Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids

Article abstract of DOI:10.1002/chem.201304927

The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd⁰ precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moie

Full text of DOI:10.1002/chem.201304927

DOI: 10.1002/chem.201304927
Full Paper
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Carbene Complexes
Substitution Effects on the Formation of T-Shaped Palladium
Carbene and Thioketone Complexes from Li/Cl Carbenoids
Sebastian Molitor, Kai-Stephan Feichtner, Claudia Kupper, and Viktoria H. Gessner*[a]
Abstract: The preparation of palladium thioketone and T-
shaped carbene complexes by treatment of thiophosphoryl
substituted Li/Cl carbenoids with a Pd0 precursor is reported.
Depending on the steric demand, the anion-stabilizing abili-
ty of the silyl moiety (by negative hyperconjugation effects)
and the remaining negative charge at the carbenic carbon
atom, isolation of a three-coordinate, T-shaped palladium
carbene complex is possible. In contrast, insufficient charge
stabilization results in the transfer of the sulfur of the thio-
phosphoryl moiety and thus in the formation of a thioketone
complex. While the thioketones are stable compounds the
carbene complexes are revealed to be highly reactive and
decompose under elimination of Pd metal. Computational
studies revealed that both complexes are formed by a substi-
tution mechanism. While the ketone turned out to be the
thermodynamically favored product, the carbene is kinetical-
ly favored and thus preferentially formed at low reaction
temperatures.
Introduction
Since the pioneering work by E. O. Fischer and R. R. Schrock,
transition-metal complexes with a metal carbon double bond
have found wide-ranging applications in stoichiometric as well
as catalytic transformations.[1] Depending on the substituents
at the carbenic carbon atom and the involved reactivity they
are often classified into Fischer-type carbene and Schrock-type
alkylidene complexes. In this context, carbene complexes
formed from geminal dilithiated bis(thiophosphoryl) or bis(imi-
nophosphoryl) methanes have gained special interest as they
seem to contradict this general classification pattern.[2] Here,
the metal carbon bond is formally formed by a four-electron
donation from the ligand to the metal, leaving a highly nucleo-
philic carbon atom bound to anion stabilizing substituents.[3,4]
This type of carbene complex was first introduced by R. G.
Cavell and co-workers, who succeeded in the isolation of titani-
um and zirconium complexes.[4c] The carbon center was report-
ed to be multiply bound to the metal (structure A in Figure 1)
and to the two phosphorus substituents. This was based on
short M–C and P–C distances found in the crystal structures
thus suggesting strong delocalization of the electron density.
This leads to the description of the electronic structure by res-
onance forms with ylidic character such as form B. In the fol-
lowing years, a variety of different carbene complexes based
on dilithio methandiides were prepared incorporating early
and late transition metals as well as lanthanides and acti-
Figure 1. Resonance structure of carbene complexes based on methan-
diides.
nides.[5] However, due to the restricted access and the extreme
sensitivity of dilithio methandiides, these studies have been
limited to bis(phosphonium)-substituted systems.[6] Such phos-
phorus(V) moieties are well known for their excellent anion sta-
bilizing ability. This allows for the facile dilithiation as well as
for the stabilization of the carbene complexes, particularly by
stabilization of the high charge accumulation at the carbenic
carbon via resonance form C.
An alternative approach to this class of carbene complexes
has been presented by P. Le Floch, N. Mꢀzailles and co-workers
in 2007.[7] They employed lithium chloride carbenoid 1 to
access palladium complex 2, which had earlier been prepared
from the corresponding dilithio methandiide (Figure 2).[8] To
[a] S. Molitor, K.-S. Feichtner, C. Kupper, Dr. V. H. Gessner
Institut fꢀr Anorganische Chemie
Julius-Maximilians-Universitꢁt Wꢀrzburg
Am Hubland, 97074 Wꢀrzburg (Germany)
E-mail: vgessner@uni-wuerzburg.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304927.
Figure 2. Reactivity of carbenoids 1 and 3 towards [Pd(PPh3)4].
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extend the applicability of this approach also on carbenoids
with other substituents than PV moieties we have recently re-
ported on the silyl derivative 3.[9] This carbenoid, however, se-
lectively reacted with [Pd(PPh3)4] under formation of the palla-
dium thioketone 4. In this case, no formation of a carbene
complex was observed. The differences in the reactivity of
both Li/Cl carbenoids were attributed to the dramatic loss of
stabilization of the negative charge by replacing the thiophos-
phoryl substituent with the trimethylsilyl group. The remaining
negative charge at the central carbon atom was thus assumed
as the driving force for the rearrangement to the thermody-
namically favored thioketone complex 4. These results prompt-
ed us to attempt a modification of our initial ligand system to
allow for further stabilization of the negative charge. Silyl
groups are known for their anion-stabilizing ability by negative
hyperconjugation into low-lying s*-SiR orbitals.[10] Thus, we en-
visioned that these interactions might be improved by the in-
troduction of phenyl substituents instead of the trimethylsilyl
group in 3. Here, we show that indeed variation of the substi-
tution pattern at the silicon allows the isolation of the desired
carbene complex. Thereby, the carbene complex turned out to
be a rare example of a T-shaped Pd complex that decomposes
under elimination of palladium metal. DFT calculations confirm
the increasing stability of the carbene complex with the intro-
duction of phenyl substituents as well as low energy pathways
to both complexes observed.
ethane. All compounds were fully characterized by multinu-
clear NMR spectroscopy in solution and elemental analysis. The
molecular structures of silanes 5b, c and e were additionally
determined by single-crystal X-ray diffraction analysis. Figure 3
exemplarily depicts the molecular structure of the MePh2Si-
substituted compound 5c (for crystallographic details and the
molecular structure of 5b and 5e, see the Supporting Informa-
tion).[11] All bond lengths and angles are in the expected
region, except for the P–C–Si angles, which are in all com-
pounds larger (118.9(1)–127.1(1)8) than the ideal tetrahedral
angle of 109.478.
Figure 3. Molecular structure of silane 5c. Selected bond lengths [ꢂ] and
angles [8] for 5b, c and e. 5b: PÀC13 1.8030(19), PÀS 1.9561(8), PÀC7
1.8133(19), PÀC1 1.812(2), SiÀC14 1.854(2), SiÀC15 1.857(2), SiÀC16 1.874(2),
SiÀC13 1.896(2); P-C13-Si 121.06(10); 5c: PÀS 1.9587(6), C21ÀSi 1.8826(16),
C15ÀSi 1.8700(16), C14ÀSi 1.8590(17), C13ÀSi 1.8902(15), C13ÀP 1.8045(15),
C7ÀP 1.8185(15), C1ÀP 1.8241(17); P-C13-Si 118.87(8); 5e: C1ÀP1 1.851(2),
C7ÀP1 1.850(2), C13ÀP1 1.827(2), C13ÀSi1 1.898(2), C14ÀSi1 1.889(2), C20ÀSi1
1.881(2), C26ÀSi1 1.8887(19), P1ÀS1 1.9698(7), P1-C13-Si1 127.07(11).
Results and Discussion
Thioketone versus carbene formation
Preliminary investigations suggested that the lack of stabiliza-
tion of the negative charge at the carbenic carbon atom is re-
sponsible for the selective formation of the palladium thioke-
tone complex 4. As phenyl substituents are known to be more
suitable to stabilize anions by negative hyperconjugation we
first aimed at the introduction of phenyl groups. The required
chlorinated precursors were synthesized as outlined in
Scheme 1. The silyl compounds 5b–d were prepared by an
analogous procedure as reported for the trimethylsilyl-substi-
tuted compound 5a. Lithiation of diphenylmethylphosphine
sulfide (or dicyclohexylmethylphosphine sulfide in the case of
5e) with butyllithium and treatment with the corresponding
chlorosilane at low temperatures afforded the a-silylated phos-
phine sulfides in moderate to good yields as colorless solids.
Chlorination was subsequently achieved by deprotonation of
the acidic methylene moiety and treatment with hexachloro-
The chlorinated silanes were then converted to the corre-
sponding Li/Cl carbenoids 7b–d by metallation with methyl-
lithium. In none of the cases was the carbenoid stable at ambi-
ent temperature.[12,13] NMR spectroscopy of the carbenoids in
C6D6 at room temperature showed the decomposition and for-
mation of multiple products, amongst others, Ph2P(S)Cl. Only
the SiPh3-substituted carbenoid 7d selectively decomposes
under dimerization by sulfur transfer.[11] However, trapping re-
actions confirmed the selective formation of the carbenoids 7
so that in situ transformations are possible. To investigate the
influence of the phenyl substituents on the formation of the
thioketone complex, we at first treated the cooled THF solu-
tion of dimethylphenyl-substituted carbenoid 7b with a solu-
tion of tetrakis(triphenylphosphine)palladium(0), [Pd(PPh3)4], at
room temperature (Scheme 2). NMR spectroscopic studies of
the reaction mixture revealed the high-yielding formation of
the thioketone complex 8b, which could be isolated as yellow
solid in 64% yield after removal of lithium chloride and tri-
phenyl phosphine. Compound 8b is characterized by a set of
three doublets of doublets in the 31P{1H} NMR spectrum, with
two signals in the expected region for coordinated triphenyl-
phosphine ligands (d=20.6 and 24.4 ppm). The signal for the
free phosphine moiety appears at d=9.51 ppm, upfield-shifted
compared to the thiophosphoryl moiety in the precursor mole-
cules 5b and 6b (d=38.3 and 45.9 ppm). The coupling con-
Scheme 1. Synthesis of the chlorinated precursors 6.
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Table 1. Ratio of thioketone 8 and carbene complex 9 depending on the
reaction temperature and the substitution pattern of the carbenoid 7.
Entry PR2
Silyl group T [8C][i] Thioketone 8 [%][ii] Carbene 9 [%]ii
1
2
3
4
5
6
7
8
9
PPh2 SiMe3
RT
RT
100 (79)
97 (64)
0
3
8
12
25
20
40
52 (15)
0
PPh2 SiMe2Ph
PPh2 SiMePh2
PPh2 SiPh3
À788C 92
RT
88 (56)
À788C 75
RT
80 (62)
À408C 60
À788C 48 (41)
À788C 100 (53)
Scheme 2. Formation of the thioketone and carbene complexes 8 and 9
from the corresponding carbenoids 7.
PCy2 SiPh3
[a] Temperature of the THF solution of [Pd(PPh3)4]. [b] Ratio of thioketone
and carbene complex in the crude reaction product determined by 1H
and 31P NMR spectroscopy; isolated yields in brackets. Isolation of the car-
bene complex was only accomplished with 9d.
2
3
stants of JPP =29.1 and JPP =23.9 and 25.6 Hz are in agree-
ment with the formulation of the thioketone complex. The
29Si NMR spectroscopic signal appeared as doublet of doublets
at d=À11.0 ppm (2JSiP =36.9, 3JSiP =5.87 Hz). Due to the syn-
thetic method complex 8b is obtained as racemic mixture. The
stereogenic carbon atom results in diastereotopic phenyl and
methyl substituents at the adjacent phosphorous and silicon
atom, respectively, and thus in the corresponding splitting in
as a Pd0 precursor resulted in the same product mixtures as
observed for the tetracoordinated congener.[14]
To examine the influence of the phosphine moiety on the
sulfur transfer we additionally prepared the bis(cyclohexyl)-
phosphine sulfide 6e. Here, we expected the sulfur transfer to
be less favorable due to the more electron-rich phosphorous,
which should hamper the reduction to the free phosphine
unit. However, treatment of the corresponding carbenoid with
[Pd(PPh3)4] at low reaction temperatures selectively delivered
the thioketone complex even in combination with the SiPh3
moiety (entry 9, Table 1). This is evidenced by three doublets
of doublets in the 31P{1H} NMR spectrum at d=18.33 (PCy2),
22.1, and 23.0 ppm. This observation clearly suggests that the
stabilization of the negative charge at the carbenic carbon
atom is the crucial factor for the carbene formation. Despite
preventing the reduction to the free phosphine, the cyclohexyl
ligands reduce the ability of the thiophosphoryl moiety for
negative hyperconjugation into low-lying s*-PR orbitals.
Hence, thioketone complex 8e and not the carbene complex
is selectively formed.
the H and 13C{1H} NMR spectra.
1
Interestingly, when the reaction was repeated with a solution
of [Pd(PPh3)4] cooled to À788C, the 31P NMR spectrum of the
reaction mixture revealed the formation of a second species in
small quantities of approximately 8%. This compound is char-
acterized by only two doublets in the 31P NMR spectrum, one
in the range for coordinated PPh3 (d=22.6 ppm), the second
downfield-shifted at d=46.4 ppm. This suggested that the in-
troduction of the phenyl substituent also enabled the stabiliza-
tion of a second palladium complex with only a single coordi-
nating PPh3 ligand and—most importantly—an intact thio-
3
phosphoryl moiety. The coupling constant of JPP =14.8 Hz is
close to that reported for the symmetric carbene complex 2
(3JPP =14.6 Hz), thus indicating the formation of a T-shaped car-
bene complex 9 (Scheme 2).
Repeating this experiment with the diphenylmethyl and the
triphenyl silyl-substituted derivatives 6c and 6d confirmed this
tendency observed with 6b. In all cases, the corresponding thi-
oketone complex was formed as the major product. However,
with increasing number of phenyl substituents an increasing
formation of the palladium carbene complex 9 was observed
(entries 3, 5, and 8 in Table 1). This is especially true for reac-
tions performed at low reaction temperatures (entry 6, 7, and
8) and thus accounts for a kinetic preference of the formation
of 9. In the case of the reaction of the triphenylsilyl-substituted
carbenoid 7d with [Pd(PPh3)4] at À788C both complexes are
formed in an almost equimolar ratio (entry 8). Here, the Pd
complexes could be separated by extraction of 9d with diethyl
ether from the highly insoluble thioketone complex 8d. It is
noteworthy, that no interconversion between the carbene and
the thioketone complex was observed even in the presence of
excessive triphenyl phosphine and at high temperatures (up to
1008C). The ratio between both compounds remained con-
stant even after prolonged storage at room temperature, thus
suggesting that both complexes are formed by different, irre-
versible reaction pathways (vide infra). Also using [Pd(PPh3)2]
All thioketone complexes were characterized by multinuclear
NMR spectroscopic studies. Elemental analyses gave consis-
tently low values for C, which we attributed to carbide forma-
tion as H and S values were consistent with the proposed for-
mulation and all spectroscopic data indicated that the samples
are pure. The molecular structure of thioketone 8b and 8d
were determined by single-crystal X-ray diffraction and 8d ad-
ditionally characterized by high-resolution mass spectrometry
(HRMS) showing a mass of m/z=1119.21 with the simulated
peak profile. The molecular structures of thioketone complexes
8b and 8d are depicted in Figure 4 (for crystallographic de-
tails, see the Supporting Information). In both complexes, the
central structural motif is formed by a Pd–C–S ring, in which
the palladium adopts a strongly distorted square-planar coor-
dination with angles between 45.94(8) and 109.90(8)8 and
45.97(8) and 110.41(8)8, respectively. Due to the short bite of
the C–S linkage also the coordination sphere around carbon
considerably deviates from the ideal tetrahedral arrangement.
The PdÀC (2.169(3) (8b), 2.177(3) (8d)) as well as the C–Si and
C–P distances are in the typical range of single bonds. On the
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Figure 5. Left: plot of the Van-der-Waals-radii of 8d (left). Right: projection
of the central unit of the thioketone complexes 8d (R=SiPh3) and its
SiPhMe2-derivative 8b (bright gray).
ents. Both tendencies are in line with the increased steric bulk
in 8d.
The carbene complex could only be isolated from the 1:1
mixture in the case of the SiPh3-substituted system. Compound
9d is characterized by two doublets in the 31P{1H} NMR spec-
trum at d=23.7 and 46.1 ppm (3JPP =16.4 Hz). The 1H NMR
spectra as well as HRMS (ESI) (m/z: 857.1212) confirm the
bonding of only a single phosphine ligand at palladium. In the
carbene complex 9d no diastereotopic splitting of the signals
of the Ph groups at phosphorus are evident in the 1H and
13C{1H} NMR spectra. This is in line with a three-coordinate
carbon atom as expected for the carbene complex. Unfortu-
nately, all crystallization attempts failed and resulted in the de-
composition (see below) of the highly sensitive complex 9d. In
general, three-coordinate palladium complexes are often pro-
posed as intermediates in palladium-catalyzed cross-cou-
plings.[17] For example, mechanistic studies by Hartwig and co-
workers have shown that key intermediates of carbon–nitro-
gen bond-formation reactions catalyzed by palladium com-
plexes with bulky triarylphosphine ligands bear only one phos-
phine ligand.[18] Yet, only few isolated and structurally charac-
terized examples of such three-coordinate palladium com-
plexes are known.[19]
Figure 4. Molecular structure of the thioketone complex 8b (top) and 8d
(bottom). Two CH2Cl2 solvent molecules in 8b and hydrogen atoms of the
phenyl substituents are omitted for clarity. Selected bond lengths [ꢂ] and
angles [8]: 8b: C13ÀS 1.748(3), C13ÀP1 1.832(3), C13ÀSi 1.885(3), C13ÀPd
2.169(3), P2ÀPd 2.3634(8), P3ÀPd 2.3183(9), PdÀS 2.2985(8); P1-C13-Si
115.05(15), S-C13-Pd 70.93(10), P1-C13-Pd 112.50(14), Si-C13-Pd 113.49(14),
C13-Pd-S 45.94(8), S-Pd-P2 98.12(3), P3-Pd-P2 106.04(3), C13-Pd-P3 109.90(8);
8d: C13ÀS 1.750(3), C13ÀP1 1.832(3), C13ÀSi 1.890(3), C13ÀPd 2.177(3), P2À
Pd 2.3451(8), P3ÀPd 2.3716(8), PdÀS 2.2953(8); P1-C13-Si 118.48(16), S-C13-
Pd 70.59(10), P1-C13-Pd 112.77(14), Si-C13-Pd 113.39(14), C13-S-Pd 63.43(9),
C13-Pd-P2 110.41(8), C13-Pd-S 45.97(8), S-Pd-P3 98.32(3), P2-Pd-P3 105.58(3).
contrary, the CÀS bond of 1.748(3) ꢂ in 8b and 1.750(3) in 8d
is shorter than a typical CÀS single bond, which indicated
some p-character. Both, the short CÀS bond and the flattened
carbon coordination sphere (torsion angle (Si-C-P-S) of
146.9(2)8 in 8b and 147.8(2) in 8d), are indicative for a p-char-
acter of the CÀS bond, so that 8b and 8d can also be viewed
The possible isolation of the T-shaped carbene complex 9
can be referred to the bulkiness of the ligand and the thus in-
volved steric protection. This is confirmed by computational
studies which also confirm the geometry of the complex (see
below). As can be seen from a space-filling model of the
as a side-on coordination complex of the Pd0 species to the C= energy-optimized structure of 9d the open side at the palladi-
S double bond.[15,16] It is interesting to note, that the bulkier
phenyl substituent of the Me2PhSi unit in complex 8b points
towards the sterically more demanding triphenyl phosphine
substituents.
um center is efficiently shielded by the phenyl substituents of
the silyl moiety (Figure 6). To evaluate an electronic contribu-
The Ph3Si-substituted thioketone complex 8d proved to be
stable towards air and moisture. Storage under ambient condi-
tions for months showed no decomposition for example, by
oxidation of the phosphine moiety. This enhanced stability
compared with the corresponding thioketone complexes incor-
porating methylsilyl or PCy2 units can easily be explained from
the plot of the van-der-Waals radii, which confirms an efficient
shielding by the phenyl groups (Figure 5). Comparison of the
bonding parameters of 8d with 8b shows, that the most pro-
nounced difference of both structures involves the Pd–P dis-
tances as well as the PÀCÀSi angle. While the PdÀP bonds are
only slightly elongated in 8d, the PÀCÀSi angle decreases from
123.1(2) to 118.5(2)8 by introduction of the phenyl substitu-
Figure 6. Energy-optimized structure and space-filling model of 9d.
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tion to the stability we investigated the electronic structure of
9d. Natural population analysis revealed a high negative
charge (qC =À1.39) at the carbenic carbon atom and a Wiberg
bond index of only 0.54 for the PdÀC bond (cf. WBI(SÀPd)=
0.45, WBI(CÀP)=1.19). Additionally, natural bond orbtial (NBO)
analysis indicates only a single bond with no p-interaction be-
tween the sp2-hybridized carbon atom and the metal center.
The remaining lone pair at the carbon atom is stabilized by
negative hyperconjugation effects into s*(PÀCPh) and s*(SiÀ
CPh) orbitals. These interactions are equally strong as the inter-
action with unoccupied orbitals at the palladium atom
(second-order perturbation theory). Despite the three-coordi-
nate palladium center, complex 9 is better described as an
alkyl than as an carbene complex with palladium in the formal
oxidation state +2 (resonance structure 9A). Overall, steric ef-
Figure 7. Molecular structure of the ylide 10. Hydrogen atoms of the phenyl
substituents are omitted for clarity. Selected bond lengths [ꢂ] and angles [8]:
C1ÀP1 1.834(3), C7ÀP1 1.839(3), C13ÀP2 1.741(3), C13ÀP1 1.769(3), C13ÀSi
1.859(3), C14ÀP2 1.829(3), C20ÀP2 1.811(3), C26ÀP2 1.825(3), C32ÀSi1
1.904(3), C38ÀSi 1.896(3), C44ÀSi 1.895(3), P1ÀS 1.9782(12); P2-C13-P1
118.18(15), P2-C13-Si 118.98(15), P1-C13-Si 121.32(15).
fects play a crucial role in the stabilization of 9d. However,
electronic stabilization of the charges is not less important.
XRD analysis of decomposition products of carbene complex
9d revealed amongst others the formation of ylide 10
(Scheme 3) and palladium phosphine complexes. Compound
performed using the B3LYP functional[20] together with the 6-
31g (H), 6-311g(d) (C,P,S,Si), and LanL2TZ(f) basis set[21] for Pd
with the corresponding effective core potential (for further
functionals and basis sets tested, see the Supporting Informa-
tion). At first, energy optimizations were performed on the real
systems with the SiMe3 and the SiPh3 substituent to evaluate
the thermodynamics of the products. Besides thioketone 8d
and carbene complex 9d three further isomers were consid-
ered (the SiPh3-substituted systems are depicted in Figure 8).
These include: 1) the cis-isomer 9d’ with the PPh3 ligand cis to
the carbene ligand, 2) the dimeric species 9d2, and 3) the bis-
(triphenylphosphine)-substituted derivative 9d–PPh3. The cal-
culations revealed that thioketone 8d is the thermodynamical-
ly most stable compound favored by 16.3 kJmolÀ1 over the
carbene complex 9d. Isomer 9d’ with the triphenyl phosphine
ligand in cis-position to the carbene ligand was found to be
Scheme 3. Formation of ylide 10 by elimination of Pd metal from carbene
complex 9d.
10 is formally formed by elimination of palladium metal from
the carbene complex 9d under additional CÀP bond forma-
tion. The molecular structure of ylide 10 is shown in Figure 7.
Ylide 10 crystallizes in the monoclinic space group P21/c. The
PÀC bond lengths of the central carbon atom C13 (1.741(3)
and 1.769(3) ꢂ) are shorter than typical PÀC single bonds, such
as those found in 5b and 5c (1.803(2) and 1.8045(15) ꢂ). This
accounts for the additional electrostatic interactions within the
S-P-C-P framework. Because P1 interacts with both negatively
charged centers (S and C13), the P–C distance to the thiophos-
phoryl moiety is longer than the one to the triphenylphospine
unit. Accordingly, the PÀS bond in 10 is slightly lengthened
compared to 5b and 5c. Scheme 3 depicts the most important
resonance structure of ylide 10.
Computational studies
To better understand the observed reactivity we performed de-
tailed computational studies on both, the observed thioketone
complexes as well as the carbene analogues. Calculations were
Figure 8. Possible isomers of complex 9d and their relative energies com-
pared to thioketone 8d (values in brackets correspond to the energies of
the SiMe3-substituted systems 8a and 9a).
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44.4 kJmolÀ1 higher in energy, thus being clearly disfavored
compared to the trans-isomer 9d. This is in line with the small
3JPP coupling constants found for all carbene complexes 9b–d,
which are comparable to the one reported for the known car-
bene complex 2. The Pd carbene complex 9d–PPh3 proved to
be no minimum on the energy surface. Optimization always re-
sulted in the loss of one phosphine ligand due to spatial over-
load. The same holds true for a dimeric structure 9d2, which
also turned out to be instable. A different picture is obtained
for the sterically less demanding trimethylsilyl systems 8a and
9a (Figure 8, energies are given in parentheses). Here, the bis(-
triphenylphosphine)-substituted derivative 9a–PPh3 is revealed
to be a minimum on the potential-energy surface; however, it
is clearly disfavored compared to the thioketone (DE=
141.5 kJmolÀ1). A clear preference of the thioketone 8a is also
observed in comparison to the carbene complexes 9a and 9a’,
which are disfavored by 74.6 and 93.0 kJmolÀ1, respectively.
Overall, thermodynamics favors the formation of the thioke-
tone complex, both in the case of the SiMe3 and the SiPh3 sys-
tems. However, this preference is by far less pronounced for
the bulkier SiPh3 systems. The calculations are well in line with
the experimental observations and thus explain the increasing
formation of the carbene complex with decreasing preference
of the thioketone. The stabilization is probably due to a combi-
nation of electronic and steric effects.
temperature. It is also noteworthy, that neither the carbene
nor the thioketone complex is accessible from the dimeric
product 11 of the carbenoid decomposition. Treatment of 11
with [Pd(PPh3)4] at À788C or room temperature always result-
ed in the formation of complex product mixtures.
As there is no pathway leading directly from the carbene to
the thioketone a different mechanism has to be active. Consid-
ering possible reactive sides (Figure 10) of the starting Li/Cl
Figure 10. Possible reaction pathways of the reaction of Li/Cl carbenoids
with a Pd0 species.
carbenoid three different mechanisms for the reaction of the
carbenoid with the Pd0 species have to be taken into account:
1) substitution reaction by nucleophilic attack of the carbenoid
carbon at the Pd species; 2) oxidative addition of the Pd spe-
cies into the carbon chlorine bond; 3) elimination of lithium
chloride under formation of a free carbene intermediate, which
subsequently binds to the palladium precursor. These path-
ways were studied by computational methods using a mono-
meric carbenoid as model system. The coordination sphere of
the lithium atom was completed by dimethyl ether ligands.
Due to computational costs, the trimethylsilyl compound to-
gether with PH3 as model for PPh3 was used. The calculations
show that the elimination mechanism possesses the highest
reaction barrier (DE° =129.2 kJmolÀ1), thus excluding the via-
bility of the reaction at low reaction temperatures. The same
holds true for the oxidative addition with a barrier of
103.4 kJmolÀ1 (see the Supporting Information). To experimen-
tally exclude the viability of an oxidative addition into the CÀ
Cl bond under mild reaction conditions we treated the chlori-
nated compound 6d with [Pd(PPh3)4] in THF. NMR spectroscop-
ic monitoring revealed no reaction even after 24 h at room
temperature. This leaves—in accordance with the studies by
Le Foch and co-workers on complex 2—the substitution pro-
cess as the most feasible pathway.
Next, we turned our attention towards possible mechanistic
pathways delivering both the thioketone and the carbene
complex. For computational cost we first chose a model
system with PPh3 replaced by PH3 ligands. After our prelimina-
ry investigations on the trimethylsilyl-substituted carbenoid,
we suggested a kind of rearrangement leading directly from
the carbene complex 9a–PPh3 to thioketone 8a.[9] The latter
would be formed selectively due to thermodynamic reasons.
However, calculations show that there is no low-energy path-
way leading directly from the carbene to the thioketone com-
plex. DFT calculations revealed
a
reaction barrier of
123.3 kJmolÀ1, which is too high to explain the formation of
the thioketone also at low reaction temperature (Figure 9).
This is especially true for the SiPh3-substituted system, for
which the corresponding carbene complex 9d–PPh3 was
found to be instable due to spatial overload (Figure 7). The ab-
sence of a low-energy pathway from the carbene to the thio-
ketone and the irreversibility of this mechanism are in accord-
ance with the experimentally observed absence of an intercon-
version between the carbene and thioketone complex at room
The substitution mechanism including the Gibbs free energy
of all intermediates and transition states relative to the mono-
meric carbenoid and [Pd(PPh3)3] is shown in Scheme 4.[22] The
first step involves the nucleophilic attack of the carbenoid
carbon at the Pd0 species (TS-1) in an SN2-type fashion. The re-
action barrier amounts to only DE° =49.0 kJmolÀ1, which is in
line with the viability of the reaction at low reaction tempera-
tures. The formed intermediate Int-1 next undergoes elimina-
tion of lithium chloride via TS-2 to form the carbene inter-
Figure 9. Direct rearrangement of carbene complex 9a–PH3 to thioketone
8a.
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mediate Int-2, which is 85 kJmolÀ1 more stable than the start-
ing reagents. This carbene complex Int-2 turned out to be the
crucial species determining the outcome of the reaction. In the
next step Int-2 can either react to the carbene complex
(path B, Scheme 4) by coordination of the thiophosphoryl
unit—and elimination of a further PH3 ligand—or it can form
and its possible isolation in the experiment. Concerning the
formation of the thioketone versus the carbene complex the
calculations predict a considerable kinetic preference of the
carbene formation. This corroborates with the experimental
observations of the preferred carbene formation at lower reac-
tion temperatures. In the first step carbene complex Int-2 loses
one phosphine ligand to form
Int-2-PPh3. Such two coordinat-
ed Pd complexes are well known
intermediates
in
palladium
chemistry and also isolable de-
pending on the coordinating li-
gands.[23] Int-2-PPh3 subsequent-
ly delivers the carbene complex
via TS-3B with a barrier of only
7.6 kJmolÀ1 or the thioketone
via TS-3A (DG° =62.7 kJmolÀ1).
The difference of 55.1 kJmolÀ1
between both reaction barriers
(TS-3A vs. TS-3B) slightly de-
creases when replacing the
SiMe3 substituent with its phenyl
analogue (DG° =42.2 kJmolÀ1).
Overall, the calculations reflect
well the experimental observa-
tions.
Scheme 4. Nucleophilic substitution mechanism for thioketone and carbene formation [B3LYP/6-311g(d)/
LanL2TZ(f)].
Conclusion
the thioketone complex (path A) by transfer of the sulfur to
the carbene carbon atom. An alternative concerted mechanism
to the thioketone by transfer of the thiophosphoryl sulfur to
the carbenoid carbon and simultaneous LiCl elimination from
Int-1 revealed a considerably higher barrier (123 molÀ1) than
the stepwise pathway via the
We reported on the impact of stabilization effects in silyl-sub-
stituted Li/Cl carbenoids on their reactivity towards Pd0 com-
plexes. An insufficient stabilization of the negative charge at
the carbenic carbon atom results in the transfer of the sulfur
carbene Int-2.
As substituent effects have
proven to crucially influence the
reaction outcome, we investigat-
ed both pathways—paths A and
B—employing the real SiMe3
and SiPh3-substituted systems as
well as PPh3 as the co-ligand. An
energy profile for both systems
is depicted in Figure 11. From
a
thermodynamical point of
view, one clearly recognizes the
increasing stability of the car-
bene complex when replacing
the SiMe3 (red) by the SiPh3 sub-
stituent (black). While in the
former case an energy difference
of 74.6 kJmolÀ1 was observed,
only
16.3 kJmolÀ1 was found for the
SiPh3-substituted thioketone.
This confirms the increased sta-
a
preference
of
Figure 11. Comparison of the formation of carbene complex 9 and thioketone 8 with the SiMe3 and the SiPh3 sub-
stituents (B3LYP//6-31g(d)/6-311g(d)/LanL2TZ(f)); energies are given relative to the respective intermediate car-
bility of the carbene complex bene species Int-2.
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from the thiophosphoryl moiety to the carbenic carbon atom
and thus in the formation of a thioketone complex. However,
with increasing anion-stabilizing ability (via negative hypercon-
jugation effects) and steric demand of the silyl and phosphoryl
moiety, the isolation of a three-coordinate, T-shaped palladium
carbene complex is possible. This formation was also found to
be temperature-dependent. While the thioketones are stable
compounds the carbene complexes revealed to be reactive
and decompose under elimination of Pd metal and formation
of a new CÀP bond. DFT studies—in line with the experimental
observations—show that the thioketone formation is thermo-
dynamically favored, while the carbene complex is the kinetic
product of the reaction. Mechanistic studies showed that there
is no direct pathway leading from the carbene to the thioke-
tone complex. Instead, both complexes are formed by a substi-
tution mechanism. Both, thermodynamics and kinetics are cru-
cially influenced by the nature of the silyl moiety.
General procedure for the precursors 5
Diphenylmethylphosphine sulfide (or dicyclohexylmethylphosphine
sulfide) was dissolved in THF and cooled to À788C. At this temper-
ature 1.2 equivalents of nBuLi (1.65m in hexane) were added and
the resultant yellow mixture stirred for 3 h at low temperature. In
a second Schlenk flask, 1.2 equiv of the corresponding chlorosilane
were dissolved in 30 mL diethyl ether and cooled to À788C. The
lithiated phosphine sulfide was added dropwise by a cannula
transfer and slowly warmed to ambient temperature after comple-
tion of the addition. After stirring for 3 h, hydrochloric acid (2n)
was added and the mixture extracted with diethyl ether. Drying
over sodium sulfate and removal of the solvent afforded a yellowish
solid, which was either washed with a mixture of diethyl ether/
pentane (v/v=1:2) or purified by flash chromatography.
1
Compound 5b: Yield: 68%; H NMR (500.1 MHz, CDCl3): d=0.32 (s,
6H; SiCH3), 2.23 (d, 2JPH =17.2 Hz, 2H; PCH2Si), 7.27–7.32 (m, 3H;
CHSiPh), 7.34–7.47 (m, 8H; CHPh), 7.80–7.86 ppm (m, 6 CHPh,ortho);
13C{1H} NMR (125.8 MHz, CDCl3): d=À1.45 (d, 3JPC =1.5 Hz; SiCH3),
21.1 (d, 1JPC =46.6 Hz; SiCH2P), 127.8 (CHSiPh,ortho), 128.3 (d, JPC
=
2
Overall, these studies show that the substitution pattern of
carbenoids can crucially influence not only the stability of the
carbenoid but also its reactivity and the reaction outcome.
Careful selection of the substituents and their electronic effects
on the carbenic carbon atom should thus allow for a control of
their reactivity and hence allow for novel applications. We are
currently investigating the reactivity of the carbenoids towards
other transition metals.
12.1 Hz; CHortho), 129.2 (CHSiPh,para), 130.6 (d, 3JPC =10.6 Hz; CHmeta),
130.9 (d, 4JPC =3.0 Hz; CHpara), 133.4 (CHSiPh,meta), 135.6 (d, JPC
=
1
80.5 Hz; Cipso), 138.5 ppm (d, 3JPC =6.3 Hz; CSiPh,ipso); 29Si{1H} NMR
(99.4 MHz, CDCl3): d=À4.30 ppm (d, 2JPSi =3.9 Hz); 31P{1H} NMR
(202.5 MHz, CDCl3): d=38.3 ppm; elemental analysis calcd (%) for
C16H21PSSi: C 68.81, H 6.32, S 8.75; found: C 68.84, H 6.53, S 8.82;
M.p. 88.68C; GCMS (EI): tR =16.299; m/z (%): 366 (18) [M+], 351 (56)
[M+ÀMe], 289 (50) [M+ÀPh], 135 (100) [SiMe2Ph+].
Compound 5e: Yield: 63%; 1H NMR (500.1 MHz, CDCl3): d=0.90–
1.10 (m, 6H; CH2,Cy), 1.27–1.31 (m, 4H; CH2,Cy), 1.50–1.58 (m, 4H;
CH2,Cy), 1.68–1.75 (m, 4H; CH2,Cy), 1.81–1.90 (m, 4H; CH2,Cy +CH,Cy),
2.09 (d, 2JPH =14.8 Hz, 2H; PCH2Si), 7.36–7.44 (m, 9H; CHpara,meta),
7.67–7.70 ppm (m, 6H; CHortho); 13C{1H} NMR (125.8 MHz, CDCl3):
d=12.2 (d, 1JPC =38.7 Hz; PCH2Si), 25.7 (d, 4JPC =1.58 Hz; PCH-
(CH2CH2)2CH2), 26.3–26.6 (5ꢃCH2), 39.6 (d, 1JPC =48.1 Hz; PCH),
Experimental Section
General
3
All experiments were carried out under a dry, oxygen-free argon at-
mosphere by using standard Schlenk techniques. Involved solvents
were purified and dried by distillation over sodium, molten potassi-
um and sodium/potassium alloy, respectively, and were stored over
activated 4 ꢂ molecular sieves. C6D6 and CD2Cl2 was degassed by
three freeze-pump-thaw cycles and stored over activated 4 ꢂ mo-
lecular sieves. H2O is distilled water. Organolithium reagents were
titrated against diphenylacetic acid prior use. 1H, 13C{1H}, 29Si{1H},
and 31P{1H} NMR spectra were recorded on a Bruker Avance AV 500
or a Bruker Avance AV 400 spectrometers at 228C. All values of the
chemical shift are in ppm regarding the d-scale. 1H and
13C{1H} NMR spectra were referenced to external tetramethylsilane
by the residual solvent peak (1H NMR spectra) or the solvent itself
(13C NMR spectra). 31P{1H} NMR spectra were referenced to external
85% H3PO4, 29Si{1H} NMR to TMS. All spin-spin coupling constants
(J) are printed in Hertz (Hz). To display multiplicities and signal
forms correctly the following abbreviations were used: s=singulet,
d=doublet, t=triplet, m=multiplet, br=broad signal. Signal as-
signment was supported by DEPT and HMQC experiments. Elemen-
tal analyses were performed on an Elementar vario MICRO-cube el-
emental analyzer. High-resolution mass spectra (ESI) were recorded
on an ESI MicrOTOF Focus spectrometer from Bruker Daltonics.
Ph2MePS, Cy2MePS, and [Pd(PPh3)2][14] were synthesized according
literature procedures. Compounds 5a, 5c, 5d, and their chlorinat-
ed analogues have been reported previously. All other reagents
were purchased from Sigma–Aldrich, ABCR, Rockwood Lithium or
Acros Organics and used without further purification. For 1H and
31P{1H} NMR spectra of all complexes, see the Supporting Informa-
tion.
127.8 (CHSiPh,meta), 129.7 (CHSiPh,para), 134.2 (d, JPC =2.39 Hz; CHSiPh,ipso),
136.2 ppm (CHSiPh,ortho); 29Si{1H} NMR (99.4 MHz, CDCl3): d=
À14.8 ppm (d, 2JPSi =5.66 Hz); 31P{1H} NMR (202.5 MHz, C6D6): d=
57.1 ppm; elemental analysis calcd (%) for C31H39PSS: C 74.06, H
7.82, S 6.38; found: C 74.48, H 7.92, S 6.09.
Preparation of 6b
Phosphine sulfide (1.36 mmol, 500 mg) was dissolved in THF
(10 mL) and cooled to À788C. n-Butyllithium (1.0 mL, 1.60 mmol;
1.55m in hexane) was added and the yellow solution was stirred
for 3 h at temperatures below À308C. In a second Schlenk flask,
hexachloroethane (379 mg, 1.60 mmol) was dissolved in diethyl
ether and cooled to À788C. The lithiated phosphine sulfide was
slowly added by cannula transfer and after complete addition
warmed to room temperature. The yellow mixture was stirred for
4 h at room temperature and then quenched by addition of 20 mL
water. Extraction with diethyl ether (3ꢃ60 mL), drying over sodium
sulfate, and removal of the solvent afforded a yellow solid. The
solid was purified by flash chromatography on silica gel (pentane/
diethyl ether=2:1) giving the product (racemic mixture) as color-
less crystalline solid (425 mg, 1.06 mmol, 78%). 1H NMR
(500.1 MHz, CDCl3): d=0.406+0.408 (s, 3H each; SiCH3), 4.31 (d,
2JPH =11.4 Hz, 1H; PCH2Si), 7.22–7.25 (m, 2H; CHSiPh,meta), 7.31–7.44
(m, 6H; CHPPh), 7.45–7.47 (m, 2H; CHSiPh,ortho), 7.48–7.52 (m, 1H;
CHSiPh,para), 7.71–7.77 (m, 2H; CHPPh,ortho), 7.99–8.04 ppm (m,
2CHPPh,ortho); 13C{1H} NMR (125.8 MHz, CDCl3): d=À2.37+À0.65
1
(SiCH3), 44.5 (d, JCP =37.1 Hz; SiCHClP), 127.8 (CHSiPh,meta), 129.1 (d,
2JPC =12.4 Hz; CHmeta), 129.5 (d, 2JCP =12.3 Hz; CHmeta), 130.6
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(CHSiPh,para), 130.7 (d, 1JPC =82.3 Hz; Cipso), 132.2 (d, 3JCP =10.0 Hz;
CHortho), 132.4 (d, JPC =3.0 Hz; CHpara), 132.8 (d, JPC =3.0 Hz; CHpara),
Preparation of the 8c and 9c
4
4
Analogous procedure as for 8b and 9b. Separation of both com-
plexes by washing with diethyl ether. Purification by washing with
toluene/hexane (v/v=1:4) to remove the remaining triphenylphos-
phine.
Compound 8c: yield: 56%; 1H NMR (400.1 MHz, C6D6): d=0.35 (d,
3JPH =1.92 Hz, 3H; SiCH3), 6.85–7.08 (m, 30H; CHPPh,meta,para), 7.09–
7.14 (m, 6H; CHPPh3,ortho), 7.32–7.38 (m, 6H; CHPPh3,ortho), 7.58–7.64 (m
3
1
133.7 (d, JPC =10.0 Hz; CHortho), 134.2 (d, JPC =82.8 Hz; Cipso), 135.2
(CHSiPh,ortho), 136.6 ppm (d, 3JPC =4.3 Hz;
C
SiPh,ipso); 29Si{1H} NMR
(99.4 MHz, CDCl3): d=0.66 ppm (d, 2JPSi =1.6 Hz); 31P{1H} NMR
(202.5 MHz, CDCl3): d=45.9 ppm; elemental analysis calcd (%) for
C16H21PSSi: C 62.90, H 5.53, S 8.00; found: C 62.57, H 5.47, S 8.21.
3
2H; CHPPh,ortho), 7.78–7.83 (m, 2H; CHPPh,ortho), 7.89 (dd, JHH =7.43 Hz,
Preparation of 6e
4JHH =1.43 Hz, 2H; CHSiPh,ortho), 7.93 (dd, 3JHH =7.60, 4JHH =1.40 Hz,
Analogous procedure as for 6b. Yield: 51%; RF =0.72; 1H NMR
(300.1 MHz, CDCl3): d=0.55–0.78 (m, 2H; CH2,PCy), 0.89–1.03 (m,
2H; CH2,PCy), 1.16–1.32 (m, 3H; CH2, PCy), 1.48–1.92 (m, 13H;
CH2,PCy), 2.14–18 (m, 1H; CHPCy), 2.26–2.39 (m, 1H; CHPCy), 4.57
(d, 2JHP=12.6 Hz, 1H; CHCl), 7.34–7.43 (m, 9H; CHPPh,meta/para),
2H; CHSiPh,ortho). 13C{1H} NMR (100.6 MHz, CD2Cl2): d=À3.16 (d, JPC
=
3
3
8.72 Hz; SiCH3), 127.2 (CHSiPh,meta), 127.48 (d, JPC =7.4 Hz; CHPPh2,meta),
127.50 (CHSiPh,meta), 127.6 (d, 3JPC =7.40 Hz; CHPPh2,meta), 128.1 (d,
3JPC =9.63 Hz; CHPPh3,meta), 128.1 (CHSiPh,para), 128.2 (d, 2JPC =9.29 Hz;
CHPPh3,meta), 128.5 (CHSiPh,para), 129.5 (d, 4JPC =1.87 Hz; CHPPh3,para),
130.0 (d, 4JPC =1.93 Hz; CHPPh3,para), 134.2 (d, 2JPC =19.1 Hz; CH
7.79–7.81 (m, 6H; CHPPh,ortho); 13C{1H} NMR: (75.5 MHz, CDCl3): d=
1
2
1
24.8–29 (m; CH2, PCy), 35.5 (d, 1JPC =46.1 Hz; PCH), 37.5 (d, JPC
=
PPh2,ortho), 134.4 (d, JPC =16.2 Hz; CHPPh3,ortho),134.7 (dd, JPC =31.3 Hz,
4JPC =0.90 Hz; CPPh3,ipso), 134.8 (d, 2JPC =22.0 Hz; CHPPh2,ortho), 135.1
(CHSiPh,ortho), 135.4 (d, 1JPC =31.6, 4JPC =2.29 Hz; CPPh3,ipso), 135.6 (dd,
2JPC =13.8, 4JCP =2.77 Hz; CHPPh3,ortho), 136.2 (CHSiPh,ortho), 135.3 (dd,
1
45.5 Hz; PCH), 39.2 (d, JPC =28.0 Hz; PCCl), 127.7 (CHPPh,meta), 129.9
(CHPPh,para), 132.8 (d, 3JPC =1.38 Hz; CPPh,ipso), 136.8 ppm (CHPPh,ortho);
29Si{1H} NMR:
(121.4 MHz, CDCl3): d=64.3 ppm.
(59.6 MHz,
CDCl3):
d=À13.5;
31P{1H} NMR:
1JPC =31.9, 3JPC =2.3 Hz; Cipso
,
PPh3), 137.3 (d, 2JPC =21.7 Hz;
CHPPh2,ortho), 141.1 ppm (m; SiCPPh2); 29Si{1H} NMR (99.4 MHz, CDCl3):
d=À16.0 (br); 31P{1H} NMR (162.0 MHz, C6D6): d=10.0 (dd, JPP
=
3
3
28.8, JPP =25.2 Hz; PPh2), 20.3 (vt, 2/3JPP =29.3; PPh3), 24.4 ppm (dd,
Preparation of the palladium complexes 8b and 9b
3
2JPP =29.4, JPP =25.1 Hz; PPh3).
The chlorinated phosphine sulfide 6b (80 mg, 0.20 mmol) was dis-
solved in THF (6 mL) and cooled to À788C. Methyllithium (0.15 mL,
0.20 mmol; 1.31m in diethyl ether) was added by syringe, upon
which the reaction mixture instantly turned yellow. The mixture
was stirred for 2 h at temperatures below À508C to prevent de-
composition of the in situ formed carbenoid. The mixture was then
added by a cannula transfer to a solution of [Pd(PPh3)4] (218 mg,
0.19 mmol) in THF (8 mL), upon which the color changed from
yellow to orange. After stirring overnight the solvent was removed
in vacuo and the orange solid taken up in dichloromethane. The
mixture was filtered from the lithium chloride and again taken to
dryness. The remaining solid was washed three times with diethyl
ether/hexane (10 mL, v/v=1:2) to remove the triphenylphosphine
giving the product as bright yellow solid (115 mg, 0.12 mmol;
64%). Single crystals of 8b were grown by slow concentration of
a solution of 9b in dichloromethane.
Compound 9c: This compound was not isolated; 31P{1H} NMR
(162.0 MHz, CD2Cl2): d=23.0 (d, 3JPP =15.0 Hz; PPh3), 45.8 ppm (d,
3JPP =15.0 Hz; SPPh2).
Preparation of 8d and 9d
Analogous procedure as for 8b and 9b. Separation of both com-
plexes by washing with diethyl ether. The solution of the more
soluble carbene complex was transferred to a second Schlenk tube
and taken to dryness. The thioketone complex was further washed
with diethyl ether and the carbene complex with pentane to
remove the remaining triphenylphosphine.
Compound 8d: Orange solid, 62% from the reaction at room tem-
perature (entry 6, Table 1); 1H NMR (500.1 MHz, CD2Cl2): d=6.53–
6.57 (m, 6H; CHPPh3,meta), 6.77–6.81 (m, 6H; CHPPh3,meta), 6.95–7.05 (m,
6H; CHPPh3,para), 6.92–6.97 (m, 6H; CHPPh3,ortho), 7.06–7.10 (m, 6H;
Compound 8b: 1H NMR (500.1 MHz, CD2Cl2): d=À0.19+0.03 (s,
6H; SiCH3), 6.74–6.78 (m, 6H; CHortho,PPh3), 7.06–7.32 (m, 37H; CHPh),
7.60–7.64 ppm (m, 2H; CHortho,PPh2); 13C{1H} NMR (125.8 MHz,
CD2Cl2): d=0.64 (d, 3JPC =4.40 Hz; SiCH3), 0.64 (d, 3JPC =6.87 Hz;
3
CHPPh3,ortho), 7.15 (vt, JHH =7.70 Hz, 6H; CHSiPh,meta), 7.23–7.36 (m, 8H;
3
3
CHPPh2), 7.31 (t, JHH =7.41 Hz, 3H; CHSiPh,para), 7.55 (dd, JHH =8.10 Hz,
4JHH =1.35 Hz, 6H; CHSiPh,ortho), 7.55–7.60 ppm (m, 2H; CHPPh,ortho);
13C{1H} NMR (125.8 MHz, CDCl3): d=127.45 (CHSiPh,meta), 127.46 (d,
3JPC =7.65 Hz; CHPPh2,meta), 127.5 (d, 3JPC =8.05 Hz; CHPPh2,meta), 118.0
(CHPPh2,para), 128.3 (d, 3JPC =9.25 Hz; CHPPh3,meta), 128.9 (CHSiPh,para),
129.6 (d, 4JPC =1.83 Hz; CHPPh3,para), 130.0 (d, 4JPC =1.84 Hz;
CHPPh3,para), 134.50 (dd, 1JPC =34.0, 4JPC =2.49 Hz; CHPPh3,ipso), 134.50
SiCH3), 127.1 (CHSiPh,meta), 127.5 (d, 2JPC =6.15 Hz; CHPPh2,meta), 127.8
2
(CHSiPh,para), 127.9 (d, 2JPC =7.19 Hz; CHPPh2,meta), 128.1 (d, JPC
=
6.22 Hz; CHPPh3,meta), 128.2 (d, 2JCP =5.90 Hz; CHPPh3,meta), 128.5+
4
4
128.9 (CHPPh2,para), 129.6 (d, JPC =1.77 Hz; CHPPh3,para), 130.1 (d, JPC
=
1.78 Hz; CHPPh3,para), 134.5 (d, 2JPC =13.2 Hz; CHPPh3,ortho),134.7 (d,
1JPC =31.5, JPC =1.0 Hz; CPPh3,ipso), 134.9 (d, JPC =13.5 Hz; CHPPh2,ortho),
135.28 (d, JPC =2.35 Hz; CSiPh,ipso), 135.3 (CHSiPh,ortho), 135.5 (dd, JPC
13.8 Hz; 4JPC =3.0 Hz; CHPPh3,ortho), 135.5 (CPPh3,ipso), 136.9 (d, JPC
3
3
3
2
(dd, 1JPC =31.6, 4JPC =0.85 Hz; CHPPh3,ipso), 134.51 (d, 3JPC =12.6 Hz;
=
=
2
2
CHPPh3,ortho), 134.53 (d, 2JPC =22.7 Hz; CHPPh2,ortho), 135.3 (dd, JPC
=
1
13.4, 5JPC =1.72 Hz; CHPPh3,ortho), 137.2 (d, 2JPC =23.0 Hz; CHPPh2,ortho),
137.8–138.0 (m; CHSiPh,ipso), 137.9 (d, 4JPC =1.56 Hz; CHSiPh,ortho),
139.9 ppm (ddd, 1JPC =22.4, 2JPC =15.7, 2JCP =5.18 Hz; CS), PPh2,ipso
19.7 Hz; CHPPh2,ortho), 141.2 ppm (d, JPC =20.8 Hz; SiCPPh2); PPh2,ipso
hidden 29Si{1H} NMR (79.5 MHz, CD2Cl2): d=À11.0 ppm (dd, JPSi
=
2
36.9, 3JPsi =5.87 Hz); 31P{1H} NMR (162.0 MHz, C6D6): d=9.51 (dd,
3JPP =23.9, 3JPP =25.6 Hz; PPh2), 20.6 (dd, 2JPP =29.1, 3JPP =25.7 Hz;
PPh3), 24.4 ppm (dd, 2JPP =29.1, 3JPP =23.9 Hz; PPh3); elemental
analysis calcd (%) for C57H51P3SSiPd: C 68.77, H 5.16, S 3.22; found:
C 66.91, H 5.14, S 2.99.
hidden; 29Si{1H} NMR (99.4 MHz, CDCl3): d=À20.7 (dd, 2JSiP =38.7,
3
3JSiP =7.66 Hz); 31P{1H} NMR (162.0 MHz, C6D6): d=À0.25 (vt, JPP
=
20.4 Hz; PPh2), 22.2 (dd, 2JPP =27.8, 3JPP =19.9 Hz; PPh3), 24.7 (dd,
2JPP =27.7, 3JPP =21.3 Hz; PPh3); elemental analysis calcd (%) for
C67H55P3SSiPd: C 71.87, H 4.95, S 2.86; found: C 61.30, H 5.18, S
2.59; HRMS (ESI): elemental analysis calcd (%) for C67H56P3SSiPd:
1119.2135; found: 1119.2141.
Compound 9b: This compound was not isolated. 31P{1H} NMR
(162.0 MHz, C6D6): d=22.6 (d, 3JPP =14.8 Hz; PPh3), 46.4 ppm (d,
3
2JPP =29.1, JPP =14.8 Hz; P(S)Ph2).
Chem. Eur. J. 2014, 20, 1 – 12
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9
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Full Paper
Compound 9d: Yellow solid, 15% yield from the reaction at À788C
tion of exponent 1.472.[26] Transition states were located either by
using the qst3 method or via freezing of the respective coordi-
nates (opt=modred) and subsequent optimization on the ob-
tained imaginary frequency. The vibrational frequency analyses
showed no imaginary frequencies for the ground states and
a single imaginary frequency for the transition states. NBO analyses
were carried out on the optimized systems using the NBO 5.G pro-
gram,[27] interfaced to the Gaussian 03 program. More detailed in-
formation concerning the calculations, including Cartesian coordi-
nates of the optimized geometries and comparison of different
methods, can be found in the Supporting Information.
1
(entry 8, Table 1); H NMR (400.1 MHz, C6D6): d=6.71–6.76 (m, 6H;
CHSiPh,meta), 6.82–7.04 (m, 18H; CHPh), 7.82–7.84 (m, 6H; CHSiPh,ortho),
7.91–7.97 (m, 6H; CHPdPPh,ortho), 8.25–8.30 ppm (m, 4H; CHPPh,ortho);
13C{1H} NMR (125.8 MHz, CD2Cl2): d=126.9 (CHSiPh,meta), 127.1 (d,
3
3JPC =12.1 Hz; CHPPh,meta), 127.7 (d, JCP =12.1 Hz; CHPdPPh,meta), 128.2
(CHSiPh,para), 129.3 (d, 4JPC =2.9 Hz; CHPPh,para), 129.8 (dd, 1JPC =88.5,
3
4JPC =3.0 Hz; CHPdPPh,ipso), 131.5 (d, JPC =2.9 Hz; CHPdPPh,para), 133.2 (d,
2
2JPC =10.2 Hz; CHPPh,ortho), 135.6 (d, JPC =12.1 Hz; CHPdPPh,ortho), 137.5
(CHSiPh,ortho), 139.0 ppm (m, CHSiPh,ipso), CHPPh,ipso and PCSi hidden;
29Si{1H} NMR: (99.4 MHz, CD2Cl2): d=À16.3 (br); 31P{1H} NMR
(202.5 MHz, CD2Cl2): d=23.7 (d, 3JPP =16.4 Hz; PPh3), 46.1 ppm (d,
3JPP =16.4 Hz; SPPh2); HRMS (ESI): elemental analysis calcd (%) for
C49H41P2SSiPd: 857.1219; found: 857.1212.
Acknowledgements
Preparation of 8e
This work was financially supported by the Deutsche For-
schungsgemeinschaft(Emmy-Noether program), the Fonds der
Chemischen Industrieand the Alexander von Humboldt Foun-
dation. We also thank Rockwood Lithium GmbH for the supply
of chemicals.
Analogous procedure as for 8b. Purification by washing with pen-
tane. Orange solid; yield: 53%; 1H NMR: (500.1 MHz, C6D6): d=
0.45–0.55 (m, 1H; PCy), 0.65–0.75 (m, 1H; PCy), 0.95–1.85 (m, 14H;
PCy), 2.05–2.15 (m, 1H; PCy), 2.25–2.6 (m, 5H; PCy), 6.78–6.83 (m,
6H; PPh3,para), 6.9–7.1 (m, 28H; CHarom), 7.12–7.18 (m, 2H; CHarom),
2
7.18–7.22 (m, 3H; CHSiPh), 8.05 ppm (m, JPH =8.1 Hz, 6H; CHPPh,ipso);
Keywords: carbene complexes
·
carbenoids
·
density
13C{1H} NMR: (125.8 MHz, C6D6): d=25.9 (s; PCHCH2CH2CH), 23.3 (d,
3JPC =14.6 Hz; PCHCH2CH2), 27.4 (d, 4JPC =2.3 Hz; PCHCH2CH2CH),
28.2 (2d, 3JPC =13.4/6.0 Hz; PCHCH2CH2), 29.3 (d, 2JPC =14.5 Hz;
functional calculations · lithium · substituent effect
2
2
4
PCHCH2), 31.1 (d, JPC =10.0 Hz; PCHCH2), 33.1 (dd, JPC =21.9, JPC
=
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2.0 Hz; PCH), 34.2 (d, JPC =19.3 Hz; PCHCH2), 38.2 (m; PCH), 128.5–
128.9 (m, 21C; Carom, overlying signals), 129.6 (dd, JCP =27.4, JPC
1.5 Hz; PPh3,meta), 134.7 (d, JPC =12.7 Hz; PPh3,ortho), 135.0 (dd, JCP
3
5
=
=
2
1
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32.0, 3JPC =2.4 Hz; PPh3,ipso), 135.1 (dd, 2JPC =12.3, 4JPC =1. Hz;
PPh3,ortho), 135.2 (dd, 1JPC =30.0 Hz; PPh3,ipso), 138.2 (m; SiPh3,ortho),
139.1 (m; SiPh3,ipso); 29Si{1H} NMR: (99.3 MHz, C6D6): d=21.39 (dd,
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3
3
2
3
(dd, JPP =20.2, JPP =8.1 Hz; PCy2), 22.1 (dd, JPP =27.4, JPP =8.2 Hz;
2
3
PdPPh3), 23.0 (dd, JPP =25.4, JPP =20.6 Hz; PPh3).
X-ray crystallography
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The crystal data of all compounds were collected on a Bruker
SMART-APEX diffractometer with a CCD area detector and multilay-
er mirror monochromated MoKa radiation. Crystals were mounted
in an inert oil (perfluoropolyalkylether). Crystal structure determina-
tions were effected at À1008C. The structures were solved using
direct methods, refined with the Shelx software package and ex-
panded using Fourier techniques. All non-hydrogen atoms were re-
fined anisotropically. All hydrogen atoms were assigned to ideal-
ized geometric positions and included in structure factors calcula-
tions. Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication:
CCDC-976964 (5b), -976965 (5c), -976966 (5e), -976967 (8b),
-976969 (8d), and -976968 (10) contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
Computational details
All calculations were performed with the Gaussian 03 (Rev. E.01)
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31g(d) basis set was used for hydrogen, the 6-311g(d) for all other
nonmetal elements. For palladium the LanL2TZ(f)[21] ECP/basis set
of triple-z quality was used augmented with an f polarization func-
&
&
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ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
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Received: December 17, 2013
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Published online on && &&, 0000
Chem. Eur. J. 2014, 20, 1 – 12
www.chemeurj.org
11
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
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Carbene Complexes
S. Molitor, K.-S. Feichtner, C. Kupper,
V. H. Gessner*
&& – &&
Complex chemistry! The reactivity of
Li/Cl carbenoids towards Pd0 precursors
has been studied. While steric and elec-
tronic stabilization allow the isolation of
a three-coordinate, T-shaped carbene
complex, insufficient charge stabilization
results in the transfer of the sulfur and
the formation of a thioketone complex
(see scheme). DFT studies show that
both complexes are formed by a substi-
tution mechanism.
Substitution Effects on the Formation
of T-Shaped Palladium Carbene and
Thioketone Complexes from Li/Cl
Carbenoids
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Chem. Eur. J. 2014, 20, 1 – 12
www.chemeurj.org
12
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!