Synthesis and electronic structure of carbene complexes based on a sulfonyl-substituted dilithio methandiide

Article abstract of DOI:10.1021/om5001277

The application of a sulfonyl-substituted dilithio methandiide in the synthesis of carbene complexes was examined. In all cases, the metal carbon interaction was found to be highly polar with only small π-contribution. Hence, the stability of these complexes was found to greatly rely on the coordination ability of the side-arms supporting the metal carbon interaction. As such, the sulfonyl moiety allowed the isolation of a carbene complex with the oxophilic zirconium, which is the first of its kind bearing no (bis)phosphonium ligand framework. On the contrary, complexes with the late transition metals ruthenium and palladium were found to be more labile due to the facile decoordination of the sulfonyl moiety. This results in the opening of a reactive coordination site at the metal center and hence in further reactions such as cyclometalation or sulfur transfer from the thiophosphoryl moiety to the carbenic carbon atom.

Full text of DOI:10.1021/om5001277

Article
pubs.acs.org/Organometallics
Synthesis and Electronic Structure of Carbene Complexes Based on a
Sulfonyl-Substituted Dilithio Methandiide
Julia Becker and Viktoria H. Gessner*
Institut fur Anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, 97074 Wurzburg, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: The application of a sulfonyl-substituted dilithio methandiide in the synthesis of carbene complexes was
examined. In all cases, the metal carbon interaction was found to be highly polar with only small π-contribution. Hence, the
stability of these complexes was found to greatly rely on the coordination ability of the side-arms supporting the metal carbon
interaction. As such, the sulfonyl moiety allowed the isolation of a carbene complex with the oxophilic zirconium, which is the
first of its kind bearing no (bis)phosphonium ligand framework. On the contrary, complexes with the late transition metals
ruthenium and palladium were found to be more labile due to the facile decoordination of the sulfonyl moiety. This results in the
opening of a reactive coordination site at the metal center and hence in further reactions such as cyclometalation or sulfur
transfer from the thiophosphoryl moiety to the carbenic carbon atom.
INTRODUCTION
■
Transition metal complexes with a metal carbon double bond
have found wide-ranging applications in various catalytic and
stoichiometric transformations.1 The reactivity of these
compounds was found to be strongly influenced by the
substituents bound to the carbenic carbon atom, thus leading to
their classification as Fischer-type carbene and Schrock-type
alkylidene complexes.2 However, in recent years carbene
complexes derived from geminal dilithiated compounds have
gained special interest, as they seem to contradict this general
classification pattern.3 Here, the metal carbon bond is formally
formed by a four-electron donation from the ligand to the
metal.4 Yet, the bonding situation in these systems was found to
vary strongly depending on the nature of the metal and its
coligands. Thus, the metal carbon interaction in these
complexes covers a range of bonding situations, starting from
a kind of masked methandiide with mainly electrostatic M2+···
C2− interactions (A), to ylidic complexes with a carbanionic
ligand, M+−C− (B), and complexes with a real MC double
bond (C) (Figure 1).5 These flexible bonding properties
allowed the isolation of a series of carbene complexes
incorporating early and late transition metals, but also
lanthanides and actinides.6
Figure 1. Bonding situations in carbene complexes based on dilithio
methandiides.
(thiophosphoryl) and bis(iminophosphoryl) methandiides,
have been the only dianionic ligand systems applied in this
carbene chemistry. Supported by the pincer-type coordination
mode, these methandiides allowed the isolation of quite
unusual carbene-like complexes with metals in various oxidation
states as reported by the groups of Cavell, Liddle, Le Floch,
́
Mezailles, Harder, and others. Among others are the first
cerium(IV)−carbon multiple bond,8 uranium-carbene com-
plexes with various oxidation states of the metal center,9 main
group metal carbene-like complexes,10 or nucleophilic carbene
complexes with late transition metals.11
In order to explore the generality of this carbene chemistry
and an extension to other methandiide ligands in order to study
the influence of the substituents at the central carbon atom on
the nature of the metal carbon bond, our group has aimed at
the development of novel dilithio methandiides.12 Recently, we
However, systematic studies on the bonding situation are
strongly restricted, due to the limited number of dianionic
starting compounds.7 In particular, the impact of the α-
substituents at the carbenic carbon atom on the metal carbon
bond and the complex stability is virtually unexplored. So far,
bis(phosphonium)-stabilized dianions, above all bis-
Received: February 4, 2014
Published: February 25, 2014
© 2014 American Chemical Society
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reported on the clean and high-yielding dilithiation of the
sulfonyl-substituted precursor 1. The stabilized methandiide 1-
Li2 was found to exhibit unique structural and electronic
properties reflecting the strong anion-stabilizing ability of both
the thiophosphoryl and the sulfonyl substituent.13 Thus, this
dianion seemed to be an ideal candidate for the transfer to
transition metals. We were particularly interested in whether
the sulfonyl substituent would change the properties of the
metal carbon bond and whether the different coordination
ability of the sulfonyl moiety would also influence the reactivity
of the metal complexes. Here, we report the synthesis of
transition metal carbene complexes and how the sulfonyl
substituent influences the ligand metal interaction and the
complex stability.
RESULTS
Figure 2. (Left) Molecular structure of complex 2. Ellipsoids are
drawn at the 50% probability level. Hydrogen atoms and solvent
molecule are omitted for clarity. Selected bond lengths [Å] and angles
[deg]: Zr−C13 2.2419(18), Zr−O2 2.3019(14), Zr−S1 2.7609(5),
S2−O1 1.4507(14), S2−O2 1.5128(14), S2−C13 1.609(2), S2−C14
1.780(2), S1−P 2.0226(7), P−C13 1.673(2), P−C7 1.8169(19), P−
C1 1.818(2); S2−C13−P 149.66(12), S2−C13−Zr 97.77(9), P−
C13−Zr 108.48(9). (Right) Extract of the molecular structure
showing the geometry of the carbene carbon atom.
■
Synthesis and Stability of the Carbene Complexes. In
order to compare the bonding properties of our new ligand
systems, we first aimed at the synthesis of complexes
comparable to compounds with the related bis(thiophosphoryl)
methandiide ligand. Thereby, we chose zirconium as early and
ruthenium and palladium as late transition metals. The
synthesis of the zirconium carbene complex was accomplished
by treatment of dianion 1-Li2 with an equivalent amount of
zirconocene dichloride in toluene. For an improved synthetic
procedure for dianion 1-Li2 from 1 see the Supporting
Information (SI). 31P{1H} NMR spectroscopy of the crude
product revealed quantitative formation of a single new species
with upfield shifted resonance (δP = 17.6 ppm) compared to
the starting compound (δP = 26.2 ppm). After removal of the
formed lithium chloride the product was isolated as a yellow
solid in 63% yield. 2 represents the first example of a carbene
complex derived from a methandiide ligand with a substituent
other than a phosphonium group. 2 was characterized by
multinuclear NMR spectroscopy and elemental and single-
crystal X-ray diffraction analysis. The 13C{1H} NMR resonance
of the carbene carbon atom appears as a doublet at 41.0 ppm
carbene complexes based on bis(phosphonium) methandiides
(e.g., 2.251 Å for LZrCp2 or 2.172 Å for LZrCl2Py2 with L =
C[P(S)Ph2]2),14 but slightly shorter than those found in NHC
complexes (2.35−2.47 Å)15 and longer than those in alkylidene
complexes (2.00−2.10 Å).16 The most remarkable feature of
the molecular structure of 2, however, concerns the geometry
of the carbene moiety. 2 features a tilt between the planes of
the P−C13−S2 and the C−Zr−S1−O2 moiety by 29.8(2)°
[dihedral P−C13−S−Zr: 25.1(1)°] and thus a slightly
pyramidalized carbon atom. Similar distortions have been
reported for some of the bis(phosphonium)-substituted
complexes.17 It is also interesting to note that the C−P
(1.673(2) Å) and C−S (1.609(2) Å) distances in the
zirconocene complex are shorter than those found for dilithio
methandiide 1-Li2 and thus shortened by approximately 10%
compared to the neutral ligand 1.13 This shortening is the result
of electrostatic interactions within the P−C−S backbone and
thus indicative for a still present charge accumulation at the
central carbon atom. This is in line with the 13C{1H} NMR
signal of the carbenic carbon atom observed at remarkable high
field. Analogously, due to negative hyperconjugation effects,
bond lengthening is observed for all other bonds to phosphorus
and sulfur (S2), respectively.
1
with a coupling constant of JPC = 107.6 Hz. This resonance is
slightly downfield shifted compared with the bis-
(thiophosphoryl)-substituted analogue, but considerably upfield
shifted compared to signals reported for other zirconium
carbene complexes.15,16 This indicates incomplete charge
transfer from the carbon to the metal and a distinct negative
charge remaining at the carbenic carbon atom. The large JPC
coupling constant accounts for a high s-character of the carbon
atom.
1
Scheme 1. Synthesis of Zirconium Carbene Complex 2 from
Methandiide 1-Li2
Overall, the methandiide ligand 1 coordinates in a pincer-
type coordination mode via both the thiophosphoryl and the
sulfonyl moiety. The coordination of only one oxygen of the
sulfonyl moiety and the pyramidalization of the carbon atom
leads to the formation of diastereomers, whereas only the RCRS
diastereomer is found in the crystal. In solution however, a
fluxional behavior is observed. At 21 °C, the 1H NMR spectrum
shows only a single somewhat broadened resonance at δ = 6.11
ppm for the cyclopentadienyl moieties as well as broadened
signals in the aromatic region. This suggests fluxional behavior
of the sulfonyl moiety at room temperature with a rapid
interconversion between the two coordination modes 2 and 2′
Single crystals for X-ray diffraction analysis of 2 were grown
by cooling of a diethyl ether solution to −30 °C. 2 crystallizes
in the non-centrosymmetric orthorhombic space group Pna21
with an additional diethyl ether molecule (not depicted in
Figure 2). The molecular structure clearly confirms the 3-fold
coordination of the central carbon atom with a C−Zr distance
of 2.232(2) Å. This bond length is in the range of zirconium
1
(Scheme 2). H NMR spectroscopy in CD2Cl2 was used to
study this isomerization process and to determine the
corresponding activation parameters (see the SI). Cooling the
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complex 3 can probably be referred to the weak coordination
ability of the sulfonyl moiety. For the related bis-
(phosphonium)-substituted carbene complex no decomposi-
tion was reported.11
Scheme 2. Fluxional Behavior of 2
Treatment of equimolar amounts of dilithio methandiide 1
with [(PPh3)3RuCl2] in toluene at room temperature instantly
results in the darkening of the reaction mixture. NMR studies
of the crude product revealed the formation of triphenyl
phosphine together with a single new compound, which was
isolated as an orange solid in 62% yield (Scheme 3). Isolation
sample to −80 °C first results in a broadening of the signals and
finally in two, well-resolved Cp resonances as well as a splitting
of the signals for the Ph groups of the Ph2PS moiety.
Coalescence was observed at Tc = −26 °C (δ = 6.10; fwhw = 49
Hz), thus allowing for an estimation of the free energy of the
activation barrier for the rotation process by applying the
Eyring equation (ΔG⧧ = 52 kJ mol−1).
Scheme 3. Synthesis of Palladium and Ruthenium
Complexes 3 and 4
To further analyze this behavior and the different isomers of
2, DFT studies were performed on the real system employing
the B3LYP functional in combination with the LANL2TZ(f)
basis set for Zr and the 6-311+G(d,p) for all other atoms. The
energy-optimized structure is in excellent agreement with the
molecular structure of 2 [Zr−C: 2.248 Å (calcd), 2.242(2) Å
(expt); P−C−S: 146.0° (calcd) 149.7(2)° (expt)] with the
bending of the carbene moiety being also well reproduced by
the calculations (dihedral C13−P−S−Zr: 24.7° (calcd) 25.1(1)
(expt)). The calculations showed no minimum for the RCSS
isomer. Energy optimization always gave the RCRS and SCSS
isomer, respectively. A planar carbene structure, however, was
found to be only slightly disfavored, by 4.6 kJ·mol−1, confirming
the pyramidalization observed in the molecular structure. The
rotation about the C−S bondto alter the coordination
between the two sulfonyl oxygen atoms and thus the
configuration of the sulfur atomwas found to require 72.8
kJ·mol−1, a barrier higher than the one derived from the VT-
NMR experiments. However including solvent effects through a
polarizable continuum model (solvent = DCM) gave an
activation energy of 53.4 kJ·mol−1, which is in good agreement
with the experiment. This value additionally confirms the
fluxional coordination behavior in solution at room temper-
ature.
and crystallization revealed the formation of the cyclo-
metalation product 4. Thereby, the metalation was found to
selectively occur at the phenyl ring of the sulfonyl moiety.
Compound 4 was characterized by multinuclear NMR as well
as elemental and single-crystal X-ray diffraction analysis. The
31P{1H} NMR spectrum features three signals of equal intensity
at 45.5 (dd), 55.3 (d), and 68.1 (d) ppm, whereas only the
phosphorus (P3, Figure 3) of the PPh3 ligand in trans position
to the central carbon atom is involved in coupling to both other
phosphorus nuclei. The proton at the metalated carbon (C13)
was found as a multiplet at 2.88 ppm in the 1H NMR spectrum.
Zirconocene complex 2 turned out to be unreactive toward
several organic substrates (benzophenone, iodomethane,
silanes, disulfides, alkynes). Even at elevated temperatures
and in different solvents (toluene, thf) no conversion was
observed (see SI). Yet, 2 is highly moisture-sensitive and readily
abstracts protons from the solvent or protic reagents such as
aldehydes. This repeatedly lead to a complete break of the
metal carbon bond and the re-formation of the protonated
ligand 1, thus accounting for a weak metal ligand interaction.
In the next step we addressed the synthesis of carbene
complexes with the late transition metals ruthenium and
palladium. Treatment of methandiide 1 with [(PPh3)2PdCl2]
showed no clean formation of a single product. Yet, the main
product, which is characterized by two doublets in the 31P{1H}
NMR spectrum resonating at δP = 17.9 and 39.9 ppm (3JPP
=
38.7 Hz), was identified as the expected carbene complex 3.
This complex was found to be also accessible via an alternative
route using a carbenoid analogue of 1, [Ph2PS(SO2Ph)C(Cl)-
Li], and the Pd(0) precursor [Pd(PPh3)4].18,19 However, 3 is
not stable at room temperature in solution and decomposed in
the course of the workup procedure to form protonated species
as well as a thioketone complex by sulfur transfer from the
phosphorus to the carbenic carbon atom. This instability of
Figure 3. (Left) Molecular structure of complex 4. Ellipsoids are
drawn at the 50% probability level. Hydrogen atoms and solvent
molecule are omitted for clarity. Selected bond lengths [Å] and angles
[deg]: C13−S2 1.724(6), C13−P1 1.779(6), C13−Ru 2.191(6),
C15−Ru 2.070(6), O1−S2 1.483(4), O1−Ru 2.332(4), O2−S2
1.443(4), P1−S1 1.998(2), P2−Ru 2.2668(16), P3−Ru 2.3731(17),
Ru−S1 2.5558(17), S2−C13−P1 116.6(3).
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Single crystals of 4 were obtained by diffusion of diethyl
ether into a saturated dichloromethane solution. The Ru
complex crystallizes in the monoclinic space group P21/c. The
ruthenium center is 6-fold coordinated, strongly deviating from
the ideal octahedral geometry. Thereby, the sulfonyl ligand acts
as a tetradentate ligand binding in a S,C,C,O-coordination
mode. Due to the coordination of only one oxygen of the
sulfonyl moiety (O1), two pairs of diastereomers are formed.
However, the cyclometalation was found to be diastereose-
lective, solely producing the (RC,SS) and (SC,RS) couple.
An analogous cyclometalation reaction was reported by Le
́
Floch, Mezailles, and co-workers with bis(phosphonium)-
substituted dianions.20 Yet, in the case of the symmetric
bis(thiophosphoryl) methandiide the isolation of the inter-
mediate carbene complex was possible and cyclometalation
occurred only at 120 °C. In the case of the sulfonyl-substituted
methandiide the cyclometalation was found to be extremely fast
at room temperature, being complete after only a couple of
minutes after mixing of the starting materials. Attempts to trap
the intermediate carbene species 4-intsuch as with
aldehydeseven at low temperatures (−78 °C) always gave
way to the clean formation of 4, indicating a low reaction
barrier.
Figure 4. Comparison of the energies for the activation of the sulfonyl-
and thiophosphoryl-bound phenyl substituent.
transformation to further cyclometalation products, but in the
decomposition to multiple products. Also, the (SC,SS) and
(RC,RS) diastereomer of 4 was revealed to be thermodynami-
cally disfavored over the isomers found in the crystal (ΔΔG =
87.7 kJ·mol−1). Overall, the calculations explain the thermal
lability of 4-int and the selective formation of complex 4.
Computational Studies on the Metal Ligand Inter-
action. The experimental studies of the three carbene
complexes 2, 3, and 4-int account for a weak ligand metal
interaction with the novel methandiide 1-Li2. To further
explore the electronic structure and the nature of the metal
carbon bonds, DFT studies were performed. Due to computa-
tional costs, the PPh3 ligands in the two phosphine complexes
were replaced by PMe3. Figure 5 depicts the atomic charges
The mechanism of the cyclometalation of the bis-
(phosphonium) ligand was reported to be a stepwise process
starting with a C−H bond activation at the ruthenium center
and followed by H-shift from the ruthenium to the central
carbon atom.20 Thereby, the rate-determining step for the
cyclometalation was found to be the decoordination of one of
the thiophosphoryl moieties prior to the C−H activation step.
The fact that the sulfonyl complex 4-int undergoes cyclo-
metalation even at −78 °C suggests that the weaker
coordination ability of the sulfonyl side-arm might be the
reason for the fast process. In order to rationalize this
mechanism also for the formation of 4, DFT studies employing
the B3LYP functional in combination with the 6-31++G(d,p)
(for all nonmetal atoms) and the LANL2TZ(f) basis set (for
Ru) were performed using a model system with PMe3 ligands
instead of PPh3. The calculations revealed an analogous
stepwise mechanism to the cyclometalation product 4 (for a
display of the whole reaction process, see the SI). An alternative
direct ortho-metalation via deprotonation of the phenyl group
by the nucleophilic carbene carbon atom showed a considerably
higher reaction barrier of 148.8 kJ·mol−1 compared to only 46.8
kJ·mol−1 (TS1, Figure 4) for the stepwise reaction pathway.
Hereby, the decoordination and rotation of the sulfonyl moiety
to allow for the proximity between the ruthenium center and
the phenyl substituent turned out to be the rate-determining
step. The remarkably low activation barrier of 46.8 kJ·mol−1
(TS1) corroborates with the failed attempts to isolate the
intermediate carbene complex 4-int and with the fast reaction
process.
Figure 5. Natural atomic charges (top) and Wiberg bond indices of
the carbene complexes.
obtained from the NBO analysis21 as well as the Wiberg bond
indices for the metal ligand interactions. In all three carbene
complexes high negative charges are observed for the central
carbon atoms, thus reflecting the high nucleophilicity of these
complexes. Thereby, the highest negative charge (qC = −1.42)
is observed for the zirconium complex 2. This, together with
the positive charge at zirconium (qZr = 1.35), accounts for a
considerable ionic nature of the metal carbon interaction.
These findings corroborate with the spectroscopic observations
(13C NMR shift, C−P/S bond shortening). The same holds
true for the ruthenium and palladium complexes. Yet, in these
cases the metal centers are more electron-rich.
The computational studies also reflect the observed
selectivities of the cyclometalation (Figure 4). The alternative
metalation of one of the phosphorus-bound phenyl substituents
showed a clearly higher reaction barrier of 117.4 kJ·mol−1
(TS1′) compared to the sulfonyl moiety (cf. 46.8 kJ·mol−1 to
4). Again, the rate-determining step is the rotation of the
thiophosphoryl moiety. These findings demonstrate that the
selective metalation of the sulfonyl phenyl substituent is due to
the different coordination abilities of the sulfonyl group
compared with the thiophosphoryl moiety. Even prolonged
heating of complex 4 in C6D6 did not result in any clear
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Ionic interactions play also an important role for the
stabilization of the negative charge within the ligand backbone.
The charges in the sulfonyl and thiophosphoryl moieties are
almost independent of the metal center. The positive charges at
the phosphorus and sulfur atoms are comparable to the charges
observed for the parent methandiide 1-Li2 and thus emphasize
the importance of electrostatic interactions also for the
stabilization of these carbene complexes.
These findings are further manifested by the NBO analyses
and Wiberg bond indices (WBI) of the complexes. In the case
of zirconium complex 2 a WBI of only 0.674 as well as a high
polarization of the Zr−C bond toward the carbon end was
found. This is true for both the σ- and π-interaction of the
metal carbon bond, as evidenced by the molecular and natural
bond orbitals. The latter features high orbital coefficients (0.89
≙ 79.7% and 0.95 ≙ 90.0%) at the carbon atom (Figure 6).22 In
ruthenium complex 4-int the bond index of the M−O bond
(WBI = 0.21) is less than half of the value calculated for the
M−S bond (0.50). These low bond indices are in line with the
fluxional behavior observed for zirconium complex 2 in solution
and the selective C−H activation of the phenyl substituent of
the sulfonyl moiety. Also, for all complexes isomers without
additional coordination of the sulfonyl moiety were found to be
only slightly disfavored over the pincer-type coordination
mode. For example in the case of the ruthenium complex 4-int
a destabilization by only 23.7 kJ·mol−1, and for the palladium
complex 3 by only 17.2 kJ·mol−1, is calculated.
Overall the metal carbon interactions in the presented
carbene complexes based on the sulfonyl-substituted meth-
andiide 1-Li2 are comparable to those reported for the widely
applied bis(phosphonium)-substituted systems. Yet, the weaker
coordination ability of the sulfonyl moiety crucially affects the
stability and thus the reactivity of the complexes. However, the
use of more electron-deficient metal centers should allow the
isolation of further carbene complexes based on 1. Here the
flexible coordination ability of the sulfonyl moiety should allow
for the approach, coordination, and activation of various
organic substrates.
CONCLUSIONS
■
In conclusion, we presented the first examples of carbene
complexes based on a non-bis(phosphonium)-substituted
methandiide. The reactivity and stability of these complexes
showed that the pincer-type coordination mode is crucial for
the stabilization of this unique type of carbene species. While
the metal carbon interactions were found to be comparable to
those in the bis(phosphonium)-based ligand systems (i.e.,
highly polar M−C interactions with small π-contribution), the
weaker coordination ability of the sulfonyl moiety limits the
stability of these complexes. These findings clearly show that
the coordination of additional side-arms is crucial to support
the metal carbon interaction in these carbene complexes and to
stabilize the unusual bonding situation. In the case of our newly
developed methandiide ligand 1-Li2 the weak coordination
ability of the sulfonyl moiety so far only allowed the isolation of
a zirconium carbene complex in good yields due to the
oxophilic nature of the metal. For ruthenium and palladium the
stabilization was found to be insufficient, resulting in further
reactions such as cyclometalation or sulfur transfer from the
thiophosphoryl moiety to the carbenic carbon atom.
These results demonstrate that also methandiides with
substituents other than phosphonium groups can be applied
for the synthesis of carbene complexes. By increasing the
ligand−metal charge transfer and thus the π-interaction of the
M−C bond, more stable carbene complexes should be
accessible. Yet, the flexible coordination behavior of sub-
stituents such as the sulfonyl moiety may allow for the creation
of open coordination sites at the metal center. This should
allow for a rich chemistry toward organic substrates and the
possibility for bond activation reactions with the participation
of the ligand framework.
Figure 6. NBO plot with the corresponding σ- and π-interactions of
the C−Zr bond (isosurface value 0.03).
the case of the ruthenium and palladium complexes even lower
bond indices are observed for the M−C bond at that level of
theory. Additionally, the NBO analyses revealed only a σ-
interaction and a remaining lone pair at the central carbon
atom. Overall, the methandiide-based carbene complexes
reported herein feature only weak π-interactions. The metal
carbon bond is thus best described by means of the bipolar
ylidic resonance structure B with little contribution of the
carbene structure C (Figure 1). Hence, the zirconium complex
2 can be viewed as an 18 valence electron complex (cf. Scheme
1) and not as a 20-electron species, as implied by a carbene-
type description.14b This is well in line with the observed
stability of 2.
These metal carbon interactions are comparable to related
bis(phosphonium)-substituted systems, in which the strong
anion-stabilizing ability of the phosphonium groups stabilizes
polarized M−C bonds. As such, a WBI(Zr−C) of 0.67 and a
negative charge at the central carbon atom of qC = −1.53 have
also been reported for a zirconocene complex analogous to 2.6a
Yet, the stability of the sulfonyl-substituted complexes was
found to be considerably lower. Judging from the results of the
NBO analysis, this increased lability cannot be referred to
changes in the electronic situation of the M−C bond. The
observations made in experiment, however, suggested that the
weaker coordination ability of the sulfonyl moiety compared
with a phosphonium group might be the origin of the different
stabilities. This is also supported by the WBIs of the related
M−O interactions (see Figure 5). These values are in all cases
considerably smaller than those found for the M−S interaction
with the thiophosphoryl moiety. For example, for the
EXPERIMENTAL SECTION
■
General Procedure. 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
P4O10, CH2Cl2) and distilled prior to use. H2O is distilled water.
Organolithium reagents were titrated against diphenylacetic acid prior
1
to use. H, 13C, and 31P NMR spectra were recorded on Avance-500,
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4
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 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 assignment was supported by
DEPT and HMQC experiments. Elemental analyses were performed
on an Elementar Vario MICRO-cube elemental analyzer. All reagents
were purchased from Sigma-Aldrich, ABCR, Rockwood Lithium, or
Acros Organics and used without further purification. For an improved
synthetic procedure for ligand 1, see the SI.
2.42 Hz; CHRu‑PPh,para), 129.2 (d, JCP = 2.42 Hz; CHRu‑PPh,para), 130.6
2
1
(d, JCP = 10.5 Hz; CHPPh,ortho), 130.8 (d, JCP = 217.4 Hz; CPPh,ipso),
2
4
131.3 (d, JCP = 12.0 Hz; CHPPh,ortho), 131.9 (d, JCP = 3.13 Hz;
CHPPh,para), 132.1 (d, 4JCP = 3.09 Hz; CHPPh,para), 134.2 (d, 2JCP = 9.48
2
Hz; CHRu‑PPh,ortho), 135.3 (d, JCP = 10.62 Hz; CHRu‑PPh,ortho), 136.2
(dd, 1JCP = 34.7, 4JCP = 0.96 Hz; CPPh,ipso), 137.0 (dd, 1JCP = 43.9, 4JCP
= 1.17 Hz; CPPh,ipso), 144.2 (CHSPPh−C5), 150.9 (CSPPh,ipso). The signal
of the central carbon atom (PCS) could not be detected in the 13C
NMR spectrum, but in the HSQC via correlation with the multiplet at
1
δ = 2.86−2.90 ppm in the H NMR spectrum, corresponding to the
proton at the metalated carbon atom. 31P{1H} NMR (162.0 MHz,
CD2Cl2): δ 45.6 (dd, JPP = 25.7 Hz, 3JPP = 7.39 Hz; SPPh2), 55.3 (d,
4
Synthesis of 1-Li2. To a solution of 350 mg (0.94 mmol) of sulfon
1 in 20 mL of dry THF at 0 °C was added 0.41 mL (2.07 mmol) of
methyllithium (1.46 M in diethyl ether). The mixture was stirred at
room temperature for 1 h, followed by a reduction of the solvent in
vacuo to about 10 mL. The resulting yellow reaction mixture was
stirred for an additional 20 h, whereupon a colorless precipitate was
formed. The solid was washed with pentane and dried in vacuo (396
mg, 0.80 mmol, 86%). The NMR data of the dilithiated compound
3JPP = 7.38 Hz; PPh3), 68.1 (d, 3JPP = 25.6 Hz; PPh3). Anal. Calcd for
C55H45O2P3RuS2: C, 66.32; H, 4.55; S, 6.44. Found: C, 66.30; H, 4.80;
S, 6.16.
X-ray Crystallographic Studies. Data collection of all com-
pounds was conducted with a Bruker APEX-CCD (D8 three-circle
goniometer). The structures were solved using direct methods, refined
with the SHELX software package,23 and expanded using Fourier
techniques. The crystals of the two compounds were mounted in an
inert oil (perfluoropolyalkyl ether). Crystal structure determinations
were effected at 100 K. The structure was solved applying direct and
Fourier methods, using SHELXS-90 (G. M. Sheldrick, University of
Gottingen 1990) and SHELXL-97 (G. M. Sheldrick, SHELXL97,
University of Gottingen 1997). Crystallographic data (excluding
structure factors) have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication nos. CCDC-980200
(2) and CCDC-980201 (4). Data collection and structure refinement
details are provided in the SI.
Computational Studies. All calculations were performed without
symmetry restrictions except for the planar isomer 2′. Starting
coordinates were obtained with Chem3DUltra 10.0 or directly from
the crystal structure analysis. All calculations were done with the
Gaussian 03 (Revision E.01) program package.24 Geometry
optimizations were performed using density functional theory
(DFT) with the B3LYP (Becke 3-parameter−Lee−Yang−Parr)
functional25 and the LANL2Tz(f) basis set for Zr, Pd, and Ru and
the 6-311+G(d,p) basis set for all other atoms. Comparative studies
were performed with the BP86 functional and the TZVP basis set (see
the SI). Harmonic vibrational frequency analyses were performed at
the same levels of theory. The vibrational frequency analyses showed
no imaginary frequencies for the ground states and a single negative
frequency for the transition states. Transition states were located by
using the qst3 method or the opt=modred keyword and subsequent
optimization of the imaginary frequency. NBO analyses were carried
out on the optimized structures at the same level of theory using the
NBO 5.0 program interfaced to the Gaussian 03 package.21 For further
details, see the SI.
13
1
agree with the published H and 31P{1H} NMR spectra.
Synthesis of Complex 2. A solution of 150 mg (0.30 mmol) of
methandiide 1-Li2 was added dropwise to a suspension of 88.9 mg
(0.30 mmol) of Cp2ZrCl2 in 5 mL of dry toluene. The pale yellow
reaction mixture was stirred for 17 h at room temperature, upon which
an intense yellow suspension formed. After filtration the solvent was
removed in vacuo, affording a solid residue. The solid was taken up in a
minimum amount of diethyl ether and cooled to −30 °C, thus
affording the diethyl ether solvate of 2 as a pale yellow, crystalline solid
(127 mg, 0.19 mmol, 63%). 1H NMR (500.1 MHz, CD2Cl2): δ 1.15 (t,
3JHH = 7.00 Hz, 6 H; CH3-Et2O), 3.43 (q, 3JHH = 6.94 Hz, 4 H; CH2-
̈
̈
3
Et2O), 6.11 (s, CHCp), 7.25 (t, JHH = 7.53 Hz, 2 H; CHPPh,para), 7.38
3
(t, JHH = 7.35 Hz, 1 H; CHSPh,para), 7.46−7.55 (m, 8 H; CHPPh,meta
,
CHSPh,ortho,meta), 7.80 (br, 4 H; CHPPh,ortho). 13C NMR (125.8 MHz,
CD2Cl2): δ 15.5 (CH3-Et2O), 41.0 (d, JPC = 108.6 Hz; PCS), 66.1
1
3
(CH2-Et2O), 113.5 (CHCp), 124.6 (CHSPh), 128.8 (d, JPC = 12.7 Hz;
CHPPh,meta), 129.0 (CHSPh), 130.8 (d, 2JPC = 12.8 Hz; CPPh,ortho), 131.1
4
1
(CHSPh,para), 131.5 (d, JPC = 3.13 Hz; CPPh,para), 137.2 (d, JPC = 79.1
Hz; CPPh,ipso), 148.4 (CSPh,ipso). 31P{H} NMR (202.5 MHz, CD2Cl2): δ
17.5. Anal. Calcd for C33H35O3PS2Zr: C, 59.51; H, 5.29; S, 9.63.
Found: C, 59.46; H, 5.44; S, 9.26.
Synthesis of Complex 3. A 74.0 mg (0.15 mmol) amount of
methandiide 1-Li2 and 105 mg (0.15 mmol) of PdCl2(PPh3)2 were
dissolved in 10 mL of dry toluene, and the red-orange reaction mixture
was stirred overnight at room temperature. After this time, 31P{1H}
NMR of the reaction mixture showed complete conversion of the
reactants. The solvent was evaporated in vacuo, and the orange residue
was washed three times with n-pentane and cold diethyl ether, leaving
an orange solid (57.7 mg, 0.08 mmol, 52%). For spectroscopic data see
ref 18.
Synthesis of Complex 4. A 137 mg (0.14 mmol) portion of
(PPh3)3RuCl2 was suspended in 4 mL of dry toluene, and a solution of
70.9 mg (0.14 mmol) of dianion 1-Li2 in 5 mL of dry toluene was
added at room temperature. After stirring of the dark brown reaction
mixture for 24 h, the solution was separated from the formed precipate
via filtration. The solvent was evaporated in vacuo, and the dark brown
crude product was purified by washing with dry diethyl ether (3 × 7
mL), yielding the product as a light orange solid (88.7 mg, 0.09 mmol,
62%). Crystals of 4 were obtained by diffusion of diethyl ether into a
ASSOCIATED CONTENT
* Supporting Information
Complete experimental procedures, analytical data, and NMR
spectra for all new compounds; crystallographic and computa-
tional details. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: vgessner@uni-wuerzburg.de.
Notes
■
1
saturated dichloromethane solution. H NMR (300.1 MHz, CD2Cl2):
δ 2.86−2.90 (ddd, 2JPH = 5.89 Hz, 3JPH = 3.72 Hz, 3JPH = 1.85 Hz, 1 H;
3
4
PCHS), 5.89 (dt, JHH = 7.72, JHH = 0.48 Hz, 1 H; CHSPh,H‑5), 6.42
(td, 3JHH = 7.47, 4JHH = 1.53 Hz, 1 H; CHSPh,H‑4), 6.66−6.73 (m, 6 H;
3
4
CHPPh3,ortho), 6.80 (td, JHH = 7.36 Hz, JHH = 0.80 Hz, 1 H;
CHSPh,H‑3), 6.93−6.98 (m, 6 H; CHPPh3,meta), 7.09−7.14 (m, 6 H;
The authors declare no competing financial interest.
CHPPh3,meta), 7.21−7.48 (m, 21 H; CHPPh3,ortho,para, CHSPh,H‑2
,
ACKNOWLEDGMENTS
This work was financially supported by the Deutsche
Forschungsgemeinschaft (Emmy-Noether Program), the
Fonds der Chemischen Industrie, the Dr.-Otto-Rohm-Gedacht-
■
CHPPh,ortho,meta,para), 7.70−7.78 (m, 2 H, CHPPh,ortho). 13C{1H} NMR
(75.5 MHz, CD2Cl2): δ 37.7 (br, PCS), 125.5 (CHSPh−C3), 124.9
1
(CHSPh−C2), 127.0 (CHSPh−C4), 127.1 (d, JCP = 220.5 Hz; CPPh,ipso),
127.6 (d, JCP = 4.63 Hz; CHRu‑PPh,meta), 127.7 (d, JCP = 4.63 Hz;
CHRu‑PPh,meta), 128.4 (d, JCP = 12.3 Hz; CHPPh,meta), 129.1 (d, JCP
3
3
̈
̈
3
4
=
nisstiftung, and the Alexander von Humboldt Foundation. We
1315
dx.doi.org/10.1021/om5001277 | Organometallics 2014, 33, 1310−1317

Organometallics
Article
Am. Chem. Soc. 2011, 133, 6162−6165. (c) Cooper, O. J.; Mills, D. P.;
McMaster, J.; Moro, F.; Davies, E. S.; Lewis, W.; Blake, A. J.; Liddle, S.
T. Angew. Chem., Int. Ed. 2011, 50, 2383−2386. (d) Cooper, O. J.;
Mills, D. P.; McMaster, J.; Moro, F.; Davies, E. S.; Lewis, W.; Blake, A.
J.; Liddle, S. T. Angew. Chem., Int. Ed. 2011, 50, 2383−2386.
(10) (a) Orzechowski, L.; Jansen, G. S.; Harder, S. J. Am. Chem. Soc.
2006, 128, 14676−14684. (b) Orzechowski, L.; Harder, S. Organo-
metallics 2007, 26, 2144−2148.
also thank Rockwood Lithium GmbH for the supply of
chemicals. We thank Dr. Rudiger Bertermann and Marie-Luise
̈
Schafer for performing the VT NMR experiments.
̈
REFERENCES
■
(1) For selected reviews, see: (a) Trnka, T. M.; Grubbs, R. H. Acc.
Chem. Res. 2001, 34, 18−29. (b) Grubbs, R. H. Tetrahedron 2004, 60,
7117−7140. (c) Schrock, R. R.; Czekelius, C. Adv. Synth. Catal. 2007,
349, 55−77. (d) Schrock, R. R. Chem. Commun. 2005, 2773−2777.
(e) Zhang, L.; Hou, Z. Chem. Sci. 2013, 4, 3395−3403. (f) Scharper,
́
(11) (a) Cantat, T.; Mezailles, N.; Ricard, L.; Jean, Y.; Le Floch, P.
Angew. Chem., Int. Ed. 2004, 43, 6382−6385. (b) Jones, N. D.; Lin, G.;
Gossage, R. A.; McDonald, R.; Cavell, R. G. Organometallics 2003, 22,
2832−2841. (c) Lin, G.; Jones, N. D.; Gossage, R. A.; McDonald, R.;
Cavell, R. G. Angew. Chem., Int. Ed. 2003, 42, 4054−4057.
L.-A.; Hock, S. J.; Hermann, W. A.; Kuhn, F. E. Angew. Chem., Int. Ed.
̈
2013, 52, 270−289. (g) Nolan, S. P. Acc. Chem. Res. 2011, 44, 91−100.
(h) Navarro, O.; Viciu, M. S. Annu. Rep. Prog. Chem., Sect. B: Org.
Chem. 2010, 106, 243−259. (i) Bantreil, X.; Broggi, J.; Nolan, S. P.
Annu. Rep. Prog. Chem., Sect. B: Org. Chem. 2009, 105, 232−263.
(2) (a) Klabunde, U.; Fischer, E. O. J. Am. Chem. Soc. 1967, 89,
7141−7142. (b) Schrock, R. R. J. Am. Chem. Soc. 1974, 96, 6796−
6797.
(12) Gessner, V. H. Organometallics 2011, 30, 4228−4231.
(13) (a) Schroter, P.; Gessner, V. H. Chem.Eur. J. 2012, 18,
̈
11223−11227. (b) Gessner, V. H. Acta Crystallogr. 2012, E68, o1045.
(14) (a) Cavell, R. G.; Babu, R. P. K.; Kasani, A.; McDonald, R. J. Am.
Chem. Soc. 1999, 121, 5805−5806. (b) Cantat, T.; Ricard, L.;
́
Mezailles, N.; Le Floch, P. Organometallics 2006, 25, 6030−6038.
(c) Babu, R. P. K.; McDonald, R.; Decker, S. A.; Klobukowski, M.;
Cavell, R. G. Organometallics 1999, 18, 4226−4229. (d) Aparna, K.;
Babu, R. P. K.; McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed.
2001, 40, 4400−4402.
(3) Mindiola, D. J.; Scott, J. Nat. Chem. 2011, 3, 15−17.
(4) For reviews, see: (a) Jones, N. D.; Cavell, R. G. J. Organomet.
́
Chem. 2005, 690, 5485−5496. (b) Cantat, T.; Mezailles, N.; Auffrant,
A.; Le Floch, P. Dalton Trans. 2008, 1957−1972. (c) Liddle, S. T.;
Mills, D. P.; Wooles, A. J. Organomet. Chem. 2010, 36, 29. (d) Harder,
S. Coord. Chem. Rev. 2011, 255, 1252−1267.
(15) (a) Spencer, L. P.; Winston, S.; Fryzuk, M. D. Organometallics
2004, 23, 3372−3374. (b) Romain, C.; Heinrich, B.; Laponnaz, S. B.;
Dagorne, S. Chem. Commun. 2012, 48, 2213−2215. (c) Romain, C.;
Miqueu, K.; Sotiropoulos, J.-M.; Bellemin-Laponnaz, S.; Dagorne, S.
Angew. Chem., Int. Ed. 2010, 49, 2198−2201. (d) Zhang, D.; Aihara,
H.; Watanabe, T.; Matsuo, T.; Kawaguchi, H. J. Organomet. Chem.
2007, 692, 234−242. (e) Niehues, M.; Erker, G.; Kehr, G.; Schwab, P.;
(5) (a) Gessner, V. H.; Meier, F.; Uhrich, D.; Kaupp, M. Chem.Eur.
J. 2013, 19, 16729−16739. (b) Vyboishchikov, S. F.; Frenking, G.
Chem.Eur. J. 1998, 4, 1428−1438.
́
(6) For examples, see: (a) Cantat, T.; Ricard, L.; Mezailles, N.; Le
Floch, P. Organometallics 2006, 25, 6030−6038. (b) Kamalesh Babu,
R. P.; McDonald, R.; Cavell, R. G. Chem. Commun. 2000, 481−482.
(c) Jones, N. D.; Lin, G.; Gossage, R. A.; McDonald, R.; Cavell, R. G.
Organometallics 2003, 22, 2832−2841. (d) Lin, G.; Jones, N. D.;
Gossage, R. A.; McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed.
Frohlich, R.; Blacque, O.; Berke, H. Organometallics 2002, 21, 3905−
̈
3911.
(16) (a) Fryzuk, M. D.; Duval, P. B.; Mao, S. S. S. H.; Zaworotko, M.
J.; MacGillivray, L. R. J. Am. Chem. Soc. 1999, 121, 2478−2487.
(b) Fryzuk, M. D.; Duval, P. B.; Mao, S. S. S. H.; Rettig, S. J.;
Zaworotko, M. J.; MacGillivray, L. R. J. Am. Chem. Soc. 1999, 121,
1707−1716. (c) Beckhaus, R. Angew. Chem., Int. Ed. Engl. 1997, 36,
686. (d) Beckhaus, R.; Santamaría, C. J. Organomet. Chem. 2001, 617−
618, 81−97.
2003, 42, 4054−4057. (e) Cantat, T.; Arliguie, T.; Noel, A.; Thuer
́
y,
ailles, N. J. Am. Chem. Soc.
2009, 131, 963−972. (f) Tourneux, J.-P.; Berthet, J.-C.; Thuery, P.;
Mezailles, N.; Le Floch, P.; Ephritikhine, M. Chem. Commun 2010,
2494−2496. (g) Heuclin, H.; Le Goff, X. F.; Mez
̈
P.; Ephritikhine, M.; Le Floch, P.; Mez
́
́
́
́
ailles, N. Chem.Eur.
́
(17) (a) Cantat, T.; Mezailles, N.; Ricard, L.; Jean, Y.; Le Floch, P.
J. 2012, 18, 16136−16144. (h) Mills, D. P.; Wooles, A. J.; McMaster,
J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Organometallics 2009, 28,
6771−6776. (i) Cooper, O. J.; Mills, D. P.; McMaster, J.; Lewis, W.;
Blake, A. J.; Liddle, S. T. Chem.Eur. J. 2013, 19, 7071−7083.
(j) Mills, D. P.; Lewis, W.; Blake, A. J.; Liddle, S. T. Organometallics
2013, 32, 1239−1250. (k) Mills, D. P.; Soutar, L.; Cooper, O. J.;
Lewis, W.; Blake, A. J.; Liddle, S. T. Organometallics 2013, 32, 1251−
1264. (l) Mills, D. P.; Soutar, L.; Lewis, W.; Blake, A. J.; Liddle, S. T. J.
Am. Chem. Soc. 2010, 132, 14379−14381. (m) Mills, D. P.; Moro, F.;
McMaster, J.; van Slageren, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Nat.
Chem. 2011, 3, 454−460. (n) Heuclin, H.; Grunstein, D.; Le Goff, X.-
Angew. Chem., Int. Ed. 2004, 43, 6382−6385. (b) Cavell, R. G.; Babu,
R. K.; Aparana, K. J. Organomet. Chem. 2001, 617−618, 158−169.
(18) Becker, J.; Gessner, V. H. Dalton Trans. 2014, DOI: 10.1039/
C3DT52800F.
(19) For the use of other carbenoids in carbene complex formation,
see: (a) Kupper, C.; Molitor, S.; Gessner, V. H. Organometallics 2014,
33, 347−353. (b) Cantat, T.; Jacques, X.; Ricard, L.; Le Goff, X. F.;
Mezailles, N.; Le Floch, P. Angew. Chem., Int. Ed. 2007, 46, 5947−
5950. (c) Poverenov, E.; Milstein, D. Chem. Commun. 2007, 3189−
3191. (d) Molitor, S.; Feichtner, K.-S.; Kupper, C.; Gessner, V. H.
Chem.Eur. J. 2014, DOI: 10.1002/chem.201304927.
́
F.; Le Floch, P.; Mezailles, N. Dalton Trans. 2010, 39, 492−499.
(7) For isolated methandiides, see: (a) Kasani, A.; Babu, R. P. K.;
́
(20) (a) Cantat, T.; Demange, M.; Mezailles, N.; Ricard, L.; Jean, Y.;
Le Floch, P. Organometallics 2005, 24, 4838−4841. (b) Heuclin, H.;
Le Goff, X. F.; Mez
McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed. 1999, 38, 1483−
1484. (b) Cantat, T.; Ricard, L.; Le Floch, P.; Mezailles, N.
́
́
ailles, N. Chem.Eur. J. 2012, 18, 16136−16144.
(21) Glendening, G. E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter,
J. E.; Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5;
Theoretical Chemistry Institute, University of Wisconsin: Madison,
WI, 2001; http://www.chem.wisc.edu/∼nbo5.
Organometallics 2006, 25, 4965−4976. (c) Orzechowski, L.; Jansen,
G.; Harder, S. Angew. Chem., Int. Ed. 2009, 48, 3825−3829.
(d) Vollhardt, J.; Gais, H.-J.; Lukas, K. L. Angew. Chem., Int. Ed.
Engl. 1985, 24, 610−611. (e) Linti, G.; Rodig, A.; Pritzkow, H. Angew.
Chem., Int. Ed. 2002, 41, 4503−4506. (f) Heuclin, H.; Fustier-
Boutignon, M.; Ho, S. Y.-F.; Le Goff, X.-F.; Carenco, S.; So, C.-W.;
(22) NBO analysis employing the TZVP basis set shows only a σ-
interaction for the Zr−C bond and a lone pair at the carbon atom.
(23) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
́
Mezailles, N. Organometallics 2013, 32, 498−508. (g) Cooper, O. J.;
(24) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
Wooles, A. J.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Angew.
Chem., Int. Ed. 2010, 49, 5570−5573.
(8) Gregson, M.; Lu, E.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle,
S. T. Angew. Chem., Int. Ed. 2013, 52, 13016−13019.
(9) (a) Mills, D. P.; Cooper, O. J.; Tuna, F.; McInnes, E. J. L.; Davies,
E. S.; McMaster, J.; Moro, F.; Lewis, W.; Blake, A. J.; Liddle, S. T. J.
Am. Chem. Soc. 2012, 134, 10047−10054. (b) Tourneux, J.-C.;
́ ́
Berthet, J.-C.; Cantat, T.; Thuery, P.; Mezailles, N.; Ephritikhine, M. J.
1316
dx.doi.org/10.1021/om5001277 | Organometallics 2014, 33, 1310−1317

Organometallics
Article
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J.
J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; M. A. Al-Laham, Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision
E.01; Gaussian, Inc.: Wallingford, CT, 2004.
(25) (a) Becke, A. D. J. J. Chem. Phys. 1993, 98, 5648−5662. (b) Lee,
C.; Yang, W.; Parr, R. Phys. Rev. B 1988, 37, 785.
1317
dx.doi.org/10.1021/om5001277 | Organometallics 2014, 33, 1310−1317