Berthold Hoge

A new synthesis of trifluoromethanethiolates—characterization and properties of tetramethylammonium, cesium and di(benzo-15-crown-5)cesium trifluoromethanethiolates

Abstract [NMe4]SCF3, CsSCF3 and [(B-15-C-5)2Cs]SCF3 (B-15-C-5: benzo-15-crown-5) are formed from reactions of the corresponding fluorides, trimethyl(trifluoromethyl)silane, Me3SiCF3, and elemental sulfur in glyme or THF. All compounds are colorless to pale ochre solids decomposing significantly above ambient temperature. Excellent agreement between experimental and theoretical vibrational frequencies, calculated at the B3PW91 level of theory, impressively confirms the salt-like nature of [NMe4]SCF3. The properties of the title compounds as nucleophilic SCF3 transfer reagents were checked with a variety of organic, organometallic and inorganic compounds.

Synthesis and properties of donor-free bis(difluoromethyl) cadmium, (CF2H)2Cd NMR spectroscopic detection and structure of tetrakis(difluoromethyl) cuprate(III) and related compounds

Abstract The reaction of CdR2 (R = Me, Et) with CF2HI has been investigated. Insertion of difluorocarbene into Cd-C bonds with formation of 1,1-difluoroethyl, 1,1-difluoropropyl and tetrafluoroethyl derivatives is described. Metathesis of CF2HI with CdEt2 in non-coordinating solvents gives very reactive, unsolvated (CF2H)2Cd in quantitative yield. Spectroscopic and chemical properties are reported. Adducts have been obtained by addition of donors such as diglyme or TMEDA. Partial F vs. Cl exchange with acetyl chloride converts the CF2H group to CFHCl derivatives. Reaction of (CF2H)2Cd with CuCl leads to the formation of thermally unstable (difluoromethyl)copper(I) species, ‘Cu(CF2H)’ and [Cu(CF2H)2]⊖, Disproportionation of the cuprate(I) or its oxidation by I2 or O2 gives the cuprate(III) anion, [CuIII(CF2H)4]⊖, which is stable in water and air. The crystal structure of [PNP][Cu(CF2H)4] has been determined. Mixed difluoromethyl/trifluoromethyl cuprates have been prepared from (CF3Cu(S2CNEt2) and (CF2H)2Cd in order to verify the square-planar arrangement of substituents by NMR spectroscopy. Identification of compounds was achieved by multinuclear NMR spectra. NMR parameters are discussed.

Synthesis of Tris‐ and Tetrakis(pentafluoroethyl)silanes

The synthesis and complete characterization of functional, highly Lewis acidic tris(pentafluoroethyl)silanes as well as tetrakis(perfluoroalkyl)silanes Si(C2F5)4 and Si(C2F5)3 CF3 by direct fluorination is described. The reaction of SiCl4 with LiC2F5 invariably affords (pentafluoroethyl)fluorosilicates. To avoid silicate formation by fluoride transfer from LiC2F5 the Lewis acidity of the silane has to be decreased by electron-donating substituents, such as dialkylamino groups. The easily accessible Si(C2F5)3 NEt2 is a valuable precursor for a series of tris(pentafluoroethyl)silanes.

Solid‐State Structure of a Li/F Carbenoid: Pentafluoroethyllithium

Lithium carbenoids are versatile compounds for synthesis owing to their intriguing ambiphilic behavior. Although this class of compounds has been known for several years, few solid-state structures exist because of their high reactivity and often low thermal stability. Using cryo X-ray techniques, we were now able to elucidate the first solid-state structure of a Li/F alkyl carbenoid, pentafluoroethyllithium (LiC2F5), finally yielding a prototype for investigating structure-reactivity relationships for this class of molecules. The compound forms a diethyl ether-solvated dimer bridged by a rare C-F-Li link. Complementary NMR spectroscopy studies in solution show dynamic processes and indicate rapid exchange of starting material and product. Theoretical investigations help to understand the formation of the observed unusual structural motif.

Synthesis of five- and six-coordinate tris(pentafluoroethyl)fluorosilicates.

The research area of perfluoroalkylsilanes is still in its infancy. Although there are already many examples of difluorotriorganylsilicates, the first example of a completely characterized trifluorotriorganylsilicate is presented, the dianion [Si(C2 F5 )3 F3 ](2-) . The strongly electron-withdrawing influence of the pentafluoroethyl groups appears to be a fundamental cause of the stability of this compound. This dianion is also the first structurally characterized example of a tris(pentafluoroethyl)silicon compound. The synthesis and complete characterization of [PPh4 ]2 [Si(C2 F5 )3 F3 ] and [PPh4 ][Si(C2 F5 )3 F2 ] along with the precursor [H(OEt2 )2 ][Si(C2 F5 )3 F2 ] was achieved from SiCl4 and LiC2 F5 .

The Bis(pentafluoroethyl)phosphinous Acid (C2F5)2POH

The industrial product (C(2)F(5))(3)PF(2) is transformed into the phosphinic acid chloride (C(2)F(5))(2)P(O)Cl, which reacts with an excess of Bu(3)SnH in a clean, multistep reaction to give the stannyl derivative (C(2)F(5))(2)POSnBu(3). Subsequent treatment with gaseous HBr leads to the formation of (C(2)F(5))(2)POH, which is isolated in 70 % yield. Besides (CF(3))(2)POH, bis(pentafluoroethyl)phosphinous acid, (C(2)F(5))(2)POH, represents the second known example of a phosphinous acid that is predicted by using density functional theory calculations at the B3PW91/6-311G(3d,p) level to be more stable than the phosphane oxide tautomer, the energy difference being 11.7 kJ mol(-1). Only the phosphinous acid isomer is detectable in the gas phase and in solution. However, investigations of the neat liquid reveal a temperature-dependent tautomeric equilibrium with the phosphane oxide isomer (C(2)F(5))(2)P(O)H, which is characterized by vibrational and multinuclear NMR spectroscopic methods in combination with quantum-chemical calculations.

Trifluoromethylmetallate anions as components of molecular charge transfer salts and superconductors

Abstract Whereas polymeric and common inorganic anions frequently deprive the synthetic chemist of a chance to modify a charge transfer salt’s structure through anion alterations, discrete organometallic anions provide a vast opportunity to probe the structure/property correlations of a material through rational synthetic methods. We have recently undertaken a research effort aimed at the crystallization of conducting charge transfer salts which possess modifiable, organometallic anions as the charge compensating entities. This research has been richly rewarded with the discovery of a new family of bis(ethylenedithio)tetrathiafulvalene (BEDT–TTF or ET) based molecular superconductors. Herein is presented a summary of over 20 κ(ET) 2 M(CF 3 ) 4 (1,1,2-trihaloethane) (M=Cu, Ag, Au) superconducting salts. Three new related salts are also reported: (ET) 2 [ trans- Ag(CF 3 ) 2 (CN) 2 ], κ L (BEDT-TSF) 2 Ag(CF 3 ) 4 (TCE), and κ L (ET) 2 Ag(CF 3 ) 3 Cl(TCE).

On the XeF+/H2O System: Synthesis and Characterization of the Xenon(II) Oxide Fluoride Cation, FXeOXeFXeF+

The reported synthesis of the H(2)OF(+) cation as a product of the oxidative fluorination of H(2)O by [XeF][PnF(6)] (Pn = As, Sb) in HF solution has been reinvestigated. The system exhibits complex equilibria, producing two new Xe(II) compounds, [Xe(3)OF(3)][PnF(6)] and [H(3)O][PnF(6)] x 2 XeF(2), refuting the original claim for the synthesis of the H(2)OF(+) cation. Both compounds have been isolated and characterized by vibrational spectroscopy and single-crystal X-ray diffraction. The X-ray crystal structures of the [Xe(3)OF(3)][PnF(6)] salts contain the Z-shaped FXeOXeFXeF(+) cation, which represents the first example of an isolated Xe(II) oxide fluoride. The crystal structure of the [H(3)O][AsF(6)] x 2 XeF(2) adduct contains XeF(2) molecules that interact with the H(3)O(+) cations. The vibrational assignments for the Xe(3)OF(3)(+) cation have been made with the aid of quantum-chemical calculations and were confirmed by (18)O-enrichment, and the assignments for [H(3)O][AsF(6)] x 2 XeF(2) were confirmed by (2)D- and (18)O-enrichment. Quantum-chemical calculations have also been carried out for H(3)O(+) x nXeF(2) (n = 1-4) and have been used to interpret the X-ray crystal structure and vibrational spectra of [H(3)O][AsF(6)] x 2 XeF(2). The energy-minimized geometries and vibrational frequencies for HOF and H(2)OF(+) have been calculated, further disproving the original report of the H(2)OF(+) cation. Both FXeOH and FXeOH(2)(+) have also been computed and are viable intermediates in the proposed equilibria between XeF(+) and H(2)O that lead to the Xe(3)OF(3)(+) cation.

Cyanide initiated perfluoroorganylations with perfluoroorgano silicon compounds

Abstract Cyanophenylphosphanes, Ph2PCN or PhP(CN)2, do not react with Me3SiCF3 or Me3SiC6F5 in the absence of cyanide ions. Catalytic amounts of ionic cyanides such as [NEt4]CN, [18-crown-6-K]CN or NaCN initiate perfluoroorganylation reactions. The trifluoromethylphosphines, Ph2PCF3 and PhP(CF3)2, as well as the pentafluorophenylphosphines, Ph2PC6F5 and PhP(C6F5)2, are isolated in 60–75% yield. In dimethylformamide or acetone solutions, side reactions are observed while reactions in CH2Cl2 and acetonitrile proceed selectively. Me3SiCF3 addition to the carbonyl groups of dimethylformamide and acetone occurs on treatment of Me3SiCF3 solutions of these solvents with catalytic amounts of cyanide, cyanate or thiocyanate salts even at low temperature. The formation of the reactive silicate [Me3Si(CN)CF3]− in reactions with an excess of [18-crown-6-K]CN is proved by low temperature NMR investigations.

Synthesis of Chlorosilicates

Chlorosilicates represent important intermediates in S(N)2 reactions of chlorosilanes. They can be stabilized by the introduction of electron-withdrawing substituents. Salts of various (pentafluoroethyl)chlorosilicates have been isolated and structurally characterized.