Product distributions in the addition of the hydride ion to cyclopentadienyliron complexes of substituted benzenes

Fifteen [C₆H₅(X)FeCp]⁺ cations with substituents X having different electron-donating or electron-withdrawing effects were treated with NaBH₄ in glyme or THF. The relative distributions of products from o-, m-, p- and ipso-additions of the hydride ion to the arene ring were determined by high resolution ¹H NMR. For the η⁶-N,N-dimethylaniline-η⁵-cyclopentadienyliron cation with the most electron-donating of the substituents studied, only m- and p-hydride addition products were obtained, while in the reaction with the η⁶-nitrobenzene-η⁵-cyclopentadienyliron cation, which contained the most electron-withdrawing of the substituents investigated, only the o-addition product was formed. For the other 13 cations, with X  C₆H₅O, CH₃O, p-CH₃C₆H₄S, C₆H₅CH₂, (CH₃)₃C, CH₃, CH₃CH₂, C₆H₅, Cl, COOCH₃, C₆H₅CO, CN and p-CH₃C₆H₄SO₂, o-, m- and p-hydride addition products were obtained in all cases, with a few instances also giving very minor amounts of ipso-adducts. The relative product distributions observed were interpreted by suggesting that while electronic effects played a major role, steric factors and free valency effects favoring o-addition as suggested by MO calculations [5] could also exert their influence in giving rise to the overall results.     

Desulfonyloxyiodination of arenesulfonic acids with mCPBA and molecular iodine

Treatment of p-alkylbenzenesulfonic acids with mCPBA and molecular iodine gave p-alkyliodobenzenes in good to moderate yields via electrophilic ipso-substitution by the iodonium species (I⁺) formed. This desulfonyloxyiodination was promoted by the addition of a catalytic amount of iodoarenes, such as o-iodobenzoic acid. The same treatment of dimethylbenzenesulfonic acids and trimethylbenzenesulfonic acids with mCPBA and molecular iodine proceeded smoothly both in the absence and in the presence of o-iodobenzoic acid to provide the corresponding monoiodo-dimethylbenzene and diiodo-dimethylbenzene, and diiodo-trimethylbenzene and triiodo-trimethylbenzene, in good to moderate yields, respectively. On the other hand, the same desulfonyloxyiodination of benzenesulfonic acid and p-chlorobenzenesulfonic acid with mCPBA and molecular iodine proceeded only in the presence of o-iodobenzoic acid to generate iodobenzene and p-chloroiodobenzene, respectively, in moderate yields.     

On the nature of the phenylazo group

Three Hammett substituent constants for the p-phenylazo group were determined. The ionization of p-phenylazobenzoic acid in 50% ethanol gives a σ_p value of 0·26. The NBS bromination of p-phenylazotoluene vs toluene in benzene at 80° gives a σ⁺ value of ?0·15. The NBS bromination of 4-phenylazo-3-cyanotoluene vs m-tolunitrile in benzene at 80° give a σ^. value of 0·28. It is concluded that the phenylazo group is a ?I substituent and either a +M or ?M substituent depending on the reaction being studied. This makes the phenylazo group an activator in nucleophilic, electrophilic and free radical reactions.     

Prediction of NHC-catalyzed chemoselective functionalizations of carbonyl compounds: a general mechanistic map

Generally, N-heterocyclic carbene (NHC) complexed with carbonyl compounds would transform into several important active intermediates, i.e., enolates, Breslow intermediates, or acylazolium intermediates, which act as either a nucleophile (Nu) or an electrophile (E) to react with the other E/Nu partner. Hence, the key to predicting the origin of chemoselectivity is to compute the activity (i.e., electrophilic index ω for E and nucleophilic index N for Nu) and stability of the intermediates and products, which are suggested in a general mechanistic map of these reactions. To support this point, we selected and studied different cases of the NHC-catalyzed reactions of carbonyl compounds in the presence of a base and/or an oxidant, in which multiple possible pathways involving acylazolium, enolate, Breslow, and α,β-unsaturated acylazolium intermediates were proposed and a novel index ω + N of the E and Nu partners was employed to exactly predict the energy barrier of the chemoselective step in theory. This work provides a guide for determining the general principle behind organocatalytic reactions with various chemoselectivities, and suggests a general application of the reaction index in predicting the chemoselectivity of the nucleophilic and electrophilic reactions.

A novel index ω + N can be used to predict the chemoselectivity according to the general NHC-catalyzed reaction mechanism.     

Excess volumes of mixing of 1,2-dichloroethane and aromatic hydrocarbons

Excess volumes of mixing, V^E, for binary mixtures of 1,2-dichloroethane with benzene, toluene, o^?, m^?, and p-xylenes have been determined at 308.15 K over the complete composition range. V^E is positive for all these mixtures and varies in the order m-xylene >o-xylene >p-xylene > benzene > toluene. The experimental data have been analyzed in terms of the Prigogine's average potential cell model coupled with Balescu's theory. The calculated V^E values do not agree with the corresponding experimental values.     

Regiospecific photoisomerization of fluorinated (E,E)-1,4-diphenyl-1,3-butadienes

Photoisomerization of five fluorinated E,E-1-(R-phenyl)-4-phenyl-1,3-butadienes in solution (R = 1: p-monofluoro, 2: m,m′-difluoro, 3: m,m′,p-trifluoro, 4: o,o′,m,m′-tetrafluoro, 5: o,o′,m,m′,p-pentafluoro) was investigated via direct irradiation. Our results indicated that cis-trans photoisomerization of the fluorinated 1,4-diphenyl-1,3-butadienes in the excited singlet state took place exclusively at the CC bonds closer to the fluorine substituents.     

DMT [(−)-(2<Emphasis Type="Italic">R</Emphasis>,3<Emphasis Type="Italic">R</Emphasis>)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol], a highly efficient host compound for nitroaromatic guests: selectivity,X-ray and thermal analyses

In this work, we reveal that the compound (?)-(2R,3R)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) is a highly efficient host material for nitroaromatics o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT) and nitrobenzene (NB). Each of these guests was included with a 2:1 host:guest ratio. The host displayed selectivity for p-NT and NB when these guests were mixed in equimolar proportions with any one of the other guest solvents, and the host recrystallized from this binary mixture. A selectivity order for the host in these conditions was thus noted to be NB?≈?p-NT?>?o-NT?>?m-NT. Furthermore, guests were also mixed in non-equimolar proportions and the host behaviour analysed, the results of which were in accordance with observations from the equimolar studies. Additionally, an equimolar quaternary experiment of all four guests provided a somewhat adjusted host selectivity order [p-NT (39.9%)?>?NB (30.2%)?>?m-NT (17.1%)?>?o-NT (12.8%)]. Single crystal diffraction analyses of all four complexes showed the crystals to share the same host packing, and comparable host–guest interactions were observed in each. However, thermal analyses, both DSC and TG, showed that the preferred guests p-NT and NB formed complexes with increased relative thermal stabilities, and this observation correlated with the selective behaviour of the host in competition experiments.     

Acute Toxicity of Cresols to Pseudomonas — An Initial Oxygen Uptake Method

Acute toxicity of cresols to both Pseudomonas I and II was estimated by an initial oxygen uptake method. Inhibition studies of toluene and cresols on the oxidation of either benzoate by Pseudomnas I or phenol by Pseudomonas II were analyzed and expressed as oxygen uptake rates. Double reciprocal plots for the inhibiton by cresols of oxygen uptake in Pseudomonas, two physical constants, Vmaxi and Ki, were obtained. The Vmaxi of o?, m? and p-cresol were 80%, 81% and 57% of Vmax in Pseudomnas I, and 10%, 25% and 36% in Pseudomonas II, respectively. Thus, the toxicity to Pseudomonas I decreases in the order p- > o- ≥ m-cresol, whereas to Pseudomonas II, the order is changed to o- > m- > p-cresol. This difference in the toxicity order is probably due to the allosteric effect of p-cresol towards Pseudomonas II. Inasmuch as most compounds inhibit noncompetively, the relative toxicity of different compounds can be estimated by a new toxicity parameter RI (relative inhibition) which is defined as 100/Ki. By comparing the RI value of each compound, the toxicity to Pseudomonas I decreases in the order m-chlorophenol > p-cresol > p-chlorophenol > o-cresol ≥ m-cresol > o-chlorophenol > toluene > phenol.     

Synthesis of p-tert-butylcalix[4]arene semitubes and their binding studies with C60

The synthesis of p-tert-butylcalix[4]arene semitubes in one step reaction with fairly good yields is described. The structures of these compounds were confirmed by ¹H NMR, ¹³CNMR and mass spectrometry. The complexation ability of these compounds with C₆₀ was investigated and found that they are able to form 1:1 complexes. The stability constants of these complexes were determined and found to be 15, 203 and 525 dm³ mol^?1 for the semitubes 3a, 3b, 3c respectively. The binding energies of each of C₆₀, the semitubes and the complexes are calculated using PM6 (Semiempirical quantum chemical) and DFT (Density Functional Theory) methods and found in the order m > p > o. On the other hand, the calculated binding energies using DFT method showed that the stabilities of both centered and side complexes are in the order p > m > o.     

The Role of Ate Complexes in the Lithium‐Sulfur,Lithium‐Selenium and Lithium‐Tellurium Exchange Reactions

Hypervalent ate complexes are presumptive intermediates in the metal‐halogen, metal‐tellurium, and related exchange reactions. The effect of o,o′‐biphenyldiyl vs. diphenyl substitution on formation of tellurium ate complexes was studied by a kinetic technique and by NMR spectroscopy. Only a modest increase in the association constant (K_ate) was measured. When Li/M exchanges of o,o′‐biphenyldiyl sulfides and selenides were made intramolecular by means of a m‐terphenyl framework ( 12‐S, 12‐Se, 21 ), enormous increases (>10⁹) in the rate of Li/S and Li/Se exchange were observed compared to acyclic models. Apparently, these systems are ideally preorganized to favor the T‐shaped geometry of the hypervalent intermediates. For the selenium systems, ate complex intermediates ( 20‐Se, 26 ) were detected spectroscopically in THF‐ or THF/HMPA‐containing solutions. A DNMR study showed that Li/Se exchange was substantially faster than exchange of the lithium reagents with the ate complex. Therefore, these ate complexes are not on the actual Li/Se exchange pathway.     

Synthesis of porous vinylnaphthalene/divinylnaphthalene copolymers and their sorptive properties towards phenol and its derivatives

Four porous vinylnaphthalene/divinylnaphthalene (VN/DVN) polymers having three different nominal crosslinking degrees (60, 80 and 100 wt.%) have been synthesized using the suspension polymerization method in the presence of toluene and decane.The use of various crosslinking levels and inert diluents was aimed at changing the extent of polymeric network-diluent interactions. The resultant polymers have specific surface area in the range 450-700 m²/g depending on the DVN content. Two sets of pores were detected in all resins: one with the diameter of ≈2 nm and the second one in the range of 30-40 nm. Their sorptive properties have been studied using dilute (0.5 mmol/l) solutions of phenol and its derivatives (o-chlorophenol, 2-methylphenol, o-nitrophenol, m-nitrophenol and p-nitrophenol). It has been found that sorption, at low equilibrium concentration, follows the order: o-nitrophenol > o-chlorophenol > m-nitrophenol > o-methylphenol > p-nitrophenol > phenol. Full characteristics of the porous structure of resultant polymers was obtained by nitrogen adsorption at 77 K and their surface properties analyzed using Inverse Gas Chromatography.     

Unexpected Migratory Insertion Reactions of M(alkyl)2 (M=Zn,Cd) and Diamidocarbenes

The electrophilic character of free diamidocarbenes (DACs) allows them to activate inert bonds in small molecules, such as NH₃ and P₄. Herein, we report that metal coordinated DACs also exhibit electrophilic reactivity, undergoing attack by Zn and Cd dialkyl precursors to afford the migratory insertion products [(6‐MesDAC‐R)MR] (M=Zn, Cd; R=Et, Me; Mes=mesityl). These species were formed via the spectroscopically characterised intermediates [(6‐MesDAC)MR₂], exhibiting barriers to migratory insertion which increase in the order MR₂ = ZnEt₂ < ZnMe₂ < CdMe₂. Compound [(6‐MesDAC‐Me)CdMe] showed limited stability, undergoing deposition of Cd metal, by an apparent β‐H elimination pathway. These results raise doubts about the suitability of diamidocarbenes as ligands in catalytic reactions involving metal species bearing nucleophilic ligands (M‐R, M‐H).     

A practical synthesis of new S,N-disubstituted derivatives of 5-(4-methylpiperidino)methyl-2-thiouracil

5-(4-Methylpiperidino)methyl-2-thiouracil (1) has been obtained via the Mannich reaction between 2-thiouracil, paraformaldehyde, and a cyclic secondary amine such as 4-methylpiperidine (4-MP) in ethanol. New S,N(1)-di-o-(m- and p-)bromo-(nitro-) benzyl-substituted derivatives have been synthesized successfully in the reactions of 1 with the corresponding o-(m- and p-)bromobenzyl bromides or o-(m- and p-) nitrobenzyl chlorides in DMF solution in the presence of K₂CO₃. The opposite method of synthesis, that is, the reaction between 2-o-(m- and p-)bromobenzylthio-1-o-(m- and p-)bromobenzyluracils and 2-o-(m- and p-)nitrobenzylthio-1-o-(m- and p-) nitrobenzyluracils (8), with paraformaldehyde and 4-methylpiperidine in ethanol failed, indicating the important role of the enol form of 2-thiouracil for the Mannich reaction to be successful.     

Synthesis and characterization of some new aromatic diamine monomers from oxidative coupling of anilines and substituted aniline with 4-amino-N,N-dimethyl aniline

New aromatic diamine monomers prepared from condensation reactions of aniline, p-chloroaniline, p-nitro aniline, p-chloro-m-nitro aniline with 4-amino-N,N-dimethylaniline (2:1) (aniline:reagent) in the presence of potassium dichromate in acidic media yielded new monomers of a highly colored violet and reddish-violet. Mechanism of the reaction of aniline with 4-amino-N,N-dimethylaniline in the presence of potassium dichromate as an oxidant is expected to proceed through nucleophilic substitution reaction, and the mechanism proceeds facilitated a nucleophilic attack of the substituted aniline ring on the –NH₂ group of the reagent; through partial protonation of their –NH₂ group, forming in diamine dye and their identification was confirmed by IR, ¹H NMR, and CHN analyses.     

Neighbouring group participation in reactions of sulphides with chloramine-t

Neighbouring group participation in reactions of chloramine-T with ortho-substituted aryl methyl sulphides and diaryl sulphides has been studied. The reaction is markedly hindered by the steric effect of the ortho substituent of the phenyl ring, but groups having a CO moiety show an anchimeric effect in the following order: o-CH₂CO₂Me ~ o-CH₂CO₂H < o-CH₂CO₂^- < o-CO₂Me ~ o-CO₂H < o-CO₂^- ? 2o-CO₂ in the rate-determining step may be ruled out on the basis of salt and isotope effect. Substituents with neighbouring group participation diminish the yield of sulphilimine in solvents containing water. The electrophilic chlorination of sulphides by TsNHCl may be assumed to be the rate-determining step with the positively charged sulphonium centre stabilized by the negatively polarized or charged carbonyl-oxygen in the transition state. This type of interaction hinders the nucleophilic attack of sulphonamidate ion at the sulphonium centre in the fast product-controlling steps, decreasing the yield of sulphilimine.     

Quantum-chemical study on reactions of isocyanates with linear methanol associates: VIII. Relative reactivity of linear phenol and methanol associates toward methyl isocyanate

The mechanisms of the reactions of methyl isocyanate with phenol monomer and linear dimer were studied at the B3LYP/6-311++G(df,p) level of theory, and the results were compared with those obtained for the reactions with methanol associates. All the examined reactions involve asymmetric concerted transition states. The addition of phenol is electrophilic, whereas the addition of methanol is nucleophilic. The formation of H-complexes with phenol and methanol molecules increases not only electron-donating power but also gasphase acidity and basicity.     

Aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene and ethyl α-cyano-phenylacetate benzyl anion

The aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene (DNHB; halogeno =F, Cl, Br) with ethyl α-cyanophenylacetate (ECPA) benzyl anion has been studied by means of UV and IR spectrophotometry as well as gas chromatography. The rates of intermediate formation and product formation were determined respectively. In contrast with common S _N Ar reactions, the formation rate constant of the intermediates, substituted cyclohexadienates, was in the order of halogen =F>Br>Cl, whereas the rate constant of product formation was in the order F>Cl>Br, which revealed that the departure of the halogen atom was the rate-limiting step for the overall reaction in the presence of a sterically hindered nucleophile. These reactions could be catalyzed by the solvated electrons. The corresponding reaction intermediates, radical species, were detected by ESR and the reactions were proved to proceed mainly by a solvated-electron induced radical chain reaction mechanism.     

Double nucleophilic attack on η6-arene(pentamethylcyclopentadienyl)iridium dications. Routes from substituted benzenes to substituted cyclohexenes by addition of two hydrides and two protons

The complexes [(C₅Me₅)Ir(η⁶-arene)][BF₄]₂ (arene = toluene, toluene-d₈, t-butylbenzene, methoxybenzene, chlorobenzene, o-xylene, p-xylene, tetralin and phenol) were prepared from the arene and reduced with NaBH₄ to the η⁵-cyclohexadienyl complexes. Attack was exo at the arene and, with one exception, never at the substituent. Toluene showed no site preference but t-butylbenzene was attacked preferentially para, and chlorobenzene, ortho. Methoxybenzene was attacked ipso as well as ortho, meta (predominant), and para, and phenol gave only the meta-isomer. p-Xylene gave one isomer and o-xylene and tetralin gave two. Further reduction occurred on reaction with stronger hydride reducers (e.g., sodium bis(methoxyethoxy)dihydroaluminate) to give mixtures of 1- and 2-substituted cyclohexa-1,3-diene complexes (t-Bu, 2- ( > 95%); Me, 1- (25%), 2- (75%); Cl, 1- ( > 95%); and OMe, 1- (33%), 2- (67%)). The p-xylene complex gave a mixture of the η⁴-1,4-dimethylcyclohexa-1,3- and 1,4-diene complexes. Reaction of the cyclohexadiene complexes with HCl gas gave the free substituted cyclohexenes and [(C₅Me₅Ir)₂Cl₄]. The product from t-butylbenzene was predominantly (92%) the 3-substituted cyclohexene; that isomer (65%) and the 1-isomer (34%) were formed from toluene and the 1- (34%) and the 4-isomer (58%) were formed from chlorobenzene. Phenol gave only cyclohexanone. Overall these reactions yield the cyclohexene from the substituted benzene by addition of two hydrides and two protons and the iridium can be recycled.     

Trifluoromethyl-containing N-acylmethylenequinone imines as novel highly electrophilic agents

The strategy of searching for highly electrophilic agents in a class of chemically inert compounds - methylenequinone imines - was developed and successfully performed. The first representative of such electrophiles - N-acyl-α-methoxycarbonyl-α-trifluoromethyl-p-methylenequinone imine 6 - was synthesized. Its reactions with N-, O- and C-nucleophiles were investigated that gave various derivatives of α-trifluoromethyl-α-amino(oxy) acids as well as ß,ß,ß-trifluoropropionic acids. 3-Chloro-3-trifluoro-1,3-dihydroindol-2-ones were first obtained and their reactions with nucleophiles were studied with 1-aza-3-trifluoroindene-2-ones being formed as intermediates.     

Etude du caractere nucleophile des radicaux lors de la reaction de transfert sur la liaison O-O des peracides

Peracids RC0₃H yield free radicals R' which react either with the peracid or with solvent giving the alcohol ROH and the hydrocarbon RH. The nucleophilic character of the free radicals was modified either by substitution of the carbon bearing the odd electron by inductive groups or by changing the free radical hybridation by the means of blocked structures such as cyclic or bicyclic free radicals. For each R, the measurement of the ratio ROH/RH establishes a reactivity scale for R with the peracid O-O bond. This reactivity does not depend on free radical stability but depends strongly on nucleophilic character. A primary free radical is less reactive than a secondary one, and is much less reactive than a tertiary one. A bridgehead free radical as the bicyclo[2.2.1]heptyle-1 does not react with the peracid. These results are interpreted to indicate a transition state with charge transfer (polar effect), the peracid being electrophilic and the free radical nucleophilic; PMO theory is discussed.