Received: May 2017

DOI 10.17677/fn20714807.2017.03.01

Fluorine Notes, 2017, 112, 1-2

Reaction of perfluorinated alkyl-, alkenyl-, and cycloalkenyltetrafluoro--λ⁵-iodanes R_FIF₄ with halide anions in non-aqueous solutions

Vadim V. Bardin

N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry of Siberian Branch of the Russian Academy of Sciences, Acad. Lavrentjev Ave., 9, 630090 Novosibirsk, Russia

e-mail: bardin@nioch.nsc.ru

Abstract: Perfluoroorganic derivatives of iodine(V) R_FIF₄ (R_F = C₆F₁₃, (CF₃)₂CFCF=CF, cyclo-C₆F₉) react with halide anions X^– (X = Cl, Br, I) in CH₂Cl₂ and/or in CF₃CH₂CF₂CH₃ (PFB) to give mainly iodides R_FI. In addition, the corresponding chlorides, bromides and R_F were formed. The relative contribution of processes depended on the constitution of perfluoroorganyl moiety. The influence of fluoride anions on the reaction route was studied too. Reaction of [Me₄N]F with perfluorocyclohexen-1-yltetrafluoro-λ⁵-iodane led to salt [Me₄N][C₆F₁₀IF₄] while isomer [Me₄N][1-cyclo-C₆F₉IF₅] was not detected.

Key words: perfluoroorganyltetrafluoro-λ⁵-iodanes, reduction, perfluorocarbanions, NMR ¹⁹F spectroscopy.

Chemistry of organoiodine(III) is well studied and achievements in this field are presented in monographs and reviews. Properties of organic derivatives of iodine(V) are significantly less studied [1-7]. The same picture is observed in series of their poly- and perfluorinated analogues [8, 9].

In 2005 we published the simple and convenient method of preparation of perfluorinated alkyl-, alkenyl- and cycloalkenyltetrafluoro-λ⁵-iodanes R_FIF₄ by the oxidative fluorination of the corresponding iodides or aryltetrafluoro-λ⁵-iodanes with xenon difluoride in the presence of BF₃ [10] (scheme 1).

Scheme 1

Chemical properties of these compounds were not investigated. Herein results of interaction of perfluorinated alkyl-, alkenyl- and cycloalkenyltetrafluoro-λ⁵-iodanes R_FIF₄ with tetraalkylammonium fluoride, chloride, bromide and iodide in dichloromethane and/or PFB are presented.

An addition of C₆F₁₃IF₄ (1) in PFB into solution of [Bu₄N]Br (in excess) in dichloromethane followed hydrolysis gave a mixture of 1-iodoperfluorohexane (2), 1-bromoperfluorohexane (3) and 1-H-perfluorohexane (4) (molar ratio 5:1:1) in total quantitative yield (scheme 2).

Scheme 2

(Here and below an excess of reagent is marked by ">".)

Reaction of perfluoro-3-methylbuten-1-yltetrafluoro-λ⁵-iodane (5) (cis : trans = 1 : 9) with [Bu₄N]Br in CH₂Cl₂ led to 1-iodoperfluoro-3-methylbuten-1 (6) and a few trans-1-H-perfluoro-3-methylbuten-1 (7). The ratio cis-6 : trans-6 is the same as in started iodanes 5 (scheme 3).

Scheme 3

Under the action of [Bu₄N]Br perfluorocyclohexen-1-yltetrafluoro-λ⁵-iodane (8) underwent to 1-iodoperfluorocyclohexene (9), 1-bromoperfluorocyclohexene (10), and bromoperfluorocyclohexane (11) (molar ratio 3 : 4 : 3) (scheme 4).

Scheme 4

These results show the processes of replacement of iodine atom by bromine and hydrogen atom that proceeded parallel to the reduction of λ⁵-iodanes to iodides. Since during the reaction of fluoride anions are formed, we performed a reaction of λ⁵-iodanes with the [Me₄N]F as a "naked" fluoride donor. The action of [Me₄N]F on C₆F₁₃IF₄ in EtCN gave C₆F₁₃I (major) and C₆F₁₃H (trace). Except they an admixture of unrecognized perfluorohexane derivative, C₆F₁₃R, was found (¹⁹F NMR). Probably, the reducing agent here is propionitrile. The interaction of iodane 5 with [Me₄N]F in MeCN yielded alkene 7 (trace) and substance which is insoluble either in MeCN and DMF (presumably, oligomer). An addition of [Me₄N]F to a solution of 8 in CH₂Cl₂ at –40 °C and sequent warming to 22 °C led to suspension. The liquid phase contained a few 1-H-perfluorocyclohexene (13) but signals of iodane 8 and perfluorocyclohexenes 9 and 10 were not observed (¹⁹F NMR). Precipitate was separated, washed with dichloromethane, dried in vacuum and dissolved in anhydrous MeCN. The ¹⁹F NMR spectrum displayed resonances of cyclohexene 13, IF₅, [IF₆]^– and salt 12. Signals of isomer [cyclo-C₆F₉IF₅]^– that contained hexacoordinated iodine atom were not detected (scheme 5). Up to date, complex [pip][C₆H₅IF₅] produced from hexamethylpiperidinium fluoride, [pip]F, and C₆H₅IF₄ is the only known representative of this family. It was characterized by ¹⁹F NMR spectroscopy and X-ray data, but chemical properties were not described [12].

Scheme 5

Spectrum ¹⁹F NMR of 12 displayed signals of IF₄ group at –13.4 (tt, ⁴J(F₄I, F^{2, 2}) = 20 Hz, ⁴J(F₄I, F^{6, 6}) = 20 Hz, 4F, IF₄) and cyclohexyl moiety at –89.3 (m, 4F, F^{2, 2, 6, 6}), –128.9 (m, 4F, F^{3, 3, 5, 5}) and –130.8 (m, 2F, F^{4, 4}) ppm. These values are very close so perfluoro-1-ethyl-cyclohexan-1-ide [–79.5 (CF₃), –101.7 (CF₂), –87.0 (4F, F^2,2,6,6), –129.0 (4F, F^3,3,5,5) and –133.0 (2F, F^4,4) ppm], that was generated by an addition of fluoride anion to perfluoro-1-ethylcyclohexene [11]. At 22 ºC salt 12 in MeCN converted slowly to cyclohexene 13 and IF₅ forming white precipitate. Within 18 h the ratio 12 : 13 was 1 : 1. After treatment of suspension with bromine cyclohexene 10 and additional amount of cyclohexene 13 were obtained (10 : 13 = 1 : 2). It is interesting that the action of [Me₄N]F and bromine on 8 in CH₂Cl₂ resulted in cyclohexenes 9 and 10 (1 : 9) (scheme 6).

Scheme 6

To complete a picture, reactions of λ⁵-iodanes 1, 5 and 8 with halide anions in the presence of BF₃OMe₂ (fluoride anion acceptor) were investigated. Notably that these iodanes resist towards BF₃OMe₂ as well as the stronger Lewis acid, BF₃ [10]. It turned out that in these conditions, iodanes 1 and 5 were transformed into appropriate iodides. Other fluoroorganic products were absent (scheme 7).

Scheme 7

Alternatively, iodane 8 formed mainly bromocyclohexene 10 while iodocyclohexene 9 was minor product (9 : 10 = 1 : 9). Bromocyclohexane 11 (cf. scheme 4) was not found (scheme 8).

Scheme 8

Iodocyclohexene 9 was the only fluoroorganic product of reaction of 8 with [Bu₄N]I and BF₃OMe₂. When 8 reacted with [Bu₄N]Cl and BF₃OMe₂ that iodocyclohexene was formed together with admixture of 1-chlorononafluorocyclohexene (14) (scheme 9).

Scheme 9

The resulting picture shows that reactions of λ⁵-iodanes R_FIF₄ with halides anions are not the simple reduction of I(V) but proceed several parallel channels. The contribution of each of them determines either by nature of halide and the constitution of perfluoroorganic moiety of iodane.

Experimental part

The ¹⁹F NMR spectra were recorded on Bruker AVANCE 300 spectrometer at 282.40 MHz. The chemical shifts are referenced to CCl₃F (¹⁹F) [with C₆F₆ as a secondary reference (162.9 ppm)]. The composition of the reaction mixtures and the yields of products were determined by ¹⁹F NMR spectroscopy using an internal quantitative standard 1,1,2-trichlorotrifluoroethane or C₆F₆. Products 2 [13], 3 [14, 15], 4 [16], 9, 10, 13, 14 [17], and 11 [18] were were identified by ¹⁹F NMR spectroscopy.

Preparations of C₆F₁₃IF₄, (CF₃)₂CFCF=CFIF₄, 1-cyclo-C₆F₉IF₄, [10] and [Me₄N]F [19], were described in literature. Dichloromethane (Baker), acetonitrile (Riedel-deHaën) were purified by standard procedures. [Bu₄N]I (Merck), [Bu₄N]Br (Fluka), [Bu₄N]Cl (Fluka) were used as supplied. 1,1,1,3,3-Pentafluorobutane (PFB) (Solvay) was stored over molecular sieves 4A. All manipulations were performed in a FEP (block copolymer of tetrafluoroethylene and hexafluoropropylene) equipment under an atmosphere of dry argon.

Reaction of C₆F₁₃IF₄ 1 with [Bu₄N]Br

A. Solution of C₆F₁₃IF₄ (42 mg, 0.08 mmol) in PFB (0.4 ml) was added into stirred solution of [Bu₄N]Br (142 mg, 0.44 mmol) in CH₂Cl₂ (0.7 ml). After 30 min, yellow solution was washed with 5% aq. Na₂SO₃, with water and dried with MgSO₄. The ¹⁹F NMR spectrum showed the formation of C₆F₁₃I (0.05 mmol), C₆F₁₃Br (0.01 mmol) and C₆F₁₃H (0.01 mmol).

B. [Bu₄N]Br (780 mg, 2.4 mmol) was added in portions into cold (0 C) stirred solution of C₆F₁₃IF₄ (208 mg, 0.40 mmol) and BF₃OMe₂ (124 mg, 1.08 mmol) in CFCl₃ (4 ml). Immediately red solution was formed. After 10 min the ¹⁹F NMR spectrum showed the quantitative formation of 1-iodoperfluorohexane.

Reaction of (CF₃)₂CFCF=CFIF₄ 5 with [Bu₄N]Br

A. Cold (–15 °C) solution of [Bu₄N]Br (317 mg, 0.98 mmol) in CH₂Cl₂ (1.0 ml) was added in portions into cold (–15 °C) solution of (CF₃)₂CFCF=CFIF₄ (cis : trans = 1 : 9) (104 mg, 0.24 mmol) in CH₂Cl₂ (0.7 ml) within 5 min. The immediately formed yellow solution was allowed to warm to 22 °C in 30 min, then it was washed with 5% aq. Na₂SO₃, with water and dried with MgSO₄. The ¹⁹F NMR spectrum showed the formation of (CF₃)₂CFCF=CFI (cis : trans = 1 : 9) (0.22 mmol) and trans-(CF₃)₂CFCF=CFH (0.02 mmol).

B. Cold (–15 °C) solution of [Bu₄N]Br (314 mg, 0.97 mmol) in CH₂Cl₂ (0.7 ml) was added in portions into cold (–15 °C) solution of (CF₃)₂CFCF=CFIF₄ (cis : trans = 1 : 9) (65 mg, 0.15 mmol) and BF₃OMe₂ (110 mg, 0.96 mmol) in CH₂Cl₂ (0.5 ml) within 5 min. The immediately formed red solution was allowed to warm to 22°C in 30 min. The ¹⁹F NMR spectrum showed resonances of (CF₃)₂CFCF=CFI (cis : trans = 1 : 9) (0.14 mmol), BF₃OMe₂ and [Bu₄N][BF₄]. After washing with 5% aq. Na₂SO₃, with water and drying with MgSO₄. yield of 6 and isomer ratio was not changed.

trans-1-Iodoperfluoro-4-methylbutene-1 (trans-6). ¹⁹F NMR (CH₂Cl₂): = –76.3 (ddd, ⁵J(F₃C, F¹) = 5 Hz, ⁴J(F₃C, F²) = 8 Hz, ³J(F₃C, F³) = 8 Hz, 6F, F₃C), –108.7 (ddsept, ⁴J(F¹, F³) = 40 Hz, ³J(F¹, F²) = 151 Hz, ⁵J(F¹, F₃C) = 5 Hz,1F, F¹), –144.1 (ddsept, ³J(F², F³) = 15 Hz, ³J(F², F¹) = 151 Hz, ⁴J(F², F₃C) = 8 Hz, 1F, F²), –187.4 (ddsept, ³J(F³, F²) = 15 Hz, ³J(F³, F¹) = 40 Hz, ³J(F³, F₃C) = 8 Hz, 1F, F³) (lit. [20] ¹⁹F NMR (neat): = –75.4 (6F, F₃C), –108.5 (1F, F¹), –141.5 (1F, F²), –186.0 (1F, F³); ⁴J(F², F₃C) = 8.9 Hz, ⁵J(F¹, F₃C) = 4.7 Hz, ³J(F₃C, F³) = 13.2 Hz, ⁴J(F¹, F³) = 41.4 Hz, ³J(F¹, F²) = 148.8 Hz).

cis-1-Iodoperfluoro-4-methylbutene-1 (cis-6). ¹⁹F NMR (CH₂Cl₂): = –75.7 (dd, ³J(F₃C, F³) = 9 Hz, ⁴J(F₃C, F²) = 9 Hz, 6F, F₃C), –83.5 (dd, ⁴J(F¹, F³) = 6 Hz, ³J(F¹, F²) = 10 Hz, 1F, F¹), –128.5 (m, 1F, F²), –177.1 (dsept, ⁴J(F³, F¹) = 6 Hz, ³J(F³, F₃C) = 9 Hz, 1F, F³).

Reaction of 1-cyclo-C₆F₉IF₄ 8 with [Bu₄N]Br

A. Solution of 1-cyclo-C₆F₉IF₄ (20 mg, 0.05 mmol) in CH₂Cl₂ (0.4 ml) was added into stirred solution of [Bu₄N]Br (58 mg, 0.18 mmol) in CH₂Cl₂ (0.2 ml). The obtained solution contained 1-cyclo-C₆F₉I (0.015 mmol), 1-cyclo-C₆F₉Br (0.019 mmol) and bromoundecafluorocyclohexane (0.015 mmol) (¹⁹F NMR). After washing with 5% aq. Na₂SO₃, with water and drying with MgSO₄. yields were not changed.

B. Solution of 1-cyclo-C₆F₉IF₄ (58 mg, 0.13 mmol) in CH₂Cl₂ (0.7 ml) was added into stirred solution of [Bu₄N]Br (188 mg, 0.58 mmol) and BF₃OMe₂ (61 mg, 0.54 mmol) in CH₂Cl₂ (0.5 ml). After 15 min, red solution contained 1-cyclo-C₆F₉I (0.01 mmol), 1-cyclo-C₆F₉Br (0.10 mmol) beside [Bu₄N][BF₄] ((F) = –151.0 ppm) (¹⁹F NMR). Solution was washed with 5% aq. Na₂SO₃, with water and dried with MgSO₄. Yields of 9 and 10 were not changed (¹⁹F NMR).

Reaction of 1-cyclo-C₆F₉IF₄ 8 with [Bu₄N]Cl and BF₃OMe₂

Solution of 1-cyclo-C₆F₉IF₄ (58 mg, 0.13 mmol) in CH₂Cl₂ (0.7 ml) was added into stirred solution of [Bu₄N]Cl (180 mg, 0.65 mmol) and BF₃OMe₂ (61 mg, 0.54 mmol) in CH₂Cl₂ (0.5 ml). After 15 min, yellow solution contained 1-iodononafluorocyclohexene (0.09 mmol) and 1-chlorononafluorocyclohexene (0.01 mmol) beside [Bu₄N][BF₄] (¹⁹F NMR).

Reaction of 1-cyclo-C₆F₉IF₄ 8 with [Bu₄N]I and BF₃OMe₂

Solid [Bu₄N]I (500 mg, 1.35 mmol) was added in portions into stirred solution of 1-cyclo-C₆F₉IF₄ (152 mg, 0.34 mmol) and BF₃OMe₂ (124 mg, 1.08 mmol) in CH₂Cl₂ (5 ml). Immediately iodine evolved and deep violet solution showed the presence of 1-cyclo-C₆F₉I and [BF₄]^- (¹⁹F NMR). Solution was washed with 5% aq. Na₂SO₃, with water and dried with MgSO₄. The ¹⁹F NMR spectrum contained resonances of 1-cyclo-C₆F₉I 9 (quantitative yield) and [BF₄]^-.

Reaction of 1-cyclo-C₆F₉IF₄ 8 with [Me₄N]F

Cold (–0 °C) solution of 1-cyclo-C₆F₉IF₄ (31 mg, 0.07 mmol) in CH₂Cl₂ (0.4 ml) was added into cold (–40 °C) stirred solution of [Me₄N]F (18 mg, 0.19 mmol) in CH₂Cl₂ (0.2 ml). The reaction mixture was warmed to 22 °C over 20 min to form suspension. After 1 h white precipitate was separated by centrifugation from brownish mother liquor which contained only trace of fluoroorganic compounds (¹⁹F NMR). Precipitate was separated by centrifugation, washed with dichloromethane and dried in vacuum to give white solid (32 mg). Freshly prepared solution in anhydrous MeCN contained 12, 13, [Me₄N][IF₆] (singlet at 11.7 ppm [21]), and IF₅ (ratio 12:42:7:39) (¹⁹F NMR). After 18 h at 22 ºC the ratio became 20:21:7:53.

Reaction of [Me₄N][C₆F₁₀IF₄] 12 with bromine in MeCN

Cold (–15 °C) solution of bromine (20 mg, 0.125 mmol) in MeCN (0.08 ml) was added into cold (–15°C) solution of 12 in MeCN (see above). Salt 12 quantitatively converted to cyclohexenes 10 and 13 (3 : 7) (¹⁹F NMR).

Reaction of 1-cyclo-C₆F₉IF₄ 8 with bromine and [Me₄N]F

Cold (–20 °C) solution of [Me₄N]F (22 mg, 0.23 mmol) in CH₂Cl₂ (0.4 ml) was added into cold (–20 °C) stirred solution of 1-cyclo-C₆F₉IF₄ (31 mg, 0.07 mmol) and bromine (32 mg, 0.20 mmol) in CH₂Cl₂ (0.7 ml). Immediately white suspension formed. The reaction mixture was warmed to 22 °C over 10 min, and precipitate was separated by centrifugation. Yellow mother liquor contained cyclohexenes 10 (0.06 mmol) and 9 (trace). Solution of solid in CH₃CN contained [Me₄N][IF₆] (¹⁹F NMR).

Reaction of C₆F₁₃IF₄ 1 with [Me₄N]F

Cold (0 °C) solution of [Me₄N]F (18 mg, 0.19 mmol) in EtCN (0.5 ml) was added into cold (–55 °C) stirred solution of 1(66 mg, 0.12 mmol) in EtCN (0.6 ml). The reaction mixture was warmed to 22 °C over 6 h. Yellow solution contained C₆F₁₃I (0.09 mmol), C₆F₁₃H (trace) and unknown product C₆F₁₃R (R ≠ IF₂, IF₄) (¹⁹F NMR).

Acknowledgements

Author gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft (436 RUS 17/12/04) and the Fonds der Chemischen Industrie.

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Recommended for publication by Prof. S. M. Igumnov

Fluorine Notes, 2017, 112, 1-2