The first perfluoro alkyl(aryl)iodonium salt synthesised on two complementary routes

Article abstract of DOI:10.1016/j.mencom.2009.03.004

The first representatives of the previously unknown perfluoroalkyl(perfluoroaryl)iodonium salts [C_nF_{2n + 1}(Ar_F)I]Y were prepared by reaction of perfluorinated alkyliodine difluorides CnF_{2n + 1}IF2 with aryldifluo

Full text of DOI:10.1016/j.mencom.2009.03.004

Mendeleev
Communications
Mendeleev Commun., 2009, 19, 67–68
The first perfluoro alkyl(aryl)iodonium
salt synthesised on two complementary routes
Hermann-Josef Frohn,*a Frank Baillya and Vadim V. Bardinb
a Department of Chemistry, University of Duisburg-Essen, D-47048 Duisburg, Germany.
Fax: +49 203 379 2231; e-mail: h-j.frohn@uni-due.de
b N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy
of Sciences, 630090 Novosibirsk, Russian Federation
DOI: 10.1016/j.mencom.2009.03.004
The first representatives of the previously unknown perfluoroalkyl(perfluoroaryl)iodonium salts [CnF2n + 1(ArF)I]Y were prepared
by reaction of perfluorinated alkyliodine difluorides CnF2n + 1IF2 with aryldifluoroborane C6F5BF2 and on the complementary
route from perfluorinated aryliodine difluoride C6F5IF2 and alkyldifluoroborane C6F13BF2.
In contrast to aryl(perfluoroalkyl)iodonium salts,1 which are
known for more than two decades and widely applied for electro-
philic perfluoroalkylation reactions in organic synthesis, their
perfluorinated analogues, as well as any perfluoroalkyl(perfluoro-
organyl)iodonium salt [CnF2n + 1(RF)I]Y, are still unknown.2
Here, we report two effective routes to perfluoro alkyl(aryl)-
iodonium salts. Both routes have in common the use of
perfluoro organyliodine difluorides RFIF22 and organyldifluoro-
boranes R'FBF23 (RF, R'F = CnF2n + 1 or C6F5).
The availability of the complementary route to [CnF2n + 1(C6F5)I]Y
salts from C6F5IF2 and CnF2n + 1BF2 was not a priori promising
because of the weak nucleophilicity of the perfluoroalkyl group,
which has to migrate from boron to iodine(III). Surprisingly,
this reaction according to Scheme 2 occurs with 2 equiv. of
perfluorohexyldifluoroborane and results in the desired iodonium
cation with the corresponding perfluoroalkyltrifluoroborate anion
in a good yield§ (Scheme 2).
The route to [CnF2n + 1(C6F5)I][BF4] salts is based on the
addition of C6F5BF2 to a solution of CnF2n + 1IF2 at low tem-
i
†
C6F5IF2 + 2C6F13BF2
[C6F13(C6F5)I][C6F13BF3]
peratures in weakly coordinating, strictly dry solvents, such as
CH2Cl2, CCl3F and 1,1,1,3,3,-C3H3F5. The salts can be easily
isolated after removal of all volatiles in a vacuum. Note that
iodonium salts with both linear and branched alkyl groups can
be obtained‡ (Scheme 1).
3
Scheme 2 Reagents and conditions: i, 1,1,1,3,3-pentafluoropropane (PFP),
–40 °C.
‡
A solution of C6F5BF2 (129 mg, 0.60 mmol) in CH2Cl2 (2 ml) was
added in portions to the stirred cold (–50 °C) solution of (CF3)2CFIF2
(201 mg, 0.60 mmol) in CH2Cl2 (1 ml). After 1 h, the precipitate was
separated by centrifugation and washed with cold (–50 °C) CH2Cl2
(0.4 ml). [(CF3)2CF(C6F5)I][BF4] 1 was obtained as a colourless solid in
~80% yield after drying in a vacuum at –40 °C. 19F NMR (MeCN,
i or ii
CnF2n + 1IF2 + C6F5BF2
[CnF2n + 1(C6F5)I][BF4]
1 CnF2n + 1 = (CF3)2CF
2 CnF2n + 1 = C6F13
3
–40 °C) d: –70.9 [d, 6F, F(2), JF(2)–F(1) 12 Hz], –118.9 (m, 2F, o-F),
Scheme 1 Reagents and conditions: i (1), CH2Cl2, –40 °C; ii (2), CCl3F,
3
4
–136.3 (tt, 1F, p-F, Jp-F–m-F 21 Hz, Jp-F–o-F 9 Hz), –138.9 [sept., 1F,
F(1), 3JF(1)–F(2) 12 Hz], –146.7 (s, 4F, [BF4]–), –154.0 (m, 2F, m-F).
A solution of C6F5BF2 (38 mg, 0.17 mmol) in CCl3F (1 ml) was
added in portions to the stirred cold (0 °C) solution of C6F13IF2 (89 mg,
0.18 mmol) in CCl3F (0.5 ml). After a few minutes, the yellowish solution
was evaporated to dryness at 0 °C in a vacuum, and the solid residue was
washed with CCl3F until CCl3F became colourless. After drying in a
vacuum at 0 °C, [C6F13(C6F5)I][BF4] 2 was isolated as a colourless
solid in > 90% yield. 19F NMR (CD3CN, –40 °C) d: –62.2 [m, 2F, F(1)],
–80.6 [t, 3F, F(6), 4JF(6)–F(4) 10 Hz], –113.8 [m, 2F, F(2)], –119.4 [m, 2F,
o-F], –121.2 [m, 2F, F(3)], –122.4 [m, 2F, F(4)], –126.1 [m, 2F, F(5)],
–138.3 [tt, 1F, p-F, 3Jp-F–m-F 20 Hz, 4Jp-F–o-F 8 Hz], –147.1 (s, 4F, [BF4]–),
–154.9 [m, 2F, m-F]. 13C NMR (CD3CN, –25 °C) d: 148.3 [dtt, C(4),
1JC(4)–p-F 263 Hz, 2JC(4)–m-F 13 Hz, 3JC(4)–o-F 6 Hz], 147.9 [dm, C(2), C(6),
1JC(2), C(6)–o-F 250 Hz], 138.9 [dm, C(3), C(5), 1JC(3), C(5)–m-F 258 Hz], 86.9
[tm, C(1), 2JC(1)–o-F 25 Hz] (C6F5 moiety); 117.5 [t, C(6), 2JC(6)–F(5) 32 Hz],
0 °C.
†
(CF3)2CFIF2. A cold fluorine–nitrogen gas mixture (3 vol%, passed
through a –78 °C copper coil) was introduced into a cold (–78 °C) stirred
solution of (CF3)2CFI (1.05 g, 3.55 mmol) in CCl3F (6 ml) until F2 was
detected at the outlet (wet KI indicator paper). The white product suspen-
sion was centrifuged at –78 °C, and the precipitate was dried in a vacuum
at –40 °C. The raw product (CF3)2CFIF2 (80–85% yield) contained
(CF3)2CFI, IF5 and (CF3)2CFIF4 (total 4–5%). Pure product was obtained
by crystallization from CCl3F: mp 39–41 °C. 19F NMR (CH2Cl2) d: –71.4
3
4
[dt, 6F, 2CF3, JF(2)–F(1) 8 Hz, JF(2)–IF 8 Hz], –140.4 [sept., 1F, F(1),
3JF(1)–F(2) 8 Hz], –169.2 [sept., 2F, IF2, 4JIF–F(2) 8 Hz]. 19F NMR (CD3CN)
d: –70.3 [dt, 6F, 2CF3, 3JF(2)–F(1) 8 Hz, 4JF(2)–IF 8 Hz], –145.9 [sept., 1F,
F(1), 3JF(1)–F(2) 8 Hz], –171.1 [sept., 2F, IF2, 4JFI–F(2) 8 Hz].
C6F13IF2. It was prepared by analogy to (CF3)2CFIF2 in 84% yield
from C6F13I (2.05 g, 4.6 mmol) in CCl3F (10 ml). The crude product was
washed with a small volume of CCl3F at –78 °C, crystallized from CCl3F
and dried in a vacuum at –40 °C: mp 53–55 °C (lit.,6 35 °C). 19F NMR
(CH2Cl2) d: –75.6 [s, 2F, F(1)], –81.3 [m, 3F, F(6)], –116.9 [m, 2F,
F(2)], –121.6 [m, 2F, F(3)], –122.8 [m, 2F, F(4)], –126.4 [m, 2F, F(5)],
–171.6 [s, 2F, IF2, t1/2 = 38 Hz]. 19F NMR (CD3CN, –40 °C) d: –80.3
[t, 3F, F(6), 4JF(6)–F(4) 10 Hz], –81.8 [m, 2F, F(1)], –117.4 [m, 2F, F(2)],
–121.3 [m, 2F, F(3)], –122.3 [m, 2F, F(4)], –125.8 [m, 2F, F(5)], –173.3
[s, 2F, IF2, t1/2 = 27 Hz].
1
2
114.1 [tt, C(1), JC(1)–F(1) 346 Hz, JC(1)–F(2) 44 Hz], 110.4 [tt, C(2),
1JC(2)–F(2) 271 Hz, JC(2)–F(1) 32 Hz], 110.3 [tt, C(3), JC(3)–F(3) 272 Hz,
2
1
2JC(3)–F(2) 32 Hz], 109.8 [tt, C(4), JC(4)–F(4) 271 Hz, JC(4)–F(3) 33 Hz],
1
2
1
2
2
108.7 [ttq, C(5), JC(5)–F(5) 270 Hz, JC(5)–F(4) 32 Hz, JC(5)–F(6) 26 Hz]
~
(C6F13 moiety). Raman (–30 °C, FEP-capillary) (n/cm–1): 1639 (14),
1521 (4), 1413 (11), 1165 (3), 1105 (4), 1012 (6), 988 (2), 883 (2), 845 (9),
809 (6), 751 (20), 644 (4), 618 (3), 588 (20), 528 (2), 496 (23), 442 (13),
354 (9), 254 (29), 202 (20), 140 (11); bands of FEP are omitted.
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© 2009 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2009, 19, 67–68
Salts 1–3 as solids are stable at room temperature for a few
This work was supported by the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie.
days. The solution of 3 in weakly coordinating PFP decomposed
above 0 °C (35% conversion at 0 °C within 2 h and 100%
conversion after 3 h at 25 °C) to yield equimolar amounts of
C6F14, C6F5I and C6F13BF2. The solution of 2 in coordinating
acetonitrile showed no decomposition at –25 °C within 8 h and
a trace of C6F5I after 5 h at 0 °C (19F NMR). However, after
5 h at 22 to 25 °C, the decomposition of 2 to C6F14, C6F5I and
BF3·NCMe exceeded 90%. The decomposition of 3 in MeCN
proceeded similarly to give C6F14, C6F5I and C6F13BF2·NCMe.
In both cases, unknown minor perfluoroalkyl-containing by-
products due to reactions with the solvent were detected by
19F NMR spectroscopy.
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A cold (–45 °C) solution of C6F13BF2 (0.45 mmol) in PFP (2 ml)4
§
was added in portions to the cold (–45 °C) stirred solution of C6F5IF2
(0.22 mmol)5 in PFP (1.5 ml). After 1 h at –40 °C the lemon-yellow
solution contained [C6F13(C6F5)I]+, [(C6F5)2I]+, [C6F13BF3]– (55:6:61)
besides BF3 (19F NMR). The 19F NMR spectra of a probe (0.4 ml) showed
35% decomposition of 3 after 2 h at 0 °C and 100% decomposition after
3 h at 25 °C under formation of equimolar amounts of C6F5I, C6F14, and
C6F13BF2. The main solution (2.1 ml) was evaporated to dryness at –20 °C
in a vacuum to yield a lemon-yellow solid, [C6F13(C6F5)I][C6F13BF3] 3
with an admixture of [(C6F5)2I][C6F13BF3] (~18%).
6 C. S. Rondestvedt, J. Am. Chem. Soc., 1969, 91, 3054.
3: 19F NMR (PFP, –40 °C) d: –52.8 [m, 2F, F(1)], –80.0 [m, 3F, F(6)],
–112.0 [m, 2F, F(2)], –119.9 [m, 2F, F(3)], –121.2 (m, 2F, o-F), –121.9
3
[m, 2F, F(4)], –125.9 [m, 2F, F(5)], –134.4 (t, 1F, p-F, Jp-F–m-F 20 Hz),
–153.4 (m, 2F, m-F) ([C6F13(C6F5)I]+ moiety); –80.1 [m, 3F, F(6)], –121.8,
–122.0, –122.7, –125.4 (8F, 4CF2), –133.3 [m, 2F, F(1)], –147 (br., 3F,
BF3–) ([C6F13BF3–] moiety).
Received: 26th November 2008; Com. 08/3242
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