Structure, bonding, and reactivity of room-temperature-stable lithium chloride carbenoids

Article abstract of DOI:10.1021/om4010862

Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and multinuclear NMR spectroscopy reveal no direct lithium-carbon interaction in the solid state and in solution. This leads to remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies confirm this nucleophilic character and show that the carbenoids can still be used as a carbene source for the formation of carbene complexes.

Full text of DOI:10.1021/om4010862

Article
pubs.acs.org/Organometallics
Structure, Bonding, and Reactivity of Room-Temperature-Stable
Lithium Chloride Carbenoids
Claudia Kupper, Sebastian Molitor, and Viktoria H. Gessner*
Institut fur Anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, 97074 Wurzburg, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Electronic stabilization of the negative charge by a thiophosphinoyl and pyridyl/quinolyl substituent allows for the
isolation of two lithium chloride carbenoids at room temperature. Molecular structure analysis by X-ray crystallography and
multinuclear NMR spectroscopy reveal no direct lithium−carbon interaction in the solid state and in solution. This leads to
remarkable thermal stability but also to a reduced ambiphilic character of the compounds. Thus, properties typically observed for
nonstabilized Li/Cl carbenoids are less pronounced. Nevertheless, computational studies still show that despite the charge
delocalization within the compound a high negative charge remains at the carbenoid carbon atom. Preliminary reactivity studies
confirm this nucleophilic character and show that the carbenoids can still be used as a “carbene” source for the formation of
carbene complexes.
stabilization), and (iii) ancillary ligands. Indeed in 2007, Le
Floch and co-workers succeeded in the isolation of the first
room-temperature-stable Li/Cl carbenoid A by employing
thiophosphinoyl moieties as stabilizing substituents.7,8 Despite
its stability this system was found to still possess an ambiphilic
character, as evidenced by the formation of a palladium carbene
complex or the activation of the B−H bond in BH3 Lewis base
adducts. Our group has focused on the impact of the
substitution pattern at the carbenoid carbon atom on the
stability and also the reactivity.9 Recently, we have shown that
the thermal stability of the carbenoid is considerably reduced
when simply replacing one of the thiophosphinoyl groups in A
with a silyl moiety (carbenoid B). This is also accompanied by a
change in the reactivity. As such, no carbene complex formation
was observed by treatment of the carbenoid B with [Pd-
(PPh3)4] but the selective formation of a thioketone complex
occurs.10 Also, B−H bond activation gave a totally different
product than was found for A.11,12
INTRODUCTION
■
Since the pioneering work by Simmons and Smith1 carbenoids
have been frequently used reagents in organic syntheses, above
all in cyclopropanation and homologation reactions.2 However,
in comparison to the related carbeneswhich have experi-
enced dramatic research interest over the past decades over a
wide range of applicationscarbenoids have almost been
neglected.3 Despite their potential as carbene precursors and
their ambiphilic nature there are only a few examples probing
their versatile reactivity and use as ligands for transition-metal
carbene complexes.4 This limitation is mainly due to the high
reactivity of carbenoids and their lack of thermal stability.2,5
This is particularly true for lithium halide carbenoids, which
normally undergo salt elimination at very low temperatures
often below −78 °Cgiving way to highly unstable carbene
species and often to complex product mixtures. Thus over the
past years, progress in more selective and controlled
applications of carbenoids has mainly been achieved with the
more covalent zinc derivatives.6
These observations prompted us to further study the impact
of the substitution pattern at the carbenoid carbon on the
stability and reactivity. Herein, we report on the preparation of
Nevertheless, it is well known that the reactivity of
carbenoids is influenced by several factors beyond the nature
of the metal atom: these are for example (i) the nature of the
leaving group (determining the electrophilicity), (ii) the
substituents at the carbenic carbon atom (electronic and spatial
Received: November 8, 2013
© XXXX American Chemical Society
A
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Figure 1. Example of Li/Cl carbenoids with different electronic
stabilization.
two novel room-temperature-stable carbenoids 3a,b incorporat-
ing N-heteroaromatic substituents (Scheme 1). We demon-
strate how the unique electronic structure correlates with the
ambiphilic character and the observed reactivity patterns of
these systems.
Scheme 1. Synthesis of Carbenoids 3a,b
Figure 2. Molecular structure of compound 2b. Ellipsoids are drawn at
the 50% probability level. Selected bond lengths (Å) and angles (deg)
for 2b: Cl1−C1 1.785(2), P1−C1 1.853(2), C1−C2 1.511(3), N1−
C2 1.319(3), S1−P1 1.9503(8), P1−C11 1.815(2), P1−C17 1.811(2);
C2−C1−P1 114.99(15), C2−C1−Cl1 112.01(16), Cl1−C1−P1
106.3(1), C1−P1−S1 115.12(8), N1−C2−C1 114.01(19). For
crystallographic data of 2a and 1b, see the Supporting Information.
solid state no decomposition was observed up to about 100 °C,
as evidenced by differential scanning calorimetry (DSC)
measurements (see the Supporting Information). Other than
the Li/Cl carbenoid A reported by Floch and co-workers in
2007 and its iodine congener,7,8 3a,b are the only room-
temperature-stable carbenoids known so far.
Both carbenoids feature well-resolved NMR spectra, thus
indicating no fluxional behavior in solution (C6D6). Addition-
ally, they were found to form THF solvates with two
coordinating ether molecules (see the Supporting Information
for NMR spectra). Carbenoid 3a is characterized by a single
resonance in the 31P{1H} NMR spectrum at δ 39.4 ppm and
RESULTS AND DISCUSSION
■
The pyridyl- and quinolyl-substituted carbenoids 3a,b were
targeted via the synthetic strategy outlined in Scheme 1. At first
the protonated precursors 1a,b were prepared by a one-pot
reaction via deprotonation of 2-picoline and 2-methylquinoline,
respectively (for details, see the Experimental Section). The
following chlorination was accomplished by lithiation and
treatment with hexachloroethane, giving 2a,b as racemic
mixtures in only moderate yields due to the formation of the
bis-chlorinated compound as a byproduct.16 All compounds
were characterized by multinuclear NMR spectroscopy and
elemental analysis. Due to the stereogenic central carbon atom
in 2 the phenyl substituents at the phosphorus become
diastereotopic and appear as separate resonances in the 1H and
13C{1H} NMR spectra. The 31P{1H} NMR signals resonate at δ
51.0 (2a) and 50.4 ppm (2b). The molecular structures of 1b
and 2a,b were additionally determined by single-crystal X-ray
diffraction analysis (see the Supporting Information). 2a
crystallizes in the monoclinic space group P21/c and 2b in
the orthorhombic space group Pbca (Figure 2). In contrast to
the molecular structure of 2b, the asymmetric unit of 2a
contains two highly disordered molecules, each consisting of
both enantiomeric forms of 2a.
Treatment of the chlorinated precursors with 1 equiv of
methyllithium at room temperature afforded the selective
formation of the carbenoids 3a,b in quantitative yields, as
evidenced by monitoring of the reaction progress by 31P{1H}
NMR spectroscopy (Scheme 1). No competing substitution
reaction was observed under these reaction conditions.
Isolation gave 3a as a bright yellow solid in quantitative yield
and 3b as an orange solid in 93% yield. Both carbenoids proved
to be stable at room temperature. At ambient temperature no
decomposition was detected in the solid state, even after
storage for weeks under an inert atmosphere. A THF solution
of carbenoid 3a is stable at temperatures up to 60 °C. In the
7
one signal at δ 1.42 ppm in the Li NMR spectrum. The
carbenoid carbon atom was found to resonate at δ 60.1 ppm
(1JPC = 127.8 Hz), which is shifted slightly downfield in
comparison to the protonated precursor 2a (δ 58.8 ppm, 1JPC
=
50.1 Hz). Such a downfield shift is typical for carbenoid species.
This observation can be explained by the polarization of the
C−X bond upon metalation and an increased carbenelike
character. However, the carbenoid 13C signal in other known
Li/Hal carbenoids is generally found to be more strongly
deshielded relative to the protonated analogues (Δδ 40−280
ppm).13 For example, lithiation of chloroform is accompanied
by a downfield shift of Δδ 65.9 ppm. Hence, the only slightly
downfield shifted resonance in 3a indicates an only weakly
pronounced polarization. Analogous spectroscopic properties
were observed for the quinolyl analogue 3b. Here, the 13C{1H}
NMR signal of the carbenoid carbon atom appears as a broad
doublet at δ 67.9 ppm (2b: δ 59.9 ppm).
Single crystals of both carbenoids were grown from THF
solutions. The molecular structures are shown in Figure 3, and
selected bond lengths and angles are given in Table 1. The
carbenoids crystallize as monomers in the monoclinic space
groups P21/n (3a) and Pn (3b), respectively. In both cases, the
lithium atom is 4-fold coordinated by the sulfur atom of the
thiophosphinoyl moiety and the pyridyl/quinolyl nitrogen as
well as two THF solvent molecules. As reported for metalated
versions of 1a, no direct contact between the lithium and the
metalated carbon atom is observed.16 This corroborates the
observations made by the NMR studies, thus suggesting that
the structure is also maintained in solution (little downfield
shift of the 13C{1H} NMR resonance, no diastereotopic
B
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C(1)−P distances of 1.740(1) (3a) and 1.746(2) Å (3b) are
shorter than in 2a or 2b (e.g., 2a: 1.854(7) Å (average)),
reflecting the electrostatic interactions known for α-metalated
P(V) species. In addition, the short C1−C2 distances of
1.409(2) (3a) and 1.401(2) Å (3b) (average C1−C2 distance
in 2a: 1.514(5) Å) indicate strong contribution of charge
delocalization into the aromatic ring systems. This is also
reflected by the distinct perturbations in the C−C and C−N
bond lengths in the heterocycles (cf. Table 1).
Overall, the structural parameters as well as the NMR data
suggest that both carbenoids possess a considerably decreased
carbenoid character. To gain further insight into the electronic
properties of 3a,b we performed DFT calculations including
natural bond orbital (NBO) studies at the B3LYP/6-311+
+g(d) level of theory. At first, a model system of 3a,b was
chosen, in which THF was replaced by Me2O. However, the
structure parameters of the energy-optimized structures are in
good agreement with the experimental data (e.g., C−Cl in 3b:
calcd 1.780 Å, exptl 1.766 Å). The HOMO of carbenoid 3a
(Figure 4; for 3b see the Supporting Information) is mainly
Figure 3. Molecular structures of carbenoids 3a (top) and 3b
(bottom). Ellipsoids are drawn at the 50% probability level. For
crystallographic and structure refinement details, see the Supporting
Information.
splitting of the Ph2P signals). In the molecular structures of
both carbenoids, the metalated carbon atom features an almost
planar geometry with sums of angles around C1 of 358.6(1)
(3a) and 358.7(1)° (3b). This is in line with a change in the
hybridization from sp3 to sp2, as suggested by the increased 1JPC
coupling constants in the 13C{1H} NMR spectrum. The C(1)−
Cl bonds amount to 1.760(1) (3a) and 1.766(2) Å (3b), which
are slightly shorter than that found in the starting compounds
(e.g. 2a 1.795(6) Å (average); see the Supporting Information).
Hence, the lengthening of the C−Cl bond typically found for
nonstabilized Li/Cl carbenoids is not observed in 3.14 The
Figure 4. (a) Molecular orbitals of 3a (isosurface value of 0.2). (b)
Natural population analysis charges and Wiberg bond indices of 3a
and 2a.
located at the nitrogen of the pyridyl substituent. On the other
hand, HOMO-5 represents the bonding π interaction between
C1 and C2, yet polarized toward C1, while the LUMO is its
antibonding counterpart. The Wiberg bond indices (WBI)
Table 1. Selected Bond Lengths (Å) and Angles (deg) of 3a,b
3a
1.760(1)
3b
1.766(2)
3a
1.377(2)
3b
1.419(2)
Cl−C1
S−P
C5−C6
N−C6
1.998(1)
1.997(1)
1.344(2)
1.379(2)
P−C1
1.740(1)
1.746(2)
S−Li
2.451(2)
2.466(3)
P−CPh
C1−C2
N−C2
C2−C3
C3−C4
C4−C5
1.818(1), 1.824(1)
1.409(2)
1.819(2), 1.824(2)
1.401(2)
Li−O
N−Li
N−Li−S
C2−C1−P
C2−C1−Cl
P−C1−Cl
1.88(1), 1.949(3)
2.041(2)
1.951(3), 1.956(3)
2.112(3)
1.375(2)
1.359(2)
107.2(1)
107.4(1)
1.428(2)
1.452(2)
123.1(1)
124.0(1)
1.367(2)
1.345(2)
118.1(1)
118.3(1)
1.397(2)
1.431(2)
117.4(1)
116.4(1)
C
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clearly confirm the partial double-bond character of the C1−C2
bond (WBI = 1.33). This value is higher than that calculated for
the starting material 2a but lower than the WBI of a “real”
double bond (WBI(ethene) = 2.04) or of an undisturbed
aromatic system (WBI(benzene) = 1.44). The WBIs also reflect
the charge delocalization into the aromatic ring system by more
pronounced differences in the bond indices in comparison to
2a. It is interesting to note that the highest WBI in the pyridyl
ring corresponds with the shortest C−C bond (C3−C4) found
in the crystal structure. The NBO charges still account for a
considerable negative charge at the “metalated” carbon atom
(qC = −0.65). This charge accumulation is slightly higher than
that of the pyridyl nitrogen (qN = −0.62) and is further
stabilized by electrostatic effects with the positively charged
phosphorus atom. Although the increase of the negative charge
upon metalation is most pronounced at the carbon atom (ΔqC
= −0.31), the calculated charges still reflect the charge
delocalization into the heterocycle (∑Δq = −0.27).
Overall, the character of compound 3a can be described as an
intermediate state between a lithium chloride carbenoid
(resonance structure A) and a β-chloro lithium amide (B). A
similar electronic structure has been reported by Stalke and co-
workers for 2-picolyllithium, also on the basis of experimental
charge density studies.15 DFT studies revealed an analogous
electronic structure for 3b with a slightly more pronounced
charge delocalization into the aromatic ring system (see the
Supporting Information). This electronic situation correlates
well with the NMR spectroscopic and crystallographic data as
well with the high thermal stability of the carbenoids. To
experimentally evaluate the carbenoid character, we next turned
our attention to preliminary reactivity studies in order to search
for a “hidden” carbene-like reactivity of 3. We challenged both
its nucleophilicity and electrophilicity (Scheme 2). Treatment
obvious in the reaction of 3a with the Pd(0) precursor.
Treatment of 3a in diethyl ether with [Pd(PPh3)4] gave way to
the selective formation of carbene complex 5 with formation of
lithium chloride. This transformation was found to be slow but
quantitative at room temperature, as evidenced by monitoring
the reaction process by 31P{1H} NMR spectroscopy. However,
due to the difficult separation of 5 from the formed PPh3, the
complex could be isolated in only 57% yield as a yellow solid. 5
is characterized by two doublets of the same intensity in the
31P{1H} NMR spectrum at 19.1 and 40.6 ppm with a coupling
constant of 3JPP = 46.2 Hz (C6D6). The 13C{1H} NMR shift of
the carbenic carbon atom resonates as a doublet of doublets at
39.0 ppm (JPC = 110 and 103 Hz), which is shifted strongly to
high field in comparison to signals for “normal” carbene
complexes but shifted downfield relative to the bis-
(thiophosphinoyl)methanediide-based carbene complex (δC
−18 ppm) previously reported by our group.16 Yet, the 13C
NMR shift of 5 still accounts for a highly ionic electronic
structure of the metal−carbon bond, C−−Pd+, with palladium
in the +2 oxidation state. All attempts to grow X-ray-quality
single crystals of 5 for diffraction analysis failed because of their
sensitivity and the difficult separation of 5 from the formed
triphenylphosphine. ESI/MS spectrometry, however, revealed
the molecular ion at m/z 676.1 with the expected peak profile,
and thus corroborating the composition of complex 5 as
concluded from NMR studies. The pincer-type N,C,S-bonding
mode of the ligand to the palladium center was additionally
confirmed by DFT calculations (see the Supporting Informa-
tion for computational details). Thereby, alternative bidentate
coordination modes were revealed to be disfavored by at least
6.2 kcal mol−1. Overall, the formation of the palladium complex
5 confirms the still present carbenoid character of 3 and its use
as a potential “carbene” source for the preparation of further
carbene complexes.
Scheme 2. Reactivity Studies of Carbenoid 3a
of 3a with electrophiles EX (MeI and Me3SnCl) resulted in
simple attack at the metalated carbon atom to form the
corresponding products 4a,b as well as the lithium halide in
high yields. Despite the localization of the HOMO at the
nitrogen of the pyridyl substituent, the substitution reactions
exclusively take place at the carbon atom.
The electrophilicity of 3a was tested by a cyclopropanation
reaction with cyclohexene as well as trans-stilbene. However, no
conversion was observed even upon heating of a solution of the
carbenoid in neat cyclohexene (or in THF or toluene solution)
at 50 °C for several hours. This is further confirmed by
computational studies on the cyclopropanation reaction of 3a
with ethene as the olefin. Here, the calculations predict an
activation barrier of 41.0 kcal mol−1 (see the Supporting
Information). Nevertheless, the carbene-like reactivity becomes
CONCLUSIONS
■
In summary, we have reported the preparation of two stable
lithium chloride carbenoids. The efficient electronic stabiliza-
tion by employing pyridyl and quinolyl moieties in combination
with a thiophosphinoyl substituent allowed their isolation at
room temperature. Spectroscopic data together with computa-
tional studies provide a clear picture of the electronic structure
and the charge delocalization within these systems. As such, X-
ray diffraction studies showed no lithium−carbon interaction
and NMR spectroscopy gave an only weakly deshielded
carbenoid 13C NMR signal. Accordingly, the electronic
situation in these compounds is best described by an
D
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8), 127.1 (d, 5JPC = 2.1 Hz; C-6), 127.7 (d, 5JPC = 1.4 Hz; C-2), 128.5
intermediate state between a lithium chloride carbenoid and a
β-chloro lithium amide. This is in line with the stability and also
reduced ambiphilicity of the carbenoids. However, reactivity
studies confirm the nucleophilic character and show that the
carbenoids can still be used as a “carbene” source for the
formation of carbene complexes. We are currently investigating
the transfer of the carbenoids to other transition metals.
3
(d, JPC = 12.4 Hz; C-13), 128.7 (bs; C-5), 129.5 (bs; C-3), 131.6 (d,
4JPC = 3.2 Hz; C-14), 131.7 (d, 2JPC = 10.4 Hz; C-12), 132.4 (d, 1JPC
=
4
4
81.6 Hz; C-11), 135.9 (bd, JPC = 1.9 Hz; C-7), 147.7 (bd, JPC = 1.7
2
Hz; C-1), 153.0 (d, JPC = 6.9 Hz; C-9). 31P{1H} NMR (162.0 MHz,
CDCl3): δ 41.2. Anal. Calcd for C22H18NPS: C, 73.52; H, 5.05; N,
3.90; S, 8.92. Found: C, 73.31; H, 5.02; N, 3.97; S, 9.04.
Preparation of 2a. A 1.3 mL portion (2.01 mmol) of n-BuLi (1.55
M in hexane) was added dropwise to a solution of 565 mg (1.83
mmol) of compound 1a in 20 mL of Et2O at −78 °C. The resulting
orange mixture was warmed to room temperature and stirred for 4 h.
In a second Schlenk flask 435 mg (1.84 mmol) of hexachloroethane
was dissolved in 20 mL of Et2O and cooled to −78 °C. The lithiated
compound was added via cannula transfer over a period of 15 min, and
the solution was slowly warmed to room temperature. After 16 h 50
mL of water was added and the mixture was extracted with diethyl
ether (3 × 50 mL). The combined organic layers were dried over
sodium sulfate and the solvent removed in vacuo, giving a brown oil,
which was purified by flash chromatography with Et2O/pentane (2/1
v/v; Rf = 0.47) as eluent, affording the product as a colorless crystalline
solid (389 mg, 1.13 mmol, 62%). Crystals suitable for XRD analysis
were grown by slow concentration of a solution of 2a in acetone at 5
°C. 1H NMR (300.1 MHz, C6D6): δ 6.15 (d, 2JPH = 3.9 Hz, 1H; H-6),
6.40−6.46 (m, 1H; H-2), 6.85−6.94 (m, 3H; H-10/4), 6.96−7.06 (m,
4H; H-9), 7.75−7.85 (m, 2H; H-3/1), 8.00 (m, 4H; H-8). 13C{1H}
EXPERIMENTAL SECTION
■
General Procedures. All experiments were carried out under a
dry, oxygen-free argon atmosphere using standard Schlenk techniques.
Solvents were dried over sodium or potassium (or over P4O10,
CH2Cl2) and distilled prior to use. H2O was distilled water.
Organolithium reagents were titrated against diphenylacetic acid
1
7
prior to use. H, Li, 13C, and 31P NMR spectra were recorded on
Avance-500, Avance-400, and Avance-300 spectrometers at 22 °C if
not stated otherwise. All values of the chemical shifts are in ppm
regarding the δ scale. All spin−spin coupling constants (J) are given 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 assignments were supported by
DEPT and HMQC experiments. The numbering scheme for the NMR
assignments is given in Chart 1.
1
NMR (75.5 MHz, C6D6): δ 58.8 (d, JPC = 50.1 Hz: C-6), 123.5 (d,
Chart 1
3
3
5JPC = 2.2 Hz; C-2), 125.9 (d, JPC = 2.6 Hz; C-4), 128.2 (d, JPC
=
3
1
12.2 Hz; C-9), 128.6 (d, JPC = 12.4 Hz; C-9), 130.8 (d, JPC = 37.5
Hz; C-7), 131.6 (d, JPC = 3.0 Hz; C-10), 131.8 (d, JPC = 3.0 Hz; C-
4
4
1
2
10), 131.9 (d, JPC = 35.9 Hz; C-7), 132.5 (d, JPC = 9.9 Hz; C-8),
132.7 (d, 2JPC = 9.9 Hz; C-8), 136.1 (d, 4JPC = 2.0 Hz; C-3), 148.2 (d,
4JPC = 1.0 Hz; C-1), 154.6 (s; C-5). 31P{1H} NMR (121.5 MHz,
C6D6): δ 51.0. Anal. Calcd for C18H15NPClS: C, 62.88; H, 4.40; N,
4.07; S, 9.32. Found: C, 62.89; H, 4.07; N, 4.12; S, 9.03.
Preparation of 2b. The procedure was analogous to that for 2a:
1
yield 26%; Rf = 0.55 (1/1 diethyl ether/pentane). H NMR (400.1
MHz, C6D6): δ 6.38 (d, 2JPH = 3.9 Hz, 1H; H-10), 6.84−6.93 (m, 3H;
H-13/14), 7.12−7.18 (m, 4H; H-13/14/8), 7.31−7.37 (m, 2H; H-3/
Elemental analyses were performed on an Elementar vario MICRO-
cube elemental analyzer and the DSC (differential scanning
calorimetry) measurements on a TA Instruments calorimeter (TA
DCS Q1000, V8.1, Build 261) with a heating rate of 10 K/min from
25 to 300 °C. Samples were prepared under an argon atmosphere in a
glovebox and sealed in a aluminum crucible. All reagents were
purchased from Sigma-Aldrich, ABCR, Rockwood Lithium, or Acros
Organics and used without further purification. Compound 1a was
prepared according to literature procedures.17
3
4), 7.62 (d, JHH = 8.7 Hz, 1H; H-Quin), 7.85−7.91 (m, 2H; H-12),
7.97 (d, 3JHH = 8.4 Hz, 1H; H-Quin), 8.14−8.21 (m, 2H; H-12), 8.35
(dd, 3JHH = 8.6 Hz, 4JHH = 0.9 Hz, 1H; H-Quin). 13C{1H} NMR (75.5
MHz, C6D6): δ 59.9 (d, 1JPC = 49.4 Hz; C-10), 122.8 (d, JPC = 1.6 Hz;
C-Quin), 127.0 (d, 3JPC = 1.0 Hz; C-8), 127.9 (d, 7JPC = 1.1 Hz; C-4),
128.1 (d, 3JPC = 12.3 Hz; C-13), 128.7 (d, 3JPC = 12.4 Hz; C-13), 129.5
(bs; C-5/3), 130.6 (d, 1JPC = 32.0 Hz; C-11), 131.6 (d, 4JPC = 3.0 Hz;
C-14), 131.8 (d, 1JPC = 31.1 Hz; C-11), 131.9 (d, 4JPC = 3.0 Hz; C-14),
2
2
132.5 (d, JPC = 9.9 Hz; C-12), 132.7 (d, JPC = 9.9 Hz; C-12), 136.6
(d, JPC = 1.6 Hz; C-Quin), 147.2 (d, 4JPC = 0.9 Hz; C-1), 154.7 (s; C-
9). C-6 covered by solvent signal. 31P{1H} NMR (162.0 MHz, C6D6):
δ 50.4. Anal. Calcd for C22H17ClNPS: C, 67.09; H, 4.35; N, 3.56; S,
8.14. Found: C, 67.26; H, 4.48; N, 3.57; S, 8.39.
Preparation of 1b. A 3.52 g portion (24.6 mmol) of 2-
methylquinoline was dissolved in 40 mL of THF and cooled to −78
°C. At this temperature 12.0 mL (28.0 mmol) of n-butyllithium (2.33
M in hexane) was added, giving a deep red solution. After it was stirred
for 1 h at low temperature, the reaction mixture was warmed to room
temperature and stirred for an additional 3 h. The mixture was then
cooled again to −78 °C and slowly added to a cooled solution of 5.97
g (27.0 mmol) of chlorodiphenylphosphine in 40 mL of THF. The
suspension was warmed to room temperature and stirred overnight.
After addition of 867 mg (27.0 mmol) of elemental sulfur the mixture
was stirred for 5 h and 100 mL water was added. The phases were
separated, and the aqueous phase was extracted with diethyl ether (3 ×
50 mL). The combined organic layers were dried over sodium sulfate
and the solvent removed in vacuo, giving a brown oil, which was
purified by flash chromatography with THF/pentane (1/2 v/v; Rf =
0.71), giving the product 1b as a slightly yellow solid (5.01 g, 13.9
mmol; 57%). Single crystals of 1b were grown by slow diffusion of
Preparation of 3a. A 300 mg portion (873 μmol) of compound
2a was dissolved in 1 mL of THF and cooled to −78 °C. A 676
μLportion (873 μmol) of methyllithium (1.29 M in Et2O) was added
dropwise with stirring. The yellow solution was warmed to room
temperature over a period of 4 h, during which time a yellow solid
precipitated. Subsequently, the mixture was cooled to −78 °C, the
solid was allowed to settle, and the supernatant solution was removed
via syringe. The product was washed three times with hexane while the
mixture was still kept at −78 °C. Finally, after removal of the solvent in
vacuo at room temperature, the product was isolated as a yellow solid
and stored in the glovebox (429 mg, 873 μmol, >98%). Crystals
suitable for XRD analysis were grown by slow concentration of a
solution of 3a in THF/pentane. 1H NMR (500.1 MHz, C6D6): δ 1.31
1
pentane into a THF solution. H NMR (400.1 MHz, CDCl3): δ 4.31
3
3
(d, 2JPH = 14.4 Hz, 1H; H-10), 7.37−7.49 (m, 7H; H-13/14/8), 7.59−
(t, JHH = 6.6 Hz, 8H; THF), 3.44 (t, JHH = 6.6 Hz, 8H; THF), 6.01
(vt, 1H; H-2), 7.00−7.08 (m, 6H; H-9/10), 7.09−7.13 (m, 1H; H-
3),7.49−7.51 (m, 1H; H-1), 7.51−7.54 (m, 1H; H-4), 8.22−8.26 (dd,
3JHH = 12.7, 4JHH = 7.3 Hz, 4H; H-8). 7Li NMR (194.4 MHz, C6D6): δ
1.42. 13C{1H} NMR (125.8 MHz, C6D6): δ 25.5 (s; THF), 60.1 (d,
7.64 (m, 2H; H-3/4), 7.74 (d, 3JHH = 8.1 Hz, 1H; H-2), 7.85 (d, 3JHH
=
3
8.4 Hz, 1H; H-5), 7.85−7.96 (m, 4H; H-12), 8.02 (d, JHH = 8.4 Hz,
1
1H; H-7).13C{1H} NMR (75.5 MHz, CDCl3): δ 44.5 (d, JPC = 49.0
7
3
Hz; C-10), 123.4 (d, JPC = 2.6 Hz; C-4), 126.4 (d, JPC = 1.3 Hz; C-
E
dx.doi.org/10.1021/om4010862 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1JPC = 127.8 Hz; C-6), 68.1 (s; THF), 106.4 (bs; C-2), 115.4 (d, 3JPC
=
days. Subsequently the solvent was removed in vacuo and the residue
taken up in 20 mL of toluene. After filtration to remove the formed
lithium chloride, the solvent was reduced to approximately 1 mL and 5
mL of hexane was added. The solvent was removed with a syringe and
the solid washed with hexane (6 × 10 mL), giving the product as a
yellow solid (94 mg, 139 μmol; 57%). 1H NMR (500.1 MHz, C6D6): δ
6.00−6.03 (m, 1H; H-2), 6.71−6.75 (m, 1H; H-3), 6.75−6.80 (m, 2H;
H-10), 6.81−6.86 (m, 4H; H-9), 6.90−6.95 (m, 9H; H-13/14), 7.65−
7.68 (m, 1H; H-1), 7.69−7.72 (m, 1H; H-4), 7.87- 7.96 (m, 6H; H-
12), 8.35−8.42 (m, 4H, H-8). 13C{1H} NMR (500.1 MHz, d8-THF):
δ 39.0 (dd, 1JPC = 111.0 Hz, 2JPC = 103.0 Hz; C-6), 113,8 (C-2), 121.8
(dd, 3JPC = 9.0 Hz, 4JPC = 4.1 Hz; C-4), 128.1 (d, 3JPC = 12.2 Hz; C-9),
8.0 Hz; C-4), 127.9 (d, 3JPC = 12.4 Hz; C-9), 130.0 (d, 4JPC = 2.8 Hz;
C-10), 133.3 (d, 2JPC = 10.3 Hz; C-8), 135.4 (s; C-3), 138.1 (d, 1JPC
=
2
92.0 Hz; C-7), 146.1 (s; C-1), 163.9 (d, JPC = 14.6 Hz; C-5). 31P
NMR (162.0 MHz, C6D6): δ 39.4. Anal. Calcd for C26H28ClLiNO2PS:
C, 63.22; H, 6.12; N, 2.84; S, 6.49. Found: C, 63.21; H, 6.20; N, 3.05;
S, 6.43.
Preparation of 3b. The procedure was analogous to that for 3a:
yield 93%. Crystals were grown by diffusion of pentane into a solution
1
of 3b in THF at −40 °C. H NMR (400.1 MHz, C6D6): δ 1.28 (m,
8H; THF), 3.46 (m, 8H, THF), 6.79−6.82 (m, 1H, H-Quin), 6.97−
7.07 (m, 8H; H-13,14,Quin), 7.10−7.15 (m, 2H; H-3,4), 7.57−7.73
7
1
128.4 (d, 3JPC = 12.6 Hz; C-13), 128.8 (dd, JPC = 91.8 Hz, 4JPC = 1.2
(m, 1H; H-8), 8.25−8.32 (m, 4H; H-12). Li NMR (194.4 MHz,
C6D6): δ 1.30. 13C{1H} NMR (75.5 MHz, C6D6): δ 25.5 (s; THF),
4
4
Hz; C-11), 129.6 (d, JPC = 2.9 Hz; CH-10), 131.5 (d, JPC = 2.9 Hz;
1
C-14), 132.5 (d, 2JPC = 10.6 Hz; C-8), 133.7 (bs, C-3), 135.2 (d, 2JPC
=
68.2 (s, THF), 67.9 (bd, JPC ≈ 115 Hz; C-10), 118.7 (s; C-Quin),
9.7 Hz; C-12), 139.6 (dd, JPC = 86.26, 4JPC = 4.1 Hz; C-7), 146.6 (d,
1
119.9 (d, JPC = 7.9 Hz; C-Quin), 121.7 (s; C-Quin), 123.0 (s; C-6),
3
3JPC = 4.0 Hz; C-1), 162.7 (d, JPC = 10.0 Hz; C-5). 31P{1H} NMR
2
128.0 (s; C-Quin), 128.0 (d, JPC = 12.5 Hz; C-13), 128,3 128.8 (s,
C3,4), 130.3 (d, 4JPC = 2.9 Hz; C-14), 133.0 (d, 2JPC = 10.3 Hz; C-12),
(500.1 MHz, C6D6) δ 19.1 (d, 3JPP = 46.2 Hz; PdPPh3), 40.6 (d, 3JPP
=
1
137.1 (d, JPC = 92.0 Hz; C-11), 150.2 (s; C-1), 161.5 (bs; C-9).
46.2 Hz; PPh2). ESI-MS: calcd for C36H30NP2SPd 676.06163, found
676.06191.
31P{1H} NMR (162.0 MHz, C6D6): δ 41.3. Anal. Calcd for
C22H17ClNPS: C, 66.23; H, 5.93; N, 2.57; S, 5.89. Found: C, 65.76;
H, 6.23; N, 2.50; S, 5.69.
Single-Crystal X-ray Structure Determination. Single crystals
were selected from a Schlenk flask under an argon atmosphere and
covered with an inert oil (perfluoropolyalkyl ether). Data were
collected on a Bruker APEX-CCD instrument (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 (SHELXS-97) and refined by
full-matrix least-squares methods against F2 (SHELXL-97).18 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 in Tables S1 and S2 in the Supporting
Information. Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data Center as
supplementary publication nos. CCDC-967265 (compound 1b),
CCDC-967266 (compound 2a), CCDC-967267 (compound 2b),
CCDC-967268 (compound 3a), and CCDC-967269 (compound 3b).
Copies of the data can be obtained free of charge on application to the
Cambridge Crystallographic Data Center, 12 Union Road, Cambridge
CB2 1EZ, U.K. (fax, (+44) 1223-336-033; e-mail, deposit@ccdc.cam.
ac.uk).
Preparation of 4a. To 238 mg (481 μmol) of carbenoid 3a in 13
mL of THF was added 30 μL (481 μmol) of MeI. The mixture was
stirred for 3 h and the solvent was subsequently removed in vacuo.
NMR spectroscopic studies showed the clean formation of the
product. For further purification the slightly brown oil was purified by
flash chromatography on silica with DCM (Rf = 0.8) as eluent, thus
1
giving the product as a colorless solid (120 mg, 335 μmol, 70%). H
3
NMR (400.1 MHz, CDCl3): δ 2.33 (d, JPH = 15.2 Hz, 3H; CH3),
7.14−7.18 (m 1H; H-2), 7.35−7.40 (m, 2H; H-9), 7.43−7.57 (m, 6H;
H-3,4,9,10), 7.95−8.00 (m, 2H; H-8), 8.13−8.19 (m, 2H; H-8), 8.44-
8.47 (bd, 1H; H-1). 13C{1H} NMR (75.5 MHz, CDCl3): δ 27.4 (d,
2JPC = 4.4 Hz; CH3), 71.4 (d, 2JPC = 46.8 Hz; C-6), 123.1 (d, 5JPC = 2.2
3
3
Hz; C-4), 124.9 (d, JPC = 2.7 Hz; C-2), 127.9 (d, JPC = 12.3 Hz; C-
3
1
9), 128.1 (d, JPC = 12.2 Hz; C-9), 129.0 (d, JPC = 80.8 Hz; C-7),
2
4
129.9 (d, JPC = 79.9 Hz; C-7), 131.9 (d, JPC = 3.0 Hz; C-10), 132.0
(d, 4JPC = 2.9 Hz; C-10), 133.9 (d, 2JPC = 9.5 Hz; C-8), 134.0 (d, 2JPC
=
9.5 Hz; C-8), 135.8 (d, 4JPC = 1.9 Hz; C-3), 147.8 (d, 4JPC = 1.6 Hz; C-
1), 156.9 (d, JPC = 1.1 Hz; C-5). 31P{1H} NMR (162.0 MHz,
2
CDCl3): δ 59.6. Anal. Calcd for C22H17ClNPS: C, 63.77; H, 4.79; N,
3.91; S, 8.96. Found: C, 63.85; H, 4.90; N, 3.84; S, 9.05.
Computational Details. All calculations were performed without
symmetry restrictions. Starting coordinates were obtained directly
from the crystal structure analyses. All calculations were done with the
Gaussian 03 and Gaussian 09 program package.19 Geometry
optimizations were performed at the density functional theory level
using the B3LYP and M062X functionals.20 For the calculation of the
carbenoids 3a,b the 6-311++G** basis set was used, for the Pd
complexes the 6-31G(d) basis set was used for hydrogen, the
LANL2TZ(f)21 basis set augmented with a f polarization function of
exponent 1.47222 was used for palladium, and the 6-311+g(d) basis set
was used for all other atoms. Harmonic vibrational frequency analyses
were performed at the same levels of theory to confirm that the
structures were indeed minima on the potential energy surface (PES).
NBO analyses were carried out on the optimized systems using the
NBO 5.0 program interfaced to the Gaussian 03 program and the
same level of theory.23
Preparation of 4b. A 30 mg portion (61.0 μmol) of carbenoid 3a
and 12.8 mg (64.0 μmol) of trimethylchlorostannane were placed in a
J. Young NMR tube and dissolved in 0.8 mL of C6D6. The slightly
yellow mixture was shaken, and NMR data were recorded, which
1
showed quantitative formation of the stannylated product. H NMR
(500.1 MHz, C6D6): δ 0.36 (s, 9H; CH3), 6.42 (m, 1H; H-2), 6.84 (m,
1H; H-4), 6.96−7.03 (m, 3H; H-9/10), 7.08−7.10 (m, 3H; H-9/10),
7.14−7.16 (m, 1H; H-3), 8.04−8.09 (m. 3H; H-8/1), 8.53−8.56 (m,
1
2H; H-8). 13C{1H} NMR (125.8 MHz, C6D6): δ −2.9 (s, JC
=
117/119
Sn
183.7 Hz, 175.6 Hz; CH3), 69.2 (d, 1JPC = 23.4 Hz; C-6), 122.2 (d, 2.9
3
3
Hz; C-2), 124.2 (d, JPC = 3.9 Hz; C-4), 127.7 (d, JPC = 11.7 Hz; C-
3
4
9), 128.0 (d, JPC = 11.9 Hz; C-9), 131.3 (d, JPC = 2.9 Hz; C-10),
131.4 (d, JPC = 75.2 Hz; C-7), 131.6 (d, JPC = 2.9 Hz; C-10), 132.4
1
4
1
2
(d, JPC = 81.0 Hz; C-7), 134.2 (bd, JPC = 13.4 Hz; C-8), 136.1 (d,
4JPC = 2.5 Hz; C-3), 147.0 (d, JPC = 1.82 Hz; C-1), 159.6 (d, JPC
=
=
4
2
2.7 Hz; C-5). 31P{1H} NMR (162.0 MHz, C6D6): δ 50.1 (2JP
117/119
Sn
16.4, 37.4 Hz).
Attempted Cyclopropanation with Cyclohexene and trans-
Stilbene. Carbenoid 3a and 1.1 equiv of olefin (cyclohexene, trans-
stilbene) were placed in a J. Young NMR tube and dissolved in THF
and toluene, respectively. The mixture was stirred for several hours at
room temperature (and at 60 °C). NMR spectroscopy showed no
conversion and decomposition of the carbenoid, respectively, after a
prolonged reaction time at elevated temperature.
Preparation of 5. A 10 mL portion of diethyl ether was added to
120 mg (244 μmol) of carbenoid 3a and 282 mg (244 μmol) of
tetrakis(triphenylphosphine)palladium(0) at −78 °C. The yellow
suspension was slowly warmed to room temperature and stirred for 3
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files, text, tables, and figures giving crystallographic data for
structures of 1b, 2a,b, and 3a,b, plots of the molecular
structures of 1b and 2b, 1H and 31P{1H} NMR spectra for all of
the synthesized compounds, crystallographic and computa-
tional details, and coordinates of the energy-optimized
structures. This material is available free of charge via the
Internet at http://pubs.acs.org.
F
dx.doi.org/10.1021/om4010862 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Seebach, D. Angew. Chem., Int. Ed. Engl. 1979, 18, 785. (c) Seebach,
AUTHOR INFORMATION
Corresponding Author
*E-mail for V.H.G.: vgessner@uni-wuerzburg.de.
Notes
■
D.; Gabriel, J.; Hassig, R. Helv. Chim. Acta 1984, 67, 1083. (d) Seebach,
̈
D.; Hassig, R.; Gabriel, J. Helv. Chim. Acta 1983, 66, 308.
̈
(14) Muller, A.; Marsch, M.; Harms, K.; Lohrenz, J. C. W; Boche, G.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1518.
̈
(15) (a) Ott, H.; Pieper, U.; Leusser, D.; Flierler, U.; Henn, J.; Stalke,
D. Angew. Chem., Int. Ed. 2009, 48, 2978. (b) Kocher, N.; Leusser, D.;
Murso, A.; Stalke, D. Chem. Eur. J. 2004, 10, 3622.
(16) Gessner, V. H.; Meier, F.; Uhrich, D.; Kaupp, M. Chem. Eur. J.
2013, 19, 16729.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the Deutsche
Forschungsgemeinschaft (Emmy-Noether program), the
Fonds der Chemischen Industrie, and the Alexander von
Humboldt Foundation. We also thank Rockwood Lithium
GmbH for the supply of chemicals and Prof. Holger
Braunschweig and his group (Kai Hammond for DSC
measurement) for support.
(17) (a) Kling, C.; Ott, H.; Schwab, G.; Stalke, D. Organometallics
2008, 27, 5038. (b) Mothes, E.; Sentets, S.; Luquin, M. A.; Mathieu,
R.; Lugan, N.; Lavigne, G. Organometallics 2008, 27, 1193−1206.
(c) Leung, W.-P.; Chan, Y.-C.; Mak, T. C. W. Organometallics 2013,
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(18) (a) SAINT v7.68A in Bruker APEX v2011.9; Bruker AXS,
Madison, WI, USA, 2008. (b) Sheldrick, G. M. SADABS 2008/2;
Universitat Gottingen, Gottingen, Germany, 2008. (c) Sheldrick, G.
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Acta Crystallogr., Sect. A 2008, 64, 112−122.
(19) (a) Gaussian 03, Revision E.01; Gaussian, Inc., Wallingford, CT,
2004. See the Supporting Information for the full citation. (b) Frisch,
M. J. et al. Gaussian 09, Revision B.01; Gaussian, Inc., Wallingford, CT,
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dx.doi.org/10.1021/om4010862 | Organometallics XXXX, XXX, XXX−XXX