispersed phase in polar regions of the micelle.

The 13 C isotropic shieldings for a series of aromatic hydrocarbons: naphthalene, azulene, acenaphtalene, fluoranthene and phenanthrene are determined. A quantum mechanical calculations of NMR chemical shifts were performed using the DFT coupled gauge-included atomic orbital calculations. The polarisable continuum model approach was used to evaluate the solvent effects on the 13 C chemical shifts of the studied molecules. To this end, the solvents: cyclohexane, triethylamine, di- n -butyl ether, diisopropyl ether, diethyl carbonate, tetrahydrofuran, butyronitrile, γ-butyrolactone, propylene carbonate, dimethyl sulfoxide, benzene, toluene, fluorobenzene, anisole, acetophenone, benzonitrile and nitrobenzene are used. A multiple linear regression analysis has been carried out using the Kamlet–Abboud–Taft solvatochromic parameters to quantify the solvent effects on the 13 C chemical shifts of the select hydrocarbons. It has been found that there is a good correlation between the solvent induced chemical shifts and π * scale of solvent polarity. The agreement between the calculated and the experimental data is good in all instances.

A cyclophane composed of fluorobenzene and phenol units was synthesized in order to observe the C−F···H−O hydrogen bond. In the crystal structure, 20% of the molecule clearly shows the intramolecular hydrogen bond and the other 80% is free from hydrogen bonding. On the other hand, a distinct low-field shift of the phenolic OH proton was observed in the 1H NMR spectrum compared to that of the F-free analog. Furthermore, O−H···F through-space coupling was observed. From the results of the crystallographic analysis, IR, and NMR spectra, the C−F···H−O hydrogen bond energy of this system was estimated to be 0.84−3.7 kJ·mol−1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

An overview is presented of our recent experimental studies of aromatic molecules using multimass ion imaging techniques. Photodissociation of benzene, fluorobenzene, toluene, m-xylene, ethylbenzene, propylbenzene and chlorotoluene at 248 nm or 193 nm was investigated under collisionless conditions. The photofragment translational energy distribution and dissociation rate of each dissociation channel were recorded. New isomerization and dissociation channels were observed from these studies. The data are discussed with reference to the ab initio potential energy surface and statistical theory results.

The effects of solvent, pH, temperature, and hydrogen pressure were determined for the reaction of fluorobenzene (PhF) with hydrogen gas catalyzed by supported rhodium metal on silica. Non-polar and aprotic solvents, heptane and 1,2-dichloroethane (DCE), favor hydrogenation to fluorocyclohexane (CyF). Polar and protic solvents, heptane/methanol and heptane/water, favor hydrodefluorination to benzene (PhH) and subsequent hydrogenation to cyclohexane (CyH). The hydrodefluorination–hydrogenation of fluorobenzene to cyclohexane via benzene proceeds fastest in heptane/water under acidic conditions. For the hydrodefluorination of fluorobenzene in heptane/water, the hydrodefluorination product, benzene, inhibited further hydrodefluorination of fluorobenzene. In heptane or DCE, a side reaction between fluorocyclohexane and hydrogen fluoride, not catalyzed by rhodium, was discovered that provides an alternate pathway to cyclohexane. Reaction conditions can be modified to yield primarily fluorocyclohexane, benzene, or cyclohexane.

Previously developed technique of charge exchange ionization in a collision cell outside the ion source, which detects ions originating from the collision gas in the cell, was used to find long-lived excited electronic states of monosubstituted benzene cations. The technique is based on the criterion that charge exchange between polyatomic species is efficient only when the energy of reaction is close to zero or negative (ΔE⩽0), or the exoergicity rule. The B 2B2 states of chlorobenzene, bromobenzene, benzonitrile, and phenyl acetylene cations were found to have long lifetimes (10 microseconds or longer) while excited electronic states with long lifetime were not detected for fluorobenzene, iodobenzene, toluene, nitrobenzene, and styrene cations. The long-lived states found were those displaying well-resolved vibrational structures in the photoelectron spectra. In particular, these were the states generated by removal of an electron from the in-plane nonbonding p orbitals of halogens or in-plane π orbita...

The fluorescence behavior of pyrene in oil droplets of a surfactant-free oil-in-water emulsion was studied for benzene, fluorobenzene, n-hexane and cyclohexane droplets in water. The excimer–monomer fluorescence ratio immediately after sonication, IE/IM(0), of the benzene/water emulsion was 8–10 times larger than for the benzene solution. The ratio IE/IM(t) increased in the first 10–20 min before it decreased to zero. Similar behavior was observed for the fluorobenzene/water emulsion, while IE/IM(0) for emulsions with n-hexane and cyclohexane was smaller than for benzene and fluorobenzene/water emulsions. IE/IM(t) hardly changed with time for the n-hexane and cyclohexane/water emulsions. This different behavior was attributed to the increased solubility of nanometer-size droplets with benzene and fluorobenzene.

An ab initio molecular orbital study using both gas-phase and B3LYP/DZVP-COSMO solvation models of the mechanism of palladium insertion into alkyne and aryl carbon–halogen bonds suggests that the mechanism of palladium insertion into alkyne species can proceed via a concerted oxidative addition across the carbon–halogen bond. A stepwise mechanism via a σ-complex is favoured when a nitro group is introduced onto the alkyne. The palladium insertion into variously substituted aryl fluorides was again found to proceed via a single-step concerted mechanism, and although a σ-complex can be located when 2,4-dinitro and 2-nitro substitution is present, the energy of this stepwise route is very similar to the concerted pathway and no clear decision on the pathway can be made. No intermediate σ-complex could be located for η6-tricarbonylchromium-complexed fluorobenzene, and only a concerted pathway was identified.