Benzyl Anion Research Articles

Adsorption of actinides by chelating agents containing benzene rings, fixed on charcoal

We studied the preparation of some specific adsorbers capable of isolating and concentrating actinides. Bases of the 8-hydroxyquinoline family, diphosphineamine and tribenzylamine, salted by benzohydroxamic, benzylic or phthalic acid, are able to complex actinides in different oxidation states. As a result of the presence of the benzene rings, all the compounds are easily incorporated into active charcoal to obtain adsorbers with a highly specific surface. The adsorption behaviors of uranyl U(VI) ion, thorium(IV) and Eu(III) were studied by evaluating their distribution coefficients, Kd. Results show that all the prepared salts can adsorb the ions in the III and IV oxidation state from weak acid solutions, whereas uranyl ion is adsorbed mainly from weak basic solutions. The prepared compounds can be used successfully to absorb and concentrate actinides from nearly neutral solutions, such as natural waters. The 8-hydroxyquinoline salt of the benzylic anion showed the highest adsorption values and thus seems to be the most appropriate salt to use in the analysis of actinides in water.

Donor and acceptor properties of the chromium tricarbonyl substituent in benzylic and homobenzylic anions, cations, and radicals.

Both benzylic cations and anions are strongly stabilized by chromium tricarbonyl complexation, while benzylic radicals are largely unaffected. Density functional theory calculations were performed on primary, secondary, and tertiary benzylic species to explore the effect of substitution on the stabilizing ability of the chromium tricarbonyl moiety. Complexed 1-indanyl species were also examined to elucidate the effect of conformational restraint. It was found that the strong stabilization of benzylic anions and the slight destabilization of benzylic radicals by chromium tricarbonyl are insensitive to skeletal changes. Chromium-complexed benzylic cations, however, are highly sensitive to changes in the organic framework, with increased substitution or constriction of conformational mobility eroding the effect of the metal. 2-Indanyl species were also examined to study the effect of the chromium tricarbonyl fragment on homobenzylic species. It was found that the metal fragment stabilizes distant anions by field and inductive effects and cations by a direct interaction of the metal with the cationic carbon. Homobenzylic radicals, however, do not interact with the chromium tricarbonyl moiety and suffer a slight inductive destabilization.

Gas-phase acidities of aryldimethylsilanes†

Gas-phase acidities of aryldimethylsilanes have been determined by measuring equilibrium constants of proton-transfer reactions using a FT ion cyclotron resonance mass spectrometer. The acidity of dimethylphenylsilane was found to be 370.5 kcal mol−1, i.e., it is a stronger acid than dimethylsilane by 2.7 kcal mol−1. The acid-enhancing effect of the phenyl group is significantly smaller than in the carbon analog. In addition, the acidities of aryldimethylsilanes were linearly correlated with the standard substituent constant (σ°), giving a ρ of 4.6, indicating that the thermodynamic stabilities of silyl anions are less sensitive to the polar effects of substituents than benzoate, phenoxide, anilide, and benzyl anions. More importantly, it was found that the p-nitro group, which has a large π-electron-accepting ability, also conforms to the σ° correlation, suggesting that π-delocalization does not play a role in the stabilization of silyl anions; this is in contrast to the π-effects observed in carbon analogs. This is supported by theoretical stabilization energies and optimized geometrical features based on ab initio calculations.

Up to Six Units of Charge and Twist-Boat Benzene Moieties: Alkali Metal Reduction of Phenyl-Perisubstituted Benzenes1

Phenyl-perisubstituted benzenes, tetraphenylbenzene (1) and hexaphenylbenzene (2), were reduced by lithium and sodium metal in THF-d8 under high vacuum. The reduction process and the nature of the reduction products were studied by NMR. Tetraphenylbenzene was reduced by both metals to yield the corresponding dianionic salt. It was found that the addition of extra charge into the system, restricted the free rotation of the four phenyl substituents about the σ bond connecting them to the central ring (G⧧181 = 7.8 ± 0.2 kcal mol-1). The reaction of the alkali metals with 2 yielded four diamagnetic species: the first three were assigned to the dianion, tetraanion, and the surprising hexaanion of 2. These species were calculated using density functional theory (DFT) and were found to have central benzene rings with an unusual twist-boat geometry. Computational and experimental evidences show that each phenyl ring and its attached carbon of the central ring behave like a benzyl anion. We therefore view the hexaanion of 2 as a cyclohexa(benzylanion). The fourth diamagnetic species was a product of a double-sided cyclization, which yielded the dianion of dihydro-9,18-diphenylphenanthro[9,10-b]triphenylene (9,18-diphenyltetrabenz[a,c,h,j]anthracene dianion, 32-). Reaction of the dianion with oxygen gave 3 in improved yields compared to literature preparations.

Alkoxides of o-silyl benzyl alcohols in cleavage reactions: approaches to benzyl and silyl anion equivalents

The alkoxides of o-silyl benzyl alcohols 4 undergo cleavage reactions under mild conditions allowing transfer of a benzyl or silyl group to an electrophile. Reactions 3a [Formula: see text] 8, and 3c or 4c [Formula: see text] 11 illustrate their potential as benzyl and silyl anion equivalents.Key words: silyl migration, benzyl anion equivalent, silyl anion equivalent, β-silyl ketone, γ-hydroxysilane.

Alkoxides of <i>o</i>-silyl benzyl alcohols in cleavage reactions: approaches to benzyl and silyl anion equivalents

Alkoxides of <i>o</i>-silyl benzyl alcohols in cleavage reactions: approaches to benzyl and silyl anion equivalents

Synthesis of PP graft copolymers via anionic living graft-from reactions of polypropylene containing reactivep-methylstyrene units

In this article, we discuss a new chemical route for preparing polypropylene (PP) graft copolymers containing a PP backbone and several (polar and nonpolar) polymer side chains, including polybutadiene, polystyrene, poly(p-methylstyrene), poly(methyl methacrylate), and polyacrylonitrile. The new PP graft copolymers had a controlled molecular structure and a known PP molecular weight, graft density, graft length, and narrow molecular weight distribution of the side chains. The chemistry involves an intermediate poly(propylene-co-p-methylstyrene) copolymer containing few p-methylstyrene (p-MS) units. The methyl group in a p-MS unit could be lithiated selectively by alkylithium to form a stable benzylic anion. Because of the insolubility of the PP copolymer at room temperature, the excess alkylithium could be removed completely from the lithiated polymer. By the addition of the anionically polymerizable monomers, including polar and nonpolar monomers, the stable benzylic anions in PP initiated a living anionic graft-from polymerization at ambient temperature to produce PP graft copolymers without any significant side reactions. The side-chain length was basically proportional to the reaction time and monomer concentration. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4176–4183, 1999

Total Synthesis of Michellamines A−C, Korupensamines A−D, and Ancistrobrevine B

Efficient syntheses of the title compounds have been developed. Several strategies for preparation of each of the naphthalene and tetrahydroisoquinoline (THIQ) portions were developed. Initial attempts to use benzyne plus furan cycloaddition reactions were thwarted by the unfavorable sense of the regiochemical outcome. An interesting annulation reaction of benzynes derived from 2,4-dibromophenol derivatives formed the core of the shortest naphthalene synthesis. An alternative annulation initiated by the addition of a benzylic sulfone anion to methyl crotonate led to an efficient naphthol synthesis amenable to large scale. The THIQ synthesis of Bringmann was used initially and subsequently complemented by a route whose key step involved the opening of N-tosyl-2-methylethyleneimine by a 3,5-dimethoxyphenylcuprate reagent. The results from a variety of aryl cross-coupling reactions are described. Suzuki coupling of the boronic acid derived from the naphthalene moiety with a THIQ-iodide was the most generally...

Chemical Hermaphroditism: The Potential of the Cr(CO)3 Moiety To Stabilize Transition States and Intermediates with Anionic, Cationic, or Radical Character at the Benzylic Position

It is known that both benzylic cations and anions are stabilized by Cr(CO)3 complexation. This unusual characteristic of chromium arenes has been the subject of many synthetic, spectroscopic, and physical organic studies over the last four decades. The effect of Cr(CO)3 on benzylic radicals has received comparatively little attention, however. In this report, cyclopropylcarbinyl anions, cations, and radicals substituted with both phenyl and Cr(CO)3-phenyl groups are shown to rearrange via ring-opening to produce, selectively, Cr(CO)3-stabilized benzylic anions, cations, and radicals, implying that the Cr(CO)3 moiety is capable of stabilizing transition states with ionic or radical character at the benzylic position. The highest selectivity (>99:<1) was observed in the anionic reaction, slightly lesser selectivity (95:5) was observed in the cationic reaction, and only modest selectivity (2.5:1) was observed in the radical reaction. A parallel trend in ground-state stabilities of Cr(CO)3-complexed benzyl an...

Structural and Energetical Characterization of Reactive Intermediates Derived from Toluene-Cr(CO)3

Considerable configurational stability even for the radical, which should allow radical transformations with retention of configuration, is one of the most striking results obtained in a theoretical investigation into the structure and energetics of reactive intermediates in the chemistry of arene–Cr(CO)3 complexes (see picture), such as the benzylic anions, cations, and radicals, by using density functional methods.

Controlled monohalogenation of phosphonates: A new route to pure α-monohalogenated diethyl benzylphosphonates

Starting from diethyl benzylphosphonates, a wide variety of diethyl α-monofluoro, chloro, bromo and iodobenzylphosphonates have been obtained in pure form by a one-pot procedure. This high yielding method implies the intermediate protection of the benzyl anion with TMSCl followed by halogenation with an electrophilic halogenating reagent.

Synthesis, properties and reactivity of the phenylcarbene anion in the gas phase †

The gas-phase synthesis and characterization of phenylcarbene anion, PhCH˙– (1˙–), are reported. This archetypal arylcarbene radical anion is produced in isomerically-pure form by dissociative electron ionization of phenyldiazirine in a flowing afterglow–triple quadrupole instrument. The structure and purity of PhCH˙– are established by authentication of its oximate derivative, PhCHNO–, by collision induced dissociation (CID). Ab initio calculations indicate a 2A″ ground state for 1˙–, with a π-radical/σ-anion electronic configuration, which is 11–12 kcal mol–1 lower in energy than the π-anion/σ-radical 2A′ state. Reactions of PhCH˙– with a series of small molecules are described that reveal its strong base and nucleophilic character. PhCH˙– abstracts a sulfur-atom from CS2 and OCS, N-atom from N2O, and H-atom from (CH3)2NH, propene and (CH3)2S. Nucleophilic displacement of Cl– from CH3Cl by 1˙– occurs at 41% of the collision rate; more than forty times faster than for the benzyl anion. PhCH˙– exchanges both the carbene hydrogen and a hydrogen in the phenyl ring upon reaction with ND3 or D2O, which is consistent with theoretical predictions that indicate similar energies for PhCH˙– and α,n-didehydrotoluene anion isomers. Acid–base bracketing and Cooks’ kinetic method were used to determine the proton affinity and electron binding energy of PhCH˙– to be 392.0 ± 2.1 kcal mol–1 and 27.8 ± 0.7 kcal mol–1, respectively. These quantities were used to derive the heat of formation of phenylcarbene. The value obtained, 103.8 ± 2.2 kcal mol–1, is in excellent agreement with that recently measured by energy-resolved collision-induced dissociation (102.8 ± 3.5 kcal mol–1: J. C. Poutsma, J. J. Nash, J. A. Paulino and R. R. Squires, J. Am. Chem. Soc., 1997, 119, 4686).

Direct Observation of the Benzyl Radical and the Benzyl Anion within Cation-Exchanged Zeolites. A Nanosecond Laser Study

Direct Observation of the Benzyl Radical and the Benzyl Anion within Cation-Exchanged Zeolites. A Nanosecond Laser Study

An AM1 MO study of bond dissociation energies in substituted benzene and toluene derivatives relative to the principle of maximum hardness

The heats of formation of a series of m- and p-substituted benzene and toluene derivatives, Ar-Y and ArCH 2-Y, and their phenyl or benzyl cations, anions, and radicals were calculated by the semiempirical AM1 MO method. Using this data and either the experimental values for the Y species or those obtained by the ab initio CBS-4 method, the heterolytic and homolytic bond dissociation energies (BDEs) were calculated along with the electron transfer energies for the ions. While the values of the homolytic BDEs were essentially independent of the ring substituents, a plot of the heterolytic BDEs versus the electron transfer energies gave a straight line of unit slope with an intercept at ΔH homo thus confirming that ΔH hot = ΔH ET + ΔH homo. Likewise, a plot of the appropriate HOMO or LUMO energies of the phenyl, benzyl, or Y ions versus ΔH hot gave a linear plot in agreement with the principle of maximum hardness. A positive charge adjacent to the bond being broken increases the ΔH homo value while a negative charge decreases ΔH homo [Display omitted] .

Formation of two deprotonated forms of benzyl acetate and higher homologues: some unusual fragmentations

Deprotonation of RCO 2CH 2Ph (R = Me, Et, iso Pr) with HO − in the gas phase yields the two (M-H) − ions (R-H) −-CO 2CH 2Ph and RCO 2 −-CHPh which do not interconvert under conditions of collisional activation. When R = tert Bu, deprotonation forms the benzylic anion exclusively. Both anions undergo fragmentation following extensive rearrangement. The enolate anions (R-H)- −CO 2CH 2Ph lose CO 2 following a Claisen type rearrangement. The benzylic anion RCO 2 −-CHPh undergoes two complex rearrangements, viz (i) a 1,2 Wittig type rearrangement yielding (Ph)(R)CHO − and CO, and (ii) loss of the elements of R. The latter reaction is not a simple cleavage of R·: deuterium labelling supports stepwise loss of [H· + (R-H)] and product ion studies suggest the reaction proceeds through the complex rearrangement pathway RCO 2- −CHPh → RCOCH(Ph)O − → RCH(O −)COPh → [PhCOCHO] −· + H· + (R-H). The last step may proceed via a cyclic radical anion/radical intermediate.

Metallation of benzylic amines via amine-borane complexes

Formation of borane complexes of N, N-dimethylbenzylamine, N, N-dimethyl(1-naphthyl)methylamine, N, N-dimethyl(2-naphthyl)methylamine, N-methyltetrahydroisoquinoline and N-methylisoindoline facilitates regioselective metallation of these systems using BuLi, giving intermediate benzylic anions which react with a range of electrophiles to give products in good yield.

Electron transfer driven reactions of transition metal π-complexes: Hydrogenation of styrene-Cr(CO) 3 derivatives by samarium(II)iodide in the presence of water

The hydrogenation of the double bond of styrene-Cr(CO) 3 and some dihydronaphthalene-Cr(CO) 3 derivatives is achieved using samarium(II)iodide in the presence of water. 1,2-Dihydronaphthalene complexes carrying olefinic side chains in 4-position are reduced with virtually complete regio- and diastereocontrol leading to 1- endo-substituted tetralin complexes. The reactions seem to proceed via Cr(CO) 3 complexed benzylic radicals which are trapped by electron transfer to give the corresponding Cr-stabilized benzylic anions.

Catalytic Si-C bond formation by nucleophilic substitution at silicon by benzyl anions generated over KNH2 loaded on alumina

The catalytic substitution at silicon occurs in the reaction of toluene and diethylsilane in the presence of KNH2 loaded on alumina, the yield of benzyldiethylsilane being 85% in 40 h at 329 K. Benzene also reacted with diethylsilane in the presence of the catalyst to afford a 7.5% yield of benzyl diethylsilane in 20 h at 329 K.

An unexpected transformation of benzyl carbamates into α-azidobenzeneacetamides

Successive treatment of benzyl carbamates 5 (Z-protected secondary amines) with lithium diisopropylamide (LDA), diphenyl phosphorochloridate (DPPC1), and NaN3 yielded the corresponding ã-azidobenzeneacetamides 6 in 45–50% yield (Schemes 2 and 3). In the case of Z-protected diisopropylamine 5b, the phosphate 7 was isolated as a minor product. A reaction mechanism for this unexpected transformation is proposed in Scheme 4, the key step being the ring closure of a benzylic anion to give an oxirane intermediate B. In cursory experiments, it was demonstrated that ã-azidobenzeneacetamides 6 can be used as 2-phenylglycine synthons in the formation of dipeptides by using a phosphine-mediated coupling (Scheme 5).

1,6-conjugate addition to o-vinylphenyloxazolines. Syntheses of chuangxinol and 3-n-butylphthalide

Phtalhides are prepared from o-vinylphenyloxazolines in one pot reaction by 1,6-conjugate addition of alkyllithium and trapping of the benzylic anion with MoOPH, followed by hydrolysis with aqueous oxalic acid. This method was applied to the syntheses of two natural products: chuangxinol and 3-n-butylphthalide.