Conformational analysis of 1,1,2,2-tetraaryl-disilanes

A study of the static stereochemistry of 1,1,2,2-tetraphenyldisilane (1) and 1,1,2,2-tetramesityldisilane (2) by empirical force field calculations, X-ray diffraction, and ¹H NMR reveals that the preference for the anti conformation, exhibited by the unclamped 1,1,2,2-tetraarylethanes, is sustained in the analogous disilanes, although in somewhat attenuated form. This anti preference stands in contrast to the gauche preference of 1,1,2,2-tetraalkyldisilanes. Examination of ³J_HH coupling constants for R₂HSiSiHR₂; (R = phenyl, mesityl, 2,6-dimethyl-phenyl, t-butyl, cyclohexyl) suggests the existence of a Karplus relation for H-Si-Si-H systems.     

Collisional energy transfer in the two-channel decomposition of 1,1,2,2-tetrafluorocyclobutane and 1-methyl-2,2,3,3-tetrafluorocyclobutane, I. Gas/gas collisons

The two-channel thermal decomposition of 1,1,2,2-tetrafluorocyclobutane (TFCB) and 1-methyl-2,2,3,3-tetrafluorocyclobutane (MTFCB) have been studied in the temperature range of 730–805 K at pressures varied from 1.1 Pa up to 4.6 kPa. In the pressure independent range, Arrhenius expressions were obtained for TFCB decomposition into 2 CH₂CF₂ (k₁) and C₂H₄+C₂F₄ (k₂), respectively. The same kinetic equations were determined for the decomposition of MTFCB into C₃H₄F₂+C₂H₂F₂ (k₃) and C₃H₆+C₂F₄(k₄). From the study of the pressure dependence of the homogeneous decomposition rates, the average downward energy transfer values of 1800±200 cm^–1 and 1600±200 cm^–1 were obtained for the TFCB and MTFCB molecules, respectively.     

Eine neue Synthese für Nitrosyl‐Salze mit schwach koordinierenden Anionen am Beispiel von NO[B(CF3)4]

A New Synthesis for Nitrosyl Salts with Weakly Coordinating Anions Exemplified by NO[B(CF₃)₄] A new synthesis for nitrosyl salts of weakly coordinating anions is described, using the corresponding guanidinium salts as starting materials. The guanidinium salt [C(NH₂)₃][B(CF₃)₄] was obtained by a metathesis reaction of K[B(CF₃)₄] with [C(NH₂)₃]Cl. Treatment of the guanidinium salt with liquid NO₂ resulted in analytical pure NO[B(CF₃)₄] in quantitative yield. The guanidinium and nitrosyl tetrakis(trifluormethyl)borates were characterized by vibrational and NMR spectroscopy as well as by DSC measurements.     

Reactions of diazoalkanes with unsaturated compounds. 14. Reactions of diazomethane,diazocyclopropane, and methyl diazoacetate with 1,1,2,2-tetrafluoro-3-vinylcyclobutane and 2,3,3-trifluoro-1-vinylcyclobutene to form [3+2] and [1+2] cycloadducts

The reactions of diazomethane and diazocyclopropane generated in situ with 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1) and 2,3,3-trifluoro-1-vinylcyclobutene (2) proceeded at the double bond of the substituent as the 1,3-dipolar cycloaddition to form the corresponding 1-pyrazolines. Under the conditions of thermolysis (340—400 °C), the resulting cyclobutylpyrazolines 4 and 5 selectively lost the dinitrogen molecule to generate 3-cyclopropyl-1,1,2,2-tetrafluorocyclobutane (6) or 1,1,2,2-tetrafluoro-3-spiropentylcyclobutane (7), respectively, in high yields. In the presence of Pd(acac)₂, the reactions of these fluorine-containing unsaturated compounds and 2-chloro-1,1,2-trifluoro-3-vinylcyclobutane (3) with diazomethane gave rise directly to cyclopropane derivatives 6, 11, and 12, respectively. The reactions of compounds 1 and 2 with methyl diazoacetate in the presence of Rh₂(OAc)₄ proceeded analogously to yield cis- and trans-disubstituted cyclopropanes.     

Investigation on the Sodium and Potassium Tetrasalts of 1,1,2,2‐Tetranitraminoethane

With respect to high‐energy dense materials with high oxygen‐content, the tetrasodium salt of 1,1,2,2‐tetranitraminoethane as monohydrate Na₄TNAE · H₂O ( 4 ) and the tetrapotassium salt as dihydrate K₄TNAE · 2H₂O ( 5 ) were synthesized and reported for the first time together with their crystal structures at 173 K. Whilst 4 cannot be dehydrated the crystal water content of 5 can be removed irreversibly at 160 °C to obtain K₄TNAE ( 6 ) as demonstrated by DTA and TGA measurements. K₄TNAE ( 6 ) was demonstrated using the small scale reactivity test to be a inferior explosive to RDX and CL‐20. However the anionic nitramine compound was measured to be less toxic against Vibrio fischeri than RDX (EC₅₀: 240 mg · L^–1) with respect to its EC₅₀ value above 15070 mg · L^–1. This demonstrates that the introduction of anionic nitramine moieties is a promising concept for the stabilization of energetic materials with lower toxicity.     

Tris- and tetrakis-(trifluoromethyl)fluorogermanates; the structure of an anion with pentacoordinated germanium

Reactions of (CF₃)₃GeX (X = halogen) or (CF₃)₄Ge with fluoride ions in aqueous or acetonitrile solutions give the trigonal-bipyramidal (CF₃)₃GeF₂⁻ and octahedral fac-(CF₃)₃GeF₃²⁻ or cis-(CF₃)₄GeF₂²⁻ anions, respectively. The crystal structure of [(CH₃)₄N][(CF₃)₃GeF₂] has been determined. The symmetry of the anion (C_s) approximates to C₃v, with axial F atoms (r_av(GeF) 1.835(8) Å) and equatorial CF₃ groups (r_av(GeC) 2.000(5) Å) (both distances corrected for libration). The bonding in the anion is discussed on the basis of structural and vibrational spectral data. The configurations of the octahedral complexes have been deduced from their ¹⁹F NMR spectra.     

Highly trifluoromethylated platinum compounds

The homoleptic, square‐planar organoplatinum(II) compound [NBu₄]₂[Pt(CF₃)₄] ( 1 ) undergoes oxidative addition of CF₃I under mild conditions to give rise to the octahedral organoplatinum(IV) complex [NBu₄]₂[Pt(CF₃)₅I] ( 2 ). This highly trifluoromethylated species reacts with Ag⁺ salts of weakly coordinating anions in Me₂CO under a wet‐air stream to afford the aquo derivative [NBu₄][Pt(CF₃)₅(OH₂)] ( 4 ) in around 75 % yield. When the reaction of 2 with the same Ag⁺ salts is carried out in MeCN, the solvento compound [NBu₄][Pt(CF₃)₅(NCMe)] ( 5 ) is obtained in around 80 % yield. The aquo ligand in 4 as well as the MeCN ligand in 5 are labile and can be cleanly replaced by neutral and anionic ligands to furnish a series of pentakis(trifluoromethyl)platinate(IV) compounds with formulae [NBu₄][Pt(CF₃)₅(L)] (L=CO ( 6 ), pyridine (py; 7 ), tetrahydrothiophene (tht; 8 )) and [NBu₄]₂[Pt(CF₃)₅X] (X=Cl ( 9 ), Br ( 10 )). The unusual carbonyl–platinum(IV) derivative [NBu₄][Pt(CF₃)₅(CO)] ( 6 ) is thermally stable and has a ν_CO of 2194 cm^?1. The crystal structures of 2? CH₂Cl₂, 5 , [PPh₄][Pt(CF₃)₅(CO)] ( 6′ ), and 7 have been established by X‐ray diffraction methods. Compound 2 has shown itself to be a convenient entry to the chemistry of highly trifluoromethylated platinum compounds. To the best of our knowledge, compounds 2 and 4 – 10 are the organoelement compounds with the highest CF₃ content to have been isolated and adequately characterized to date.     

ESR study of radicals formed by the reduction of α-diketones C(O)C(O)CF3 (R=(CF3)2CF, C6F5, (CF3)3C) with several group I–III metals

The ESR spectra of radical anions formed by reduction of α-diketones RC(O)C(O)CF₃ (R=(CF₃)₂CF, C₆F₅, (CF₃)₃C) with metals (Li, Na, K, Mg, Cd, Zn, Hg, In, and TI) in THF were studied. For R=(CF₃)₂CF and C₆F₅, the radical anions are formed ascis-isomers, whereas for R=(CF₃)₃C,trans-isomers are obtained. Line broadening due to solvation and desolvation of the cation is observed in the latter case. The reduction of α-diketone (CF₃)₂CFC(O)C(O)CF₃ with Group II metals (Mg, Cd, Zn) results in the formation of radical pairs. Translated fromIzvestiya Akadmii Nauk. Seriya Khimicheskaya, No. 11, pp. 2228–2231, November, 1998.     

Ruthenium-catalyzed cycloisomerization of 1,1,2,2-tetramethyl-1,2-divinyldisilane: Selective formation of a five-membered silacycle

The cycloisomerization of 1,1,2,2-tetramethyl-1,2-divinyldisilane (1) in the presence of ruthenium-diphosphine complexes has been examined. A ruthenium-dppe (8) or a ruthenium-dppv (12) complex selectively catalyzed the reaction and 1,1,2,3,3-pentamethyl-1,3-disilycyclopent-4-ene (3) was isolated as the major product. The reaction was also carried out in the presence of a deuterated ruthenium-PⁱPr₃ complex and the incorporation of deuterium to 1,1,4,4-tetramethyl-1,4-disilacyclohex-2-ene (2) was observed. The mechanism of this reaction has been proposed.     

The reaction of boron trihalides with CF3Sn(CH3)3 in the presence of trimethylamine

The reaction of CF₃Sn(CH₃)₃ with BCl₃ and BBr₃ in the presence of trimethylamine has been investigated. The volatile adducts CF₂XBF₂·N(CH₃)₃ (X = F, Cl and Br) have been isolated from the complex reaction mixture while the anions BF^?₄, CF₂XBF^?₃, CF₃BF₂CF₂X^? and (CF₂X)₂BF^?₂ have been identified in the residue. [(CH₃)₃NH][CF₂ClBF₃] has been isolated. The formation of the CF₂XB derivatives is likely to occur via CF₂ insertion, which is promoted by the presence of N(CH₃)₃. NMR, IR, Raman and mass spectra of the novel fluoromethyl borane derivatives are reported.     

Nestlike Silver(I) Thiolate Clusters with Tunable Emission Color Templated by Heteroanions

Four silver thiolate clusters, [H₃O][(Ag₃S₃)(BF₄)@Ag₂₇(tBuS)₁₈(hfac)₆H₂O] ⋅ H₂O ( 1 ; hfac = hexafluoroacetylacetone), [(Ag₃S₃)(CF₃CO₂)@Ag₃₀(tBuS)₁₆(CF₃CO₂)₉(CH₃CN)₄] ⋅ CF₃CO₂ ⋅ 4 CH₃CN ( 2 ), [(Ag₃S₃)(MoO₄)@Ag₃₀(tBuS)₁₆(CF₃CO₂)₉(CH₃CN)₄] ⋅ 2 CH₃CN ( 3 ), and [(Ag₃S₃)(CrO₄)@Ag₃₀(tBuS)₁₆(CF₃CO₂)₉(CH₃CN)₄] ⋅ 4 CH₃CN ( 4 ), were isolated. They have similar nestlike structures assembled by an [Ag₃S₃]³⁻ template together with one of the BF₄⁻, CF₃CO₂⁻, MoO₄²⁻, or CrO₄²⁻ anions. Interestingly, the solid-state emissions of 2 – 4 are dependent on the templating anions and are tunable from green to orange and then to red by changing the template from CF₃CO₂⁻ to MoO₄²⁻ and to CrO₄²⁻, and this may be correlated to the charge transfer between these templates to metal atoms. This work helps to understand the templating role of heteroanions and the relationship between structure and properties.     

Effect of 1,1,2,2-tetrachloroethane on the ionizing ability of complexes of HCl with DMF

The acidity function (H _o) of solutions of HCI (0–7.1 mol L^?1) in an equimolar mixture of DMF-1,1,2,2-tetrachloroethane (TCE) has been determined by the indicator method at 25 °C. Data on the relative ionizing activity of complexes of HCI with DMF with various compositions and structures have been obtained. In the ternary system HCI-DMF-TCE, the ionizing ability of the complexes of DMF with HCI of the compositions 2 : 1 and 1 : 1 with a quasiionic structure decreases compared to the HCI-DMF system, and that of the complex of the composition DMF · 2HC1 with a structure of an ion pair Me₂NHCOH⁺ · (CIHCI)^? with a strong centrosymmetrical H-bond in the anion increases.     

Coordination of the new weakly coordinating anions Al(OCH(CF3)2)4−, Al(OC(CH3)(CF3)2)4−, and Al(OC(Ph)(CF3)2)4− to the monovalent metal ions Li+ and Tl+

The structures of Li⁺ or Tl⁺ salts of three new fluoroalkoxide-containing aluminate anions were determined by X-ray crystallography. For LiAl(OC(Ph)(CF₃)₂)₄, monoclinic, C2/c, a=42.297(6), b=10.641(1), c=19.132(2) Å, β=114.808(9)°, Z=8, T=−100°C, R=0.052; for TlAl(OC(CH₃)(CF₃)₂)₄, monoclinic, P2₁/c, a=12.650(3), b=9.970(2), c=21.237(4) Å, β=94.00(3)°, Z=4, T=−100°C, R=0.073; for TlAl(OCH(CF₃)₂)₄, monoclinic, P2₁/n, a=14.261(1), b=9.8024(9), c=16.911(2) Å, β=93.467(8), Z=4, T=−130°C, R=0.053. The monatomic, monovalent cations interact with their respective anions by means of M–O and M–F bonds. The Tl⁺ cations in TlAl(OCH(CF₃)₂)₄ and TlAl(OC(CH₃)(CF₃)₂)₄ interact with three different aluminate anions. The Li⁺ cation in LiAl(OC(Ph)(CF₃)₂)₄ interacts with only one aluminate anion, forming a rare trigonal–prismatic LiO₂F₄ coordination unit.     

Anodic oxidation of organometallic sandwich complexes using [Al(OC(CF3)3)4] or [AsF6] as the supporting electrolyte anion

Anodic voltammetry and electrolysis of the metallocenes ferrocene, ruthenocene, and nickelocene have been studied in dichloromethane containing two different fluorine-containing anions in the supporting electrolyte. The perfluoroalkoxyaluminate anion [Al(OC(CF₃)₃)₄]⁻ has very low nucleophilicity, as shown by its inertness towards the strong electrophile [RuCp₂]⁺ and by computation of its electrostatic potential in comparison to other frequently used electrolyte anions. The low ion-pairing ability of this anion was shown by the large spread in E_1/2 potentials (ΔE_1/2 = 769 mV) for the two one-electron oxidations of bis(fulvalene)dinickel. The hexafluoroarsenate anion [AsF₆]⁻, on the other hand, reacts rapidly with the ruthenocenium ion and is much more strongly ion-pairing towards oxidized bis(fulvalene)dinickel (ΔE_1/2 = 492 mV). In terms of applications of these two anions to the anodic oxidation of organometallic sandwich complexes, the behavior of [Al(OC(CF₃)₃)₄]⁻ is similar to that of other weakly-coordinating anions such as [B(C₆F₅)₄]⁻, whereas that of [AsF₆]⁻ is similar to the more traditional electrolyte anions such as [PF₆]⁻ and [BF₄]⁻. Additionally, the synthesis and crystal structure of [Cp₂Fe][Al(OC(CF₃)₃)₄] are reported.     

Synthesis and characterization of a new class of polyfluorinated alkanes: tetrakis(perfluoroalkyl)alkane

The synthesis and physico-chemical characterization of 1,1,2,2-tetrakis(perfluoroalkyl-methylene)ethane {[F(CF₂)_nCH₂]₂CH}₂ (n=6, TK6; n=8, TK8) are reported. The synthesis consists of four steps: (1) addition of allyl alcohol to a perfluoroalkyl iodide, F(CF₂)_nI (n=6,8) to give the corresponding iodo-adduct; (2) dehalogenation of the adduct by treatment with zinc in aqueous acetic acid, yielding 3-perfluoro-n-alkyl-1-propene; (3) addition of 3-perfluoro-n-alkyl-l-propene to perfluoroalkyl iodide, F(CF₂)_nI (n=6,8) to give 1,3-perfluoro-n-alkyl-2-iodo-propane; (4) coupling of 1,3-perfluoro-n-alkyl-2-iodo-propane by zinc in acetic anhydride giving the final products. TK6 and TK8 are characterized by very low surface tension values and exhibit very good properties as potential ski-waxes.     

Trifluoromethylsulfonyl-Based Salts of BEDT-TTF: Crystal and Electronic Structures and Physical Properties11

Three 2 : 1 salts of the organic donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) with trifluoromethylsulfonyl-based anions N(SO₂CF₃)₂⁻, CH(SO₂CF₃)₂⁻ and C(SO₂CF₃)₃⁻ were prepared by electrocrystallization. These salts were characterized by single-crystal X-ray diffraction, electron spin resonance (ESR) spectroscopy, electrical resistivity measurements and electronic band structure calculations. (ET)₂N(SO₂CF₃)₂ is a two-dimensional (2D) metal, but its ESR spin susceptibility above 150 K shows a weakly semiconducting behavior, presumably because during ESR measurements the sample cooling rate is slow hence allowing the disordered anions to readjust their positions. (ET)₂CH (SO₂CF₃)₂ is a 2D metal and undergoes a metal-to-insulator (MI) transition at 110 K due probably to a geometry change of the donor molecule layers. (ET)₂C(SO₂CF₃)₃ is a one-dimensional (1D) metal and undergoes an MI between 180 and 240 K, which is expected to be of charge density wave type.     

Electroreductive synthesis of organomercurials from n-perfluorobutyl-1,4-diiodide

Electroreduction of the n-perfluorobutyl 1,4 diodide I-(CF₂)₄-I, is studied in dimethylformamide as a solvent. During the electrolysis their is intermediate production of I-(CF₂)₄-H and of H-(CF₂)₄-Hg-I, the final product being the symmetrical mercurial H-(CF₂)₄-Hg-(CF₂)₄-H. The results are compared with previous studies on monoiodide CF₃-(CF₂)₅-I and the dibromide Br-(CH₂)₄-Br.     

The Role of Ate Complexes in the Copper‐Mediated Trifluoromethylation of Alkynes

Trifluoromethylation reactions have recently received increased attention because of the beneficial effect of the trifluoromethyl group on the pharmacological properties of numerous substances. A common method to introduce the trifluoromethyl group employs the Ruppert–Prakash reagent, that is, Si(CH₃)₃CF₃, together with a copper(I) halide. We have applied this method to the trifluoromethylation of aromatic alkynes and used electrospray‐ionization mass spectrometry to investigate the mechanism of these reactions in tetrahydrofuran, dichloromethane, and acetonitrile as well as with and without added 1,10‐phenanthroline. In the absence of the alkyne component, the homoleptic ate complexes [Cu(CF₃)₂]^? and [Cu(CF₃)₄]^? were observed. In the presence of the alkynes RH, the heteroleptic complexes [Cu(CF₃)₃R]^? were detected as well. Upon gas‐phase fragmentation, these key intermediates released the cross‐coupling products R?CF₃ with perfect selectivity. Apparently, the [Cu(CF₃)₃R]^? complexes did not originate from homoleptic cuprate anions, but from unobservable neutral precursors. The present results moreover point to the involvement of oxygen as the oxidizing agent.     

Structural Design of Ionic Conduction Paths in Molecular Crystals for Selective and Enhanced Lithium Ion Conduction

The molecular crystals [Li{N(SO₂CF₃)₂}{C₆H₄(OCH₃)₂}₂] and [Li{N(SO₂CF₃)₂}{C₆F₂H₂(OCH₃)₂}₂] with solid‐state lithium ion conductivity have been synthesized by the addition of two equivalents of 1,2‐dimethoxybenzene or 1,2‐difluoro‐4,5‐dimethoxybenzene to Li{N(SO₂CF₃)₂}, respectively. Single‐crystal X‐ray diffraction analysis revealed the formation of ionic conduction paths with an ordered arrangement of lithium ions in these crystal structures, afforded by the self‐ assembled stacking of molecular‐based channels consisting of N(SO₂CF₃)₂ anion and 1,2‐dimethoxybenzene frameworks as a result of intermolecular aromatic and hydrogen interactions. These compounds show selective lithium ion conductivity as the anions behave as a component unit of the conduction paths. The relationship between the crystal structure and ionic conductivity of the molecular crystals provides a clue to the development of novel solid electrolytes based on molecular crystals showing fast and selective lithium ion conduction.     

Synthesis and Reactivity of Fluoroalkyl Copper Complexes by the Oxycupration of Tetrafluoroethylene

The copper(I)‐mediated generation of ‐OCF₂CF₂‐ moieties by the oxycupration of tetrafluoroethylene (TFE) using either copper aryloxides or alkoxides is disclosed. The key intermediates, 2‐aryloxy‐1,1,2,2‐tetrafluoroethyl and 2‐alkoxy‐1,1,2,2‐tetrafluoroethyl copper complexes, were obtained from the reaction of the corresponding aryloxy and alkoxy copper complexes with TFE, and their structures in solution and in the solid state were unambiguously determined by multinuclear NMR spectroscopy and X‐ray diffraction analysis. These copper complexes subsequently reacted with aryl iodides (ArI) to afford ROCF₂CF₂Ar (R=aryl or alkyl) in high yields.