Supramolecular Aggregation of Perfluoroorganyl Iodane Reagents in the Solid State and in Solution

Article abstract of DOI:10.1002/ejoc.201800358

The crystal structures of different perfluoroorganyl iodanes are described, including those of four new benziodoxole derivatives with R_F = n-C₃F₇, n-C₄F₉, n-C₈F₁₇, and C₆F₅. In all of the compounds, the iodine atom shows significant Lewis acidity, and the fourth coordination site is readily filled by secondary bonding interactions to produce square-planar coordination. Although this geometry is a good model for benziodoxoles, benziodoxolone derivatives tend to aggregate further through additional weak I···O or I···aryl contacts. The different interactions lead to the formation of various assemblies with different dimensions in the solid state. The protonation of the reagents results in the formation of entirely different supramolecular structures, which are supported by hydrogen bonding. The structural features of the reagents in the solid state reflect well their behavior in solution, and the I–C(R_F) bond is influenced by the coordination of Lewis basic solvents to the iodine atom and by hydrogen bonding with protic solvents. These solvent effects are more pronounced for reagents containing the trifluoromethyl fragment than for derivatives with longer R_F chains.

Full text of DOI:10.1002/ejoc.201800358

A Journal of
Accepted Article
Title: Supramolecular Aggregation of Perfluoroorganyl Iodane
Reagents in the Solid State and in Solution
Authors: Antonio Togni, Phil Liebing, Ewa Pietrasiak, Elisabeth Otth,
Jorna Kalim, and Dustin Bornemann
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201800358
Link to VoR: http://dx.doi.org/10.1002/ejoc.201800358
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
Supramolecular Aggregation of Perfluoroorganyl Iodane
Reagents in the Solid State and in Solution
Phil Liebing,[a] Ewa Pietrasiak,[a] Elisabeth Otth,[a] Jorna Kalim,[a] Dustin Bornemann,[a] and Antonio
Togni*[a]
Abstract: The crystal structures of different perfluoroorganyl
iodanes are described, including four new benziodoxole derivatives
with RF = nC3F7, nC4F9, nC8F17 and C6F5. In all compounds, the iodine
atom shows significant Lewis acidity, and the fourth coordination site
is readily filled by secondary bonding interactions, giving rise to a
square-planar coordination. While the latter is a good model for
benziodoxoles, benziodoxolone derivatives tend to further
aggregation by additional weak I∙∙∙O or I∙∙∙Aryl contacts. The different
interactions lead to the formation of various assemblies with different
dimensions in the solid state. Protonation of the reagents results in
formation of entirely different supramolecular structures, which are
supported by hydrogen bonding. The structural features of the
reagents in the solid state reflects well the behavior in solution, and
the I-C(RF) bond is influenced by coordination of Lewis-basic
solvents to iodine and by hydrogen bonding with protic solvents.
These solvent effects are more pronounced in reagents containing
the trifluoromethyl fragment than in derivatives with longer RF chains.
well as an acid reagent with the nC3F7 group (3).[9] Reagents for
the transfer of long perfluoroalkyl chains are interesting for
potential applications in material sciences, e.g. for the
development of coatings and organic electronics,[10] as well as
liquid crystals.[11] Therefore, we decided to prepare derivatives
with extended RF groups and to study their structures and
properties. Furthermore, we were interested in the question if
corresponding reagents with perfluoroaryl groups are accessible
using known synthetic strategies.
For the preparation of acid- and alcohol-type perfluoroalkyl
iodane reagents, different protocols exist, all employing a silane
as a perfluoroalkyl source. The trifluoromethyl acid reagent 1 is
most conveniently prepared in a one-pot procedure, including
chlorine-fluorine exchange from the corresponding chloroiodane
with potassium fluoride, and reaction of the in situ formed
fluoroiodane with Me3SiCF3 (Scheme 1a).[12] The C2F5 (2)[7] and
n-C3F7 acid reagent (3)[9] have been prepared from the
corresponding acetoxyiodane (Scheme 1b). A key precursor for
the preparation of alcohol reagents with various perfluoroalkyl
groups (4–8) is the corresponding fluoroiodane. As this
compound is more stable than the acid analog, it can be isolated
and used for further derivatization.[2,5,13] The fluorine atom is
readily substituted by a perfluoroalkyl group upon reaction with
the corresponding silane and an appropriate fluoride catalyst
such as tetrabutylammonium difluorotriphenylsilicate (TBAT) in
dry acetonitrile. We show here that this method is also well
suited for the preparation of the pentafluorophenyl (C6F5)
substituted derivative 9 (Scheme 1c).[2]
Introduction
Hypervalent iodine reagents for electrophilic perfluoroalkylation
are readily accessible, bench-stable crystalline solids. The first
developed and most popular members of this reagent class are
1-(trifluoromethyl)-1,2-benziodoxol-3(1H)-one (“acid reagent”, as
derived from ortho-iodobenzoic acid; 1)[1,2] and trifluoromethyl-
1,3-dihydro-3,3-dimethyl-1,2-benziodoxole (“alcohol reagent”, as
derived from a tertiary alcohol; 4).[2,3] The versatility of these
reagents has been widely demonstrated in perfluoroalkylations
of various organic substrates.[2] Very recently, we demonstrated
that this class of reagents is also suitable for oxidative
perfluoroalkylation of cobalt(II) complexes.[4] In the past five
years, the library of iodane reagents has continuously been
growing and now includes acid and alcohol reagents with
functionalized CF2CF2X moieties (X = e.g. OAr, SAr, pyrazolyl).[5]
Furthermore, we have shown that acid reagent analogs
containing a hypervalent atom other than iodine are accessible,
namely with tellurium. This reagent class is compatible with new
fluorinated substituents, e.g. CHF2 and C6F5.[6] However,
knowledge regarding the preparation, molecular structures, and
reactivity of iodane reagents with “simple” perfluoroalkyl chains
is still very limited. Acid and alcohol reagents with the C2F5
group (2, 5) have been briefly mentioned in the literature,[7, 8] as
F3C
I
O
I
a) Cl
O
1) excess KF, MeCN
2) RF SiMe3
O
O
O
1
I
O
b)
c)
I
RF
AcO
O
RF SiMe3, cat. CsF
MeCN
O
2
3
(RF = C2F5)
(RF = n-C3F7)
F
I
O
Me
4 (RF = CF3)
Me
5 (RF = C2F5)
6 (RF = n-C3F7)
7 (RF = n-C4F9)
I
O
RF
[a]
P. Liebing, E. Pietrasiak, E: Otth, J. Kalim, D. Bornemann, A. Togni*
Department of Chemistry and Applied Biosciences
Swiss Federal Institute of Technology, ETH Zurich
Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
E-mail: antonio.togni@inorg.chem.ethz.ch
RF SiMe3,
Me
8
9
(RF = n-C8F17)
(RF = C6F5)
cat. TBAT,
MeCN
Me
Web: http://www.tognigroup.ethz.ch/
Scheme 1. Common synthetic routes to perfluoroorganyl iodanes of the acid
reagent (a and b; 1–3) and the alcohol reagent family (c; 4–9).
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
A characteristic structural feature of both acid and alcohol
reagents is a T-shaped coordination of the iodine atom by the
perfluoroalkyl group, an oxygen atom and an aryl substituent.[1–
3,5,8] Typical for the iodane reagents is a significant Lewis acidity,
which has been traced back to a σ-hole at the iodine atom.[14]
This finding agrees well with the crystal structures of many
oxygen containing compounds of trivalent iodine, where the
fourth coordination site is occupied by short I∙∙∙O contacts to
adjacent molecules.[15–17] Thereby, a square-planar coordination
of the iodine atom is highly favored, which suggests comparison
with structurally related metal compounds such as gold(III)
complexes. In the latter, the Au atom is well-known to display a
square-planar coordination with four ligands, but additionally the
fifth and the sixth coordination site are readily occupied in the
crystalline state by secondary bonding interactions with free
donor moieties (Scheme 2a).[18–20] For this reason, we wondered
if similar additional bonding interactions are relevant for trivalent
iodine, formally leading to penta- or hexa-coordination of the
latter. Thus, it could be meaningful to distinguish between
“secondary” bonding interactions (i.e. the occupancy of the
fourth coordination site leading to square-planar coordination)
and “tertiary” bonding interactions, i.e. the occupancy of further
coordination sites by even weaker iodine-donor contacts
(Scheme 2b).
to dynamic exchange of coordinated solvent molecules.
Moreover, it has been shown that acid reagent 1 can be
activated by nucleophiles such as iodide[21] and tertiary
amines.[22] In the latter contribution, the existence of a distinct
1
Lewis acid-base adduct was supported by H NMR titration, but
the formation constant of such an adduct with N-
methylmorphiline has been determined to be quite low at 3.83
l/mol.[22] In contrast, it has been found in our group that alcohol
reagent 4 forms more stable adducts with Lewis acids, based on
the oxygen atom as a nucleophilic functionality. For instance, the
formation constant of an 1:1 adduct with ZnBr2 has been
determined to be 234(25) l/mol.[23] A similar behavior is reported
for an acid reagent related to 1, forming a crystalline 2:1
complex with Zn(OTf)2 under coordination of the exposed
carbonyl oxygen atom.[2,24,25] Moreover, several examples for a
clean protonation of both acid and alcohol reagents with strong
acids have been reported, revealing fairly stable iodonium
salts.[2,25–29] For instance, 1 forms an adduct with one equiv.
H[SbF6], [1-H][SbF6],[26,27] while protonation of
“Brookhart’s acid” [H(OEt)2]BArF (BArF Tetrakis(3,5-bis-
4
with
=
(trifluoromethyl)phenyl)borate)[30] furnishes the mixed-protonated
salt [(4)2H]BArF.[2,25] Both species have been briefly mentioned
in previous review articles, and we now provide the full
characterization thereof, together with the new triflimide salt [4-
H]NTf2.[27]
Since the crystal structures of literature-known iodane reagents
have not been evaluated concerning non-covalent bonding
interactions thus far, we hereby report a thorough study on
supramolecular assemblies appearing in the crystal structures of
different acid- and alcohol-type reagents, including four new
alcohol reagents. We also include a detailed discussion of the
crystal structures of the acid adducts [1-H][SbF6], [4-H]NTf2, and
[(4)2H]BArF, since we have been particularly interested in the
influence of protonation on the supramolecular aggregation of
the reagents. Moreover, to also expand on the knowledge about
the species present in solution, we conducted a 19F NMR study
with different reagents in various donor and acceptor solvents.
Similarities and differences between acid and alcohol reagents
and between derivatives with different RF groups, as well as
possible influences on the reactivity of the compounds are
discussed.
Scheme 2. Orders of bonding interactions in gold(III) complexes (a) and in
compounds of trivalent iodine (b): primary bonds (bold continuous lines),
secondary bonding interactions (bold dashed lines) and proposed tertiary
bonding interaction (thin dashed lines; L = ligand/substituent).
The different bonding interactions might be relevant for reactions
of the hypervalent iodine reagents with nucleophilic substrates,
as a pre-organization of the reactants by adduct formation could
take place. To gain a deeper understanding of the relationship
between structures and reactivity of perfluoroorganyl iodane
reagents, it is reasonable to investigate non-covalent bonding
interactions of the compounds in the solid state and in solution. Results and Discussion
On the one hand, the coordinative unsaturation of the iodine
atom can be expected to govern the solid state structures of the
reagents, and analysis of intermolecular contacts can provide
valuable information about possible modes of interaction. On the
other hand, since chemical reactions of the iodanes occur
usually in solution, we were interested in the interaction of these
compounds with different solvents. The Lewis acidic nature of
the reagents enables the formation of adducts with coordinating
solvents, which can contribute to the solvent dependency of the
reactivity. Adduct formation has been previously discussed for
The new alcohol reagents 6–9 were prepared by reaction of the
appropriate trimethylsilane RF-SiMe3 with the corresponding
fluoroiodane in acetonitrile, following a previously described
procedure (cf. Scheme 1c).[5] The synthesis of alcohol reagents
4[13] and 5,[8] as well as the synthesis of the acid reagents 1–
3[7,9,12] was reproduced from previously described procedures.
All reagents are crystalline solids, which are stable at –20 °C for
several months. The compounds are well soluble in acetonitrile,
chloroform and methylene chloride. The new derivatives 6–9
1
have been characterized by H, 13C and 19F NMR spectroscopy
an alcohol reagent containing
a functionalized CF2CF2-o-
OC6H4Br group.[5] In this case, a sharp 19F NMR signal has been
obtained in CDCl3, while in CD3CN the signal is broadened due
as well as elemental analysis (C, H) and high-resolution mass
spectroscopy. The crystalline H[SbF6] adduct of acid reagent 1,
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
[1-H][SbF6]∙H2O, was accidentally obtained by hydrolysis of
NO[SbF6] in a mixture with reagent 1 in CH2Cl2 (Scheme 3a).[27]
However, the water turned out to be important for crystallization,
and the very reactive compound seems to be stabilized by
hydrogen bonding. X-ray structural analyses revealed that the
acidic proton is unambiguously located at the exposed oxygen
atom of the iodane molecule (see below). Nonetheless, attempts
to isolate significant amounts of the product for full
characterization have not been successful. Acid adducts of the
alcohol reagent 4 are more easily prepared. Thus, the fairly
stable, crystalline [(4)2H]BArF has been obtained in almost
quantitative yield by treatment of a CH2Cl2 solution of 4 with 0.5
equiv. [H(OEt)2]BArF at r.t. (Scheme 3b). Attempts to prepare a
corresponding 1:1 adduct, [4-H]BArF, led to a rather undefined
amorphous material. The preference of the mixed-protonated
adduct over a simple [4-H]BArF salt can most likely be explained
by a more favorable crystal packing of the large [(4)2H]+ cation
with the bulky BArF– counterion. Nevertheless, we also
succeeded in preparing a fully protonated form of 4 by treatment
with triflimide (HNTf2) in CH2Cl2, revealing [4-H]NTf2 in a straight-
forward manner (Scheme 3c). The latter compound is more
reactive than [(4)2H]BArF and tends to decomposition at ambient
temperature. In both acid adducts of 4, the acidic proton is
unambiguously located at the iodane oxygen atom, as it has
been verified by X-ray structural analysis (see below).
Additionally, the two products could be fully characterized by 1H,
19F and 13C NMR signals of the iodane, indicating that the acidic
proton undergoes rapid dynamic exchange between the two
iodane moieties. The 19F NMR signal is drastically downfield-
shifted as compared to 4 (–40.1 ppm), and for both compounds
the shift is remarkably similar at –22.9 ppm ([4-H]NTf2) and –
22.6 ppm ([(4)2H]BArF). The downfield shift is typical for
trifluoromethyl iodanes with enhanced iodonium character, as it
has been repeatedly reported.[2,23–28] Moreover, we noticed that
the value of |1JC,F| is strongly influenced by protonation as well,
decreasing from 396 Hz for 4 in CDCl3, to 371 Hz ([4-H]NTf2) or
372 Hz ([(4)2H]BArF), respectively.
Crystal structures:
Single crystals of 2, 3 and 7–9 suitable for X-ray structure
analysis have been obtained directly from the reaction mixture or
by recrystallization from an appropriate solvent (see
Experimental section). The molecular structures are illustrated in
Figures S1–S4 in the SI, while crystallographic details are given
in Table S1 in the SI. Selected geometric parameters are
summarized in Table 1. The crystals obtained of 6 were
unsuitable for X-ray diffraction. The crystal structures of 1
(CSD[31] ref. code IXOKAH),[1]
4
(KEWNUW)[3] and
5
(AWEFUF)[8] have been reported previously and are included in
the discussion of supramolecular aggregation. In all of these
compounds, well-defined molecules with a typical T-shaped
coordination of the iodine atom are present, where the O-I-C(RF)
fragment slightly deviates from linearity with a bond angle of
168.0(6)–173.63(6)°. The I-C(RF) bond length is primarily
determined by the nature of the oxygen donor group trans to the
RF substituent, as described previously.[2,3] Thus, in the alcohol
reagents 4, 5, 7 and 8 comprising a strongly electron-donating
alkoxy moiety, the I-C(RF) bond is significantly elongated, while
the I-O bond is strongly shortened as compared to the acid
reagents 1–3. Moreover, the I-C(RF) bond length was found to
depend also on the nature of the RF group itself, being elongated
on going from CF3 to longer perfluoroalkyl chains.
1
19F and 13C NMR spectroscopy. For [4-H]NTf2, a sharp H NMR
signal of the acidic proton at 6.76 ppm in dry CDCl3 was
observed, while the same was not visible in the case of
[(4)2H]BArF. The latter compound displays only one set of 1H,
Table 1. Selected interatomic distances (pm) and angles (deg.) in
compounds 1–5, 7 and 8.
Compound
I-C(RF)
I-O
O-I-RF
I∙∙∙O[a]
1[1]
2
221.9(4)
224.1(2)
223.9(2)
226.7(3)
229.9(2)
230.8(2)
230.2(2)
228.3(2)
227.5(2)
227.3(2)
211.8(2)
211.8(1)
212.3(1)
212.9(1)
170.5(1)
172.81(8)
168.93(7)
169.78(7)
173.53(6)
173.63(6)
172.36(6)
302.1(3)
309.8(2)
303.7(2)
299.8(1)
298.4(2)
297.5(1)
292.9(1)
3
4[3]
5[6]
7
8
Scheme 3. Protonation of the trifluoromethyl derivatives 1 and 4 with in situ
generated HSbF6 (a), with “Brookhart’s acid” [H(OEt)2]BArF (b; BArF
Tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), and with HNTf2 (c).
=
[a] Shortest intermolecular contact.
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
Scheme 4. Schematic representation of the environment of the iodine atom in the acid reagents 1 (a),[1] 2 (b), and 3 (c).
As foreshadowed above, the crystal structures of compounds 1–
9 go beyond simple monomeric molecules, and intermolecular
I∙∙∙O contacts far below the sum of Van-der-Waals radii of I and
O (which is 350 pm[17]) have been found in all compounds. In the
acid reagents 1–3, the iodine atom displays a pseudo-square-
planar coordination resulting from chelating coordination of a
carboxy moiety of an adjacent molecule, comprising a short
(302.1(3)–309.8(2) pm) and a longer (310.1(2)–327.3(2) pm)
I∙∙∙O contact. It is worth mentioning that the carboxy moiety
shows no tendency towards chelating coordination in some
related acid reagents, namely with CSD[31] ref. code GUGZUF
(I∙∙∙O 276.4(4) pm)[32] and WACBOU (I∙∙∙O 305.0(2) pm).[5]
Chelating carboxylate coordination similar as in 1–3 has also
been observed in other compounds of trivalent iodine, e.g. 1-
the formation of puckered two-dimensional arrays in the crystal
(Figure 1b, c). In 1, the sixth coordination site may be regarded
as occupied by a weak I∙∙∙F contact to a CF3 group to an
adjacent layer (I∙∙∙F 345.5(2) pm; cf. sum of Van der Waals radii
of I and F 333 pm[37]), while it remains free in 3.
Since no additional oxygen donor atom is present in the alcohol
reagents 4–9, coordinative saturation of the iodine center is
realized by µ-bridging coordination of the alkoxide O atom. As a
result, supramolecular dimers are formed in all perfluoroalkyl
derivatives 4–8, featuring a cyclic planar I2O2 core (Figure 2).
The corresponding I∙∙∙O contacts are comparatively short at
292.9(1)–299.8(1) pm, which is in agreement with the electron-
rich nature of the alkoxy donor groups. Not surprisingly, similar
dimers can be found upon analysis of previously published
crystal structures of related compounds (e.g. CSD[31] entries
OCIFIQ (I∙∙∙O 304.0(2) pm),[1] HUQVEV (I∙∙∙O 304.5(1) pm)[40]
Acetoxy-1,2-benziodoxol-3(1H)-one (CSD[31] ref. code ABZIOX)
[33]
and
PhI(OOCCF3)2 (CSD[31] ref. code CEZBEO01).[34]
Regardless of the different coordination mode of the COO group, and HUQTAP (I∙∙∙O 298.1(3) pm)[40]), as well as in the
the secondary I∙∙∙O interactions lead to the formation of
supramolecular polymeric chains in all acid-type iodane
reagents (Figure 1a). In all 1–3, the fifth coordination site at
iodine seems to be occupied by a I∙∙∙Aryl interaction with an
adjacent molecule, which is best described as a η2-coordination
of the ortho-phenylene ring in each case (cf. Figures S5–S7 in
the SI). Even though adducts of elemental iodine with π-donors
are well-characterized by spectroscopic techniques,[35,36] crystal
structure data on I∙∙∙Aryl contacts are lacking. The shortest I∙∙∙C
contacts in 1–3 are 367.6(4)–384.8(2) pm, which is close to the
sum of Van der Waals radii of I and C, 368 pm.[37] In 1 and 3,
these interactions lead to dimeric motifs (Scheme 4a, c), which
may be further supported by π-π interactions between the
phenylene rings. The closest C∙∙∙C contacts are 365.9(5) pm (1)
and 371.0(3) pm (3), respectively, which is in the range of weak
attractive interaction.[38,39] In contrast, a chain-like arrangement
is realized in 2 (Scheme 4b). This aggregation mode is most
likely supported by another relevant I∙∙∙O contact of 344.7(2) pm,
which formally occupies the sixth coordination site at iodine. The
significance of this “tertiary” I∙∙∙O bond is corroborated by its
influence on the other bonds around iodine. In particular, the
secondary I∙∙∙O bond in 2 is comparatively long at 309.8(2) pm,
while the same is shorter in 1 (302.1(3) pm)[1] and 3 (303.7(2)
pm). Both the tertiary I∙∙∙O and I∙∙∙Aryl interactions in 1–3 lead to
corresponding fluoroiodane (YAYDAF; I∙∙∙O 294.7(4) and
304.6(4) pm)[41] and chloroiodane (HUQSES; I∙∙∙O 291.8(3)
pm).[40] As to the formation of supramolecular dimers,
alkoxyiodanes such as 4–8 can formally be regarded as
intermediates between non-metal derivatives of alcohols and
metal alkoxide complexes. While classical non-metal
compounds contain a distinct NM-O single bond without any
tendency toward dimerization (NM = non-metal, e.g. C in
ethers),[42] metal complexes with alkoxide ligands exist
frequently as discrete dimers with two M-O bonds per M atom (M
= metal).[43,44] (Scheme 5).
Scheme 5. Typical motifs in the molecular structure of alkoxides of different
elements: non-metal (a), hypervalent iodine (b), metal (c).
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
coordination numbers higher than four. Additionally, a more
efficient shielding of the iodine center by the methyl groups in
the alcohol reagents might also be of relevance. An exception is
the trifluoromethyl derivative 4, where a conspicuously short
I∙∙∙H-C contact to a perpendicularly oriented phenylene group
exists (I∙∙∙H 326.9(3) pm; Scheme 6a; cf. Figure S7 in the SI).
This is very close to the upper limit of significant I∙∙∙H bonds,
which is defined in the literature to be 325 pm.[45] Therefore, the
environment of the iodine atom in 4 can formally be described
with a square-pyramidal [3+1+1] coordination with the weak
I∙∙∙H-C contact at the apex. This arrangement might be further
supported by an O∙∙∙H-C contact to the same phenylene group
(O∙∙∙H 282.3(3) pm).
Figure 2. Supramolecular dimers in alcohol reagents as exemplified by the n-
C4F9 derivative 7 (H atoms are omitted for clarity).
Figure 1. Supramolecular polymeric chains in acid reagents as exemplified by
1[1] (a), two-dimensional arrays formed by further aggregation of these chains
Scheme 6. Schematic representation of the environment of the iodine atom in
the alcohol reagents 4 (a),[3] and 5–8 (b),[8]
by I∙∙∙Aryl contacts in
1 (b), and by additional I∙∙∙O contacts in 2 (c;
coordination squares around the I atoms of two adjacent chains highlighted in
different colours).
The single crystals of the pentafluorophenyl alcohol reagent 9
did not allow for full structure refinement, but we decided to
include this compound in the discussion since its supramolecular
structure is surprisingly different than that of the perfluoroalkyl
derivatives 4–8. Namely, µ-bridging coordination of the oxygen
donor results in the formation of polymeric chains rather than
dimers (Figure 3). This arrangement seems not to be supported
by π-interactions between the ortho-phenylene and C6F5
moieties by significant extent, as they are not properly oriented
(e.g. angle between ortho-phenylene and C6F5 planes approx.
In the alcohol reagents 4–8, the square-planar coordination of
the iodine atom seems to be a good approximation to reality,
since no defined interactions of the fifth and sixth coordination
site of the iodine atom can be assigned in most of the
compounds (Scheme 6b). As compared to the acid-type
reagents, this finding might be traced back to a lower Lewis
acidity of the iodine center due to the strongly electron-donating
alkoxy group, which leads to reduced tendency toward
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10.1002/ejoc.201800358
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60°). It has been discussed earlier that a slightly displaced
parallel orientation between a hydrocarbon and a perfluoro-
carbon aryl ring is energetically most favored, while between two
perfluoroarenes non-directed van-der-Waals interactions are of
more importance.[46] The iodine atom in 9 displays no defined
tertiary bond interactions with any donor moieties, which can
most likely be addressed to efficient shielding of the iodine
center by the bulky C6F5 group.
255.3(3) pm, O∙∙∙H approx. 158 pm) relative to literature
data.[45,48] The two hydrogen bond donor moieties of the H2O
ligand are involved in O-H∙∙∙F bonding with [SbF6]– counterions
(O∙∙∙F 272.8(4) and 288.4(4) pm; H∙∙∙F approx. 190 and 203 pm).
Figure 4. Supramolecular dimer of contact ion pairs of [1-H][SbF6]∙H2O in the
crystal (H atoms attached to C atoms omitted for clarity).
Figure 3. Supramolecular polymeric chains in the perfluorophenyl alcohol
reagent 9 (H atoms omitted for clarity).
In [4-H]NTf2, protonation of the alkoxy moiety results in drastic
elongation of the I-O bond from 211.8(2) pm in 4,[3] to 249.5(1)
pm. Different from the protonated acid reagent [1-H][SbF6]∙H2O,
the I-CF3 bond in [4-H]NTf2 is significantly shortened to 219.9(2)
pm, as compared to free 4.[3] The iodine atom displays an
irregular hexa-coordination by a chelating Tf2N– anion (I∙∙∙O
322.7(1) and 324.1(1) pm), and a weaker contact to another
Tf2N– anion (I∙∙∙O 346.2(1) pm; cf. Figure S13 in the SI). The
latter counterion is additionally fixed by an O-H∙∙∙N bond (O∙∙∙N
282.1(2) pm; H∙∙∙N approx. 203 pm), which is comparable in
strength with O-H∙∙∙N bonds in classical organic molecules such
as amides.[48] This connectivity pattern leads to a polymeric
zigzag chain architecture (Figure 5).
Crystallographic details on the acid adducts [1-H][SbF6]∙H2O, [4-
H]NTf2, and [(4)2H]BArF are summarized in Table S2 in the SI,
and the molecular structures are illustrated in Figures S8–S11 in
the SI. The hexafluoroantimonate salt of protonated acid reagent
1 crystallizes as a hydrate, [1-H][SbF6]∙H2O. In this compound,
the proton is located at the exposed O atom of the carboxyl
moiety. As a result of protonation, the I-O bond is considerably
elongated from 228.3(2) pm in 1,[1] to 245.2(3) pm. In contrast,
the I-CF3 bond length remains virtually unchanged at 220.8(3)
pm. The supramolecular structure of [1-H][SbF6]∙H2O is entirely
different from that in 1. It is best described as a dimer of contact
ion pairs, featuring a centrosymmetric I2O2 ring as a central
structural motif (Figure 4; cf. Figure S12 in the SI). The fourth
coordination site of the iodine atom is occupied by a close
contact to the [SbF6]– counterion (I∙∙∙F 299.9(3) pm), which is
comparable in length to that observed in previously reported
–
BF4 salts of related iodonium species, e.g. CSD[31] entries
FAKNUD (I∙∙∙F 292.4(3) pm),[28] and HUQTIX (I∙∙∙F 302.8(3)
pm).[40] However, the I∙∙∙F bond in [1-H][SbF6]∙H2O is displaced
from the iodane’s coordination plane with an angle of approx.
65°. This can be traced back to two additional relevant bonding
interactions of the iodine atom, namely coordination of an H2O
molecule (I∙∙∙OH2 327.7(3) pm), and a weak I∙∙∙O(carbonyl)
contact to the adjacent iodane molecule (I∙∙∙O 341.9(3) pm). The
dimeric supramolecular structure of [1-H][SbF6]∙H2O might be
further supported by another weak I∙∙∙F contact of 356.4(3) pm.
Consequently, the bonding of the iodine atom can be described
as a rather irregular [3+1+3] coordination. The H2O ligand is
additionally fixed by an ꢀꢁꢁ(12)-type[47] O-H∙∙∙O bond to the
protonated carboxyl group, which is comparatively strong (O∙∙∙O
Figure 5. Supramolecular “zigzag” chains of [4-H]NTf2 in the crystal (H atoms
attached to C atoms omitted for clarity).
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
The molecular structure of [(4)2H]BArF is more complex than
that of [4-H]NTf2, as comprising a protonated and a non-
protonated molecule of 4 (Figure 6). These two units are linked
by an asymmetric O-H∙∙∙O bond, i.e. the proton is clearly located
at one of the molecules. This hydrogen bond can be regarded as
moderately strong with an O∙∙∙O separation of 258.4(4) pm
(H∙∙∙O approx. 160 pm).[45,48] The asymmetric nature of the
hydrogen bond is corroborated by the I-O bond lengths, which
are very different in the two molecules. The I-O bond in the
protonated molecule is 244.0(3) pm and therefore similar as in
[4-H]NTf2, while the non-protonated part of the [(4)2H]+ cation
contains a considerably shorter I-O bond of 225.7(2) pm.
Nonetheless, both values are much larger than in free reagent
4.[3] The I-CF3 bond length within the protonated iodane moiety
is similar to that in [4-H]NTf2, at 221.4(6) pm. However, the I-CF3
bond in the non-protonated iodane moiety is also slightly
shortened as compared to free 4, to 223.4(5) pm. The assembly
of the two iodane molecules within the [(4)2H]+ cation seems to
be promoted not exclusively by the mentioned O-H∙∙∙O bond, but
also by mutual weak I∙∙∙Aryl interactions between the two parts
of the aggregate. For both iodine atoms, this interaction is best
described as a η2-coordination, with the closest I∙∙∙C separations
being 370.7(4) pm for the exposed and 381.1(4) pm for the inner
iodine atom. These values are in the same range as in 1–3. The
mixed protonation of the two iodane molecules results in
different contribution to further supramolecular aggregation (cf.
Figure S14 in the SI). The non-protonated part of the [(4)2H]+
cation undergoes typical dimerization via µ-bridging coordination
of the alkoxy moiety, leading to a centrosymmetric I2O2 ring just
as in free 4. The same does not take place in the protonated
iodane moiety, since protonation of the alkoxy moiety disables µ-
bridging coordination. Instead, the fourth coordination site of the
specific iodine atom is occupied by a close contact to a CF3
group of the BArF– counterion. Consequently, the supra-
molecular structure of [(4)2H]BArF can be, similarly as in the
case of [1-H][SbF6]∙H2O, described as a dimer of contact ion
pairs. The shortest I∙∙∙F contact is relatively long at 317.1(2) pm,
which can be explained by the weak donor ability of the CF3
group as compared to SbF6– and BF4–.[28,40] The fifth coordination
site of both iodine atoms is efficiently blocked by the above-
mentioned I∙∙∙Aryl contacts. For the exposed iodine atom, the
sixth coordination site may be filled by a weak I∙∙∙F contact to
another BArF– anion (I∙∙∙F 351.3(3) pm), while in the case of the
inner iodine atom spacial proximity to methyl groups prevents an
additional contact to any donor moiety.
Solution NMR studies:
Since compounds 1–3 and 9 are well soluble in organic solvents,
it can be expected that the polymeric supramolecular
aggregates present in the solid state are readily broken down to
small molecular entities in solution. However, the dimers existent
in 4–8 might be of relevance in solutions of low polarity solvents.
Aside from monomer-dimer equilibria for the latter compounds,
we were interested in the interaction with different donor and
acceptor solvents. Regarding the solid state structures of
reagents 1–9 and the protonated reagents [1-H][SbF6]∙H2O, [4-
H]NTf2 and [(4)2H]BArF, the bonding and reactivity can be
expected to be influenced both by hydrogen bonding and by
1
coordination of donor solvents to the iodine atom. The JC,F
coupling constant of the CF3 or CF2 moiety directly attached to
iodine turned out to be a useful measure for these reagent-
solvent interactions. Chemical shifts are less suited, since they
are more strongly influenced by non-bonding solute/solvent
interactions and are therefore usually difficult to interpret (with
the exception of protonation, which leads to strong downfield-
shift of the 19F NMR signal in the CF3 derivatives 1 and 4[2,23–28]
;
cf. Figures S47–S49 in the SI). To compare acid- and alcohol-
type reagents on the one hand, and CF3 and longer RF groups
on the other hand, the values of |1JC,F| (which are readily
available from the 19F NMR spectra, cf. Figure S50 in the SI)
have been determined for solutions of compounds 1, 2, and 4
and 5 in a variety of solvents with different donor and acceptor
properties (Table 2). In CH2Cl2 which is both a poor donor and a
poor acceptor, the value of |1JC,F| is 381 Hz for the CF3 acid
reagent 1, and 398 Hz for the corresponding alcohol reagent 4.
This difference reflects the more electron-rich nature of the
alkoxy moiety as compared to the carboxy moiety, which results
in a higher electron-density at the CF3 fragment. High |1JC,F
|
values have generally been observed in compounds with a high
negative charge density at the C atom (e.g. in trifluoromethyl
silicates[49] or metal complexes with CF3 ligands[4,50]), while
considerably smaller values are reported for CF3 compounds
having an electronegative group attached to the C atom.[51]
However, the |1JC,F| values of the α-CF2 group of the acid- and
alcohol-type C2F5 derivatives are virtually equal at 334 Hz (2)
and 335 Hz (5). Consequently, |1JC,F
| is not exclusively
Figure 6. Supramolecular dimer of contact ion pairs of [(4)2H]BArF in the
crystal (H atoms attached to C atoms omitted for clarity; BArF– anions reduced
to CF3 groups with contact to iodine).
determined by the I-C(RF) bond length, as the latter is
significantly different in 2 and 5 (cf. Table 1). For the CF3
derivatives 1 and 4, the value of |1JC,F| is slightly but significantly
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
increased (assuming an error of ±1 Hz for the measured values)
in coordinating solvents with respect to the values for CH2Cl2 as
a reference, e.g. in DMSO to 383 Hz (1) and 402 Hz (4),
respectively. This finding can be regarded as evidence for the
presence of solvent adducts according to Scheme 7a. The
increase of |1JC,F| by solvent coordination can be interpreted
taking into account electron donation of the newly added ligand,
which also results in an increased electron density at the CF3
group (as it stabilizes the positive formal charge at the iodine
center). Slightly increased |1JC,F| values for 1 and 4 have also
been obtained in benzene and toluene, which are typical π-
donating solvents. These examples suggest (in agreement with
the proposed I∙∙∙Aryl interactions in the crystal structures of 1–4)
that the above-described effect is not limited to classical σ-
donating solvents, and that the iodane reagents seem to be able
reagents 1 and 2 turned out to readily undergo undefined
decomposition in NEt3 (and all tested reagents 1, 2, 4 and 5 in
hexamethylphosphoric amide, HMPA, too). Generally, a major
disadvantage of Gutmann’s model for the quantification of
solvent donor strength is its simplicity, e.g. not differentiating
between hard and soft donors.[53]
to form π-complexes with arenes. Plotting the observed |1JC,F
|
values against Gutmann’s donor numbers[52] of the
corresponding solvents, no clear correlation can be inferred
(Figure 7). For instance, high coupling constants for 4 have been
found in pyridine and DMSO featuring high donicity, but the
extremely strong donor solvent NEt3 gave an unexpectedly small
|1JC,F| value. Nonetheless, it is to be assumed that a strong
interaction with high donicity solvents exists, as the acid
Scheme 7. Proposed influence of a) donor (D) and b) protic acceptor (HA)
solvents on the electron distribution within reagent 4.
1
Table 2. JF,C values (Hz) for selected perfluoroalkyl iodane reagents (1, 2,
4, 5) in various solvents (rounded to integers; for C2F5 derivatives 4 and 5:
values for the CF2 moiety).
Solvent
1
2
4
5
CH2Cl2
CHCl3
Benzene
Toluene
Et2O
381
380
384
384
383
380
383
384
383
384
334
336
336
335
398
396
400
400
398
399
399
400
402
401
399
394
393
385
367
335
334
335
334
334
335
334
334
336
335
335
334
334
334
[a]
–
MeCN
P(OMe)3
THF
333
332
332
334
334
Figure 7. Plot of selected |1JC,F| values observed for 4 against solvent donor
numbers (DN; values taken from [52]).
In contrast, protic solvents such as EtOH, H2O and HOAc turned
out to exert the opposite effect on the C-F coupling, thus
resulting in a decrease of |1JC,F| as compared to the respective
value for CH2Cl2. Less surprising, this effect is particularly
pronounced in the strongly acidic solvent trifluoroacetic acid
(TFA), where drastically decreased |1JC,F| values of 368 Hz (1)
and 367 Hz (4) indicate full protonation of the reagent. The value
for 4 in TFA is similar to the values observed for the isolated
acid adducts [4-H]NTf2 and [(4)2H]BArF. Generally, decrease of
|1JC,F| in protic solvents can be attributed to an electron-
withdrawing effect by formation of a hydrogen bond including the
iodane’s O atom, formally enhancing iodonium cation character
of the iodane (Scheme 7b). Plotting |1JC,F| against Gutmann’s
solvent acceptor numbers,[53] a clear correlation can only be
distinguished for protic solvents exhibiting high acceptor
DMSO
Py
[d]
[d]
NEt3
–
–
EtOH
H2O[b]
HOAc
TFA
380
377
377
368
334
334
335
[c]
[c]
–
–
[a] 13C satellites not resolved due to low solubility. [b] with ca. 30 vol.-%
MeCN to improve solubility. [c] α-CF2 signal overlapped by solvent signal.
[d] fast decomposition.
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
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numbers, showing decreasing |1JC,F| with increasing acceptor
number (Figure 8). The poor correlation for the other solvents
may be again due to missing differentiation between hard and
soft Lewis acids,[53] and to the opposing effect of donating
solvents on the coupling constant (e.g. MeCN is both a donor
and acceptor solvents (e.g. MeCN, NEt3, EtOH; cf. Figures S51
and S52 in the SI). Consequently, we assume that the dynamic
exchange of solvent molecules is too fast to be resolved by
NMR techniques. The energies of aggregation as well as the
molecular structures of defined solvated species could be the
and acceptor solvent). For the most acidic solvents CHCl3, EtOH, subject of computational studies in future research.
H2O, HOAc and TFA, the |1JC,F| values correlate much better
with the solvents’ pKA values.[54] (Figure 9). This correlation is
best described with a typical exponential growth function,
running toward a limit value of 397 Hz for high pKA values. This
agrees well with the value of 398 Hz for CH2Cl2, which is a very
poor acceptor.[52] Experiments with 4 in different CH2Cl2/EtOH,
CH2Cl2/HOAc and CH2Cl2/TFA mixtures revealed a strong
impact on |1JC,F
| even at low percentages of the protic
component, which is in agreement with the previous finding that
1:1 adducts as shown in Scheme 7b are readily formed (cf.
Figure S54 in the SI).[25,27] In contrast, the effect of donor
solvents on |1JC,F| only becomes significant at a large excess of
the donor, as experiments with different CH2Cl2/toluene,
CH2Cl2/pyridine and CH2Cl2/DMSO mixtures have shown (cf.
Figure S53 in the SI). Consequently, the interaction of the
reagents with donor solvents can be assumed to be weaker than
with acceptor solvents, being in agreement with the small adduct
formation constant reported for 1 with N-methylmorpholine.[22] In
the C2F5 derivatives 2 and 5, the discussed solvent effects seem
to be generally much less pronounced than in the CF3
derivatives 1 and 4, as |1JC,F| values have been obtained in a
very narrow range of 334±2 Hz (2) or 335±1 Hz (5), respectively.
Figure 9. Plot of |1JC,F| values observed for 4 in protic solvents against solvent
pKA values (taken from [54]).
Conclusions
Notwithstanding the simple molecular structure of perfluoroalkyl
and perfluoroaryl iodane reagents, these compounds show a
rich supramolecular structural chemistry. In summarizing the
results reported here, we have shown that the iodine atom can
be formally regarded as coordinatively unsaturated, which is the
reason for the pronounced tendency toward supramolecular
aggregation in the solid state. Thereby,
a square-planar
coordination of the iodine atom is strongly favored and realized
by a secondary I∙∙∙O or I∙∙∙F bond. While this model seems to be
well suited for the alcohol reagents 4–9, we have demonstrated
that coordination numbers higher than four are also feasible. In
the case of the acid reagents 1–3, introduction of the term
“tertiary bonding interactions” with regard to the fifth and sixth
coordination site of the iodine atom seems legitimate. This
includes not only weak I∙∙∙O or I∙∙∙F contacts, but also I∙∙∙Aryl
interactions. Nevertheless, there is
a fine line between
secondary and tertiary bonding interactions, and particularly in
the case of the iodonium salts [1-H][SbF6]∙H2O and [4-H]NTf2 the
two categories cannot be clearly distinguished. The crystal
structure analyses of the acid adducts of 1 and 4 also
demonstrate impressively that protonation exert considerable
influence on the molecular and supramolecular structures of the
reagents.
The solution NMR studies presented in this work agree well with
our findings from the crystal structure analyses, indicating that
similar intermolecular interactions are relevant in solution. This
includes coordination of donor solvents to iodine on the one
Figure 8. Plot of selected |1JC,F| values observed for 4 against solvent
acceptor numbers (AN; values taken from [52]).
In spite of the above discussed evidence for interactions of 1–9
with different solvents, attempts to detect well-defined dissolved
species by 19F NMR spectroscopy failed. Thus, for each
compound and solvent only one sharp signal has been obtained.
For 4 (whose high solubility allowed for low temperature
experiments), a single sharp resonance was observed even at
–90 °C in CD2Cl2, and 1:1 mixtures thereof with various donor
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
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though this approach is somewhat arguable for crystal structures
containing iodine as a heavy atom, it led to meaningful results due to the
high quality of the dataset in each case. Further experimental data and
details on structure refinement are summarized in Tables S1 and S2 in
the SI. Crystallographic data including structure factors have been
deposited at the CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the
depository numbers 875434 and 1825241–1825246 (cf. Tables S1 and
S2 in the SI), or the publication DOI (http://www.ccdc.cam.ac.uk).
hand, and hydrogen bonding with protic solvents on the other
hand. Both types of interactions can be assumed to exert a
significant impact on the reactivity of the dissolved reagent. As
discussed earlier, perfluoroalkyl iodane reagents can serve
formally as a RF+ source when activated with a Lewis acid, while
they feature
a pronounced radical chemistry under other
conditions (transition metal catalysis, one-electron reduction,
etc.).[2,55] Exploiting the different solvent effects can help
enhance or suppress a particular reaction pathway. While clean
+
Synthesis of Trimethyl(perfluorophenyl)silane: The compound was
prepared following a modified literature procedure.[61–63] A solution of
pentafluorobenzene (1.3 ml, 11.9 mmol, 1.0 equiv.) in diethyl ether ( 10
ml) was added dropwise to a mixture of nBuLi (8.9 ml, 1.6 mol/l in
hexanes, 14.3 mmol, 1.2 equiv.) and diethyl ether (60 ml) at –78 °C. The
resulting pale yellow solution was stirred for 1 h at –78 °C, and
subsequently Me3SiCl (3.0 ml, 23.8 mmol, 2.0 equiv.) was added
dropwise. Stirring was continued overnight, allowing the mixture to warm
to room temperature. A white, water-soluble precipitate (presumably LiCl)
was formed during this time. The mixture was poured into ice water (100
ml) and the reaction vessel rinsed with ice water and tert-butyl methyl
ether. The organic phase was separated and the aqueous phase
extracted with tert-butyl methyl ether (2 × 90 ml). The combined organic
extracts were dried over MgSO4 and filtered over a pad of Celite. The
solvent was removed on a rotary evaporator (35 °C, 500 mbar), and the
residue distilled under reduced pressure at a bath temp. of 85 °C,
revealing the product as colourless oil (b.p. 57–60 °C at 2 mbar). Yield:
electrophilic RF reactivity can be expected to be prominent in
acceptor solvents, reactions including RF radicals seem to be
more pronounced in donor solvents.[22] The different aggregation
modes in solution also give insight into possible pre-organization
of the reagent and a substrate in solution by σ-donation, π-
donation, or hydrogen bonding. Knowledge regarding these
interactions is valuable in predicting and understanding the
reactivity of known and new acid- and alcohol-type reagents in
future research.
Experimental Section
General: Preparation of the compounds was carried out with the
exclusion of moisture under an inert argon atmosphere using standard
Schlenk techniques. Solvents were obtained from common suppliers,
distilled and dried over molecular sieves (4 Å). Fluoro-1,3-dihydro-3,3-
1.36
g (48%). The identity of the compound was established by
comparison of the NMR data with reference data.[64]
dimethyl-1,2-benziodoxole
(“Fluoroiodane”),[13]
the
silanes
(n-
C4F9)SiMe3[56] and (n-C8F17)SiMe3[56], as well as the known perfluoroalkyl
iodanes 1,[12] 2,[7] 3,[9] and 4[13] were prepared according to published
procedures. All other starting materials were obtained from commercial
sourced and used without further purification. Automated flash column
chromatography was performed on a CombiFlash Rf200 System from
Teledyne ISCO with built-in UV-detector and fraction collector. Teledyne
ISCO RediSep Rf flash columns used have a 0.035–0.070 mm particle
size and 230–400 mesh. NMR spectra were recorded on a Bruker
Avance III HD Nanobay 300 (300 MHz), Bruker DPX-400 (400 MHz), or a
Bruker DPX-500 (500 MHz) spectrometer, in Chloroform-D at ambient
temperature (298(2) K). 1H NMR shifts are referenced to the residual 1H
signal of the deuterated solvent (CHCl3: δH = 7.260 ppm), 13C NMR shifts
to the deuterated solvent itself (CDCl3: δC = 77.16 ppm). 19F NMR shifts
are referenced to neat CFCl3 (δF = 0.00 ppm). 13C chemical shifts of CF2
and CF3 groups have been determined from 19F/13C HMBC spectra.
Elemental analyses (C, H) were performed with a LECO TruSpec Micro
apparatus. High-resolution mass spectra (HRMS) were measured on a
Bruker Daltonics maXis ESI-QTOF or a Bruker UltraFlex II MALDI-TOF
mass spectrometer.
General procedure for preparation of reagents 5–9: To a suspension
of Fluoroiodane (475 mg, 1.7 mmol, 1.3 equiv.*) in acetonitrile (5 ml),
TBAT (7 mg, 0.01 mmol,
1 mol-%) was added at –20 °C. The
corresponding (perfluoroorganyl)trimethylsilane (1.3 mmol, 1.0 equiv.)
was subsequently added dropwise within 20 min. The yellow to brownish
mixture was stirred for 1 h at –20 °C and for 30 min at r.t. For compounds
6 and 9, the reaction mixture was evaporated to dryness and the product
isolated by automated flash column chromatography. For compounds 5,
7 and 8, the reaction solution was cooled to –50 °C to ensure complete
precipitation of the product. The precipitate was filtered off in the cold,
washed with –50 °C cold acetonitrile (2×3 ml) and carefully dried in vacuo,
revealing a colourless crystalline solid (Caution: prolonged drying in high
vacuum can lead to sublimation of the product).
3,3-Dimethyl-1-(perfluoro-n-propyl)-1,3-dihydro-1λ3-benzo[d][1,2]-
iodoxole (“n-C3F7 alcohol reagent”; 6): Yield: 480 mg (86%). M.p.
50 °C, Anal. calcd. for C12H10F7IO (M = 430.10 g/mol): C 33.51, H
2.34 %; Found: C 33.89, H 2.41 %. HRMS: m/z calcd. for [M+H]+,
C12H11F7IO: 430.9737; Found: 430.9743. 1H NMR: δ 1.49 (s, 6H; CH3),
7.35–7.42 (2×m, 2H; CH), 7.49 (2×m, 2H; CH) ppm. 19F NMR: δ –79.8 (t,
3JF,F = 8.4 Hz, 3F; CF3), –96.3 (m, 2F; α-CF2), –121.7 (s, 2F; β-CF2) ppm.
13C NMR: δ 30.6 (s; CH3), 77.2 (s; CMe2), 109.6 (m; β-CF2), 111.4 (s; C-
I), 112.5 (m; α-CF2), 117.2 (m; CF3), 127.4 (s; CH), 128.6 (m; CH), 129.7
(s; CH), 130.5 (s; CH), 149.7 (s; C-CMe2) ppm.
Single crystal X-ray diffraction: Single crystals of the literature-known
acid reagents suitable for X-ray structural analysis have been obtained
from a saturated CH2Cl2/Et2O (v:v approx. 1:1) solution at –18 °C (2) or
by slow evaporation of a CH2Cl2 solution at 5 °C (3). Single-crystals of
the new compounds 7–9, [1-H][SbF6]∙H2O, [4-H]NTf2, and [(4)2]BArF
have been obtained as described below. X-ray intensity data have been
collected on a Bruker Apex II diffractometer equipped with a Apex II CCD
area detector, using graphite-monochromated Mo-Kα radiation, at T =
100(2) K. The structures were solved by intrinsic phasing methods
(SHELXT-2014/5[57]) and refined by full matrix least-squares methods on
F2 (SHELXL-2014/7[58]), using Olex 1.2.[59] For compound 2, the absolute
configuration was determined using [(I+)–(I–)]/[(I+)+(I–)] quotients.[60] For
[1-H][SbF6]∙H2O, [4-H]NTf2, and [(4)2]BArF, the position of the acidic
proton was located in the difference Fourier map and refined freely. Even
3,3-Dimethyl-1-(perfluoro-n-butyl)-1,3-dihydro-1λ3-benzo[d][1,2]-
iodoxole (“n-C4F9 alcohol reagent”; 7): Rf = 0.31 (n-hexane/ethyl
acetate 80/20). Yield: 318 mg (51%). The m.p. of the low-melting solid
could not be determined reliably. Anal. calcd. for C13H10F9IO (M = 480.11
g/mol): C 32.52, H 2.10 %; Found: C 32.43, H 2.17 %. HRMS: m/z calcd.
for [M+H]+, C13H11F9IO: 480.9705; Found: 480.9702. 1H NMR: δ 1.50 (s,
6H; CH3), 7.35–7.44 (2×m, 2H; CH), 7.49–7.57 (2×m, 2H; CH) ppm. 19F
3
4
3
NMR: δ –80.9 (tt, JF,F = 9.6 Hz, JF,F = 2.7 Hz, 3F; CF3), –95.5 (t, JF,F
=
12.4 Hz, 2F; α-CF2), –118.0 (m, 2F; CF2), –125.8 (m, 2F; CF2) ppm. 13C
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10.1002/ejoc.201800358
European Journal of Organic Chemistry
FULL PAPER
NMR: δ 30.6 (s; CH3), 77.3 (s; CMe2), 108.5 (m; CF2), 111.2 (m; CF2),
111.5 (s; C-I), 117.7 (m; CF3), 127.5 (s; CH), 128.6 (s; CH), 129.8 (s; CH),
130.6 (s; CH), 150.1 (s; C-CMe2) ppm; α-CF2 not observed. Single
crystals of 7 suitable for X-ray structural analysis were obtained directly
from the reaction solution.
methane (2 ml), the insoluble matter (NaCl) removed by filtration and
rinsed with further dichloromethane (0.5 ml). The so-obtained
[H(OEt)2]BArF30 solution was added dropwise to a stirred solution of 4
(48 mg, 0.147 mmol) in dichloromethane (1 ml) at r.t., and stirring was
continued for 10 min. The solution was subsequently reduced to 0.5 ml,
and then stored at –20 °C until colourless crystals have formed (ca. 4 h).
n-Pentane (1 ml) was added to the cold solution to ensure complete
crystallization of the product. The crystals were isolated by filtration,
washed with n-pentane (2 ml), and dried in vacuo. Yield: 105 mg (95 %).
Anal. calcd. for C52H33BF30I2O2 (M = 1524.39 g/mol): C 40.97, H 2.18 %;
3,3-Dimethyl-1-(perfluoro-n-octyl)-1,3-dihydro-1λ3-benzo[d][1,2]-
iodoxole (“n-C8F17 alcohol reagent”; 8): Rf = 0.21 (n-hexane/ethyl
acetate 85/15). Yield: 565 mg (64%). M.p. 82 °C. Anal. calcd. for
C17H10F17IO (M = 680.14 g/mol): C 30.02, H 1.48 %; Found: C 30.17, H
1.54 %. HRMS: m/z calcd. for [M+H]+, C17H11F17IO: 680.9578; Found:
1
Found: C 41.02, H 2.22 %. H NMR: δ 1.68 (s, 6H; CH3), 7.23 (s br, 2H;
CH), 7.44–7.70 (5×m, 18H; CH) ppm; OH not observed. 19F NMR: δ
–62.4 (s, 24F; Ar-CF3 BArF), –22.6 (s, 6F; I-CF3) ppm. 13C NMR: δ 30.0
(s; CH3), 109.7 (s; C-I), 124.7 (q, |1JC,F| = 272 Hz; CF3 BArF), 128.5–
133.2 (unresolved signals of iodane and BArF), 134.9 (s; 2,6-CH BArF),
146.4 (s; C-CMe2) ppm. 11B NMR: δ –6.6 (s) ppm.
1
680.9575. H NMR: δ 1.50 (s, 6H; CH3), 7.35–7.44 (2×m, 2H; CH), 7.49–
3
7.58 (2×m, 2H; CH) ppm. 19F NMR: δ –80.7 (t, JF,F = 9.9 Hz, 3F; CF3), –
95.2 (m br, 2F; α-CF2), –116.9 (s br, 2F; CF2), –121.4 (s br, 2F; CF2), –
121.8 (s br, 4F; 2×CF2), –122.6 (s br, 2F; CF2), –126.0 (s br, 2F; CF2)
ppm. 13C NMR: δ 30.6 (s; CH3), 77.2 (s; CMe2), 108.4 (m; CF2), 110.2
(m; CF2), 111.3–110.3 (m; 3×CF2), 111.3 (m; CF2), 111.4 (s; C-I), 117.2
(m; CF3), 127.6 (s; CH), 128.7 (s br; CH), 129.8 (s; CH), 130.6 (s; CH),
150.0 (s; C-CMe2) ppm; α-CF2 not observed. Single crystals of 8 suitable
for X-ray structural analysis were obtained directly from the reaction
solution.
Acknowledgements
We thank Dr. Nils Trapp from the Small Molecule
Crystallography Center (SMoCC) of ETH Zurich for
determination of the crystal structure of compound 9. General
financial support by ETH Zurich is gratefully acknowledged.
3,3-Dimethyl-1-(perfluorophenyl)-1,3-dihydro-1λ3-benzo[d][1,2]-
iodoxole (“C6F5 alcohol reagent”; 9): *A larger excess of Fluoroiodane
(910 mg, 2.3 equiv.) was used for preparation. Rf = 0.19 (n-hexane/ethyl
acetate 50/50). Yield: 455 mg (82%). M.p. 83–86 °C. Anal. calcd. for
C15H10F5IO (M = 428.14 g/mol): C 42.08, H 2.35 %; Found: C 41.82, H
2.56 %. HRMS: m/z calcd. for [M+H]+, C15H11F5IO: 428.9769; Found:
428.9773. 1H NMR: δ 1.54 (s, 6H; CH3), 6.72 (m, 1H; CH), 7.26 (m, 1H;
CH), 7.40 (m, 1H; CH), 7.50 (m, 1H; CH) ppm. 19F NMR: δ –157.4 (m,
2F; m-CF), –148.8 (m, 1F; p-CF), –123.5 (m, 2F; o-CF) ppm. 13C NMR: δ
31.0 (s; CH3), 76.5 (s; CMe2), 101.1 (m; i-C C6F5), 111.6 (s; C-I of ortho-
phenylene), 126.0 (s; CH), 127.2 (s; CH), 129.6 (s; CH), 130.6 (s; CH),
137.1 (m; o-CF), 143.7 (m; p-CF), 146.5 (m; m-CF), 149.0 (s; C-CMe2)
ppm. Single crystals of 9 suitable for X-ray structural analysis were
obtained by slow evaporation of a CH2Cl2 solution at r.t.
Keywords: Perfluoroalkyl • Perfluoroaryl • Hypervalent Iodine •
Crystal Structure • Supramolecular • Secondary Bonding
Interactions • Iodonium • 19F NMR
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FULL PAPER
Entry for the Table of Contents
Layout 1:
FULL PAPER
The solid state structures of
Hypervalent Iodine Reagents
perfluoroorganyl iodane reagents are
governed by secondary I∙∙∙O bonds,
giving rise to square-planar
coordination of the iodine atom in a
first approximation. In solution, the I-
C(RF) bond is influenced by
Phil Liebing, Ewa Pietrasiak, Elisabeth
Otth, Jorna Kalim, Dustin Bornemann,
and Antonio Togni*
Page No. – Page No.
Supramolecular Aggregation of
Perfluoroorganyl Iodane Reagents in
the Solid State and in Solution
coordination of Lewis-basic solvents
to iodine, and by hydrogen bonding
with protic solvents.
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