Redox reactions of uranium hexafluoride. Comparison with phosphorus pentafluoride and preparation of copper(I) hexafluorouranate(V) [1]

Molecular iodine is oxidised by phosphorus pentafluoride in iodine pentafluoride at room temperature giving I₂⁺, PF₆^?, and PF₃. I₂⁺ is formed from uranium hexafluoride under similar conditions, but further oxidation occurs depending on the reaction stoicheiometry used. In all cases uranium pentafluoride is formed. Copper(II) fluoride reacts with UF₅ in acetonitrile at room temperature to give copper(II) hexafluorouranate(V), which is reduced by copper metal to give the copper(I) salt. The latter compound is formed from UF₆ and Cu metal, via the Cu^II salt, only if a fresh Cu surface is used for the reduction step.     

Redox reactions involving rhenium and uranium hexafluorides,a convenient synthesis of β-uranium pentafluoride

Rhenium and uranium hexafluorides oxidise elemental iodine in iodine pentafluoride at ambient temperature to give the I₂⁺ cation. With UF₆ an additional reaction occurs to give β-uranium pentafluoride as one product, β-UF₅ is soluble in acetonitrile without disproportionation and is also formed from the reduction of UF₆ by MeCN. Copper, cadmium, and thallium metals are oxidised by ReF₆ in MeCN giving Cu^I, Cd^II, and Tl^I hexafluororhenates(V) but the reactions are complicated by reaction between ReF₆ and the solvent.     

Chemistry in hydrogen fluoride V. Catalysts for reaction of HF with halogenated olefins

Tantalum pentafluoride, niobium pentafluoride, titanium tetrachloride, and molybdenum pentachloride catalyze the addition of hydrogen fluoride to $\text{tetra}$- and $\text{tri}$chloroethene and related compounds. Hydrogenation of tetrachloroethene to 1,1,2,2-tetrachloroethane was observed using hydrogen, methylcyclopentane, and TaF₅ in HF.     

Branching ratio for the production of I2Psol12) in the photodissociation of I2

The production of atomic iodine in the ground (²Pfrsol|3/2) and electronically excited (²P$\text{1}\text{3}$) states following laser-induced photodissociation of I₂ the region 425–498 nm was monitored directly by resonance spectroscopy. The branching ratio for iodine atom formation. R = [I(²P$\text{1}\text{2}$)]/[I(²P$\text{3}\text{2}$)], is above 0.5 in the region 495–498 nm in agreement with the recent observation of laser action on the atomic transition at 1315 nm following photolysis of I₂ using a dye laser. The present experiments permitted deconvolution of the I₂ continuous absorption spectrum below 498 into contributions from the B³ Π_o,u → X ¹Σ_g⁺ and ¹Π_tu → X¹σ_g^? transitions.     

The behaviour of copper and thallium hexafluoromolybdates(V) in acetonitrile

Copper(I), copper(II), and thallium(III) hexafluoromolybdates(V), prepared by the oxidation of the metals in acetonitrile with molybdenum hexafluoride (A. Prescott, D.W.A.Sharp, and J.M. Winfield, $\text{J. Chem. Soc., Dalton Trans.}$, 1975, 963) have been investigated by cyclic voltametry. Half wave potentials, E_{$\text{1}\text{2}$} V vs. Ag^p+/Ag were obtained using a evacuable cell equipped with anexternal Ag^p+/Ag electrode, enabling strict anerobic conditions to be maintained. A number of reversible or quasi-reversible electron transfer processes have been observed, enabling comparison with synthetic work to be made. Results for Cu^I and Cu^II hexafluoromolybdates(V) are in accord with preparative experience. MoF₆. Mo^VI/Mo^VE_{$\text{1}\text{2}$} +1.600V, oxidises Cu metal to Cu^II in MeCN, and Cu^II is reduced by Cu^O to Cu^I , Cu^lI/Cu^IE_{$\text{1}\text{2}$} = +0.750 or +0.710V for Cu^I and Cu^II solutes respectively, Cu^I/Cu^OE$\text{1}\text{2}$ = ?0.720V not reversible. A wave at E_{$\text{1}\text{2}$} = ?0.350V is assigned to Mo^V/Mo^IV by analogy with Ag^I hexafluoromolybdate (D.W.A. Sharp, unpublished work). E_{$\text{1}\text{2}$} data for I₂ in MeCN, I₂/I₃^- = 0.280, I₃^?/I^? = -0.116V, suggest that reduction of MoF₆^? by I is not likely, in contrast to the situation in SO₂ (A.J. Edwards and R.D. Peacock, $\text{Chem. Ind.}$, 1960, 1441). Reduction of MoF₆^? by Cu^o in MeCN should be feasible, but appears to be very slow. Pure Tλ^III hexafluoromolybdate(V) is obtained from Tλ^o and MoF₆ only when the mole ratio MoF₆:Tλ>5:1. Smaller ratios produce yellow solids in which Mo:Tλ is $\text{ca}$. 2:1. Tλ^III is a stronger oxidising agent than Cu^II in MeCN, as oxidation of Cu^I by Tλ^III is rapid and quantitative. However a reversible electron transfer wave assignable to Tλ^III/Tλ^I is not observed in the expected fange +1.600 to +0.710V possibly because of solute-electrode interactions.     

Coulometric titration of iodide and iodine with electrolytically generated hypobromite

Conditions for the quantitative coulometric titration of iodide and iodine with electrolytically generated hypobromite in the presence of borax buffer have been established. Iodide and iodine are oxidized to iodate. The method, with biamperometric indication of the equivalence point, was successfully applied for a wide range of iodide concentrations (6.21–2115μg with reliability intervals of ±0.21–±11μg) and iodine concentrations (24.26–3311μg with reliability intervals of ±0.36–±11.7μg). The determinations are accurate and sensitive even in the presence of large amounts of bromides and chlorides ($\text{Br}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}$= 1.2·10⁶ and $\text{C}\text{l}$^?I^?=4.0·10^{3), as well as in the presence of oxidizing agents such as IO₃?, BrO₃? and CrO₄2? ($\text{I}\text{O}$₃?/I₂)=3.2·105, $\text{I}\text{O}$₃?/I₂=3.1·103, $\text{Br}\text{O}$-₃/I₂}=1.1·10⁴ and $\text{Cr}\text{O}$^2-₄/I₂=1.0·10⁴, as was confirmed by statistical tests. The oxidation mechanism under the conditions of coulometric titrations is discussed.     

The effect of internal excitation on the collision induced dissociation of I+2(2Πg,υ) ions

Cross sections for collision induced dissociation of 0.65 to 3.2 keV I⁺₂(²Π_g, υ) ions in I⁺₂(²Π_g, υ) + N₂(X ¹Σ⁺_g, υ = 0) interactions have been determined. Reaction cross sections for I⁺₂(²Π_{$\text{3}\text{2}$,g}, υ) ions in low vibrational levels vary smoothly from 6 to 10 A² with increasing kinetic energy. Dissociation cross sections for I⁺₂(²Π_{$\text{1}\text{2}$,g}, υ) ions are larger than those involving ground state ions. Processes involving highly excited metastable states of I⁺₂ are not observed in this investigation.     

Amino-sulphur-fluorine derivatives as fluoride ion donors: preparation of three- and four-coordinated cations of sulphur (IV) and (VI) [1,2]

Pentacoordinated aminosulphur (IV) trifluorides, R₂N$\text{S}$F₃, (in this paper the lone pair in S(IV)-derivatives is always considered as a ligand) and aminosulphur(VI)-oxidetrifluorides, R₂NS(O)F₃, readily lose a fluoride ion to Lewis acids (AsF₅, SbF₅, BF₃) to give sulphur-containing cationic species [R₂N$\text{S}$F₂]⁺ and [R₂NS(O)F₂]⁺ with tetracoordinated sulphur. Tetracoordinated neutral dialkylaminosulphur(IV)-oxidefluorides, R₂N$\text{S}$(O)F, and amino-imino sulphur(IV)fluorides, R₂N$\text{S}$(=NR_f)F, give three-coordinated sulphur cations [R₂N$\text{S}$O]⁺] or [R₂N$\text{S}$NR_f]⁺.The three-coordinated sulphur(VI)cation [R₂NS(O)NR]₊ has also been formed.     

[(C6F5)2IF2][BF4], the First Salt with the Electrophilic Cation [(C6F5)2IF2]+: Synthesis,Reactivity, and Structure

The substitution of hypervalently bonded fluorine atoms in C₆F₅IF₄ was performed with C₆F₅BF₂ and resulted in the new salt [(C₆F₅)₂IF₂][BF₄]. The iodonium(V) salt was characterized by multi‐NMR and Raman spectroscopy and X‐ray crystal structure analysis. The fluorinating ability of the new electrophilic cation [(C₆F₅)₂IF₂]⁺ was exemplified in reactions with monovalent iodine compounds (C₆F₅I, p‐FC₆H₄I, and I₂) and with electron‐poor tri(organyl)pnictanes ER₃ (E = P, As, Sb, Bi; R = C₆F₅). In a heterogeneous reaction with CsF in MeCN the [(C₆F₅)₂IF₂]⁺ cation forms the dinuclear [{(C₆F₅)₂IF₂}₂F]⁺ cation.     

Reactions of coordinated trimethylphosphite with binary fluorides

Fluorination of free trimethylphosphite by phosphorus pentafluoride or tungsten hexafluoride involves complex formation followed by rapid F-for-OCH₃ exchange and Michaelis-Arbusov rearrangement reactions (D.W.A. Sharp et al., $\text{J. Chem. Soc. A}$, 1969, 872; J.M. Winfield et al., $\text{ibid}$, 1970, 501). Reactions between WF₆ or PF₅ and P(OCH₃)₃, coordinated to Fe^II (low spin d⁶-inert) or Cu^I (d¹⁰ -labile) cations in CH₃CN, counter anions PF₆^? or AsF₆^?, are very different as evidenced by an n.m.r. study.Reactions between Fe^IIP(OCH₃)₃ and WF₆ are very slow at room temperature; the major products are CH₃PF₄ and WOF₄.NCCH₃. Reactions between Cu^IP(OCH₃)₃ and WF₆ or PF₅ are rapid, even below room temperature, and depend on the stoicheiometry. The major products are W₂O₂F₉^? and a PF₅X^? species, or OPF₃, minor products include CH₃OPF₂, (CH₃O)₂PF, and PF₃. When the mole ratio coordinated P(OCH₃)₃:WF₆ is 1:1, additional W₂O₂F₉ and PF₅X n.m.r. signals are observed.The reactions involve fluorination of free P(OCH₃)₃ whose concentration in solution is limited by the metal cation, and in the reaction between PF₅ and Cu^IP(OCH₃)₃ PF₅.P(OCH₃)₃ has been identified as the initial product. Conventional Michaelis-Arbusov rearrangements are of minor importance as CH₃CN acts as a sink for CH₃⁺, but the final step in the formation of CH₃PF₄ is of this type.     

The structures of fluorides X. Neutron powder diffraction profile studies of UF6 at 193°K and 293°K

Neutron diffraction studies on polycrystalline UF₆ have been carried out at 193°K and 293°K. At both temperatures, UF₆ is orthorhombic with the space group Pnma (D¹⁶_2h) and Z = 4. Measured lattice parameters are a = 9.924 (10) Å, b = 8.954 (9) Å, c = 5.198 (5)Å at 293°K and a = 9.843 (11), b = 8.920 (10), c = 5.173 (6) Å at 193°K. The neutron diffraction patterns were analyzed by the least-squares profile-fitting technique. The final values of $\text{R =}\text{∑}\text{i}\text{(|I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}\text{? I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}\text{|)/∑ I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}$ over the pattern points, where I_oi is a background corrected measured intensity, were 0.081 at 193°K and 0.133 at 293°K.On cooling, the hexagonal close-packing tends to become more regular, and the FF distances external to a UF₆ octahedron contract. The octahedra are nearly regular with a mean UF distance of 1.98 Å, a mean FF edge of 2.80 Å, and a FUF angle of 90.0° at 193°K.     

H3N·PF5 and H2NPF5−, new compounds in the system H3N/PF5

Phosphorus pentafluoride was reported long ago to give adducts 2 PF₅ ·5 NH₃ (1) and nNH₃·PF₅ (n= 1 ? 4) (2). None of the compounds was characterised in detail. Repeating the reaction of PF₅ and NH₃ we found the adduct H₃N·PF₅, $\text{1}$, in 8% yield besides (H₂N) ₂PF₃ (3) and NH₄PF₆. However, HF and (F₂P=N)₃ gave $\text{1}$ in 41% yield. The ¹H, ¹⁹F, and ³¹P n.m.r. spectra of $\text{1}$ exhibit ¹⁴NH, ¹⁴NPF(cis), and ¹⁴NP coupling. The x-ray structure determination shows almost perfect octahedral geometry at phosphorus with a PN bond length of 1.842 ā. Compound $\text{1}$ is soluble in water without decomposition. Treatment with NH₃ leads to the anion H₂NPF₅^?. Upon heating $\text{1}$ forms in good yield H₂NPF₄ and NH₄PF₆. Without a solvent $\text{1}$ and NH₃ react to give (H₂N) ₂PF₃. A mechanism for the ammonolysis of PF₅ is proposed.     

The quenching of excited iodine atoms by oxygen molecules as studied by opto-acoustic spectroscopy

The opto-acoustic spectrum of I₂ in the presence of various quenching gases — NO, O₂, CH₃I, SO₂, C₃H_S, N₂, and He — has been studied. Of these, the I₂/O₂ spectrum is quite different due to the near-resonant energy transfer I(²P$\text{1}\text{2}$) + O₂(³Σ) → I(²P$\text{3}\text{2}$) + O₂(^IΔ), wherein the resistance of the O₂((^IΔ) species to collisional relaxation severely distorts the acoustic signal. The photochemical production of excited ²P$\text{1}\text{2}$ iodine atoms commences at wavelengths considerably longer than the dissociation limit of the I₂B? state.     

The preparation of copper(II) and copper(I) salts in acetonitrile using group VA and VB pentafluorides

Copper(II) fluorine reacts with the pentafluorides, TaF₅, PF₅, and AsF₅, in acetonitrile to give solvated Cu^II, hexafluoroanion salts. These react with copper metal to give the corresponding Cu^I compounds. Similar reactions occur between AsF₅ and silver(I) or thallium(I) fluorides, but silver(II) fluoride reacts with MeCN, and Ag^I hexafluoroarsenate is formed. PF₅ oxidises Cu slowly in MeCN to give Cu^I hexafluorophosphate, but AsF₅ has no oxidising ability towards metals in MeCN. Spectroscopic data for Cu(MF₆)₂·5MeCN and Cu(MF₆)·4MeCN (M = Ta or P) are discussed.     

A raman,infra-red and n.m.r. spectroscopic study of the pentafluorotellurate(IV) ion

The Raman, and infra-red spectra of Na⁺, K⁺, Rb⁺, Cs⁺, NH₄⁺, C₅H₅NH⁺ and $\text{n}$-Bu₄N⁺ salts of the TeF₅^- ion are reported. They are assigned C_s symmetry. ¹⁹F n.m.r. spectra of the $\text{n}$-Bu₄N⁺ salt show J(F_ax-F_eq)50.4Hz, J(¹⁹F_eq-¹²⁵Te)1375.7Hz, J(¹⁹F_ax-¹²⁵Te)2883.3Hz and J(¹⁹F_eq-¹²³Te)1143.8Hz. No n.m.r. evidence was found for TeF₆^2-.     

Synthesis and some reactions of n5-pentamethylcyclopentadienylnickel complexes

Reaction of Me₅C₅Li and Ni(CO)₄ gave [(n⁵-Me₅C₅)Ni(CO)]₂ ($\text{I}$) in 40 % yield. Reaction of $\text{I}$ with iodine followed by addition of a tertiary phosphine or reaction of (PPh₃)₂NiX₂ with Me₅C₅Li or Me₅C₅SnBu₃ gave (n⁵-Me₅C₅)Ni(L)X ($\text{II}$) (L = tertiary phosphine, X = halogen). Treatment of $\text{II}$ with RLi (R = Me, PhCC) afforded (n⁵-Me₅C₅)Ni(L)R ($\text{III}$). The spectroscopic properties and the reactivities of n⁵-pentamethylcyclopentadienylnickel complexes indicate that the n⁵-Me₅C₅ ligand is more electron-donating and a sterically more bulky than the n⁵-C₅H₅ ligand.     

Reactions of triphenylarsine oxide with aqueous hydrogen fluoride: Crystal structure of bis(triphenylarsine oxide)hydrogen(I) tetrafluoroborate

Fluorination of triphenylarsine oxide by aqueous hydrogen fluoride (1–40%) in the absence of glass readily gives triphenylarsine difluoride. When the reaction with dilute (1%) aqueous hydrogen fluoride is carried out in borosilicate glass apparatus, the glass participates in the reaction resulting in the formation of the crystalline 2:1 adduct 2Ph₃AsO·HBF₄. Crystals of this compound are monoclinic, $\text{P}$2₁/$\text{c}$, $\text{a}$ = 12.926(4), $\text{b}$ = 17.819(6), $\text{c}$ = 14.994(4) Å, β = 98.97(3)°, Z = 4. The structure contains cations [(Ph₃AsO)₂H]⁺ in which $\text{O}\text{?}$O is 2.44(2)Å, and anions BF₄^?.     

Isonitrilsynthesen am komplex: V. Desulfurierung von isothiocyanaten in carbonylmetallat-additions-verbindungen

The isocyanide complexes [Fe(η-C₅H₅)(CO)₂CNR][PF₆] and Cr(CO)₅CNR (R = CH₃, C₆H₁₁, C₆H₅) are conveniently prepared at ?50°C from carbonyl metallates, isothiocyanates, and phosgene. At room temperature Na[Fe(η-C₅H₅)(CO)₂] reacts with isothiocyanates ($\text{1}\text{1}$) to give the isocyanide bridged complexes [Fe₂(η-C₅H₅)₂(μ-CO)(μ-CNR)(CO)₂].     

Antimonypentafluoroorthotellurates: Sb(OTeF5)3, Sb(OTeF5)5 and salts of Sb(OTeF5)6−

Antimony(III)pentafluoroorthotellurate has been synthesized from SbF₃ and B(OTeF₅)₃. Contrary to a previous report it is a low melting, sublimable solid (mp = 28°, bp (0.1 torr) = 68°, ¹⁹F - NMR: AB₄ spinsystem δ (A) = ?42.7, δ (B) = ?38.1, J (AB) = 186 Hz). It reacts with F₂, Cl₂ and Br₂ to give SbF₂(OTeF₅)₃, SbCl₄⁺Sb(OTeF₅)₆^? and SbBr₄⁺ Sb(OTeF₅)₆^? respectively. Interaction of Xe(OTeF₅)₂ and Sb(OTeF₅)₃ yields Sb(OTeF₅)₅, which is unstable at room temperature. Salts containing the new anion Sb(OTeF₅)₆^? have been synthesized either from Sb(OTeF₅)₅ and a corresponding pentafluoroorthotellurate e.g. Sb(OTeF₅)₅ + NMe₄⁺ OTeF₅^? = NMe₄⁺ Sb(OTeF₅)₆^?, or from SbCl₄ Sb(OTeF₅)₆^? and an appropriate chloride SbCl₄⁺ Sb(OTeF₅)₆^? + NOCl = SbCl₅ + NO⁺ Sb(OTeF₅)₆^?, or oxidatively, using a mixture of Xe(OTeF₅)₂ and Sb(OTeF₅)₅, e.g. C₆F₆ + $\text{1}\text{2}$ Xe(OTeF₅)₂ + Sb(OTeF₅)₅ = C₆F₆⁺ Sb(OTeF₅)₆^? + $\text{1}\text{2}$ Xe.     

Organometallics in organic synthesis:tricarbonyl-(3-methoxycyclohexa-2,4-dien-1-yl)-iron(1+). A synthetic equivalent of the C-5 cation of cyclohexenone.

Tricarbonyl-(3-methoxycyclohexa-2,4-dien-1-yl)-iron(1+) PF₆(1-) $\text{2}$ reacts with a variety of nucleophiles to give 5-substituted cyclohex-2-enones. $\text{2}$ is shown to be a useful precursor for a convergent synthesis of 5-substituted cyclohex-2-enones and to be synthetically equivalent to the 5-cyclohex-2-enone cation $\text{1}$.