Transition Metal Complexes of Phosphinous Acids Featuring a Quasichelating Unit: Synthesis, Characterization, and Hetero-bimetallic Complexes.

Diorganophosphane oxides were employed as preligands for the synthesis of catalytically active transition metal complexes of the phosphinous acids (CF3)2POH and (C2F5)2POH. Their reactions with solid PtCl2 and PdCl2 led to the formation of mononuclear phosphinous acid complexes [Cl2M{P(R(f))2OH}2] (M = Pd, Pt; R(f) = C2F5, CF3), which can be crystallized, for example, as its pyridinium salts, 2[HPy](+)[Cl2Pd{P(CF3)2O}2](2-). In vacuo HCl is liberated from the neutral palladium complexes affording mixtures of di- and polynuclear complexes. Moreover, (C2F5)2POH was reacted with several ß-diketonato complexes of palladium, platinum, and nickel yielding air- and moisture-stable complexes [(acac)M{[P(R(f))2O]2H}], featuring a quasichelating phosphinous acid phosphinito unit {P(R(f))2O···H···O(R(f))2P}(-). Treatment of [Ni(Cp)2] (Cp = cyclopentadienyl) and [(cod)RhCl]2 (cod = 1,5-cyclooctadiene) with (C2F5)2POH leads to the substitution of one Cp or chloro ligand by a quasichelating unit. The novel coordination compounds were characterized by NMR and IR spectroscopies, mass spectrometry, and X-ray diffraction analysis. The platinum complex [(acac)Pt{[P(C2F5)2O]2H}] (acac = acetylacetonato) was used for the construction of hetero-bimetallic complexes by the treatment with [(cod)RhCl]2 and [Ni(Cp)2]. The trinuclear bimetallic complex [{(acac)Pt[P(C2F5)2O]2}2Ni] is the first structurally characterized hetero-bimetallic species containing a bis(perfluoroalkyl)phosphinito bridge.

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

Phosphinic acids, R(f)P(O)(OH)H (R(f)=CF3, C2F5, C6F5), turned out to be excellent preligands for the coordination of phosphonous acids, R(f)P(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 [R(f)P(OH)O](-) and R(f)P(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 [Pd2(µ-Cl)2{[P(C2F5)(OH)O]2H}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 [Pd2(µ-Cl)2{[P(C6F5)(OH)O]2H}2] as well as the CF3 derivative [Pd2(µ-Cl)2 {[P(CF3)(OH)O]2H}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.

Functionalized Pentafluoroethylphosphanes.

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 C2F5 P(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.

Synthesis and reactivity of new functionalized perfluoroalkylfluorophosphates.

A new efficient synthesis of functionalized perfluoroalkyl fluorophosphates by oxidative addition of Me2NCH2F to the electron-deficient phosphanes (C2F5)(n)PF(3-n) (n=0-3) is reported. The initially formed zwitterionic, hexacoordinated phosphates [(C2F5)(n)F(5-n)P(CH2NMe2-CH2NMe2)] are converted into the corresponding phosphonium salts [(Me3PCH2NMe2](+)[(C2F5)(n)F(5-n)P(CH2NMe2)](-) by treatment with PMe3. In addition [(C2F5)3F2P(CH2NMe2-CH2NMe2)] can undergo a 1,3-methyl shift from the internal to the terminal nitrogen--a structural characterization was achieved from the CF3 analogue. Reaction of [(C2F5)3F2P(CH2NMe-CH2NMe3)] and PMe3 gave rise to the formation of the zwitterionic phosphonium phosphate [(C2F5)3F2P(CH2NMe-CH2PMe3)], which was fully characterized by X-ray diffraction analysis. Moreover, an efficient one-pot synthesis of Cs(+)[(C2F5)3F2P(CH2NMe2)](-) was pursued. This salt turned out to be a useful nucleophile in several alkylation reactions.

Synthesis of unsymmetrically substituted phosphane oxides (R(1)R(2)P(O)H) and phosphinous acids (R(1)R(2)POH).

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 , C6 F5 , C6 H5 ) with LiC2 F5 . On treatment with para-toluenesulfonic acid the isolated aminophosphanes R(C2 F5 )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 )(C2 F5 )POH as a stable phosphinous acid, whereas the pentafluorophenyl and phenyl derivatives constitute a solvent dependent equilibrium between the acid and the oxide tautomer.

Carbene complexes of phosphorus(V) fluorides substituted with perfluoroalkyl-groups synthesized by oxidative addition. Cleavage of the complexes reveals a new synthetic protocol for ionic liquids.

The crystal structures of the previously reported 2,2-difluoro-1,3-dimethylimidazolidine and its acyclic analog were determined by in situ crystallization. Both liquid fluorinating agents have recently been introduced as potent precursors for the synthesis of p-block element carbene complexes. These fluorine compounds were compared with chloro-amidinium chlorides, which are already established carbene precursors. The chlorides were characterized as ion pairs and contrasted to the previous interpretation as charge-transfer complexes between carbene and dichlorine. Furthermore, the two precursors are used for the synthesis of a series of new carbene complexes of phosphorus(v) fluorides substituted with perfluoroalkyl-groups. These unusually stable hexacoordinate phosphorus(v) complexes were treated with anhydrous hydrogen fluoride to yield imidazolium phosphates. This procedure allows the synthesis of salts used as ionic liquids in high yield and high purity.