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

Phosphinous acid or phosphane oxide? Both tautomers of (C₂F₅)₂POH (see picture) are found in the neat liquid, whereas only phosphinous acid is present in the gas phase or in solution. The synthesis starting from (C₂F₅)₃PF₂, the thermodynamics of the tautomerization, and the detection and thermodynamics of the cis‐/trans‐P? OH rotamers of the acid are described.

     

Stable phosphinous acids

The electronic properties of organyl element compounds are strongly influenced by the electronic characteristics of the organic substituents. The bonding of two CF₃ groups to a phosphorus atom effects a drastically decreased basicity. That is the phosphorus atom is the least basic centre in the compound (CF₃)₂POH. This compound, synthesized in 1960 by Burg and Griffiths, is the only known example of a phosphinous acid, although there should be a general interest in this class of compounds. However, only a few investigations have been reported which may be explained by the tedious and risky synthesis. In this paper a safe one step and high yield synthesis of (CF₃)₂POH is described. The compound (C₆F₅)₂POH, originally claimed as a phosphinous acid, is proved to exist at room temperature exclusively in the tautomeric oxide form. (C₆F₅)₂P(O)H crystallizes in the triclinic space group (no. 2) with a 992.9(1) pm; b 1501.9(2) pm; c 1539.4(2) pm; α 117.48(1)°; β 100.39(1)°; γ 96.02(1)° and Z 6.Quantum chemical investigations prove the electron withdrawing effect of s-triazinyl groups (1,3,5-triazin-4-yl derivatives) to be much stronger than that of pentafluorophenyl groups. Quantum chemical calculations at the B3PW91/6-311G(3d,p) level of theory predict for the bis(s-triazinyl) derivative (C₃N₃H₂)₂POH the phosphinous acid isomer to be favored by ΔE_ZP = 22 kJ/mol in relation to the corresponding phosphane oxide isomer. The phosphinous acid (CF₃)₂POH (C_s symmetry) is favored at the same level of theory by about ΔE_ZP = 14 kJ/mol compared with the phosphane oxide structure (C_s symmetry).     

Bis(fluorbenzoyloxy)methylphosphanoxide

Bis(fluorbenzoyloxy)methyl phosphane oxides CH₃P(O)[OC(O)R]₂ [R = C₆H₄2F (1), C₆H₄3F (2), C₆H₄4F (3), C₆H₃2,6F₂ (4), C₆H2,3,5,6F₄ (5)] were prepared by treating silver salts of carboxylic acids AgOC(O)R with CH₃P(O)C?₂ (IR-, ¹H-, ¹⁹?F-and ³¹P{¹H}-NMR-data). The mixed anhydrides 1–5 show unusual thermal stability at room temperature. Stability against hydrolysis decreases with increasing number of fluorine-atoms. The reaction of R′P(O)C?₂ [R′ = CH₃, C₆H₅, (CH₃)₃C] with M^IOC(O)R_F [R_F = CF₃, C₂F₅, C₆F₅; M^I = Ag^I, Na^I T?^I] was investigated.     

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.     

A Convenient,Selective Synthesis of Bis[2,4‐bis(trifluoromethyl)phenyl]phosphane Derivatives Starting from 1,3‐Bis(trifluoromethyl)benzene

The reaction of the sterically shielded phosphane derivative, dichlorodiethylaminophosphane, Cl₂PNEt₂, with an excess of a mixture of 2,6‐bis(trifluoromethyl) and 2,4‐bis(trifluoromethyl)phenyl lithium gives bis[2,4‐bis(trifluoromethyl)phenyl]diethylaminophosphane, [2,4‐(CF₃)₂C₆H₃]₂PNEt₂, in 72 % yield as a colourless solid, while 2,6‐bis(trifluoromethyl)phenyl lithium remains unchanged in solution. The amino derivative crystallizes in the monoclinic space group P2₁/c (a 869.2(1), b 1857.4(1), c 1357.6(1) pm, β 100.57(4)°, Z = 4). Treatment of [2,4‐(CF₃)₂C₆H₃]₂PNEt₂ in CHCl₃ solution with conc. HCl allows the synthesis of [2,4‐(CF₃)₂C₆H₃)]₂PCl. [2,4‐(CF₃)₂C₆H₃]₂PCl reacts with H₂O in THF solution with quantitative formation of the corresponding secondary phosphane oxide. To obtain bis[2,4‐bis(trifluoromethyl)phenyl]phosphinic acid, [2,4‐(CF₃)₂C₆H₃]₂P(O)OH, quantitatively, a CHCl₃ solution of [2,4‐(CF₃)₂C₆H₃]₂P(O)H, has to be stirred in an NO₂ atmosphere. The phosphinic acid crystallizes is the triclinic space group (a 754.2(1), b 927.6(2), c 1305.5(2) pm, α 85.11(2)°, β 75.45(1)°, γ 79.99(2)°, Z = 2). From the reaction of the phosphinic acid with either elemental sodium or with cyanide salts, the corresponding phosphinate salts are obtained in an almost quantitatively yield.     

A Widely Applicable Synthetic Approach to Alk‐1‐yn‐1‐yl(polyfluoroorganyl)‐iodonium Salts [(RC≡C)(R′)I][BF4]

The reaction of alkynyldifluoroboranes RC≡CBF₂ (R = (CH₃)₃C, CF₃, (CF₃)₂CF) with organyliodine difluoride R′IF₂ bearing electron‐withdrawing polyfluoroorganyl groups R′ = C₆F₅, (CF₃)₂CFCF=CF, C₄F₉, and CF₃CH₂ leads to the corresponding alkynyl(organyl)iodonium salts [(RC≡C)(R′)I][BF₄]. This approach uses a widely applicable method as demonstrated for a representative series of polyfluorinated aryl‐, alkenyl‐, and alkyliodine difluorides. Generally, these syntheses proceed with good yields and deliver pure iodonium salts. The distinct electrophilic nature of their [(RC≡C)(R′)I]⁺ cations is deduced from multinuclear magnetic resonance data. Within the series of new iodonium salts [CF₃C≡C(C₄F₉)I][BF₄] is an intrinsic unstable one and decomposed forming CF₃C≡CI and C₄F₁₀.     

The Reaction of 2‐X‐1, 2‐Difluoroalk‐1‐enyldifluoroboranes with Xenon Difluoride. A Methodical Approach to 1, 2‐Difluoroalk‐1‐enylxenon(II) Salts

2‐X‐1, 2‐Difluoroalk‐1‐enylxenon(II) salts were prepared by the reaction of XeF₂ with XCF=CFBF₂ (X = F, trans‐H, cis‐Cl, trans‐Cl, cis‐CF₃, cis‐C₂F₅) but no organoxenon(II) compounds were obtained when the trans‐isomers of boranes, trans‐XCF=CFBF₂ (X = CF₃, C₄F₉, C₄H₉, Et₃Si), were used under similar conditions.     

Fluoroborates by Cleavage of Trimethylamine‐bis(trifluoromethyl)boranes with NEt3 × 3 HF. Structures of C6F5(CF3)2B · NMe3, K[C6H5CH2(CF3)2BF], and K[C6H5(CF3)2BF]

Trimethylamine‐bis(trifluoromethyl)boranes R(CF₃)₂B · NMe₃ (R = cis/trans‐CF₃CF=CF ( 1/2 ), HC≡C ( 3 ), H₂C=CH ( 4 ), C₂H₅ ( 5 ), C₆H₅CH₂ ( 6 ), C₆F₅ ( 7 ), C₆H₅ ( 8 )) react with NEt₃ × 3 HF depending on the nature of R at 155–200 °C under replacement of the trimethylamine ligand to form the corresponding fluoro‐bis(trifluoromethyl)borates [R(CF₃)₂BF]^– ( 1 a/2 a – 8 a ). The structures of 7 , K[C₆H₅CH₂(CF₃)₂BF] ( K‐6 a ), and K[C₆H₅(CF₃)₂BF] ( K‐8 a ) have been investigated by single‐crystal X‐ray diffraction. In 7 the CF₃ groups make short repulsive contacts with NMe₃ and C₆F₅ entities – the B–CF₃ bonds being unusually long. The B–F bond lengths of K‐6 a and K‐8 a (1.446(3) and 1.452(2) Å, respectively) are long for a fluoroborate.     

Synthese und Eigenschaften von Diethyldithiocarbaminsäureperfluororganylestern, (C2H5)2NC(S)SRf (Rf = CF3, C2F5, i‐C3F7, n‐C4F9, C6F5)

Syntheses and Properties of Perfluoroorgano Esters of the Diethyldithiocarbamic Acid, (C₂H₅)₂NC(S)SR_f (R_f = CF₃, C₂F₅, i‐C₃F₇, n‐C₄F₉, C₆F₅) Tetraethylthiuram disulfide reacts under different conditions with perfluoroorgano silver(I), AgR_f, and perfluoroorgano cadmium compounds, Cd(R_f)₂, to give the corresponding perfluoroorgano esters of diethyldithiocarbamic acid, (C₂H₅)₂NC(S)SR_f (R_f = CF₃, C₂F₅, i‐C₃F₇, n‐C₄F₉, C₆F₅), and metal diethyldithiocarbamates, AgSC(S)N(C₂H₅)₂ and Cd[SC(S)N(C₂H₅)₂]₂. The mechanisms of the reactions with AgR_f and Cd(R_f)₂ are discussed.     

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

Molybdenum(VI) bis(imido) complexes [Mo(NtBu)₂(L^R)₂] (R=H 1 a ; R=CF₃ 1 b ) combined with B(C₆F₅)₃ ( 1 a /B(C₆F₅)₃, 1 b /B(C₆F₅)₃) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H₂ and Et₃SiH affords ion pairs [Mo(NtBu)(NHtBu)(L^R)₂][HB(C₆F₅)₃] (R=H 2 a ; R=CF₃ 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H₂O leads to [Mo(NtBu)(NHtBu)(L^R)₂][(HO)B(C₆F₅)₃] (R=H 3 a ; R=CF₃ 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C₆F₅)₃]⁻. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L^R)₂][{PhCH₂O}B(C₆F₅)₃] (R=H 4 a ; R=CF₃ 4 b ). Catalysis occurs at [HB(C₆F₅)₃]⁻ while [Mo(NtBu)(NHtBu)(L^R)₂]⁺ (R=H or CF₃) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC).     

Atmospheric pressure deposition of fluorine‐doped SnO2 thin films from organotin fluorocarboxylate precursors

Nine organotin fluorocarboxylates R_nSnO₂CR_f (n = 3, R = Bu, R_f = CF₃, C₂F₅, C₃F₇, C₇F₁₅; R = Et, R_f = CF₃, C₂F₅; R = Me, R_f = C₂F₅; n = 2, R = Me, R_f = CF₃) have been synthesized; key examples have been used to deposit fluorine‐doped SnO₂ thin films by atmospheric pressure chemical vapour deposition. Et₃SnO₂CC₂F₅, in particular, gives high‐quality films with fast deposition rates despite adopting a polymeric, carboxylate‐bridged structure in the solid state, as determined by X‐ray crystallography. Gas‐phase electron diffraction on the model compound Me₃SnO₂CC₂F₅ shows that accessible conformations do not allow contact between tin and fluorine, and that direct transfer is therefore unlikely to be part of the mechanism for fluorine incorporation in SnO₂ films. The structure of Me₂Sn(O₂CCF₃)₂(H₂O) has also been determined and adopts a trans‐Me₂SnO₃ coordination sphere about tin in which each carboxylate group is monodentate. Copyright © 2005 John Wiley & Sons, Ltd.     

[2+4] and [2+2] Cycloaddition Reactions of N‐Sulfinyl Carboxylic Acid Amides with (CF3)2BNMe2. Crystal Structure of cyclo‐(CF3)2B‐NMe2‐S(=O)‐N=C(p‐CH3C6H4)‐O

N‐sulfinylacylamides R‐C(=O)‐N=S=O react with (CF₃)₂BNMe₂ ( 1 ) to form, by [2+4] cycloaddition, six‐membered rings cyclo‐(CF₃)₂B‐NMe₂‐S(=O)‐N=C(R)‐O for R = Me ( 2 ), t‐Bu ( 3 ), C₆H₅ ( 4 ), and p‐CH₃C₆H₄ ( 5 ) while N‐sulfinylcarbamic acid esters R‐O‐C(=O)‐N=S=O react with 1 to yield mixtures of six‐membered (cyclo‐(CF₃)₂B‐NMe₂‐S(=O)‐N=C(OR)‐O) and four‐membered rings (cyclo‐(CF₃)₂B‐NMe₂‐S(=O)‐N(C=O)OR) for R = Me ( 6 and 9 ), Et ( 7 and 10 ), and C₆H₅ ( 8 and 11 ). The structure of 5 has been determined by X‐ray diffraction.     

Strategies for the synthesis of chiral, bidentate bis(perfluoroorganyl)phosphane ligands

Chiral, bidentate phosphane ligands, so-called PP ligands, are most frequently synthesized by reacting chiral ditosylates with diarylphosphanide ions.To use the P(CF₃)₂⁻ ion in nucleophilic substitution reactions, it is necessary to reduce the negative hyperconjugation, which is associated with a C-F activation. For this reason we synthesized different bis(trifluoromethyl)phosphanido complexes of mercury, silver and tungsten and investigated their use in nucleophilic substitution reactions. The most reactive compound, resulting from this study so far, is the pentacarbonylbis(trifluoromethyl)phosphanidotungstenate, [W{P(CF₃)₂}(CO)₅]⁻, which exhibits nearly the same bonding situation for the P(CF₃)₂ unit as in the free P(CF₃)₂⁻ ion. For use in synthesis of bis(trifluoromethyl)phosphane derivatives, Lewis acids are desirable, which stabilize the P(CF₃)₂⁻ ion by an intermediary formation of a donor acceptor adduct and can be split off after the synthesis of bis(trifluoromethyl)phosphane derivatives, as could be achieved using the extremely weak Lewis acids, CS₂ and acetone. These results could be established in the synthesis of the first example of an chiral, bidentate bis(trifluoromethyl)phosphane derivative.To synthesize a chiral, bidentate bis(pentafluorophenyl)phosphane derivative, a different synthetic strategy is necessary that does not involve the P(C₆F₅)₂⁻ ion, which decomposes even at low temperature. The implementation of functional P(CN)₂⁻ ions leads to the synthesis of functional, chiral bidentate dicyanophosphane derivatives which finally can be transformed into the corresponding bis(pentafluorophenyl)phosphane derivatives.     

Two molybdenum pentacarbonyl complexes with electroneutral phosphane ligands: [bis(morpholin‐4‐yl)(pentafluoroethyl)phosphane‐κP]pentacarbonylmolybdenum(0) and pentacarbonyl[(pentafluoroethyl)bis(piperidin‐1‐yl)phosphane‐κP]molybdenum(0)

The crystal structures of the title compounds, [Mo{(C₄H₈NO)₂P(C₂F₅)}(CO)₅], (1a), and [Mo{(C₅H₁₀N)₂P(C₂F₅)}(CO)₅], (2a), were determined as part of a larger project that focuses on the synthesis and coordination chemistry of phosphane ligands possessing moderate (electroneutral, i.e. neither electron‐rich nor electron‐deficient) electronic characteristics. Both complexes feature a slightly distorted octahedral geometry at the metal center, due to the electronic and steric repulsions between two of the four equatorial CO groups and the pentafluoroethyl group attached to the phosphane ligand. Bond length and angle data for (1a) and (2a) support the conclusion that the free phosphane ligands are electroneutral. For complex (1a), the Mo—P, Mo—C_ax and Mo—C_eq(ave) bond lengths are 2.5063 (5), 2.018 (2) and 2.048 (2) Å, respectively, and for complex (2a) these values are 2.5274 (5), 2.009 (3) and 2.050 (3) Å, respectively. Geometric data for (1a) and (2a) are compared with similar data reported for analogous Mo(CO)₅ complexes.     

The formation of dimetallocycles from reactions of alkynes with (η-C5Me5)2Rh2(CO)2; X-ray structure of [(η-C5Me5)2Rh2(η-CO) {μ-η2,η2-C(O)C2-(CF3)2}]

The complexes (η-C₅Me₅)₂Rh₂(μ-CO) {μ-η²,η²-C(O)CRCR} are obtained from reactions between (η-C₅Me₅)₂Rh₂(CO)₂ and the alkynes RCCR (R  CF₃, CO₂Me, or Ph) at 25°C. The molecular geometry of the complex with R  CF₃ has been established by X-ray diffraction; the bridging 'ene-one' unit adopts a μ-η²,η² conformation. Other complexes isolated from these reactions include (η-C₅Me₅)Rh(C₆R₆) (R  CF₃, CO₂Me), (η-C₅Me)₂Rh₂(C₄R₄) (R  CO₂Me) and (η-C₅Me₅)₂Rh₂(CO₂C₂R₂) (R  Ph). The reaction between (η-C₅Me₅)₂Rh₂(CO)₂ and C₆F₅CCC₆F₅ gives (η-C₅Me₅)₂Rh₂(CO)₂(C₆F₅C₂C₆F₅). Mononuclear complexes such as (η-C₅Me₅)Co(C₄R₄CO) are the major products isolated from reactions between (η-C₅Me₅)₂CO₂(CO)₂ and alkynes at 25°C.     

Synthesen und Eigenschaften von Tetrakis(perfluoralkyl)tellur Te(Rf)4 (Rf = CF3, C2F5, C2F5, C3F7, C4F9)

Synthesis and Properties of Tetrakis(Perfluoroalkyl)Tellurium Te(R_f)₄ (R_f = CF₃, C₂F₅, C₃F₇, C₄F₉) Te(CF₃)₄ is obtained from the reaction of Te(CF₃)Cl₂ with Cd(CF₃)₂ complexes as a complex with e. g. CH₃CN, DMF. It is a light and temperature sensitive hydrolysable liquid. The reaction with fluorides yields the complex anion [Te(CF₃)₄F]⁻, with fluoride ion acceptors the complex cation [Te(CF₃)₃]⁺. With traces of water an acidic solution is formed. Te(CF₃)₄ acts as a trifluoromethylation reagent. The reaction with XeF₂ gives hints for the formation of Ye(CF₃)₄F₂. Properties and NMR spectra are discussed. The much more stable complexes of Te(R_f)₄ (R_f = C₂F₅, C₃F₇, C₄F₉) are formed from the reaction of TeCl₄ with the corresponding Cd(R_f)₂ complexes.     

The Reactivity of Potassium Polyfluoroaryl‐, Polyfluoroalkenyl‐, and Perfluoroalkyltrifluoroborates and their Hydrocarbon Analogues towards Acids of Different Strength: A Systematic Study of the Hydrodeboration

The hydrodeboration of the (fluoroorgano)trifluoroborates K [R_FBF₃] [R_F = C₆F₅, XCF=CF (X = F, cis‐ and trans‐Cl, C₃F₇O, cis‐C₂F₅, trans‐C₄F₉, ‐C₄H₉) and C₆F₁₃] and of the organotrifluoroborates K [RBF₃] (R = C₆H₅, cis‐ and trans‐C₄H₉CH=CH, C₄H₉ and C₈H₁₇) with CH₃CO₂H (100 %), CF₃CO₂H (100 %), aqueous HF and anhydrous HF was investigated. In the alkenyltrifluoroborates K [R'CF=CFBF₃] the formal replacement of BF₃ by a proton occurred stereospecifically under retention of the configuration. The ¹⁹F NMR spectra of K [R_FBF₃] in acids indicate strong interactions of the BF₃ group with protons or acid molecules.     

Single‐Step Gas‐Phase Polyperfluoroalkylation of Naphthalene Leads to Thermodynamic Products

High‐temperature gas‐phase, solvent‐ and catalyst‐free reaction of naphthalene with an excess of R_FI reagent (R_F?CF₃, C₂F₅, n‐C₃F₇, and n‐C₄F₉) was used for the first time to produce a series of highly perfluoroalkylated naphthalene products NAPH(R_F)_n with n=2–5. Four 95+ % pure 1,3,5,7‐NAPH(R_F)₄ with R_F?CF₃, C₂F₅, n‐C₃F₇, and n‐C₄F₉ were isolated using a simple chromatography‐free procedure. These new compounds were fully characterized by ¹⁹F and ¹H NMR spectroscopy, X‐ray crystallography (for R_F?CF₃ and C₂F₅), atmospheric‐pressure chemical ionization mass spectrometry, and cyclic and square‐wave voltammetry. DFT calculations confirm that the proposed synthesis yields the most stable isomers that have not been accessed by alternative preparation techniques.     

The Bis(pentafluoroethyl)germylene Trimethylphosphane Adduct (C2F5)2Ge⋅PMe3: Characterization,Ligand Properties,and Reactivity

The synthesis of the germylene phosphane adduct (C₂F₅)₂Ge?PMe₃ is described. Starting from (C₂F₅)₃GeH in an excess of PMe₃, heating was applied, whereupon reductive elimination of C₂F₅H occurred. The molecular structure was ascertained by X‐ray diffraction and compared with information obtained by quantum chemical methods. The ligand properties were derived by studying the IR spectrum of the nickel(0) complex [Ni(CO)₃{Ge(C₂F₅)₂(PMe₃)}] in the CO region. (C₂F₅)₂Ge?PMe₃ turned out to be a π‐accepting ligand comparable to PMe₃, in terms of Tolman's electronic parameter. Furthermore a [2+4] cycloaddition reaction with 2,3‐dimethyl‐1,3‐butadiene, and σ‐bond insertion reactions were recorded. Activation of the C?Cl bond in dichloromethane gives rise to the formation of the phosphonium ylide complex [(C₂F₅)₂Cl₂Ge‐CH₂PMe₃], which was fully characterized by X‐ray diffraction.