Synthesis of Functional Phosphates [P(C2F5)(3)F2X](-) from the Phosphorane Adduct [P(C2F5)(3)F-2(dmap)]

Bader J, Ignat'ev N, Hoge B. Synthesis of Functional Phosphates [P(C2F5)(3)F2X](-) from the Phosphorane Adduct [P(C2F5)(3)F-2(dmap)]. Inorganic Chemistry. 2014;53(14):7547-7553.Weakly coordinating anions (WCAs) are of great academic as well as industrial interest. To advance the fluoroallcyl phosphate anion [P(C2F5)(3)F-3](-), which is ideally suited for technical applications, functional substituents X are attached to the Lewis acid (C2F5)(3)PF2. In keeping with this, the reaction of (C2F5)(3)PF2 with 4-(dimethylamino)pyridine (DMAP) yields the corresponding adduct [P(C2F5)(3)F-2(dmap)]. Treatment of this adduct with Bronsted acids (HX) leads to the selective formation of the corresponding phosphate anions [P(C2F5)(3)F2X](-) by trapping the proton with the liberated base DMAP. In this way, OH functions can be transformed in one step into WCAs, slightly increasing the coordination properties of the corresponding anion. An ion exchange to the corresponding [PPh4] salts results in solids, whereas the corresponding imidazolium salts are obtained as room-temperature ionic liquids

Synthesis of Unsymmetrically Substituted Phosphane Oxides ((RRP)-R-1-P-2(O)H) and Phosphinous Acids ((RRPOH)-R-1-P-2)

Allefeld N, Grasse M, Ignat'ev N, Hoge B. Synthesis of Unsymmetrically Substituted Phosphane Oxides ((RRP)-R-1-P-2(O)H) and Phosphinous Acids ((RRPOH)-R-1-P-2). Chemistry - A European Journal. 2014;20(28):8615-8620.This paper describes the synthesis of unsymmetrically substituted phosphinous acids and phosphane oxides featuring at least one electron-withdrawing pentafluoroethyl group. The presence of a diethylamino function as a protecting group allows a selective reaction of RClPNEt2 (R=CF3, C6F5, C6H5) with LiC2F5. On treatment with para-toluenesulfonic acid the isolated aminophosphanes R(C2F5)PNEt2 are readily converted into the corresponding phosphinous acids or phosphane oxides, respectively. Investigation of the tautomeric equilibrium between oxide and acid tautomer revealed (CF3)(C2F5)POH as a stable phosphinous acid, whereas the pentafluorophenyl and phenyl derivatives constitute a solvent dependent equilibrium between the acid and the oxide tautomer

Borylation of fluorinated arenes using the boron centred nucleophile B(CN)3_{3}2−^{2-} - a unique entry to aryltricyanoborates

The potassium salt of the boron-centred nucleophile B(CN)$_{3}$$^{2-}$(1) readily reacts with perfluorinated arenes, such as hexafluorobenzene, decafluorobiphenyl, octafluoronaphthalene and pentafluoropyridine, which results in KF and the K$^{+}$ salts of the respective borate anions with one {B(CN)$_{3}$} unit bonded to the (hetero)arene. An excess of K$_{2}$1 leads to the successive reaction of two or, in the case of perfluoropyridine, even three C–F moieties and the formation of di- and trianions, respectively. Moreover, all of the 11 partially fluorinated benzene derivatives, C$_{6}$F$_{6-n}$H$_{n}$ (n = 1–5), generally react with K$_{2}$1 to give new tricyano(phenyl)borate anions with high chemo- and regioselectivity. A decreasing number of fluorine substituents on benzene results in a decrease in the reaction rate. In the cases of partially fluorinated benzenes, the addition of LiCl is advantageous or even necessary to facilitate the reaction. Also, pentafluorobenzenes R–C$_{6}$F$_{5}$ (R = –CN, –OMe, –Me, or –CF$_{3}$) react via C–F/C–B exchange that mostly occurs in the para position and to a lesser extent in the meta or ortho positions. Most of the reactions proceed via an S$_{N}$Ar mechanism. The reaction of 1,4-F$_{2}$C$_{6}$H$_{4}$ with K$_{2}$1 shows that an aryne mechanism has to be considered in some cases as well. In summary, a wealth of new stable tricyano(aryl)borates have been synthesised and fully characterized using multi-NMR spectroscopy and most of them were characterised using single-crystal X-ray diffraction

Synthesis of Tris(pentafluoroethyl)germanes

Pelzer S, Neumann B, Stammler H-G, Ignat'ev N, Hoge B. Synthesis of Tris(pentafluoroethyl)germanes. CHEMISTRY-A EUROPEAN JOURNAL. 2016;22(10):3327-3332.The synthesis of tris(pentafluoroethyl)germanium derivatives is described. The reaction of germanium tetrachloride with three equivalents of the pentafluoroethylation reagent LiC2F5 does not lead selectively to the formation of tris(pentafluoroethyl)chlorogermane, (C2F5)(3)GeCl. Here the introduction of a diethylamino function as a protecting group was beneficial. Thus, treatment of Cl3GeNEt2 with LiC2F5 smoothly afforded (C2F5)(3)GeNEt2. The replacement of the amino substituent by halides was accomplished by reaction with HBr or HCl on a multigram scale. The combination of (C2F5)(3)GeCl with Ag2CO3 gave rise to the formation of the digermoxane [(C2F5)(3)Ge](2)O. An obtuse Ge-O-Ge angle of 150.2(1)degrees was determined by X-ray diffraction. Attempted hydrolysis of the digermoxane leads to an equilibrium mixture of the precursor, (C2F5)(3)GeOH, and water

Activation of Acetonitrile with (C2F5)(3)PF2 and Amines

Bader J, Neumann B, Stammler H-G, Ignat'ev N, Hoge B. Activation of Acetonitrile with (C2F5)(3)PF2 and Amines. CHEMISTRY-A EUROPEAN JOURNAL. 2018;24(27):6975-6982.Acetonitrile is deprotonated by a combination of the strong Lewis acid (C2F5)(3)PF2 and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt3][P(C2F5)(3)F-2(CH2CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN)(2)](+) and [Ag(MeCN)](+) derivatives in which the CH2CN substituent of the anion [P(C2F5)(3)F-2(CH2CN)](-) coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C2F5)(3)F-2(CH2CN)] shows an uptake of 1.7equivalents of isobutene from a propane/isobutene mixture. The reaction of (C2F5)(3)PF2 with acetonitrile and diethylamine furnishes [P(C2F5)(3)F-2{NHC(CH3)NEt2}]a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt2. Exchange of HNEt2 with the primary amines H2NPh and H2NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism

Synthesis of Tris- and Tetrakis(pentafluoroethyl)silanes

Steinhauer S, Bader J, Stammler H-G, Ignat'ev N, Hoge B. Synthesis of Tris- and Tetrakis(pentafluoroethyl)silanes. Angewandte Chemie International Edition. 2014;53(20):5206-5209.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

Hypervalent Pentafluoroethylgermanium Compounds, [(C2F5)(n)GeX5-n](-) and [(C2F5)(3)GeF3](2-) (X=F, Cl; n=2<bold>-5)</bold>

Pelzer S, Neumann B, Stammler H-G, Ignat'ev N, Hoge B. Hypervalent Pentafluoroethylgermanium Compounds, [(C2F5)(n)GeX5-n](-) and [(C2F5)(3)GeF3](2-) (X=F, Cl; n=2&lt;bold&gt;-5)&lt;/bold&gt;. CHEMISTRY-A EUROPEAN JOURNAL. 2016;22(46):16460-16466.This paper gives an account on hypervalent fluoro- and chloro(pentafluoroethyl)germanium compounds. The selective synthesis of the tris(pentafluoroethyl)dichlorogermanate salt [PNP][(C2F5)(3)GeCl2] as well as its X-ray structural analysis is described. As a representative example for pentafluoroethylfluorogermanates, the synthesis and structure of 2,4,6-triphenylpyryliumtris(pentafluoroethyl)difluorogermanate [C23H17O][(C2F5)(3)GeF2] is reported. Fluoride-ion affinities for pentafluoroethylgermanes were calculated using quantum chemical methods, disclosing (C2F5)(3)GeF as a weaker Lewis acid than (C2F5)(3)SiF or (C2F5)(3)PF2. The theoretical results were confirmed by experiments and give the basis of a synthetic protocol for (C2F5)(3)GeF. Pentakis(pentafluoroethyl)germanate [PPh4][Ge(C2F5)(5)] was detected as an intermediate during the synthesis of [PPh4][(C2F5)(4)GeF] starting from tris(pentafluoroethyl)difluorogermanate and LiC2F5

Metal-free dehydrogenation of tri- and diethylamine with (C₂F₅)₃PF₂

Bader J, Neumann B, Stammler H-G, Ignat'ev N, Hoge B. Metal-free dehydrogenation of tri- and diethylamine with (C&lt;sub&gt;2&lt;/sub&gt;F&lt;sub&gt;5&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;PF&lt;sub&gt;2&lt;/sub&gt;. JOURNAL OF FLUORINE CHEMISTRY. 2018;207:12-17.The reaction of the strong Lewis acid (C2F5)(3)PF2 with triethylamine leads to an initial hydride abstraction, resulting in the formation of the hydridophosphate anion [P(C2F5)(3)F2H](-) and the iminium ion [CH3CH = NEt2](+). The latter is deprotonated by a second molecule NEt3 which corresponds to a formal hydrogen abstraction from the amine. The resulting nucleophilic enamine is trapped by a second equivalent of (C2F5)(3)PF2, ultimately yielding the beta-aminovinylphosphorane derivative (C2F5)(2)PF2C2H2NEt2. The beta-aminovinylphosphorane reacts with CsF to the corresponding trifluorophosphate derivative, [P(C2F5)(2)F3C2H2NEt2](-), which hydrolyzes to the aldehyde [P(C2F5)(2)F3CH2CHO](-), while the reaction with anhydrous HF yields the zwitterionic species [P(C2F5)(2)F3C2H3NEt2]

Functionalized Pentafluoroethylphosphanes

Allefeld N, Neumann B, Stammler H-G, Ignat'ev N, Hoge B. Functionalized Pentafluoroethylphosphanes. Chemistry - A European Journal. 2015;21(35):12326-12336.Bis(diethylamino)pentafluoroethylphosphane represents a versatile starting material for the synthesis of functionalized pentafluoroethylphosphanes. Perfluoroalkyl substituted aminophosphanes themselves already exhibit interesting coordination properties and were treated with the catalytically relevant salts PtCl2 and PdCl2 affording trans[Cl2M{P(C2F5)(NEt2)(2)}(2)]. The hitherto unknown (C2F5)PBr2, accessible in good yields by treatment of C2F5P(NEt2)(2) with HBr, was smoothly transformed into the corresponding phosphane, C2F5PH2, or fluoro derivative, C2F5PF2. Acidic hydrolysis of C2F5P(NEt2)(2) yielded the phosphinic acid C2F5P(O)(OH)H, the anion of which was structurally characterized. The phosphinic acid smoothly adds to the carbonyl group of acetone under P-C bond formation. An analogous reaction with aldehydes, for example, salicyl aldehyde, offers the possibility to generate stereocenters

Coordination Properties of Perfluoroethyl- and Perfluorophenyl-Substituted Phosphonous acids, (RP)-P-f(OH)(2)

Allefeld N, Kurscheid B, Neumann B, Stammler H-G, Ignat'ev N, Hoge B. Coordination Properties of Perfluoroethyl- and Perfluorophenyl-Substituted Phosphonous acids, (RP)-P-f(OH)(2). Chemistry - A European Journal. 2015;21(39):13666-13675.Phosphinic acids, (RP)-P-f(O)(OH)H (R-f=CF3, C2F5, C6F5), turned out to be excellent preligands for the coordination of phosphonous acids, (RP)-P-f(OH)(2). Addition of C2F5P(O)(OH)H to solid PtCl2 under different reaction conditions allows the isolation and full characterization of the mononuclear complexes [ClPt{P(C2F5)(OH)O}{P(C2F5)(OH)(2)}(2)] and [Pt{P(C2F5)(OH)O}(2){P(C2F5)(OH)(2)}] containing hydrogen-bridged [(RP)-P-f(OH)O](-) and (RP)-P-f(OH)(2) units. Further deprotonation of [Pt{P(C2F5)(OH)O}(2){P(C2F5)(OH)(2)}(2)] leads to the formation of the dianionic platinate, [Pt{P(C2F5)(OH)O}(4)](2-), revealing four intramolecular hydrogen bridges. With PdCl2 the dinuclear complex [Pd-2(-Cl)(2){[P(C2F5)(OH)O](2)H}(2)] was isolated and characterized. The Cl- free complex [Pd{P(C2F5)(OH)O}(2){P(C2F5)(OH)(2)}(2)] was also prepared and deprotonated to the dianionic palladate, [Pd{P(C2F5)(OH)O}(4)](2-). Both compounds were characterized by NMR spectroscopy, IR spectroscopy, and X-ray analyses. In addition, the C6F5 derivatives [ClPt{P(C6F5)(OH)O}{P(C6F5)(OH)(2)}(2)] and [Pd-2(-Cl)(2){[P(C6F5)(OH)O](2)H}(2)] as well as the CF3 derivative [Pd-2(-Cl)(2){[P(CF3)(OH)O](2)H}(2)] were synthesized and fully characterized. Phosphonous acid complexes are inert towards air and moisture and can be stored for several months without decomposition. The catalytic activity of the palladium complexes in the Suzuki cross-coupling reaction between 1-bromo-3-fluorobenzene and phenyl boronic acid was demonstrated