Interaction of the electrophilic bis(pentafluorophenyl)iodonium cation [(C6F5)2I]+ with the ambident pseudohalogenide anions [SCN]- and [CN]-

Article abstract of DOI:10.1016/j.jfluchem.2014.04.006

The iodonium pseudohalide compounds, [(C₆F₅) ₂I][X] (X = SCN and CN) were synthesized by means of fluoride substitution in [(C₆F₅)₂I][F] with the Lewis acidic reagents (CH₃)₃Si-NCS and (CH₃) ₃Si-CN. The isolated iodonium pseudohalides are intrinsically unstable solids. Decomposition resulted in equimolar amounts of C ₆F₅I and C₆F₅SCN or C ₆F₅I and C₆F₅CN, respectively. In case of [(C₆F₅)₂I][SCN] single crystals could be grown from CH₂Cl₂. The crystal structure revealed a dimer with an eight membered ring formed by two ambident anions bridging the iodine atoms of two cations by N and S coordination. The favored dimerization of [(C₆F₅)₂I][SCN] and [(C₆F ₅)₂I][CN] in the gas phase is supported by ab initio computations.

Full text of DOI:10.1016/j.jfluchem.2014.04.006

Journal of Fluorine Chemistry 163 (2014) 28–33
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Interaction of the electrophilic bis(pentafluorophenyl)iodonium
cation [(C6F5)2I]+ with the ambident pseudohalogenide anions
[SCN]ꢀ and [CN]ꢀ
a
Markus E. Hirschberg a,1, Peter Barthen a,2, Hermann-Josef Frohn a, , Dieter Bla¨ser ,
*
Briac Tobey b, Georg Jansen b
a Institute of Inorganic Chemistry, University of Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany
b
¨
Institute of Theoretical Chemistry, University of Duisburg-Essen, Universitatstr. 2, D-45117 Essen, Germany
A R T I C L E I N F O
A B S T R A C T
Article history:
The iodonium pseudohalide compounds, [(C6F5)2I][X] (X = SCN and CN) were synthesized by means of
fluoride substitution in [(C6F5)2I][F] with the Lewis acidic reagents (CH3)3Si–NCS and (CH3)3Si–CN. The
isolated iodonium pseudohalides are intrinsically unstable solids. Decomposition resulted in equimolar
amounts of C6F5I and C6F5SCN or C6F5I and C6F5CN, respectively. In case of [(C6F5)2I][SCN] single crystals
could be grown from CH2Cl2. The crystal structure revealed a dimer with an eight membered ring formed
by two ambident anions bridging the iodine atoms of two cations by N and S coordination. The favored
dimerization of [(C6F5)2I][SCN] and [(C6F5)2I][CN] in the gas phase is supported by ab initio
computations.
Received 25 March 2014
Received in revised form 8 April 2014
Accepted 9 April 2014
Available online 23 April 2014
Keywords:
Bis(pentafluorophenyl)iodonium salts
Anion metathesis
ß 2014 Published by Elsevier B.V.
Ambident pseudohalides
Molecular structure
Ab initio computations
1. Introduction
the organyl groups increases the electrophilicity of the iodonium
cation. Thus, the bis(pentafluorophenyl)iodonium cation is char-
Non-fluorinated iodonium salts belong to the class of polyvalent
iodine(III) compounds. First examples were very early synthesized
by Viktor Meyer in 1894, namely phenyl(p-iodophenyl)iodonium
salts with the anions Clꢀ, Brꢀ, Iꢀ, and NO3ꢀ [1]. Generally, iodonium
salts represent the most common type of iodine(III) compounds and
havefoundnumerousapplications, e.g. ascationicphotoinitiatorsor
as reagents in organic chemistry [2–6].
Non-fluorinated 1-alkynyl(phenyl)- and vinyl(phenyl)iodo-
nium salts, with thiocyanate anions are mentioned in literature
as intermediates for the synthesis of 1-alkynyl- and vinylthiocya-
nates, respectively [7,8]. Already in 1903 [3-CH3C6H4(4-
CH3C6H4)I][CN] was reported as a first example of an iodonium
salt with the cyanide anion and characterized by a m.p. of 104–
108 8C [9]. Salts with perfluoroorganyliodonium cations, [(RF)2I][X]
have been known for ca. 50 years [10]. Generally, perfluorination of
acterized by a significantly higher electrophilicity in relation to the
non-fluorinated diphenyliodonium cation, which is related to the
higher partial positive charge on iodine(III). Consequently, the
[(C6F5)2I]+ cation shows remarkable cation—anion contacts even in
combination with weakly coordinating anions such as [BF4]ꢀ [11].
In combination with anions of high nucleophilicity, molecular
species are accessible, e.g. in combination with Fꢀ the oligomeric
molecular compound {[(C6F5)2I][F]}n could be isolated.
{[(C6F5)2I][F]}n with a
c-octahedral molecular geometry, contains
two equivalent C6F5 groups and polar I–F bonds. In contrast,
(C6F5)3I with a [(C6F5)2I] fragment too, which is obtained from
{[(C6F5)2I][F]}n by F/C6F5 substitution, is an example for a
trigonal bipyramidal molecular geometry [12].
c-
In the present contribution, we continue our investigations of
bis(pentafluorophenyl)iodine compounds, which in the past
covered the fields of alternative synthetic approaches [13],
structural features [11], and electrochemical properties [14]. The
ambident anions Xꢀ (X = [SCN] and [CN]) possess one site with a
remarkable nucleophilicity. We describe the interaction of these
anions with the electrophilic [(C6F5)2I]+ cation as cation—anion
contacts, (C6F5)2I—X, but present their formula in the simplified
ionic way, [(C6F5)2I][X].
*
Corresponding author. Tel.: +49 2152 7868; fax: +49 2152 988349.
E-mail address: h-j.frohn@uni-due.de (H.-J. Frohn).
1
Present address: 3M-Dyneon GmbH, Industrieparkstr. 1, D-84508 Burgkirchen,
Germany.
2
Present address: Institute of Inorganic Chemistry, Heinrich-Heine-University,
D-40225 Du¨sseldorf, Germany.
http://dx.doi.org/10.1016/j.jfluchem.2014.04.006
0022-1139/ß 2014 Published by Elsevier B.V.

M.E. Hirschberg et al. / Journal of Fluorine Chemistry 163 (2014) 28–33
29
Scheme 1.
Scheme 2.
2. Results and discussion
<[C6F5]+> from the iodonium cation and addition of <[C6F5]+>
to the soft nucleophilic terminus of the ambident anions (Scheme
1). More likely, the reaction route will be initiated by an electron
transfer from the soft terminus of the anion to iodine(III) in the
cation. After fragmentation of the radical [(C6F5)2I]ꢃ into C6F5I (a
favored leaving group) and the [C6F5]ꢃ radical, the latter can add to
the pseudohalogen radical (Scheme 2).
The two products [(C6F5)2I][X] (X = CN and SCN) are intrinsi-
cally unstable, even in the solid state, and decompose under
formation of equimolar amounts of C6F5I and C6F5–CN or C6F5I and
C6F5–SCN, respectively (Schemes 1 and 2).
2.1. Syntheses of bis(pentafluorophenyl)iodonium thiocyanate and
cyanide
For the synthetic approach, [(C6F5)2I][Hal] (Hal = Cl, F) with a
diaryliodonium fragment was chosen and a Hal/X substitution step
(X = SCN or CN). The starting material [(C6F5)2I][F] was synthesized
in a good yield from C6F5IF2 and Bi(C6F5)3 in CH2Cl2 (Eq. 1) and
[(C6F5)2I][Cl] from the reaction of [(C6F5)2I][F] with (CH3)3SiCl in
CH2Cl2 (Eq. 2).
The easy decomposition in solution represented a challenge to
grow suitable single crystals. Fortunately, single crystals of
[(C6F5)2I][SCN] were obtained from CH2Cl2 solutions at 10 8C.
The attempt to get single crystals of [(C6F5)2I][CN] from CH2Cl2 or
CH3CN solutions at ꢀ10 to ꢀ20 8C failed.
CH2Cl2
3C6F5IF2 þ BiðC6F5Þ3 ꢀ! 3½ðC6F5Þ2Iꢁ½Fꢁ þ BiF3
(1)
½ðC6F5Þ2Iꢁ½Fꢁ þ ðCH3Þ3SiClCꢀH!2Cl2½ðC6F5Þ2Iꢁ½Clꢁ þ ðCH3Þ3SiF
(2)
The crystallographic data of [(C6F5)2I][SCN] are summarized in
Table 1. The unit cell contains 18 molecules, which are arranged to
9 dimers. In the dimer (Fig. 1), each iodonium cation is coordinated
by one N and S atom of the two bridging anions, which result in an
eight membered ring with IIII—S–C–N—IIII and N—IIII—S subunits.
The crystals of [(C6F5)2I][SCN] contain one symmetry independent
molecule with a [(C6F5)2I]+ cation that features an almost right C–
I–C angle (91.16(8)8). Each cation shows two contacts with I—N
For the synthesis of [(C6F5)2I][CN], two iodonium starting
materials were investigated. No reaction proceeded when
[(C6F5)2I][Cl] was treated with (CH3)3SiCN in CH2Cl2 at 20 8C
(Eq. 3). The reaction of [(C6F5)2I][F] with trimethylsilyl cyanide was
successful (Eq. 4a). Therefore, [(C6F5)2I][F] was also applied in the
reaction with trimethylsilyl isothiocyanate (Eq. 4b).
½ðC6F5Þ2Iꢁ½Clꢁ þ ðCH3Þ3SiCN ‰ ½ðC6F5Þ2Iꢁ½CNꢁ þ ðCH3Þ3SiCl
½ðC6F5Þ2Iꢁ½Fꢁ þ ðCH3Þ3SiCNCꢀH!2Cl2½ðC6F5Þ2Iꢁ½CNꢁ þ ðCH3Þ3SiF
(3)
˚
˚
and I—S distances of 2.668(2) A and 2.9361(6) A, respectively.
These distances are 24% and 22% shorter than the sum of van der
(4a)
20 ꢂ
C
˚
˚
Waals radii I–N (3.53 A) and I–S (3.78 A) [16] and 33% or 24% longer
than estimated I–N and I–S single bonds. The angle under which
the N- and S-terminus of the linear [SCN]ꢀ anion coordinates to IIII
differs significantly. The I—S–C angle was determined at 89.24(8)8
whereas the I—N–C angle was 162.7(2)8.
½ðC6F5Þ2Iꢁ½Fꢁ þ ðCH3Þ3Si-NCSCꢀH!2Cl2½ðC6F5Þ2Iꢁ½SCNꢁ þ ðCH3Þ3SiF (4b)
20 ꢂ
C
The F/CN substitution with the moderate Lewis acidic reagents
trimethylsilyl cyanide, (CH3)3Si–CN, and trimethylsilyl isothiocy-
anate, (CH3)3Si–NCS, can be described as an acid-assisted
nucleophilic substitution at the iodine(III)–fluorine bond. After
addition of the Lewis acidic reagent, the original suspension turned
into a solution which subsequently changed back to a suspension.
The driving force for these reactions is the high Si–F bond strength
(e.g. the bond dissociation energy for F–SiF3 is reported to 694 kJ/
mol) [15]) of the by-product, (CH3)3SiF. Both products,
[(C6F5)2I][X], (X = CN and SCN) were isolated as white solids.
The thermal decomposition of the neat products can be
described formally by two subsequent steps: elimination of
The anion in the I—SCN—I bridge deviates only negligible from
˚
linearity (178.3(2)8). Comparison of the C–S distance (1.655(2) A)
˚
and the C–N distance (1.154(3) A) in the bridging SCN anion with
˚
˚
typical C–S single (1.81 A) or C55S double (1.61 A) bonds and
˚
˚
typical C55N double (1.22 A) or triple CBB N (1.11 A) distances in
combination with the coordination angle to [(C6F5)2I]+ lead to the
valence bond representation [S55C55N]ꢀ.
The coordination of N and S on iodine in the approximately
square planar environment (
c-octahedral molecular geometry)
exerts influence on the opposite C–I bond. The distance C(8)–I
˚
(trans to I—S, coordination of soft sulfur) is elongated (2.118(2) A)

30
M.E. Hirschberg et al. / Journal of Fluorine Chemistry 163 (2014) 28–33
Table 1
Crystallographic and refinement data for [(C6F5)2I][SCN].
Compound
[(C6F5)2I][SCN]
Empirical formula
Crystal size (mm)
Crystal system
Space group
C13F10INS
0.37 mm ꢅ 0.12 mm ꢅ 0.10 mm
Trigonal
¯
R3
˚
Unit cell dimensions
a = 29.0436(19) A
a
b
= 908
= 908
˚
b = 29.0436(19) A
˚
c = 12.0175(8) A
g
= 1208
3
˚
Volume
8779.0(10) A
Z
18
Density (calculated)
Temperature
Radiation
1.767 g cmꢀ3
100(1) K
˚
MoK
(
l
= 0.71073 A)
a
F(0 0 0)
4392
1.40–30.558
R1 = 0.0289, wR2 = 0.0637
Theta range for data
Final R indices
Fig. 1. X-ray crystal structure of [(C6F5)2I][SCN]. Thermal ellipsoids are shown at the
˚
˚
50% probability level. Selected distances/A and angles/: I(1)–C(2) 2.100(2), I(1)–C(8)
2.118(2), C(1)–S(1) 1.655(2), C(1)–N(1) 1.154(3), I(1)—S(1) 2.9361(6), I(1)—N(1A)
2.668(2), C(2)–I(1)–C(8) 91.16(8), I(1)–S(1)–C(1) 89.24(8), S(1)–C(1)–N(1) 178.3(2),
I(1)–N(1A)–C(1A) 162.7(2).
relative to the C(2)–I distance (trans to I—N, coordination of hard
˚
nitrogen) of 2.100(4) A. The elongation of the C–I bond in trans-
position can be interpreted by a transfer of partial charge from S to
IIII cf. the proposed ET reaction path in Scheme 2.
The Raman bands in [(C6F5)2I][CN] at 197 cmꢀ1 and 2110 cmꢀ1
can be assigned to
191 cmꢀ1, 463 cmꢀ1, 747 cmꢀ1, and 2079 cmꢀ1 are characteristic
for [(C6F5)2I][SCN]. The band at 191 cmꢀ1 can be assigned to
(C–I).
Three fundamental vibrations exist for the linear NCS ligand (point
n(C–I) and to n(CBB N). The Raman bands at
Iodonium compounds [(C6F5)2I][X] with a strong cation—anion
interaction are soluble in coordinating and ‘‘non-coordinating’’
solvents and thus their 19F NMR data allow to conclude on the
molecular dispersed species in solution (Table 2). In contrast,
typical ionic iodonium salts, such as [(C6F5)2I][BF4] with a weakly
coordinating counter anion are insoluble in ‘‘non-coordinating’’
solvents such as CH2Cl2 (DN: 0 kJ/mol) [17]) but well soluble in
coordinating CH3CN (DN: 14.1 kJ/mol) [18]. In a CH3CN solution of
[(C6F5)2I][BF4] a weakly by acetonitril coordinated [(C6F5)2I]+
cation is present indicated by the F4 resonance at high frequency of
ꢀ141.4 ppm. The F4 resonance in [(C6F5)2I][SCN] in CH3CN is
significantly shifted to lower frequency indicative for a strong
anion coordination. Comparable 19F NMR data are obtained for
[(C6F5)2I][SCN] in CH2Cl2 solutions. All three 19F NMR signals of the
pentafluorophenyl groups appear in both solvents as well resolved
signals, which contrasts to [(C6F5)2I][CN], where all three signals of
the C6F5 groups appear as broad singlets (Dn1/2 ꢄ 63 Hz). The
absence of high resolved signals in combination with the low
solubility of [(C6F5)2I][CN] in both CH2Cl2 and CH3CN solvents
suggest an oligomeric structure in solution. The presence of one set
of four 19F NMR resonances for both C6F5 groups is in agreement
with a coordination number of 4 at iodine. Additionally, it is worth
mentioning that in [(C6F5)2I][CN] the F4 signal appears 6.4 ppm at
lower frequency relative [(C6F5)2I][BF4]. In [(C6F5)2I][CN] there is a
stronger cation—anion contact than in [(C6F5)2I][SCN], comparable
to that in [(C6F5)2I][F].
n
group C1V), namely the two stretching vibrations
and the twofold degenerated deformation mode
n
d
(CN) and
(SCN) [19]. The
n , n
(CN) is expected at 2079 cmꢀ1 (CS) at 747 cmꢀ1, and
n(CS)
vibration
(SCN) at 463 cmꢀ1
[(C6F5)2I][SCN] and [(C6F5)2I][CN] are intrinsically unstable,
d
.
even in the solid state. [(C6F5)2I][SCN] shows a sharp decomposi-
tion point at 148 8C. Decomposition in a sealed glass capillary
under dry Ar at 150 8C gave C6F5SCN [20] and C6F5I in a 1:1 molar
ratio.
[(C6F5)2I][CN] – like fluoroaryliodine dicyanides [21] – has no
melting point and decomposes at 94 8C. Decomposition in a sealed
glass capillary at 94 8C under dry Ar resulted in C6F5CN [22] and
C6F5I in a 1:1 molar ratio.
Ab initio computations were performed on the RHF level using
the LANL2DZ basis set to obtain bond distances and angles and
natural population analysis charges for the monomeric gas phase
molecules (C6F5)2I–NCS (1), (C6F5)2I–SCN (2), (C6F5)2I–CN (3), and
(C6F5)2I–NC (4) (1–4: see Fig. A in Table 3) and for the dimeric gas
phase molecules {(C6F5)2I–NCS–(C6F5)2I–SCN-} (5, see Fig. B in
Table 3) and {(C6F5)2I–CN–(C6F5)2I–NC–} (6, see Fig. B in Table 3).
Important bond distances and angles and natural population
analysis charges are compiled in Tables 3 and 4.
Table 2
19F NMR shift values
d/ppm of [(C6F5)2I][SCN], [(C6F5)2I][CN], [(C6F5)2I][F], [(C6F5)2I][Cl], and [(C6F5)2I][BF4] in CH2Cl2 and CH3CN.
Compound
Solvent
Temp. (8C)
F2,6 (ppm)
F4 (ppm)
F3,5 (ppm)
[(C6F5)2I][SCN]
CH2Cl2
CH3CN
0
0
ꢀ123.7
ꢀ123.4
ꢀ144.7
ꢀ145.3
ꢀ156.6
ꢀ156.5
a
[(C6F5)2I][CN]
[(C6F5)2I][F]
[(C6F5)2I][Cl]
CH2Cl2
ꢀ10
ꢀ40
ꢀ125.5
ꢀ125.5
ꢀ147.9
ꢀ148.0
ꢀ158.5
ꢀ157.5
CH3CNa
CH2Cl2
CH3CN
24
24
ꢀ124.4
ꢀ124.4
ꢀ147.8
ꢀ148.3
ꢀ158.3
ꢀ158.1
CH2Cl2
CH3CN
24
24
ꢀ122.9
ꢀ124.0
ꢀ144.6
ꢀ146.2
ꢀ156.3
ꢀ156.9
[(C6F5)2I][BF4][11]b
CH3CN
24
ꢀ120.4
ꢀ141.4
ꢀ155.7
a
Broad singlets (Dn1/2 ꢄ 63 Hz).
b
This ionic compound is insoluble in CH2Cl2 at 24 8C.

M.E. Hirschberg et al. / Journal of Fluorine Chemistry 163 (2014) 28–33
31
Table 3
ꢀ
Calculateda bond distances/A, angles/8, and natural population analysis charges NC/e of [(C6F5)2I]+ compounds with ambident anions Xꢀ
.
˚
{[(C6F5)2I]X}n
Figure C1–I
C7–I
A(C1–I–C7 A(C2–C1–C6 A(C8–C7–C12 D(C1–I–C7–C8) D(C7–I–C1–C2) NC(C1) NC(Ar1) NC(C7) NC(Ar2) NC(I)
X = NCS, n = 1
X = SCN, n = 1
X = SCN, n = 2d
X = CN, n = 1
X = NC, n = 1
X = CN, n = 2e
A
A
B
A
A
B
2.091b 2.176c 89.07
2.095b 2.175c 90.20
119.10
119.21
118.16
118.99
118.96
118.44
117.05
117.64
118.41
116.61
116.69
117.76
121.08
121.46
113.52
124.23
122.54
116.36
108.71
107.94
108.68
107.04
108.52
113.19
ꢀ0.405 ꢀ0.188
ꢀ0.424 ꢀ0.164
ꢀ0.497 ꢀ0.404
ꢀ0.464 ꢀ0.348
1.426
1.224
2.108
2.112
92.04
ꢀ0.454 ꢀ0.269d ꢀ0.429 ꢀ0.250d 1.365
2.095b 2.245c 86.48
2.092b 2.210c 87.43
2.098e 2.130e 92.07
ꢀ0.412 ꢀ0.202
ꢀ0.406 ꢀ0.207
ꢀ0.429 ꢀ0.243
ꢀ0.507 ꢀ0.489
ꢀ0.505 ꢀ0.459
ꢀ0.463 ꢀ0.318
1.307
1.434
1.408
a
RHF level, LANL2DZ basis set.
b
c
Aryl group in the equatorial position of the
c-tbp moiety of iodine (Fig. A, idealized).
c-tbp moiety of iodine (Fig. A, idealized).
Aryl group in the axial position of the
d
e
Two SCN anions bridge ambidently two iodonium cations: C1 (Ar1) is trans to the nitrogen contact, C7 (Ar2) is trans to the sulfur contact.
Two CN anions bridge ambidently two iodonium cations: C1 (Ar1) is trans to the carbon contact, C7 (Ar2) is trans to the nitrogen contact.
C6
C1
C6
C1
C8
C7
X
X
C2
C12
C12
C2
C2
C12
I
I
I
C7
C8
C7
C8
C
X'
C6
A
B
Table 4
ꢀ
Calculateda cation—anion contacts/A, angles/8, and natural population analysis charges NC/e of [(C6F5)2I]+ compounds with ambident anions Xꢀ.
˚
{[(C6F5)2I]X}n
Figure
I—X
I—X0
A(X—I–C1)
A(X—I–C7)
A(X0—I–C1)
A(X0—I–C7)
A(X—I—X0)
NC(X)
NC(X0)
X = NCS, n = 1
X = SCN, n = 1f
X = SCN, n = 2
X = CN, n = 1
X = NC, n = 1
X = CN, n = 2
A
A
B
A
A
B
2.267
2.963
2.649h
2.299
2.197
2.962p
–
79.59
84.13
169.5j
81.78
80.91
175.68
168.58
174.24
77.7k
–
–
–
–
–
ꢀ0.834e
ꢀ0.713g
ꢀ0.846l
ꢀ0.617n
ꢀ0.768o
0.051
–
–
–
79.2
–
–
3.219i
170.6
–
111.2
–
ꢀ0.846m
–
168.20
168.28
92.03
–
–
–
–
–
–
2.499q
173.22
81.24
94.65
ꢀ0.899
a
RHF level, LANL2DZ basis set.
e
f
NC(N) = ꢀ0.908, NC(C) = 0.350, NC(S) = ꢀ0.276.
A(I—S–C) = 98.38.
g
h
i
NC(S) = ꢀ0.355, NC(C) = 0.123, NC(N) =ꢀ0.481.
I—N cation—anion contact; A(I—N–C) = 157.58.
I—S cation—anion contact; A(I—S–C) = 93.08.
A(C1–I— N).
j
k
l
A(C7–I— N).
NC(N) = ꢀ0.718, NC(C) = 0.284, NC(S) =ꢀ0.412.
NC(S) = 0.412, NC(C) = 0.284, NC(N) = ꢀ0.718.
NC(C) = ꢀ0.205, NC(N) = ꢀ0.412.
m
n
o
p
q
NC(N) = ꢀ1.081, NC(C) = 0.313.
I—C cation—anion contact; A(I—C–N) = 119.88.
I—N cation—anion contact; A(I—N–C) = 145.58.
The calculated bond distances and angles for 1–4 are
of both bridging SCN ligands in the solid state structure is also
found in the gas state, even though with slight deviations: A(I—S–
C) 89.24(1)8 vs. 93.08 and A(I—N–C) 162.7(2)8 vs. 157.5. In 5 the
value of the partial positive charge on iodine is situated between
that of the monomeric isomers 1 and 2. In agreement with a nearly
discussed regarding their approximate
˚
c-tbp molecular geome-
try. The I—N distance in 1 (2.267 A) is significantly longer than in
7
˚
4 (2.197 A) and the corresponding I–C bond in trans-position
shorter, respectively. The triad C7–I—N behaves like an
asymmetric hypervalent bond. The partial positive charge on
iodine in 1 and 4 is higher than in their isomers 2 and 3 with I—S
and I—C contacts. In agreement with the concept of hyperva-
lency the partial charge as well of the aryl group, Ar2, in trans-
position of 1–4 as of the ipso-carbon atom, C7, is more negative
than that of Ar1 and C1, respectively. I—S in 2 was determined at
c
-octahedral molecular geometry of 5 the negative partial charge
of the aryl groups Ar1 and Ar2 is of similar quantity.
Dimer 6 contains a central six membered nearly planar (D(I–C–
N–I) = 1.58) ring with two CN ligands and two iodine atoms. The
coordination of N on I resembles a sp2 hybridized C-atom, whereas
the angle I—N–C was determined at 145.58. The angles A(C1–I–
2.963 A. The distance I—CN (2.299 A) in 3 is only slightly longer
C7) = 92.18 and A(NC—I—N) = 94.78 fit well with the
molecular geometry of 6.
c-octahedral
˚
˚
than I–C7 in trans-position (2.245 A), but significantly longer
than I–C1 (2.095 A).
˚
˚
The total energy of monomer 1 with the more polar I—N contact
(partial charges: I = 1.426 eꢀ, N = ꢀ0.908 eꢀ) compared to
monomer 2 with I—S (partial charges: I = 1.224 eꢀ, S = ꢀ0.355
eꢀ) is 19.8 kJ/mol lower. Dimerization of 1 or 2 is accompanied by a
win of energy of 125.1 or 164.8 kJ/mol, respectively, and explains
the dimerization of 5 in the solid state. Furthermore, the thermal
decomposition in the solid state under formation of equimolar
amounts of C6F5SCN and C6F5I becomes plausible when an electron
The dimers 5 and 6 are discussed regarding their
c-octahedral
molecular geometry. In dimer 5, the two bridging SCN ligands and
the two iodine centers form a planar eight membered ring. In 5 the
˚
I—N distance (2.649 A) is strongly elongated with respect to
˚
monomer 1 (2.267 A). It fits satisfactorily with the value in the
˚
crystal structure (2.668(2) A) whereas the I—S distance is over-
estimated. The different coordination modus of sulfur and nitrogen

32
M.E. Hirschberg et al. / Journal of Fluorine Chemistry 163 (2014) 28–33
transfer proceeded from (soft and easy oxidizable) S to IIII in the
dimer 5.
corresponding to highly disordered dichloromethane and acetoni-
trile molecules. The peaks attributed to chlorine and three to carbon
A qualitatively similar but quantitatively less distinct trend is
found for 3, 4, and 6. Monomer 4 with a I—N contact is favored over
3 with a I—C contact by only 13.3 kJ/mol. Dimerization of 3 and 4 to
6 is accompanied by a win of total energy of 91.6 kJ/mol and
65.0 kJ/mol, respectively.
atoms result in R1 = 0.0562.
3
˚
The SQUEEZE refinement revealed voids with volumes of 800 A
at the positions 0,0,0; 1/3, 2/3, 0.58; and 2/3, 1/3, 0.25
corresponding to 337 electrons each [24].
Crystal structure data have been deposited at the Cambridge
Crystallographic Data Centre (CCDC). Enquiries for data can be
directed to Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge, U.K., CB2 1EZ or (e-mail) deposit@ccdc.cam.ac.uk
or (fax) +44 (0) 1223 336033. Any requests sent to the Cambridge
Crystallographic Data Centre for this material should quote the full
literature citation and the reference number CCDC 989837.
DSC analyses were performed on a Netzsch 204 Phoenix
instrument equipped with a CC220 controller; a TASC414/3A
microprocessor system, and a personal computer. The solid
samples (ca. 5 mg) were weighed in aluminum pans and closed
by a pierced aluminum lid inside a glove box. The temperature
difference between the sample and the empty reference pan with a
pierced lid was measured choosing a temperature program of 10 K/
min. The raw data were processed using the Netzsch Proteus
Software Version 4.2.
3. Conclusions
Iodonium salts with the strongly oxidizing cation [(C6F5)2I]+
form in combination with the ambident pseudohalide anions
[SCN]ꢀor [CN]ꢀ in solution and in the gas phase oligomeric species
with a c-octahedral molecular geometry. In case of [(C6F5)2I][SCN],
a dimer was verified in the solid state by its single crystal structure.
In the gas phase, the dimers are energetically favored over the
monomeric isomers with
c-trigonalbipyramidal molecular geom-
etry. The monomers with the more polar I—N contact show a lower
total energy than those with I—S or I—C contacts. Dimerization in
the gas phase comes along with a remarkable win of energy and
explains the high tendency to dimeric or oligomeric arrangements
in solid state and in solution. The clear reaction path in the thermal
decomposition of the neat iodonium compounds under formation
of equimolar amounts of C6F5I and C6F5SCN or C6F5CN, respective-
ly, becomes plausible for the dimeric structure, which enables an
electron transfer from the soft terminus of the ambident anion to
IIII. Fragmentation of the [(C6F5)2I]ꢃ radical into C6F5I and the
[C6F5]ꢃ radical is followed by combination of the [C6F5]ꢃ and [X]ꢃ
radical in neighborhood or in the solvent cage.
4.2. Synthesis of [(C6F5)2I][F]
A solution of C6F5IF2 (1.294 g, 3.898 mmol) in CH2Cl2 (3 mL)
was added to an intensively stirred solution of Bi(C6F5)3 (0.927 g,
1.307 mmol) in CH2Cl2 (20 mL) in an FEP trap (di = 23 mm). After
1 h, a solution of NaF (0.42 g, 10 mmol) in H2O (10 mL) was added
to the colorless solution. The stoppered trap was shaken
intensively. At first, two ‘‘liquid’’ phases resulted, a turbid, colorless
upper and a yellow-greenish lower which contained a white solid.
Thereafter, the system changed into a three phase one with a
colorless aqueous upper phase, a jellylike middle, and a colorless
organic lower phase. At first, ca. 90% of the lower phase were
carefully separated. Further, the remaining phases were 3-times
extracted with CH2Cl2 (each 10 mL). The combined organic phases
were washed with H2O (8 mL) and cooled to ꢀ78 8C. A white solid
precipitated which was isolated and washed in sequence with
CH2Cl2 and n-pentane (each 10 mL) at ꢀ60 8C. Afterwards
crystallization from CH2Cl2 (each 3 mL, from 20 8C to ꢀ80 8C)
was performed twice. Finally, the crystals were washed with n-
pentane (2 mL) and dried in vacuum (0.05 hPa, 20 8C, 3 h; 100 8C,
1 h; 100–135 8C, 40 min).
4. Experimental part
4.1. General
Moisture sensitive compounds were handled under an atmo-
sphere of dry argon. Reactions which were not corrosive for SiO2
surfaces were carried out in standard glass equipment. Fluoro
compounds which can undergo hydrolysis were handled in traps
made from FEP tubes (outer/inner diameters: o.d. = 4.1 mm,
i.d. = 3.5 mm, o.d. = 9.0 mm, i.d. = 8.0 mm, or o.d. = 25 mm,
i.d. = 23 mm). CH3CN (KMF) was purified by reflux and distillation
in sequence over KMnO4 and P4O10, respectively. CH2Cl2 (KMF)
was washed in sequence with conc. H2SO4, aq solutions of Na2CO3,
and H2O. Finally, it was refluxed and distilled from P4O10
.
(CH3)3SiCl (Janssen Chimica, >97%) was distilled under dry Ar
before use. (CH3)3SiCN was synthesized by literature procedure
[23]. Trimethylsilyl isothiocyanate, (CH3)3SiNCS (ACROS ORGAN-
ICS), was used as delivered.
Yield 91% (1.703 g, 3.458 mmol). Dec. 203 8C (vis.); 212 8C (DSC,
exothermic, TOnset). 19F NMR (CH2Cl2, 24 8C)
d
ꢀ12.5 (s, Dn1/2
= 11 Hz, 1F, IF), ꢀ124.4 (m, 4F, F2,6
,
C6F5), ꢀ147.8 (t,
3J(F4,F3,5) = 20 Hz, 2F, F4, C6F5), ꢀ158.3 (m, 4F, F3,5, C6F5). 19F
NMR spectra were recorded on a Bruker spectrometer AVANCE
300 (19F at 282.40 MHz). The chemical shifts were referenced to
NMR (CH3CN, 24 8C)
d
ꢀ10.3 (s, Dn1/2 = 24 Hz, 1F, IF), ꢀ124.4 (m,
4F, F2,6, C6F5), ꢀ148.3 (t, 3J(F4,F3,5) = 21 Hz, 2F, F4, C6F5), ꢀ158.1 (m,
4F, F3,5, C6F5). Raman (20 8C) cmꢀ1 72 (13), 84 (14), 114 (7), 125
(14), 159 (5), 176 (7), 196 (34), 230 (4), 255 (5), 280 (12), 352 (23),
386 (40), 441 (32), 492 (100), 586 (39), 615 (4), 720 (2), 772 (2), 797
(9), 803 (11), 1089 (8), 1144 (4), 1516 (3), 1635 (9).
CCl3F (19F) (C6F6 as a secondary reference,
d
= ꢀ162.9 ppm). Raman
spectra were recorded on the Bruker FT-Raman spectrometer RFS
100/S using the 1064 nm line of a Nd/YAG laser. The back-scattered
(1808) radiation was sampled and analyzed (Stoke range: 50–
4000 cmꢀ1). The samples were placed in glass capillaries.
X-ray diffraction data were collected at 100 ꢆ 1 K using a Bruker
D8 KAPPA series II diffractometer equipped with an APEX II area
detector system. Crystal structure solution by Direct Methods and
refinement on F2 were performed using the Bruker AXS SHELXTL
software suite Version 2008/4/ß 2008 after data reduction and
empirical absorption correction was performed using the Bruker AXS
APEX 2 program Version 3/2009. For crystallographic and refinement
details see Table 1.
A small quantity of [(C6F5)2I][F] was decomposed in a sealed
glass capillary under dry Ar when heated up to 220 8C. After cooling
to 20 8C, the content of the capillary was dissolved in CH2Cl2. The
products C6F5I and C6F6 and the molar ratio 1:1 were proven by 19
NMR spectroscopy.
F
4.3. Synthesis of [(C6F5)2I][Cl]
(CH3)3SiCl (50
mL, 0.39 mmol) dissolved in CH2Cl2 (2 mL) was
The refinement was performed with ‘solvent-free reflection data’
following PLATON/SQUEEZE run. A refinement of the untreated
reflection data set produces several peaks with 2.5–4.3 e\A3
added to a suspension of [(C6F5)2I][F] (0.130 g, 0.271 mmol) in
CH2Cl2 (4 mL) at 20 8C. A solution was formed. After 10 min, a
white solid precipitated and the supernatant was separated. The

M.E. Hirschberg et al. / Journal of Fluorine Chemistry 163 (2014) 28–33
33
white solid was washed with n-pentane (4 mL) and dried in
vacuum (0.05 hPa, 20 8C, 1 h).
(tt, 3J(F4,F3,5) = 21 Hz, 4J(F4,F2,6) = 5 Hz, 2F, F4, C6F5), ꢀ156.6 (m, 4F,
F
3,5, C6F5). 19F NMR (CH3CN, 0 8C)
d
ꢀ123.4 (m, 4F, F2,6, C6F5),
Yield 91% (0.122 g, 0.246 mmol). Dec. (vis.) 231 8C. 19F NMR
ꢀ145.3 (t, 3J(F4,F3,5) = 20 Hz, 2F, F4, C6F5), ꢀ156.5 (m, 4F, F3,5, C6F5).
(CH2Cl2, 24 8C)
d
ꢀ122.9 (m, 4F, F2,6
,
C6F5), ꢀ144.6 (t,
Ra (20 8C) cmꢀ1 85 (27), 103 (32), 156 (18), 191 (100)
n(C–I), 237
3J(F4,F3,5) = 20 Hz, 2F, F4, C6F5), ꢀ156.3 (m, 4F, F3,5, C6F5); 19F
(6), 278 (12), 349 (31), 387 (13), 440 (5), 463 (4), 490 (49), 584 (8),
609(3), 716 (2), 747 (3), 788 (38), 802 (7), 1086 (15), 1286 (7), 1394
(18), 1408 (7), 1513 (2), 1634 (3), 2079 (46) n(CN).
A small amount of [(C6F5)2I][SCN] was decomposed in a sealed
glass capillary under dry Ar when heated up to 150 8C. After cooling
to 20 8C, the content in the capillary was dissolved in CH2Cl2. The
products C6F5SCN [20] and C6F5I were determined by 19F NMR
spectroscopy. They were present in a 1:1 molar ratio.
NMR (CH3CN, 24 8C)
d
ꢀ124.0 (m, 4F, F2,6, C6F5), ꢀ146.2 (tt,
3J(F4,F3,5) = 20 Hz, 4J(F4,F2,6) = 3 Hz, 2F, F4, C6F5), ꢀ156.9 (m, 4F, F3,5
,
C6F5). Raman (20 8C) cmꢀ1 73 (35), 83 (38), 101 (49), 118 (24), 176
(33), 194 (96), 234 (8), 280 (17), 351 (49), 385 (39), 440 (15), 491
(100), 584 (21), 618 (8), 715 (3), 790 (33), 1086 (20), 1286 (7), 1394
(7), 1634 (5).
A small amount of [(C6F5)2I][Cl] was decomposed in a sealed
glass capillary under dry Ar by heating up to 235 8C. After cooling to
20 8C, the product was dissolved in CH2Cl2 and C6F5I and C6F5Cl
(molar ratio 1:1) were determined by 19F NMR spectroscopy.
Acknowledgement
We gratefully acknowledge financial support by the Fonds der
Chemischen Industrie.
4.4. Synthesis of [(C6F5)2I][CN]
(CH3)3Si–CN (55
mL, 0.412 mmol) dissolved in CH2Cl2 (0.8 mL)
was added to a suspension of [(C6F5)2I][F] (0.114 g, 0.237 mmol) in
CH2Cl2 (2 mL) at 20 8C. A solution occurred immediately. After
2 min, a white solid precipitated. After 20 min, the supernatant
became pale yellow and was separated. The white solid was
washed with n-pentane (2 mL) and dried in vacuum (0.05 hPa,
20 8C, 20 min).
References
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[2] T. Umemoto, Chem. Rev. 96 (1996) 1757–1777.
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Yield 88% (0.102 g, 0.209 mmol). Dec. 94 8C (DSC, exothermic,
TOnset). 19F NMR (CH2Cl2, ꢀ10 8C)
d
ꢀ125.5 (br, Dn1/2 = 63 Hz, 4F, F2,6
,
=
C6F5), ꢀ147.9 (br, Dn1/2 = 70 Hz, 2F, F4, C6F5), ꢀ158.5 (br, Dn1/2
69 Hz, 4F, F3,5, C6F5). 19F NMR (CH3CN, ꢀ40 8C)
d
ꢀ125.5 (br, Dn1/2
= 106 Hz, 4F, F2,6, C6F5), ꢀ148.0 (br, 2F, F4, C6F5), ꢀ157.5 (br, Dn1/2
=
111 Hz, 4F, F3,5, C6F5). Raman (20 8C) cmꢀ1 84 (70), 118 (22), 137 (53),
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2419–2427.
168 (69), 177 (63), 197 (100) n(C–I), 212 (23), 231 (10), 279 (18), 348
(31), 354 (36), 388 (43), 442 (32), 490 (91), 534 (4), 586 (29), 611 (5),
779 (23), 805 (15), 1080 (9), 1093 (12), 1277 (11), 1386 (8), 1635 (9),
[12] H.-J. Frohn, P. Barthen, F. Bailly, K. Koppe, in: Proceedings of the First International
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764–770;
2110 (97) n(CN).
A small sample of [(C6F5)2I][CN] was decomposed under dry Ar
in a sealed glass capillary by heating up to 94 8C. After cooling to
20 8C the content of the capillary was dissolved in CH2Cl2. The
products C6F5CN [22] and C6F5I were formed in a 1:1 molar ratio
(e) M.E. Hirschberg, A. Wenda, H.-J. Frohn, N.V. Ignat’ev, J. Fluorine Chem. 138
(2012) 24–27;
(f) H.-J. Frohn, V.V. Bardin, Inorg. Chem. 51 (2012) 2616–2620.
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Stuttgart, New York, 1982.
[20] R.J. Neil, M.E. Peach, J. Fluorine Chem. 1 (1971/72) 257–267.
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(2008) 2539–2550.
[22] L.N. Pushkina, A.P. Stepanov, V.S. Zhukov, A.D. Naumov, Org. Magn. Reson. 4
(1972) 607–623.
(
19F NMR).
4.5. Synthesis of [(C6F5)2I][SCN]
(CH3)3Si–NCS (20 L, 0.142 mmol) dissolved in CH2Cl2 (0.5 mL)
m
was added to a suspension of [(C6F5)2I][F] (0.050 g, 0.104 mmol) in
CH2Cl2 (0.4 mL) at 20 8C. Spontaneously, a yellow solution was
formed. After 5 min a white solid precipitated. After 1 h, the
supernatant was separated. The white solid was washed with n-
pentane (1.2 mL) and dried in vacuum (0.05 hPa, 20 8C, 30 min).
Yield 50% (0.027 g, 0.052 mmol). Dec. 148 8C (DSC, exothermic,
[23] M.T. Reetz, I. Chatziiosifidis, Synthesis 1982 (1982) 330.
[24] A.L. Spek, Acta Cryst. A46 (1990) C-34.
TOnset). 19F NMR (CH2Cl2, 0 8C)
d
ꢀ123.7 (m, 4F, F2,6, C6F5), ꢀ144.7