Unsymmetrically substituted N-heterocyclic phosphenium ions

Article abstract of DOI:10.1016/j.crci.2010.04.020

Reduction of an unsymmetrically substituted α-diimine followed by condensation with PCl₃ yielded a P-chloro-N-aryl-N-alkyl diazaphospholene which was further converted into an unsymmetrical diazaphospholium triflate by reaction with trimethylsi

Full text of DOI:10.1016/j.crci.2010.04.020

C. R. Chimie 13 (2010) 998–1005
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Full paper/Memoire
Unsymmetrically substituted N-heterocyclic phosphenium ions
Dirk Schmid a, Denis Bubrin a, Daniela Fo¨rster a, Martin Nieger b, Eric Roeben a,
Sabine Strobel a, Dietrich Gudat a,
*
a Institut fu¨r Anorganische Chemie, Universita¨t Stuttgart, Stuttgart, Germany
b Laboratory of Inorganic Chemistry, University of Helsinki, A.I. Virtasen aukio 1, Helsinki, Finland
A R T I C L E I N F O
A B S T R A C T
Article history:
Reduction of an unsymmetrically substituted
a-diimine followed by condensation with
PCl3 yielded a P-chloro-N-aryl-N0-alkyl diazaphospholene which was further converted
into an unsymmetrical diazaphospholium triflate by reaction with trimethylsilyl triflate.
Reaction of tetramers of N-H- or N-alkyl-benzo-1,3,2-diazaphospholes with methyl triflate
or triflic acid led in one step to triflate salts of unsymmetrically substituted benzo-1,3,2-
diazaphospholium cations. Determination of the crystal structures of two of these
derivatives by single-crystal X-ray diffraction studies revealed that individual cations and
Received 28 January 2010
Accepted after revision 19 April 2010
Available online 9 June 2010
Keywords:
Phosphorus heterocycles
Nitrogen heterocycles
Cations
anions in the crystal lattice interact via specific electrostatic,
p-stacking, or van-der-Waals
type interactions to form supramolecular assemblies. Thermoanalytical measurements
disclosed that benzo-diazaphospholium triflates with medium length alkyl chains melt
below 100 8C and exhibit a strong tendency to form supercooled liquids.
Carbene homologues
X-ray diffraction
Noncovalent interactions
Thermal analysis
´
ß 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
cations (IV, R1,2 = alkyl/aryl) are known [4–7] and have
also proven useful for selected applications [7].
Molten salts with melting points below 100 8C are
commonly denoted ionic liquids (ILs) and have, during the
last years, received a tremendous amount of attention
owing to their usability for a variety of applications [1]. ILs
are nowadays employed in battery electrolytes, separation
processes, as lubricants and – not only at a lab scale – as
(catalytically active) solvents in synthetic chemistry [2,3].
The chemical nature of ILs was during the last two decades
dominated by the combination of stable tetraalkylammo-
nium (I, Chart 1), 1,3-dialkylimidazolium (II) or N-alkyl-
pyridinium (III) cations with suitable anions such as
halides, complex halides, triflate, or triflamide [1].
Compared to the use of the nitrogen-based cations,
phosphorus-containing species have much less frequently
been employed for the design of ILs, although some
specimen containing tetrasubstituted phosphonium
A well-known aspect of phosphorus chemistry is that
beside phosphonium ions [R4P]+ a second class of stable
cations exists. These phosphenium ions of composition
[R2P]+ are distinguished by a divalent rather than a
tetravalent central atom and can generally be isolated in
the form of thermally stable salts if the electron deficiency
at the phosphorus atom is intramolecularly mediated by
suitable
p-donor substituents (in most cases amino
groups) [8]. A particularly interesting group of such cations
are N-heterocyclic diazaphospholium ions V, which were
first synthesized by the groups of Pudovik [9], Denk [10],
and Cowley [11], and can be regarded as isovalent
analogues of 1,3-disubstituted imidazolium ions II. These
cations exhibit both an exceptionally high stability [12]
and a peculiar reactivity, e.g., owing to their ability to bind
as ligands to transition metals [13,14], or to act as Lewis
acidic catalysts [15]. Although these features would make
their use in ILs rewarding, it appears that, as yet, no such
attempts have been undertaken. In view of the fact that in
imidazolium-based ILs the presence of different substi-
tuents on the heterocyclic core of the cations has generally
* Corresponding author.
E-mail addresses: martin.nieger@helsinki.fi (M. Nieger),
gudat@iac.uni-stuttgart.de (D. Gudat).
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.04.020

D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
999
Chart 1. Important types of ionic liquids.
Scheme 1. Synthesis of a N-alkyl-N0-aryl-1,3,2-diazaphospholium salt (Dipp = 2,6-diisopropylphenyl, Cy = cyclohexyl, Tms = Me3Si, OTfꢀ = triflate).
a beneficial effect on the desired melting behavior, the best
candidates for phosphenium-based ILs would be cations V
with an unsymmetrical substitution pattern (i.e., R1 ¼ R2).
Since the reported syntheses [9–11,16] focused mainly on
symmetrical derivatives (with R1 = R2), we felt the need for
Both phosphorus heterocycles 2 and 3 were character-
ized by analytical and spectroscopic data. The 1H and 13C
shifts are as expected, and the 31P chemical shifts match
those of known symmetrically substituted derivatives
[18]. The P-chloro-diazaphospholene 2 was further char-
acterized by a single-crystal X-ray diffraction study. The
asymmetric unit contains two crystallographically inde-
pendent molecules whose structural parameters (Fig. 1)
are very similar to each other and also to those of the
symmetrical 2-chloro-1,3-bis(2,6-diisopropyl)phenyl-4,5-
dimethyl-1,3,2-diazaphospholene (4, Chart 2). Worth
mentioning is the finding that the P–Cl bond (2.357(2)/
the development of
a dedicated synthetic route to
unsymmetrically substituted N-heteroyclic phosphenium
ions V. We report here on two approaches which allow the
assembly of monocyclic or benzannulated derivatives with
different N-substituents, and the characterization of the
triflates by spectroscopic, thermoanalytical measurements
and, in selected cases, by single-crystal X-ray diffraction
studies.
˚
2.340(2) A) in 2 is slightly but perceptibly longer than in 4
˚
(2.325(1) A) [18], which reflects not only the commonly
2. Results and discussion
observed ionic bond polarization in P-chloro-diazapho-
spholenes, but fits also into the trend that this effect
becomes particularly large for compounds with N-alkyl
substituents, presumably as a consequence of the superior
The ring system of N-heterocyclic phosphenium ions V
is commonly assembled by joining a P1 fragment with a
NCCN building block which is normally derived from an
a
-
s-donor capability of N-alkyl as compared to N-aryl groups
diimine precursor [9–11,16]. The synthesis of derivatives
with two different N-substituents according to the same
route would then require the use of a non-symmetrically
substituted diimine precursor. Compounds of this type are
accessible according to Rieger et al. [17] who performed
first a condensation of a diketone with an equimolar
amount of a bulky primary amine to give an isolable
ketimine, and then coupled this product with a second
amino component. Following this approach, we prepared
the non-symmetrical aryl/alkyl diimine 1 by stepwise
reaction of diacetyl with 2,6-diisopropylaniline and
cyclohexylamine. Conversion of this product into the
non-symmetrical P-chloro-diazaphospholene 2 and sub-
sequent chloride abstraction with trimethylsilyl trifluor-
omethanesulfonate (triflate) to give the salt 3 was then
accomplished by using the same protocol as had been
employed for the synthesis of symmetrical diazapho-
spholenes (Scheme 1) [16].
[18]. Analysis of the thermal behavior of 3 by means of
differential scanning calorimetry (DSC) disclosed that
around 32 8C a glassy phase was formed which displayed
no further detectable phase transitions until above 310 8C
an irreversible decomposition was observed.
Even though the synthetic approach leading to 3 should
allow to access a variety of mixed aryl/alkyl-substituted
diazaphospholene derivatives, these are limited to sterically
hindered products with at least one extremely bulky N-aryl
substituent.1 In order to circumvent this restriction, we
considered an alternative scheme which should also permit
1
The limitation is in fact introduced by the restricted availability of
isolable ketimines needed as precursors to 1; in attempting to prepare
such derivatives from sterically less demanding N-aryl amines or more
basic N-alkyl amines, we obtained only inseparable mixtures of the
desired ketimines with the corresponding symmetrical
were useless for the further synthesis.
a-diimines that

1000
D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
Fig. 1. Molecular structure of one of the crystallographically independent
molecules in crystalline 2 (H–atoms omitted for clarity; 50% probability
˚
thermal ellipsoids); selected bond lengths [A] (values for the second
molecule are given in brackets): Cl1–P1 2.357(2) [2.340(2)], P1–N5
1.669(4) [1.663(4)], P1–N2 1.674(4) [1.672(4)], N2–C3 1.421(7)
[1.424(6)], C3–C4 1.358(7) [1.354(7)], C4–N5 1.412(6) [1.419(6)].
Fig. 2. Section of one of the columnar stacks showing the packing of
anions and cations in crystalline 6d (H-atoms omitted for clarity; 50%
˚
probability thermal ellipsoids); selected bond lengths [A]: P1–N1
1.649(2), P1–N2 1.665(2), N1–C1 1.396(3), N2–C6 1.392(3), C6–C1
1.399(3), C6–C5 1.404(3), C5–C4 1.376(3), C3–C2 1.382(3), C3–C4
˚
1.406(3), C2–C1 1.394(3), intermolecular distances [A]: P1–O1
3.111(2), P1–O2 3.092(2) (O1 and O2 are symmetry generated;
operators: O1: ꢀx, 1 ꢀ y, 1 ꢀ z; O2: 1 ꢀ x, 1 ꢀ y, 1 ꢀ z).
Chart 2. Molecular structure of 4 (Dipp = 2,6-diisopropylphenyl).
the preparation of non-symmetric dialkylated N-heterocy-
clic phosphenium ions without steric protection. The basis
of our approach are earlier results by Malavaud et al. [19]
who established that N-alkyl-benzo-1,3,2-diazaphosphole
tetramers 5 (Scheme 2) react with Lewis acids under
cleavage of the tetramer and formation of monomeric Lewis
complexes, and by Lopez et al. [20] who used the reaction of
5 with acyl halides to produce asymmetrically substituted
N-acyl-N0-alkyl-2-chloro-benzodiazaphospholenes. As both
reactions proceed with electrophile induced cleavage of the
tetramers and attachment of an electrophile to the
unsubstituted nitrogen atom, we reckoned that a similar
electrophilic alkylation of 5 should render the desired N,N0-
dialkyl-benzodiazaphospholene derivatives. In line with
this anticipation, we found that 5a–d reacted with methyl
triflate (‘‘magic methyl’’) to give in one step the N-alkylated
benzo-1,3,2-diazaphospholium triflates 6a–f (Scheme 2)
which were isolated in yields of 60–92% after removal of the
solvent. A similar reaction as with methyl triflate was also
observable between 5 and triflic acid and enabled the
formation of NH-substituted phosphenium salts. As a
prominent representative of such compounds, we isolated
the salt 8 with the parent benzo-1,3,2-diazaphospholium
ion [21]. This species constitutes one of still very few
examples where stabilization of a phosphenium cation
exhibits Brønsted acid properties [21]. It should be noted
that a tetrachloroaluminate salt containing the same
symmetric cation as 6a had previously been obtained via
Lewis-acid promoted halide abstraction from a P-chloro-
substituted precursor [23].
The salts 6a–f and 8 were characterized by analytical
and spectroscopic studies and, in case of 6d, f, also by
single-crystal X-ray diffraction studies. The NMR data of all
compounds do not deviate significantly from one another
and match the previously reported data of 1,3-dimethyl-
benzo-1,3,2-diazaphospholium tetrachloroaluminate [23]
and monocyclic 1,3,2-diazaphospholium triflates [18]. The
individual bond distances and angles as well as the
shortest intermolecular contacts in 6d, f (Figs. 2 and 3)
are likewise closely similar to those of 8 [21] and
previously published data of other N-heterocyclic phos-
phenium salts [18,23], but the two structures show
nonetheless, some interesting differences in molecular
conformations and crystal packing. Thus, the cations in
crystalline 6d are arranged in a way that the planar
heterocyclic ring systems form shifted
p-stacks along the
crystallographic a-axis (Fig. 2). The center of gravity of
adjacent benzo-diazaphospholenium units in each stack is
horizontally displaced from the common axis, and the
phosphorus atoms point into opposite directions. The n-
relies exclusively on
p
-delocalisation without contribution
butyl chains display a gauche-conformation at the a-
by steric or inductive influences of N-substituents,2 and
carbon atom, and are thus rotated out of the aromatic ring
plane and oriented in such a way as to group adjacent
cations in the stack into centrosymmetric pairs. The triflate
anions are arranged in piles that fill the gaps between the
cation stacks. Two oxygen atoms of each anion exhibit
2
A
further example is exemplified in the isolation of a parent
benzazathiaphospholium salt [22].

D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
1001
Scheme 2. Synthesis of benzo-1,3,2-diazaphospholium triflates from benzo-1,3,2-diazaphosphole tetramers (R1 = Me (5a, 6a), Et (5b, 6b), Pr (5b, 6c), Bu
(5d, 6b), n-pentyl (5e, 6e), n-hexyl (5f, 6f), H (7, 8); R2 = Me (5a–f, 6a–f), H (7, 8)).
Fig. 3. (a) Molecular structure of a single cation in crystalline 6f showing the atom numbering scheme and the closest intermolecular cation–anion contacts
˚
(H–atoms omitted for clarity; 50% probability thermal ellipsoids); selected bond lengths [A]: P1–N5 1.648(3), P1–N2 1.658(3), N2–C3 1.385(5), N5–C4
˚
1.397(4), C3–C4 1.400(5), C4–C6 1.396(5), C6–C7 1.374(5), C7–C8 1.413(5), C8–C9 1.369(5), C9–C3 1.401(5), intermolecular distances [A]: P1–O2#1
3.047(3), P1–O3#2 3.126(3) (#1: ꢀx + 1, ꢀy + 2, ꢀz + 1; #2: ꢀx + 1, y ꢀ 0.5, ꢀz + 0.5). (b) Representation of a part of the crystal packing of 6f viewed along the
crystallographic c-axis showing sections of four of the columnar cation-anion stacks linked by P O contacts.

1002
D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
intermolecular contacts to the phosphorus atoms of every
˚
other unit in the cation stack (Fig. 2; the distances of 3.11 A
˚
(P1–O1) and 3.09 A (P1–O2) are of similar magnitude as in
other N-heterocyclic phosphenium triflates [18,21]), so
that the whole crystal structure can be described as a
columnar array of interlocking one-dimensional chains of
mutually connected cations and anions.
In contrast, the n-hexyl chains of the cations in
crystalline 6f display an all-trans conformation and are
practically aligned in the plane of the fused aromatic ring
system (Fig. 3). The phosphorus atom of each cation
exhibits close intermolecular contacts to oxygen atoms of
˚
˚
two triflate ions (P1–O2 3.05 A, P1–O3 3.13 A) which leads,
in a similar way as in 6d, to the formation of zigzag chains
of alternating anions and cations in the direction of the
crystallographic c-axis (Fig. 3). Each cation exhibits further
Fig. 4. Melting temperatures (diamonds) and solidification temperatures
(squares) of 6a–f. Circles denote the temperature of a second exothermal
process during the cooling phase which we assign to a further phase
transition.
a p-stacking interaction to a cation in a neighboring chain
which links parallel one-dimensional ion stacks together
to give a two-dimensional double-layer superstructure
which is terminated on both sides by n-hexyl substituents
and is oriented parallel to the crystallographic b,c-plane
(Fig. 3). The third dimension of the crystal is generated by
stacking the double-layers with an interlocking arrange-
ment of the hexyl-substituents in the cations, and a
pairwise grouping of the CF3-groups in the anions, of
adjacent layers. The whole arrangement has a certain
appeal as the individual cations and anions in the crystal
interact in one direction by (electrostatically dominated)
of all endothermic and exothermic processes match well
for 6a–d, the fusion energies of 6e,f are by some 17–25%
higher than the energies of the endothermic process;
furthermore, visual inspection of samples of crystalline
6e,f that had been subjected to a melting/cooling cycle in a
melting-point determination apparatus revealed a glassy
rather than a specific crystalline appearance. We interpret
these findings by assuming that cooling of molten samples
of 6a–f produces first a phase that is thermodynamically
less stable than the starting material and is possibly
amorphous. The observation of a second exothermic phase
transition for 6a–c is then attributable to conversion of the
unordered into a crystalline phase at lower temperature,
whereas in case of 6d both processes seem to occur at
comparable temperatures and are therefore not resolved.
In case of 6e,f, where the first phase transition occurs at
still lower temperature, crystallization is apparently
totally inhibited, presumably as a consequence of a
significantly increased viscosity.
P
O contacts, in the second direction by p-stacking
interactions, and in the third dimension preferably by
dispersive interactions between (fluoro)alkyl groups.
A study of the thermal behavior of 6a-f by differential
scanning calorimetry (DSC) revealed that all compounds
melt reversibly between 80 and 125 8C and are thermally
stable up to at least 200 8C. A plot of fusion temperatures
vs. the chain length of the N-alkyl group R1 (Fig. 4) shows
that derivatives with even-numbered chain lengths of R1
melt at slightly lower temperatures than those with odd-
numbered chain lengths (just opposite to the known
behavior of n-alkanes), and that the lowest fusion points of
all compounds are observed for the N-ethyl and N-butyl
derivative, respectively. All DSC curves give evidence for at
least one exothermal process during the cooling phase
which we interpret as solidification; the associated
temperatures show no alternating behavior but decrease
continuously with growing chain length of R1. In case of 6b,
recording the DSC curve through repeated heating/cooling
cycles revealed that regular solidification during the
cooling phase was only observed for the first cycle,
whereas in the remaining cycles delayed solidification
occurred only during the warm-up phase. A similar
behavior which indicates a strong tendency to form
supercooled liquids is also known for imidazolium-based
ILs [24]. The DSC curves of the lighter homologues 6a–c
3. Conclusions
Two approaches for the controlled synthesis of 1,3,2-
diazaphospholium cations with two different N-substitu-
ents have been derived. Reduction and condensation with
PCl3 of unsymmetrically substituted
a-diimines should
give access to both unsymmetrical aryl/alkyl and diaryl
cations with isolated rings, but is restricted to the
preparation of derivatives with at least one sterically
demanding substituent. In contrast, electrophilic depoly-
merisation and alkylation/protonation of benzo-1,3,2-
diazaphosphole-tetramers provides unsymmetrically
substituted benzannulated N-heterocyclic phosphenium
ions which need not be stabilized by bulky substituents.
Single-crystal X-ray diffraction studies of two of these
phosphenium salts give insight into interesting supramo-
lecular interactions in the crystalline state. Studies of the
thermal behavior of benzodiazaphospholium triflates
reveal that melting temperatures are higher than those
of common imidazolium-based ILs, but that, in particular,
cations with medium length alkyl chains melt below
display further
a second exothermic peak at lower
temperature (with energies amounting to 25–50% of that
of the first exothermic process), which we assign to a
further phase transition. The observed behavior during a
full heating/cooling cycle suggests that this transition is
not reversible, and that the intermediate phase is upon re-
heating only accessible via the melt. Whereas the energies

D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
1003
100 8C and display a strong tendency to form supercooled
liquids at even lower temperatures. These results should
encourage further investigations of the use of these
phosphenium salts as ionic liquids.
diene (5.11 g, 16 mmol) in THF (15 mL). The mixture was
stirred for 12 h at r.t. Remaining lithium was removed, and
the deeply colored solution formed was cooled to ꢀ78 8C.
Solid triethylamine hydrochloride (4.74 g, 34 mmol) was
added in several portions, and the reaction mixture was
allowed to warm slowly to r.t. and stirred for 4 h at this
temperature. The solution was then again cooled to ꢀ78 8C,
and phosphorus trichloride (1.4 mL, 16 mmol) was added
dropwise via syringe. The reaction mixture was allowed to
warm to r.t. and was stirred for 12 h at this temperature.
The solvent was evaporated under reduced pressure, the
residue dissolved in toluene (15 mL), and filtered. The
filtrate was concentrated under reduced pressure until the
solution became turbid, and the product was then isolated
4. Experimental section
All manipulations were carried out under an atmosphere
of dry argon using standard vacuum line techniques.
Solvents were dried by standard procedures. Cyclotetra-
phosphazanes were prepared as previously described by
Malavaud et al. [19]. 2,3-Butanedione-(2,6-diisopropylphe-
nyl)imine was synthesized as described by Rieger et al. [17].
NMR spectra were recorded on Bruker Avance 400 (1H:
400.1 MHz, 13C: 100.5 MHz, 31P: 161.9 MHz) or Avance 250
(1H: 250.1 MHz, 13C: 62.8 MHz, 31P: 101.2 MHz) NMR
spectrometers at 303 K. Chemical shifts are referenced to
by crystallization at 4 8C; yield 3.7 g (60%, m.p. 177.0 8C). –
3
1H NMR (CDCl3):
d
= 7.42 (t, 1 H, JHH = 7.8 Hz, p-CH), 7.25
3
(d, 2 H, JHH = 7.2 Hz, m-CH), 4.09–4.26 (br, 1 H, N–CH),
2.48–2.64 (m, 2 H), 2.42 (s, 3 H), 2.34–2.48 (m, 2 H), 1.86 (s,
3 H), 1.67–2.06 (m, 4 H), 1.41–1.62 (m, 2 H), 1.24–1.41 (m,
2 H), 1.20, (d, 6 H, JHH = 6.8 Hz, CH3), 1.13, (d, 6 H,
3JHH = 6.7 Hz, CH3). 13C{1H} NMR (CDCl3; not all quaternary
J
ext. TMS (1H, 13C) or 85% H3PO4 ( = 40.480747 MHz, 31P),
and coupling constants are given as absolute values if not
indicated otherwise; i, o, m, p denote the positions in N-aryl
rings. EI-MS: Varian MAT 711, 70 eV. Elemental analysis:
Perkin-Elmer 24000CHN/O Analyzer. Differential scanning
calorimetry (DSC) measurements were performed with a
NETZSCH DSC-204 Phoenix thermal analyzer using heating
and cooling rates of 10 K minꢀ1 (in some experiments also
rates of 5 K minꢀ1 were used), respectively. Sample prepa-
ration was carried out under inert atmosphere in a glove
box. The given fusion and solidification temperatures
representthe onset pointsoftheexothermicorendothermic
peaks in the DSC curves which are independent on heating
orcooling rates, respectively. Molarheatsoffusioncould not
be determined due to the lack of a possibility to determine
sufficiently accurate sample weights under inert atmo-
sphere conditions. Evaluation of the areas under all peaks
observed during one heating/cooling cycle indicated that for
6a–d, the energies of the exothermic and endothermic
processes are comparable (deviations of <10% are presum-
ably to a good deal attributable to the temperature
dependence of the heat capacities); for 6e,f, the fusion
energy is by 17–25% higher than the energy of the
exothermic phase transition observed during the cooling
phase.
3
carbon atoms detected due to signal broadening and
insufficient signal-to-noise ratio): d = 147.4 (i-C), 130.3 (p-
C), 124.5 (m-C), 58.8 (d, 2JCP = 8 Hz, NCH), 35.2 (CH2), 35.0
(CH2), 28.3 (HC), 25.9 (CH3), 25.8 (CH2), 25.0 (CH2), 23.8
(CH3), 12.5 (CH3), 11.5 (CH3). 31P{1H} NMR (CDCl3):
d
= 182.3 (s). – Calcd. for C22H34N2PCl (392.95): C 67.24
H 8.72 N 7.13; found: C 66.74 H 8.83 N 6.77.
1-Cyclohexyl-3-(2,6-diisopropylphenyl)-4,5-dimeth-
yl-1,3,2-diazaphospholium trifluoromethanesulfonate
3: Trimethylsilyl trifluoromethanesulfonate (0.59 mL,
3 mmol) was added dropwise to a stirred solution of 2-
chloro-1-cyclohexyl-3-(2,6-diisopropylphenyl)-4,5-di-
methyl-1,3,2-diazaphospholene (0.86 g, 2 mmol) in tolu-
ene (5 mL). The mixture was stirred for 1 h, and all volatiles
were removed in vacuum. The residue was extracted three
times with diethyl ether (5 mL) and dried in vacuum (yield
1.19 g, 99%; dec. > 300 8C). 1H NMR (CDCl3):
d = 7.54 (t, 1 H,
3JHH = 7.8 Hz, p-CH), 7.34 (d, 2 H, 3JHH = 7.8 Hz, m-CH), 4.56
(quint, 1 H, 3JHH = 3.6 Hz, N–CH), 2.67 (d, 3 H, 5JPH = 1.3 Hz,
CH3), 2.52–2.65 (m, 2 H, CH2), 2.29 (sept, 2 H, 3JHH = 6.8 Hz,
5
CH), 2.08 (d, 3 H, JPH = 1.9 Hz, CH3), 1.89–2.04 (m, 2 H,
3
1-cyclohexyl-4-(2,6-diisopropylphenyl)-1,4-diazabu-
tadiene 1: A flask containing a solution of 2,3-butane-
dione-(2,6-diisopropylphenyl)imine (8.00 g, 33 mmol),
cyclohexylamine (4.1 mL, 36 mmol), and 4-toluenesulfonic
acid monohydrate (100 mg) in benzene (125 mL) was
connected with a water separator and a reflux condenser.
The solution was refluxed for 4 h. The solvent was
evaporated under reduced pressure. Vacuum distillation
gave 10.10 g (95%) of product, b.p. 118–124 8C/0.05–
CH2), 1.80–1.89 (m, 1 H, CH2), 1.64 (t, 4 H, JHH = 10.1 Hz,
CH2), 1.30 (m 1 H, CH2), 1.18 (d,3JHH = 6.8 Hz, 6 H, CH3), 1.15
3
(d, JHH = 6.8 Hz,
6 H, CH3). –
13C{1H}-NMR (CDCl3):
d
= 157.0 (i-C), 146.1 (o-C), 142.61 (C–N), 142.56 (C–N),
131.7 (p-C), 125.0 (m-C), 60.7 (d, 2JCP = 7.3 Hz, CH–N), 36.7
3
(d, JCP = 13.4 Hz, CH2), 28.2 (CH), 25.9 (CH3), 25.5 (CH2),
24.9 (CH2), 23.1 (CH3), 13.6 (CH3), 12.4 (CH3). – 31P{1H}
NMR (CDCl3): d = 203.8 (s). – MS (EI, 70 eV, 415K): m/e (%):
506.1 ([M]+, 20), 357.2 ([M –SO3CF3]+, 100), 275.1 ([M –
SO3CF3C6H10], 17), 202.1 ([M –SO3CF3C6H11NPC2H2]+, 5). –
Calcd. for C23H34N2O3PSF3 (506.56): C 54.53 H 6.77 N 5.53
P 6.11, found: C 53.51 H 7.05 N 5.33.
0.4 mm Hg. 1H NMR (CDCl3):
d = 6.88–7.16 (m, 3 H), 3.53
(m, 1 H, 3JHH = 4.7 Hz, NCH), 2.44–2.71 (m, 2 H), 2.20 (s, 3 H,
CH3), 1.84 (s, 3 H, CH3), 1.90–1.23 (8 H), 1.19 (d, 6 H,
3JHH = 6.1 Hz, CH3), 1.11 (d, 6 H, 3J = 6.9 Hz, CH3). – 13C{1H}
1-Methyl-3-alkyl-benzo-1,3,2-diazaphospholium
trifluoromethanesulfonates 6a–f (general procedure): A
suspension of the appropriate cyclotetra-1-alkyl-benzo-
1,3,2-diazaphosphole [19] (1.1 mmol) and methyl trifluor-
omethanesulfonate (0.6 mL, 5.4 mmol) in xylene (15 mL)
was refluxed until the solid had completely dissolved
(about 1.5 h). The mixture was allowed to cool to room
NMR (CDCl3):
d = 169.0, 164.1, 146.6, 135.1, 123.2, 122.8,
60.3, 33.4, 28.1, 25.8, 24.6, 23.1, 22.7, 16.2, 12.4.
2-Chloro-1-cyclohexyl-3-(2,6-diisopropylphenyl)-
4,5-dimethyl-1,3,2-diazaphospholene 2: A piece of lithi-
um (380 mg, 55 mmol) was added to a solution of
1-cyclohexyl-4-(2,6-diisopropylphenyl)-1,4-diazabuta-

1004
D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
temperature and about three quarters of the solvent were
evaporated under reduced pressure. A suspension formed
from which the rest of solvent was separated from the solid
phase with a syringe. The remaining solid was washed
twice with hexane (5 mL) and once with hexane-diethyl
ether (1:1, total volume 3 mL). The remaining product was
dried in vacuum.
NCCH2), 1.39–1.47 (m, 4 H, CH2), 0.92 (t, 3 H, 3JHH = 7.0 Hz,
CH3). – 13C{1H} NMR (CDCl3): = 139.1 (d, 2JCP = 6.3 Hz, C),
137.8 (d, 2JCP = 6.1 Hz, C), 127.2 (d, 4JCP = 1.8 Hz, CH), 126.9
d
4
3
(d, JCP = 1.8 Hz, CH), 113.4 (d, JCP = 1.3 Hz, CH), 113.2 (d,
2
3JCP = 1.5 Hz, CH), 47.6 (d, JCP = 13.3 Hz, NCH2), 33.3 (d,
2JCP = 17.5 Hz, NCH3), 29.7 (d, 3JCP = 8.5 Hz, NCCH2), 28.9 (d,
4JCP = 1.6 Hz, NCCCH2), 22.0 (s, CH2), 13.7 (s, CH3). – 19F
1,3-Dimethyl-benzo-1,3,2-diazaphospholium
tri-
NMR (CDCl3):
d = 216.0 (s). – Calcd. for C13H18F3N2O3PS (370.33): C
d
= ꢀ78.5 (s). – 31P{1H} NMR (CDCl3):
fluoromethanesulfonate (6a): Yield 1.26 g (98%), m.p.
123.1 8C. – 1H NMR (CDCl3):
d
= 7.62–7.67 (m, 4 H, CH), 4.13
42.16 H 4.90 N 7.56, found C 41.65 H 4.97 N 7.36.
1-Hexyl-3-methyl-benzo-1,3,2-diazaphospholium
trifluoromethanesulfonate (6f): Yield 0.75 g (60%), m.p.
3
(d, 3 H, JHP = 11.0 Hz, NCH3). – 13C{1H} NMR (CDCl3):
2
4
d
= 138.6 (d, JCP = 6.1 Hz, C), 127.1 (d, JCP = 1.9 Hz, CH),
3
2
113.0 (d, JCP = 1.9 Hz, CH), 33.1 (d, JCP = 17.6 Hz, NCH3). –
31P{1H}NMR(CDCl3):
= 215.5(s).Calcd. forC9H10F3N2O3PS
100.5 8C. – 1H NMR (CDCl3):
d = 7.61–7.65 (m, 4 H, CH), 4.45
3
3
d
(dt, 2 H, JHH = 7.6 Hz, JHP = 10.7 Hz, NCH2), 4.14 (d, 3 H,
3JHP = 11.0 Hz, NCH3), 2.11 (quint, 2 H, 3JHH = 7.5 Hz, NCCH2),
(314.22): C 34.40 H 3.21 N 8.92, found C 34.00 H 3.38 N 8.72.
1-Ethyl-3-methyl-benzo-1,3,2-diazaphospholium
trifluoromethansulfonate (6b): Yield 0.80 g (86%), m.p.
3
1.28–1.53 (m, 6 H, CH2), 0.89 (t, 3 H, JHH = 7.1 Hz, CH3). –
13C{1H} NMR (CDCl3):
d
= 140.0 (d, 2JCP = 5.9 Hz, C), 137.1 (d,
82.7 8C. – 1H NMR (CDCl3):
d
= 7.63–7.64 (m, 4 H, CH), 4.53
2JCP = 5.0 Hz, C), 127.2 (d, JCP = 1.8 Hz, CH), 126.9 (d,
4
3
3
3
(dq, 2 H, JHH = 7.2 Hz, JHP = 11.4 Hz, NCH2), 4.12 (d, 3 H,
4JCP = 1.9 Hz, CH), 113.3 (d, JCP = 1.3 Hz, CH), 113.2 (d,
3JHP = 11.0 Hz, NCH3), 1.80 (dt,
3
H, JHH = 7.2 Hz,
3JCP = 1.4 Hz, CH), 47.6 (d, JCP = 13.2 Hz, NCH2), 33.3 (d,
3
2
4JHP = 1.0 Hz, CCH3). – 13C{1H} NMR (CDCl3):
d
= 139.1 (d,
2JCP = 17.4 Hz, NCH3), 31.0 (s, CH2), 29.9 (d, JCP = 8.6 Hz,
3
2JCP = 6.2 Hz, C), 137.8 (d, JCP = 6.0 Hz, C), 127.2 (d,
NCCH2), 26.6 (d, 4JCP = 1.6 Hz, NCCCH2), 22.3 (s, CH2), 13.8 (s,
2
4JCP = 1.8 Hz, CH), 126.9 (d, JCP = 1.9 Hz, CH), 113.3 (d,
CH3). – 19F NMR (CDCl3):
d
= ꢀ78.5 (s). – 31P{1H} NMR
4
3JCP = 1.4 Hz, CH), 113.2 (d, JCP = 1.4 Hz, CH), 42.9 (d,
(CDCl3): d = 215.9 (s). – Calcd. for C14H20F3N2O3PS (384.35):
3
2JCP = 14.6 Hz, NCH2), 33.3 (d, 2JCP = 17.7 Hz, NCH3), 15.5 (d,
C 43.75 H 5.24 N 7.29, found C 43.03 H 5.31 N 6.87.
3JCP = 10.9 Hz, CCH3). – 31P{1H} NMR (CDCl3):
d
= 215.9 (s).
1,3-benzo-1,3,2-diazaphospholium trifluorometha-
nesulfonate (8) [21]: The synthesis was carried out by
analogy to that of the 1,3-dialkyl derivatives except that a
solution of the appropriate amount of trifluoromethane-
sulfonic acid in 10 mL xylene was used instead of the methyl
ester and that the solid remaining after evaporation of the
solvent was washed three times with diethyl ether. Cooling
of the washing liquid to ꢀ20 8C produced a further quantity
of product in the form of colorless crystals (m.p. 132.0 8C)
which were suitable for single-crystal X-ray diffraction
studies. The combined yield was 0.84 g (99%). 1H NMR
– Calcd. for C10H12F3N2O3PS (328.25): C 36.59 H 3.68 N
8.53, found C 37.14 H 3.63 N 8.62.
1-Methyl-3-propyl-benzo-1,3,2-diazaphospholium
trifluoromethanesulfonate (6c): Yield 1.34 g (87%), m.p.
95.5 8C. – 1H NMR (CDCl3):
d = 7.61–7.65 (m, 4 H, CH), 4.43
(m, 2 H, NCH2), 4.14 (d, 3 H, 3JHP = 11.0 Hz, NCH3), 2.16 (m,
2 H, CCH2), 1.12 (t, 3 H, 3JHH = 7.4 Hz, CH3). – 13C{1H} NMR
(CDCl3):
d
= 139.0 (d, 2JCP = 6.3 Hz, C), 137.7 (d,,
4
2JCP = 5.5 Hz, C), 127.2 (d, JCP = 1.8 Hz, CH), 126.9 (d,
4JCP = 1.8 Hz, CH), 113.3 (d, JCP = 1.4 Hz, CH), 113.2 (d,
3
3JCP = 1.4 Hz, CH), 49.1 (d, JCP = 13.3 Hz, NCH2), 33.3 (d,
(CD3CN):d = 12.50 (broad, 2H, NH), 7.53–7.90 (m, 4H, CH). –
2
2JCP = 17.5 Hz, NCH3), 23.4 (d, JCP = 8.6 Hz, CCH2), 11.3 (d,
13C{1H}NMR(CD3CN):
d
= 137.5(d,2JCP = 6.7 Hz, C), 127.3(d,
3
4JCP = 1.7 Hz, CCH3). – 31P{1H} NMR (CDCl3):
d
= 215.8 (s). –
JCP = 1.9 Hz, CH), 115.3 (d, 3JCP = 1.2 Hz, CH). – 31P{1H} NMR
4
´
Calcd. for C11H14F3N2O3PS (342.27): C 38.60 H 4.12 N 8.18,
found C 39.09 H 3.98 N 8.13.
1-Butyl-3-methyl-benzo-1,3,2-diazaphospholium
trifluoromethanesulfonate (6d): Yield 0.72 g (92%), m.p.
(CD3CN): d = 212.0 (s). – Calcd. forC7H6F3N2O3PS (286.17): C
64.84 H 8.16 N 12.60; found C 64.84 H 8.35 N 12.61.
Crystallography. The crystal structure determinations
of 2 and 6d,f were performed on Bruker-Nonius Kappa-CCD
80.8 8C. – 1H NMR (CDCl3):
d
= 7.61–7.65 (m, 4 H, CH), 4.46
diffractometers at 100(2) K (2, 6d) or 123(2) K (6f),
3
3
˚
(dt, 2 H JHH = 7.5 Hz, JPH = 10.7 Hz, NCH2), 4.14 (d, 3 H
3JHP = 11.0 Hz, NCH3), 2.10 (quint, 2 H 3JHH = 7.5 Hz, NCCH2),
respectively, using Mo-K radiation (
l
= 0.71073 A). Direct
a
Methods (SHELXS-97) [25] were used for structure solution,
and refinement was carried out using SHELXL-97 (full-
matrix least-squares on F2) [25]. Hydrogen atoms were
refined using a riding model. The studied crystal of 3 was a
non-merohedral twin with two domains (80:20; BASF
0.206(2)), twin-matrix: (ꢀ1 0 0, ꢀ0.108 1 ꢀ0.020, 0 0 ꢀ1)
[26].
3
1.53 (sext, 2 H, JHH = 7.4 Hz, NCCCH2), 1.01 (t, 3 H,
3JHH = 7.3 Hz, CH3) 13C{1H} NMR (CDCl3):
d = 139.1 (d,
2JCP = 6.9 Hz, C), 137.8 (d, JCP = 5.5 Hz, C), 127.2 (d,
2
4JCP = 1.8 Hz, CH), 126.9 (d, JCP = 1.8 Hz, CH), 113.3 (d,
4
3JCP = 1.3 Hz, CH), 113.2 (d, JCP = 1.5 Hz, CH), 47.3 (d,
3
2JCP = 13.3 Hz, NCH2), 33.3 (d, JCP = 17.4 Hz, NCH3), 31.9
2
(d, 3JCP = 8.4 Hz, NCCH2), 20.1 (d, 4JCP = 1.7 Hz, NCCCH2), 13.4
2: colorless crystals, C22H34ClN2P, M = 392.93, crystal
(s, CCH3). – 31P{1H} NMR (CDCl3):
d
= 216.0 (s). – Calcd. for
12H16F3N2O3PS (356.30): C 40.45 H 4.53 N 7.86, found C
40.11 H 4.62 N 7.76.
size 0.20 ꢁ 0.10 ꢁ 0.03 mm, triclinic, space group P1 ðNo: 2Þ,
¯
˚
˚
C
a = 11.1169(3) A, b = 13.2635(4) A, c = 14.7574(4)
˚
A,
a
= 89.127(2)8,
b
= 84.693(2)8,
(calcd) = 1.206 Mg/m3,
max = 508),
7571 unique [Rint = 0.000], 474 parameters, GooF = 1.16, R1
g = 87.350(2)8,
3
˚
1-Methyl-3-pentyl-benzo-1,3,2-diazaphospholium
V = 2164.19(11) A , Z = 4,
= 0.26 mmꢀ1, 7571 reflections (2
F(000) = 848, m u
r
trifluoromethanesulfonate (6e): Yield 0.93 g (67%), m.p.
97.5 8C. – 1H NMR (CDCl3):
(dt, 2 H, JHH = 7.6 Hz, JPH = 10.7 Hz, NCH2), 4.13 (d, 3 H,
3JHP = 11.0 Hz, NCH3), 2.11 (quint,
d
= 7.61–7.65 (m, 4 H, CH), 4.45
3
3
(I > 2s(I)) = 0.079, wR2 (all data) = 0.212, largest diff. peak
3
2
H, JHH = 7.4 Hz,
and hole 0.496/ꢀ0.463 e Aꢀ3
.

D. Schmid et al. / C. R. Chimie 13 (2010) 998–1005
1005
References
6d: colorless crystals, C12H16F3N2O3PS, M = 356.30,
crystal size 0.40 ꢁ 0.40 ꢁ 0.20 mm, triclinic, space group
[1] C.M. Gordon, M.J. Muldoon, in: P. Wasserscheid, T. Welton (Eds.), Ionic
Liquids in Synthesis, Wiley VCH, Weinheim, 2003, p. 8ff.
[2] W.M. Reichert, J.D. Holbrey, K.B. Vigour, T.D. Morgan, G.A. Broker, R.D.
Rogers, Chem. Commun. (2006) 4767–4779.
[3] N.V. Plechkova, K.R. Seddon, Chem. Soc. Rev. 37 (2008) 123–150.
[4] S.E. Fry, N.J. Pienta, J. Am. Chem. Soc. 107 (1985) 6399–6400.
[5] J. McNulty, A. Capretta, J. Wilson, J. Dyck, G. Adjabeng, A. Robertson,
Chem. Comm. (2002) 1986–1987.
[6] J. McNulty, S. Cheekoori, J.J. Nair, V. Larichev, A. Capretta, A.J. Robertson,
Tetrahedron Lett. 46 (2005) 3641–3644.
[7] P. Wasserscheid, W. Keim, Angew. Chem. 112 (2000) 3926–3945 (and
cited refs).
˚
˚
˚
¯
P1 (No. 2), a = 6.842(4) A, b = 8.792(5) A, c = 13.740(7) A,
3
˚
a
= 78.49(4)8,
Z = 2,
(calcd) = 1.471 Mg/m3, F(000) = 368,
3438 reflections (2 max = 528), 3160 unique [Rint = 0.027],
201 parameters, no restraints, GooF = 0.961, R1
b
= 85.24(2)8,
g
= 84.24(2)8, V = 804.2(7) A ,
r
m ,
= 0.34 mmꢀ1
u
(I > 2s(I)) = 0.040, wR2 (all data) = 0.1086, largest diff.
peak and hole 0.377/ꢀ0.330 e Aꢀ3
.
6f: colorless crystals,
C14H20F3N2O3PS, M = 384.35,
crystal size 0.40 ꢁ 0.10 ꢁ 0.05 mm, monoclinic, space
[8] Selected reviews: A.H. Cowley, R. Kemp, Chem. Rev. 85 (1985) 367–382.
˚
˚
group P 21/c (No. 14), a = 15.017(2) A, b = 8.913(1) A,
`
´
M. Sanchez, M.R. Mazieres, L. Lamande, R. Wolf, in: M. Regitz, O. Scherer
(Eds.), Multiple Bonds and Low Coordination Chemistry in Phosphorus
Chemistry, Georg Thieme Verlag, Stuttgart, 1990, p. 129ff ;
D. Gudat, Coord. Chem. Rev. 173 (1997) 71–106.
[9] I.A. Litvinov, V.A. Naumov, T.V. Gryaznova, A.M. Kibardin, A.N. Pudovik,
Dokl. Akad. Nauk SSSR 324 (1990) 623–625.
3
˚
˚
c = 13.245(1) A,
(calcd) = 1.455 Mg/m3, F(000) = 800,
14489 reflections (2 max = 508), 3086 unique [Rint = 0.094],
217 parameters, GooF = 1.03, R1 (I > 2
(I)) = 0.057, wR2 (all
b
= 98.21(1)8, V = 1754.6(3) A , Z = 4,
r
m
= 0.32 mmꢀ1
,
u
s
data) = 0.143, largest diff. peak and hole 0.401/
[10] M. Denk, S. Gupta, R. Ramachandran, Tetrahedron Lett. 50 (1996) 9025–
9028.
[11] C.J. Carmalt, V. Lomeli, G.B. McBurnett, A.H. Cowley, J. Chem. Soc.
Commun. (1997) 2095–2096.
[12] D. Gudat, Eur. J. Inorg. Chem. (1998) 1087–1094.
[13] D. Gudat, A. Haghverdi, M. Nieger, J. Organomet. Chem. 617 (2001)
383–394.
[14] C.A. Caputo, A.L. Brazeau, Z. Hynes, J.T. Price, H.M. Tuononen, N.D. Jones,
Organometallics 28 (2009) 5261–5265.
ꢀ0.288 e Aꢀ3
.
CCDC-762960 (2), CCDC-763485 (6d), and CCDC-
762959 (6f), contain the supplementary (Supplementary
data) crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam.ac.uk/
data_request/cif.
[15] S. Burck, D. Fo¨rster, D. Gudat, Chem. Commun. (2006) 2810–2812.
[16] S. Burck, D. Gudat, M. Nieger, W.W. du Mont, J. Am. Chem. Soc. 128
(2006) 3946–3955.
Acknowledgments
[17] M. Schmid, R. Eberhardt, J. Kukral, B. Rieger, Z. Naturforsch. 57b (2002)
1141–1146.
[18] S. Burck, D. Gudat, K. Na¨ttinen, M. Nieger, M. Niemeyer, D. Schmid, Eur.
We thank J. Trinkner and K. Wohlbold (Institut fu¨r
Organische Chemie, University of Stuttgart) for recording
the mass spectra and C. Schneck (Institut fu¨r Anorganische
Chemie, University of Stuttgart) for thermoanalytical
measurements. The Deutsche Forschungsgemeinschaft is
acknowledged for financial support. D.F. thanks further the
DAAD, D.G. COST (action CM0802), and M.N. the Academy
of Finland (proj. no. 128800) for financial support.
J. Inorg. Chem. (2007) 5112–5119.
´
´
[19] C. Malavaud, T.NG. MPondo, L. Lopez, J. Barrans, Can. J. Chem. 62 (1984)
43–50.
[20] Y.K. Rodi, A. El Hallaoui, E.M. Essassi, C. Dargelas, L. Lopez, J. Bellan,
Phosphorus Sulfur Silicon Relat. Elem. 159 (2000) 215–227.
[21] D. Schmid, S. Loscher, D. Gudat, D. Bubrin, I. Hartenbach, T. Schleid, Z.
˝
´
Benko, L. Nyulaszi, Chem. Commun. (2009) 830–832.
[22] N. Burford, A.I. Dipchand, B.W. Royan, P.S. White, Inorg. Chem. 29
(1990) 4938–4944.
[23] N. Burford, A.I. Dipchand, B.W. Royan, P.S. White, Acta Crystallogr. C45
(1989) 1345.
ˆ
¨
[24] P. Bonhote, A.-P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grat-
Appendix A. Supplementary data
zel, Inorg. Chem. 35 (1996) 1168–1178.
[25] G.M. Sheldrick, Acta Crystallogr. A64 (2008) 112.
[26] A.L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht, The Netherlands, 2010.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.crci.2010.04.020.