Alkali Metal Chlorine and Bromine Carbenoids: Their Thermal Stability and Structural Properties

Article abstract of DOI:10.1002/chem.201701911

The synthesis and structures of a series of M/X carbenoids of the type [Ph₂P(S)]₂CMX with M=Li, Na, and K and X=Cl and Br are reported, amongst the first isolated Na/Br and K/Br carbenoids. NMR spectroscopic as well as crystallographic studies showed distinct differences between the lithium carbenoids and their heavier congeners. In the solid state, all carbenoids showed no direct metal–carbon interaction, but an interaction between the metal and the halogen atom. This contact is only very weak in the case of the Li/Br carbenoid, but much more pronounced in the corresponding potassium and sodium compounds. Nevertheless, these interactions did not significantly influence the stability of the carbenoids by weakening the C?X bond and facilitating the MX elimination. As such all compounds were found to be stable up to approximately 60 °C in solution. Hence, M?X interactions—albeit being an essential feature for the structure formation of carbenoids—are not the only criterion determining the stability of such compounds. In the present systems, the stabilization by the thiophosphinoyl moieties is more important than the metal/halogen combination.

Full text of DOI:10.1002/chem.201701911

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Accepted Article
Title: Alkali metal chlorine and bromine carbenoids: Their thermal
stability and structural properties
Authors: Sebastian Molitor and Viktoria H. Gessner
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Alkali metal chlorine and bromine carbenoids: Their thermal stability
and structural properties
Sebastian Molitor[b] and Viktoria H. Gessner*[a]
Dedication ((optional))
Abstract: The synthesis and structures of a series of M/X carbenoids
of the type [Ph2P(S)]2CMX with M = Li, Na and K and X = Cl and Br
are reported, amongst the first isolated Na/Br and K/Br carbenoids.
NMR spectroscopic as well as crystallographic studies showed
distinct differences between the lithium carbenoids and their heavier
congeners. In the solid-state, all carbenoids showed no direct metal
carbon interaction, but an interaction between the metal and the
halogen atom. This contact is only very weak in case of the Li/Br
carbenoid, but much more pronounced in the corresponding
potassium and sodium compounds. Nevertheless, these interactions
did not significantly influence the stability of the carbenoids by
weakening the C–X bond and facilitating the MX elimination. As such
all compounds were found to be stable up to approx. 60 °C in solution.
Hence, M–X interactions – albeit being an essential feature for the
structure formation of carbenoids – are not the only criterion
determining the stability of such compounds. In the present systems,
the stabilization by the thiophosphinoyl moieties is more important
than the metal halogen combination.
The stability control of carbenoid species is probably best
reflected by means of lithium chloride carbenoids. Due to the
facile LiCl elimination this metal halogen combination typically
results in extremely reactive compounds, which are thus usually
only applied in in situ transformations. The first isolation of a Li/Cl
alkylcarbenoid was accomplished by Boche and co-workers 1996.
They successfully isolated and structurally characterized the
simple carbenoid, dichloromethyllithium (I), which decomposes at
temperatures above –100 °C (Figure 1).[ 8 ] Introduction of
thiophosphoryl moieties however, delivers the room temperature
stable system II, which impressively demonstrates the impact of
the substitution pattern at the carbenoid carbon atom on the
stability.[9] Only very recently, our group has reported on the
impact of the nature of the alkali metal on the carbenoid stability
using the silyl system III-M (with M = Li, Na, K). Interestingly,
replacement of lithium by the heavier congeners, sodium and
potassium, resulted in a remarkable increase of stability, which
allowed for selectivity control in carbene transfer reactions.[10]
Introduction
Carbenoid chemistry has quite a long history, beginning with
the pioneering work by Simmons and Smith as well as Gloss and
Moss in the 1950s on cyclopropanation reactions.[1] However, the
last two decades have experienced a renaissance in this
chemistry.[2] This is connected with the nowadays convenient
handling of these typically reactive and thermolabile species by
standard inert gas techniques as well as with the obtained
understanding of the electronic structure and aggregation of these
species, which allows for tailoring properties and reactivities by
molecular design and adjustment of reaction conditions. This has
led to the development of new applications beyond classical
cyclopropanation reactions[ 3 ] such as in bond activation and
coupling reactions,[ 4 ] in homologation[ 5 ] and carbene transfer
reactions[6] as well as first catalytic transformations.[7]
Figure 1. Isolated metal chloride carbenoids and their decomposition
temperatures TD.
Although many reports have appeared in the last years focussing
on the influence of the substitution pattern[11] and the M/X combi-
nation (M = Li, Mg, Zn; X = Hal, OR, NR, SR)[12] on the carbenoid
reactivity, systematic studies particularly on the structural
properties of a given system depending on the M/X combination
are missing. For example, while several structures of Li/Cl
carbenoids have been elucidated until today,[8-11] no structure of
any Li/Br carbenoid – except for a phosphaalkene system
reported by Niecke[13] – is known so far. Likewise, studies on
sodium or potassium compounds are limited to the chloro
compounds III-Na and III-K (Figure 1).[10] To provide further
knowledge about the structural diversity of carbenoids, we
addressed the systematic synthesis and structure elucidation of
chlorine and bromine systems with different alkali metals.[14] We
were particularly interested in the metal carbon and metal halogen
interactions in the corresponding structures, which have shown to
crucially influence the stability and reactivity of these
[a]
[b]
Prof. Dr. V. H. Gessner
Inorganic Chemistry II, Faculty of Chemistry and Biochemistry,
Ruhr-Universität Bochum
Universitätsstraße 150, 44801 Bochum, Germany
Email: viktoria.gessner@rub.de
Homepage: http://www.ruhr-uni-bochum.de/ac2
Dr. S. Molitor
Institut für Anorganische Chemie,
Julius-Maximilians-Universität Würzburg
Am Hubland, 97074 Würzburg, Germany
Supporting information for this article is given via a link at the end of
the document.
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compounds.[15,16] We chose the bis(thiophosphinoyl)-substituted
system like in II as model system for our studies, since this
backbone efficiently stabilizes carbanionic compounds and
should thus allow for the isolation of carbenoids with different M/X
combinations.
Under an inert atmosphere no decomposition was observed in
solution as well as in solid state, even after storage for several
days. Hence, all carbenoids could be isolated as yellow solids in
excellent yields of 89 to 99%. All compounds were characterized
by NMR spectroscopy, elemental as well as single-crystal X-ray
diffraction analysis.
In THF solutions, all carbenoids exhibited highly symmetric NMR
patterns, thus suggesting the formation of symmetric monomers
or aggregates in solution. Only the 1H NMR spectrum of 1-K
showed the coordination of THF in solution (see the SI for NMR
spectra). In case of all other carbenoids no obvious solvent
coordination was observed. [17] However, elemental analyses as
well as single-crystal X-ray diffraction analyses (see below)
suggest coordination of THF also in the lithium and sodium
compounds. We thus assume that solvent exchange in these
compounds is too fast to be detected on the NMR time scale. The
31P{1H} NMR signals of all carbenoids appear at around δP = 47
ppm and are thus comparable to those observed for the
protonated precursors and almost independent of the M/X
combination (see Table 1 for NMR data). The 13C{1H} NMR signal
of the carbenoid carbon atoms, which is typically the most
significant NMR parameter for carbenoids, appears as sharp
triplet slightly up-field shifted compared to the signal of the
protonated precursors 1 and 2. This is the reverse trend typically
observed for the labile Li/Cl carbenoids.[18] However, analogous
observations have been made for other highly stabilized lithium
carbenoids such as II.[9,11] A closer look at the 13C NMR signals of
the central carbon atoms in the carbenoids and their protonated
starting materials reveals that the shift ∆δ of the signal is more
pronounced for the chloro compounds 1-M than for the bromine
systems 2-M.
Results and Discussion
Synthesis, decomposition and NMR spectroscopic
studies
The halogenated compounds 1 and 2 were prepared from the
diprotonated precursor via deprotonation with n-butyllithium at low
reaction temperature and subsequent halogenation with
hexachloroethane and 1,2-dibromotetrachloroethane, respec-
tively (Scheme 1). 1 and 2 could be isolated as colorless solids in
moderate to good yields. The synthesis of 1 has been reported
previously via hydrolysis of Li/Cl carbenoid II.[9]
characterized by NMR spectroscopy as well as elemental and X-
ray diffraction analysis (see the Experimental section for details).
2 was
It is interesting to note, that the sodium and potassium
compounds exhibit remarkable differences in the NMR data
compared with their lithium congeners. While the Na and K
systems show almost identical 13C{1H} NMR shifts (δC = 45 and
40 ppm, respectively for 1-Na/K and 2-Na/K), the signals of the
lithium compounds are up-field shifted by approx. 10 ppm. Also,
1
the JPC coupling constant is significantly higher for the lithium
compounds, suggesting a higher s-character in the P–C bonds
and hence a higher p-character in the C–Cl/Br bond relative to
1/2-Na and 1/2-K. The latter accounts for a weaker C–Hal
interaction in the lithium carbenoids and thus suggests a higher
stability of the heavier carbenoids as has previously been
observed for the more labile silyl substituted systems III.[10]
Studies on the thermal stability of 1-M and 2-M showed that all
systems are stable in solid state as well as in THF solution up to
60 °C. Only the lithium compound showed small amounts of
decomposition products when heated at 60 °C for 5h in THF
solution. Decomposition of all compounds was observed upon
heating for several hours in refluxing THF. No significant
differences in the stabilities of the different sodium and potassium
systems could be observed. Thus, the only labile
bis(thiophosphinoyl)-substituted carbenoid is the corresponding
Li/F system, which was found to decompose at temperatures
above 0 °C.[15] All other carbenoids are stable up to approx. 60 °C.
The decomposition of 1-M and 2-M via MCl or MBr formation,
occurred in a rather selective way and resulted in the formation of
Scheme 1. Preparation of M/X carbenoids from their halogenated precursors 1
and 2.
Deprotonation to the alkali metal carbenoids was accomplished
by treatment of a THF solution of the bromo and chloro compound,
respectively, with 1 equiv. of a corresponding metal base
(LiN(SiMe3)2, NaN(SiMe3)2 or KN(SiMe3)2) at room temperature.
Reaction monitoring by 31P{1H} NMR spectroscopy always
confirmed selective deprotonation with no accompanying side-
reactions, such metal-halide exchange. Analogous to the known
Li/Cl carbenoid reported by Le Floch and coworkers all M/X
combinations gave rise to room temperature stable systems.
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the cyclic, bisylidic compound 3, which has previously been
reported by Chivers and coworkers from the decomposition
reaction of the Li/I carbenoid (Scheme 2).[19] Compound 3 was
isolated in 70% yield from the decomposition of 1-K. Interestingly,
the thermal stability of the carbenoids was also found to depend
on the solvent used. As such, dissolving of the THF coordinated
K/Cl carbenoid 1-K in toluene already led to its decomposition at
55 °C. This underlines the importance of the choice of the right
solvent in carbenoid chemistry. The generally observed higher
stability of carbenoids in coordinating solvents such as THF has
been explained by the coordination of the solvent to the metal
center, which results in the weakening or cleavage of the M–X
interaction and thus hampers MX elimination.[2]
diffraction analysis could be obtained by slow diffusion of pentane
into a concentrated THF solution. XRD analysis allowed the
elucidation of 4 as a Ci symmetric isomer of the pseudo-CS
symmetric bisylide 3. The molecular structure of 4 is shown in
Figure 2, the structure of 3 is given in the SI. Comparing 4 with its
precursor 3 shows that a P–S and C–S bond cleavage must have
occurred in the starting material to form 4. 4 crystallizes in the
triclinic space group P–1 with two halves of the dimeric molecule
and two additional THF molecules in the asymmetric unit (only
one molecule of 4 is shown in figure 2). The central structural motif
consists of a (PCS)2 six-membered ring, which adopts a chair-like
confirmation. This chair confirmation is well in line with the
broadened signals in the 1H NMR spectrum. Apart from the
connectivity of the central six-membered ring, the structural
parameters of both bisylidic compounds are comparable to each
other. As such, 4 also exhibits an almost planar environment of
the ylidic carbon atom with a sum of angles of 355.7(1)° and P–C
distances, which are – owing to the negative charge at the ylidic
carbon atom – somewhat shorter than typical P–C single
bonds.[20]
Scheme 2. Decomposition of the chloro and bromo carbenoids.
Crystallographic studies of the M/X carbenoids
Single crystals of all carbenoids could be obtained by slow
diffusion of pentane into a concentrated THF solution at –28 °C.
Figure 3 and 4 display the molecular structure of the Li/Br, Na/Cl
and K/Cl carbenoids. The structures of the Na/Cl and Na/Br
system as well of the K/Cl and K/Br system are almost identical
and thus only one of each is depicted here (see the SI). A
comparison of the most relevant bond lengths and angles of all
carbenoids together with those of the protonated precursors 1 and
2 is given in Table 1. To the best of our knowledge, 2-Na and 2-K
are the first isolated and structurally characterized Na and K
bromine carbenoids and 2-Li the first isolated alkyl Li/Br system.
The only Li/Br carbenoid reported before was a vinyl lithium
species.[13]
The lithium and sodium carbenoids form – independent of the
halogen substituent – monomeric structures in solid state with the
coordination sphere of the metal being completed by the
coordination of THF, the thiophosphinoyl moieties and the
halogen atom. Contrary to these monomeric structures, the K/Cl
and K/Br carbenoids form almost identical, centrosymmetric
dimers (triclinic space group P–1, monoclinic space group C2/c).
Comparable to the lighter congeners, the coordination sphere of
potassium is completed by the coordination of two THF molecules,
the thiophosphinoyl moieties and the halogen atom thus giving
rise to an octahedral environment of the metal. The Li/Br
carbenoid features two independent molecules in the asymmetric
unit, which differ in the conformation of the two thiophosphinoyl
moieties. In contrast to the Li/Cl system reported by Le Floch and
coworkers, 2-Li shows no planar geometry of the central carbon
atom, but a clear pyramidalization with sum of angles of approx.
340°. This deviation from planarity has been explained by a weak
interaction between the metal and the halogen atom or – in case
of fluorine systems[21] – by the tendency to minimize Coulombic
repulsion between the negative charges at the carbon and
halogen atom. Since the latter is less pronounced in case of the
Figure 2. Molecular structure of decomposition product 4. Displacement
ellipsoids are drawn at the 50% probability level. All hydrogen atoms have been
omitted for clarity. Selected bond lengths [Å] and angles [°]: P1–S1 1.966(1),
P2–S2 2.110(1), P1–C1 1.765(2), P2–C1' 1.713(2), C1–S2 1.773(2), P1–C1–
P2' 122.5(1), P1–C1–S2 119.3(1), S2–C1–P2' 113.9(1), C1–S2–P2 105.1(1).
Details on the structure elucidation of 3 is given in the Supporting Information.
During the decomposition studies, we noticed that at elevated
temperatures not only the bisylidic compound 3 is formed after
MX elimination. As such, refluxing of 3 in toluene for three days
resulted in the formation of a second new species in 80% yield.
The new compound 4 gave rise to a new set of multiplets in the
31P NMR spectrum at δP = 44.1 and 55.6 ppm with a coupling
constant of 2JPP = 54.2 Hz (3: δP = 41.1 and 45.4 ppm; 2JPP = 97.2
Hz). The broadened signals in the 1H and 13C NMR spectrum
indicated a fluxional behavior of 4 in solution. Due to similar
solubilities the separation of 3 and 4 was not possible. Luckily,
single crystals of 4 (in a mixture with 3) suitable for X-ray
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Table 1. Comparison of Xray crystallographic and NMR spectroscopic properties of the different M/X carbenoids 1-M and 2-M and their protonated precursors
1 and 2.
H/Cla
Li/Cla
Na/Cl
K/Cl
H/Br
Li/Br
Na/Br
K/Br
1
1-Li
1-Na
1-K
2
2-Li
2-Na
2-K
1.756(3)
1.750(3)
1.856(2)
1.856(2)
1.752(5)
1.753(5)
1.752(3)
1.755(3)
C1–P [Å]
C1–X [Å]
P–S [Å]
1.860(4)
1.726(2)
1.781(2)
1.991(1)
-
1.745(2)
1.794(2)
1.993(1)
3.159(1)
3.281(1)
125.8(1)
90.1(1)
1.756(2)
1.967(2)
1.989(1)
3.436(1)
3.259(1)
121.0(1)
91.1(1)
1.811(2)
1.816(2)
1.964(2)
1.965(2)
1.962(5)
1.961(5)
1.973(2)
1.972(2)
1.796(4)
1.982(1)
1.983(1)
1.950(1)
1.949(1)
1.995(2)
1.993(2)
1.984(2)
1.988(1)
1.944(2)
3.016(1)
3.122(1)
3.704(10)
3.630(8)
3.227(1)
3.135(1)
X–M [Å]
-
-
-
2.897(1)
2.868(1)
2.443(10)
2.451(10)
2.878(3)
2.904(1)
S–M [Å]
-
2.450(3)
127.7(1)
-
121.2(1)
126.2(2)
118.3(1)
116.4(1)
122.6(3)
121.2(3)
125.2(2)
121.1(1)
P1–C1–P2 [°]
C1–X–M [°]
(C1) [°]
116.4(2)
-
90.7(1)
87.8(1)
71.4
70.9
85.0(1)
88.2(1)
-
338.2(1)
341.1(1)
338.1(2)
339.1(2)
339.5(1)
336.6(1)
-
360.0(1)
45.5
349.3(1)
46.6
-
340.4
46.4
P [ppm]
46.3
47.1
47.0
45.9
46.9
C
[ppm]
53.7
38.1
38.5
80.0
44.9
54.2
45.5,
59.7
44.9
32.8
30.8
59.4
40.4
41.4
40.9
47.4
1JPC [Hz]
[a] Data according to reference 9.
bigger and heavier halogen atoms, the pyramidalization in 2-Li
suggests a weak Li–Br interaction in the solid-state. Indeed, 2-Li
shows a rather small Li–C1–Br angle of only 77.3(2) and 77.5(2)°
and a distortion of the ideal tetrahedral environment of the lithium
atom with the two thiophosphinoyl ligands and THF molecules.
The CP2S2Li six-membered ring thus adopts a boat instead of the
typical chair conformation. In case of the Li/Cl system a much
larger Li–C1–Cl angle of 155.1(1)° has been found.[9]
Nevertheless, the Li–Br distances of 3.630(8) and 3.704(10) Å are
rather large and in the range of the sum of the van-der-Waals
radii.[22] Hence, only a weak lithium-halogen interaction can be
present in 2-Li, particularly in comparison with Li/F carbenoids,
which usually form strong Li–F contacts in the solid state.[15,23]
be more pronounced than in the lithium analogue. As such, the
Na–X and K–X interactions are shorter than in 2-Li (despite of the
smaller radius of lithium) and significantly smaller than the sum of
the van-der-Waals radii of the two atoms (see Table 1). Compared
with the lithium compound, which showed a ratio between the Li–
Br bond length and the sum of VdW radii of approx. 1, the Na and
K systems feature ratios between 0.70 and 0.77. For example, the
K–Cl distance in 1-K amounts to 3.159(1) Å, while the sum of
VDW radii amounts to 4.50 Å.[22] Consistently, the halogen atom
adopts one site of the octahedral environment of the sodium and
potassium atom, respectively. The distinctly smaller 1JPC coupling
constants for 1-Na/K and 2-Na/K compared to their lithium
congeners also argue for a different hybridization of the carbon
atom in these compounds in solution. Hence, in contrast to the
Li/Cl and Li/Br carbenoids the carbenoid carbon atom in the
sodium and potassium compounds might also be sp3 hybridized
in solution. Overall, the metal halogen interactions seem to be
more pronounced for the heavier metals than for lithium. This is
in contrast to the corresponding fluorine systems, where the Li–F
interaction is much stronger and was – amongst others – used as
explanation for the more facile LiF elimination.[15] If the strength of
the metal halogen interaction in the structure of carbenoids was
the only criterion for the carbenoid stability, the observations
made for the chlorine and bromine systems would suggest a
reverse trend, namely a lower stability of 1-Na/K and 2-Na/K. This
clearly shows, that the reactivity of carbenoids is a complex matter.
1
Looking at the NMR spectroscopic data – especially the JPC
coupling constant – we assume that the Li–Br interaction in 2-Li
is not present in solution and solely a solid state or packing effect
in the crystal. As such 2-Li exhibits the largest coupling constant
in the 2-M series of compounds, which is 26.6 Hz larger than the
value of the protonated precursor 2. This indicates a change in
hybridization from sp3 in 2 to sp2 in 2-Li, which contrasts the
pyramidal geometry of the carbenoid carbon atom observed in the
molecular structure.
Similar to the lithium carbenoid, the metalated carbon atoms in
the sodium and potassium systems are equally pyramidalized
with sum of angles between 338.1(2) and 349.3(1)°. However, in
these heavier analogues the metal-halogen interactions seem to
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Stabilities can thus not only be deduced from structural features,
but are the result of a combination of different factors.
lengthened due to negative hyperconjugation effects. Hence, the
molecular structures nicely reflect the stability of the carbenoids.
Figure 3. Representations of the molecular structure of the lithium carbenoid 2-
Li. Displacement ellipsoids drawn at the 50% probability level. All hydrogen
atoms have been omitted for clarity. For selected bond lengths [Å] and angles
[°] see Table 1.
Figure 4. Molecular structures of the sodium and potassium carbenoids 2-Na
and 1-K. Displacement ellipsoids drawn at the 50% probability level. All
hydrogen atoms have been omitted for clarity. For selected bond lengths [Å]
and angles [°], see Table 1. The chlorine derivative 1-Na and the bromine
derivative 2-K form analogous structures in the solid-state (see the SI).
It is also interesting to note, that despite the metal-halogen
interaction none of the carbenoids exhibits a contact between the
metal and the carbon atom. Such an arrangement has also been
observed for other alkali metal carbenoids and has been
described as carbene-donor complex,[10,24] in contrast to bridged
and classical structures with direct M–C bonds. Despite the metal-
halogen interactions the carbon-halogen bonds in 1-M and 2-M
show no obvious elongation compared to the protonated starting
materials 1 and 2, respectively. Such a C–X bond elongation is a
typical structural feature of lithium chloride carbenoids and can be
explained by the increased bond polarization. Hence, the M–X
interactions in 1-M and 2-M are – despite being pronounced in the
molecular structures – too weak to result in any significant
polarization and weakening of the C–X bond. This is well in line
with the thermal stability of the compounds and their reduced
reactivity. This stabilization is mostly the result of the efficient
stabilization of the negative charge at the carbenoid carbon atom
by the thiophosphinoyl moieties.[ 25 ] This is reflected by the
structural parameters. While electrostatic interactions within the
P–C–P linkage result in a shortening of the C1–P bonds by ∆d =
10-13 ppm relative to 1 and 2, the P–S bonds are slightly
Conclusions
In summary, we have successfully synthesized and isolated of a
series of alkali metal chlorine and bromine carbenoids, amongst
the first Na/Br and K/Br systems. NMR spectroscopic as well as
crystallographic studies showed distinct structural differences
between the lithium carbenoids and their heavier congeners. In
the solid-state pronounced M–X interactions were observed for
the potassium and sodium systems, while the Li/Br carbenoid
showed only
a very weak intramolecular contact. These
interactions however, did not significantly influence the stability of
the systems by facilitating the MX elimination. As such all
compounds were found to be stable up to approx. 60 °C in THF
solution. Overall, these studies show that M–X interactions are an
important feature in the structure formation of carbenoids.
However, their presence is not the only criterion determining the
stability of such compounds. We are currently examining the
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pentane (10 mL) was added to the orange residue. The mixture was stirred
for 10 min, the solid was allowed to settle and the solvent was
subsequently removed with a syringe. This process was repeated four
times and after drying in vacuo the product could be obtained as yellow
solid (155 mg, 306 µmol, 99%). 1H NMR: (500.1 MHz, d8-THF):  = 7.06-
7.13 (m, 12H; CHmeta and CHpara), 7.97-8.02 (m, 8H; CHortho). 13C{1H} NMR:
(125.8 MHz, d8-THF):  = 44.9 (t, 1JCP = 54.2 Hz; CCl), 127.7 (pt; CHmeta),
130.0 (CHpara), 133.6 (pt; CHortho), 137.7 (m; Cipso),. 31P{1H} NMR: (202.5
MHz, d8-THF):  = 47.1. Anal. Calcd. for C29H28ClNaOP2S2: Calc: C,
60.36; H, 4.89; S, 11.11. Found: C, 60.58; H, 4.94; S, 10.64.
impact of further additives to manipulate the strength of the C–X
bond in carbenoids and thus to tune their reactivity.
Experimental Section
General conditions. All experiments were carried out under a dry,
oxygen-free argon atmosphere using standard Schlenk techniques.
Involved solvents were dried over sodium or potassium (or over MgSO4,
iPrOH) and distilled prior to use. H2O is distilled water. 1H, 7Li, 13C{1H} and
31P{1H} NMR spectra were recorded on Avance-500, Avance-400 or
Avance-300 spectrometers at 22 °C if not stated otherwise. All values of
the chemical shift are in ppm regarding the δ-scale. All spin-spin coupling
constants (J) are printed in Hertz (Hz). To display multiplicities and signal
forms correctly the following abbreviations were used: s = singlet, d =
doublet, t = triplet, m = multiplet, br = broad signal. Signal assignment was
supported by DEPT experiments. For NMR spectra see the Supporting
Information. Elemental analyses were performed on an Elementar vario
MICRO-cube elemental analyzer. All reagents were purchased from
Sigma-Aldrich, ABCR or Acros Organics and used without further
purification.
Preparation of carbenoid 1-K. Phosphine sulfide 1 (147 mg, 304 µmol)
and KN(SiMe3)2 (66.8 mg, 335 µmol) were dissolved in THF (10 mL) and
stirred for 1 h at room temperature. After evaporation of the solvent,
pentane (10 mL) was added to the orange residue. The mixture was stirred
for 10 min, the solid was allowed to settle and the solvent was removed
with a syringe. This process was repeated twice again and after drying in
vacuo the product could be obtained as yellow solid (157 mg, 301 µmol,
99%). 1H NMR: (500.1 MHz, d8-THF):  = 7.04-7.09 (m, 12H; CHmeta and
CHpara), 7.98-8.02 (m, 8H; CHortho). 13C{1H} NMR: (125.8 MHz, d8-THF): 
= 45.4 (t, 1JCP = 59.7 Hz; CCl), 127.6 (pt; CHmeta), 129.9 (CHpara), 133.7 (pt;
CHortho), 139.2 (m; Cipso),. 31P{1H} NMR: (202.5 MHz, d8-THF):  = 46.6.
Anal. Calcd. for C25H20ClKP2S2: Calc: C, 57.63; H, 3.87; S, 12.31. Found:
C, 57.55; H, 4.15; S, 11.61.
Preparation of phosphine sulfide 1. The diprotonated precursor (1.45 g,
3.23 mmol) was dissolved in THF (15 mL) and cooled to –78 °C. n-
Butyllithium (1.5 mL, 3.39 mmol, 2.26 M in hexane) was added and the
yellow solution was stirred for 18 h at room temperature. In a second
Schlenk flask, hexachloroethane (803 mg, 3.39 mmol) was dissolved in
THF (20 mL) and cooled to –78 °C. The lithiated phosphine sulfide was
slowly added by cannula transfer and after complete addition warmed to
room temperature. After stirring the yellow mixture for 3 h at room
temperature the solution was quenched by addition of water (30 mL).
Extraction with DCM (3 x 30 mL), drying over sodium sulfate and removal
of the solvent afforded a brown solid. The solid was purified by flash
chromatography on silica gel (DCM/pentane = 2:1) giving the product as
colorless solid (730 mg, 1.51 mmol, 47%). The NMR spectroscopic data
match the literature reports.[9]
Preparation of carbenoid 2-Li. Phosphine sulfide 2 (210 mg, 398 µmol)
and LiN(SiMe3)2 (73.3 mg, 438 µmol) were dissolved in THF (10 mL) and
stirred for 4 h at room temperature. After evaporation of the solvent,
pentane (10 mL) was added to the orange residue, stirred for 10 min and
the solvent subsequently removed with a syringe. This process was
repeated twice and after drying in vacuo the product could be obtained as
yellow solid (240 mg, 354 µmol, 89%). 1H NMR: (500.1 MHz, d8-THF):  =
7.13-7.20 (m, 12H; CHmeta and CHpara), 7.94-7.99 (m, 8H; CHortho). 7Li NMR
(155.5 MHz, d8-THF):  = 0.76. 13C{1H} NMR: (125.8 MHz, d8-THF):  =
30.8 (t, 1JCP = 59.4 Hz; CBr), 127.8 (pt; CHmeta), 130.2 (CHpara), 133.6 (pt;
CHortho), 138.8 (m; Cipso),. 31P{1H} NMR: (202.5 MHz, d8-THF):  = 45.9.
Anal. Calcd. for C33H36BrLiO2P2S2: Calc: C, 58.50; H, 5.36; S, 9.46. Found:
C, 58.19; H, 5.18; S, 9.18.
Preparation of phosphine sulfide 2. The diprotonated precursor (1.04 g,
2.32 mmol) was dissolved in THF (20 mL) and cooled to –78 °C. n-
Butyllithium (1.03 mL, 2.43 mmol, 2.36 M in hexane) was added and the
yellow solution was stirred at room temperature for 18 h. In a second
Schlenk flask, 1,2-dibromotetrachloroethane (793 mg, 2.43 mmol) was
dissolved in THF (20 mL) and cooled to –78 °C. The lithiated phosphine
sulfide was slowly added by cannula transfer and – after complete addition
– warmed to room temperature. After stirring the yellow mixture for 3 h at
room temperature the solution was quenched by addition of water (30 mL).
Extraction with diethylether (3 x 30 mL), drying over sodium sulfate and
removal of the solvent afforded a brown solid. The solid was purified by
flash chromatography on silica gel (DCM/pentane = 2:1) giving the product
as colorless solid (1.05 g, 1.99 mmol, 86%). 1H NMR: (500.1 MHz, CDCl3):
 = 5.59 (t, 2JHP = 9.1 Hz, 1H; CHBr), 7.36-7.41 (m, 8H; CHmeta), 7.43-7.49
(m, 4H; CHpara), 7.93-7.97 (m, 4H; CHortho), 8.01-8.06 (m, 4H; CHortho).
Preparation of carbenoid 2-Na. Phosphine sulfide 2 (150 mg, 284 µmol)
and NaN(SiMe3)2 (57.4 mg, 313 µmol) were dissolved in THF (10 mL) and
stirred for 18 h at room temperature. After evaporation of the solvent,
pentane (10 mL) was added to the orange residue and the suspension was
stirred for 10 min. Subsequently the solid was allowed to settle and the
supernatant solvent was removed with a syringe. This process was
repeated twice and after drying in vacuo the product was obtained as
yellow solid (150 mg, 273 µmol, 96%). 1H NMR: (500.1 MHz, d8-THF):  =
7.05-7.11 (m, 12H; CHmeta and CHpara), 7.99-8.04 (m, 8H; CHortho). 13C{1H}
1
NMR: (125.8 MHz, d8-THF):  = 40.4 (t, JCP = 41.4 Hz; CBr), 127.7 (pt;
CHmeta), 130.5 (CHpara), 133.6 (pt; CHortho), 139.1 (m; Cipso),. 31P{1H} NMR:
(202.5 MHz, d8-THF):  = 46.9. Anal. Calcd. for C29H28BrNaOP2S2: Calc:
C, 56.04; H, 4.54; S, 10.32. Found: C, 55.80; H, 4.57; S, 9.98.
1
13C{1H} NMR: (125.8 MHz, CDCl3):  = 44.9 (t, JCP = 32.8 Hz; CHBr),
Preparation of carbenoid 2-K. Phosphine sulfide 2 (151 mg, 286 µmol)
and KN(SiMe3)2 (62.8 mg, 315 µmol) were dissolved in THF (10 mL) and
stirred for 18 h at room temperature. After evaporating the solvent, pentane
(10 mL) was added to the orange residue and the mixture was stirred for
10 min. Subsequently the solid was allowed to settle and the supernatant
solvent was removed with a syringe. This process was repeated three
times and after drying in vacuo the product could be obtained as yellow
solid (160 mg, 283 µmol, 99%). 1H NMR: (500.1 MHz, d8-THF):  = 7.03-
7.08 (m, 12H; CHmeta and CHpara), 8.00-8.04 (m, 8H; CHortho). 13C{1H} NMR:
(125.8 MHz, d8-THF):  = 40.9 (t, 1JCP = 47.4 Hz; CBr), 127.6 (pt; CHmeta),
129.8 (CHpara), 133.7 (pt; CHortho), 139.5 (m; Cipso),. 31P{1H} NMR: (202.5
128.2 (d, 3JCP = 13.1 Hz; CHmeta), 128.5 (d, 3JCP = 13.1 Hz; CHmeta), 130.3
(dd, 1JCP = 85.4 Hz, 3JCP = 1.8 Hz; Cipso), 131.9 (d, 4JCP = 3.1 Hz; CHpara),
132.1 (d, 1JCP = 85.0 Hz; Cipso), 132.2 (d, 4JCP = 3.1 Hz; CHpara), 132.4 (d,
2
2JCP = 10.6 Hz; CHortho), 133.1 (d, JCP = 10.5 Hz; CHortho). 31P{1H} NMR:
(202.5 MHz, CDCl3):  = 47.0. Anal. Calcd. for C25H21BrP2S2: Calc: C,
56.93; H, 4.01; S, 12.16. Found: C, 56.88; H, 4.08; S, 12.21.
Preparation of carbenoid 1-Na. Phosphine sulfide 1 (150 mg, 311 µmol)
and NaN(SiMe3)2 (62.6 mg, 342 µmol) were dissolved in THF (10 mL) and
stirred for 3 h at room temperature. After evaporation of the solvent
This article is protected by copyright. All rights reserved.

10.1002/chem.201701911
Chemistry - A European Journal
FULL PAPER
MHz, d8-THF):  = 46.4. Anal. Calcd. for C25H20BrKP2S2: Calc: C, 53.10;
H, 3.56; S, 11.34. Found: C, 53.01; H, 3.81; S, 10.98.
11.4102(4), b = 11.6120(4), c = 15.3383(5) Å; α = 70.888(1),  = 86.135(1),
γ = 72.503(1)°; V = 1830.3(1) Å3; Z = 4; ρcalcd = 1.338 g∙cm–3;  = 0.455
mm–1; F(000) = 776; T = 100(2) K; R1 = 0.0382 and wR2 = 0.0788 [I > 2(I)];
R1 = 0.0374 and wR2 = 0.0817 (all refl.); 24776 reflections were measured
(θ < 26.43°), 7532 reflections were unique, of which were 6723 observed;
426 parameters were refined with no restraints; residual electron density
between 1.147 and –1.184 e∙Å-3.
Preparation of bisylide 3. Potassium carbenoid 1-K (93.3 mg, 193 µmol)
was dissolved in THF (10 mL) and heated at reflux for 15 h. After cooling
to room temperature overnight and evaporation of the solvent in vacuo
toluene (10 mL) was added. The resulting suspension was filtered to
remove the formed KCl. Subsequently, the solvent was removed and the
residue was washed with diethylether (2 x 10 mL). After drying in vacuo
the product was obtained as yellow solid (60.0 mg, 67.2 µmol, 70%).
HRMS (ESI): calc for C40H40P4S4 ([M + H]+·) m/z = 893.1036; found m/z =
893.1018. NMR data match literature reports.[19] Single-crystals suitable
for X-ray diffraction analysis were obtained by slow diffusion of pentane
into a concentrated THF solution of a mixture of 4 and 4. The thus obtained
crystals of 3 crystallize in a different space group as reported before by
Chivers et al.[19]
Crystal data for compound 2-Li: C33H36BrLiO2P2S2; Mr = 677.53; yellow
plate; 0.16 x 0.13 x 0.03 mm3; triclinic; space group P-1; a = 9.6626(7), b
= 16.5992(11), c = 20.8175(14) Å; α = 81.635(2),  = 89.801(2), γ =
78.799(2)°; V = 3239.4(4) Å3; Z = 4; ρcalcd = 1.389 g∙cm–3;  = 1.525 mm–
1; F(000) = 1400; T = 100(2) K; R1 = 0.0633 and wR2 = 0.1245 [I > 2(I)];
R1 = 0.1309 and wR2 = 0.1474 (all refl.); 36127 reflections were measured
(θ < 26.43°), 13224 reflections were unique, of which were 7818 observed;
719 parameters were refined with no restraints; residual electron density
between 1.082 and –1.096 e∙Å-3.
Preparation of bisylide 4. Bisylide 3 (10.2 mg, 11.4 µmol) was dissolved
in toluene (0.5 mL) in a J. Young NMR tube and heated over night at 80 °C.
After evaporation of the solvent in vacuo the reaction mixture was studied
by NMR spectroscopy. 1H NMR: (500.1 MHz, d8-THF): not possible to
assign the signals. 31P{1H} NMR: (202.5 MHz, d8-THF):  = 44.1 (m; PPh2),
55.6 (br d, 2JPP = 54.3 Hz; SPPh2).
Crystal data for compound 2-Na: C37H44BrNaO3P2S2; Mr = 430.47;
yellow block; 0.22 x 0.22 x 0.10 mm3; monoclinic; space group P21/n; a =
23.4065(18), b = 14.3277(12), c = 23.4380(18) Å;  = 110.076(3)°; V =
7382.6(1) Å3; Z = 8; ρcalcd = 1.378 g∙cm–3;  = 1.360 mm–1; F(000) = 3184;
T = 100(2) K; R1 = 0.0336 and wR2 = 0.0731 [I > 2(I)]; R1 = 0.0565 and
wR2 = 0.0832 (all refl.); 93315 reflections were measured (θ < 25.00°),
12992 reflections were unique, of which were 9882 observed; 881
parameters were refined with 12 restraints; residual electron density
between 0.611 and –0.526 e∙Å-3.
Crystal structure analyses. Single crystals were selected from a Schlenk
flask under an argon atmosphere and covered with an inert oil (perfluoro-
polyalkylether). Data were collected on a Bruker APEX-CCD (D8 three-
circle goniometer) (Bruker AXS). Integration was conducted with SAINT
and an empirical absorption correction (SADABS) was applied. The
structures were solved by direct methods and refined by full-matrix least-
squares methods against F2 (SHELXL-08).[26] All non-hydrogen atoms
were refined with anisotropic displacement parameters. Hydrogen atoms
were placed in calculated positions and refined using the riding model.
Relevant details about the structure refinements are given Table S1a-S1c
(Supporting Information). Crystallographic data (including structure
factors) have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-1545113-1545120.
Copies of the data can be obtained free of charge on application to
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; [fax: (+44) 1223-336-033; email: deposit@ccdc.cam.ac.uk].
Crystal data for compound 2-K: C37H45BrKO3P2S2; Mr = 782.80; yellow
block; 0.21 x 0.19 x 0.11 mm3; monoclinic; space group P21/n; a =
13.7998(4), b = 24.7574(8), c = 22.1116(7) Å;  = 97.534(1)°; V =
7489.2(4) Å3; Z = 8; ρcalcd = 1.389 g∙cm–3;  = 1.440 mm–1; F(000) = 3256;
T = 100(2) K; R1 = 0.0348 and wR2 = 0.0967 [I > 2(I)]; R1 = 0.0448 and
wR2 = 0.1033 (all refl.); 17319 reflections were measured (θ < 26.49°),
7693 reflections were unique, of which were 6547 observed; 456
parameters were refined with 13 restraints; residual electron density
between 0.838 and –0.535 e∙Å-3.
Crystal data for compound 3: C54H48OP4S4; Mr = 965.04; yellow plate;
0.30 x 0.10 x 0.09 mm3; triclinic; space group P-1; a = 11.5857(10), b =
11.8370(10), c = 20.0508(17) Å; α = 80.675(3),  = 79.012(3), γ =
61.447(3)°; V = 2363.0(3) Å3; Z = 2; ρcalcd = 1.356 g∙cm–3;  = 0.377 mm–1
;
F(000) = 1008; T = 100(2) K; R1 = 0.0602 and wR2 = 0.1527 [I > 2(I)]; R1
= 0.0861 and wR2 = 0.1686 (all refl.); 31683 reflections were measured (θ
< 26.48°), 9709 reflections were unique, of which were 7176 observed;
556 parameters were refined with no restraints; residual electron density
between 1.504 and –0.782 e∙Å-3.
Crystal data for compound 2: C25H21BrP2S2; Mr = 527.39; colorless
block; 0.38 x 0.24 x 0.24 mm3; monoclinic; space group P21/c; a =
24.3130(11), b = 9.8424(3), c = 21.9315(8) Å;  = 116.404(1)°; V =
4700.7(3) Å3; Z = 8; ρcalcd = 1.490 g∙cm–3;  = 2.074 mm–1; F(000) = 2144;
T = 100(2) K; R1 = 0.0285 and wR2 = 0.0648 [I > 2(I)]; R1 = 0.0389 and
wR2 = 0.0680 (all refl.); 35613 reflections were measured (θ < 26.42°),
9628 reflections were unique, of which were 8098 observed; 541
parameters were refined with no restraints; residual electron density
between 0.752 and –0.418 e∙Å-3.
Crystal data for compound 4: C29H28OP2S2; Mr = 518.57; yellow block;
0.29 x 0.17 x 0.16 mm3; triclinic; space group P-1; a = 11.1661(7), b =
12.5139(8),
c = 22.2148(14) Å; α = 80.426(2),  = 84.087(2), γ =
Crystal data for compound 1-Na: C74H88Cl2Na2O6P4S2; Mr = 1442.44;
yellow block; 0.44 x 0.17 x 0.12 mm3; monoclinic; space group P21/n; a =
23.1322(8), b = 14.3370(5), c = 23.4514(9) Å;  = 109.428(1)°; V =
7334.7(5) Å3; Z = 4; ρcalcd = 1.306 g∙cm–3;  = 0.352 mm–1; F(000) = 3040;
T = 100(2) K; R1 = 0.0416 and wR2 = 0.0868 [I > 2(I)]; R1 = 0.0704 and
wR2 = 0.1001 (all refl.); 86676 reflections were measured (θ < 25.00°),
12919 reflections were unique, of which were 9404 observed; 861
parameters were refined with no restraints; residual electron density
between 0.959 and –0.592 e∙Å-3.
64.807(2)°; V = 2767.9(3) Å3; Z = 4; ρcalcd = 1.244 g∙cm–3;  = 0.328 mm–
1; F(000) = 1088; T = 100(2) K; R1 = 0.0409 and wR2 = 0.0999 [I > 2(I)];
R1 = 0.0530 and wR2 = 0.1071 (all refl.); 35309 reflections were measured
(θ < 25.00°), 9730 reflections were unique, of which were 8059 observed;
647 parameters were refined with no restraints; residual electron density
between 0.600 and –0.439 e∙Å-3.
Acknowledgements
Crystal data for compound 1-K: C18.5H22Cl0.5K0.5O1.5PS; Mr = 368.66;
yellow block; 0.72 x 0.52 x 0.32 mm3; triclinic; space group P-1; a =
This article is protected by copyright. All rights reserved.

10.1002/chem.201701911
Chemistry - A European Journal
FULL PAPER
We thank the German Research Foundation (Emmy Noether
grant DA1402/1), and the Fonds der Chemischen Industrie for
financial support and Rockwood Lithium GmbH for the supply of
chemicals. We further acknowledge the German Research
Foundation for support within the Cluster of Excellence RESOLV
EXC1069.
Keywords: alkali metal • carbenoids • carbanions • lithium •
structure elucidation
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10.1002/chem.201701911
Chemistry - A European Journal
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Room-temperature stable carbenoids
with different metal/halogen
S. Molitor, V. H. Gessner*
Page No. – Page No.
combinations were isolated and
characterized, amongst the first
sodium and potassium bromine
systems. Metal-halogen interactions
were found to be important factors for
structure formation, but did not
significantly influence the stability of
the carbenoids.
Alkali metal chlorine and bromine
carbenoids: Their thermal stability
and structural properties
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