The new NH-acid HN(C6F5)(C(CF3) 3) and its crystalline and volatile alkaline and earth alkaline metal salts

Article abstract of DOI:10.1021/ic5001717

Herein we report on the new NH-acid N-(2,3,4,5,6-pentafluorophenyl)-N- nonafluoro-tert-butylamine, HN(C₆F₅)(C(CF ₃)₃), bearing two different sterically demanding and strongly electron-withdrawing perfluorinated

Full text of DOI:10.1021/ic5001717

Article
pubs.acs.org/IC
The New NH-Acid HN(C6F5)(C(CF3)3) and Its Crystalline and Volatile
Alkaline and Earth Alkaline Metal Salts
Julius F. Kogel, Lars H. Finger, Nicolas Frank, and Jorg Sundermeyer*
̈
̈
Fachbereich Chemie, Philipps-Universitat Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany
̈
S
* Supporting Information
ABSTRACT: Herein we report on the new NH-acid N-(2,3,4,5,6-pentafluorophenyl)-N-nonafluoro-
tert-butylamine, HN(C6F5)(C(CF3)3), bearing two different sterically demanding and strongly electron-
withdrawing perfluorinated amine substituents. The title compound and seven of its alkaline and
alkaline earth metal salts were synthesized and investigated concerning their thermal, spectroscopic, and
structural properties. The Li, Na, K, Cs, and Mg salts were investigated by single-crystal XRD analysis.
The molecular structures reveal interesting motifs such as manifold fluorine metal secondary
interactions. The lithium and magnesium compounds exhibit a remarkable thermal stability and an
unexpectedly high volatility. We believe that this report will provoke investigations to apply the
corresponding anion in ionic liquids, in lithium electrolytes, and as a weakly electron-donating ligand in
the preparation of highly Lewis-acidic main group, rare earth, or transition metal complexes.
lanthanum complexes stabilized by M···F interactions.14
INTRODUCTION
■
[N(C6F5)2]− is also found as a ligand for the transition metals
titanium, zirconium, vanadium, iron, cobalt,15 and tungsten.16
The two unsymmetrical hybrids of bis(perfluoroalkyl-
sulfonyl)imide and bis(pentafluorophenyl)amine, HN(C6F5)-
(SO2CF3) and HN(C6F5)(SO2C4F9), have also been applied to
the preparation of imidazolium- and phosphonium-based ionic
liquids in the same way as their parent compound HN-
(C6F5)2.17 Furthermore, their corresponding lithium salts were
studied as electrolytes in lithium ion batteries.18
Highly Brønsted acidic amines or imides HNRR′ with two
electron-withdrawing perfluorinated alkyl, aryl, or acid
functionalities, so-called NH-acids, have attracted considerable
scientific interest during the last decades. In particular, the most
prominent representative bis(trifluoromethylsulfonyl) imide,
HN(SO2CF3)2,1 has found widespread use: Its corresponding
anion has been used as a component of ionic liquids2 or
electrochemical devices3 due to its weakly coordinating nature.
Exhibiting a higher acidity in the gas phase than hydrogen
iodide, HN(SO2CF3)2 has been the subject of manifold
experimental and theoretical investigations on its acidic
behavior.4 The extraordinary acidity allows the use of
bis(trifluoromethylsulfonyl)imide as a Brønsted acid catalyst
in imine amidation reactions,5 hetero-Michael additions,6 and
enantioselective Diels−Alder7 or cyclization reactions of
siloxyalkynes with arenes and alkenes.8 Furthermore, various
metal complexes of HN(SO2CF3)2 have been applied to
reactions catalyzed by Lewis acids, which was recently reviewed
by Antoniotti et al.9 The weakly donating property of the
corresponding anion was used to design copper and silver
complexes [M(L)N(SO2CF3)2] with high binding affinity
toward arenes and olefins L.10
Although being less acidic than HN(SO2CF3)2 by several
orders of magnitude, bis(pentafluorophenyl)amine first re-
ported by Brooke et al. has also been a subject of research.11
Metal amido complexes of HN(C6F5)2 show interesting metal
fluorine interactions in many cases since this ligand offers only
aromatic fluorine atoms as possible donors besides the nitrogen
atom. For example, this has been observed for the lithium salts
LiN(C6F5)2·Et2O and LiN(C6F5)2·THF12 and the neodymium
complex (η6-toluene)Nd[N(C6F5)2]3.13 Recently Yin et al.
reported the preparation of the homoleptic cerium and
Perfluorinated alcohols, in particular those with a sterically
demanding nonafluor-tert-butyl group, have been used by
Krossing et al. to prepare the Lewis superacidic aluminum
complex Al(OC(CF3)3)3.19 Corresponding perfluorinated
secondary amines and their complexes containing the
electron-withdrawing C(CF3)3 group have not been thoroughly
investigated so far. Therefore we set out to synthesize one
example of such an acidic amine, in particular the title
compound HN(C6F5)(C(CF3)3) and its basic group 1 and 2
amido metal coordination compounds. It is expected that the
two different sterically demanding N-substituents are compet-
ing in their specific secondary C−F···M interactions next to the
primary N−M interaction. Other points of interest of such
metal perfluoramides are their thermal stability, their solubility
in organic solvents, and their ability to form crystalline
perfluoramido metal Lewis acids.
SYNTHESES
■
The synthesis of N-(2,3,4,5,6-pentafluorophenyl)-N-nona-
fluoro-tert-butylamine, HN(C6F5)(C(CF3)3), starts with the
Received: January 22, 2014
Published: March 17, 2014
© 2014 American Chemical Society
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Scheme 2. Preparation of Alkaline and Earth Alkaline Metal
Salts of HN(C6F5)(C(CF3)3)
Figure 1. Examples of symmetric and unsymmetric NH-acids.
reaction of pentafluoroaniline with hexafluoroacetone followed
by the addition of phosphoryl chloride, giving N-pentafluor-
ophenyl-2-iminohexafluoropropane with a yield of up to 87%.20
The transfer of a trifluoromethyl group to the imine carbon
atom is achieved by trifluoromethyltrimethylsilane, the so-called
Ruppert’s reagent,21 in the presence of 1.2 equivalents of
cesium fluoride in THF following a protocol by Petrov used for
other derivatives.22 In our case, the cesium salt was isolated and
extensively dried to remove traces of THF. Protonation with
10% aqueous hydrochloric acid yielded pure HN(C6F5)(C-
(CF3)3) as a colorless oil (Scheme 1).
The lithium, sodium, and potassium salts were obtained by
deprotonation of HN(C6F5)(C(CF3)3) with the corresponding
bis(trimethylsilyl)amides in hexane or toluene. Ca[N(C6F5)-
(C(CF3)3)]2 and Ba[N(C6F5)(C(CF3)3)]2 were prepared in an
analogous manner, whereas the corresponding magnesium salt
was obtained from the reaction of the NH-acid with di-n-
butylmagnesium.
1
show almost equal JCF coupling constants, suggesting that a
complete dissociation into solvated cations [M(dmso)x]+/2+
and anions [N(C6F5)(C(CF3)3)(dmso)y]− is occurring. The
19F NMR signals for the anion solvated in DMSO-d6 show a
considerable high-field shift compared to the solvated NH-acid
that is especially distinct for the para-fluorine atoms (e.g.,
−185.0 ppm in the case of Li(dmso)xN(C6F5)(C(CF3)3)
compared to −153.0 ppm for the NH-acid).
A qualitative competition experiment versus bis-
(pentafluorophenyl)amine (gas phase acidity: 316.5 kcal/
mol)4a in DMSO solution was performed to estimate the
acidity of HN(C6F5)(C(CF3)3) and the electron-withdrawing
character of the perfluorinated tert-butyl group.
The observation that HN(C6F5)2 fully protonates LiN-
(C6F5)(C(CF3)3) (1:1 molar ratio) suggests that the symmetric
NH-acid is more acidic in DMSO than HN(C6F5)(C(CF3)3)
by at least 1 order of magnitude.23 Furthermore, we could show
that the strong acid HN(SO2CF3)2 (gas phase acidity: 286.5
kcal/mol)4b is not able to protonate the amine HN(C6F5)(C-
(CF3)3) in DMSO to form an ammonium salt.
SPECTROSCOPIC AND ACIDIC PROPERTIES
■
All compounds described herein were analyzed by 1H, 13C, and
19F NMR spectroscopy, IR spectroscopy, and elemental
analysis. The proton NMR spectrum of HN(C6F5)(C(CF3)3)
shows a singlet, whereas its chemical shift is strongly solvent
dependent, as it has already been observed for related NH-
acids. The 13C NMR signals of carbon atoms carrying fluorine
1
atoms show large JFC coupling constants between 251.3 and
1
STRUCTURAL FEATURES
292.2 Hz. For most compounds studied herein, only the JFC
■
2
3
coupling constant can be determined, whereas JFC and JFC
coupling constants remain unresolved. A triplet with a chemical
shift of −69.6 ppm in benzene-d6 and a coupling constant of 7.1
Hz is observed for the CF3 groups in the 19F NMR spectrum of
HN(C6F5)(C(CF3)3), which can be referred to a coupling
through space with the aromatic ortho-fluorine atoms. The IR
spectrum shows an absorption band for the NH stretch
vibration at 3406 cm−1 (HN(C6F5)2: 3423 cm−1,11b HN(C-
(CF3)3)2: 3454 cm−1).22 Furthermore, the molecular ion peak
of [N(C6F5)(C(CF3)3)]− was detected in the (−)-ESI mass
spectrum.
All of the reported complexes are slightly soluble in toluene,
the solvent that was mainly used for the metalation of the
perfluorinated amine title compound. This underlines a certain
molecular nature of the complexes. Their latent ionic character
is manifested in strongly donating solvents such as DMSO-d6:
Independently of the cation, the 13C and 19F NMR spectra
exhibit nearly identical chemical shifts and the 13C NMR signals
The molecular structures of the lithium, sodium, and potassium
salts (Figures 2−5) display dinuclear molecular complexes:
Two metal atoms are bridged by the nitrogen atoms of two
[N(C6F5)(C(CF3)3)]− moieties (d(Li−N) 2.08(1) and 2.10(1)
Å; d(Na−N) 2.477(2) and 2.442(2) Å; d(K−N) 2.822(1) and
2.904(1) Å). As expected, the nonbonding N···N distances
within the dimers increase when advancing from the small
lithium ion (3.234(8) Å) to the larger sodium (3.481(2) Å) and
potassium (3.744(1) Å) ions. Furthermore, the small size of the
lithium atom results in a small Li−N−Li angle of 78.7(5)° and
a large N−Li−N angle of 101.3(5)°, whereas the corresponding
values invert with increasing size of the metal ion (Na−N−Na
89.58(5)°; N−Na−N 90.42(5)°; K−N−K 98.36(3)°; N−K−N
81.64(3)°). In addition to the coordination of the metal atoms
by nitrogen donors, the formation of several metal fluorine
contacts is observed (illustrated as dashed lines in Figures
2−8). The lithium salt shows three particularly short Li···F
distances between 2.02(1) and 2.12(1) Å and three additional
Scheme 1. Preparation of HN(C6F5)(C(CF3)3) Starting from Pentafluoronaniline
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Table 1. Crystal Data and Experimental Conditions
LiN(C6F5)(C4F9)
empirical formula C10F14LiN
NaN(C6F5)(C4F9)
KN(C6F5)(C4F9)
C10F14KN
CsN(C6F5)(C4F9)
C10F14CsN, C7H8
Mg[N(C6F5)(C4F9)]2
C10F14NaN
423.10
C20F28MgN2
824.53
mol weight
407.05
439.21
625.15
[g mol−1
]
cryst habit
colorless block
colorless needle
0.35 × 0.11 × 0.10
triclinic
colorless plate
0.25 × 0.23 × 0.07
monoclinic
C2/c
colorless plate
0.32 × 0.10 × 0.07
monoclinic
P121/m1
10.0049(9)
20.860(2)
10.3310(10)
90
colorless block
0.26 × 0.22 × 0.16
triclinic
cryst size [mm3] 0.11 × 0.10 × 0.10
cryst system
space group
a [Å]
orthorhombic
Pccn
P1
̅
P1
̅
18.685(3)
10.6119(12)
12.2994(16)
90
6.9421(5)
9.8740(6)
10.4269(6)
64.0980(17)
75.0294(19)
74.6100(20)
611.46(7)
2
15.9930(5)
13.9077(6)
11.7967(4)
90
6.785(5)
10.022(5)
10.497(4)
61.91(3)
85.492(11)
74.112(5)
604.6(6)
1
b [Å]
c [Å]
α [deg]
β [deg]
90
95.485(3)
90
112.852(3)
90
γ [deg]
volume [Å3]
90
2438.8(6)
8
2611.88(16)
8
1986.8(3)
4
Z
density [g cm−3
T [K]
]
2.217
2.298
2.234
2.090
2.265
100(2)
0.281
100(2)
100(2)
100(2)
100(2)
absorp coeff
0.318
0.584
1.997
0.310
[mm−1
]
θ range [deg]
2.2 to 25.0
2.2 to 26.2
1.9 to 26.8
2.2 to 27.2
2.2 to 26.0
index ranges
−22 ≤ h ≤ 19, −12 ≤ k ≤ −8 ≤ h ≤ 8, −12 ≤ k ≤ −20 ≤ h ≤ 20, −17 ≤ k ≤ −12 ≤ h ≤ 12, −26 ≤ k ≤ −8 ≤ h ≤ 8, −12 ≤ k ≤
11, −14 ≤ l ≤ 12 12, −12 ≤ l ≤ 11 17, −14 ≤ l ≤ 14 26, −13 ≤ l ≤ 13 12, −12 ≤ l ≤ 12
reflns collected
indep reflns
absorp corr
6827 12 094 17 992 31 732 5614
2162 [R(int) = 0.1524]
multiscan
2457 [R(int) = 0.0596]
multiscan
2775 [R(int) = 0.0409]
multiscan
4535 [R(int) = 0.0406]
multiscan
2368 [R(int) = 0.0849]
multiscan
max. and min.
transmn
0.9719 and 0.9673
0.969 and 0.959
0.9645 and 0.8222
0.7455 and 0.6153
1.2918 and 0.6145
data/restraints/
params
2162/2/205
2457/0/235
1.059
2775/0/235
1.029
4535/6/314
1.203
2368/0/232
0.981
goodness-of-fit on 0.488
F2
final R indices [I R1 = 0.0417
> 2σ(I)]
R1 = 0.0350
wR2 = 0.0956
0.54/−0.35
R1 = 0.0214
wR2 = 0.0537
0.36/−0.26
R1 = 0.0235
wR2 = 0.0704
0.72/−0.47
constr
R1 = 0.0460
wR2 = 0.1217
0.57/−0.51
R indices (all
data)
wR2 = 0.0727
larg diff peak/
0.34/−0.29
hole [e Å−3
]
treatment of H
atoms
Li···F contacts exhibiting lengths between 2.94(1) and 3.14(1)
Å, which are only slightly below the sum of the van der Waals
radii of lithium and fluorine.24 The bigger sodium ion allows
the coordination of eight fluorine atoms and shows a broad
range of Na···F distances from 2.336(2) to 3.348(1) Å. The
potassium is coordinated by seven fluorine atoms with K···F
distances between 2.7255(8) and 2.9939(8) Å. Plenio, who
reviewed the field of interactions between metals and
organically bound fluorine atoms, reported a maximum
between 2.45 and 2.75 Å in the distribution of Na···F distances
and between 2.85 and 3.05 Å in the case of K···F contacts.25
Thus, most of the corresponding values observed for
KN(C6F5)(C(CF3)3) are comparably short, which can be
referred to the fact that the ligand exhibits only one nitrogen
donor atom beside the fluorine atoms. The crystal structures of
LiN(C6F5)(C(CF3)3), NaN(C6F5)(C(CF3)3), and KN(C6F5)-
(C(CF3)3) reveal the interaction of neighboring dimers via M···
F contacts. The fact that single crystals of LiN(C6F5)(C(CF3)3)
were obtained via sublimation at 120 °C and 1.3 × 10−3 mbar is
in accord with only weak Li···F contacts between the dimers.
Furthermore, this unexpected behavior proves the remarkable
thermal stability of LiN(C6F5)(C(CF3)3) with respect to LiF
elimination. We could show that LiN(C6F5)2 readily eliminates
lithium fluoride during attempts to sublime it.18 A high
volatility is known for fluorinated alkoxides that are used for
chemical vapor deposition26 and for alkaline metal bistrime-
thylsilylamides, but it is unique for lithium (and magnesium, see
below) amides with perfluorinated ligands.
In the case of the sodium salt the formation of two-
dimensional chains can be observed in the crystal structure
(Figure 4), whereas the lithium and the potassium salts form
complicated three-dimensional networks. Dimeric substructures
revealing metal fluorine contacts were also found for LiN-
(C6F5)2·Et2O (d(Li−N) between 2.09(1) and 2.12(1) Å, d(Li···
Li) 2.67(1) Å, N−Li−N 100.7(4)° and 101.4(4)°, Li−N−Li
78.4(4)° and 79.1(4)°) and LiN(C6F5)2·THF (d(Li−N)
between 2.080(6) and 2.178(6) Å, d(Li···Li) 2.675(8) Å, N−
Li−N 103.2(3)° and 99.2(3)°, Li−N−Li 79.2(2)° and
77.8(2)°), which exhibit similar N−Li and Li···Li distances as
well as N−Li−N and Li−N−Li angles to the lithium salt
discussed herein.12 The shortest Li···F contact observed in
these structures is longer than in the solvent-free lithium salt
discussed herein (LiN(C6F5)2·Et2O: 2.196(9) Å, LiN(C6F5)2·
THF: 2.098(6) Å).
The crystal structure of (η6-toluene)CsN(C6F5)(C(CF3)3)
(Figure 6) also reveals nitrogen-bridged dimers, but addition-
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Figure 4. Two-dimensional chains observed in the crystal structure of
NaN(C6F5)(C(CF3)3).
Figure 2. Molecular structure of LiN(C6F5)(C(CF3)3) (ellipsoids with
30% probability). Selected bond lengths (Å) and angles (deg): Li1−
N1 2.10(1), Li1−N(1−x, −y, 1−z) 2.08(1), Li1···F1(1−x, −-y, 1−z)
2.02(1), Li1···F2(x, 0.5−y, −0.5+z) 2.06(1), Li1···F6 3.10(1), Li1···
F11(1−x, −y, 1−z) 3.14(1), Li1···F13(1−x, −y, 1−z) 2.12(1), Li1···
F14 2.94(1), Li1···Li(1−x, −y, 1−z) 2.65(2), Li1−N1−Li1(1−x, −y,
1−z) 98.36(3).
Figure 5. Molecular structure of KN(C6F5)(C(CF3)3) (ellipsoids with
30% probability). Selected bond lengths (Å) and angles (deg): K1−
N1 2.904(1), K1−N(1.5−x, 0.5−y, 2−z) 2.822(1), K1···F1(1.5−x,
0.5−y, 2−z) 2.8259(9), K1···F4(2−x, y, 2.5−z) 2.9939(8), K1···F5
2.7978(7), K1···F7(1.5−x, 0.5−y, 2−z) 2.7633(8), K1···F9 (x, 1−y,
0.5+z) 2.9865(9), K1···F11 2.7255(8), K1···F12(x, 1−y, 0.5+z)
2.9865(9), K1···K(1.5−x, 0.5−y, 2−z) 4.3337(4), K1−N1−K1(1.5−
x, 0.5−y, 2−z) 78.7(5).
nitrogen atoms, two fluorine atoms belonging to CF3 groups,
and one aromatic fluorine atom as donor atoms. The third
[N(C6F5)(C(CF3)3)]− moiety coordinates with one meta- and
the para-fluorine atom of a C6F5 moiety to the metal center.
The distances between the cesium atom and coordinating
fluorine atoms range from 3.054(1) to 3.653(2) Å. Plenio
reported a maximum in the distribution between 3.20 and 3.40
Å for weakly bonding Cs···F contacts.25 The M−N−M
(96.07(5)°) and the N−M−N angles (83.93(5)°) in (η6-
toluene)CsN(C6F5)(C(CF3)3) are similar to the corresponding
values found in the potassium salt (98.36(3)° and 81.64(3)°).
As expected, the cesium salt shows the largest M−N bond
lengths (3.212(2) and 3.330(2) Å) and nonbonding N···N
distance (4.375(2) Å) among the structures studied herein.
A different coordination mode is found for the magnesium
compound (Figure 8) in which a distorted octahedron formed
by two [N(C6F5)(C(CF3)3)]− moieties is observed, whereas
the asymmetric unit contains only half of the octahedron.
Neighboring octahedra interact via π-stacking of C6F5 moieties.
The fact that single crystals of Mg[N(C6F5)(C(CF3)3)]2 were
obtained by sublimation at 115 °C and atmospheric pressure
suggests comparably weak intermolecular interactions and a
remarkable thermal stability. The magnesium atom is
coordinated by two nitrogen atoms trans to each other
(d(Mg−N) 1.981(2) and 1.981(2) Å) and four fluorine
Figure 3. Molecular structure of NaN(C6F5)(C(CF3)3) (ellipsoids
with 30% probability). Selected bond lengths (Å) and angles (deg):
Na1−N1 2.477(2), Na1−N(1−x, −y, 1−z) 2.442(2), Na1···F1(1+x, y,
z) 2.336(2), Na1···F1(1−x, −y, 1−z) 3.117(1), Na1···F5 2.483(2),
Na1···F7(1−x, −y, 1−z) 2.558(1), Na1···F8 2.420(1), Na1···F11
2.804(1), Na1···F13(1+x, y, z) 2.688(1), Na1···F13(1−x, −y, 1−z)
3.348(1), Na1···Na(1−x, −y, 1−z) 3.466(1), Na1−N1−Na1(1−x, −y,
1−z) 89.58(5).
ally contains a toluene molecule showing η6-coordination to
two cesium atoms, which emphasizes the soft Lewis-acidic
character of this metal center (distance between Cs and the
center of toluene: 3.4092(4) Å). The Cs···CAr distances are
between 3.625(2) and 3.739(2) Å and thus lie within the range
from 3.3 to 3.8 Å that was reported for cesium arene
interactions.27 The toluene ligands link two vicinal dimers in
each case (Figure 7). Each cesium atom shows interactions with
three [N(C6F5)(C(CF3)3)]− units. Two of these provide their
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Figure 6. Molecular structure of (η6-toluene)CsN(C6F5)(C(CF3)3)
(ellipsoids with 30% probability). Cs···F contacts are shown only for
Cs1. Selected bond lengths (Å) and angles (deg): Cs1−N1 3.212(2),
Cs1−N1(1−x, 1−y, 1−z) 3.330(2), Cs1···F1 3.082(2), Cs1···F2(2−x,
1−x, 1−z) 3.454(2), Cs1···F3(2−x, 1−x, 1−z) 3.303(2), Cs1···F5(1−
x, 1−y, 1−z) 3.054(1), Cs1···F6 3.079(2), Cs1···F7 3.140(2), Cs1···F9
3.356(2), Cs1···F13 3.653(2), Cs1···Cs1(1−x, 1−y, 1−z) 4.8648(4),
Cs1−N1−Cs1(1−x, 1−y, 1−z) 96.07(5).
Figure 8. Molecular structure of Mg[N(C6F5)(C(CF3)3)]2 (ellipsoids
with 30% probability). Selected bond lengths (Å) and angles (deg):
Mg1−N1 1.981(2), Mg1···F7 2.186(2), Mg1···F9 2.223(1), N1−Mg−
N1 180, F9−Mg1−F7 72.14(5).
and a longer Mg−N distance of 2.013(3) Å than found for
Mg[N(C6F5)(C(CF3)3)]2. Similar Mg···F distances of 2.200(2)
and 2.199(3) Å to the magnesium complex studied herein were
found in a literature-known magnesium amide with a cyclam
ligand.29 An octahedral coordination of a magnesium atom
involving Mg···F contacts was also observed for the homoleptic
magnesium complex of HN(C6F5)((CH2)2NMe2) showing
Mg···F distances of 2.431(3) Å.30
Generally, we notice a trend that more fluorine atoms
belonging to CF3 groups than to aromatic fluorine atoms are
involved in M···F contacts.31 This can be explained by the
higher flexibility of the aliphatically bound fluorine atoms due
to rotation around the N−Ctert and the Ctert−C bonds, allowing
a less constrained alignment of the fluorine lone pairs to the
metal center. However, we have to be aware that some of the
longer M···F contacts originate from the inevitable vicinity of
the metal cations and fluorine atoms caused by the extremely
bulky perfluorinated ligands or packing effects rather than
solely from an energetically favorable interaction. Thus, the
higher number of M···F contacts involving CF3 groups might
also be a result of the higher number of aliphatic compared to
aromatic fluorine atoms.
Figure 7. Connection of dimers by η6-coordinated toluene molecules
in (η6-toluene)CsN(C6F5)(C(CF3)3).
atoms that are part of tert-butyl moieties (d(Mg···F) 2.186(2)
and 2.223(1) Å). It seems that the harder cation Mg2+ favors
the interaction with sp3 C−F donors of the tert-butyl moiety,
while the softer alkali cations M+ are much less specific in their
competitive sp2 C−F vs sp3 C−F interaction and in their
coordinative configuration. The linear N−Mg−N axis is tilted
toward the plane formed by the four coordinating fluorine
atoms by 15.57(5)°. The F−Mg−F angle of fluorine atoms
belonging to the same [N(C6F5)(C(CF3)3)]− unit is 72.14(5)°,
whereas this value is 107.86(5)° for fluorine atoms of different
[N(C6F5)(C(CF3)3)]− moieties. The C−F distances involving
coordinating fluorine atoms (1.388(3) and 1.385(3) Å) are
considerably longer compared to noncoordinating fluorine
atoms bound to aliphatic carbon atoms (ranging from 1.313(3)
to 1.333(3) Å). Whereas literature-known alkaline earth metal
complexes of HNPh2 such as (thf)2Mg(NPh2)2, (dme)2Ca-
(NPh2)2, (thf)4Sr(NPh2)2, and (thf)4Ba(NPh2)2 reveal the
coordination of ether molecules to the metal center,28 the
magnesium complex reported herein is a rare example of a
solvent-free group II metal amide coordinated only by
organically bound fluorine atoms in addition to two nitrogen
donors. The two diphenylamide ligands and the two THF
molecules in (thf)2Mg(NPh2)2 form a distorted tetrahedron
CONCLUSION AND OUTLOOK
■
We have presented the synthesis of a new secondary amine
with strongly electron-withdrawing and sterically demanding
perfluorinated phenyl and tert-butyl substituents. N-(2,3,4,5,6-
Pentafluorophenyl)-N-nonafluoro-tert-butylamine, HN(C6F5)-
(C(CF3)3), was obtained via a CF3-group transfer reaction
from trifluoromethyltrimethylsilane to the corresponding imine
precursor. This NH-acid was fully characterized and used for
the synthesis of the alkaline metal salts of lithium, sodium,
potassium, and cesium. In addition, the homoleptic complexes
of the earth alkaline metals magnesium, calcium, and barium
were prepared. We observed a rather unusual volatility for the
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Table 2. Selected Structural Features of the Crystal Structures of LiN(C6F5)(C(CF3)3), KN(C6F5)(C(CF3)3),
a
CsN(C6F5)(C(CF3)3), and Mg[N(C6F5)(C(CF3)3)]2 )
M···F
coordinating [N(C6F5)
(C(CF3)3)]− units
N−M
contacts
CN
8
M···FAr
M···FAl
N···N
N−M−N
M−N−M
LiN(C6F5)(C(CF3)3)
2.08(1)
6
8
3
3
2.12(1)
3.234(8)
101.3(5)
78.7(5)
2.02(1)
2.06(1)
2.94(1)
2.10(1)
3.10(1)
3.14(1)
NaN(C6F5)(C(CF3)3) 2.442(2)
2.477(2)
10
9
2.420(1)
2.558(1)
2.688(1)
2.804(1)
3.348(1)
2.7255(8)
2.7633(8)
2.7930(8)
2.8831(8)
2.9865(9)
3.079(2)
3.140(2)
3.356(2)
3.653(2)
2.186(2)
2.186(1)
2.223(1)
2.223(1)
3.481(2)
3.744(1)
90.42(5)
81.64(3)
89.58(5)
98.36(3)
96.07(5)
2.336(2)
2.483(2)
3.117(1)
KN(C6F5)(C(CF3)3)
CsN(C6F5)(C(CF3)3)
2.822(1)
7
4
2.7978(7)
2.8259(9)
2.9939(8)
2.904(1)
3.212(2)
3.330(2)
1.981(2)
1.981(2)
8
4
3
2
10
6
3.054(1)
3.082(1)
3.303(2)
3.454(2)
4.375(2)
3.962(3)
83.93(5)
180.0
Mg[N(C6F5)
(C(CF3)3)]2
a
Bond lengths in Å, angles in deg, CN = coordination number, FAr = aromatic fluorine atoms, FAl = fluorine atoms of CF3 groups.
(CF3)3) (6.34 g, 11.89 mmol, 73%) as a red solid. Single crystals
suitable for structure determination were obtained by slowly cooling a
saturated solution of CsN(C6F5)(C(CF3)3) in toluene from 90 °C to
lithium and the magnesium salts, which reveal certain covalent
character. This was used to grow single crystals via sublimation.
Molecular structures of the lithium, sodium, potassium, cesium,
and magnesium salts reveal interesting coordination motifs with
manifold labile metal fluorine contacts. Due to its low basicity,
we anticipate that the anion [N(C6F5)(C(CF3)3)]− is a
promising rather weakly coordinating ligand for the generation
of highly Lewis-acidic main group, rare earth, or transition
metal complexes. The alkaline metal salts reported herein could
serve as starting materials for the synthesis of such Lewis
superacids via salt elimination reactions, or they could prove to
be valuable precursors for the preparation of highly hydro-
phobic electrolyte systems.
1
−30 °C. 13C NMR (101 MHz, DMSO-d6): δ 142.7 (d, JFC = 231.2
1
2
Hz, o-CAr), 137.6 (dm, JFC = 239.4 Hz, m-CAr), 133.2 (t, JFC = 12.1
Hz, ipso-CAr), 128.1 (dt, 1JFC = 231.5 Hz, 2JFC = 14.5 Hz, p-CAr), 123.0
(q, 1JFC = 297.0 Hz, −CF3), 76.1 ppm (dec, 2JFC = 25.4 Hz, C(CF3)3).
19F NMR (282 MHz, DMSO-d6): δ −68.8 (t,
J
= 9.7 Hz, 9F,
FF
ts
−CF3), −156.7 (br s, 2F, o-FAr), −170.1 (t, 3JFF = 21.7 Hz, 2F, m-FAr),
−184.1 ppm (br s, 1F, p-FAr). IR: ν 1615 (w), 1507 (m), 1481 (m),
̃
1412 (m), 1279 (m), 1234 (s), 1214 (s), 1190 (s), 1112 (w), 1072 (s),
1025 (w), 972 (s), 930 (s), 771 (w), 756 (w), 721 (s), 673 (m), 582
(w), 556 (w), 537 (w), 497 (w), 449 cm−1 (w). (−)-ESI-MS (MeCN):
m/z (%) 400 (32) [M]−, 219 (100) [M − C6F5N]−, 180 (8) [M −
C4F9]−, 167 (18) [M − C4F9N]−. HRMS ((−)-ESI): m/z calcd for
C10F14N− 399.9813 [M]−; found 399.9817. Anal. Calcd (%) for
C10CsF14N (533.00): C 22.53, H 0.00, N 2.63. Found: C 22.29, H
0.19, N 2.78.
EXPERIMENTAL SECTION
■
Reactions were carried out under an inert atmosphere using standard
Schlenk techniques. Moisture- and air-sensitive substances were stored
in a conventional nitrogen-flushed glovebox. Solvents were purified
according to literature procedures and kept under an inert atmosphere.
N-Pentafluorophenyl-2-iminohexafluoropropane was prepared as
described above.20 The metal precursors LiN(SiMe3)2,32 NaN-
(SiMe3)2,32 KN(SiMe3)2,33 Ca[N(SiMe3)2]2,34 and Ba[N(SiMe3)2]2·
THF35 were synthesized according to literature procedures. Spectra
were recorded on the following spectrometers. NMR: Bruker ARX300,
Bruker DRX400, Bruker DRX500. IR: ATR-FT-IR. MS: LTQ-FT or
QStarPulsar i (Finnigan). Elemental analysis: CHN-Rapid (Heraeus).
Synthesis of HN(C6F5)(C(CF3)3). A suspension of CsN(C6F5)(C-
(CF3)3) (1000 mg, 1.876 mmol) in 50 mL of dichloromethane was
extracted with 40 mL of hydrochloric acid (10%). The aqueous phase
was additionally extracted twice with 75 mL of dichloromethane, and
the combined organic phases were dried over MgSO4. The solvent was
removed at the rotary evaporator, and the remaining oily residue was
distilled at 74 °C and 57 mbar to give HN(C6F5)(C(CF3)3) (675 mg
1.687 mmol, 90%) as a colorless oil, which was stored under an inert
1
atmosphere. H NMR (300 MHz, benzene-d6): δ 2.58 ppm (s, 1H,
1
NH). 13C NMR (101 MHz, benzene-d6): δ 146.4 (dm, JFC = 251.3
Hz, CAr), 141.3 (dm, 1JFC = 256.1 Hz, p-CAr), 137.7 (dm, 1JFC = 251.3
Synthesis of CsN(C6F5)(C(CF3)3).
A mixture of N-
1
2
Hz, CAr), 121.0 (q, JFC = 292.2 Hz, −CF3), 113.8 (t, JFC = 14.8 Hz,
pentafluorophenylbis(trifluoromethyl)methyleneimine (5.37 g, 16.23
mmol, 1.0 equiv) and trifluoromethyltrimethylsilane (2.54 g, 17.85
mmol 1.1 equiv) was added dropwise to a suspension of cesium
fluoride (2.98 g, 19.47 mmol, 1.2 equiv) in 40 mL of THF over 30
min. The reaction mixture changed color to yellow and turned red
after stirring overnight. The suspension was filtered over Celite, and
the filtrate was evaporated to dryness in vacuo. The red residue was
washed with 40 mL of hexane, and the remaining solid was excessively
dried in vacuo to remove traces of THF and obtain CsN(C6F5)(C-
ipso-CAr), 69.0 ppm (dec, JFC = 28.4 Hz, C(CF3)3). 19F NMR (282
2
ts
MHz, benzene-d6): δ −69.6 (t, JFF = 7.1 Hz, 9F, −CF3), −143.2 to
3
−143.3 (m, 2F, FAr), −153.0 (t, JFF = 22.2 Hz, 1F, p-FAr), −162.9
3
̃
̃
ppm (t, JFF = 19.6 Hz, 2F, FAr). IR: ν
3406 (w, ν(N−H)), 1522 (s),
1243 (s), 1114 (m), 1018 (s), 989 (s), 959 (s), 757 (w), 726 (s), 686
(w), 667 (m), 540 (m), 473 cm−1 (w). (−)-ESI-MS (MeCN): m/z
(%) 400 (2) [M]−, 167 (8) [C6F5]−. HRMS ((−)-ESI): m/z calcd for
C10F14N− 399.9813 [M]−; found 399.9815. Anal. Calcd (%) for
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C10HF14N (401.10): C 29.94, H 0.25, N 3.49. Found: C 30.55, H 0.39,
N 4.03.
477 cm−1 (w). Anal. Calcd (%) for C10KF14N (439.19): C 27.35, H
0.00, N 3.19. Found: C 27.21, H 0.14, N 3.39.
Synthesis of LiN(C6F5)(C(CF3)3). A solution of LiHMDS (1.137 g,
6.79 mmol, 1.0 equiv) in 30 mL of hexane was added dropwise to a
solution of HN(C6F5)(C(CF3)3) (2.727 g, 6.79 mmol, 1.0 equiv) in 30
mL of hexane. A colorless solid precipitated, and the reaction mixture
was stirred for 2 h at room temperature. The precipitate was separated
by centrifugation and washed twice with 20 mL of pentane. It was
dried in vacuo to give LiN(C6F5)(C(CF3)3) (2.222 g, 5.45 mmol, 80%)
as a white solid. Single crystals suitable for structure determination
were obtained by sublimation of LiN(C6F5)(C(CF3)3) at 120 °C and
6.3 × 10−3 mbar. 13C NMR (101 MHz, DMSO-d6): δ 142.5 (dm, 1JFC
= 230.9 Hz, o-CAr), 137.5 (dm, 1JFC = 239.0 Hz, m-CAr), 133.5 (t, 2JFC
= 13.0 Hz, ipso-CAr), 127.7 (dm, 1JFC = 230.7 Hz, p-CAr), 123.0 (q, 1JFC
Synthesis of Mg[N(C6F5)(C(CF3)3)]2. A solution of di-n-
butylmagnesium (1 mol/L in heptane, 0.722 mL, 0.722 mmol, 1.0
equiv) was added dropwise to a solution of HN(C6F5)(C(CF3)3) (401
mg, 1.444 mmol, 2.0 equiv) in 20 mL of toluene. A gray solid
precipitated, and the reaction mixture was stirred overnight at room
temperature. The precipitate was separated by centrifugation and
washed with 15 mL of hexane. It was dried in vacuo to give
Mg[N(C6F5)(C(CF3)3)]2 (192 mg, 0.233 mmol, 32%) as a light gray
solid. Single crystals suitable for structure determination were obtained
by sublimation of Mg[N(C6F5)(C(CF3)3)]2 at 117 °C and 1 mbar.
13C NMR (101 MHz, DMSO-d6): δ 142.7 (d, 1JFC = 231.4 Hz, o-CAr),
137.5 (dm, 1JFC = 240.4 Hz, m-CAr), 132.9 (t, 2JFC = 12.9 Hz, ipso-CAr),
2
= 297.1 Hz, −CF3), 76.2 ppm (dec, JFC = 25.3 Hz, C(CF3)3). 19F
1
2
1
128.3 (dt, JFC = 232.1 Hz, JFC = 14.1 Hz, p-CAr), 123.0 (q, JFC
=
ts
NMR (376 MHz, DMSO-d6): δ −69.0 (t, JFF = 10.6 Hz, 9F, −CF3),
296.9 Hz, −CF3), 75.9 ppm (dec, 2JFC = 25.4 Hz, C(CF3)3). 19F NMR
3
−157.1 to −157.3 (m, 2F, o-FAr), −170.5 (t, JFF = 23.3 Hz, 2F, m-
ts
(282 MHz, DMSO-d6): δ −68.8 (t,
J
= 10.5 Hz, 18F, −CF3),
FAr), −185.0 ppm (tt, 3JFF = 24.1 Hz, 4JFF = 11.6 Hz, 1F, p-FAr). IR: ν
̃
FF
3
−156.9 to −157.2 (m, 4F, o-FAr), −170.3 (t, JFF = 23.1 Hz, 4F, m-
1516 (m), 1490 (m), 1427 (w), 1285 (w), 1250 (m), 1228 (m), 1196
(m), 1165 (m), 1125 (w), 1074 (s), 991 (s), 972 (s), 948 (s), 874 (w),
793 (w), 758 (w), 723 (m), 685 (m), 668 (w), 631 (w), 599 (w), 563
(w), 538 (w), 516 (m), 483 (w), 467 (w), 446 cm−1 (w). (−)-ESI-MS
(MeCN): m/z (%) 400 (8) [M]−, 167 (100) [C6F5]−. HRMS
((−)-ESI): m/z calcd for C10F14N− 399.9813 [M]−; found 399.9811.
Anal. Calcd (%) for C10LiF14N (407.03): C 29.51, H 0.00, N 3.44.
Found: C 29.15, H 0.00, N 3.74.
FAr), −184.8 ppm (tt, 3JFF = 23.9 Hz, 4JFF = 11.8 Hz, 2F, p-FAr). IR: ν
̃
1513 (m), 1495 (w), 1260 (br), 1181 (m), 1083 (s), 984 (s), 932 (s),
730 (m), 532 (w), 433 cm−1 (w), Anal. Calcd (%) for C20F28MgN2
(824.49): C 29.13, H 0.00, N 3.40. Found: C 29.32, H 0.32, N 3.46.
Synthesis of Ca[N(C6F5)(C(CF3)3)]2. A solution of HN(C6F5)(C-
(CF3)3) (470 mg, 1.170 mmol, 2.0 equiv) in 15 mL of toluene was
added dropwise to a solution of Ca(HMDS)2 (211 mg, 0.585 mmol,
1.0 equiv) in 15 mL of toluene. A brown solid precipitated, and the
reaction mixture was stirred overnight at room temperature. The
precipitate was separated by centrifugation and washed twice with 15
mL of hexane. It was dried in vacuo to give Ca[N(C6F5)(C(CF3)3)]2
(300 mg, 0.373 mmol, 64%) as a beige solid. 13C NMR (101 MHz,
Synthesis of NaN(C6F5)(C(CF3)3). A solution of NaHMDS (104
mg, 0.567 mmol, 1.0 equiv) in 10 mL of toluene was added dropwise
to a solution of HN(C6F5)(C(CF3)3) (226 mg, 0.567 mmol, 1.0
equiv) in 10 mL of toluene. A gray solid precipitated, and the reaction
mixture was stirred overnight at room temperature. The precipitate
was separated by centrifugation and washed twice with 10 mL of
hexane. It was dried in vacuo to give NaN(C6F5)(C(CF3)3) (106 mg,
0.251 mmol, 44%) as a light gray solid. Single crystals suitable for
structure determination were obtained by the slow diffusion of a
solution of HN(C6F5)(C(CF3)3) in pentane into a solution of
NaHMDS in toluene. 13C NMR (101 MHz, DMSO-d6): δ 142.5 (dt,
1JFC = 231.2 Hz, 2JFC = 8.4 Hz, o-CAr), 137.6 (dm, 1JFC = 239.4 Hz, m-
1
1
DMSO-d6): δ 142.5 (d, JFC = 231.3 Hz, o-CAr), 137.6 (dm, JFC
=
=
239.1 Hz, m-CAr), 133.6 (t, 2JFC = 14.2 Hz, ipso-CAr), 127.7 (dm, 1JFC
1
230.9 Hz, p-CAr), 123.0 (q, JFC = 297.3 Hz, −CF3), 76.0 ppm (dec,
2JFC = 24.9 Hz, C(CF3)3). 19F NMR (282 MHz, DMSO-d6): δ −68.8
ts
(t,
J
= 10.3 Hz, 18F, −CF3), −156.9 to −157.1 (m, 4F, o-FAr),
FF
−170.3 (t, 3JFF = 22.9 Hz, 4F, m-FAr), −184.6 ppm (s, 2F, p-FAr). IR: ν
̃
1517 (m), 1482 (m), 1421 (w), 1224 (br), 1076 (s), 974 (s), 941 (s),
816 (s), 758 (s), 561 cm−1 (w). Anal. Calcd (%) for C20F28CaN2
(840.26): C 28.59, H 0.00, N 3.33. Found: C 28.38, H 0.22, N 3.56.
Synthesis of Ba[N(C6F5)(C(CF3)3)]2·THF. A solution of HN-
(C6F5)(C(CF3)3) (190 mg, 0.474 mmol, 2.0 equiv) in 10 mL of
toluene was added dropwise to a solution of Ba(HMDS)2·THF (126
mg, 0.237 mmol, 1.0 equiv) in 10 mL of toluene. The reaction mixture
was stirred overnight at room temperature, and all volatiles were
removed in vacuo. The remaining residue was washed twice with 15
mL of hexane. It was dried in vacuo to give Ba[N(C6F5)(C(CF3)3)]2·
2
1
CAr), 133.6 (t, JFC = 13.2 Hz, ipso-CAr), 127.8 (dtt, JFC = 230.9 Hz,
2JFC = 14.7 Hz, 3JFC = 4.8 Hz, p-CAr), 123.1 (q, 1JFC = 297.0 Hz, CF3),
76.2 ppm (dec, JFC = 25.4 Hz, C(CF3)3). 19F NMR (282 MHz,
2
DMSO-d6): δ −69.3 (t, tsJFF = 10.3 Hz, 9F, −CF3), −157.5 to −157.8
(m, 2F, o-FAr), −170.9 (t, 3JFF = 23.0 Hz, 2F, m-FAr), −185.4 ppm (tt,
4
3JFF = 24.2 Hz, JFF = 11.9 Hz, 1F, p-FAr). IR: ν
̃
1516 (m), 1480 (m),
1420 (w), 1180 (br), 1076 (m), 965 (s), 934 (s), 774, (w), 721 (m),
668 (w), 538 cm−1 (w). (−)-ESI-MS (MeCN): m/z (%): 219 (10)
[C4F9]−, 167 (25) [C6F5]−. HRMS ((−)-ESI): m/z calcd for
C10F14N− 399.9813 [M]−; found 399.9813. Anal. Calcd (%) for
C10NaF14N (423.08): C 28.39, H 0.00, N 3.31. Found: C 28.59, H
0.29, N 3.46.
Synthesis of KN(C6F5)(C(CF3)3). A solution of KHMDS (644 mg,
3.22 mmol, 1.0 equiv) in 20 mL of toluene was added dropwise to a
solution of HN(C6F5)(C(CF3)3) (1292 mg, 3.22 mmol, 1.0 equiv) in
15 mL of hexane. A colorless solid precipitated, and the reaction
mixture was stirred for 2 h at room temperature. The precipitate was
separated by centrifugation and washed twice with 20 mL of hexane. It
was dried in vacuo to give KN(C6F5)(C(CF3)3) (956 mg, 2.18 mmol,
68%) as a white solid. Single crystals suitable for structure
determination were obtained by layering a saturated solution of
KN(C6F5)(C(CF3)3) in toluene with hexane. 13C NMR (63 MHz,
DMSO-d6): δ 142.5 (dt, 1JFC = 231.3 Hz, 2JFC = 8.9 Hz, o-CAr), 137.6
(dm, 1JFC = 239.3 Hz, m-CAr), 133.6 (t, 2JFC = 12.6 Hz, ipso-CAr), 127.8
1
THF (110 mg, 0.109 mmol, 46%) as a light brown solid. H NMR
(300.1 MHz, DMSO-d6): δ 3.60 (br s, 4H, OCH2), 1.76 ppm (br s,
4H, OCH2CH2). 13C NMR (125.8 MHz, DMSO-d6): δ 142.5 (dt, 1JFC
= 231.0 Hz, 2JFC = 7.7 Hz, o-CAr), 137.5 (dm, 1JFC = 238.8 Hz, m-CAr),
2
1
2
133.5 (t, JFC = 13.8 Hz, ipso-CAr), 127.7 (dtt, JFC = 231.2 Hz, JFC
=
14.7 Hz, 3JFC = 4.7 Hz, p-CAr), 123.0 (q, 1JFC = 297.2 Hz, −CF3), 76.2
(dec, 2JFC = 25.5 Hz, C(CF3)3), 66.9 (OCH2), 25.0 ppm (OCH2CH2).
19F NMR (282.4 MHz, DMSO-d6): δ -69.6 (t,
J
= 10.4 Hz, 18F,
ts
FF
3
−CF3), −157.7 to −158.0 (m, 4F, o-FAr), −171.1 (t, JFF = 23.0 Hz,
4F, m-FAr), −185.6 ppm (tt, 3JFF = 23.9 Hz, 4JFF = 11.8 Hz, 2F, p-FAr).
̃
IR: ν 1508 (m), 1483 (m), 1440 (w), 1200 (br), 1076 (s), 982 (s), 935
(s), 873 (m), 804 (m), 719 (m), 665 (w), 538 cm−1 (w). Anal. Calcd
(%) for C24H8BaF28N2O (1009.62): C 28.55, H 0.80, N 2.77. Found:
C 27.93, H 1.64, N 2.21.
1
2
3
(dtt, JFC = 230.9 Hz, JFC = 14.6 Hz, JFC = 4.8 Hz, p-CAr), 123.1 (q,
1JFC = 297.1 Hz, −CF3), 76.2 ppm (dec, 2JFC = 25.4 Hz, C(CF3)3). 19
F
ASSOCIATED CONTENT
■
ts
NMR (376 MHz, DMSO-d6): δ −69.0 (t, JFF3 = 9.9 Hz, 9F, −CF3),
S
* Supporting Information
−157.1 to −157.3 (m, 2F, o-FAr), −170.5 (t, JFF = 23.3 Hz, 2F, m-
FAr), −185.5 ppm (tt, 3JFF = 24.1 Hz, 4JFF = 11.6 Hz, 1F, p-FAr). IR: ν
̃
Supporting Information contains the bond valence analyses of
the Mg−N and Mg···F interactions. This material is available
free of charge via the Internet at http://pubs.acs.org.
1642 (w), 1496 (s), 1465 (s), 1341 (m), 1256 (w), 1120 (w), 1018
(s), 997 (s), 972 (s), 817 (w), 729 (w), 708 (m), 645 (m), 564 (m),
3845
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Article
(16) Peryshkov, D. V.; Schrock, R. R. Organometallics 2012, 31,
7278−7286.
(17) Linder, T.; Sundermeyer, J. Chem. Commun. 2009, 20, 2914−
2916.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jsu@staff.uni-marburg.de.
■
(18) (a) Sundermeyer, J.; Roling, B.; Linder, T.; Froemling, T.;
Huber, B. Eur. Pat. Appl. EP 2314572 A1, 20110427, 2011.
(b) Sundermeyer, J.; Roling, B.; Linder, T.; Huber, B.; Froemling,
T. PCT Int. Appl. WO 2011048152 A1, 20110428, 2011. (c) Huber,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank Fonds der Chemischen Industrie (doctoral scholar-
ship for J.F.K. and L.H.F.) for support of this work. We thank
■
B.; Linder, T.; Hormann, K.; Fromling, T.; Sundermeyer, J.; Roling, B.
̈
Z. Phys. Chem. 2012, 212, 377−390.
(19) (a) Muller, L. O.; Himmel, D.; Stauffer, J.; Steinfeld, G.; Slattery,
̈
Dr. Klaus Harms and Fabian Schroder for their valuable
support with crystal structure refinement. We thank Felicia
Weber for her synthetic contribution.
̈
J.; Santiso-Quinones, G.; Brecht, V.; Krossing, I. Angew. Chem. 2008,
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