Dimeric Dianion Research Articles

Low‐Valent Titanium Induced Cyclization of Dimeric Dianions of Anils with Triphosgene: A Safe and Efficient Method for the Syntheses of Substituted Imidazolidine 2‐ones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Exceptionally Long (> or =2.9 A) CC bonding interactions in pi-[TCNE]2(2-) dimers: two-electron four-center cation-mediated CC bonding interactions involving pi* electrons.

Three groups of singlet ground state [TCNE](2) (2-) (TCNE=tetracyanoethylene) dimers with characteristic intradimer CC separations (r) and dihedral angles (d) [i.e., group S(t) (r approximately 1.6 A; d=180 degrees ), L(t) (r approximately 3.5 A; d=180 degrees ), and L(c) (r approximately 2.9 A; d= approximately 0 degrees ); notation: S/L: short/long bond length; subscript t/c: trans/cis, respectively] are experimentally characterized. The S(t) group is comprised of sigma-dimers of [TCNE](.-) and octacyanobutanediide, [C(4)(CN)(8)](2-), which have a typical, albeit long, sp(3)-sp(3) sigma bond (r approximately 1.6 A) between each [TCNE](.-) moiety and characteristic nu(CN), nu(CC), and delta(CCN) IR absorptions. The L groups are structurally characterized as pi-dimers of [TCNE](.-) that are either eclipsed with r approximately 2.9 A (L(c)) and the nitriles bend away from the nominal TCNE plane away from the center of the dimer by 5.0 degrees (approximately sp(2.17)) or are noneclipsed with r approximately 3.5 A (L(t)) and the nitriles bend toward the center of the dimer by 1.9 degrees ( approximately sp(2.06)). Ab initio computations on isolated dimers were used to study the formation and stability of these exceptionally long CC (> or =2.9 A) bonding interactions as well as the process of pi-[TCNE](2) (2-) dimer formation for the L(c) and L(t) groups. The results of these computational studies show that the ground-state potential curve is that of a closed-shell/open-shell singlet, depending on the distance. The short S(t) group (r approximately 1.6 A) of dimers in this surface are true minimum-energy structures; however, the L(t) and L(c) groups are unstable, although two different nonphysical minima are found when imposing a double occupancy of the orbitals. These minima are metastable relative to dissociation into the isolated [TCNE](.-) units. Consequently, the existence of dimer dianions in crystals is due to cation.[TCNE](-) interactions, which provide the electrostatic stabilization necessary to overcome the intradimer electrostatic repulsion. This cation-mediated pi*-pi* [TCNE](-).[TCNE](-) interaction complies with Pauling's definition of a chemical bond. This bonding interaction involves the pi* orbitals of each fragment, and arise from the overlap of the b(2g) SOMO on each of the two [TCNE](.-)s to form a filled b(2u) [TCNE](2) (2-) orbital. Although a pi dimer typically forms, if the fragments are close enough a sigma dimer can form. Due to the presence of cation-mediated intradimer CC bonding interactions the L(c) group of pi-[TCNE](2) (2-) dimers exhibits experimentally observable nu(CN) IR absorptions at 2191+/-2 (m), 2173+/-3 (s), and 2162+/-3 cm(-1) (s) and nu(CC) at 1364+/-3 cm(-1) (s) as well as a new UV-Vis feature in the range of 15 000 to 18 200 cm(-1) (549 to 667 nm) and averaging 16 825+/-1180 cm(-1) (594 nm) assigned to the predicted new intradimer (1)A(1g) --> (1)B(1u) transition and is purple on reflected light. Upon cooling to 77 K in 2-methyl tetrahydrofuran, this new band occurs at 18 940 cm(-1) (528 nm) for [[Et(4)N](+)](2)[TCNE](2) (2-), and the yellow solution turns deep red. Group L(t) is characterized by nu(CN) absorptions at 2215+/-2, 2197+/-3, and 2180+/-4 cm(-1) and nu(CC) at 1209+/-9 cm(-1) (w), while group S(T) has nu(CN) bands at 2215+/-4, 2157+/-3, and 2107+/-4 cm(-1) and nu(CC) at 1385+/-1 cm(-1) (vs).

Kinetically Controlled Regioselective Formation of a Tail-to-Tail Dimer Dianion of 4-(N,N-Dimethylamino)styrene

Kinetically Controlled Regioselective Formation of a Tail-to-Tail Dimer Dianion of 4-(<i>N</i>,<i>N</i>-Dimethylamino)styrene

Formation of different framework structured dimeric dianions formed from the reduction of 2,4,6-tricyano-1,3,5-triazine and 1,3,5-tricyanobenzeneDedicated to Michael Hanack on the occasion of the 70th birthday.

Reduction of 2,4,6-tricyano-1,3,5-triazine (1) and 1,3,5-tricyanobenzene (2) leads to dianionic dimers with long, ∼1.57 Å, central C–C bonds. In contrast to 1, which dimerizes at the nitrile substituted carbon, 2 has a different motif as it dimerizes at the hydrogen substituted carbon.

Implementation of the expert system EXPIRS for interpretation of infrared spectra of negative ions of organic compounds

A knowledge base and a correlation table with infrared spectral band characteristics — frequency intervals, intensity and bandwidth — of anion-radicals, carbanions, monomeric dianions, dimeric dianions, N-anions and oxyanions of organic cyano, isocyano, carbonyl, nitro, ethine and azomethine compounds were created. The expert system EXPIRS designed for the interpretation of infrared spectra was successfully applied for the assignment of negative ion bands of cyano, isocyano, carbonyl, nitro, ethine and azomethine functional groups. Dividing the knowledge base into subbases helps in the reduction of the alternative sets of negative species possibly presenting in the sample satisfying the current infrared spectrum and shortened the processing time. The predicting ability of the system for determining the kind of anions of studied organic and bio-organic compounds and also elucidating reaction mechanisms with their participation is demonstrated.

Electrosynthesis Cell for X-Ray Absorption Fine Structure Measurement: Reduction of Air-Sensitive Iron-Sulfur Compounds

The design of a small-volume continuous-flow electrosynthesis cell, and its associated X-ray absorption fine structure (XAFS) cell, are reported. The extent of electrosynthesis of the solution used for collection of the XAFS data may be monitored, in line, by infrared (IR) or ultraviolet&amp;#8211;visible (UV&amp;#8211;vis) spectroscopy. The operation of the cell is demonstrated by the reduction of Fe&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;2&lt;/sub&gt;(CO)&lt;sub&gt;6&lt;/sub&gt; to the related dimer dianion, &amp;#91;Fe&lt;sub&gt;4&lt;/sub&gt;S&lt;sub&gt;4&lt;/sub&gt;(CO)&lt;sub&gt;12&lt;/sub&gt;&amp;#93;&lt;sup&gt;2-&lt;/sup&gt;. While the immediate coordination environment about the iron is similar for the two compounds, dimer formation results in an additional Fe&amp;#8211;S interaction at 3.62 &amp;#197;, which contributes to significant changes in the XAFS data in the region 10&amp;#8211;12 &amp;#197;&lt;sup&gt;-1&lt;/sup&gt;. Analysis of the XAFS for the reduced species gave a full structural model which yielded a calculated multiple scattering (MS) XAFS pattern in good agreement with the data. Inclusion of the longer range Fe&amp;#8211;Fe interactions (&amp;#62; 5 &amp;#197;) did not give convergent fits within this formalism. These experiments demonstrate that ex situ electrosynthetic approaches provide an effective means of generating reactive species in a form suitable for XAFS examination.

Synthesis and reactivity of the stable silylene N,N'-di-tert-butyl-1,3-diaza-2-sila-2-ylidene

The synthesis and several reactions of the stable silylene 1 (N,N'-di-tert-butyl-1,3-diaza-2-sila-2-ylidene) are reported. Overreduction of 1 with alkali metals results in the formation of a dimeric dianion, which can be trapped with a proton source to give the dihydride derivative 9. In the solid state or in concentrated solutions, 1 undergoes a reversible conversion into the novel tetrameric disilene, 10. 1 reacts with ethanol, phenol, and water via insertion into the O—H bond, and with iodomethane by insertion into the C—I bond. A reaction of 1 with the diene 2,3-dimethyl-1,3-butadiene affords the silacyclopentene, 15. This reaction is markedly different from the one found for the unsaturated analog of the silylene, 2, which catalyzes the conversion of this diene into a highly cross-linked polymer.Key words: silylene, carbene analog, disilene, divalent compounds, N-heterocycles.

Preparation and redox properties of longitudinally twinned TCNQ: Hexacyanostilbenequinodimethane dianion

Abstract A new extended π-conjugated TCNQ, hexacyanostilbenequinodimethane, was isolated as a dianion salt. Its cyclic voltammograms show that the dianion is reduced reversibly to a trianion radical, while the oxidized species, a monoradical anion, dimerizes to give the dimer dianion, which is further electrochemically oxidized to a neutral polymer.

Investigation of Free Singly and Doubly Charged Alkali Metal Sulfate Ion Pairs: M+(SO42-) and [M+(SO42-)]2 (M = Na, K)

The authors present a combined experimental and theoretical investigation of alkali metal sulfate ion pairs and their doubly charged dimers in the gas phase: Na{sup +}SO{sub 4}{sup 2{minus}}, K{sup +}SO{sub 4}{sup 2{minus}}, (NaSO{sub 4}){sub 2}{sup 2{minus}}, (KSO{sub 4}){sub 2}{sup 2{minus}}, and NaK(SO{sub 4}){sub 2}{sup 2{minus}}. They produced these anions using an electrospray technique and measured their photoelectron spectra at three photon energies, 355, 266, and 193 nm. The photoelectron spectra of each anion exhibit two detachment features, which approximately correspond to detachment from the HOMO and HOMO-1 of the SO{sub 4}{sup 2{minus}} group perturbed by the cations. The electron binding energies of the dimer dianions are lower than those of the monomers because of the strong electron-electron repulsion in the dianions. The authors also observed the repulsive Coulomb barriers in the dianions and their effects on the photodetachment spectra. They used density functional theory and ab initio molecular orbital theory to obtain the geometric and electronic structure of the ion pairs. The calculated electron binding energies and orbital energy separations are in reasonable agreement with the experimental values. The authors found that the MSO{sub 4}{sup {minus}} ion pairs have C{sub 3v} symmetry with a C{sub 2v} structure slightly higher inmore » energy. In the dimer dianions the two alkali metal cations bridge the two SO{sub 4}{sup 2{minus}} groups.« less

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO) 5− anion

The complex [Et 4N][W(CO) 5OMe] ( 1) has been prepared from the reaction of the photochemically generated W(CO) 5THF adduct and [Et 4N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO) 4OMe] 2 2−. The resulting THF insoluble salt [Et 4N] 2[W(CO) 4OMe] 2 ( 2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et 4N] 3[W 2(CO) 6(OMe) 3] ( 3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et 4N] 4[W(CO) 3OMe] 4 ( 4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ 3-methoxide groups and W(CO) 3 units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et 4N] 3[W 2(CO) 6(OCH 2CH 2OH) 3] ( 5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2 1/ n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2 12 12 1, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et 4N][W(CO) 5OR] (R = C 6H 5 and 3,5-F 2C 6H 3) were measured to be 2.15 × 10 −2 and 1.31 × 10 −3 s −1, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10 −2 s −1 establishes a lower limit for the first-order rate constant for CO loss in the W(CO) 5OMe − anion, since the methoxide ligand is a better π-donating group than phenoxide.

Bond distortion and electronic state of C 60 dimer by two electrons uptake

In order to study the electron doping effect on the neutral C 60 dimer with the linkage through a [2+2] cycloaddition, structures of the neutral dimer and its dianion have been energetically optimized by the semiempirical Hamiltonian PM-3, The (C 60) 2 2− has turned out to have a slightly squashed and equatorially swollen geometry in each C 60 compared to the structure of the (C 60) 2. But both have the same symmetry of D 2 h . The doped electrons in the dianion will be largely on an equator zone of each C 60 ball. The intermolecular center-to-center distance is longer by about 0.03 angstrom in the C 60 dimer dianion than in its neutral case.

Study on the reduction species of sulfur by alkali metals in nonaqueous solvents

Rechargeable cells with a sulfur cathode, a lithium anode and a nonaqueous electrolyte operating at ambient temperature have been extensively studied as a possible application of sulfur combined with nonaqueous solvent. However, the behavior of the chemical species formed by the reduction of sulfur with alkali metals in nonaqueous solvent has not yet been clarified. In this report, sulfur is reduced in tetrahydrofuran (THF) by alkali metals (M: Na, K, Li and Cs), by anthracene radical anions or by diphenylethylene dimer dianions with alkali metal counter cations mainly under the experimental condition of [S 8] [M] > 0.25 . The system produced by the reduction is the yellow solution consisting of polysulfide dianions ( S m 2−, m > 1) and radical anions ( S n −, n > 1) which changes into a blue solution by the addition of hexamethylphosphoric triamide with a much higher polarity than THF. The influence of the kind of alkali metal, the temperature and the addition of solvents such as crown ether on the behavior of the chemical species formed are examined by ultraviolet ( uv)-visual electronic spectra, electron spin resonance (ESR) spectra and Raman spectra measurements. In addition, γ-irradiation with 60Co was carried out to reduce sulfur in glassy solid 2-methyl-THF at — 196 °C. Furthermore, the reaction between the yellow solution and aliphatic bromide is investigated. As a result, it is revealed that the yellow species is S 4 2−, the blue species is S 3 − and several polysulfide dianions and radial anions are in a state of equilibrium.

Die Reduktion von Azulen mit Natrium zum Kontaktionen-Tripel [Dinatrium-(1,1′,6,6′-Tetrahydro-6,6′-bi(azulen)-1,1′-diid)-bis (diglyme)]∞

The Sodium Reduction of Azulene to the Contact-Ion Triple [Disodium-(1,1′,6,6′-Tetrahydro-6,6′-bi(azulene)-1,1′-diide)–bis(diglyme)]∞ Colorless air-sensitive single crystals can be grown from a diglyme solution after the reduction of azulene by a Na-metal mirror. Structure determination at 150 K reveals a dimer dianion, in which the seven-membered rings are connected in 6,6′-positions and doubly diglyme-solvated Na+ counter cations η5-coordinate to the five-membered rings. Based on preceding cyclovoltammetric measurements in aprotic azulene solutions as well as on extensive MNDO enthalpy of formation calculations, a proposal is forwarded how possibly the contact ion triple is formed along a microscopic pathway.

Electroorganic Reactions. Part 45. The Highly Stereoselective Electrochemical Hydrodimerisation of Methyl 4-tert-Butylcyclohex-1-enecarboxylate.

Methyl 4-tert-butylcyclohex-1-enecarboxylate undergoes 1 F reduction at a mercury cathode in DMF solution to give as the major single product a hydrodimer in which the cyclohexyl rings are joined axially and the methoxycarbonyl groups are also axial. The structure is confirmed by X-ray crystallography. Kinetic experiments, combined with force field calculations, indicate radicalanion/radical-anion coupling which is under stereoelectronic control and which dictates diaxial coupling of the cyclohexyl rings. Protonation of the resulting dimeric dianion is under thermodynamic control.

Einkristall‐Strukturen eines Donator‐Akzeptor‐substituierten Cyclopentadiens, seines Kations und seines dimeren Anions: Verschiedenartige Störungen eines Kohlenstoff‐Fünfringes

Single‐Crystal Structures of a Donor‐Acceptor‐Substituted Cyclopentadiene, Its Cation and Its Anion Dimer: Different Distortion of a Five‐Membered Carbon Ring1,4‐Dimethyl‐2,3,4,6‐tetrahydro‐1 H‐cyclopentapyrazine‐5,7‐dicarbonitrile, its molecular cation, and its dimer dianion, generated by hydride abstraction or deprotonation, and crystallized, differ remarkably in their structures: the five‐membered ring in the neutral compound is of (Z)‐butadiene‐type, whereas, in the tetrafluorborate salt, a peripheric NCCCCCN⊕ cyanine distortion occurs and in the sodium derivatives, solvated by either one or two 1,2‐dimethoxyethane molecules, a cyclopentadienyl anion is formed. The structural perturbations induced by changing molecular charges are rationalized by extensive MNDO calculations, which on geometry optimization, reproduce the experimental structures and, in addition, provide charge distributions, further confirming the nN/π and π/π interactions already recognizable from the structural parameters.

Synthetic and structural Studies on Organomolybdenum‐Bismuth Halide Complexes

AbstractThe reactions between either BiBr2Ph and Na/K[Mo(CO)3(ηC5H5)], [BiPh{Mo(CO)3(ηC5H5)}2] and BiBr2Ph, or BiBr3 and BiPh3 and [Bi{Mo(CO)3(ηC5H5)}3] afford the complex [BiBrPh{Mo(CO)3(ηC5H5)}] 1 which has been characterised by X‐ray crystallography. Complex 1 comprises a bismuth centre bonded to a bromine atom, a phenyl group and a Mo(CO)3(ηC5H5) fragment together with a longer secondary intermolecular interaction between a bromine from an adjacent molecule which results in a one‐dimensional polymeric structure. Addition of a source of bromide anion to 1 affords the anionic complex [BiBr2Ph{Mo(CO)3(ηC5H5)}]− 3− although prolonged reaction results in the complex [BiBr2{Mo(CO)3(ηC5H5)}2]− 5− which was characterised by X‐ray crystallography as its [Ph4P]+ salt. Complex 5− comprises a mononuclear bismuth centre bonded to two bromine atoms and two Mo(CO)3(ηC5H5) fragments in a geometry which lies between equatorially vacant trigonal bipyramidal and tetrahedral. The complex [PPN]2[Bi2Cl6{Mo(CO)3(ηC5H5)}2] 8 has also been synthesised and characterised by X‐ray crystallography. A dimeric dianion is observed which can be viewed as two edge‐shared square‐based pyramids with chlorine atoms in the basal planes and Mo(CO)3(ηC5H5) fragments in the apical positions on opposite sides of the Bi2Cl6 plane.

Equilibria between Contact and Solvent-Separated Ion Pairs of 1,1-Diphenylethylene Dimer Dianion and Tetraphenylethylene Dianion

Abstract Temperature-dependent 1H NMR chemical shifts of the two title carbanions have been measured in three solvents and with three counter ions. The equilibria between two types of ion pairs of the carbanions have been discussed in terms of solvent, counter ion, and temperature.

Synthesis and molecular structures of some novel anionic diselenides

The anions [Se(S)CC(CN)2]2–(imnts) and [Se2CC(CN)2]2–(imns) undergo oxidative dimerization reactions which have been studied by cyclic voltammetry. They proceed via a one-electron oxidation followed by a rapid chemical radical dimerization (ECirr mechanism) with Eimnts=–0.2 V and Eimns=–0.3 V versus SCE. The resulting anionic diselenides have been characterized by X-ray structure analysis of [NBu4]2[{(NC)2CC(S)Se–}2]1, [AsPh4]2[{(NC)2CC(S)Se–}2]2 and [AsPh4]2[{(NC)2CC(Se)Se–}2]3. The anions in 1–3 all exhibit a trans arrangement with an inversion centre bisecting the Se–Se bridges. The average Se–Se bond length is 2.330 A. There are two types of bonds involving sp2-hybridized carbon and different chalcogen atoms. The average Se–C bond distance involving selenium of the diselenide group is 1.936 A and corresponds to a single bond. The chalcogen–carbon bonds involving anionic sulfur atoms of 1 and 2 as well as Se of 3 are 1.668, 1.669 and 1.81 A respectively and seem indicative of some double-bond character with charge delocalization over the dimeric dianions.

Electrohydrodimerization of α,β‐Unsaturated Alicyclic and Aliphatic Ketones in Hydroethanolic Solutions on a Mercury Electrode: I . Reduction of 2‐Cyclopenten‐1‐One

Electrohydrodimerization (EHD) of 2‐cyclopenten‐1‐one in buffered hydroethanolic solutions containing 50% (v/v) ethanol over the pH range 3.5–12.5 on mercury has been studied by polarography, cyclic voltammetry, and controlled‐potential electrolysis. A one‐electron reduction process is always found, the electroactive species being either its protonated form below pH 6.0 or its unprotonated form above pH 6.3. The diketone (1,1′‐bicyclopentyl)‐3,3′‐dione is obtained as reaction product in all tested media. Voltammetric data allow the proposition that the protonated form is reduced in a one‐electron step to give the corresponding neutral radical, which subsequently couples to yield the final diketone. For the unprotonated form, however, different EHD mechanisms can be established depending on the solution pH. All these pathways are initiated by generation of the radical anion via a one‐electron reduction step. In the pH region 6.3–7.5, the final diketone is formed by dimerization of the neutral radical obtained by protonation of the radical anion with H+ ion. In the pH zone 8.0–11.0, the same hydrodimer is generated via coupling of the radical anion with the neutral radical, followed by protonation of the resulting dimer anion. Under such conditions, voltammetric results indicate that at pH 8.0–8.5, the proton donor is either boric acid of the buffer or H+ ion, whereas at pH 9.0–11.0 it is only the H+ ion. Above pH 11.0 the radical anion couples to form a dimer dianion, which is further protonated by water to give the final diketone. The rate‐determining step of each EHD reaction depends on the voltammetric conditions employed.

Anionic vinyl polymerization and polycombination reactions induced by electron transfer reactions

1, 1-Diphenylethylene is not capable of being homopolymerized, neither by radical nor by anionic mechanism. This is due to both electronical and sterical reasons. 1, 1-Diphenylethylene, however, is eligible to electron transfer reactions to yield the radical anion which subsequently upon combination reaction forms the dimeric dianion. On the other hand, 1, 1-diphenylethylene may be subjected to the nucleophilic addition of strong nucleophiles such as carbanions, e.g., butyllithium or polystyryllithium. Upon this reaction, a carbanion is formed the nucleophilicity of which is significantly reduced as compared with that of the starting carbanion. Molecules containing the characteristic group of 1, 1-diphenylethylene twice, in analogous reactions, may be subjected to polycombination reactions upon electron transfer. The polymers exhibit cyclic or linear structure depending on the molecular structure of the starting divinylidene compound. Upon reaction with carbanionic species, biscarbanions are formed which may be used as initiators for the anionic polymerization of suitable monomers. A variety of divinylidene compounds and their specific features are presented.