Protonation of CH3N3 and CF3N3 in Superacids: Isolation and Structural Characterization of Long‐Lived Methyl‐ and Trifluoromethylamino Diazonium Ions

The methylamino diazonium cations [CH₃N(H)N₂]⁺ and [CF₃N(H)N₂]⁺ were prepared as their low‐temperature stable [AsF₆]^? salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH₃N₃?AsF₅ and CF₃N₃?AsF₅ were also prepared and characterized by low‐temperature NMR and Raman spectroscopy, and also by X‐ray structure determination for CH₃N₃?AsF₅. Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl‐ and trifluoromethylamino diazonium ions were unsuccessful.     

Reactions of Doubly Ionized Benzene with Nitrogen and Water: A Nitrogen‐Mediated Entry into Superacid Chemistry

Even in the highly diluted gas phase, rather than electron transfer the benzene dication C₆H₆²⁺ undergoes association with dinitrogen to form a transient C₆H₆N₂²⁺ dication which is best described as a ring‐protonated phenyl diazonium ion. Isotopic labeling studies, photoionization experiments using synchrotron radiation, and quantum chemical computations fully support the formation of protonated diazonium, which is in turn a prototype species of superacidic chemistry in solution. Additionally, reactions of C₆H₆²⁺ with background water involve the transient formation of diprotonated phenol and, among other things, afford a long‐lived C₆H₆OH₂²⁺ dication, which is attributed to the hydration product of Hogeveen’s elusive pyramidal structure of C₆H₆²⁺, as the global minimum of doubly ionized benzene. Nitrogen is essential for the formation of the C₆H₆OH₂²⁺ dication in that it mediates the formation of the water adduct, while the bimolecular encounter of the C₆H₆²⁺ dication with water only leads to (dissociative) electron transfer.     

Clusters of Ammonium Cation—Hydrogen Bond versus σ‐Hole Bond

MP2/6‐311++G(d,p) calculations were performed on the NH₄⁺ ??? (HCN)_n and NH₄⁺ ??? (N₂)_n clusters (n=1–8), and interactions within them were analyzed. It was found that for molecules of N₂ and HCN, the N centers play the role of the Lewis bases, whereas the ammonium cation acts as the Lewis acid, as it is characterized by sites of positive electrostatic potential, that is, H atoms and the sites located at the N atom in the extension of the H?N bonds. Hence, the coordination number for the ammonium cation is eight, and two types of interactions of this cation with the Lewis base centers are possible: N?H ??? N hydrogen bonds and H?N ??? N interactions that are classified as σ‐hole bonds. Redistribution of the electronic charge resulting from complexation of the ammonium cation was analyzed. On the one hand, the interactions are similar, as they lead to electronic charge transfer from the Lewis base (HCN or N₂ in this study) to NH₄⁺. On the other hand, the hydrogen bond results in the accumulation of electronic charge on the N atom of the NH₄⁺ ion, whereas the σ‐hole bond results in the depletion of the electronic charge on this atom. Quantum theory of “atoms in molecules” and the natural bond orbital method were applied to deepen the understanding of the nature of the interactions analyzed. Density functional theory/natural energy decomposition analysis was used to analyze the interactions of the ammonium ion with various types of Lewis bases. Different correlations between the geometrical, energetic, and topological parameters were found and discussed.     

Über die Entstehung von α-Keto-carbonium-Ionen bei der säurekatalysierten Hydrolyse von Diazoketonen. (Vorläufige Mitteilung)

Secondary deactivated aliphatic diazo compounds (diazo-ketones R CO CN₂ R′; diazo-esters ROOC CN₂ R′; 1, 1, 1-trifluoro-2-diazopropane) are hydrolysed by the A S_E2 mechanism comprising rate determining protonation of the substrate, followed by decomposition. Product analysis shows that the decomposition of the secondary diazonium ions is monomolecular, without intervention of a nucleophile. The corresponding primary diazo compounds (R CO CHN₂, ROOC CHN₂ and CF₃ CHN₂) are hydrolysed by the A-2 mechanism comprising preequilibrium protonation; the primary diazonium ion reacts with a nucleophile in a bimolecular displacement step. The only exception observed is found in p-nitrophenyl-diazomethane, which follows A S_E2 mechanism. The observations are discussed in terms of the stability of the corresponding secondary resp. primary α-keto-carbonium ions.     

Dediazoniation of Arenediazonium Ions in Homogeneous Solutions. Part XVI. Kinetics and mechanisms of dediazoniation of p-chlorobenzenediazonium tetrafluoroborate in weakly alkaline aqueous solutions under nitrogen gas

The kinetics of reactions of p-chlorobenzenediazonium ions in aqueous buffer solutions (pH 9.0–10.6) under N₂ (< 5 ppb of O₂) have been measured between 20 and 50°C. The formation of trans-diazotate is first-order with respect to the concentration of hydroxyl ions and to the equilibrium concentration of diazonium ions, if the diazonium ion?cis-diazotate equilibrium is considered as a fast prior equilibrium. This indicates that the p-chlorobenzenediazonium ion, in contrast to all previous investigations with the p-nitrobenzenediazonium ion and benzenediazonium ions carrying similar substituents with a ?M effect, rearranges from the cis- to the trans-configuration as diazohydroxide and not as diazotate. The formation of trans-diazotate is catalyzed by carbonate and inhibited by hydrogen carbonate ions; mechanisms of these catalyses are discussed, and the solvent isotope effect K_H2O/K_D2O measured by an ¹H-NMR. technique reported. The kinetics of the dediazoniations can be analyzed as a mixture of two reactions, a relatively fast first reaction, reaction A, which is responsible for about 5% of the total reaction, and a second reaction F. Both are first-order with respect to diazonium ion; reaction A is also first-order in hydroxyl ions. There are some indications that reaction A corresponds to the hydrolysis of the diazonium ion to give eventually amine and nitrite ions. Reaction F shows a complex dependence on hydroxyl ions; it is related to the homolytic dediazoniation.     

A theoretical investigation of the electron-transfer reactions of the SiF2+3 dication with the rare gases,neon, argon,krypton and xenon

The relative product ion intensities from the electron-transfer reactions between SiF²⁺₃ and the rare gases neon, argon, krypton and xenon have been rationalized using a combination of ab initio electronic structure calculations and Landau-Zener reaction window theory. The calculations show that the experimentally observed products derived from the dication (SiF⁺₃, SiF⁺₂ and SiF⁺) require the ions in the dication beam to be present in three different electronic states. The predicted and experimental product ion distributions, given this dication energy distribution, are in very close agreement. The combined computational approach adopted in this study is valuable for large molecular systems where the reactant molecule has several degrees of freedom and adopts markedly different equilibrium geometries depending on the degree of ionisation.     

Molecular engineering of CxNy: Topologies,electronic structures and multidisciplinary applications

As a class of metal-free two-dimensional (2D) semiconductor materials, polymeric carbon nitrides have attracted wide attention recently due to its facile regulation of the molecular and electronic structures, availability in abundance and high stability. According to the different ratios of C and N atoms in the framework, a series of C_xN_y materials have been successfully synthesized by virtue of various precursors, which further triggers extensive investigations of broad applications ranging from sustainable photocatalytic reactions and highly sensitive optoelectronic biosensing. In view of topological structures on their electronic structures and material properties, the as-reported C_xN_y could be generally classified into two main categories with three- or six-bond-extending frameworks. Owing to the effective n→π* transition in most C_xN_y materials, the relative energy level of the lone-pair electrons on N atoms is high, which thus endows the materials with the capability of visible light absorption. Meanwhile, the different repeating units, bridging groups and defect sites of these two kinds of C_xN_y allow them to effectively drive a diverse of promising applications that require specific electronic, interfacial and geometric properties. This review paper aims to summarize the recent progress in topological structure design and the relevant electronic band structures and striking properties of C_xN_y materials. In the final part, we also discuss the existing challenges of C_xN_y and outlook the prospect possibilities.     

Solvent induced quadrupole polarization of the molecules of diazo and diazocarbonyl compounds: Quantum-chemical investigation

Equilibrium structural parameters, atomic charges, and quadrupole moments of the molecules of 2,4,6-tris(diazo)cyclohexane-1,3,5-trione, 3,6-bis(diazo)cyclohexane-1,2,4,5-tetraone and its anion, isomeric 3,6-bis(diazonium)cyclohexanediondioles and 4,4′-bis(diazonium)-1,1′-biphenyl in a vacuum and in dichloromethane were calculated by the quantum chemical method PBE0/cc-pVTZ using the polarizable continuum model (PCM).The p-quinoid dication is more favorable than o-quinoid dication by 20 kcal mol-1 in a vacuum and by 13 kcal mol⁻¹ in dichloromethane.The norm of the quadrupole moment of the centrosymmetric molecules in a polarizable medium increases while that of the dications decreases. The quadrupole polarization of molecules and molecular ions by the solvent does not change their symmetry point group.     

Promoting the Hydrosilylation of Benzaldehyde by Using a Dicationic Antimony‐Based Lewis Acid: Evidence for the Double Electrophilic Activation of the Carbonyl Substrate

The concomitant activation of carbonyl substrates by two Lewis acids has been investigated by using [1,2‐(Ph₂MeSb)₂C₆H₄]²⁺ ([ 1 ]²⁺), an antimony‐based bidentate Lewis acid obtained by methylation of the corresponding distibine. Unlike the simple stibonium cation [Ph₃MeSb]⁺, dication [ 1 ]²⁺ efficiently catalyzes the hydrosilylation of benzaldehyde under mild conditions. The catalytic activity of this dication is correlated to its ability to doubly activate the carbonyl functionality of the organic substrate. This view is supported by the isolation of [ 1 ‐μ₂‐DMF][OTf]₂, an adduct, in which the DMF oxygen atom bridges the two antimony centers.     

Terminal N2 Dissociation in [(PNN)Fe(N2)]2(μ-N2) Leads to Local Spin-State Changes and Augmented Bridging N2 Activation

Nitrogen fixation at iron centres is a fundamental catalytic step for N₂ utilisation, relevant to biological (nitrogenase) and industrial (Haber-Bosch) processes. This step is coupled with important electronic structure changes which are currently poorly understood. We show here for the first time that terminal dinitrogen dissociation from iron complexes that coordinate N₂ in a terminal and bridging fashion leaves the Fe-N₂-Fe unit intact but significantly enhances the degree of N₂ activation (Δν≈180 cm⁻¹, Raman spectroscopy) through charge redistribution. The transformation proceeds with local spin state change at the iron centre (S= →S=³/₂). Further dissociation of the bridging N₂ can be induced under thermolytic conditions, triggering a disproportionation reaction, from which the tetrahedral (PNN)₂Fe could be isolated. This work shows that dinitrogen activation can be induced in the absence of external chemical stimuli such as reducing agents or Lewis acids.     

Formation and reactions of substituted diazocyclopropanes and cyclopropyldiazonium ions

Decomposition of N-nitroso-N-cyclopropylureas at 5—7 °C on treatment with K₂CO₃ containing 15—20% H₂O allows simultaneous generation of both substituted diazocyclopropanes and cyclopropyldiazonium ions, which can react according to 1,3-dipolar cycloaddition or azo-coupling pattern with appropriate substrates. The nature of substituents in the cyclopropyl ring have a pronounced influence on the product ratio (and, probably, on the equilibrium between the diazo compound and the diazonium ion). Thus, on treatment with a base in the presence of equimolar amounts of methyl metacrylate as a trap for the diazo compound and 2-naphthol as a trap for the diazonium ion, N-cyclopropyl- and N-(2,2-dimethylcyclopropyl)-N-nitrosourea azo coupling products predominate. Conversely, N-(2,2-dichlorocyclopropyl)-N-nitrosourea is transformed predominantly into 1,3-cycloaddition products. A rationalization for the experimental data is proposed.     

Carbodicarbenes and Related Divalent Carbon(0) Compounds

Quantum‐chemical calculations using DFT and ab initio methods have been carried out for fourteen divalent carbon(0) compounds (carbones), in which the bonding situation at the two‐coordinate carbon atom can be described in terms of donor–acceptor interactions L→C←L. The charge‐ and energy‐decomposition analysis of the electronic structure of compounds 1 – 10 reveals divalent carbon(0) character in different degrees for all molecules. Carbone‐type bonding L→C←L is particularly strong for the carbodicarbenes 1 and 2 , for the “bent allenes” 3 a , 3 b , 4 a , and 4 b , and for the carbocarbenephosphoranes 7 a , 7 b , and 7 c . The last‐named molecules have very large first and large second proton affinities. They also bind two BH₃ ligands with very high bond energies, which are large enough that the bis‐adducts should be isolable in a condensed phase. The second proton affinities of the complexes 5 , 6 , and 8 – 10 bearing CO or N₂ as ligand are significantly lower than those of the other molecules. However, they give stable complexes with two BH₃ ligands and thus are twofold Lewis bases. The calculated data thus identify 1 – 10 as carbones L→C←L in which the carbon atom has two electron pairs. The chemistry of carbones is different from that of carbenes because divalent carbon(0) compounds CL₂ are π donors and thus may serve as double Lewis bases, while divalent carbon(II) compounds are π acceptors. The theoretical results point toward new directions for experimental research in the field of low‐coordinate carbon compounds.     

Superelectrophiles

Electrophiles that are capable of further interaction (coordination, solvation) with strong Brønsted or Lewis acids can be activated in this way. The resulting enhancement of their reactivity is great compared to that of their parent compounds under conventional conditions and indicates superelectrophile formation (i.e., electrophiles with doubly electrodeficient (dipositive) nature whose reactivity substantially exceeds that of their parent electrophiles). As representative examples the protolytic or electrophilic activation of the following electrophiles in superacidic and related strongly electrophilic media is discussed: oxonium, carboxonium, sulfonium, selenonium, and telluronium ions; acyl cations; protonated CO, CO₂, COS, and carbonic and thiocarbonic acids; heteroatom-substituted carbocations (and some of their boron analogs); halonium ions; azonium (including nitronium) and carbazonium ions. Emphasis is placed on both experimental chemical investigations and theoretical treatment of the involved systems. As prototypes for protolytically activated onium ions, the protohydronium dication (diprotonated water) and its sulfur analogue, the protosulfonium dication, are of particular significance. The protoacetyl and protoformyl dication (diprotonated carbon monoxide), diprotonated carbonic acid and carbon dioxide, diprotonated hydrogen cyanide and nitriles, as well as the protonitronium dication among others—and their emerging chemistry are discussed as examples of superelectrophiles.     

Dediazoniations of Arenediazonium Ions. Part XXI. Dediazoniation of Arenediazonium Ions Complexed with Crown Ethers

The evaluation of the dediazoniation kinetics of various m- and p-substituted benzenediazonium tetrafluoroborates in 1,2-dichloroethane at 50° in the presence of 18-crown-6, 21-crown-7 and dicyclohexano-24-crown-8 demonstrates that the rate constant for the dediazoniation within the complex (k₂) is smallest, and the equilibrium constant for complex formation (K) is largest for the complexes with 21-crown-7 (cf. Scheme 1). The logarithms of the equilibrium constants (K) for complex formation with each of the crown ethers studied correlate well with Hammett's substituent constants, σ, to give reaction constants ρ = 1.18–1.38. A linear correlation between the logarithms of the rate constants for the dediazoniation within the complex with those of the dediazoniation rate constants of uncomplexed diazonium ions (log k₂ vs. log.k₁), found for most substituted diazonium salts, indicates that the dediazoniation mechanism of the complexed diazonium ions is not significantly different from that of the free ions. For very electrophilic diazonium ions (p-Cl, m-CN), k₂ was much larger than expected on the basis of the linear log k₂ vs. log k₁ relationship. Analysis of the dediazoniation products showed that this was due to a change in mechanism from heterolytic to homolytic dediazoniation. The complexation rate of diazonium salts by crown ethers (k_c) is practically diffusion controlled and does not change much with the size of the crown ether. The decomplexation rate (k_d), however, is significantly lower for complexes with 21-crown-7, than for those with 18-crown-6 and dicyclohexano-24-crown-8, and is therefore the reason for the variations in the equilibrium constant (K) and thus for the fact that complexes of arenediazonium salts with 21-crown-7 are the most stable. The amounts of the N_α-N_β rearrangement, as well as those of the exchange of the ¹⁵N-labelled diazonio group with external nitrogen during dediazoniation of p-toluenediazonium salt were independent of the addition of crown ethers. A dediazoniation mechanism involving a charge transfer, as well as an insertion-type diazonium ion-crown ether complex is proposed. In this mechanism, dediazoniation of the insertion complex does not take place directly, but through the charge-transfer complex.     

Experimental and kinetic modeling of the reduction of NO by isobutane in a Jsr at 1 atm

A kinetic study of the reduction of nitric oxide (NO) by isobutane in simulated conditions of the reburning zone was carried out in a fused silica jet‐stirred reactor operating at 1 atm, at temperatures ranging from 1100 to 1450 K. In this new series of experiments, the initial mole fraction of NO was 1000 ppm, that of isobutane was 2200 ppm, and the equivalence ratio was varied from 0.75 to 2. It was demonstrated that for a given temperature, the reduction of NO is favored when the temperature is increased and a maximum NO reduction occurs slightly above stoichiometric conditions. The present results generally follow those reported in previous studies of the reduction of NO by C₁ to C₃ hydrocarbons or natural gas as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme (979 reversible reactions and 130 species). An overall reasonable agreement between the present data and the modeling was obtained. Furthermore, the proposed kinetic mechanism can be successfully used to model the reduction of NO by ethylene, ethane, acetylene, a natural gas blend (methane‐ethane 10:1), propene, and HCN. According to this study, the main route to NO reduction by isobutane involves ketenyl radical. The model indicates that the reduction of NO proceeds through the reaction path: iC₄H₁₀ → C₃H₆ → C₂H₄ → C₂H₃ → C₂H₂ → HCCO; HCCO + NO → HCNO + CO and HCN + CO₂; HCNO + H → HCN → NCO → NH; NH + NO → N₂ and NH + H → followed by N + NO → N₂; NH + NO → N₂O followed by N₂O + H → N₂. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 365–377, 2000     

Hexane‐1,6‐diaminium chloride [hydrogen bis(chloroacetate)]

In the structure of the title compound, C₆H₁₈N₂²⁺·H(C₂H₂ClO₂)₂⁻·Cl⁻, the hexane‐1,6‐diaminium dication is disordered over two sets of positions, with almost equal occupancies. Both alternative positions of the dication are in the fully extended conformation, situated on an inversion centre at (, , ). Two chloroacetic acid moieties, related by another centre of symmetry at (, , ), are connected by a very short symmetrical O...H...O hydrogen bond [O...O = 2.452 (2) Å], with the H atom at the centre of inversion. These two fragments thus effectively form the hydrogen bis(chloroacetate) monoanion, and the overall charge is balanced by an additional chloride anion which resides on a twofold axis. The ions form a layer structure, with alternating layers of dications and anions running along the [101] direction, linked via hydrogen bonds. There are two N—H...O interactions and two N—H...Cl⁻ interactions.     

Hexaaquanickel(II) disulfato(1,4,8,11‐tetraazacyclotetradecane)nickelate(II) dihydrate

The title compound, [Ni(H₂O)₆][Ni(SO₄)₂(C₁₀H₂₄N₄)]·2H₂O, is an unusual compound in that it is composed of a hexaaqua complex, formally a dication, and a mixed‐donor complex (four N and two O atoms), formally a dianion, with substantial charge separation between the two nickel centres (6.536 Å). The homoleptic dication complex consists of the weaker‐field ligands, whilst the dianion retains the coordination of all the higher‐field donors. Both nickel ions are located at centres of symmetry. This rare compound is placed in the context of previously reported structures which emphasizes its peculiarity.     

Syntheses,Structures, and Reactivities of Two Chalcogen‐Stabilized Carbones

Electronic effects on the central carbon atom of carbone, generated by the replacement of the S^IV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph₂E, E=S or Se), were investigated. The carbones Ph₂E→C←SPh₂(NMe) [E=S( 1 ) or Se( 2 )] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2 , which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2 > 1 >CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four‐electron donor.     

Syntheses,Structures, and Reactivities of Two Chalcogen‐Stabilized Carbones

Electronic effects on the central carbon atom of carbone, generated by the replacement of the S^IV ligand of carbodisulfane (CDS) with other chalcogen ligands (Ph₂E, E=S or Se), were investigated. The carbones Ph₂E→C←SPh₂(NMe) [E=S( 1 ) or Se( 2 )] were synthesized from the corresponding salts, and their molecular structures and electronic properties were characterized. The carbone 2 is the first carbone containing selenium as the coordinated atom. DFT calculations revealed the electronic structures of 1 and 2 , which have two lone pairs of electrons at the carbon center. The trend in HOMO energy levels, estimated by cyclic voltammetry measurements, for the carbones and CDS follows the order of 2 > 1 >CDS. Analysis of a doubly protonated dication and trication complex revealed that the central carbon atom of 2 behaves as a four‐electron donor.     

Nitrogen as Leaving Group: Aliphatic Diazonium Ions

Nitrogen is one of the best known leaving groups. Decomposition of aliphatic diazonium ions has rendered carbocations (carbon cations) accessible in cases where the solvolysis of halides or sulfonic esters follows different pathways. The limits of unassisted decomposition are seen in primary diazonium ions, where the participation of external nucleophiles and of neighboring groups in the elimination of nitrogen becomes noticeable. Cyclopropanediazonium ions occupy a position intermediate between aliphatic and aromatic diazonium ions. New versatile methods of generating aliphatic diazonium ions facilitate their preparative use.