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In this contribution, we report on the “free” [P(C2F5)2F2]−ion and its ligand properties in transition metal complex chemistry. For this purpose, Ag[P(C2F5)2F2] was treated with [{(Et2N)3P═N}3P═NHC(CH3)3]Cl ([EtP4H]Cl) to yield [EtP4H][P(C2F5)2F2], featuring a weakly coordinating phosphazenium cation. Due to the weak interaction between the cation and anion, the [P(C2F5)2F2]−ion meets the so-called pseudo-gas-phase conditions. To determine the Tolman electronic parameter, [EtP4H][Ni(CO)3{P(C2F5)2F2}] was prepared from [EtP4H][P(C2F5)2F2] and [Ni(CO)4], facilitating the classification of the P(C2F5)2F2moiety as a moderately π-acidic ligand. By treatment of [EtP4H][P(C2F5)2F2] with [AuCl(tht)], the neutral tetrahydrothiophene ligand was substituted by the phosphoranide ion, yielding [EtP4H][AuCl{P(C2F5)2F2}]. When Ag[P(C2F5)2F2] was treated with [AuCl(tht)], on the other hand, the chloride was substituted. Transmetalation reactions of this type proved to be an efficient transfer method of the P(C2F5)2F2moiety, as further demonstrated by the reactions of Ag[P(C2F5)2F2] with [FeCl(CO)2Cp], [FeCl(CO)2Cp*], and [PdCl2(NCMe)2]. Surprisingly, P(C2F5)2F demonstrated fluorinating abilities toward [FeCl(CO)2Cp], [FeCl(CO)2Cp*], [AuCl(tht)], and [PdCl2(NCMe)2]. Apparently, fluorido transition metal complexes were generated in situ under the formation of P(C2F5)2Cl. The fluorido iron and palladium complexes transfer their fluoride ions onto P(C2F5)2F, yielding the respective phosphoranido complexes, featuring the P(C2F5)2F2moiety.

Despite the fact that different metal tetrafluorophosphoranides, M[PF4] (M = Cs, Ag, K), decompose readily, we successfully enhanced the stability of such species by the replacement of two fluorine atoms with electron withdrawing pentafluoroethyl groups. Thus, AgF adds to P(C2F5)2F, yielding Ag[P(C2F5)2F2], which served as a starting material for the synthesis of mono-, bis-, and tris[difluorobis(pentafluoroethyl)phosphoranido]silver complexes. Addition of 2,2′-bipyridine allowed for the isolation of stable [Ag(bipy){P(C2F5)2F2}], whereas the reaction with the chlorides [NMe4]Cl and CoCl2afforded the bis- and trisphosphoranidoargentates [NMe4][Ag{P(C2F5)2F2}2(OEt2)] and [Co(NCMe)6][Ag{P(C2F5)2F2}3]·2MeCN, respectively. Altogether, the difluorobis(pentafluoroethyl)phosphoranido moiety serves as a novel, small, noncyclic phosphoranido ligand. It provided access to the first homoleptic phosphoranidometal complex, [Co(NCMe)6][Ag{P(C2F5)2F2}3]·2MeCN, which itself features the unusual structural motif of an [AgX3]2–ion.

Unlike silanolates [SiR3O]−(R = alkyl, aryl), which have been intensely studied, the heavier derivatives [SiR3E]−(E = S, Se, Te) have been much less examined. Among such species, virtually nothing is known about perfluoroalkyl-substituted silylchalcogenolates. In this contribution, a convenient synthesis of tris(pentafluoroethyl)silylchalcogenolate salts [{(Et2N)3P═N}3PN(H)tBu][Si(C2F5)3E] (E = S, Se, Te; tBu = tert-butyl) is presented. All representatives were isolated and fully characterized by multinuclear NMR spectroscopy, IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction studies. Furthermore, first reactivity studies of these novel species toward selected metal halide complexes were performed. In this course, metal complexes [HgPh{SSi(C2F5)3}] (2) and [Au(PPh3){SSi(C2F5)3}] (3) were isolated and characterized.

This manuscript describes the selective synthesis of2, 4‐bis(trifluoromethyl)phenylphosphinic acid, (Rf)P(O)(H)OH.Reaction of chlorobis(diethylamino)phosphane with a mixture of 2, 4‐(CF3)2C6H3Li and 2, 6‐(CF3)2C6H3Li results in the formation of 2, 4‐bis(trifluoromethyl)phenylbis(diethylamino)phosphane, (Rf)P(NEt2)2. The following in situ reaction with gaseous HBr leads to the cleavage of the phosphorus nitrogen bonds resulting in the selective formation of the corresponding dibromophosphane (Rf)PBr2.2, 4‐Bis(trifluoromethyl)phenylphosphinic acid is available via two different synthetic strategies starting from the dibromophosphane (Rf)PBr2. Reduction of the dibromophosphane with tributyltin hydride affords selectively the phosphane (Rf)PH2. The following oxidation to the phosphinic acid (Rf)P(O)(H)OH, however, only proceeds in moderate yields. A more efficient synthesis is achieved via the hydrolysis of the dibromophosphane (Rf)PBr2in dichloromethane solution. 2, 4‐bis(trifluoromethyl)phenylphosphinic acid, (Rf)P(O)(H)OH, is surprisingly stable towards air and water. The water soluble phosphinic acid reacts sluggishly with a 30 % H2O2solution, yielding only 23 % of the corresponding phosphonic acid (Rf)P(O)(OH)2after seven days at ambient temperature.In principle a tautomerization of the phosphinic acid (Rf)P(O)(H)OH to the corresponding phosphonous acid (Rf)P(OH)2– analogously to the phosphane oxide (Rf)2P(O)H and the phosphinous acid (Rf)2POH – is conceivable. However, the phosphonous acid could not be detected with spectroscopic methods. The energy difference between the phosphinic acid and the phosphonous acid is calculated by quantum chemical calculations at the B3LYP/6‐311+G(2df, p) level of theory to 30.1 kJ·mol–1. This high value explains why the phosphonous acid tautomer could not be detected by spectroscopic methods so far.As transition metal complexes featuring phosphonous acid ligands are of significant interest for the application as homogeneous catalysts we studied the coordination chemistry of the related phosphinic acid in more detail. The preligand 2, 4‐bis(trifluoromethyl)phenylphosphinic acid reacts smoothly with palladium dichloride in THF to the dinuclear complex [Pd2(μ‐Cl)2{[2, 4‐(CF3)2C6H3P(OH)O]2H}2], featuring a phosphonous acid phosphonato unit, with a strong hydrogen bridge substantiated by an O···O distance of 247.7(3) pm. The dinuclear phosphonous acid palladium complex exhibits a high catalytic activity in the Suzuki cross‐coupling. Alternatively, the phosphinic acid can be used as preligand for the in situ formation of a phosphonous acid palladium complex. These compounds combine catalytic activity with a very high stability towards air and water.

Secondary phosphane oxides, R2P(O)H, are commonly used as preligands for transition‐metal complexes of phosphinous acids, R2POH (R=alkyl, aryl), which are relevant as efficient catalysts in cross‐coupling processes. In contrast to previous work by other groups, we are interested in the ligating properties of an electron‐deficient phosphinous acid, (Rf)2POH, bearing the strongly electron‐withdrawing and sterically demanding 2,4‐bis(trifluoromethyl)phenyl group towards catalysis‐relevant metals, such as palladium and platinum. The preligand bis[2,4‐bis(trifluoromethyl)phenyl]phosphane oxide, (Rf)2P(O)H, reacts smoothly with solid platinum(II) dichloride yielding the trans‐configured phosphinous acid platinum complex trans‐[PtCl2({2,4‐(CF3)2C6H3}2POH)2]. The deprotonation of one phosphinous acid ligand with an appropriate base leads to the cis‐configured monoanion complex cis‐[PtCl2({2,4‐(CF3)2C6H3}2‐ PO)2H]−, featuring the quasi‐chelating phosphinous acid phosphinito unit, (Rf)2POH⋅⋅⋅OP(Rf)2, which exhibits a strong hydrogen bridge substantiated by an O⋅⋅⋅O distance of 245.1(4) pm. The second deprotonation step is accompanied by a rearrangement to afford the trans‐configured dianion trans‐[PtCl2({2,4‐(CF3)2C6H3}2PO)2]2−. The reaction of (Rf)2P(O)H with solid palladium(II) dichloride initially yields a mononuclear palladium complex [PdCl2({2,4‐(CF3)2C6H3}2POH)2], which condenses under liberation of HCl to the neutral dinuclear palladium complex [Pd2(μ‐Cl)2{({2,4‐(CF3)2C6H3}2PO)2H}2]. The equilibrium between the mononuclear [PdCl2({2,4‐(CF3)2C6H3}2POH)2] and dinuclear [Pd2(μ‐Cl)2{({2,4‐(CF3)2C6H3}2PO)2H}2] palladium complexes is reversible and can be shifted in each direction by the addition of base or HCl, respectively. Treatment of palladium(II) hexafluoroacetylacetonate, [Pd(F6acac)2], with a slight excess of (Rf)2P(O)H yields the complex [Pd(F6acac)({2,4‐(CF3)2C6H3}2‐ PO)2H]. The quasi‐chelating phosphinous acid phosphinito unit, which is formed by the liberation of HF6acac, is characterized by a O⋅⋅⋅O distance of 244.1(3) pm. These transition metal complexes are stable towards air and moisture and can be stored for months without any evidence of decomposition.

The unusual form of a phosphinous acid can be stabilized by strongly electron‐withdrawing substituents such as trifluoromethyl and pentafluoroethyl groups. The less electron‐withdrawing pentafluorophenyl group favors the phosphane oxide tautomer (Rf)2P(O)H in the solid state, whereas in solution a solvent‐dependent equilibrium with the phosphinous acid tautomer (Rf)2POH is observed. The increasing donating ability of the solvent leads to an increasing amount of the corresponding phosphinous acid tautomer. In accord with quantum chemical calculations, the electron‐withdrawing effects of the p‐tetrafluoropyridyl and 2,4‐bis(trifluoromethyl)phenyl groups exceed the pentafluorophenyl group and should therefore be ideally suited to stabilize the corresponding phosphinous acid tautomer (Rf)2POH. The syntheses of bis(tetrafluoropyridyl)‐ and bis[2,4‐bis(trifluoromethyl)phenyl]phosphane oxide enabled the investigation of the solvent‐dependent tautomerism by NMR spectroscopy. Introduction of the tetrafluoropyridyl group shifts the tautomeric equilibrium significantly towards the phosphinous acid. Surprisingly, the comparably electron‐withdrawing but more bulky 2,4‐bis(trifluoromethyl)phenyl group favors the oxide tautomer. The experimental results have been confirmed by DFT calculations. In summary, electron‐withdrawing substituents stabilize the phosphinous acid tautomer, whereas it is destabilized by space‐demanding groups by an increased C–P–C angle.

Ring or chain?The two known phosphinous acids, (CF3)2POH and (C2F5)2POH, reveal hydrogen‐bridged aggregates in the solid state (see figure). The CF3derivative forms helical chains, whereas the increased sterical demand of the C2F5group leads to the formation of tetramers. The high catalytic activity of their palladium complexes (TON 24500) is highlighted in the field of cross‐coupling reactions.

(C2F5)2PCl is now accessible through a significantly improved synthesis protocol starting from the technical product (C2F5)3PF2. (C2F5)3PF2was reduced in the first step with NaBH4in a solvent‐free reaction at 120 °C. The product, P(C2F5)3, was treated with an excess of an aqueous sodium hydroxide solution to afford the corresponding phosphinite salt Na+(C2F5)2PO−selectively under liberation of pentafluoroethane. Subsequent chlorination with PhPCl4resulted in the selective formation of (C2F5)2PCl, which was isolated by fractional condensation in an overall yield of 66 %. The gas electron diffraction (GED) pattern for (C2F5)2PCl was recorded and found to be described by a two‐conformer model. A quantum chemical investigation of the potential‐energy surface revealed the possible existence of many low‐energy conformers, each with a number of low‐frequency vibrational modes and therefore large‐amplitude motions. The conformer calculated to be most stable was also found to be most abundant by GED and comprised 61(5) % of the total. The molecular structure parameters determined by GED were in good agreement with those calculated at the MP2/TZVPP level of theory; the only significant difference was a discrepancy of about 3° in the C‐P‐C angle, which, for the lowest‐energy conformer, was refined to 98.2(4)° and was calculated to be 94.9°.

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.

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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 (a869.2(1), b1857.4(1), c1357.6(1) pm, β 100.57(4)°, Z = 4).

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The reaction of a C2‐symmetric diiodo compound, 1,4‐dideoxy‐1,4‐diiodo‐2,3,‐O‐isopropyliden‐L‐threitole, with [K([18]crown‐6)]P(CN)2led to the generation of a corresponding bidentate dicyanophosphorus derivative. The in situ reaction with excess methanol and phenol yielded the corresponding bidentate dimethyl‐ and diphenylphosphonites, respectively. The isolated liquids were characterized by multinuclear NMR spectroscopy, elemental analysis, and mass spectrometry. The bidentate diphenylphosphonite ligand (a diphenoxyphosphane derivative) represents one of the very few functional bidentate phosphane derivatives: a DIOP [(2,2‐dimethyl‐1,3‐dioxolane‐4,5‐diyl)bis(methylene)]bis(diphenylphosphane) modification, in which the phenyl groups at the phosphorus atoms are replaced by functional phenoxy groups. Treatment of the bidentate diphenylphosphonite derivative with C6F5MgBr and p‐C5NF4MgBr allowed the isolation and full characterization of the comparable bidentate bis(pentafluorophenyl) and bis(p‐tetrafluoropyridyl)phosphanes. The ligand properties of the novel bidentate ligand systems were evaluated through the synthesis and vibrational investigation of their tetracarbonyl–molybdenum and cyclopentadienyl–iron complexes. The π acidity of the synthesized ligands increases in the order methoxy‐

Lewis acid/Lewis base adduct formation of the P(CF3)2−ion and acetone leads to a reduced negative hyperconjugation and, therefore, limits the CF bond activation. The resulting increased thermal stability of the P(CF3)2−ion in the presence of acetone allows selective substitutions and enables the synthesis of the first example of a chiral, bidentate bis(trifluoromethyl)phosphane ligand: a DIOP derivative, [(2,2‐dimethyl‐1,3‐dioxolane‐4,5‐diyl)bis(methylene)]bis(diphenylphosphane), in which the phenyl groups at the phosphorus atoms are replaced by strong electron‐withdrawing trifluoromethyl groups. The resulting high electron‐acceptor strength of the synthesized bidentate (CF3)2P ligand is demonstrated by a structural and vibrational study of the corresponding tetracarbonyl–molybdenum complex. The stabilization of the P(CF3)2−ion in the presence of acetone is based on the formation of a dynamic Lewis acid/Lewis base couple, (CF3)2PC(CH3)2O−. Although there is no spectroscopic evidence for the formation of the formulated alcoholate ion, the intermediate formation of (CF3)2PC(CH3)2O−could be proved through the reaction with (CF3)2PP(CF3)2, which yields the novel phosphane–phosphinite ligand (CF3)2PC(CH3)2OP(CF3)2. This ligand readily forms square‐planar Pt(II) complexes upon treatment with solid PtCl2.

The bis(trifluoromethyl)phosphinous acid, (CF3)2POH, is the only known example of a thermally stable phosphinous acid. Although this compound has been known since 1960, little is known about the chemistry of this extraordinary compound; this might be due to the tedious, and in some part risky, synthesis that was originally published. An improved, simple, and safe synthesis that is based on the treatment of the easily accessible (CF3)2PNEt2, with at least three equivalents of p‐toluene sulfonic acid, is presented. The reaction results in a complete conversion to the phosphinous acid, which is isolated in almost 90 % yield. The compound exists in an equilibrium of two POH rotational isomers, a fact which is supported by quantum chemical calculations. The relative enthalpy difference of 6.4 kJ mol−1, calculated at the B3PW91/6‐311G(3d,p) level, is in excellent agreement with the experimental value of 5.9 kJ mol−1, which was determined from the temperature dependence of the $\tilde \nu $(OH) bands of the two rotational isomers. The complete experimental vibrational spectra of both rotamers, their predicted vibrational spectra obtained by using quantum chemical calculations, and an attempt at photoinduced isomerization of matrix‐isolated (CF3)2POH is presented. The experimental structure, obtained from an electron‐diffraction study in the gas phase, is reproduced very well by ab initio and density functional theory (DFT) methods.

Reactions of trimethyl(trifluoromethyl)silane in the presence of “naked” fluoride proceed up to a temperature of +5 °C mainly with formation of [Me3Si(CF3)2]−. A further rise of temperature up to about 20 °C gives evidence for the formation of a salt with the 1,1,1,2,3,6,6,6‐octafluoro‐2,4,4,5,5‐pentakis(trifluoromethyl)hexan‐3‐ide anion. This intermediate decomposes at room temperature into the 1,1,1,3,5,5,5‐heptafluoro‐2,4‐bis(trifluoromethyl)pentenide anion. The bis([15]crown‐5)cesium salt, [Cs([15]crown‐5)2][(CF3)2CCFC(CF3)2] has been characterized unambiguously as the stable final product of this reaction sequence. Thermal decomposition of this salt opens a convenient nontoxic route to obtain 1,1,3,3‐tetrakis(trifluoromethyl)allene, (F3C)2CCC(CF3)2.

Ionische und subvalente Verbindungen, molekulare Cluster und die Renaissance der Azide markieren den Fortschritt in der Hauptgruppenelementchemie. Die Koordinationschemie wächst „über das Molekül hinaus”︁. Proteinkristallographie und Modellstudien sind die Motoren der Bioanorganischen Chemie. Ionische und subvalente Verbindungen, molekulare Cluster und die Renaissance der Azide markieren den Fortschritt in der Hauptgruppenelementchemie. Die Koordinationschemie wächst „über das Molekül hinaus”︁. Proteinkristallographie und Modellstudien sind die Motoren der Bioanorganischen Chemie.

The hydrolysis of [Hg{P(CF3)2}2(PMe3)2] yields colourless crystals of [Hg{OP(O)CF3(OH)}2(PMe3)3]. The proposed multistep reaction proceeds via primary hydrolysis of the starting material giving HgO and HP(CF3)2. The latter is directly oxidized by HgO to (CF3)2P(O)OH. The bis(trifluoromethyl)phosphinic acid hydrolyses to CF3P(O)(OH)2which reacts with [Hg{P(CF3)2}2(PMe3)2] in the presence of PMe3to the title compound. The crystal structure was determined by X‐ray single‐crystal analysis (triclinic; P1¯; a= 860.7(1), b= 1007.6(2), c= 1625.0(3) pm; α= 96.09(2), β= 101.09(2), γ= 107.79(2)°; Z = 2) and exhibits distorted trigonal bipyramidal mercury complexes which are connected to polymeric chains. The acidic units, {OP(O)CF3(OH)}—, are connected via intermolecular hydrogen bridges, forming two individual centrosymmetric eight membered rings with asymmetric hydrogen bridges with O—O distances of 249.4(8) and 250.8(8) pm.

The NMR spectra of the square-planar silver(III) anions [Ag(CF3)4]⁻ and [Ag(CF2H)4]⁻ were investigated. The signs of ¹J(¹⁰⁹Ag,¹³C), ²J(¹⁰⁹Ag,¹⁹F) and ²J(¹⁰⁹Ag,¹H) and those of the long-range couplings ⁴J(¹⁹F,¹⁹F), ³J(¹⁹F,¹³C), ³J(¹³C,¹H) and ⁴J(¹⁹F,¹H) were determined by analysis of higher order spin systems and from 2D heteronuclear correlations. All determined reduced coupling constants are positive with respect to ¹J(¹³C,¹H)>0 or ¹J(¹⁹F,¹³C)<0. Correlations between couplings for a variety of CF3Ag(III) compounds suggest that no sign crossover occurs. © 1997 John Wiley & Sons, Ltd.

Sterische und elektronische Eigenschaftender sperrigen, stark elektronenziehenden 2,4‐(CF3)2C6H3‐Gruppe sind ideal, um die außergewöhnliche Form eines Diphosphoxans, R2POPR2– das Anhydrid einer Phosphinigsäure –, zu stabilisieren. Die effiziente Synthese und strukturanalytische Charakterisierung eines Tetraorganodiphosphoxans werden beschrieben (siehe Strukturbild; C grau, H weiß, O rot, F gelb, P grün).

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Nach drei bilateralen deutsch‐amerikanischen Treffen von Nachwuchswissenschaftlern in Seeon (2000, 2004) und Durham, New Hampshire (2002), waren in diesem Jahr erstmals britische Kollegen mit von der Partie: Statt „German‐American Frontiers of Chemistry”︁ nun der Ausbau des Erfolgsmodells zu den „Transatlantic Frontiers of Chemistry”︁.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.