Naphthalene Radical Anion Research Articles

A new access route to dimetal sandwich complexes, including a radical anion.

The amide in Cr[N(SiMe3)2]2(THF)2 is displaced by equimolar [K(18-crown-6)][naphthalene] to form the dimetal sandwich Cr2(naphthalene)2- as a radical anion paired with [K(18-crown-6)]+. Two Cr atoms in the sandwich do not form any multiple Cr/Cr bonds, and instead each interacts with one naphthalene in an η6 fashion and with the second naphthalene in an η4 connectivity mode. The naphthalene C/C distances show the effect of back donation from two chromium atoms to a greater extent than simply by 1 electron ring reduction, in comparison to the naphthalene radical anion. The SOMO of the product was established by variable temperature EPR spectroscopy, and the atom ratios and elemental purity were supported by XPS. The possible generality of the displacement of N(SiMe3)2- from a low valent metal is discussed.

Localized Reduction of Graphene Oxide by Electrogenerated Naphthalene Radical Anions and Subsequent Diazonium Electrografting

Herein, we describe a new localized functionalization method of graphene oxide (GO) deposited on a silicon oxide surface. The functionalization starts with the reduction of GO by electrogenerated naphthalene radical anions. The source of reducers is a microelectrode moving close to the substrate in a typical scanning electrochemical microscopy (SECM) configuration. Then, the recovery of electronic conductivity upon reduction enables the selective electrochemical functionalization of the patterns. The illustrative example is the electrografting of reduced-GO with a diazonium salt bearing a protonated amino group that can further immobilize gold nanoparticles by simple immersion. This study opens new routes for the construction of multifunctional patterned surfaces.

Naphthalene and Anthracene Cobaltates(1−): Useful Storable Sources of an Atomic Cobalt Anion

Reductions of CoBr(2) or cobaltocene by 3 equiv of potassium anthracene radical anion in tetrahydrofuran (THF) afford 60-80% yields of bis(anthracene)cobaltate(1-) (1), of interest as a readily accessible and quite labile source of spin-paired atomic Co(-). Although the unsolvated potassium salt of 1 is thermally unstable at 20 °C, the [K(18-crown-6)(THF)(2)](+) salt of 1 functions as a useful storable crystalline reagent for Co(-) in several reactions. Previously known classic cobaltates, [CoL(4)](-), for L = 1/2 (1,3-butadiene) (2), PF(3) (3), and P(OiPr)(3) (5), were obtained directly from 1 and structurally characterized for the first time. Anion 3 is noteworthy because it appears to possess the shortest known Co-P distance, av = 2.012(4) Å. Although the naphthalene analogue of 1 is not yet available as a pure substance, low-temperature reductions of CoBr(2) or cobaltocene by naphthalene radical anion in the presence of 1,5-cyclooctadiene (COD) afford variable yields (80-90% from CoCp(2)) of (naphthalene)(COD)cobaltate(1-) (10). Ready displacement of naphthalene in 10 by L = 1,3-butadiene, 2,2'-bipyridine, and COD occurs to give good yields of the respective [Co(L)(COD)](-), all of which have been structurally characterized. Both ligands in 10 are displaced by tert-butylisocyanide to afford [Co(CNtBu)(4)](-) (16), the first isolable and structurally characterized homoleptic alkylisocyanometalate. The molecular structure of 16 shows unprecedented bending of the isocyanides, av C-N-C = 137(2)°, for homoleptic isocyanide complexes.

Active-alkali metal-promoted reductive cleavage of chlorinated phenols

We investigated the degradation of chlorinated phenols under reductive electron transfer reaction conditions. Although Li and Na metal proved useless, activated forms of these metals, either their soluble naphthalene radical anions or 1,2-diarylethane dianions, promoted the degradation of the starting materials to various extents. Additionally, efficient dehalogenation of the sodium salts of several mono-, di-, and tri-chlorophenols was obtained by their reduction with an excess of Na metal and a catalytic amount of naphthalene. .

Bis(η6-naphthalene)molybdenum(0)

The title compound, [Mo(C10H8)2], was prepared from the naphthalene radical anion and MoCl4(thf)2 (thf is tetra­hydro­furan). In the crystal, the mol­ecule is located on an inversion center. The Mo atom is equally disordered over two positions; the range of Mo—C distances is 2.2244 (19)–2.3400 (17) Å for both components of the disorder.

A convenient route to modified multiwall carbon nanotubes with liquid crystal molecules via covalent functionalization

AbstractA novel nanocomposite of the rod‐like liquid crystal (LC) molecules' waist positions anchored on the surface (sidewalls and ends) of multiwall carbon nanotubes (MWNTs) was prepared by using a dissolving metal reduction method for the first time. The MWNTs carbanion complexes of lithium were first synthesized in tetrahydrofuran with an electron transfer from lithium naphthalene radical anion on the surface of MWNTs. Then the novel material (LC‐MWNTs) was obtained by treating the carbanion complexes with bromic liquid crystalline aromatic amide compound. The formation of the LC‐MWNTs was confirmed by both Raman and FTIR spectroscopies. HRTEM demonstrates that the rod‐like LC molecules are anchored on the surface of MWNTs via covalent attachment, with a wrapped thickness approximately 3‐4 nm. The loss‐weight fraction of the LC layers for the LC‐MWNTs can be roughly estimated as 23% by TGA. The experiments of solubility exhibit that the LC‐MWNTs forms a stable suspension solution in polar solvents such as dimethylformamide. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Electron-transfer-induced reductive cleavage of chlorinated aryloxyalkanoic acids

We investigated the degradation of chlorinated herbicides, with an aryloxyalkanoic acid skeleton, under reductive electron transfer reaction conditions. Although Li and Na metals proved useless, activated forms of these metals, either their soluble naphthalene radical anions or 1,2-diarylethane dianions, promoted the degradation of the starting materials to various extents. Indeed, lithium naphthalenide promoted both extensive dehalogenation and dealkylation of chlorinated aryloxyalkanoic acids, with formation of the corresponding phenols as the main reaction products. In contrast, the employment of 1,2-diphenyl-1,2-disodioethane as a reducing agent led, in most examples, to the chemoselective recovery of the corresponding dechlorinated acids.

Radiation Chemistry of Fluoronaphthalene as a Candidate for Absorption Enhancement Component of Chemically Amplified Extreme Ultraviolet Resists

With the reduction of resist thickness accompanying the miniaturization of feature sizes, increasing the absorption coefficient of extreme ultraviolet (EUV) resists is becoming increasingly important from the viewpoint of the efficient use of incident radiation. The fluorination of the resist polymer is the most effective means of increasing the absorption coefficient. However, it has been pointed out that the dissociative electron attachment of the fluorinated polymer is a problem in the application of the fluorinated polymer to chemically amplified resists used for ionizing radiation. In this study, the electron flow in fluorinated resists was examined using fluoronaphthalene as a possible candidate for suppressing the dissociative electron attachment. The molecular structure dependence of the reactivity with tetrahydrofuran-solvated electrons, the electron transfer from fluoronaphthalene radical anions to triphenylsulfonium-triflate, the dissociation of fluoronaphthalene radical anions, and the charge recombination of fluoronaphthalene radical anions with protons were clarified by the comparison of octafluoronaphthalene, 1-fluoronaphthalene, and naphthalene. The dissociation of fluoronaphthalene radical anions was negligibly slow. Also, the recombination of octafluoronaphthalene radical anions with protons was significantly delayed compared with that of naphthalene radical anions. These results suggest that the molecular structure of fluoronaphthalene is suitable for the molecular design of chemically amplified EUV resists from the viewpoint of the control of electron flow in the acid generation processes.

ChemInform Abstract: Homogeneous Rate Constants for Coupling Between Electrochemically Generated Aromatic Anion Radicals and Alkyl Radicals

Rate constants have been measured for the coupling between hexenyl radicals and 2,2-dimethylhexenyl radicals and electrogenerated anion radicals of anthracene, 9,10-diphenylanthracene, benzophenone and quinoxaline. The rate constant for all four reactions in N,N-dimethylformamide is log k 2 =9.1(5), which is in accordance previous results in 1,2-dimethoxyethane for naphthalene and benzophenone anion radicals and 1-hexenyl radicals. The conclusion is that the coupling reaction between aromatic anion radicals and alkyl radicals has all the characteristics of a radical-radical coupling

Theoretical study of intramolecular anion radical cycloaddition of the phenyl-substituted bis(enone)

DFT (U)B3LYP calculations with the 6-31G(d,p), 6-31+G(d,p), and 6-311+G(d,p) basis sets were carried out to investigate the mechanisms of the three reactions from the phenyl-substituted bis(enone) anion radical to the cis-bicyclobutane anion radical (cis-P −) [ R - → cis- P - (1)], to the trans-bicyclobutane anion radical (trans-P −) [ R - → trans- P - (2)], and to the Diels–Alder cycloaddition anion radical (da-P −) [ R - → da- P - (3)], respectively, in both the vacuum and the tetrahydrofuran (THF) solvent. The calculations indicate that the reactions occurring in both phases have the same skeleton of the energy profile for each of the three channels. The three reaction processes all consist of two reaction steps. The first step for reaction (1) is to form a trans-intermediate having a five-atom ring via a trans-transition state and the second step is to form the cis-P − product via a cis-transition state. The first steps of reactions (2) and (3) are both to form a cis-intermediate having a five-atom ring via a cis-transition state and the second steps are to form the trans-P − product via a trans-transition state for reaction (2) and to form the da-P − product via a transition state for reaction (3). The B3LYP calculations indicate that trans-P − is the dominant product in both the vacuum and the THF solvent. The possibilities of the electron transfers from the three kinds of aromatic anion radicals (the chrysene, anthracene, and naphthalene anion radicals) to the neutral reactant and from the trans-P −, cis-P −, and da-P − products to the neutral reactant were explored using the B3LYP/6-311+G(d,p) method by means of calculating the electron affinities of the respective neutral species. The calculations indicate that the chain reaction mechanism for the anion radical cyclobutanation of the phenyl-substituted bis(enone) suggested by experimentalists is feasible thermodynamically.

Photoresist and Fluorocarbon Postplasma Etch Residue Removal Using Electrochemically Generated Radical Anions

Integration of new materials into semiconductor manufacturing sequences demands cleaning processes that are compatible with copper and low dielectric constant (low-k) materials. Conventional oxidative cleaning processes are currently used to remove fluorocarbon-based postplasma etch residues; however, these processes are generally incompatible with organic-containing low-k candidate materials. A photoresist removal and etch residue cleaning process based on reductive naphthalene radical anion chemistry has been developed and evaluated on patterned low-k etch residue samples. Solutions of naphthalene radical anions are generated by electrolysis using platinum electrodes in a split electrochemical cell. The radical anion process cleans effectively at room temperature and thus requires no elevated temperature steps for film removal or surface drying. The removal mechanism is a synergistic combination of solvent swelling and fluorocarbon attack, resulting in effective etch-residue removal; removal from vias as small as has been demonstrated. Preliminary investigations indicate chemical compatibility with both Coral and methylsilsesquioxane low-k materials.

Ring-current aromaticity in open-shell systems

The ab initio ipsocentric approach to calculation and mapping of induced orbital current density is extended to open-shell π systems. ROHF/6-31G ∗∗ calculations document the (magnetic) aromaticity of planar 4 nπ triplet states of 4π/8π annulenes and isobenzofulvene, and quintet excited-state azulene. An orbital model for currents rationalises the generalised form of Baird’s rules, by which 4 n + 2 annulenes are aromatic (antiaromatic) in states of even (odd) total spin (vice versa for 4 nπ annulenes). In contrast to geometric criteria, ring-currents predict antiaromaticity for the doublet naphthalene radical anion.

Determinação de ascarel em óleo isolante de transformadores

The contamination level of silicon oil used as insulation liquid in high-voltage transformers by ascarel (PCBs) is above those permitted by the Brazilian law. Thus new techniques able to detect ascarel, with low operational costs, are very attractive. The present work proposes an analysis of the contamination levels of silicon oil using the following techniques: naphthalene anion radical reaction for ascarel dechlorination; and potentiometry with an ion-selective electrode for chloride ion determination. The data obtained with the proposed methodology agree well with those from the official methodology, (method IEC 61619).

Metal Chloride Reductions with Aromatic Radical Anions. The Magnesium Chloride Catalysed Cleavage of Tetrahydrofuran by Sodium Naphthalene Radical Anion

Activated metals for organic synthesis are often prepared by reduction of metal salts using alkali metal aromatic radical anions. The reduction of magnesium chloride has been examined by NMR. Whereas the expected reduction to the metal occurred with lithium or potassium naphthalene radical anion, under certain conditions, with sodium naphthalene radical anion, no metallic magnesium was precipitated and dark red solutions were obtained. It was also found that solutions of sodium naphthalene radical anion in tetrahydrofuran, in the presence of a catalytic amount of magnesium chloride, quickly became diamagnetic. A mechanism involving bimetallic species is postulated to explain the results.

Calorimetrically Measurable Enthalpic Isotope Effect

Calorimetric techniques have revealed that the enthalpy of reaction with water is more exothermic by about 2.2 kcal/mol, for the perdeuteriated naphthalene anion radical (K+C10D8*-(s) + H2O(liq) --> 1/2C10D8H2(s) + 1/2C10D8(s) + KOH(aq)) than it is for the perprotiated system. These results, when coupled with the known enthalpy of electron transfer between naphthalene and its perdeuteriated analogue imply that the heat of hydrogenation of naphthalene decreases by about 1.8 kcal/mol upon perdeuteriation of the naphthalene.

Study on the NaNp/Al 2O 3–SiO 2 system

Sodium naphthenide (NaNp) deposited on aluminosilicate gels yields systems that exhibit signals in EPR spectra, the multiplicity, g values, and intensities of which depend on the gel composition. The symmetrical singlets (I) of a g 1 value of 2.00 were assigned to the complexed naphthalene anion radicals on the centers occurring on the surfaces of the alumina and silica phases of the gels studied. Those radicals complexed on surface Lewis acid sites are of hard acid/hard base type according to Pearson theory, and are bonded to the sites by ionic forces. The asymmetrical singlets (II) described by the value g 2 = 1.95 were assigned to naphthalene anion radicals, which are complexed by the centers of the aluminosilicate phase of the gels studied. Those radicals, complexed on surface Lewis acid sites of this phase, are of soft acid/soft base type and are bonded to the sites by covalent bonds. The highest intensity of the singlet (I) was recorded for the system containing alumina gel. The highest intensity of the singlet (II) was recorded for the system containing Al 2O 3 in 30 wt%. The structures of Lewis acid sites on aluminosilicate phases are postulated to be different from those on alumina or silica phases.

Dechlorination of polychlorinated organic compounds by electrochemical reduction with naphthalene radical anion as mediator

Electrochemical reduction with electrochemically generated naphthalene radical anion in N, N-dimethylformamide was applied to the dechlorination of five representative POPs, namely HCB, lindane, DDT, PCP and aldrin. Rapid and complete dechlorination was possible for lindane and DDT to give nearly quantitative yields of benzene and 1,1-diphenylethane, respectively. HCB was reduced through complex reaction pathways to yield unknown products. Dechlorination of PCP and aldrin beyond dichlorinated compounds was difficult because of their very negative reduction potential. The reaction pathways for each dechlorination were proposed with the identification of intermediates.

Dechlorination of PCBs by electrochemical reduction with aromatic radical anion as mediator

Mediated electrochemical reduction was applied to the dechlorination of polychlorinated biphenyls (PCBs) in tetra- n-butylammonium perchlorate/dimethylformamide solution. Rapid and complete dechlorination was possible with biphenyl or naphthalene as the mediator, whereas the reaction was much slower with anthracene or 9,10-diphenylanthracene. The reaction rate was so high with naphthalene or biphenyl radical anion that differences in reactivity could not be observed between congeners. Side reactions, other than biphenyl formation, could occur depending upon the mediators and the substrates, but contributed less than 10% of the total products in the case of naphthalene-mediated dechlorination. Almost all chloride ion formed in the dechlorination remained in the cathode solution. The order of the reaction was determined to be 0.5 for the substrate and 1 for the mediator (naphthalene) in the dechlorination of 2-chlorobiphenyl; identical to results for the mediated dechlorination of 1-chloronaphthalene. The reaction rate in practical PCB dechlorination could be estimated with the use of the initial concentration of the mediator and chlorine content of the solution provided that the problem of the deactivation of the electrode surface could be solved.

Photophysics of 1,8-Bis(dimethylamino)naphthalene in Solution: Internal Charge Transfer with a Twist

The photophysical properties of the excited states of 1,8-(bisdimethylamino)naphthalene have been investigated by a combination of experimental spectroscopic methods and quantum chemical calculations. The experiments show that vertical excitation occurs to an 1La-type state from which internal conversion occurs to a state with dominant internal charge-transfer character. This character gives rise to weak emissive properties, a strong solvent dependence of the emission, and transient absorption spectra that carry the signature of the steady-state absorption spectra of the naphthalene radical anion. The quantum chemical calculations support the interpretation of the experimental studies, and enable us to put their results into a broader perspective. They explain the order of the lower excited states of 1,8-(bisdimethylamino)naphthalene and related compounds as well as the role of intramolecular relaxation upon excitation, thereby elucidating the large Stokes shift already observed in nonpolar solvents.

Vibrational spectra and electron–vibration interactions of the naphthalene radical anion — Experimental and theoretical study

Vibrational analysis is carried out for the radical anions of naphthalene-h8 and -d8. Their infrared (IR) spectra are observed in tetrahydrofuran by using a cell designed for IR measurements of unstable species. The vibrational force field and the IR intensities are calculated by the ab initio molecular orbital and density functional methods at various theoretical levels. As found in the cases of the radical cations of many polycyclic aromatic hydrocarbons (PAHs), a few strong IR bands with intensities of the order of 102 km mol–1 are observed in the 1700–900 cm–1 region. These observed spectral features are well reproduced by the calculations at the CASSCF (complete active space self-consistent field) and B3LYP (Becke's three-parameter hybrid method using the Lee–Yang–Parr correlation functional) levels. The calculation at the B3LYP level gives a better fit between the observed and calculated absolute IR intensities. Normal modes and the origin of the strong IR intensities characteristic of the radical anions are discussed in terms of molecular symmetry coordinates and the dipole derivatives based on these coordinates. It is found that the IR intensities of the b2u modes below 2000 cm–1 are dominated by the contribution from one molecular symmetry coordinate, in which the C—C bonds in one ring stretch while those in the other ring shrink. The mechanism that gives rise to the strong IR intensity for this vibration is discussed by examining the changes in the electronic structure induced by this vibration.Key words: vibrational spectra, electron–vibration interaction, naphthalene, radical anion.