Polyfluorinated functionalized m-terphenyls. New substituents and ligands in organometallic synthesis

Article abstract of DOI:10.1021/om500244y

The synthesis and structural characterization of polyfluorinated arenes 2,4,6-(C₆F₅)₃C₆H₂X and 2,6-(C₆F₅)₂-4-BrC₆H₂X (X = NO₂, Cl, Br) obtained in the Ullmann-type cross coupling reaction is reported. The nitro derivatives were reduced to the aromatic amines. The α-diimine [2,4,6-(C₆F₅)₃C ₆H₂NCMe]₂ and 2,4,6-(C₆F ₅)₃C₆H₂I were obtained in condensation and Sandmeyer reactions, respectively, from the corresponding amine. The syntheses of 2,4,6-(C₆F₅)₃C ₆H₂NHC(O)H, 2,4,6-(C₆F₅) ₃C₆H₂NC, and 2,4,6-(C₆F ₅)₃C₆H₂Si(X)Me₂ (X = H, F, Cl) are also described.

Full text of DOI:10.1021/om500244y

Article
pubs.acs.org/Organometallics
Polyfluorinated Functionalized m‑Terphenyls. New Substituents and
Ligands in Organometallic Synthesis
Marian Olaru,†,‡ Jens Beckmann,‡ and Ciprian I. Rat*,†
̧
†Centre of Supramolecular Organic and Organometallic Chemistry, Department of Chemistry, Faculty of Chemistry and Chemical
Engineering, Babes-Bolyai University, 11 Arany Janos Street, 400028 Cluj-Napoca, Romania
‡Institut fur Anorganische Chemie, Universitat Bremen, Leobener Street, 28359 Bremen, Germany
̧
̈
̈
S
* Supporting Information
ABSTRACT: The synthesis and structural characterization of polyfluorinated arenes 2,4,6-(C6F5)3C6H2X and 2,6-(C6F5)2-4-
BrC6H2X (X = NO2, Cl, Br) obtained in the Ullmann-type cross coupling reaction is reported. The nitro derivatives were
reduced to the aromatic amines. The α-diimine [2,4,6-(C6F5)3C6H2NCMe]2 and 2,4,6-(C6F5)3C6H2I were obtained in
condensation and Sandmeyer reactions, respectively, from the corresponding amine. The syntheses of 2,4,6-(C6F5)3C6H2NHC-
(O)H, 2,4,6-(C6F5)3C6H2NC, and 2,4,6-(C6F5)3C6H2Si(X)Me2 (X = H, F, Cl) are also described.
properties of the molybdenum complexes were attributed to
the electron-deficient character of the polyfluorinated terphe-
nolates in combination with their steric bulk.23,24 Isocyanide
derivatives with an electron withdrawing m-terphenyl backbone
were recently used as ligands in molybdenum coordination
chemistry.25
Aromatic C−C bond formation with an aromatic group
containing fluorine atoms has been done in Suzuki cross-
coupling reactions,26−28 by direct arylation reactions (C−H
functionalization) between aryl halides and electron-deficient
fluorinated benzenes,29,30 and in Ullmann-type cross-coupling
reactions.31−33 The related 2,6-(2′,6′-F2C6H3)2C6H3I was
prepared by a Negishi coupling of a 2,6-dibromosubstituted
triazene with the corresponding organozinc halide.15
We envisaged the design of novel substituents with a m-
terphenyl backbone which contain electron-deficient penta-
fluorophenyl groups in flanking positions. m-Terphenyl
substituents with electron withdrawing flanking groups are
less commonly used in coordination and organometallic
chemistry. We hence became interested in studying the
advantages and limitations of these substituents in comparison
with the classical m-terphenyl ligands.
ulky aryl groups are widely used to kinetically stabilize
1,2
Bcompounds with remarkable structures,
and they offer
the possibility to explore the reactivity of rare species.3−6 Large
bulky groups also provide thermodynamic stability to the
unsaturated monomers, with respect to oligomers.7,8 However,
some bulky groups, e.g. the supermesityl group, have an adverse
effect on the stability as steric pressure gives rise to repulsion
and formation of byproducts.9,10
Among the most common and widely used m-terphenyls are
those of type 2,6-Ar2C6H3X (Ar = aryl group, X = functional
group),11 in contrast to those of type 3,5-Ar2C6H3X.12 The
synthesis of both type m-terphenyl precursors is based on the
procedure developed by Hart.13,14 Later on Power et al.
proposed further improvements to the originally used 2,6-
Ar2C6H3X.11 Siegel et al. synthesized and used for the
stabilization of silylium ions the first m-terphenyls containing
fluorine atoms.15,16 Wehmschulte et al. have reported thermally
m-terphenyl stabilized cationic aluminum species.17,18 A rich
and interesting coordination chemistry using sterically
encumbering isocyanide ligands has also been developed.19−22
Recently Schrock et al. investigated the catalytic properties of
some 2,6-bis(pentafluorophenyl)phenoxide complexes of mo-
lybdenum and reported a different behavior compared to
complexes containing phenolates of the type 2,6-Ar2C6H3O−
(Ar = 2,4,6-Me3C6H2 or 2,4,6-iPr3C6H2). The different catalytic
Received: March 11, 2014
© XXXX American Chemical Society
A
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Theoretical studies have shown that the electron deficient
arenes can stabilize both cations and especially anions.34−36 In
theory, novel types of compounds could be stabilized using
these ligands, through intramolecular interactions between the
electron-deficient groups and a metal center located in their
common ortho position due to the fact that C6F5 groups have
both dipole and quadrupole moments. Moreover, the C6F5
groups could also stabilize a heteroatom located in their
common ortho position by F → M intramolecular coordination,
as previously reported for the related ligand 2,6-(2′,6′-
F2C6H3)2C6H3.15,16
We report here a series of polyfluorinated arenes with m-
terphenyl backbone 2,4,6-(C6F5)3C6H2X [X = Cl (1), Br (2),
NO2 (3)] and 2,6-(C6F5)2-4-BrC6H2X [X = Cl (4), NO2 (5)].
Reduction of 3 and 5 affords 2,4,6-(C6F5)3C6H2NH2 (6) and
2,6-(C6F5)2-4-Br-C6H2NH2 (7), respectively. Also we present
functional group transformations that allowed the synthesis of
2,4,6-(C6F5)3C6H2I (8), [2,4,6-(C6F5)3C6H2NCMe]2 (9), and
2,4,6-(C6F5)3C6H2NHC(O)H (10). Isocyanide 2,4,6-
(C6F5)3C6H2NC (11) can be obtained almost quantitatively
starting from 10. The symmetrical derivative 1,3,5-(C6F5)3C6H3
(12) is obtained in better yields than previously reported,37
using 6 as starting material. Metalation with nBuLi of 2 or 8 and
subsequent reaction with Me2Si(H)Cl and Me2SiCl2, respec-
tively, afford 2,4,6-(C6F5)3C6H2Si(H)Me2 (13) and 2,4,6-
(C6F5)3C6H2Si(Cl)Me2 (14). Reaction of 14 with TlPF6 yields
2,4,6-(C6F5)3C6H2Si(F)Me2 (15). Improved synthesis methods
for known starting materials 1,3,5-Br3C6H2X [X = Cl (16),
NO2 (17)] and 1,3,5-I3C6H2X [X = NH2 (18), Cl (19), Br
(20)] are also provided.
material were unsatisfactory. In this case the reaction does not
proceed selectively and 8 is obtained together with other
coupling products. We also attempted to prepare alternatively
2,6-(C6F5)2C6H3I by a route adapted from the Hart procedure.
In our hands, this method failed to give the desired product.
The compounds 2,6-(C6F5)2-4-BrC6H2X [X = Cl (4), NO2
(5)] were synthesized using 2.6 and 3.6 equiv of C6F5Cu and
16 and 17, respectively. These m-terphenyl derivatives, with a
design similar to that of the bulky groups used by Schrock,12 are
of particular importance because the bromine can be
substituted with a different organic fragment or can be replaced
by another functional group. Despite the prolonged reaction
time (11 h), the isolated yield of 4 was low (39%). In the same
reaction, 1 was also isolated in 10% yield as a side-product. The
derivative 5 was obtained after 4 h of reflux in a good yield
(77%).
In all the reactions carried out to prepare 4 and 5, only the
coupling products in positions 2 and 6, with respect to the
functional group (NO2 or Cl), were obtained, suggesting that
the reactions take place regioselectively. Apparently the
substitution of the bromine atoms from position 2 and 6
takes place more readily than the substitution of bromine from
position 4.
Reduction of 3 and 5 with Fe0 and acetic acid (Scheme 2), in
ethanol, afforded the corresponding aniline derivatives 2,4,6-
(C6F5)3C6H2NH2 (6) and 2,6-(C6F5)2-4-BrC6H2NH2 (7),
respectively, in very good yields.
Scheme 2. Synthesis of 6 and 7
Compounds 1−20 were characterized by multinuclear NMR
spectroscopy and HRMS. The molecular structures of 3−5, 9,
13, and 17 were determined by single-crystal X-ray diffraction.
Although the structure of 17 was previously reported,38 the
crystallographic data are not included in CSD. The reduced cell
of 17 is different from that previously reported.
RESULTS AND DISCUSSION
■
Iodide 8, for which a direct method of synthesis could not be
developed, was obtained by diazotation of the aniline derivative
6 (Scheme 3). By using the previously reported methods for
the diazotation of weakly basic amines,40 only the symmetrical
hydrocarbon 1,3,5-(C6F5)3C6H3 (12) was isolated in 80% yield.
The synthesis with low yields (less than 3%) of 12 was
previously reported.37 The 19F NMR data of 12 are now
available.
Synthesis. The compounds 2,4,6-(C6F5)3C6H2X [X = Cl
(1), NO2 (3)] were synthesized by the reaction of 6 equiv of
pentafluorophenylcopper with 16 or 17, respectively, in a
mixture of toluene, dioxane, and THF at 95 °C (Scheme 1).39
2,4,6-(C6F5)3C6H2X [X = Cl (1), Br (2)] can also be prepared
using 19 or 20 as starting materials.
Scheme 1. Synthesis of the Polyfluorinated Arenes 1−5
By using a modified procedure of Krasnokutskaya et al.,41
compound 8 was obtained in 85% yield. The aniline derivative
6 was diazotized at −15 °C in less than 5 min in the presence of
HCl and NaNO2 in acetonitrile. Subsequent reaction of the
diazonium salt with KI afforded 8. Longer reaction time or
higher temperature led to formation of 12 as side product.
The α-diimine [2,4,6-(C6F5)3C6H2NCMe]2 (9) was ob-
tained in the reaction of amine 6 with 2,3-butandione in the
presence of 2 equiv of p-toluenesulfonic acid and 4 Å molecular
sieves in a poor yield (8%) after approximately 5 days of
heating the reaction mixture at 130 °C.
The chloride 1 was obtained in a modest yield (26%) when
16 was used as starting material. Using 19 instead, under the
same reaction conditions, the yield of 1 was increased to 92%.
Reaction of 20 with C6F5Cu proceeded selectively to afford 2 in
high yields (84−88%). Attempts to obtain directly the iodide
2,4,6-(C6F5)3C6H2I (8) by using 1,2,3,5-I4C6H2 as starting
Formamide 10 was obtained in 78−83% yields by heating 6
in formic acid for 5 h. The product begins to precipitate after
approximately 3 h. Although in the NMR spectra resonances
for both isomers of 10 are present (vide infra), in the IR spectra
only one set of bands was observed. The CO stretching
vibration (1705 cm−1) of 10 has a value similar to that of 2,6-
B
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In order to investigate the reactivity of 13 and the behavior of
the 2,4,6-(C6F5)3C6H2 substituent, the synthesis of a silylium
ion, similar to those reported by Siegel,44 was attempted.
Reactions of 13 with [Ph3C][B(C6F5)4] in C6D6 did not lead to
the formation of the expected product, neither at rt or high
temperature. In order to understand the low reactivity of 13
toward [Ph3C][B(C6F5)4], DFT calculations were carried out
(vide infra).
Scheme 3. Synthesis of 8−11
In light of the lack of reactivity of 13, the preparation of the
related silylium ion [2,4,6-(C6F5)3C6H2SiMe2][PF6] by using
14 as starting material was attempted. However, the reactions
of 14 with TlPF6 in acetonitrile at rt afforded only 2,4,6-
(C6F5)3C6H2Si(F)Me2 (15) in almost quantitative yield. This
reaction suggests that the silylilum ion had formed in situ but
abstracted a fluorine atom from the [PF6]− anion with
formation of 15 and PF5.
NMR Studies. The 19F NMR spectra of compounds 1−3, 6,
8, 10, 11, and 13−15 exhibit two sets of resonance signals
corresponding to ortho, para, and meta fluorine atoms of the
two nonequivalent pentafluorophenyl rings located in positions
ortho and para with respect to the functional group.
The 13C NMR spectra of these compounds show the
expected singlet resonances corresponding to the carbon atoms
of the central aromatic rings. Also the two signals (triplets or
triplets of doublets) given by the ipso carbon atoms of the two
nonequivalent F5C6 groups are easily distinguished.
(3′,5′-(CF3)2C6H3)2C6H3NHC(O)H (1707 cm−1)25 or 2,6-
(2′,6′-iPr2C6H3)2C6H3NHC(O)H (1699 cm−1),42 but different
from that of 2,6-Mes2C6H3NHC(O)H (1682 cm−1).43
The 19F NMR spectra of compounds 4 and 5 exhibit one set
of resonance signals corresponding to the ortho, para, and meta
fluorine atoms of the equivalent F5C6 groups. Accordingly, only
one signal corresponding to the ipso carbon atoms of the
pentafluorophenyl rings was observed in the 13C NMR spectra
for these compounds. The signals corresponding to the carbon
atoms directly bonded to fluorine show as distinct doublets of
Dehydration of 10 with POCl3 in the presence of
triethylamine proceeded readily to afford the isocyanide 11
almost quantitatively. The NC stretching vibration of 11 is
2121 cm−1 and is comparable with those of 2,6-(3′,5′-
(CF3)2C6H3)2C6H3NC (2119 cm−1),25 2,6-(2′,6′-iPr2C6H3)2-
C6H3NC (2124 cm−1),42 or 2,6-Mes2C6H3NC (2120 cm−1).43
Metalation in hexane with nBuLi of 2 at rt or of 8 at −78 °C
affords 2,4,6-(C6F5)3C6H2Li. The use of THF as solvent in the
metalation reaction of 8 is not suitable due to nucleophilic
attack of the more reactive nBuLi at the F5C6 groups.
The reaction of Me2Si(H)Cl or Me2SiCl2 with the in situ
formed 2,4,6-(C6F5)3C6H2Li gives 2,4,6-(C6F5)3C6H2Si(H)Me2
(13) and 2,4,6-(C6F5)3C6H2Si(Cl)Me2 (14), respectively
(Scheme 4). Alternatively 14 can be obtained by reacting 13
with SO2Cl2 in dry CH2Cl2 for 18 h. As it does not require any
additional purification of the moisture sensitive derivative 14,
the latter synthetic approach is recommended.
1
multiplets with JC−F coupling constants around 250 Hz.
1
While the H NMR spectra of [2,4,6-(C6F5)3C6H2NCMe]2
(9) exhibit only one set of resonances for both methyl and
aromatic protons, the 19F NMR spectra exhibit two sets of
resonances for the ortho and meta fluorine atoms and one set
for the para fluorine atoms of the C6F5 groups in positions 2
and 6. Although in the 13C NMR spectra the nonequivalence of
the carbon atoms bonded to fluorine is not clear due to broad
resonances caused by C−F couplings, only one set of signals
were observed for the Cipso atoms of the C6F5 groups in
positions 2 and 6, and one set for the C6F5 groups in positions
4. This pattern suggests that the rotation of C6F5 groups is
restricted around an axis containing a fluorine atom in the para
Scheme 4. Synthesis of Silanes 13−15
position and Cipso
.
1
In the H and 19F NMR in (CD3)2CO, C6D6, and CDCl3,
both Z and E isomers of 10 were observed. The molar ratios of
the isomers, calculated based on the integrals of the
1
corresponding resonances in H NMR spectra, are 1:0.13 in
(CD3)2CO, 1:0.21 in C6D6, and 1:0.56 in CDCl3. The
assignment of the resonance signals for the Z and E isomers
1
in the H NMR spectra of 10 was based on COSY, ROESY,
and HSQC experiments. The ratio of the integral values
observed for the two isomers in the 1H NMR was also found in
the 19F NMR spectra.
1
In variable temperature H and 19F NMR spectra of 10 in
(CD3)2CO up to 46 °C or in C6D6 up to 70 °C, the
coalescence was not reached. This suggests that the amide bond
rotation energy barrier of 10 is larger than that in less hindered
similar molecules such as N-phenylformamide.45 Indeed, the
rotation energy barrier in the gas phase calculated for 2,6-
C
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(C6F5)2C6H3NHC(O)H, a simplified model for 10, at the DFT
level is 83 kJ/mol. In the same model, at the specified theory
level, the energy of the Z isomer is 3 kJ/mol smaller than that
of the E isomer.
In the 1H NMR spectrum of 13 the chemical shift
corresponding to the silicon bonded hydrogen atom is
comparable to those observed for previously reported m-
terphenyl substituted silanes.15,16,44 The resonance signals for
the aromatic and methyl protons of 14 and 15 are slightly
downfield shifted compared to the corresponding signal of 13.
In the 29Si NMR spectrum of 13, the chemical shift of silicon
(−19.1 ppm) is also similar to those of other m-terphenyl
substituted silanes.15,16,44 The 29Si NMR spectra of 14 and 15
exhibit resonance signals similar to those reported for
Figure 2. Thermal ellipsoid representation (25% probability) of the
molecular structure of 4.
46
PhSi(Cl)Me2 or 9-(chlorodimethylsilyl)anthracene.47
Molecular Structures of 3−5, 9, and 13. In the
molecular structure of 3 (Figure 1), the pentafluorophenyl
Figure 3. Thermal ellipsoid representation (25% probability) of the
molecular structure of 5.
Figure 1. Thermal ellipsoid representation (25% probability) of the
molecular structure of 3.
groups are twisted with respect to the central aromatic ring due
to intramolecular C−H···F bonds being established between
the hydrogen atoms of the central aryl group and a fluorine
atom of the C6F5 groups in positions 2 and 6 with respect to
the NO2 group, and both fluorine atoms of the C6F5 in position
4. This leads to a propeller-like arrangement with angles
between the planes containing the C6F5 groups and the plane of
the central benzene ring of 60.6(1), 51.9(2), and 36.1(1)°. The
angle between the plane containing the NO2 group and the
plane of the central benzene ring is 47.2(3)°.
Figure 4. Thermal ellipsoid representation (25% probability) of the
molecular structure of 9.
Intermolecular C−H···F contacts are observed between the
one hydrogen atom of the methyl groups and a fluorine atom
(see Supporting Information).
In the crystal, the molecules of 3 are interconnected through
C−F···π interactions (see Supporting Information).
The molecular structure of 13 is depicted in Figure 5. The
Si−Caryl bond length [1.906(6) Å] is in the range of those
found in 2,6-(2′,4′,6′-iPr3C6H2)2C6H3Si(H)F2 [1.990(2) Å]48
or 2,6-(2′,4′,6′-iPr3C6H2)2C6H3Si(H)R (R = 9,10-dihydroan-
thracendi-9,10-yl) [1.8908(17), 1.8946(16) Å],49 2,6-(2′,4′,6′-
iPr3C6H2)2C6H3Si(H)R (R = 9,10-dihydroanthracen-9-yl)
[1.8890(19) Å],49 or 2,6-Mes2C6H3Si(H)Ph2 [1.9043(18)
Å].49 The angles between the planes containing the central
benzene ring and the flanking C6F5 are 88.0(2) and 85.5(2)°.
The C6F5 group in the position para to silicon is rotated by
45.4(2)° with respect to the central benzene ring. Also in the
crystals of 13 there are intermolecular C−F···π and C−H···π
interactions which lead to supramolecular assemblies. The
representation of these interactions as well as interatomic
distances and angles is included in the Supporting Information.
In the molecular structures of 4 (Figure 2) and 5 (Figure 3),
the angles between the planes containing the C6F5 groups and
the central benzene ring are larger than those in 3 [4: 65.9(1),
73.7(1)°; 5: 63.2(1), 78.7(2)°]. In 5 the plane containing the
NO2 group is rotated with 44.9(3)° with respect to the plane of
the central benzene ring, similar to the value found in 3. In the
crystals of 4 and 5, there are a plethora of C−X···π (X =
halogen) intermolecular interactions which lead to supra-
molecular assemblies (see Supporting Information).
In the crystal, molecules of 9 are centrosymmetric with
respect to an inversion center located at half the distance
between the carbon atoms of the imino groups (Figure 4). The
C6F5 groups in positions 2 and 6 form a wedge shape cavity in
which the methyl and imino groups are located.
D
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layer chromatography was used 0.060−0.200 mm, 60 Å silica gel, and
silica gel 60 coated aluminum sheets with F254 indicator, respectively.
The NMR spectra were recorded on Bruker Avance III DPX-360,
1
Bruker Avance III 400, and Bruker Avance III 600 spectrometers. H
and 13C chemical shifts are reported in δ units (ppm) relative to the
residual peak of solvent (CHCl3, 7.26 ppm; CD3C(O)CD2H 2.05
ppm; C6D5H 7.16 ppm) in the 1H NMR spectra and to the peak of the
deuterated solvent (CDCl3 77.16 ppm; (CD3)2CO 29.84 ppm; C6D6
128.06 ppm) in 13C NMR spectra.50 19F and 29Si NMR spectra are
reported in δ units (ppm) relative to CFCl3 (0 ppm) and Me4Si (0
ppm), respectively, using the chemical shift of the lock solvent as a
1
reference. The 13C, 19F, and 29Si reported spectra are H decoupled.
The chemical shifts in the 13C NMR spectra of the compounds
substituted with pentafluorophenyl groups in positions 2, 4, and 6 are
given only as ranges for the observed multiplets, without taking into
1
account the JC−F coupling constants.
HRMS APCI(+) spectra were recorded on a Thermo Scientific
Orbitrap XL spectrometer. Data analysis and calculations of the
theoretical isotopic patterns were carried out with the Xcalibur
software package.51
Figure 5. Thermal ellipsoid representation (30% probability) of the
molecular structure of 13.
X-ray Crystallography. Crystallographic data were collected at rt
on a Bruker Smart APEX II (3−5, 9, 17) or at 173 K on a STOE IPDS
(13) diffractometer with graphite monocromators using Mo Kα
radiation (0.71073 Å). Crystals were mounted on a loop using Paraton
or Kel-F (13) oil. The structures were solved and refined with the
SHELXL-97 or SHELX-2013 software package.52 All the non-
hydrogen atoms were treated anisotropically. Hydrogen atoms were
included in riding positions with the isotropic thermal parameters set
1.2 times the thermal parameters of the carbon atoms directly attached
for the aromatic hydrogen atoms and 1.5 times for the hydrogen atoms
of the methyl groups. The hydrogen atom bonded to silicon in 13 was
located in the electron density map and its position and isotropic
temperature factor refined. The ring centroids and intramolecular and
intermolecular interactions were calculated using PLATON.53 The
representation of the crystallographic data and calculations of the
angles between the planes were carried out using Diamond.54
Theoretical Calculations. Theoretical calculations at the DFT
level on 2,6-(C6F5)2C6H3NHC(O)H, a slightly smaller model for
compound 10, were carried out using ORCA 2.9.1 whereas ORCA
3.0.0 and 3.0.1 were used for 2,6-(2′,6′-F2C6H3)2C6H3Si(H)Me2 and
2,6-(2′,6′-Me2C6H3)2C6H3Si(H)Me2 13 and the silylium ions.55 The
calculations were carried out using the BP86 functional and atom-
pairwise dispersion correction with the zero-damping scheme.56−58
The def2-TVP basis set was used for all the atoms of 10,59,60 and def2-
SVP for all the atoms of 13, 2,6-(2′,6′-F2C6H3)2C6H3Si(H)Me2, 2,6-
(2′,6′-Me2C6H3)2C6H3Si(H)Me2, and the corresponding silylium ions.
The energy minimum for the calculated structures was confirmed by
the frequencies calculation. Wiberg bond indices were calculated with
NBO 5.9.61 The DFT calculated molecular structures were
represented using Chemcraft, whereas the electrostatic potential
maps were represented using PyMOL 1.7.0.1.62
Synthesis of 2,4,6-(C6F5)3C6H2Cl (1). A 100 mL, three-necked,
round-bottom flask fitted with a reflux condenser, argon inlet, and
dropping funnel was charged with magnesium turnings (0.68 g, 27.94
mmol). Anhydrous THF (50 mL) was collected in the dropping
funnel. After THF (20 mL) was introduced into the flask, C6F5Br
(5.75 g, 23.3 mmol) was added in the dropping funnel. Via syringe,
1,2-Br2C2H4 (0.875 g, 4.66 mmol) was introduced in the flask and the
mixture was heated gently to reflux. Continuing to heat the reaction
mixture, the solution of C6F5Br in THF was added dropwise from the
dropping funnel at a rate that afforded a gentle reflux. The reaction
mixture was stirred at 86 °C (oil bath temperature) for 1.5 h and then
was allowed to cool to rt. The resulting dark brown solution
containing the C6F5MgBr was added over anhydrous copper(I)
bromide (5.01 g 34.9 mmol), under argon atmosphere, in a 250 mL
three-necked, round-bottom flask fitted with a reflux condenser, argon
inlet, and dropping funnel. The brown suspension was stirred at rt for
30 min, dioxane (7 mL) was added to the reaction mixture, and the
resulting gray suspension was stirred at rt for another 30 min. To this
suspension was added a solution of 19 (1.900 g, 3.88 mmol) in 50 mL
Theoretical Studies. Theoretical calculations at the DFT
level were carried out on 13 as well as on the related 2,6-(2′,6′-
F2C6H3)2C6H3Si(H)Me2 and 2,6-(2′,6′-Me2C6H3)2C6H3Si(H)-
Me2. The last two compounds were successfully used as starting
materials for compounds containing silylium ions.15,44
The comparison of the calculated and determined bond
lengths and bonding angles for 13 is presented in Supporting
Information, Table 15. The Si−C bond lengths and C−Si−C
and C−Si−H bond angles are within 3% agreement to those
determined from the crystallographic data. In the calculated
structure the pentafluorophenyl groups are oriented slightly
differently with respect to the central benzene ring. The Wiberg
bond indices for Si−H in the calculated structures have similar
values for 2,6-(2′,6′-F2C6H3)2C6H3Si(H)Me2 (0.9217) and for
13 (0.9211) and are slightly larger than those for 2,6-(2′,6′-
Me2C6H3)2C6H3Si(H)Me2 (0.9178). The calculated bond
indices suggest that in 13 the Si−H bond is stronger than
that in the previously reported silanes. These values are also
consistent with the IR data.
The energies of the reactions between 2,6-(2′,6′-
F2C6H3)2C6H3Si(H)Me2, 2,6-(2′,6′-Me2C6H3)2C6H3Si(H)-
Me2, 13, and [Ph3C]+ with formation of the corresponding
silylium ions and Ph3CH are −37.89, −25.29, and 14.82 kJ·
mol−1, respectively. These values indicate that, at the employed
theory level, the reaction between the trityl cation and 13 is not
energetically favorable.
CONCLUSIONS
■
In conclusion, we report a simple synthetic method for
polyfluorinated functionalized m-terphenyls that may be useful
ligands and substituents in novel organometallic compounds
with sterically demanding electron withdrawing substituents.
Further studies on the use of these m-terphenyls in the main
group organometallic chemistry are in progress.
EXPERIMENTAL SECTION
■
General Considerations. Unless otherwise indicated, starting
materials were used without further purification. The solvents were
distilled, under argon atmosphere, from appropriate drying agents
(sodium for dioxane, hexane, and toluene, potassium for tetrahy-
drofuran, phosphorus oxide for dichloromethane, calcium hydride for
acetonitrile) prior to use. All the other solvents were used as received.
The preparations of compounds 1−5, 9, 11, and 13−15 were
performed under an argon atmosphere, and the work up of the
reactions was carried out in air except for 14. For the column and thin
E
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of toluene. The mixture was stirred at 95 °C (oil bath temperature) for
approximately 18 h over 3 days. The reaction mixture was filtered
through a pad of silica gel approximately 6 cm thick. The solvents were
removed from the filtrate using a rotary evaporator. The residue was
heated at 65−75 °C (2 × 10−2 mbar) in a sublimation apparatus to
remove decafluorobiphenyl. The remaining residue was dissolved in
petroleum ether (150 mL) and the solution filtered through a 6 cm
thick pad of silica gel. The silica gel pad was further washed with 150
mL of petroleum ether. Evaporation of the solvent gave 1 (2.19 g
149.84 (s), 146.21−145.65 (m), 144.18−143.56 (m), 142.87−142.28
(m), 140.79−139.30 (m), 136.95−136.03 (m), 135.78 (s), 131.04 (s),
122.89 (s), 112.08 (td, J = 16, 4 Hz), 110.29 (td, J = 18, 4 Hz); 19F
NMR (CDCl3, 282 MHz): δ −139.85 − −140.06 (m, 4F), −142.18 −
−142.41 (m, 2F), −150.46 (t, J = 21.0 Hz, 1F), −150.65 (t, J = 21.0
Hz, 2F), −159.68 − −160.11 (m, 6F); HRMS-APCI (m/z): [M]+
calcd for C24H2F15NO2, 620.98405; found, 620.98489.
Synthesis of 2,6-(C6F5)2-4-BrC6H2Cl (4). To a solution of
C6F5MgBr in THF (50 mL), prepared as described for the synthesis
of 1 from magnesium turnings (0.568 g, 23.4 mmol), was added 1,2-
Br2C2H4 (1.01 g, 5.4 mmol) and C6F5Br (4.45 g, 18 mmol) over
anhydrous copper(I) bromide (3.87 g, 27 mmol), placed under argon
atmosphere, in a 250 mL three-necked, round-bottom flask fitted with
a reflux condenser, argon inlet, and dropping funnel. The brown
suspension was stirred at rt for 30 min, and afterward, dioxane (6 mL)
was added and the resulting gray suspension was stirred at rt for
another 30 min. To this suspension was added a solution of 16 (1.772
g, 5 mmol) in toluene (50 mL). The reaction mixture was stirred at 95
°C (oil bath temperature) for a total of 11 h over 2 days. The reaction
mixture was filtered through an approximately 6 cm thick pad of silica
gel. The solvents were removed from the filtrate using a rotary
evaporator, resulting a brown oil. Separation by column chromatog-
raphy with petroleum ether using silica gel as stationary phase afforded
4 (1.02 g, 39%) as a colorless oil, which solidified upon addition of
1
(92%)) as a white solid. Mp 168−170 °C; H NMR (CDCl3, 300
MHz): δ 7.57 (s, 2H); 13C NMR (CDCl3, 75 MHz): δ 146.23−145.74
(m), 143.85−143.37 (m), 142.87−142.47 (m), 140.46−139.30 (m),
136.78−136.17 (m), 136.11 (s), 134.96 (s), 128.11 (s), 126.01 (s),
113.06 (td, J = 16, 4 Hz), 112.42 (td, J = 19, 4 Hz); 19F NMR (CDCl3,
282 MHz): δ −138.88 to −139.09 (m, 4F), −142.58 to −142.78 (m,
2F), −152.14 (tt, J = 21 Hz, 2F), −152.48 (t, J = 21.0 Hz, 1F),
−160.56 to −160.81 (m, 2F), −160.85 to −161.11 (m, 4F); HRMS-
APCI (m/z): [M]+ calcd for C24H2ClF15, 609.96000; found,
609.95886.
Synthesis of 2,4,6-(C6F5)3C6H2Br (2). To a solution of C6F5MgBr
in THF (100 mL), prepared as described for the synthesis of 1 from
magnesium turnings (2.19 g, 90 mmol), was added 1,2-Br2C2H4 (2.82
g, 15 mmol) and C6F5Br (18.5 g, 75 mmol) over anhydrous copper(I)
bromide (13.1 g, 91 mmol), placed, under argon atmosphere, in a 500
mL three-necked, round-bottom flask fitted with a reflux condenser,
argon inlet, and dropping funnel. The brown suspension was stirred at
rt for 30 min; afterward, dioxane (30 mL) was added over the reaction
mixture and the resulting gray suspension was stirred at rt for another
30 min. To this suspension was added a solution of 20 (6.668 g, 12.5
mmol) in toluene (100 mL). The reaction mixture was stirred at 95 °C
(oil bath temperature) for approximately 16 h over 3 days. The
reaction mixture was filtered through a pad of silica gel approximately
6 cm thick. The solvents were removed from the filtrate using a rotary
evaporator affording a slightly oily solid. This product was heated at
75−105 °C (2 × 10−2 mbar) in a sublimation apparatus to remove
decafluorobiphenyl and other impurities. The remaining residue (8.1
g) was dissolved in 500 mL of heptane and filtered through a pad of
silica gel approximately 6 cm thick. The solvent was recovered and
reused to wash again the silica gel pad. 2 (7.22 g, 88%) was obtained as
a white solid which contained approximately 3% mol (calculated based
1
ethanol, and 1 (0.300 g, 10%) as side product. Mp 111−113 °C; H
NMR (CDCl3, 300 MHz): δ 7.62 (s, 2H); 13C NMR (CDCl3, 75
MHz): δ 144.28 (dm, J = 250 Hz), 141.95 (dm, J = 256 Hz), 137.96
(dm, J = 250 Hz), 136.18 (s), 134.09 (s), 128.93 (s), 120.58 (s),
112.03 (td, J = 19, 4 Hz); 19F NMR (CDCl3, 282 MHz): δ −138.92 −
−139.17 (m, 4F), −152.06 (tt, J = 21, 2 Hz, 2F), −160.87 − −161.12
(m, 4F); HRMS-APCI (m/z): [M]+ calcd for C18H2BrClF10,
521.88632; found, 521.88890.
Synthesis of 2,6-(C6F5)2-4-BrC6H2NO2 (5). To a solution of
C6F5MgBr in THF (60 mL), prepared as described for the synthesis of
1 from magnesium turnings (0.410 g, 16.9 mmol), was added 1,2-
Br2C2H4 (0.732 g, 3.9 mmol) and C6F5Br (3.21 g, 13 mmol) over
anhydrous copper(I) bromide (2.79 g, 19.5 mmol), placed, under
argon atmosphere, in a 250 mL three-necked, round-bottom flask
fitted with a reflux condenser, argon inlet, and a dropping funnel. The
brown suspension was stirred at rt for 30 min; afterward, dioxane (6
mL) was added and the resulting gray suspension was stirred at rt for
another 30 min. To this suspension was added a solution of 17 (1.800
g, 5 mmol) in toluene (60 mL). The reaction mixture was stirred at 95
°C (oil bath temperature) for approximately 4 h and at rt overnight.
The contents of the flask were filtered through an approximately 6 cm
thick pad of silica gel. The solvents were removed from the filtrate
using a rotary evaporator. The residue was triturated with
approximately 30 mL of petroleum ether, and then the solvent was
removed to leave a slightly yellow solid. The solid was heated at 85−
95 °C (2 × 10−2 mbar) in a sublimation apparatus to remove
decafluorobiphenyl. Further heating at 120 °C (2 × 10−2 mbar)
afforded the sublimation of 5 (2.048 g, 77%) as a light yellow solid.
1
on NMR integral ratio) of 12. Mp 170−172 °C; H NMR (CDCl3,
400 MHz): δ 7.53 (s, 2H); 13C NMR (CDCl3, 101 MHz): δ 145.73−
145.25 (m), 143.44−142.44 (m), 140.89−140.43 (m), 140.36−139.79
(m), 139.76−138.91 (m), 137.25−136.41 (m), 134.65 (s), 130.65 (s),
127.90 (s), 126.76 (s), 114.43 (td, J = 19, 4 Hz), 113.11 (td, J = 16, 4
Hz); 19F NMR (CDCl3, 376 MHz): δ −138.87 − −139.05 (m, 4F),
−142.56 − −142.71 (m, 2F), −152.29 (t, J = 21 Hz, 2F), −152.46 (t, J
= 21 Hz, 1F), −160.60 − −160.82 (m, 2F), −160.90 − −161.11 (m,
4F); HRMS-APCI (m/z): [M]+ calcd for C24H2BrF15, 653.90949;
found, 653.90750.
Synthesis of 2,4,6-(C6F5)3C6H2NO2 (3). A solution of C6F5MgBr
in THF (100 mL), prepared as described for the synthesis of 1 from
magnesium turnings (1.75 g, 72 mmol), was added 1,2-Br2C2H4 (2.25
g, 12 mmol) and C6F5Br (14.8 g, 60 mmol) over anhydrous copper(I)
bromide (12.9 g, 90 mmol), placed, under argon atmosphere, in a 500
mL three-necked, round-bottom flask fitted with a reflux condenser,
argon inlet, and dropping funnel. The brown suspension was stirred at
rt for 30 min; afterward, dioxane (20 mL) was added over the reaction
mixture and the resulting gray suspension was stirred at rt for another
30 min. To this suspension was added a solution of 17 (3.600 g, 10
mmol) in toluene (100 mL). The reaction mixture was stirred at 95 °C
(oil bath temperature) for approximately 36 h over 4 days. The
reaction mixture was filtered through a pad of silica gel approximately
6 cm thick. The solvents were removed from the filtrate using a rotary
evaporator affording a slightly oily solid. This product was heated at
85−95 °C (2 × 10−2 mbar) in a sublimation apparatus to remove
decafluorobiphenyl. The remaining residue was washed with pentane
(4 × 10 mL) and decanted, and the solid was dried at reduced pressure
1
Mp 147−149 °C; H NMR (CDCl3, 300 MHz): δ 7.76 (s, 2H); 13C
NMR (CDCl3, 75 MHz): δ 148.92 (s), 144.18 (dm, J = 250 Hz),
142.23 (dm, J = 258 Hz), 137.97 (dm, J = 252 Hz), 136.89 (s), 126.38
(s), 123.71 (m), 109.90 (td, J = 18, 4 Hz); 19F NMR (CDCl3, 282
MHz): δ −139.75 − −139.95 (m, 4F), −150.62 (tt, J = 21, 2 Hz, 2F),
−159.92 − −160.16 (m, 4F); HRMS-APCI (m/z): [M]+ calcd for
C18H2BrF10NO2, 532.91037; found 532.91106.
Synthesis of 2,4,6-(C6F5)3C6H2NH2 (6). To a solution of 3 (3.790
g, 6.1 mmol) in ethanol (75 mL) was added iron powder (1.370 g,
24.4 mmol) and glacial acetic acid (4.2 mL). The mixture was
vigorously stirred at 70 °C for 3 h, and afterward, all volatiles were
removed with a rotary evaporator. Over the red residue was added
dichloromethane (50 mL), and the suspension was filtered through a
pad of Celite. The filtrate was washed with 3 × 10 mL of distilled
water, and the organic fraction was dried on Na2SO4 and filtered.
Removal of the solvent afforded 6 (3.48 g, 98%) as an off-white solid.
1
1
to give 3 (3.93 g, 63%) as a tan solid. Mp 185−187 °C; H NMR
Mp 171−173 °C; H NMR (CDCl3, 300 MHz): δ 7.33 (s, 2H, CH),
(CDCl3, 300 MHz): δ 7.72 (s, 2H); 13C NMR (CDCl3, 75 MHz): δ
3.80 (br, 2H, NH); 13C NMR (CDCl3, 75 MHz): δ 146.58−145.71
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(m), 144.04 (s), 143.68−142.43 (m), 142.35−141.74 (m), 140.3−
139.48 (m), 138.98−138.38 (m), 136.93−136.12 (m), 134.90 (s),
116.41 (s), 114.40 (td, J = 17, 4 Hz), 112.79 (s), 111.64 (td, J = 19, 4
Hz); 19F NMR (CDCl3, 282 MHz): δ −138.30 − −138.54 (m, 4F),
−143.57 (dd, J = 23, 8 Hz, 2F), −152.68 (t, J = 21 Hz, 2F), −155.51
(t, J = 21 Hz, 1F), −160.17 − −160.41 (m, 4F), −161.90 − −162.13
a consequence, more TsOH·H2O (190 mg, 1.00 mmol) was added
together with additional 4 Å molecular sieves and the mixture was
heated to 130 °C over another 3 days. The molecular sieves were
removed by filtration, the solution was washed with water (2 × 20
mL), and the organic phase was separated and dried on Na2SO4. The
residue obtained after filtration and solvent removal was dissolved in
ethanol and cooled to 0 °C. The precipitate was filtered and washed
with a small amount of chloroform and then with pentane, and was
dried at reduced pressure to give 9 (205 mg, 8%) as a yellow solid. Mp
1
(m, 2F); H NMR ((CD3)2CO, 300 MHz): δ 7.50 (s, 2H, CH), 5.35
(br, 2H, NH); 13C NMR ((CD3)2CO, 75 MHz): δ 147.87−147.31
(m), 147.19 (s), 147.05−146.57 (m), 144.57−144.07 (m), 144.01−
143.36 (m), 142.77−142.10 (m), 141.00−140.08 (m), 139.54−138.85
(m), 137.69−136.88 (m), 135.61 (s), 115.93 (td, J = 17, 4 Hz), 114.71
(s), 113.35 (td, J = 20, 4 Hz), 112.46 (s); 19F NMR ((CD3)2CO, 282
MHz): δ −141.07 (dd, J = 23, 8 Hz, 4F), −145.23 (dd, J = 23, 8 Hz,
2F), −157.97 (t, J = 21 Hz, 2F), −159.16 (t, J = 21 Hz, 1F), −164.28
− −164.57 (m, 4F), −164.85 − −165.11 (m, 2F); HRMS-APCI (m/
z): [M]+ calcd for C24H4F15N, 591.00987; found, 591.00913; [M +
H]+ calcd for C24H5F15N, 592.01770; found, 592.01652.
1
295−297 °C; H NMR ((CD3)2CO, 300 MHz): δ 7.86 (s, 4H, CH),
1.66 (s, 6H, CH3); 13C NMR ((CD3)2CO, 75 MHz): δ 170.52 (s),
149.49 (s), 147.42−146.68 (m), 146.31−145.78 (m), 144.23−143.03
(m), 143.06−142.44 (m), 140.91−139.62 (m), 137.60−136.47 (m),
135.97 (s), 123.96 (s), 118.14 (s), 114.84 (td, J = 17, 4 Hz), 113.19
(td, J = 19, 3 Hz), 16.27 (s); 19F NMR ((CD3)2CO, 282 MHz): δ
−139.38 (dd, J = 22, 6 Hz, 4F), −142.94 (dd, J = 22, 5 Hz, 4F),
−144.68 (dd, J = 22, 8 Hz, 4F), −155.59 (t, J = 15 Hz, 4F), −157.03
(t, J = 21 Hz, 2F), −163.53 − −163.87 (m, 4F), −164.21 − −164.67
(m, 8F); HRMS-APCI (m/z): [M + H]+ calcd for C52H11F30N2,
1233.04377; found, 1233.04513.
Synthesis of 2,6-(C6F5)2-4-BrC6H2NH2 (7). To a solution of 5
(1.000 g, 1.87 mmol) in ethanol (50 mL) was added iron powder
(0.419 g, 7.5 mmol) and glacial acetic acid (1.3 mL). The mixture was
vigorously stirred at 70 °C for 3 h, and afterward, all volatiles were
removed with a rotary evaporator. Over the red residue was added
dichloromethane (40 mL), and the suspension was filtered through a
pad of Celite. The filtrate was washed with 3 × 10 mL of distilled
water, and the organic fraction was dried on Na2SO4 and filtered. After
evaporation of the solvent at reduced pressure, the oily residue was
triturated with 3 mL of cold pentane. The solution was decanted off,
and the remaining solid was washed with cold pentane (2 × 2 mL).
The solid was dried at reduced pressure to obtain 7 (0.647 g, 72%) as
Synthesis of 2,4,6-(C6F5)3C6H2NHC(O)H (10). A 10 mL round-
bottom flask was charged with 6 (118 mg, 0.2 mmol) and formic acid
(3 mL). The flask was fitted with a reflux condenser, and the mixture
was heated at 70 °C (oil bath temperature) for 5 h. After
approximately 2.5−3 h, a white precipitate formed. All volatiles were
removed at reduced pressure. The product was separated by column
chromatography with dichloromethane using silica gel as stationary
phase. Removal of the solvent afforded 10 (103 mg, 83%) as an off-
1
white solid. Mp 221−223 °C; H NMR ((CD3)2CO, 400 MHz): δ Z
1
a white solid. Mp 136−138 °C; H NMR (CDCl3, 300 MHz): δ 7.33
isomer 9.26 (s, 1H, NH), 7.97 (s, C(O)H), 7.91 (s, CH); E isomer
9.11 (br, 0.13H, NH), 7.99 (s, CH), 7,95 (br, C(O)H); 13C NMR
((CD3)2CO, 101 MHz): δ 163.15 (s), 159.73 (s), 159.65 (s), 146.77−
146.35 (m), 144.31−143.93 (m), 143.53−142.91 (m), 141.02−140.42
(m), 140.39−139.72 (m), 137.92−137.22 (m), 137.07 (s), 136.95 (s),
136.45 (s), 135.65 (s), 126.78 (s), 126.50 (s), 126.09 (s), 114.86 (td, J
= 17, 4 Hz), 113.95 (td, J = 19, 4 Hz); 19F NMR ((CD3)2CO, 376
MHz): δ Z isomer −141.38 − −141.53 (m, 4F), −156.75 (t, J = 21
Hz, 0.96F), −157.10 (t, J = 20 Hz, 2.01F), −164.50 − −164.70 (m,
3.81F); E isomer −141.08 − −141.24 (m, 0.52F), −155.78 (t, J = 20
Hz, 0.25F), −156.47 (t, J = 21 Hz, 0.12F), −163.62 − −163.83 (m,
0.47F); overlapped resonance signals of Z and E isomers −144.40 −
−144.56 (m, 2.16F), −164.12 − −164.39 (m, 2.04F); 1H NMR
(C6D6, 600 MHz): δ E isomer 7.66 (d, J = 10 Hz, 0.21H, C(O)H),
7.28 and 7.27 (d corresponding to NH overlapped with the singlet
corresponding to CH, 0.75H); Z isomer 7.35 (s, CH, 2H), 7.11 (s,
C(O)H, 1.15H), 5.76 (s, NH, 1H); 19F NMR (C6D6, 565 MHz): δ E
isomer −140.52 − −140.64 (m, 0.85F), −143.68 (dd, J = 23, 7 Hz,
0.43F), −151.07 (t, J = 22 Hz, 0.39F), −152.91 (t, J = 22 Hz, 0.21F),
−159.85 − −160.04 (m, 0.73F), −160.90 − −161.05 (m, 0.37F); Z
isomer −140.24 (dd, J = 23, 7 Hz, 4F), −143.57 (dd, J = 23, 8 Hz, 2F),
−153.04 (t, J = 22 Hz, 1.90F), −153.39 (t, J = 22 Hz, 0.95F), −161.19
− −161.37 (m, 5.24F); 1H NMR (CDCl3, 600 MHz): δ Z isomer 7.96
(s, 1H, C(O)H), 7.62 (s, 2H, CH), 7.03 (s, 1H, NH); E isomer 7.80
(d, J = 10 Hz, 0.56H, C(O)H), 7.65 (s, 1.25H, CH), 7.06 (d, J = 11
Hz, 0.6H, NH); 19F NMR (CDCl3, 565 MHz): δ Z isomer −139.93
(dd, J = 22, 7 Hz, 4F), −142.62 (dd, J = 23, 8 Hz), −152.13 (t, J = 21
Hz), −152.63 (t, J = 21 Hz, 0.92F), −160.67 − −160.82 (m, 1.70F); E
isomer −139.59 (dd, J = 22, 7 Hz, 2.44F), −142.69 (dd, J = 27, 8 Hz),
−150.64 (t, J = 21 Hz, 1.15F), −152.05 (t, 21 Hz), −159.24 −
−159.43 (m, 2.13F); overlapped resonance signals of Z and E isomers
−160.27 − −160.54 (m, 4.50F); IR (KBr pellet, υ, cm−1): 3231 (br,
NH), 2886 (s, CH carbonyl) 1705 (s, CO); HRMS-APCI (m/z): [M
+ H]+ calcd for C25H5F15NO, 620.01261; found, 620.01513.
(s, 2H, CH), 3.58 (s, 2H, NH); 13C NMR (CDCl3, 75 MHz): δ 144.51
(dm, J = 250 Hz), 143.67−143.07 (m), 142.50 (s), 140.32−139.54
(m), 136.90−136.18 (m), 135.52 (s), 114.27 (s), 111.19 (td, J = 19, 4
Hz), 109.79 (s); 19F NMR (CDCl3, 282 MHz): δ −138.40 (dd, J = 23,
8 Hz, 4F), −152.40 (t, J = 21 Hz, 2F), −160.04 − −160.32 (m, 4F);
HRMS-APCI (m/z): [M]+ calcd for C18H4BrF10N, 502.93620; found,
502.93597; [M + H]+ calcd for C18H5BrF10N, 503.94402; found,
503.94338.
Synthesis of 2,4,6-(C6F5)3C6H2I (8). A 50 mL round-bottom flask
was charged with 6 (0.39 g, 0.57 mmol) acetonitrile (8 mL) and 12 M
HCl (0.2 mL; 2.40 mmol). The mixture was cooled to −15 °C in an
ice-salt bath. A solution of sodium nitrite (0.079 g, 1.14 mmol) in
water (0.3 mL) was added dropwise to the reaction mixture. The
resulting yellow solution was stirred at −15 °C for a time not
exceeding 5 min, and a solution of KI (0.237 g, 1.43 mmol) in water
(0.3 mL) was added. Longer reaction times lead to the formation of
1,3,5-(C6F5)3C6H3 as side product. The reaction mixture was stirred
for 15 min at −15 °C and another 30 min at rt, and afterward, water
(40 mL) was added. The formed precipitate was filtered, washed with
3 × 15 mL of water, and then collected from the glass frit and dried at
reduced pressure. Sublimation at 130 °C (2 × 10−2 mbar) afforded 8
1
(0.345 g, 86%) as a white solid. Mp 180−182 °C; H NMR (CDCl3,
600 MHz): δ 7.45 (s, 2H); 13C NMR (CDCl3, 151 MHz): δ 145.21−
144.78 (m), 143.56−143.14 (m), 143.05−142.68 (m), 142.41−142.04
(m), 141.35−140.98 (m), 140.68−140.34 (m), 140.68−140.34 (m),
137.61−137.03 (m), 135.54 (s), 133.34 (s), 127.73 (s), 117.97 (td, J =
19, 4 Hz), 113.17 (td, J = 16, 4 Hz), 107.14 (s); 19F NMR (CDCl3,
565 MHz): δ −138.95 (dd, J = 22, 7 Hz, 4F), −142.56 (dd, J = 22, 8
Hz, 2F), −152.36 (t, J = 21 Hz, 2F), −152.46 (t, J = 21 Hz, 1F),
−160.61 − −160.81 (m, 2F), −160.82 − −160.98 (m, 4F); HRMS-
APCI (m/z): [M]+ calcd for C24H2F15I, 701.89562; found, 701.89714.
Synthesis of [2,4,6-(C6F5)3C6H2NCMe]2 (9). A 250 mL, three-
necked, round-bottom flask fitted with a reflux condenser, argon inlet,
and dropping funnel was charged with 6 (2.40 g, 4 mmol) and TsOH·
H2O (190 mg, 1.00 mmol). The installation was evacuated and refilled
with argon (repeated twice), and then, activated 4 Å molecular sieves,
dry toluene (100 mL), and 2,3-butandione (172 mg, 2.00 mmol) were
added and the mixture was heated to 85 °C (oil bath temperature) for
10 h and then at 130 °C over 2 days. At this time two reaction
products formed but the aniline was still present (verified by TLC). As
Synthesis of 2,4,6-(C6F5)3C6H2NC (11). Under argon atmos-
phere, to a solution of 10 (204 mg, 0.33 mmol) in anhydrous CHCl3
(20 mL) was added triethylamine (191 mg, 1.89 mmol), and
afterward, the mixture was cooled to 0 °C on an ice bath. Via syringe,
POCl3 (124 mg, 0.80 mmol) was carefully added dropwise. The
reaction mixture was allowed to reach rt and was stirred for another 72
h. Afterward, a 1.5 M solution of Na2CO3 (10 mL) was added. After
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30 min of stirring, the organic fraction was separated, washed with
water (3 × 10 mL), dried over Na2SO4, and filtered. The solvent was
removed at reduced pressure using a rotary evaporator. Separation by
column chromatography with petroleum ether/ethyl acetate 5/0.5
using silica gel as stationary phase afforded 11 (192 mg, 97%) as a
white solid. Mp 189−191 °C; 1H NMR (CDCl3, 300 MHz): δ 7.68 (s,
2H); 13C NMR (CDCl3, 75 MHz): δ 173.79 (s), 146.34−145.66 (m),
144.49−143.83 (m), 143.82−143.03 (m), 143.04−142.34 (m),
141.09−140.39 (m), 140.37−139.54 (m), 137.08−136.17 (m),
134.72 (s), 128.53 (s), 127 (s), 126.40 (s), 112.61 (td, J = 16, 4
Hz), 110.31 (td, J = 18, 4 Hz); 19F NMR (CDCl3, 282 MHz): δ
−138.85 to −139.10 (m, 4F), −142.47 to −142.68 (m, 2F), −150.35
(t, J = 21 Hz, 2F), −151.33 (t, J = 21 Hz, 1F), −159.82 to −160.08
(m, 4F), −160.08 to −160.32 (m, 2F); IR (KBr pellet, υ, cm−1): 2121
(s, NC); HRMS-APCI (m/z): [M + H]+ calcd for C25H3F15N,
602.00205; found, 602.00107.
Synthesis of 1,3,5-(C6F5)3C6H3 (12). A 100 mL round-bottom
flask was charged with 6 (887 mg, 1.5 mmol) and 95% sulfuric acid
(13 mL), and the mixture was stirred until all aniline derivative had
dissolved. Sodium nitrite (311 mg, 4.5 mmol) was added portion-wise,
and afterward the reaction mixture was heated at 50 °C for 3 h. After
the mixture was cooled to rt, copper(I) iodide (855 mg, 4.5 mmol)
was added portion-wise. When the evolution of nitrogen ceased, the
stirring was continued at 50 °C for another 3 h. The reaction mixture
was poured in water with ice and extracted with diethyl ether (3 × 25
mL) and dichloromethane (2 × 30 mL). The organic fractions were
combined, washed with a 5% (w/v) sodium sulfite solution (50 mL)
and distilled water (50 mL), and dried over Na2SO4. After filtration
and evaporation of the solvents, the resulting solid was dried at
reduced pressure and heated at 90 °C (2 × 10−2 mbar) in a
sublimation apparatus to remove volatile impurities. Further heating at
160 °C (2 × 10−2 mbar) allowed the sublimation of a slightly yellow
solid. This solid was collected and washed with pentane (6 × 5 mL).
After drying at reduced pressure, 12 (692 mg, 80%) remained as a
white solid. Mp 234−236 °C (232−236 °C lit.);37 1H NMR (CDCl3,
400 MHz): δ 7.63 (s, 3H); 13C NMR (CDCl3, 101 MHz): δ 144.36
(dm, J = 249), 141.23 (dm, J = 255 Hz), 138.20 (dm, J = 254 Hz),
132.79 (s), 127.99 (s), 114.26 (td, J = 17, 4 Hz); 19F NMR (CDCl3,
376 MHz): δ −142.87 (dd, J = 23, 8 Hz, 6F), −153.31 (t, J = 21 Hz,
3F), −160.96 to −161.14 (m, 6F); HRMS-APCI (m/z): [M]+ calcd
for C24H3F15, 575.99897; found, 575.99800.
Synthesis of 2,4,6-(C6F5)3C6H2Si(H)Me2 (13). A 50 mL Schlenk
flask charged with 8 (318 mg, 0.45 mmol) was evacuated and
backfilled with argon (the cycle was performed three times); then
hexane (20 mL) was added, the solution was cooled to −78 °C, and a
2.5 M nBuLi solution in hexane (0.4 mL, 1.0 mmol) was added. The
reaction was stirred at −78 °C and, after 2 h, Me2Si(H)Cl (189 mg,
2.0 mmol) was introduced. After 30 min the cooling bath was removed
and the reaction mixture was stirred at rt for another hour. The
content of the flask was transferred to a separatory funnel. Water (15
mL) and Et2O (15 mL) were added, and the organic layer was
separated and washed with water (3 × 15 mL). The organic layer was
dried over Na2SO4 and filtered, and the solvents were evaporated. The
residue was separated by column chromatography with hexane using
alumina as stationary phase to afford 13 (210 mg, 74%) as a white
solid. Mp 117−119 °C; 1H NMR (CDCl3, 400 MHz): δ 7.43 (s, 2H),
3.87 (s, 1H), −0.02 (d, J = 4 Hz, 6H); 13C NMR (CDCl3, 101 MHz):
δ 145.90−145.40 (m), 143.46−142.24 (m), 141.10 (s), 140.53−
139.68 (m), 139.66−138.81 (m), 137.26−136.21 (m), 134.40 (s),
133.25 (s), 128.44 (s), 116.27 (td, J = 20, 4 Hz), 113.75 (td, J = 16, 4
Hz), −3.48 (s); 19F NMR (CDCl3, 376 MHz): δ −138.84 (dd, J = 23,
8 Hz), −142.66 (dd, J = 23, 8 Hz), −153.12 (t, J = 21 Hz), −153.21 (t,
J = 21 Hz), −161.12 (td, J = 22, 8 Hz), −161.37 (dt, J = 23, 8 Hz); 29Si
NMR (CDCl3, 79 MHz): δ −19.09 (s); IR (KBr pellet, υ, cm−1): 2174
(s, SiH). HRMS-APCI (m/z): [M − H]+ calcd for C26H8F15Si,
633.01503; found, 633.01417.
stirring for 17 h at rt, all volatiles were evaporated at reduced pressure.
Product 14 was obtained as a white moisture sensitive solid. Mp 152−
1
154; H NMR (CDCl3, 400 MHz): δ 7.45 (s, 2H), 0.30 (s, 6H); 13C
NMR (CDCl3, 101 MHz): δ 146.13−145.36 (m), 143.62−142.33
(m), 140.80−140.30 (m), 140.30−139.83 (m), 139.34 (s), 139.74−
138.93 (m), 137.24−136.40 (m), 134.22 (s), 134.15 (s), 129.30 (s, J =
13.4 Hz), 116.51 (td, J = 20, 4 Hz), 113.29 (td, J = 16, 4.0 Hz), 4.47
(s); 19F NMR (CDCl3, 376 MHz): δ −138.11 to −138.66 (m, 4F),
−142.39 to −142.70 (m, 2F), −152.33 to −152.71 (two overlapped
triplets, 3F), −160.76 to −161.00 (m, 2F), −161.00 to −161.27 (m,
4F); 29Si NMR (CDCl3, 79 MHz): δ 18.67 (s); HRMS-APCI (m/z):
[M − Cl]+ calcd for C26H8F15Si, 633.01503; found, 633.01489.
Synthesis of 2,4,6-(C6F5)3C6H2Si(F)Me2 (15). Under argon
atmosphere, a solution of TlPF6 (124 mg, 0.35 mmol) in dry
acetonitrile (3 mL) was added via syringe to 14 (237 mg, 0.35 mmol)
dissolved in dry acetonitrile (3 mL). A white precipitate formed
instantly. The reaction mixture was stirred overnight at rt. The clear
solution was separated from the decanted precipitate, which was
washed with dry toluene (6 mL). After the evaporation of all volatiles
at reduced pressure from the combined solutions, 15 (225 mg, 97%)
was obtained as a white solid. Mp 125−127 °C; 1H NMR (CDCl3, 400
MHz): δ 7.45 (s, 2H), 0.14 (d, 6H, 3JF,H = 8 Hz); 13C NMR (CDCl3,
101 MHz): δ 145.90−145.43 (m), 143.44−142.42 (m), 140.49−
139.87 (m), 139.61−139.25 (m), 139.18−138.78 (m), 137.14−136.70
(m), 136.66−136.32 (m), 133.68−133.62 (two s overlapped), 129.15,
116.13 (td, J = 20, 3 Hz), 113.49 (td, J = 16, 4 Hz), 0.17 (d, J = 15.2
Hz); 19F NMR (CDCl3, 376 MHz): δ −139.07 (dd, J = 23.1, 8.3 Hz,
4F), −142.39 to −142.99 (m, 2F), −152.75 (t, J = 20.6 Hz, 1 F),
−152.87 (d, J = 20.9 Hz, 2F), −155.63 (s, 1F), −160.87 to −161.06
(m, 2F), −161.35 to −161.54 (m, 4F); 29Si NMR (CDCl3, 79 MHz):
1
δ 21.24 (d, JSi,F = 280 Hz); HRMS-APCI (m/z): [M]+ calcd for
C26H8F16Si, 652.01343; found, 652.01504.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 13C and 19F NMR and HRMS spectra, crystal data,
refinement details, depiction of the C−F···π and F···H−C
interactions, CIFs, coordinates of the calculated molecular
structures for Z and E isomers of 2,6-(C6F5)2C6H3NHC(O)H,
13, 2,6-(2,6-X2C6H3)2C6H3Si(H)Me2 (X = F, Me) and of the
corresponding silylium ions. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ciprian.rat@ubbcluj.ro.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Dedicated to Professor Hans J. Breunig on the occasion of his
69th birthday. This work was supported by the National
University Research Council (CNCS) of Romania (Project
TE295/2010). C.I.R. is grateful to Babes-̧ Bolyai University for
Grant-in-Aid GTC34065/2013. We thank Dr. Albert Soran, Dr.
Enno Lork, Dr. Richard A. Varga, and Peter Brackmann for the
crystallographic determinations, and Professor Cristian Silves-
tru for helpful suggestions.
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