Structurally Diverse Boron–Nitrogen Heterocycles from an N2O23− Formazanate Ligand

Five new compounds comprised of unprecedented boron–nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N₂O₂³⁻ formazanate ligand with BF₃⋅OEt₂ and NEt₃. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox-active heterocycles were characterized using UV/vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography.     

[SnBi3]5− —A Carbonate Analogue Comprising Exclusively Metal Atoms

The new [SnBi₃]⁵⁻ polyanion is obtained by the reaction of K₃Bi₂ with K₄Sn₉ or K₁₂Sn₁₇ in liquid ammonia. The anion is iso(valence)electronic with and structurally analogous to the carbonate ion. Despite the high negative charge of the anion, the Sn−Bi bond lengths range between single and double bonds. Quantum‐chemical calculations at a DFT‐PBE0/def2‐TZVPP/COSMO level of theory reveal that the partial double bond character between the heavy main‐group atoms Bi and Sn originates from a delocalized π‐electronic system. The structure of the anion is determined by single‐crystal X‐ray diffraction analyses of the compounds K₅[SnBi₃] 9 NH₃ ( 1 ) and K₉[K(18‐crown‐6)][SnBi₃]₂⋅15 NH₃ ( 2 ). The [SnBi₃]⁵⁻ unit is the first example of a carbonate‐like anion obtained from solution, and it consists exclusively of metal atoms and completes the series of metal analogues of CO and CO₂.     

Synthesis and antimicrobial activity of a new class of methyleneamine‐linked bis‐heterocycles

A new class of methyleneamine‐linked bis‐heterocycles that exhibit antimicrobial activity was synthesized. Bromination of 1 followed by condensation with thiourea gave 3 . The reaction of 3 with propargyl bromide in dry toluene under inert atmosphere led to the formation of 4 . Its subsequent reaction with different aromatic azides 5 using CuSO₄.5H₂O‐sodiumascorbate system in a 2:1 mixture of water and tert‐butylalcohol yielded the title compounds 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j in good yields. The identities of these compounds were confirmed following elemental analysis, IR, ¹H, ¹³C NMR, and mass spectral studies. All the title compounds exhibited pronounced in vitro antibacterial and antifungal activities. J. Heterocyclic Chem., (2011).     

The 2‐Arsaethynolate Anion: Synthesis and Reactivity Towards Heteroallenes

The synthesis and isolation of the 2‐arsaethynolate anion, AsCO^?, and its subsequent reactivity towards heteroallenes is reported. Reactions with ketenes and carbodiimides afford four‐membered anionic heterocycles in formal [2+2] cycloaddition reactions. By contrast, reaction with an isocyanate yielded a 1,4,2‐diazaarsolidine‐3,5‐dionide anion and the unprecedented cluster anions As₁₀^2? and As₁₂^4?. These preliminary reactivity studies hint at the enormous potential synthetic utility of this novel anion, which may be employed as an arsenide (As^?) source.     

Synthesis,Characterization, and In Vitro Antimicrobial Activity of Methyleneamine‐Linked Bis‐heterocycles

A new class of methyleneamine‐linked bis‐heterocycles that exhibit antimicrobial activity was synthesized. Bromination of 1 followed by condensation with thiourea gave 3 . The reaction of 3 with propargyl bromide in dry toluene under inert atmosphere led to the formation of 4 . Its subsequent reaction with different nitrile oxides using CuSO₄.5H₂O–sodiumascorbate system in a 2:1 mixture of water and tert‐butyl alcohol yielded the title compounds 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j , 6k , 6l in good yields. The identities of these compounds were confirmed following elemental analysis, IR, ¹H, ¹³C NMR, and mass spectral studies. All the title compounds exhibited pronounced in vitro antibacterial and antifungal activities.     

Dual Role of the 1,2,3‐Triazolium Ring as a Hydrogen‐Bond Donor and Anion–π Receptor in Anion‐Recognition Processes

Several bis(triazolium)‐based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side‐arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen‐bond donor, the other as an anion–π receptor. Receptors 9²⁺?2BF₄ ^? (C₆H₅), 11²⁺?2BF₄ ^? (4‐NO₂?C₆H₄), and 13²⁺?2BF^4? (ferrocenyl) bind HP₂O₇^3? anions in a mixed‐binding mode that features a combination of hydrogen‐bonding and anion–π interactions and results in strong binding. On the other hand, receptor 10²⁺?2 BF₄ ^? (4‐CH₃O?C₆H₄) only displays combined Csp₂?H/anion–π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)⁺???anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H₂PO₄^? anions. That suggests that only hydrogen‐bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) C?H donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum‐energy conformation for all the complexes that explains their measured properties.     

Synthesis,Characterization, and Antimicrobial Screening of Ethylene‐Spaced Bis‐heterocycles

A new class of ethylene‐spaced bis‐heterocycles that was synthesized in a simple and efficient method from the one‐pot, three‐component reaction of amine 2 , propargyl halide 3 , and indolyl azide 1 in water is described. The identities of these compounds were confirmed following elemental analysis, IR, ¹H, ¹³C NMR, and mass spectral studies. All the title compounds exhibited pronounced in vitro antibacterial and antifungal activities.     

Diselenastanna‐, ‐sila‐ and ‐carbacycles with an annelated dicarba‐closo‐dodecaborane(12) unit

The reactions of the 1,2‐diselenolato‐1,2‐dicarba‐closo‐dodecaborane(12) dianion 1 with diorganoelement(IV) dichlorides (Ph₂CCl₂, Me₂SiCl₂, Ph₂SiCl₂, Me₂SnCl₂, Ph₂SnCl₂) gave novel five‐member heterocycles along with other products. The molecular structures of the five‐member rings containing CPh₂ ( 2 ) and SnPh₂ ( 9 ) moieties between the selenium atoms were determined by X‐ray analyses. In the case of the chlorosilanes, the analogous five‐member ring containing the SiPh₂ unit ( 4 ) could be identified in mixtures. The expected reaction was accompanied by rearrangement leading to formation of another five‐member ring 6 containing the Ph₂Si? Se? Se moiety. Oxidative addition of the five‐member heterocycles containing tin ( 7, 9 ) to ethene‐bis(triphenylphosphane)platinum(0) gave at low temperature the bis(triphenylphosphane)platinum(II) complexes 12 and 13 , where the Pt(PPh₃)₂ fragment had been inserted into one of the Sn? Se bonds. Extensive decomposition of these complexes was observed above ? 20 °C. The proposed solution‐state structures of the new compounds are supported by multinuclear magnetic resonance data (¹H, ¹¹B, ¹³C, ²⁹Si, ³¹P, ⁷⁷Se, ¹¹⁹Sn and ¹⁹⁵Pt NMR). Copyright © 2007 John Wiley & Sons, Ltd.     

Hydrogen‐bonded sheets in 2‐(2‐aminophenyl)‐1H‐benzimidazol‐3‐ium dihydrogen phosphate

The title salt, C₁₃H₁₂N₃⁺·H₂PO₄⁻, contains a nonplanar 2‐(2‐aminophenyl)‐1H‐benzimidazol‐3‐ium cation and two different dihydrogen phosphate anions, both situated on twofold rotation axes in the space group C2. The anions are linked by O—H...O hydrogen bonds into chains of R₂²(8) rings. The anion chains are linked by the cations, via hydrogen‐bonding complementarities and electrostatic interactions, giving rise to a sheet structure with alternating rows of organic cations and inorganic anions. Comparison of this structure with that of the pure amine reveals that the two compounds generate characteristically different sheet structures. The anion–anion chain serves as a template for the assembly of the cations, suggesting a possible application in the design of solid‐state materials.     

10‐Methyl‐ and 9,10‐dimethyl­acridinium methyl sulfate

The title compounds, C₁₄H₁₂N⁺·CH₃O₄S^?, (I), and C₁₅H₁₄N⁺·CH₃O₄S^?, (II), respectively, crystallize with the planar 10‐methylacridinium or 9,10‐di­methyl­acridinium cations arranged in layers, parallel to the twofold axis in (I) and perpendicular to the 2₁ axis in (II). Adjacent cations in both compounds are packed in a `head‐to‐tail' manner. The methyl sulfate anion only exhibits planar symmetry in (II). The cations and anions are linked through C—H?O interactions involving three O atoms of the anion, six acridine H atoms and the CH₃ group on the N atom in (I), and the four O atoms of the anion, three acridine H atoms and the carbon‐bound CH₃ group in (II). The methyl sulfate anions are oriented differently in the two compounds relative to the cations, being nearly perpendicular in (I) but parallel in (II). Electrostatic interaction between the ions and the network of C—H?O interactions leads to relatively compact crystal lattices in both structures.     

Reaction of “Non‐Symmetrical” 1,2,4‐Trithiolanes with [(phosphane)Pt0(η2‐nbe)] Complexes

Two unsymmetrical 1,2,4‐trithiolanes ( 1d and 1e ) were reacted with [Pt⁰(PPh₃)₂(η²‐nbe)] ( 6 ; nbe=norborn‐2‐ene) and [Pt⁰(dppn)(η²‐nbe)] ( 11 ; dppn=1,8‐bis(diphenylphosphanyl)naphthalene)), respectively. Their treatment with compound 6 resulted in the formation of six‐membered platinacycles of type 7 , which selectively underwent fragmentation into dithiolato complexes and thiobenzophenone ( 4b ). The isolation of the first stable C‐substituted member of this class of compounds (i.e., compound 7e ) permitted kinetic studies of this process by using UV/Vis spectroscopy. These results, together with DFT calculations, allowed us to propose a mechanism for the reactions of compound 6 with 1,2,4‐trithiolanes. In contrast, similar treatment of compound 11 with compounds 1d and 1e at room temperature did not result in any reaction. Heating the appropriate samples to 110 °C led to the formation of dithiolato complexes and η²‐thioketone compounds, thus pointing to a thermally induced [3+2]‐cycloreversion of the heterocycles as an initial step of the reaction.     

CH Bond Activation by Early Transition Metal Carbide Cluster Anion MoC3−

Although early transition metal (ETM) carbides can activate C?H bonds in condensed‐phase systems, the electronic‐level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, C?H activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC₃^?) under thermal‐collision conditions has been identified by using high‐resolution mass spectrometry, photoelectron imaging spectroscopy, and high‐level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC₃^? with C₂H₆. The C?H activation follows a mechanism of oxidative addition that is much more favorable in the carbon‐stabilized low‐spin ground electronic state than in the high‐spin excited state. The reaction efficiency between the MoC₃^? anion and C₂H₆ is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt⁺+C₂H₆) was made. It turned out that the potential‐energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different.     

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

In this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C₆(mim)]⁺_X^?, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C₆(mim)₂X₂], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl^? and Br^? anions prefer to locate almost in the plane of the imidazolium ring whereas the I^? anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl^? and Br^? anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.     

Phosphaketenes as Building Blocks for the Synthesis of Triphospha Heterocycles

Unsaturated phosphorus compounds, such as phosphaalkenes and phosphaalkynes, show a versatile reactivity in cycloadditions. Although phosphaketenes (R?P?C?O) have been known for three decades, their chemistry has remained limited. Herein, we show that heteroatom‐substituted phosphaketenes, R₃E?P?C?O (E=Si, Sn), are building blocks for silyl‐ and stannyl‐substituted five‐membered heterocycles containing three phosphorous atoms. The structure of the heterocyclic anion depends on the nature of the tetrel atom involved. Although the silyl analogue [P₃C₂(OSiR₃)₂]^? is an aromatic 1,2,4‐triphospholide, the stannyl compound [P(CO)₂(PSnR₃)₂]^? is a 1,2,4‐triphosphacyclopenta‐3,5‐dionate with a delocalized OCPCO fragment. Because of their anionic character, these compounds can easily be used as building blocks, for example, in the preparation of a silyl‐functionalized hexaphosphaferrocene or the parent 1,2,4‐triphosphacyclopenta‐3,5‐dionate [P(CO)₂(PH)₂]^?. NMR spectroscopic investigations and computations have shown that the heterocycle‐formation reactions presented herein are remarkably complex.     

Conformation‐Determined Through‐Bond versus Through‐Space Electronic Communication in Mixed‐Valence Systems with a Cross‐Conjugated Urea Bridge

Bis‐triarylamine 2 and cyclometalated diruthenium 6 (PF₆)₂ with a linear trans,trans‐urea bridge have been prepared, together with the bis‐triarylamine 3 and cyclometalated diruthenium 8 (PF₆)₂ with a folded cis,cis‐N,N‐dimethylurea bridge. The linear or folded conformations of these molecules are supported by single‐crystal X‐ray structures of 2 , 3 , and other related compounds. These compounds display two consecutive anodic redox waves (N ^{. +/0} or Ru^III/II processes) with a potential separation of 110–170 mV. This suggests that an efficient electronic coupling is present between two redox termini through the cross‐conjugated urea bridge. The degree of electronic coupling has been investigated by using spectroelectrochemical measurements. Distinct intervalence charge‐transfer (IVCT) transitions have been observed for mixed‐valent (MV) compounds with a linear conformation. The IVCT transitions can also be identified for the folded MV compounds, albeit with a much weaker intensity. DFT results support that the electronic communication occurs by a through‐bond and through‐space pathway for the linear and folded compounds, respectively. The IVCT transitions of the MV compounds have been reproduced by TDDFT calculations. For the purpose of comparison, a bistriarylamine and a diruthenium complex with an imidazolidin‐2‐one bridge and a urea‐containing mono‐triarylamine and monoruthenium complex have been synthesized and studied.     

Ferrocenyl Ionic Compounds Containing [Fe(CN)6]3– Anions: Synthesis,Characterization, and Catalytic Effects during Combustion

Twenty‐eight novel ferrocenyl ionic compounds, composed of mononuclear 1‐ferrocenylmethylalkyldimethylammoniums, 1‐ferrocenylmethyl‐3‐alkylimidazoliums, or their dinuclear analogs and [Fe(CN)₆]^3– anion, were designed and synthesized to tackle significant volatility and migration tendency of ferrocene‐based burning rate catalysts (BRCs) used currently in the composite solid propellants. The new compounds were characterized by UV/Vis, FT‐IR, and elementary analysis. The crystal structures of compounds 2· 5H₂O and 3· CH₂Cl₂ · 4H₂O verified the successful preparation of the desired ionic compounds. The TG tests at 70 °C for 24 h revealed that the new compounds exhibit lower volatility than catocene. The cyclic‐voltammetry results suggested that new compounds are quasi‐reversible or irreversible redox systems. TheTG/DSC analyses exhibited that the compounds are of highly thermal stability. Their catalytic effects on the thermal degradation of ammonium perchlorate (AP), 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX), and 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazacyclooctane (HMX) were investigated. The results showed that most of the compounds exert great effects on the thermal degradation of AP and RDX during combustion. 11 and 2 are comparable to catocene in the thermal decomposition of AP and RDX, respectively, and can therefore be used as alternatives of catocene in a composite solid propellant. Some new compounds are unexpectedly active in promoting the thermal disintegration of HMX.     

Nitroradical Anion Formation from some Iodo‐Substituted Nitroimidazoles

The electrochemical behavior of iodo nitroimidazole derivatives such as 1‐methyl‐4‐iodo‐5‐nitroimidazole (M‐I‐NIm) and 1‐methyl‐2,4‐diiodo‐5‐nitroimidazole (M‐I₂‐NIm) and the parent compound 1‐methyl‐5‐nitroimidazole (M‐NIm), was studied in protic, mixed and non‐aqueous media. The electrochemical study was carried out using Differential Pulse Polarography (DPP), Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV) and coulometry and as working electrodes mercury and glassy carbon were used. As can be expected, in all media, the effect of introduce iodo as substituent in the nitroimidazole ring produced a decrease of the energy requirements of the nitro group reduction. Certainly, this fact can be explained by the electron withdrawing character of the iodo substituent that acts diminishing the electronic density on the nitro group thus facilitating their reduction. In all the studied media the reduction of M‐NIm produced a detectable signal for a nitro radical anion derivative. In the case of M‐I‐NIm the nitro radical anion was only detectable in both mixed and non‐aqueous media. On the other hand the nitro radical anion for the M‐I₂‐NIm was detected only in non‐aqueous medium. When glassy carbon electrode was used as the working electrode in a mixed medium a detectable nitro radical anion derivative appeared for all compounds, thus permitting an adequate comparison between them. The obtained values of k₂ for M‐NIm, M‐I‐NIm and M‐I₂‐NIm in non‐aqueous medium were 5.81×10², 132×10² and 1100×10² M^?1 s^?1, respectively. From the obtained k₂ and t_1/2 values in this medium, it is concluded that there is a direct dependence between the presence of iodo substitution in the nitroimidazole ring with the stability of the nitro radical anion.     

Ion‐Pairing Assemblies Based on Pentacyano‐Substituted Cyclopentadienide as a π‐Electronic Anion

Pentacyanocyclopentadienide (PCCp^?), a stable π‐electronic anion, provided various ion‐pairing assemblies in combination with various cations. PCCp^?‐based assemblies exist as single crystals and mesophases owing to interionic interactions with π‐electronic and aliphatic cations with a variety of geometries, substituents, and electronic structures. Single‐crystal X‐ray analysis revealed that PCCp^? formed cation‐dependent arrangements with contributions from charge‐by‐charge and charge‐segregated assembly modes for ion pairs with π‐electronic and aliphatic cations, respectively. Furthermore, some aliphatic cations gave dimension‐controlled organized structures with PCCp^?, as observed in the mesophases, for which synchrotron XRD analysis suggested the formation of charge‐segregated modes. Noncontact evaluation of conductivity for (C₁₂H₂₅)₃MeN⁺ ? PCCp^? films revealed potential hole‐transporting properties, yielding a local‐scale hole mobility of 0.4 cm² V^?1 s^?1 at semiconductor–insulator interfaces.     

Ion‐Pairing Assemblies of Porphyrin–AuIII Complexes in Combination with π‐Electronic Receptor–Anion Complexes

Anion complexes of anion‐responsive π‐electronic molecules can behave as pseudo π‐electronic anions providing various ion pairs in combination with countercations. In this study, single crystals of ion‐pairing assemblies comprising porphyrin–Au^III complexes and Cl^? complexes of dipyrrolyldiketone BF₂ complexes were prepared from 1:1 mixtures of anion receptors and the Cl^? salts of cationic porphyrins in solution. In the solid state, the ion pairs formed characteristic assemblies, depending on the substituents of the anion receptors and porphyrin–Au^III complexes. Theoretical calculations on the ion pairs revealed that the stacking structures are stabilized by compensating positive and negative charges as well as π–π interactions.     

New Synthesis and Reactions of Ethyl 5‐amino‐4‐cyano‐1‐phenyl‐1H‐pyrazole‐3‐carboxylate

Synthesis of ethyl 5‐amino‐4‐cyano‐1‐phenyl‐1H‐pyrazole‐3‐carboxylate 5 has been achieved via abnormal Beckmann rearrangement of o‐chloroaldehyde 1 . Reaction of o‐aminocarbonitrile 5 with concentrated H₂SO₄ furnished expected o‐aminocarboxamide pyrazole 6 . Key intermediates o‐aminocarbonitrile 5 and o‐aminocarboxamide 6 were successfully utilized for the synthesis of pyrazolopyrimidine derivatives. The replacement of Cl in o‐chlorocarbonitrile 3 with secondary amine furnished new synthon 13 , which was further used for the synthesis of polysubstituted heterocycles. The obtained new products were well characterized by IR, ¹H and ¹³C NMR, and mass spectra.