Bis(functionalized NHC) palladium(II) complexes via a postmodification approach

Article abstract of DOI:10.1021/om500274c

A series of 20 bis(functionalized NHC) Pd(II) complexes have been conveniently synthesized through postmodification reactions of the common parent NHC complexes trans-[PdBr₂(C₃Br-bimy)₂] (1a) and trans-[PdBr₂(C₃Br-imy)₂] (1b) (C ₃Br-bimy = 1-benzyl-3-(3-bromopropyl)benzimidazolin-2-ylidene and C₃Br-imy = 1-benzyl-3-(3-bromopropyl)imidazolin-2-ylidene) with an N-C₃Br tether. Depending on the nature of the nucleophiles added, competing bromido ligand displacements also occurred. In comparison to the conventional access to functionalized NHC complexes, which involves metalation of individually prefunctionalized azolium salts, this highly modular method proves more effective in cost and time savings. The tetraalkylammonium- functionalized complex trans-[PdBr₂(C₃NEt ₃-bimy)₂]Br₂ (14) as a product of the second-generation postmodification of complex 1a was also tested for its catalytic activity in Mizoroki-Heck coupling reactions to study and model the effect of a catalytic amount of ammonium salt additive in Pd-catalyzed C-C coupling reactions. The ammonium functionalities in this complex exhibit a positive effect on the catalysis in comparison to its parent complexes.

Full text of DOI:10.1021/om500274c

Article
pubs.acs.org/Organometallics
Bis(functionalized NHC) Palladium(II) Complexes via a
Postmodification Approach
Qiaoqiao Teng, Daniel Upmann, Sheena Ai Zi Ng Wijaya, and Han Vinh Huynh*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore
S
* Supporting Information
ABSTRACT: A series of 20 bis(functionalized NHC) Pd(II) complexes have been conveniently synthesized through
postmodification reactions of the common parent NHC complexes trans-[PdBr2(C3Br-bimy)2] (1a) and trans-[PdBr2(C3Br-
imy)2] (1b) (C3Br-bimy = 1-benzyl-3-(3-bromopropyl)benzimidazolin-2-ylidene and C3Br-imy = 1-benzyl-3-(3-bromopropyl)-
imidazolin-2-ylidene) with an N-C3Br tether. Depending on the nature of the nucleophiles added, competing bromido ligand
displacements also occurred. In comparison to the conventional access to functionalized NHC complexes, which involves
metalation of individually prefunctionalized azolium salts, this highly modular method proves more effective in cost and time
savings. The tetraalkylammonium-functionalized complex trans-[PdBr2(C3NEt3-bimy)2]Br2 (14) as a product of the second-
generation postmodification of complex 1a was also tested for its catalytic activity in Mizoroki−Heck coupling reactions to study
and model the effect of a catalytic amount of ammonium salt additive in Pd-catalyzed C−C coupling reactions. The ammonium
functionalities in this complex exhibit a positive effect on the catalysis in comparison to its parent complexes.
An alternative approach, where functional group trans-
formations can be done with a single and easily accessible
NHC complex, would represent a substantial improvement in
terms of cost, labor, time, and waste reduction.6b,9 Moreover,
new complexes could be envisaged, which are not accessible via
the traditional way due to incompatibility of the desired
functional group with the conditions required for complex
formation. In this regard, we have previously reported dimeric
thiolato-NHC complexes, which resulted from hydrolysis of
thioester-functionalized azolium salts during palladation, due to
the incompatibility of the thioester functional group with
Pd(OAc)2.10
Along this line, we recently communicated a [PdBr2(C3Br-
bimy)(pyridine)] complex, which bears one benzimidazole-
derived NHC (C3Br-bimy) with an N-bromopropyl tether
capable of nucleophilic substitution reactions.11 Versatile first-,
second-, and third-generation postmodifications from this
complex afforded a series of functionalized mono(NHC)
Pd(II) complexes, including thioester- and isothiocyanate-
functionalized NHC complexes, which were previously not
INTRODUCTION
■
N-heterocyclic carbenes (NHC) are state of the art ligands in
organometallic chemistry1 and catalysis.2 The nitrogen atoms in
the heterocycle offer ample possibilities for tuning the ligand
structure. Through an change in the N substituents, steric
demands and electronic properties of the ligand can be altered
to provide complexes with enhanced catalytic performances.3
More interestingly, various functional groups can also be
introduced, resulting in complexes with wider applications.4 For
example, introduction of a suitable donor group can lead to
versatile structures in ditopic complexes or enhanced catalytic
performance of complexes with hemilabile ligands.5 Potentially
antibacterial compounds have also been made by the
introduction of a biologically active function.6 In addition,
complexes of bifunctional ligands can be immobilized or their
solubilities altered by suitable functionalization to afford
recoverable catalysts.7
Routinely, functionalized NHC complexes are obtained by
metalation of an already prefunctionalized NHC precursor.8
Due to the individual prefunctionalization and subsequent
metalation steps required for each ligand precursor, this
strategy becomes tedious and labor intensive if a library of
functionalized NHC complexes is targeted.
Received: March 14, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 1. Synthesis of Bis(NHC) Pd(II) Parent Complexes
1
Figure 1. H NMR spectrum for complex 1a in the aliphatic region.
accessible via the traditional route. As a natural extension of this
study, we report the synthesis of bis(NHC) Pd(II) complexes
containing two benzimidazole- (C3Br-bimy) or imidazole-
derived (C3Br-imy) NHCs with N-bromopropyl substituents
and postmodifications thereof to give a library of bis-
(functionalized NHC) Pd complexes.
Due to the unsymmetrical nature of the NHC ligands, two
sets of signals with slightly different integrals are observed in
12
1
both H and 13C NMR spectra of the two complexes. Two
closely spaced carbene signals are observed at 182.6/182.5 ppm
(1a) and 170.3/170.2 ppm (1b), respectively. These values are
indicative of trans-configured dibromido-bis(NHC) complexes
of benzimidazole-13 and imidazole-derived14 NHCs, respec-
tively, while values at higher field are expected for their cis
isomers. The more intense signals at 182.6 and 170.3 ppm are
assigned to the trans-anti rotamers of 1a,b, while the weaker
signals at 182.5 and 170.2 ppm are attributed to the trans-syn
forms, respectively. This assignment is further corroborated by
their 1H NMR spectra, where two sets of well-separated signals
are observed for the aliphatic protons. These can be
unambiguously assigned by considering the shielding effect
exerted by the phenyl ring of the benzyl substituent.14 In the
anti rotamer the bromopropyl arm is situated in the shielded
area of the phenyl ring, giving rise to more upfield signals
(Figure 1; small signals of impurities were possible due to
hydrolysis products). The benzylic CH2 protons in the anti
rotamer, on the other hand, do not experience this shielding
effect and appear more downfield. In the syn form, the situation
is reversed, and the bromopropyl signals are more downfield,
while the benzylic protons are more upfield. The chemical shift
differences of equivalent groups in the anti and syn rotamers
decrease in the order BrCH2 (0.39/0.20 ppm, 1a/1b) >
NCH2Ph (0.23/0.15 ppm) > CH2 (0.22/0.14 ppm) > NCH2
(0.13/0.09 ppm), indicating the relative sensitivity of these
functions to the shielding effect of the phenyl ring. This trend is
observed for most of the complexes (vide infra). As expected,
the anti rotamer was generated as the major product due to
steric reasons.
RESULTS AND DISCUSSION
■
Synthesis of Bis(NHC)-Pd(II) Parent Complexes. The
parent bis(carbene) complexes trans-[PdBr2(C3Br-bimy)2] (1a)
and trans-[PdBr2(C3Br-imy)2] (1b) (C3Br-bimy = 1-benzyl-3-
(3-bromopropyl)benzimidazolin-2-ylidene and C3Br-imy = 1-
benzyl-3-(3-bromopropyl)imidazolin-2-ylidene) were synthe-
sized by the common silver carbene transfer method. The
bromopropyl-functionalized azolium salts C3Br-bimyH+Br− (A)
and C3Br-imyH+Br− (B) were reacted with Ag2O to afford the
respective Ag NHC intermediates, which were directly used for
transmetalation to palladium(II) in a 2:1 ratio to afford the
desired bis(NHC) complexes (Scheme 1). Notably, the
sequence of addition showed a significant influence on the
product yield. When the silver species was added into a solution
of [PdBr2(CH3CN)2] in acetonitrile, only 50% of bis(NHC)
complex 1a was isolated, and the known dinuclear
[PdBr2(C3Br-bimy)]2 complex11 was isolated as a side product
in a yield of 43%. However, the yield of 1a was quantitative
when the [PdBr2(CH3CN)2] solution was added dropwise to
the Ag NHC. Complex 1b was obtained using the latter
sequence of addition in a yield of 86%.
Complexes 1a,b are pale yellow powders with good
solubilities in THF, CH2Cl2, DMSO, and DMF, but they are
poorly soluble in ethanol and nonpolar solvents, such as hexane
and diethyl ether. In their ESI mass spectra, base peaks at m/z
843 or 743 are observed for the respective [M − Br]+
fragments.
Single crystals of 1a were grown by slow evaporation of a
saturated solution in CH2Cl2, and the molecular structure
B
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
determined by X-ray diffraction analysis is shown in Figure 2.
The Pd(II) centers are coordinated by two trans-anti oriented
Scheme 2. Hydrolysis of trans-[PdBr2(C3Br-bimy)2] (1a) to
trans-[PdBr2(C3OH-bimy)2] (2)
bonds are strong, displacements of the bromido ligands are
more likely in the latter case. The reactions of 1a with an excess
(10 equiv) of KOAc, HNEt2, or NaN3 exclusively yielded the
complexes trans-[PdBr2(C3X-bimy)2] (X = OAc (3a), NEt2
(4a), N3 (5a)) in almost quantitative yields, showing selectivity
for nucleophilic substitution at the bromopropyl tether. On the
other hand, complexes of the type trans-[PdX2(C3X-bimy)2] (X
= I (6a), SPh (7a), SCN (8a)) were formed when excess KI,
NaSPh, and KSCN were used. This reactivity difference is
ascribed to the soft nature of the palladium Lewis acid, which
prefers binding of the softer iodido and sulfur-containing
ligands over bromido coordination. Reducing the amount of
the nucleophiles to 2.2 equiv with respect to parent complex 1a
gave complicated mixtures of unreacted 1a, partially exchanged
complexes, and fully substituted complexes. Among the three
complexes 6a−8a, only trans-[Pd(SCN)2(C3SCN-bimy)2] was
obtained by heating. The reaction at ambient temperature gave
selectively the complex [Pd(SCN)2(C3Br-bimy)2] (9a), where
only ligand displacement took place.
Figure 2. Molecular structure of 1a showing 50% probability
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and bond angles (deg): Pd1−C1 2.024(4), Pd1−Br1
2.4334(4); C1−Pd1−Br1 88.34(10), C1−Pd1−Br1A 91.66(10).
PdC2Br2/NHC dihedral angle: 75°.
carbene and two bromido ligands in a square-planar geometry.
The two benzimidazolin-2-ylidene rings are coplanar as a result
of symmetry but are twisted from the coordination plane with
dihedral angles of 75°.
Coalescence of trans-anti and trans-syn rotamers in a similar
bis(NHC) Pd(II) complex has been previously observed at
14
1
∼107 °C by high-temperature H NMR spectroscopy, and a
similar study was conducted on complex 1a in CDCl3.
However, no change was observed upon raising the temper-
ature to 50 °C. To achieve higher temperatures, d6-DMSO was
used as the solvent instead. No ratio change or coalescence was
recorded up to 100 °C, suggesting a higher rotational barrier
about the Pd−C bond in this case. With further increase of the
temperature to 110 °C, two sets of new signals close to the
original ones appeared, which remained after cooling the
sample back to room temperature, indicating the formation of a
new rotameric pair. In order to achieve full conversion, the
same sample was heated at 110 °C for 1 day. Subsequent NMR
analysis showed that the original signals due to complex 1a
were completely replaced by two new sets of signals, indicating
rotamers of a new species. Notably, a new triplet is observed at
∼4.62 ppm, which upon successful hydrogen−deuterium
exchange by addition of D2O was assigned to OH protons.
Additional evidence was found in the positive mode ESI mass
spectrum of the sample, where a new base peak was observed at
m/z 719 with the correct isotopic pattern for the [M − Br]+
fragment of the alcohol-functionalized complex 2 (Scheme 2).
First-Generation Postmodifications. The bromo func-
tion of the N substituent allows for easy functional group
transformations via nucleophilic substitutions. First-generation
postfunctionalization of complexes 1a,b was conducted with
various nucleophiles (Scheme 3). As 1a,b showed similar
reactivities, which gave rise to complexes with similar structural
and spectroscopic characteristics, only reactions involving 1a as
a representative will be discussed in greater detail. In general,
the exposure of the complex to nucleophiles can lead to two
types of reactions, i.e. (i) nucleophilic substitution at C−Br and
(ii) ligand displacement at the Pd(II) center. Since Pd−NHC
Complexes 3a−8a share similar NMR spectra with their
parent complex 1a and the alcohol-functionalized counterpart
2. Two sets of signals are generally observed for the trans-anti
and trans-syn rotamers. Table 1 summarizes their α-CH2 1H
13
and
C
NMR data. The occurrences of nucleophilic
carbene
1
reactions on the C3 arm are best evidenced by H NMR
resonance changes of the α-CH2 group. In accord with results
obtained for the monocarbene series, an increase of the
negative inductive (−I) effect in the order SCN < SPh < I < N3
< Br < OH < OAc was concluded on the grounds of a gradual
downfield shift of the α-CH2 1H NMR signals. Complexes 1a−
13
5a have very similar
C
resonances at ∼182.5 ppm in
carbene
CDCl3 due to a similar coordination sphere, which is not
affected by different functionalities five bonds away. The greater
difference in complex 2 (181.1 ppm) is a result of solvent
effects arising from the d6-DMSO solvent used.
On the other hand, displacement of the bromido ligands
from the Pd(II) center leads to significant changes of the
13
C
resonances in comparison to those observed for 1a, as
carbene
evidenced by values ranging from 180.6 to 191.5 ppm for
complexes 6a−9a, respectively. Complexes 8a and 9a have very
13
close
C
signals, as they solely differ in the terminal
carbene
functionality of the propyl arm.
Formation of these complexes is also supported by ESI mass
spectrometry. Base peaks of [M − Br]+ fragments for
complexes 3a and 5a and the molecular ion [M]+ for 4a are
observed, while those for complexes 6a and 7a are assigned to
[M − X]+ fragments. Complexes 8a and 9a show weak
palladium-containing isotopic patterns for [M + H + CH3CN]+
or [M − SCN]+ fragments.
C
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 3. Postmodifications of Complexes 1a,b
Single crystals of complexes 3a, 7a−9a, and 7b were
obtained by slow evaporation of their saturated solutions in
CH2Cl2 (7a,b, 8a, and 9a) or CH2Cl2/CH3CN (3a). Their
molecular structures are depicted in Figure 3. All five complexes
D
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
confirms the successful and selective substitution of the
iodopropyl arm. The palladium center is coordinated by two
iodido ligands and two SCN-functionalized NHC ligands in the
trans-anti configuration.
Table 1. α-CH2 and Ccarbene NMR Resonances and ESI Mass
Signals of Complexes 1, 2, and 3−9
a
b
a
complex
X
coligand δ(1H) δ(13Ccarbene
)
main signal in ESI MS
1a
Br
Br
3.63,
3.25
182.57,
182.49
843 [M − Br]+
Second-generation postmodification was also conducted on
the amino-functionalized NHC complex trans-[PdBr2(C3NEt2-
bimy)2] (4a) by ethylating the two tertiary amino functions to
afford the ammonium-functionalized complex trans-
[PdBr2(C3NEt3-bimy)2]Br2 (14) (Scheme 3). After the
reaction mixture was heated overnight, complex 14 was
collected as the precipitate. Minor amounts of undesired
monoalkylated side product can be washed off with acetonitrile.
The solubility of complex 14 decreases on going from
methanol to acetonitrile and chlorinated solvents. It is insoluble
in hexane, diethyl ether, and water. Evidence of its formation
can be found in its ESI spectrum, which shows a base peak at
m/z 1047 attributed to the [M − Br]+ fragment and a weaker
signal at m/z 483 for the [M − 2Br]2+ dication. Two sets of
signals due to the trans-anti and trans-syn rotamers are still
observed in its NMR spectra, while the anti:syn rotameric ratio
increases from 1.9 for the parent 4a to 4.5 in complex 14. The
increased preference for the anti rotamer can be rationalized by
the intramolecular electrostatic repulsion between the two
positively charged ammonium groups only present in the syn
rotamer.
Mizoroki−Heck Catalysis Study. The addition of excess
tetraalkylammonium salts to stabilize palladium catalysts in C−
C coupling reactions to enhance reaction rates is known as
Jeffery conditions.15−17 The complex trans-[PdBr2(C3NEt3-
bimy)2]Br2 (14) can be regarded as a potential Pd catalyst that
is already decorated with two tetraalkylammonium moieties and
two bromide counteranions. Therefore, the catalytic activity of
complex 14 was evaluated and compared to that of its
analogues trans-[PdBr2(C3X-bimy)2] (X = Br (1a), OAc (3a),
NEt2 (4a)) to discern any influences brought about by different
functionalities. We were particularly interested to see if the
tetraalkylammonium bromide tether would lead to any notable
increased catalytic activity. The double Mizoroki−Heck
coupling of 1,4-dibromobenzene with tert-butyl acrylate at 1
mol % catalyst loading was chosen as a standard test reaction.
Under these conditions, complex 14 indeed displayed the best
activity in forming the 1,4-phenylene-dicinnamate in a yield of
82%. However, the yield is not as good as that with a
[PdCl(IMes)(N,N-dimethylbenzylamine)] complex, where
only 0.5 mol % was required to afford 81% product
formation.18 Among 1a, 3a, and 4a, the amine-functionalized
complex performed better than the ester analogue, followed by
the parent bromo complex (Table 3, entries 1−4), which is
understandable since the amine moiety is easily protonated to
form an ammonium tether in the course of the catalytic
reaction. As expected, addition of 1.5 equiv of tetrabutylammo-
nium bromide (TBAB) to the reaction with 1a or 4a
significantly improves the product yield from 56 and 76% to
92 and 93%, respectively, which is merely ∼10% better than
that of the reaction with pure 14 containing only catalytic
amounts of a tethered ammonium salt. In comparison,
additional TBAB improves the activity of 14 further, giving a
near-quantitative yield of 98%.
1b
2
3.50,
3.30
170.31,
170.23
743 [M − Br]+
719 [M − Br]+
803 [M − Br]+
703 [M − Br]+
909 [M]+
OH
Br
Br
3.64,
3.34
181.17,
181.10
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
OAc
4.31,
3.99
182.58,
182.54
4.21,
4.03
170.31,
170.22
NEt2
N3
Br
Br
I
2.69,
2.39
182.53,
182.49
2.61,
2.47
170.10,
170.05
809 [M]+
3.60,
3.23
182.62,
182.58
769 [M − Br]+
669 [M − Br]+
985 [M − I]+
885 [M − I]+
931 [M − SPh]+
831 [M − SPh]+
3.47,
3.25
170.32,
170.26
I
3.38,
3.03
181.84,
181.75
3.24,
3.08
168.42,
168.35
SPh
SCN
Br
SPh
3.25,
3.02
191.07,
191.02
3.07,
2.97
178.21
(2×)
c
SCN 3.19,
2.79
180.82,
180.73
878/778 [M + H +
CH3CN]+
3.13,
2.91
168.57,
168.49
SCN 3.66,
3.35
181.02
(2×)
822 [M − SCN]+
722 [M − SCN]+
c
3.56,
3.42
168.59,
168.55
a
b
c
Measured in CDCl3. Measured in d6-DMSO. The carbene signals
for the trans-anti and trans-syn rotamers are coincident.
crystallized as trans-anti rotamers with the palladium centers
coordinated by two functionalized carbenes and two anionic
coligands in square-planar fashions. The Pd−Ccarbene bond
distances fall in a narrow range from 2.020(3) to 2.0353(15)Å.
Second-Generation Postmodifications. Second-genera-
tion postmodifications were subsequently done on the complex
trans-[PdI2(C3I-bimy)2] (6a). The softer iodido ligands in this
complex are expected to form stronger Pd−I bonds in order to
prevent further ligand exchange reactions and therefore direct
selectivity to substitutions at the iodopropyl tether. Indeed,
complexes of the type trans-[PdI2(C3X-bimy)2] (X = N3 (10),
SPh (11), SAc (12), SCN (13)) were afforded in reactions with
the respective nucleophiles (Scheme 3). The low yield of
complex 12 is attributed to hydrolysis of the thioester function
by the wet solvent, but attempts to isolate defined hydrolysis
products were not successful.
All four complexes showed base peaks for the respective [M
− I]+ fragments in their ESI mass spectra, indicating successful
reactions. Similar to the case for complexes 2−9, their
formations are further discerned by their α-CH2 1H NMR
resonances in accord with the inductive effects of the newly
introduced function, which are given in Table 2. As expected,
13
The reaction scope was extended to other polyhalogenated
benzenes using complex 14 without additional TBAB. Good
and comparable yields of approximately 84% were obtained for
all three isomers of the dicinnamates (entries 4−6). Increasing
the number of bromo substituents on the benzene ring to 3 and
the
C
carbene
resonances at ∼181.7 ppm show little variations.
The solid-state structure of trans-[PdI2(C3SCN-bimy)2] (13)
was obtained by an X-ray diffraction study on single crystals
obtained by slow evaporation of a saturated solution in
chloroform/hexane. The structure depicted in Figure 4
E
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 3. Molecular structures of 3a, 7a,b, 8a, and 9a showing 50% probability ellipsoids. For the sake of clarity, hydrogen atoms, phenyl rings of the
coligands in 7a,b, and the N-benzyl substituents in 8a and 9a are omitted. Selected bond lengths (Å) and bond angles (deg) are as follows. 3a: Pd1−
C1 2.020(3), Pd1−Br1 2.4359(3); C1−Pd1−Br1 92.49(8), C1−Pd1−Br1A 87.51(8). PdC2Br2/NHC dihedral angle: 80°. 7a: Pd1−C1 2.027(2),
Pd1−S2 2.3541(6); C1−Pd1−S2 87.15(7), C1−Pd1−S2A 92.85(7). PdC2S2/NHC dihedral angle: 73°. 7b: Pd1−C1 2.0353(15), Pd1−S2
2.3333(5); C1−Pd1−S2 95.44(4), C1−Pd1−S2A 84.56(4). PdC2S2/NHC dihedral angle: 68°. 8a: Pd1−C1 2.016(4), Pd1−S1 2.3229(11); C1−
Pd1−S1 87.27(11), C1−Pd1−S1A 92.73(11). PdC2S2/NHC dihedral angle: 89°. 9a: Pd1−C1 2.024(4), Pd1−S1 2.3399(12); C1−Pd1−S1
92.46(13), C1−Pd1−S1A 87.54(13). PdC2S2/NHC dihedral angle: 86°.
Table 2. α-CH2 and Ccarbene NMR Resonances and ESI Mass
a
Signals of Complexes 6a and 10−13
complex
X
δ(1H)
δ(13Ccarbene
)
main signal in ESI MS
6a
10
11
12
13
I
3.38, 3.03
3.59, 3.28
3.12, 2.85
3.12, 2.81
3.19, 2.77
181.84, 181.75
181.85, 181.82
181.71, 181.66
181.69, 181.61
181.65, 181.53
985 [M − I]+
815 [M − I]+
951 [M − I]+
881 [M − I]+
847 [M − I]+
N3
SPh
SAc
SCN
a
Measured in CDCl3.
4 allowed us to isolate the respective tri- and tetracinnamates as
major products (76% and 38%, entries 7 and 8). The yield of
the tricinnamate is higher than that previously obtained using a
Pd(OAc)2/tri-o-tolylphophine catalytic system (62%).19 Parti-
ally olefinated substrates were observed as minor byproducts as
well. In comparison, reaction with 1,2-dichlorobenzene only
gave the monocinnamate as a major product in a low yield of
10% (entry 9). The yield of monocinnamate was improved to
23% from the reaction with 1,2,4,5-tetrachlorobenzene (entry
10). In these more challenging cases, the addition of TBAB
only led to a small improvement in the yields of the major
product (monocinnamate). In addition to the benzene halides,
bromo heterocycles were coupled with tert-butyl acrylate with
good yields of up to 92% (entries 11 and 12).
Figure 4. Molecular structure of 13 showing 50% probability
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and bond angles (deg): Pd1−C1 2.038(3), Pd1−I1
2.6043(3); C1−Pd1−I1 88.00(8), C1−Pd1−I1A 92.00(8). PdC2I2/
NHC dihedral angle: 76.8°.
metathesis to yield the complex trans-[PdBr2(C3NEt3-bimy)2]-
−
(HCO2)2 (15). The presence of the HCO2 anion is
A preliminary study was carried out to identify any active
Pd(0) species derived from complex 14 by formate reduction.
For this purpose, silver formate was added to 14, and instant
AgBr precipitation was seen, indicating successful anion
1
corroborated by a downfield H singlet at 8.61 ppm and a
13C signal at 167.7 ppm. All other signals remain largely
unchanged upon metathesis. In addition, a base peak is
F
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(16; X = Br, HCO2).21 The absence of rotamers for 16, as
indicated by the NMR analysis, is consistent with observations
made for other d10 metal complexes, i.e. Ag(I) and Au(I), with
linearly coordinated bis(NHC) ligands.22 To the best of our
knowledge, complex 16 is the first example of a 14-electron
Pd(0) complex coordinated by two benzimidazolin-2-ylidene
ligands.
a
Table 3. Mizoroki−Heck Coupling Reactions
CONCLUSION
■
We have presented a versatile and modular synthetic pathway
to a library of 20 functionalized bis(NHC) Pd(II) complexes by
first- and second-generation postmodifications via nucleophilic
substitution and ligand displacement reactions of trans-
[PdBr2(C3Br-bimy)2] (1a) and trans-[PdBr2(C3Br-imy)2]
(1b) as the common parents. Depending on the nature of
nucleophiles used and the reaction temperature, different types
of complexes have been isolated. As a preliminary and
additional study, the catalytic activity of trans-[PdBr2(C3NEt3-
bimy)2]Br2 (14) bearing two tetraalkylammonium tethers was
compared to that of selected other analogues bearing neutral
tethers in the Mizoroki−Heck coupling reactions of poly-
halogenated benzenes with tert-butyl acrylate. The superior
performance of complex 14 in this reaction in comparison to its
neutral analogue suggests that a “catalytic amount” of
tetraalkylammonium bromide already has a positive effect due
to a better stabilization of the active catalysts via formation of
intramolecular ion pairs. However, a large excess of ammonium
salts is still more beneficial for such stabilization. The deliberate
reduction of 14 using formate resulted in the isolation of the
complex [Pd0(C3NEt3-bimy)2]X2 (16; X = Br, HCO2).
Research is underway to extend this modular and versatile
postmodification methodology to other transition metals and
explore their use in other catalytic applications.
a
Reaction conditions: 1/n mmol of aryl halide (n = number of halide
on aryl ring); 1.5 mmol of tert-butyl acrylate; 1.5 mmol of NaOAc; 3
b
mL of DMF; 0.01 mmol of precatalyst; 130 °C, 20 h. Isolated yields
for an average of two runs. With addition of 1.5 equiv of [N(n-
C4H9)4]Br.
c
observed at m/z 483 for the [M − 2HCO2]2+ ion in the
positive ESI mass spectrum.
Interestingly, the NMR sample of 15 showed a color change
from gray to yellow on standing, and a small amount of Pd
black was also observed. NMR analysis of this resulting yellow
mixture showed enormous differences: (i) the 1H NMR
spectrum shows only one set of signals, (ii) the integral ratio
EXPERIMENTAL SECTION
■
for the formate 1H singlet at 8.61 ppm is reduced, and (iii) the
General Considerations. All manipulations were carried out
without precautions to exclude air and moisture unless otherwise
stated. Solvents were used as received. The salt precursor A was
prepared by following a reported procedure.3d 1H and 13C NMR
chemical shifts (δ) were internally referenced to the residual solvent
signals relative to tetramethylsilane. Some aromatic carbon signals
could not be resolved due to accidental overlap.
13
original two
C
signals at 182.4 and 182.2 ppm for the
carbene
rotamers of 15 have been replaced by a new and more
downfield 13Ccarbene signal at 193.4 ppm. Both the color change
and the spectroscopic differences suggest that Pd(0) species
might be generated. In particular, the enhanced downfield shift
of the carbene carbon is indicative of a more electron rich metal
center, in line with a reduction of Pd(II) to Pd(0).16a,20 Scheme
4 displays a possible pathway, which is supposedly initiated by a
ligand exchange between the inner and outer spheres involving
bromido and formato ligands. The resulting ionization isomer
of 15 subsequently undergoes decarboxylation, generating an
intermediate hydrido species, which reductively eliminates HBr
to give the respective Pd(0) species [Pd0(C3NEt3-bimy)2]X2
1-Benzyl-3-(3-bromopropyl)imidazolium Bromide (B). Salt B
was synthesized in analogy to A by reacting 1-benzylimidazole with
1
1,3-dibromopropane. H NMR (400 MHz, CDCl3): δ 10.23 (s, 1 H,
NCHN), 7.63 (s, 1 H, Ar-H), 7.41 (s, 1 H, Ar-H), 7.37−7.36 (m, 2 H,
Ar-H), 7.21−7.19 (m, 3 H, Ar-H), 5.46 (s, 2 H, NCH2Ph), 4.40 (t,
3
3J(H,H) = 6.8 Hz, 2 H, NCH2), 3.30 (t, J(H,H) = 6.0 Hz, 2 H,
3
CH2Br), 2.38 (m, J(H,H) = 6.4 Hz, 2 H, CH2CH2CH2). 13C{1H}
NMR (100.62 MHz, CDCl3): δ 137.0 (NCHN), 133.4, 129.7, 129.6,
Scheme 4. Reduction of trans-[PdBr2(C3NEt3-bimy)2]Br2 (14) to [Pd(C3NEt3-bimy)2]X2 (16)
G
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
129.3, 123.4, 122.6 (Ar-C), 53.6 (NCH2Ph), 48.7 (NCH2), 32.9
(CH2Br), 29.6 (CH2CH2CH2). MS (ESI): m/z 279 [M − Br]+.
trans-Dibromidobis{1-benzyl-3-(3-bromopropyl)azolin-2-
ylidene}palladium(II) (1a,b). A mixture of Ag2O (232 mg, 1.00
mmol) and azolium salt (410/360 mg, 2.00 mmol) was suspended in
CH2Cl2 (60 mL) and the suspension stirred at ambient temperature
for 3 h shielded from light. A solution of [PdBr2(CH3CN)2], which
was prepared in turn by heating PdBr2 (266 mg, 1.00 mmol) in
CH3CN (200 mL) under reflux for 6 h, was added. The reaction
mixture was stirred for 20 h, and the resulting suspension was filtered
through a sintered funnel. Removal of the solvent under vacuum
yielded complex 1a as an off-white powder. For complex 1b, the
filtrate was concentrated to 20 mL and left to crystallize to afford the
pale yellow solid product. Yields and syn:anti ratios: 1a, 922 mg, 1.00
mmol, >99%, 1:2.2; 1b, 709 mg, 0.86 mmol, 86%, 1:1.1. Data for 1a
ratios: 3a, 79 mg, 0.09 mmol, 90%, 1:1.5; 3b, 78 mg, 0.10 mmol,
>99%, 1:1.2. Data for 3a are as follows. 1H NMR (500 MHz, CDCl3):
δ 7.66 (d, 5 H, Ar-H), 7.42−7.31 (m, 15 H, Ar-H), 7.22 (m, 9 H, Ar-
H), 7.12−7.11 (m, 7 H, Ar-H); syn, 5.95 (s, 4 H, NCH2Ph), 4.98 (t,
3
3J(H,H) = 7.3 Hz, 4 H, NCH2), 4.31 (t, J(H,H) = 6.0 Hz, 4 H,
CH2O), 2.74 (m, 4 H, 3J(H,H) = 6.5 Hz, CH2CH2CH2), 2.12 (s, 6 H,
3
CH3); anti, 6.17 (s, 4 H, NCH2Ph), 4.85 (t, J(H,H) = 7.5 Hz, 4 H,
3
3
NCH2), 3.99 (t, J(H,H) = 6.0 Hz, 4 H, CH2O), 2.53 (m, J(H,H) =
6.8 Hz, 4 H, CH2CH2CH2), 1.96 (s, 6 H, CH3). 13C{1H} NMR
(125.77 MHz, CDCl3): δ 182.6, 182.5 (Ccarbene), 171.5, 171.4 (CO),
135.9, 135.8, 135.54, 135.49, 135.0, 134.8, 129.5, 129.3, 128.8, 128.42,
128.35, 126.2, 126.1, 123.72, 123.71, 123.69, 112.2, 112.0, 110.74,
110.69 (Ar-C), 62.6, 62.4 (CH2O), 53.6, 53.3 (NCH2Ph), 45.8 (2 ×
NCH2), 29.7, 29.5 (CH2CH2CH2), 21.6, 21.4 (CH3). Anal. Calcd for
C38H40Br2N4O4Pd: C, 51.69; H, 4.57; N, 6.35. Found: C, 51.76; H,
4.18; N, 6.15. MS (ESI): m/z 803 [M − Br]+. Data for 3b are as
follows. 1H NMR (300 MHz, CDCl3): δ 7.50 (ps-d, 6 H, Ar-H), 7.39−
7.36 (m, 11 H, Ar-H), 7.28−7.25 (m, 3 H, Ar-H), 6.87−6.84 (m,
3J(H,H) = 2.0 Hz, 4 H, NCH), 6.67−6.65 (m, 3J(H,H) = 2.0 Hz, 4 H,
1
are as follows. H NMR (300 MHz, CDCl3): δ 7.62 (d, 5 H, Ar-H),
7.56 (d, 2 H, Ar-H), 7.49 (d, 3 H, Ar-H), 7.42−7.33 (m, 11 H, Ar-H),
7.23 (m, 8 H, Ar-H), 7.17−7.12 (m, 7 H, Ar-H); syn, 5.95 (s, 4 H,
NCH2Ph), 5.05 (t, 3J(H,H) = 7.0 Hz, 4 H, NCH2), 3.63 (t, 3J(H,H) =
6.0 Hz, 4 H, CH2Br), 2.96 (m, 3J(H,H) = 6.5 Hz, 4 H, CH2CH2CH2);
anti, 6.18 (s, 4 H, NCH2Ph), 4.92 (t, 3J(H,H) = 7.2 Hz, 4 H, NCH2),
3.25 (t, 3J(H,H) = 6.0 Hz, 4 H, CH2Br), 2.73 (m, 3J(H,H) = 6.5 Hz, 4
H, CH2CH2CH2). 13C{1H} NMR (75.47 MHz, CDCl3): δ 182.6,
182.5 (Ccarbene), 135.9, 135.8, 135.6, 135.5, 135.1, 134.9, 129.6, 129.3,
128.8, 128.5, 128.3, 123.9, 123.8, 112.1, 112.0, 111.1, 111.0 (Ar-C, 3 ×
coincident), 53.7, 53.3 (NCH2Ph), 47.1 (2 × NCH2), 33.5, 33.2
(CH2Br), 31.7, 31.2 (CH2CH2CH2). Anal. Calcd for C34H34Br4N4Pd:
C, 44.16; H, 3.71; N, 6.06. Found: C, 44.12; H, 3.60; N, 6.12. MS
(ESI): m/z 843 [M − Br]+. Data for 1b are as follows. 1H NMR (300
MHz, CDCl3): δ 7.50 (ps-d, 5 H, Ar-H), 7.39−7.36 (m, 10 H, Ar-H),
7.29−7.27 (ps-d, 5 H, Ar-H), 6.95 (d, 3J(H,H) = 1.8 Hz, 2 H, NCH),
3
NCH); syn, 5.62 (s, 4 H, NCH2Ph), 4.59 (t, J(H,H) = 7.0 Hz, 4 H,
3
3
NCH2), 4.21 (t, J(H,H) = 6.0 Hz, 4 H, CH2O), 2.55 (m, J(H,H) =
6.5 Hz, 4 H, CH2CH2CH2), 2.09 (s, 6 H, CH3); anti, 5.77 (s, 4 H,
NCH2Ph), 4.50 (t, 3J(H,H) = 7.2 Hz, 4 H, NCH2), 4.03 (t, 3J(H,H) =
6.0 Hz, 4 H, CH2O), 2.43 (m, 3J(H,H) = 6.7 Hz, 4 H, CH2CH2CH2),
1.93 (s, 6 H, CH3). 13C{1H} NMR (75.48 MHz, CDCl3): δ 171.6,
171.5 (CO), 170.3, 170.2 (Ccarbene), 136.53, 136.50, 129.6, 129.44,
129.37, 129.2, 129.0, 128.8, 122.5, 122.4, 121.3, 121.2 (Ar-C), 62.2,
62,1 (CH2O), 55.34, 55.28 (NCH2Ph), 48.5, 48.4 (NCH2), 30.6, 30.5
(CH2CH2CH2), 21.7, 21.5 (CH3). Anal. Calcd for C30H36Br2N4O4Pd:
C, 46.03; H, 4.64; N, 7.16. Found: C, 46.06; H, 4.24; N, 7.01. MS
(ESI): m/z 703 [M − Br]+.
3
3
6.93 (d, J(H,H) = 1.8 Hz, 2 H, NCH), 6.69 (d, J(H,H) = 1.8 Hz, 2
trans-Dibromidobis{1-benzyl-3-(3-diethylaminopropyl)-
azolin-2-ylidene}palladium(II) (4a,b). Complex 1a,b (186/166 mg,
0.20 mmol) and diethylamine (0.20 mL, 2.00 mmol) were dissolved in
CHCl3 (15 mL) and reflux at 70 °C for 1 day. The resulting orange
liquid was dried under reduced pressure and washed with H2O (3 × 5
mL) to give brown solids. Yields and syn:anti ratios: 4a, 182 mg, 0.20
mmol, >99%, 1:1.9; 4b, 162 mg, 0.20 mmol, >99%, 1:1.3. Data for 4a
3
H, NCH), 6.67 (d, J(H,H) = 1.8 Hz, 2 H, NCH); syn, 5.63 (s, 4 H,
NCH2Ph), 4.66 (t, 3J(H,H) = 6.6 Hz, 4 H, NCH2), 3.50 (t, 3J(H,H) =
6.0 Hz, 4 H, CH2Br), 2.80 (m, 3J(H,H) = 6.2 Hz, 4 H, CH2CH2CH2);
anti, 5.78 (s, 4 H, NCH2Ph), 4.57 (t, 3J(H,H) = 6.7 Hz, 4 H, NCH2),
3.30 (t, 3J(H,H) = 6.0 Hz, 4 H, CH2Br), 2.66 (m, 3J(H,H) = 6.4 Hz, 4
H, CH2CH2CH2). 13C{1H} NMR (75.48 MHz, CDCl3): δ 170.3,
170.2 (Ccarbene), 136.5, 136.4, 129.6, 129.5, 129.4, 129.2, 129.0, 128.9,
123.2, 122.9, 121.3, 121.2 (Ar-C), 55.4, 55.3 (NCH2Ph), 49.5, 49.4
(NCH2), 33.8, 33.7 (CH2Br), 31.5, 31.4 (CH2CH2CH2). Anal. Calcd
for C26H30Br4N4Pd: C, 37.87; H, 3.67; N, 6.79. Found: C, 37.98; H,
3.59; N, 7.00. MS (ESI): m/z 743 [M − Br]+.
1
are as follows. H NMR (500 MHz, CDCl3): δ 7.66 (d, 5 H, Ar-H),
7.50 (d, 1 H, Ar-H), 7.42 (d, 5 H, Ar-H), 7.37 (t, 6 H, Ar-H), 7.31 (t, 3
H, Ar-H), 7.21−7.20 (m, 8 H, Ar-H), 7.10−7.06 (m, 8 H, Ar-H); syn,
3
5.96 (s, 4 H, NCH2Ph), 4.94 (t, J(H,H) = 7.4 Hz, 4 H, NCH2CH2),
3
3
2.69 (t, J(H,H) = 6.9 Hz, 4 H, CH2NCH2CH3), 2.62 (m, J(H,H) =
7.1 Hz, 8 H, CH2NCH2CH3), 2.50 (m, 3J(H,H) = 7.2 Hz, 4 H,
CH2CH2CH2), 1.07 (t, 3J(H,H) = 7.1 Hz, 12 H, CH3); anti, 6.18 (s, 4
H, NCH2Ph), 4.82 (t, 3J(H,H) = 7.6 Hz, 4 H, NCH2CH2), 2.41−2.39
trans-Dibromidobis{1-benzyl-3-(3-hydroxypropyl)-
benzimidazolin-2-ylidene}palladium(II) (2). Complex 1a was
suspended in d6-DMSO (0.6 mL) and heated to 110 °C for 1 day
before NMR. syn:anti ratios: 1:1.4. 1H NMR (400 MHz, d6-DMSO): δ
7.74 (d, 5 H, Ar-H), 7.67 (d, 2 H, Ar-H), 7.60−7.58 (m, 4 H, Ar-H),
7.37−7.29 (m, 14 H, Ar-H), 7.25−7.21 (m, 11 H, Ar-H); syn, 6.15 (s,
3
(m, 12 H, CH2NCH2CH3 and CH2NCH2CH3), 2.31 (m, J(H,H) =
3
7.2 Hz, 4 H, CH2CH2CH2), 0.91 (t, J(H,H) = 7.2 Hz, 12 H, CH3).
13C{1H} NMR (125.77 MHz, CDCl3): δ 182.53, 182.49 (Ccarbene),
136.17, 136.15, 135.7, 135.6, 135.1, 134.9, 129.5, 129.4, 129.2, 128.7,
128.6, 128.5, 128.38, 123.37, 123.5, 123.4, 112.1, 111.9, 111.4, 111.2
(Ar-C), 53.8, 53.3 (NCH2Ph), 51.2, 50.9, 47.4, 47.3, 47.2 (2×)
(NCH2), 28.3, 28.1 (CH2CH2CH2), 12.2, 12.1 (CH3). Anal. Calcd for
C42H54Br2N6Pd: C, 55.49; H, 5.99; N, 9.24. Found: C, 55.11; H, 5.98;
3
4 H, NCH2Ph), 4.82 (t, J(H,H) = 7.6 Hz, 4 H, NCH2), 3.34 (t,
3
3J(H,H) = 6.0 Hz, 4 H, CH2O), 2.23 (m, 4 H, J(H,H) = 6.8 Hz,
3
CH2CH2CH2); anti, 6.00 (s, 4 H, NCH2Ph), 4.93 (t, J(H,H) = 7.2
3
Hz, 4 H, NCH2), 3.64 (t, J(H,H) = 6.0 Hz, 4 H, CH2O), 2.36 (m,
3J(H,H) = 6.7 Hz, 4 H, CH2CH2CH2), the OH signals are found at
3
4.62 (t, J(H,H) = 4.9 Hz, 2 H, OH). 13C{1H} NMR (100.62 MHz,
N, 8.93. MS (ESI): m/z 909 [M]+. Data for 4b are as follows. H
1
d6-DMSO): δ 181.2, 181.1 (Ccarbene), 135.84, 135.76, 134.3, 134.2,
133.5, 133.3, 128.5, 128.3, 128.0, 127.8, 127.7, 123.1, 123.00, 122.97,
111.5, 111.4, 111.0, 110.9 (Ar-C, 2 × coincident), 58.1, 57.8 (CH2O),
51.7, 51.5 (NCH2Ph), 44.91, 44.86 (NCH2), 32.7, 32.5
(CH2CH2CH2). Anal. Calcd for C34H36Br2N4O2Pd: C, 51.12; H,
4.54; N, 7.01. Found: C, 51.38; H, 4.26; N, 6.95. MS (ESI): m/z 719
[M − Br]+.
trans-Dibromidobis{1-benzyl-3-(3-acetoxypropyl)azolin-2-
ylidene}palladium(II) (3a,b). A mixture of complex 1 (93/83 mg,
0.10 mmol) and potassium acetate (98 mg, 1.00 mmol) was suspended
in CH3CN (20 mL) and heated to reflux at 85 °C for 1 day. The
resulting product was dried under reduced pressure followed by
addition of 30 mL of CH2Cl2. The resulting yellow suspension was
filtered over Celite, and the solvent of the filtrate was removed in
vacuo, affording the products as yellow solids. Yields and syn:anti
NMR (500 MHz, CDCl3): δ 7.50 (ps-d, 5 H, Ar-H), 7.40−7.34 (m, 11
H, Ar-H), 7.28−7.26 (m, 4 H, Ar-H), 6.91 (d, 3J(H,H) = 1.9 Hz, 2 H,
NCH), 6.89 (d, 3J(H,H) = 1.9 Hz, 2 H, NCH), 6.65 (d, 3J(H,H) = 1.9
Hz, 2 H, NCH), 6.63 (d, 3J(H,H) = 1.9 Hz, 2 H, NCH); syn, 5.62 (s,
4 H, NCH2Ph), 4.56 (t, 3J(H,H) = 6.9 Hz, 4 H, NCH2CH2), 2.61 (m,
3
12 H, CH2NCH2CH3 and CH2NCH2CH3), 2.35 (m, J(H,H) = 7.1
Hz, 4 H, CH2CH2CH2), 1.05 (t, 3J(H,H) = 7.2 Hz, 12 H, CH3); anti,
3
5.78 (s, 4 H, NCH2Ph), 4.48 (t, J(H,H) = 6.9 Hz, 4 H, NCH2CH2),
2.47 (m, 12 H, CH2NCH2CH3 and CH2NCH2CH3), 2.23 (m,
3
3J(H,H) = 7.2 Hz, 4 H, CH2CH2CH2), 0.94 (t, J(H,H) = 7.2 Hz, 12
H, CH3). 13C{1H} NMR (125.76 MHz, CDCl3): δ 170.1, 170.0
(Ccarbene), 136.74, 136.67, 129.5, 129.43, 129.37, 129.3, 128.9, 128.7,
122.5, 122.4, 121.1, 121.0 (Ar-C), 55.25, 55.18 (NCH2Ph), 50.5, 50.4,
49.7, 49.5, 47.3, 47.2 (NCH2), 28.6, 28.5 (CH2CH2CH2), 11.9, 11.7
H
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(CH3). Anal. Calcd for C34H50Br2N6Pd: C, 50.48; H, 6.23; N, 10.39.
Found: C, 50.75; H, 5.85; N, 9.98. MS (ESI): m/z 809 [M]+.
trans-Dibromidobis{1-benzyl-3-(3-azidopropyl)azolin-2-
ylidene}palladium(II) (5a,b). These complexes were prepared in
analogy to complexes 3a,b from complexes 1a,b (93/83 mg, 0.10
mmol) and sodium azide (65 mg, 1.00 mmol). Yields and syn:anti
ratios: 5a, 85 mg, 0.10 mmol, >99%, 1:2.1; 5b, 75 mg, 0.10 mmol,
>99%, 1:1.3. Data for 5a are as follows. 1H NMR (500 MHz, CDCl3):
δ 7.64 (d, 4 H, Ar-H), 7.47 (d, 2 H, Ar-H), 7.40 (ps-t, 10 H, Ar-H),
7.34 (ps-t, 3 H, Ar-H), 7.28−7.21 (m, 9 H, Ar-H), 7.13−7.12 (m, 8 H,
6.5 Hz, 4 H, CH2CH2CH2); anti, 5.65 (s, 4 H, NCH2Ph), 4.44 (t,
3
3J(H,H) = 6.7 Hz, 4 H, NCH2), 3.08 (t, J(H,H) = 6.3 Hz, 4 H,
CH2I), 2.58 (m, 3J(H,H) = 6.6 Hz, 4 H, CH2CH2CH2). 13C{1H}
NMR (125.77 MHz, CDCl3): δ 168.4, 168.3 (Ccarbene), 136.0, 135.9,
129.7, 129.5, 129.44, 129.35, 128.94, 128.86, 123.2, 123.0, 121.42,
121.35 (Ar-C), 55.8, 55.7 (NCH2Ph), 51.84, 51.77 (NCH2), 33.5, 33.4
(CH2I), 4.3, 4.0 (CH2CH2CH2). Anal. Calcd for C26H30I4N4Pd: C,
30.84; H, 2.99; N, 5.53. Found: C, 30.81; H, 2.98; N, 5.49. MS (ESI):
m/z 885 [M − I]+.
t r a n s - B i s ( b e n z e n e t h i o l a t o ) b i s { 1 - b e n z y l - 3 - ( 3 -
phenylthiopropyl)azolin-2-ylidene}palladium(II) (7a,b). Com-
plex 1a,b (93/82 mg, 0.10 mmol) and freshly made sodium
thiophenolate (132 mg, 1.00 mmol) were suspended in degassed
THF (30 mL) and stirred overnight. The suspension was dried under
reduced pressure, and CH2Cl2 (50 mL) was added. The liquid was
collected by filtration, concentrated to 5 mL, and subjected to colum
chromatography (SiO2, ethyl acetate/hexane 1/8). The products were
collected as bright yellow solids. Yields and syn:anti ratios: 7a, 81 mg,
0.08 mmol, 78%, 1:1.5; 7b, 78 mg, 0.08 mmol, 83%, 1:1.3. Data for 7a
3
Ar-H); syn, 5.95 (s, 4 H, NCH2Ph), 4.98 (t, J(H,H) = 7.1 Hz, 4 H,
NCH2), 3.60 (t, 3J(H,H) = 6.0 Hz, 4 H, CH2N3), 2.62 (m, 3J(H,H) =
6.4 Hz, 4 H, CH2CH2CH2); anti, 6.19 (s, 4 H, NCH2Ph), 4.83 (t,
3
3J(H,H) = 7.3 Hz, 4 H, NCH2), 3.23 (t, J(H,H) = 6.1 Hz, 4 H,
3
CH2N3), 2.40 (m, J(H,H) = 6.5 Hz, 4 H, CH2CH2CH2). 13C{1H}
NMR (125.77 MHz, CDCl3): δ 182.62, 182.58 (Ccarbene), 136.0, 135.9,
135.53, 135.46, 135.1, 134.9, 129.6, 129.3, 128.8, 128.5, 128.35,
128.33, 123.89, 123.88, 123.80, 112.2, 112.1, 111.0, 110.9 (Ar-C, 1 ×
coincident), 53.7, 53.3 (NCH2Ph), 49.5, 49.3 (CH2N3), 46.0, 45.9
(NCH2), 29.9, 29.7 (CH2CH2CH2). Anal. Calcd for C34H34Br2N10Pd:
C, 48.10; H, 4.04; N, 16.50. Found: C, 48.06; H, 3.45; N, 15.80 (best
result obtained). 1H and 13C NMR spectra are given in the Supporting
Information. MS (ESI): m/z 769 [M − Br]+. Data for 5b are as
1
are as follows. H NMR (500 MHz, CDCl3): δ 7.77 (d, 4 H, Ar-H),
7.59 (d, 3 H, Ar-H), 7.52 (t, 1 H, Ar-H), 7.47 (d, 2 H, Ar-H), 7.43−
7.38 (m, 5 H, Ar-H), 7.33−7.26 (m, 22 H, Ar-H), 7.19 (t, 6 H, Ar-H),
7.11−7.06 (m, 7 H, Ar-H), 7.01 (t, 4 H, Ar-H), 6.96 (d, 4 H, Ar-H),
6.91 (d, 5 H, Ar-H), 6.86 (d, 2 H, Ar-H), 6.60−6.53 (m, 4 H, Ar-H),
6.46−6.42 (m, 7 H, Ar-H); syn, 5.72 (s, 4 H, NCH2Ph), 4.93 (t,
1
follows. H NMR (500 MHz, CDCl3): δ 7.51 (d, 2 H, Ar-H), 7.40−
7.37 (m, 5 H, Ar-H), 7.35−7.32 (ps-t, 4 H, Ar-H), 7.29−7.24 (m, 9 H,
3
3J(H,H) = 7.5 Hz, 4 H, NCH2), 3.25 (t, J(H,H) = 6.6 Hz, 4 H,
Ar-H), 6.86 (d, 3J(H,H) = 1.9 Hz, 2 H, NCH), 6.85 (d, 3J(H,H) = 1.9
CH2S), 2.69 (m, 3J(H,H) = 7.2 Hz, 4 H, CH2CH2CH2); anti, 5.98 (s,
3
Hz, 2 H, NCH), 6.68 (d, J(H,H) = 1.9 Hz, 2 H, NCH), 6.66 (d,
3
3J(H,H) = 1.9 Hz, 2 H, NCH); syn, 5.62 (s, 4 H, NCH2Ph), 4.59 (t,
4 H, NCH2Ph), 4.71 (t, J(H,H) = 7.7 Hz, 4 H, NCH2), 3.02 (t,
3
3J(H,H) = 6.6 Hz, 4 H, CH2S), 2.56 (m, J(H,H) = 7.4 Hz, 4 H,
3
3J(H,H) = 6.9 Hz, 4 H, NCH2), 3.47 (t, J(H,H) = 6.3 Hz, 4 H,
CH2CH2CH2). 13C{1H} NMR (125.77 MHz, CDCl3): δ 191.1, 191.0
(Ccarbene), 145.1, 145.0, 136.9, 136.8, 136.5, 135.8, 135.5, 135.4, 135.1,
135.02, 134.96, 130.0, 129.9, 129.7, 129.6, 129.4, 129.3, 129.0, 128.9,
128.7, 128.6, 128.5, 127.5, 127.4, 126.8, 126.7, 124.02, 123.96, 123.03,
122.98, 122.95, 111.8, 111.7, 110.6 (Ar-C, 2 × coincident), 53.8, 53.4
(NCH2Ph), 47.8 (2 × NCH2), 32.2, 31.9 (CH2S), 29.5, 29.4
(CH2CH2CH2). Anal. Calcd for C58H54N4PdS4: C, 66.87; H, 5.23;
N, 5.38. Found: C, 66.50; H, 5.09; N, 5.32. MS (ESI): m/z 931 [M −
SPh]+. Data for 7b are as follows. 1H NMR (500 MHz, CDCl3): δ 7.53
(d, 4 H, Ar-H), 7.47 (d, 4 H, Ar-H), 7.40−7.15 (m, 32 H, Ar-H),
7.10−7.06 (m, 8 H, Ar-H), 6.84−6.78 (m, 12 H, Ar-H), 6.47 (d,
3J(H,H) = 1.8 Hz, 2 H, NCH), 6.56 (d, 3J(H,H) = 1.8 Hz, 2 H, NCH),
CH2N3), 2.45 (m, 3J(H,H) = 6.6 Hz, 4 H, CH2CH2CH2); anti, 5.78 (s,
3
4 H, NCH2Ph), 4.48 (t, J(H,H) = 7.1 Hz, 4 H, NCH2), 3.25 (t,
3
3J(H,H) = 6.3 Hz, 4 H, CH2N3), 2.32 (m, J(H,H) = 6.7 Hz, 4 H,
CH2CH2CH2). 13C{1H} NMR (125.77 MHz, CDCl3): δ 170.32,
170.26 (Ccarbene), 136.5, 136.4, 129.5, 129.40, 129.38, 129.2, 128.9,
128.8, 122.6, 122.4, 121.4, 121.3 (Ar-C), 55.3, 55.2 (NCH2Ph), 49.1,
49.0 (CH2N3), 48.6, 48.5 (NCH2), 30.6, 30.5 (CH2CH2CH2). Anal.
Calcd for C26H30Br2N10Pd: C, 41.70; H, 4.04; N, 18.71. Found: C,
1
41.28; H, 3.58; N, 17.90 (best result obtained). H and 13C NMR
spectra are given in the Supporting Information. MS (ESI): m/z 669
[M − Br]+.
trans-Diiodido-bis{1-benzyl-3-(3-iodopropyl)azolin-2-
ylidene}palladium(II) (6a,b). A 50 mL portion of an NaI (0.30 g,
2.00 mmol) solution in acetone was added to a suspension of complex
1a,b (93/83 mg, 0.10 mmol) in CH2Cl2 (20 mL), and the mixture was
stirred overnight. The solvent of the suspension was removed in vacuo,
and 100 mL of CH2Cl2 was added. The resulting yellow suspension
was filtered over Celite, and the solvent was removed under reduced
pressure to give the products as yellow powders. Yields and syn:anti
ratios: 6a, 106 mg, 0.10 mmol, 95%, 1:1.2; 6b, 98 mg, 0.97 mmol, 97%,
3
3
6.38 (d, J(H,H) = 1.8 Hz, 2 H, NCH), 6.36 (d, J(H,H) = 1.8 Hz, 2
3
H, NCH); syn, 5.56 (s, 4 H, NCH2Ph), 4.54 (t, J(H,H) = 7.1 Hz, 4
H, NCH2), 3.07 (t, 3J(H,H) = 6.8 Hz, 4 H, CH2S), 2.43 (m, 3J(H,H) =
7.1 Hz, 4 H, CH2CH2CH2); anti, 5.64 (s, 4 H, NCH2Ph), 4.48 (t,
3J(H,H) = 7.3 Hz, 4 H, NCH2), 2.97 (t, J(H,H) = 6.8 Hz, 4 H,
3
CH2S), 2.38 (m, J(H,H) = 7.1 Hz, 4 H, CH2CH2CH2). 13C{1H}
3
NMR (125.77 MHz, CDCl3): δ 178.2 (2 × Ccarbene), 146.4, 146.3,
136.8, 136.7, 136.6, 136.5, 135.8, 134.78, 134.71, 134.69, 130.1,
130.02, 129.98, 129.87, 129.7, 129.6, 129.5, 129.4, 128.9, 128.8, 127.8,
126.8, 126.6, 123.61, 123.59, 121.4, 120.62, 120.61 (Ar-C), 55.24,
55.18 (NCH2Ph), 49.9, 49.8 (NCH2), 31.7, 31.6 (CH2S), 30.3 (2 ×
CH2CH2CH2). Anal. Calcd for C50H50N4PdS4: C, 63.78; H, 5.35; N,
5.95. Found: C, 64.12; H, 5.23; N, 5.74. MS (ESI): m/z 831 [M −
SPh]+.
1
1:1.4. Data for 6a are as follows. H NMR (500 MHz, CDCl3): δ
7.59−7.55 (m, 6 H, Ar-H), 7.48 (d, 2 H, Ar-H), 7.38 (t, 8 H, Ar-H),
7.34 (d, 2 H, Ar-H), 7.24 (m, 10 H, Ar-H), 7.14−7.09 (m, 4 H, Ar-H),
3
7.03 (t, 4 H, Ar-H); syn, 5.85 (s, 4 H, NCH2Ph), 4.89 (t, J(H,H) =
7.3 Hz, 4 H, NCH2), 3.38 (t, 3J(H,H) = 6.4 Hz, 4 H, CH2I), 2.89 (m,
3J(H,H) = 7.2 Hz, 4 H, CH2CH2CH2); anti, 6.06 (s, 4 H, NCH2Ph),
t r a n s - B i s ( t h i o c y a n a t o - κ S ) b i s { 1 - b e n z y l - 3 - ( 3 -
thiocyanopropyl)azolin-2-ylidene}palladium(II) (8a,b). Complex
1a,b (93/82 mg, 0.10 mmol) and potassium thiocyanate (98 mg, 1.00
mmol) were suspended in CH3CN (30 mL) and refluxed overnight.
The resulting yellow suspension was dried in vacuo before CH2Cl2 (20
mL) was added. The suspension was then filtered and dried to give the
pure products as pale yellow solids. Yields and syn:anti ratios: 8a, 82
mg, 0.10 mmol, 98%, 1:1.9; 8b, 74 mg, 0.10 mmol, 99%, 1:1.3. Data
for 8a are as follows. 1H NMR (500 MHz, CDCl3): δ 7.54 (d, 2 H, Ar-
H), 7.50 (d, 2 H, Ar-H), 7.47−7.40 (m, 12 H, Ar-H), 7.35−7.31 (m, 4
H, Ar-H), 7.29−7.28 (m, 6 H, Ar-H), 7.23−7.17 (m, 10 H, Ar-H); syn,
5.89 (s, 4 H, NCH2Ph), 5.03 (t, 3J(H,H) = 6.9 Hz, 4 H, NCH2), 3.19
(t, 3J(H,H) = 6.8 Hz, 4 H, CH2SCN), 2.88 (m, 3J(H,H) = 6.9 Hz, 4 H,
3
3
4.78 (t, J(H,H) = 7.5 Hz, 4 H, NCH2), 3.03 (t, J(H,H) = 6.3 Hz, 4
H, CH2I), 2.68 (m, J(H,H) = 7.4 Hz, 4 H, CH2CH2CH2). 13C{1H}
3
NMR (125.77 MHz, CDCl3): δ 181.8, 181.7 (Ccarbene), 136.0, 135.9,
135.57, 135.56, 135.4, 129.6, 129.3, 128.8, 128.58, 128.56, 128.54,
123.72, 123.68, 112.3, 112.2, 111.1, 111.0 (Ar-C, 3 × coincident), 54.7,
54.2 (NCH2Ph), 49.9 (2 × CH2I), 33.2, 32.8 (NCH2), 3.84, 3.20
(CH2CH2CH2). Anal. Calcd for C34H34I4N4Pd: C, 36.70; H, 3.08; N,
5.04. Found: C, 36.49; H, 3.43; N, 4.98. MS (ESI): m/z 985 [M − I]+.
Data for 6b are as follows. 1H NMR (500 MHz, CDCl3): δ 7.50 (d, 5
H, Ar-H), 7.43−7.35 (m, 10 H, Ar-H), 7.30 (m, 5 H, Ar-H), 6.99 (d,
3J(H,H) = 1.6 Hz, 2 H, NCH), 6.98 (d, 3J(H,H) = 1.6 Hz, 2 H, NCH),
3
3
6.67 (d, J(H,H) = 1.6 Hz, 2 H, NCH), 6.65 (d, J(H,H) = 1.6 Hz, 2
3
3
H, NCH); syn, 5.53 (s, 4 H, NCH2Ph), 4.51 (t, J(H,H) = 6.6 Hz, 4
CH2CH2CH2); anti, 6.21 (s, 4 H, NCH2Ph), 4.90 (t, J(H,H) = 6.9
H, NCH2), 3.24 (t, 3J(H,H) = 6.4 Hz, 4 H, CH2I), 2.70 (m, 3J(H,H) =
Hz, 4 H, NCH2), 2.79 (t, 4 H, 3J(H,H) = 6.7 Hz, CH2SCN), 2.60 (m,
I
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3J(H,H) = 6.8 Hz, 4 H, CH2CH2CH2). 13C{1H} NMR (125.77 MHz,
CDCl3): δ 180.8, 180.7 (Ccarbene), 136.0, 135.90, 135.88, 135.8, 135.1,
135.0, 130.0, 129.63, 129.60, 129.2, 128.9, 127.5, 127.4, 124.99, 124.95
124.91 (Ar-C), 120.5, 120.4 (PdSCN), 112.7, 112.5 (Ar-C), 112.4,
112.3 (CH2SCN), 112.1, 111.2 (Ar-C), 53.4, 53.1 (NCH2Ph), 47.0,
46.7 (NCH2), 31.8, 31.3 (CH2SCN), 30.6, 30.0 (CH2CH2CH2). Anal.
Calcd for C38H34N8PdS4: C, 54.50; H, 4.09; N, 13.38. Found: C,
yellow powder (75 mg, 0.80 mmol, 99%) in a syn:anti ratio of 1:1.7.
1H NMR (500 MHz, CDCl3): δ 7.62 (d, 4 H, Ar-H), 7.47 (d, 2 H, Ar-
H), 7.42−7.38 (m, 10 H, Ar-H), 7.36−7.33 (m, 2 H, Ar-H), 7.28−7.22
(m, 9 H, Ar-H), 7.14−7.09 (m, 4 H, Ar-H), 7.04 (t, 4 H, Ar-H), 6.99
(s, 1 H, Ar-H); syn, 5.87 (s, 4 H, NCH2Ph), 4.89 (t, 3J(H,H) = 7.3 Hz,
3
4 H, NCH2), 3.59 (t, J(H,H) = 6.1 Hz, 4 H, CH2N3), 2.61 (m,
3J(H,H) = 7.2 Hz, 4 H, CH2CH2CH2); anti, 6.09 (s, 4 H, NCH2Ph),
1
54.41; H, 4.39; N, 12.92 (best result obtained). H and 13C NMR
3
3
4.77 (t, J(H,H) = 7.5 Hz, 4 H, NCH2), 3.28 (t, J(H,H) = 6.2 Hz, 4
H, CH2N3), 2.42 (m, 3J(H,H) = 7.3 Hz, 4 H, CH2CH2CH2). 13C{1H}
NMR (125.77 MHz, CDCl3): δ 181.9, 181.8 (Ccarbene), 135.95, 135.87,
135.64, 135.59, 135.5, 135.3, 129.5, 129.3, 128.8, 128.6, 128.5, 126.2,
123.7, 123.64, 123.60, 112.3, 112.2 110.9, 110.8 (Ar-C, 1 ×
coincident), 54.5, 54.2 (NCH2Ph), 49.6, 49.3 (CH2N3), 46.6, 46.4
(NCH2), 29.2, 29.0 (CH2CH2CH2). Anal. Calcd for C34H34I2N10Pd:
C, 43.31; H, 3.65; N, 14.85. Found: C, 43.64; H, 3.81; N, 12.89 (best
spectra are given in the Supporting Information. MS (ESI): m/z 878
[M + H + CH3CN]+. Data for 8b are as follows. 1H NMR (500 MHz,
CDCl3): δ 7.46−7.40 (m, 11 H, Ar-H), 7.34−7.31 (m, 9 H, Ar-H),
3
3
7.07 (d, J(H,H) = 1.9 Hz, 2 H, NCH), 7.06 (d, J(H,H) = 1.9 Hz, 2
H, NCH), 6.90 (d, 3J(H,H) = 1.9 Hz, 2 H, NCH), 6.87 (d, 3J(H,H) =
1.9 Hz, 2 H, NCH); syn, 5.54 (s, 4 H, NCH2Ph), 4.69 (t, J(H,H) =
3
6.5 Hz, 4 H, NCH2), 3.13 (t, 3J(H,H) = 6.7 Hz, 4 H, CH2SCN), 2.68
(m, 3J(H,H) = 6.6 Hz, 4 H, CH2CH2CH2); anti, 5.75 (s, 4 H,
NCH2Ph), 4.58 (t, 3J(H,H) = 6.4 Hz, 4 H, NCH2), 2.91 (t, 3J(H,H) =
6.7 Hz, 4 H, CH2SCN), 2.51 (m, 3J(H,H) = 6.6 Hz, 4 H,
CH2CH2CH2). 13C{1H} NMR (125.77 MHz, CDCl3): δ 168.6,
168.5 (Ccarbene), 135.3, 129.9, 129.7, 129.4, 129.3, 129.0, 128.8, 124.4,
124.3, 123.8, 123.7 (Ar-C, one is coincident), 121.3, 121.1 (PdSCN),
112.4, 112.1 (CH2SCN), 55.29, 55.26 (NCH2Ph), 49.0, 48.8 (NCH2),
31.4, 31.1 (CH2SCN), 31.0, 30.8 (CH2CH2CH2). Anal. Calcd for
C30H30N8PdS4: C, 48.87; H, 4.10; N, 15.20. Found: C, 48.56; H, 3.86;
N, 14.98. MS (ESI): 778 [M + H + CH3CN]+.
1
result obtained after multiple trials). H and 13C NMR spectra are
given in the Supporting Information. MS (ESI): m/z 815 [M − I]+.
trans-Diiodidobis{1-benzyl-3-(3-phenylthiopropyl)-
benzimidazolin-2-ylidene}palladium(II) (11). This complex was
prepared in analogy to complex 10 from the reaction of NaSPh (18
mg, 0.14 mmol) and complex 6a (56 mg, 0.05 mmol). Yield and
1
syn:anti ratio: 48 mg, 0.44 mmol, 89%, 1:1.3. H NMR (500 MHz,
CDCl3): δ 7.60 (d, 4 H, Ar-H), 7.51 (d, 1 H, Ar-H), 7.42−7.29 (m, 22
H, Ar-H), 7.26−7.21 (m, 15 H, Ar-H), 7.20−7.15 (m, 6 H, Ar-H),
7.10−7.06 (m, 4 H, Ar-H), 7.02−7.00 (m, 4 H, Ar-H); syn, 5.86 (s, 4
3
trans-Bis(thiocyanato-κS)bis{1-benzyl-3-(3-bromopropyl)-
azolin-2-ylidene}palladium(II) (9a,b). Complex 1a,b (93/82 mg,
0.10 mmol) and potassium thiocyanate (98 mg, 1.00 mmol) were
suspended in THF (30 mL) and stirred overnight. The resulting
yellow suspension was filtered before the filtrate was dried in vacuo
and CH2Cl2 (20 mL) was added. The CH2Cl2 layer was collected by
filtration and slowly evaporated to afford the products as yellow
crystals. Yields and syn:anti ratios: 9a, 67 mg, 0.08 mmol, 76%, 1:2.6;
9b, 44 mg, 0.06 mmol, 56%, 1:1.1. Data for 9a are as follows. 1H NMR
(500 MHz, CDCl3): δ 7.63 (d, 1 H, Ar-H), 7.55 (d, 3 H, Ar-H), 7.47−
7.41 (m, 12 H, Ar-H), 7.39−7.37 (m, 4 H, Ar-H), 7.32−7.28 (m, 8 H,
Ar-H), 7.17 (t, 5 H, Ar-H), 7.13 (d, 3 H, Ar-H); syn, 5.88 (s, 4 H,
H, NCH2Ph), 4.93 (t, J(H,H) = 7.4 Hz, 4 H, NCH2), 3.12 (t, 4 H,
3J(H,H) = 6.6 Hz, CH2S), 2.65 (m, 3J(H,H) = 7.2 Hz, 4 H,
3
CH2CH2CH2); anti, 6.08 (s, 4 H, NCH2Ph), 4.83 (t, J(H,H) = 7.5
3
Hz, 4 H, NCH2), 2.85 (t, J(H,H) = 6.5 Hz, 4 H, CH2S), 2.49 (m,
3J(H,H) = 7.3 Hz, 4 H, CH2CH2CH2). 13C{1H} NMR (125.77 MHz,
CDCl3): δ 181.71, 181.66 (Ccarbene), 136.4, 136.3, 135.9, 135.8, 135.7,
135.5, 135.3, 130.4, 130.1, 129.8, 129.7, 129.6, 129.5, 129.3, 128.7,
128.59, 128.57, 128.5, 128.1, 127.0, 126.8, 123.52, 123.47, 123.45,
112.2, 112.0, 111.04, 110.96 (Ar-C), 54.6, 54.1 (NCH2Ph), 48.0, 47.9
(NCH2), 32.0, 31.5 (CH2S), 28.8, 28.5 (CH2CH2CH2). Anal. Calcd
for C46H44I2N4PdS2: C, 51.29; H, 4.12; N, 5.20. Found: C, 51.68; H,
1
4.58; N, 4.66 (best result obtained after multiple trials). H and 13C
3
NCH2Ph), 5.02 (t, J(H,H) = 7.2 Hz, 4 H, NCH2), 3.66 (t, 4 H,
NMR spectra are given in the Supporting Information. MS (ESI): m/z
3J(H,H) = 5.9 Hz, CH2Br), 2.88 (m, 3J(H,H) = 6.5 Hz, 4 H,
951 [M − I]+.
3
CH2CH2CH2); anti, 6.19 (s, 4 H, NCH2Ph), 4.89 (t, J(H,H) = 7.4
trans-Diiodidobis{1-benzyl-3-(3-acetoxypropyl)-
benzimidazolin-2-ylidene}palladium(II) (12). This complex was
prepared in analogy to complex 10 from KSAc (30 mg, 0.26 mmol)
and complex 6a (78 mg, 0.07 mmol). Column chromatography
(hexane/ethyl acetate 2.5/1) afforded the product as a yellow solid (14
3
Hz, 4 H, NCH2), 3.35 (t, J(H,H) = 5.8 Hz, 4 H, CH2Br), 2.67 (m,
3J(H,H) = 6.7 Hz, 4 H, CH2CH2CH2). 13C{1H} NMR (125.77 MHz,
CDCl3): δ 181.0 (2 × Ccarbene), 136.4, 136.3, 136.0, 135.8, 135.3,
135.2, 129.8, 129.71, 129.65, 129.1, 128.9, 128.1, 127.8, 127.7, 124.69,
124.67 (Ar-C), 120.64, 120.61 (PdSCN), 112.7, 112.3, 111.5, 111.3
(Ar-C), 53.7, 53.1 (NCH2Ph), 47.5 (2 × NCH2), 33.5, 33.1 (CH2Br),
31.4, 30.9 (CH2CH2CH2). Anal. Calcd for C36H34Br2N6PdS2: C,
49.08; H, 3.89; N, 9.54. Found: C, 49.06; H, 4.17; N, 9.47. MS (ESI):
1
mg, 0.014 mmol, 20%) in a syn:anti ratio of 1:1.1. H NMR (500
MHz, CDCl3): δ 7.63 (d, 4 H, Ar-H), 7.44 (d, 2 H, Ar-H), 7.39−7.36
(m, 12 H, Ar-H), 7.33 (d, 2 H, Ar-H), 7.24−7.20 (m, 8 H, Ar-H),
7.12−7.07 (m, 4 H, Ar-H), 7.01 (t, 4 H, Ar-H); syn, 5.85 (s, 4 H,
NCH2Ph), 4.86 (t, 3J(H,H) = 7.5 Hz, 4 H, NCH2), 3.12 (t, 3J(H,H) =
7.1 Hz, 4 H, CH2S), 2.64, (m, 3J(H,H) = 7.4 Hz, 4 H, CH2CH2CH2),
1
m/z 822 [M − SCN]+. Data for 9b are as follows. H NMR (500
MHz, CDCl3): δ 7.43 (ps-d, 9 H, Ar-H), 7.34 (br-s, 11 H, Ar-H), 7.10
3
3
3
(d, J(H,H) = 1.9 Hz, 2 H, NCH), 7.08 (d, J(H,H) = 1.9 Hz, 2 H,
2.40 (s, 6 H, CH3); anti, 6.09 (s, 4 H, NCH2Ph), 4.72 (t, J(H,H) =
7.7 Hz, 4 H, NCH2), 2.81 (t, 3J(H,H) = 6.9 Hz, 4 H, CH2S), 2.44 (m,
3J(H,H) = 7.4 Hz, 4 H, CH2CH2CH2), 2.16 (s, 6 H, CH3). 13C{1H}
NCH), 6.83 (m, 4 H, NCH); syn, 5.56 (s, 4 H, NCH2Ph), 4.67 (t,
3
3J(H,H) = 6.7 Hz, 4 H, NCH2), 3.56 (t, J(H,H) = 5.9 Hz, 4 H,
CH2Br), 2.69 (m, 3J(H,H) = 6.1 Hz, 4 H, CH2CH2CH2); anti, 5.75 (s,
NMR (125.77 MHz, CDCl3): δ 196.2, 196.1 (CO), 181.7, 181.6
(Ccarbene), 135.9, 135.8, 135.7, 135.6, 135.4, 129.5, 129.3, 128.79,
128.77, 128.63, 128.61, 128.5, 123.61, 123.56, 123.5, 112.4, 112.3,
112.2, 111.0, 110.9 (Ar-C), 54.7, 54.2 (NCH2Ph), 48.3, 48.2 (NCH2),
31.4, 31.1 (CH2S), 29.8, 29.4 (CH2CH2CH2), 27.4, 27.1 (CH3). Anal.
Calcd for C38H40I2N4O2PdS2: C, 45.23; H, 4.00; N, 5.35. Found: C,
45.48; H, 3.87; N, 5.59. MS (ESI): m/z 881 [M − I]+.
trans-Diiodidobis{1-benzyl-3-(3-thiocyanopropyl)-
benzimidazolin-2-ylidene}palladium(II) (13). This complex was
prepared in analogy to complex 10 from the reaction of KSCN (15
mg, 0.15 mmol) and complex 6a (56 mg, 0.05 mmol). It was isolated
as a yellow powder in a syn:anti ratio of 1:1.8. Yield: 36 mg, 0.04
mmol, 74%. 1H NMR (500 MHz, CDCl3): δ 7.52 (d, 5 H, Ar-H), 7.48
(d, 2 H, Ar-H), 7.44−7.35 (m, 8 H, Ar-H), 7.32−7.22 (m, 12 H, Ar-
H), 7.15 (t, 5 H, Ar-H), 7.06 (ps-d, 4 H, Ar-H); syn, 5.84 (s, 4 H,
NCH2Ph), 4.97 (t, 3J(H,H) = 6.8 Hz, 4 H, NCH2), 3.19 (t, 3J(H,H) =
6.8 Hz, 4 H, CH2SCN), 2.91 (m, 3J(H,H) = 6.8 Hz, 4 H,
3
4 H, NCH2Ph), 4.59 (t, J(H,H) = 6.8 Hz, 4 H, NCH2), 3.42 (t,
3
3J(H,H) = 5.8 Hz, 4 H, CH2Br), 2.59 (m, J(H,H) = 6.1 Hz, 4 H,
CH2CH2CH2). 13C{1H} NMR (125.77 MHz, CDCl3): δ 168.59,
168.55 (Ccarbene), 135.5, 135.4, 129.9, 129.8, 129.4, 129.3, 129.2, 124.7,
124.6, 123.8, 123.7 (Ar-C, 1 × coincident), 123.6 (2 × PdSCN), 55.4,
55.3 (NCH2Ph), 49.62, 49.58 (NCH2), 33.8, 33.7 (CH2Br), 31.1, 30.9
(CH2CH2CH2). Anal. Calcd for C28H30Br2N6PdS2: C, 43.06; H, 3.87;
N, 10.76. Found: C, 43.28; H, 3.64; N, 10.81. MS (ESI): m/z 722 [M
− SCN]+.
trans-Diiodidobis{1-benzyl-3-(3-azidopropyl)-
benzimidazolin-2-ylidene}palladium(II) (10). NaN3 (52 mg, 0.80
mmol) was added to a suspension of complex 6a (89 mg, 0.08 mmol)
in CH3CN (20 mL) and stirred overnight. The solvent of the
suspension was removed in vacuo, and 50 mL of CH2Cl2 was added.
The resulting yellow suspension was filtered over Celite and the
solvent removed under reduced pressure to give the product as a
J
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
CH2CH2CH2); anti, 6.10 (s, 4 H, NCH2Ph), 4.86 (t, J(H,H) = 6.8
Hz, 4 H, NCH2), 2.77 (t, 3J(H,H) = 6.6 Hz, 4 H, CH2SCN), 2.63 (m,
3J(H,H) = 6.7 Hz, 4 H, CH2CH2CH2). 13C{1H} NMR (125.77 MHz,
(NCH2), 23.1 (CH2CH2CH2), 7.8 (CH3). MS (ESI): m/z 429 [M +
MeOH + H2O]2+.
Mizoroki−Heck Catalysis. In a typical run, a reaction tube was
charged with a mixture of aryl halide (1 mmol for monohalides, 0.5
mmol for dihalides, 0.33 mmol for trihalides, and 0.25 mmol for
tetrahalides), NaOAc (1.5 equiv per halide present), tert-butyl acrylate
(1.5 equiv per halide present), catalyst (1 mol % per halide present),
and DMF (3 mL). The reaction mixture was stirred and heated to 130
°C for 20 h. After the mixture was cooled to ambient temperature,
dichloromethane (5 mL) was added. The organic layer was then
washed with water (5 × 10 mL) and dried over Na2SO4. The solvent
was reduced, and the residue was subjected to column chromatog-
raphy (hexane/ethyl acetate).
CDCl3): δ 181.6, 181.5 (Ccarbene), 135.7, 135.54, 135.48, 135.3, 129.7,
129.3, 129.0, 128.6, 128.4, 128.1, 124.10, 124.06, 124.0, 112.5 (Ar-C),
112.40, 112.38 (SCN), 110.9 (Ar-C, 5 × coincident), 54.5, 54.1
(NCH2Ph), 47.2, 47.1 (NCH2), 32.1, 31.6 (CH2SCN), 29.6, 29.0
(CH2CH2CH2). Anal. Calcd for C36H34I2N6PdS2: C, 44.35; H, 3.51;
N, 8.62. Found: C, 44.59, H, 3.63; N, 8.32. MS (ESI): m/z 847 [M −
I]+.
trans-Dibromidobis{1-benzyl-3-(3-triethylammoniopropyl)-
benzimidazolin-2-ylidene}palladium(II) Dibromide (14). Com-
plex 4a (1.20 g, 1.30 mmol) was dissolved in ethyl bromide (15 mL,
200 mmol) in a sealed Schlenk tube and stirred overnight at 70 °C.
The precipitate was collected by filtration and washed with CH3CN (3
× 5 mL) to give the product as an off-white solid (1.20 g, 1.10 mmol,
1,2,4,5-Tetra-tert-butylcinnamates. 1H NMR (500 MHz,
3
CDCl3): δ 7.86 (d, J(H,H) = 15.8 Hz, 4 H, CH), 7.70 (s, 2 H, Ar-
3
H), 6.32 (d, J(H,H) = 15.8 Hz, 4 H, CH), 1.53 (s, 36 H, CH3).
13C{1H} NMR (125.77 MHz, CDCl3): δ 166.0 (CO), 139.8, 136.1,
127.3, 125.5 (Ar-C and CHCH), 81.7 (C(CH3)3), 28.9 (CH3).
Anal. Calcd for C34H46O8: C, 70.08; H, 7.96. Found: C,70.00, H, 8.11.
MS (ESI): m/z 663 [M + K + CH3CN]+.
1
86%) in a syn:anti ratio of 1:4.5. H NMR (500 MHz, d6-DMSO): δ
7.98 (d, 1 H, Ar-H), 7.91 (d, 3 H, Ar-H), 7.60 (d, 6 H, Ar-H), 7.55 (d,
2 H, Ar-H), 7.42−7.32 (m, 15 H, Ar-H), 7.26 (ps-d, 7 H, Ar-H), 7.21
(ps-d, 2 H, Ar-H); syn, 6.05 (s, 4 H, NCH2Ph), 5.02 (t, 3J(H,H) = 6.7
Hz, 4 H, NCH2CH2), 3.53 (t, J(H,H) = 7.3 Hz, 4 H, CH2CH2N+),
3
X-ray Diffraction Studies. X-ray data were collected with a
Bruker AXS SMART APEX diffractometer, using Mo Kα radiation
with the SMART suite of programs.23 Data were processed and
corrected for Lorentz and polarization effects with SAINT24 and for
absorption effects with SADABS.25 Structure solution and refinement
were carried out with the SHELXTL suite of programs.26 The
structure was solved by direct methods to locate the heavy atoms,
followed by difference maps for the light, non-hydrogen atoms. All
non-hydrogen atoms were generally given anisotropic displacement
parameters in the final model. All H atoms were placed at calculated
positions.
3.30 (m, J(H,H) = 6.7 Hz, 12 H, N+CH2CH3), 2.62 (br-m, 4 H,
3
CH2CH2CH2), 1.15 (t, 3J(H,H) = 7.1 Hz, 18 H, CH3); anti, 6.25 (s, 4
3
H, NCH2Ph), 4.97 (t, J(H,H) = 6.7 Hz, 4 H, NCH2CH2), 3.20 (t,
3J(H,H) = 7.5 Hz, 4 H, CH2CH2N+), 3.00 (m, J(H,H) = 7.0 Hz, 12
3
H, N+CH2CH3), 2.36 (br-m, 4 H, CH2CH2CH2), 0.96 (t, J(H,H) =
3
7.1 Hz, 18 H, CH3). 13C{1H} NMR (125.77 MHz, d6-DMSO): δ
180.7, 180.5 (Ccarbene), 135.7, 135.4, 134.0, 133.9, 133.7, 133.3, 128.5,
128.3, 127.90, 127.87, 127.7, 123.6, 123.5, 111.9, 111.7, 111.6, 111.4
(Ar-C, 3 × coincident), 53.7 (2 × NCH2Ph), 52.3, 52.1 (2 × ), 51.8
(N+CH2), 44.7 (2 × NCH2), 21.7 (2 × CH2CH2CH2), 7.3, 7.0 (CH3).
Anal. Calcd for C46H64Br4N6Pd: C, 49.02; H, 5.72; N, 7.46. Found: C,
49.41; H, 5.48; N, 6.99 (best result obtained). 1H and 13C NMR
spectra are given in the Supporting Information. MS (ESI): m/z 483
[M − 2Br]2+, 1047 [M − Br]+.
ASSOCIATED CONTENT
* Supporting Information
■
S
Tables and CIF files giving crystallographic data for 1a, 3a,
7a,b, 8a, 9a, and 13 and a summary of the most important
crystallographic data and figures giving NMR spectra for 5a,b,
8a, 10, 11, and 14. This material is available free of charge via
the Internet at http://pubs.acs.org.
trans-Dibromidobis{1-benzyl-3-(3-triethylammoniopropyl)-
benzimidazolin-2-ylidene}palladium(II) Diformate (15). Com-
plex 14 (48 mg, 0.04 mmol) and silver formate (13 mg, 0.09 mmol)
were mixed in CH2Cl2/MeOH (10/5 mL). The mixture was stirred
for 2 h before the precipitate was filtered off through Celite. Removal
of the solvent gave an off-white solid, which was dissolved in CD3CN
for NMR. The syn:anti ratio is 1:2.9. 1H NMR (300 MHz, CD3CN): δ
8.60 (s, 2 H, HCOO−), 7.81 (d, 1 H, Ar-H), 7.74 (d, 3 H, Ar-H),
7.55−7.53 (m, 6 H, Ar-H), 7.48−7.45 (m, 2 H, Ar-H), 7.39−7.30 (m,
15 H, Ar-H), 7.24−7.18 (m, 9 H, Ar-H); syn, 6.02 (s, 4 H, NCH2Ph),
5.08 (t, 3J(H,H) = 6.7 Hz, 4 H, NCH2CH2), 3.58 (m, 4 H,
CH2CH2N+), 1.14 (t, 3J(H,H) = 7.2 Hz, 18 H, CH3), the N+CH2CH3
protons are overlapped with CH2CH2N+ protons of the anti isomer at
3.26−3.16 (m, 20 H), the CH2CH2CH2 protons are overlapped with
the water signal at 2.69 ppm; anti, 6.25 (s, 4 H, NCH2Ph), 4.98 (t,
3J(H,H) = 6.3 Hz, 4 H, NCH2CH2), 2.93 (m, 3J(H,H) = 7.5 Hz, 12 H,
AUTHOR INFORMATION
Corresponding Author
*E-mail for H.V.H.: chmhhv@nus.edu.sg.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the National University of Singapore and
the Singapore Ministry of Education (MOE) for financial
support (WBS R-143-000-483-112). Technical support from
the staff at the CMMAC of our department is appreciated.
N+CH2CH3), 2.37 (m, 4 H, CH2CH2CH2), 0.94 (t, 3J(H,H) = 7.2 Hz,
18 H, CH3). 13C{1H} NMR (75.48 MHz, CD3CN): δ 182.4, 182.2
(Ccarbene), 167.7 (HCOO−), 137.3, 136.7, 135.4, 134.8, 129.7, 129.6,
129.5, 129.1, 128.9, 128.8, 128.6, 128.5, 124.8, 124.6, 124.2, 124.1,
112.7, 112.24, 112.15, 111.9 (Ar-C), 55.34, 55.25 (NCH2Ph), 53.6 (2
× ), 53.34, 53.27 (N+CH2), 46.1, 45.8 (NCH2), 22.99, 22.90
(CH2CH2CH2), 7.8, 7.7 (CH3). MS (ESI): m/z 483 [M − 2Br]2+.
Bis{1-benzyl-3-(3-triethylammoniopropyl)benzimidazolin-2-
ylidene}palladium(0) X2 (16; X = Br, HCO2). Complex 15 was left
REFERENCES
■
(1) (a) Herrmann, W. A.; Kocher, C. Angew. Chem., Int. Ed. Engl.
̈
1997, 36, 2162. (b) Bourissou, D.; Guerret, O.; Gabbaï, P.; Bertrand,
G. Chem. Rev. 2000, 100, 39. (c) Hahn, F. E.; Jahnke, M. C. Angew.
Chem., Int. Ed. 2009, 47, 3122. (d) Lin, J. C. Y.; Huang, R. T. W.; Lee,
C. S.; Bhattacharyya, A.; Hwang, W. S.; Lin, I. J. B. Chem. Rev. 2009,
109, 3561. (e) Arnold, P.; Casely, I. J. Chem. Rev. 2009, 109, 3599.
(f) Schuster, O.; Yang, L. R.; Raubenheimer, G.; Albrecht, M. Chem.
Rev. 2009, 109, 3445.
1
in CD3CN for 2 h to convert to this complex. H NMR (500 MHz,
CD3CN): δ 8.62 (s, 1 H, HCOO−), 7.76 (d, 2 H, Ar-H), 7.53 (br-s, 4
H, Ar-H), 7.34−7.33 (m, 7 H, Ar-H), 7.28−7.22 (m, 5 H, Ar-H), 6.05
(s, 4 H, NCH2Ph), 5.84 (br-s, 4 H, NCH2CH2), 3.32 (br-s, 4 H,
CH2CH2N+), 3.03 (m, J(H,H) = 7.0 Hz, 12 H, N+CH2CH3), 2.41
3
(2) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
3
(br-s, 4 H, CH2CH2CH2), 0.94 (t, J(H,H) = 6.8 Hz, 18 H, CH3).
́
(b) Dıez-Gonzal
3612. (c) Fortman, G. C.; Nolan, S. P. Chem. Soc. Rev. 2011, 40, 5151.
(d) Valente, C.; Calimsiz, S.; Hoi, K. H.; Mallik, D.; Sayah, M.; Organ,
M. G. Angew. Chem., Int. Ed. 2012, 51, 3314.
́
ez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109,
13C{1H} NMR (125.77 MHz, CD3CN): δ 193.4 (Ccarbene), 167.7
(HCOO−), 137.4, 135.4, 135.1, 129.6, 128.9, 128.6, 124.2, 124.1,
112.2, 111.9 (Ar-C), 55.3 (NCH2Ph), 53.7, 53.3 (N+CH2), 46.2
̧
K
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(3) (a) Seo, H.; Kim, B. Y.; Lee, J. H.; Park, H. J.; Son, S. U.; Chung,
Y. K. Organometallics 2003, 22, 4783. (b) Huynh, H. V.; Wong, L. R.;
Ng, P. S. Organometallics 2008, 27, 2231. (c) Yuan, D.; Tang, H. Y.;
Xiao, L. F.; Huynh, H. V. Dalton Trans. 2011, 40, 8788. (d) Huynh, H.
V.; Jothibasu, R. J. Organomet. Chem. 2011, 696, 3369. (e) Busetto, L.;
Cassani, M. C.; Femoni, C.; Mancinelli, M.; Mazzanti, A.; Mazzoni, R.;
Solinas, G. Organometallics 2011, 30, 5258.
P.; Mahapatra, A.; Dinda, J. Inorg. Chim. Acta 2012, 384, 239.
(d) Hirtenlehner, C.; Krims, C.; Holbling, J.; List, M.; Zabel, M.;
̈
Fleck, M.; Berger, R. J. F.; Schoefberger, W.; Monkowius, U. Dalton
Trans. 2011, 40, 9899. (e) Sivaram, H.; Jothibasu, R.; Huynh, H. V.
Organometallics 2012, 31, 1195.
(23) SMART version 5.628; Bruker AXS Inc., Madison, WI, 2001.
(24) SAINT+version 6.22a; Bruker AXS Inc., Madison, WI, 2001.
(25) Sheldrick, G. W. SADABS version 2.10; University of Gottingen,
̈
(4) (a) Kuhl, O. Chem. Soc. Rev. 2007, 36, 592. (b) John, A.; Ghosh,
̈
Gottingen, Germany, 2001.
̈
P. Dalton Trans. 2010, 39, 7183.
(26) SHELXTL version 6.14; Bruker AXS Inc., Madison, WI, 2000.
(5) Selected examples: (a) Fliedel, C.; Braunstein, P. J. Organomet.
Chem. 2014, 751, 286. (b) Normand, A. T.; Cavell, K. J. Eur. J. Inorg.
Chem. 2008, 2781. (c) Bierenstiel, M.; Cross, E. D. Coord. Chem. Rev.
2011, 255, 574. (d) Huynh, H. V.; Yeo, C. H.; Tan, G. K. Chem.
Commun. 2006, 3833. (e) Huynh, H. V.; Yeo, C. H.; Chew, Y. X.
Organometallics 2010, 29, 1479. (f) Jimen
J.; Perez-Torrente, J. J.; Modrego, F. J.; Winterle, S.; Cunchillos, C.;
Lahoz, F. J.; Oro, L. A. Organometallics 2011, 30, 5493.
́ ́
ez, M. V.; Fernandez-Tornos,
́
(6) (a) Lemke, J.; Metzler-Nolte, N. Eur. J. Inorg. Chem. 2008, 3359.
(b) Chardon, E.; Puleo, G. L.; Dahm, G.; Guichard, G.; Bellemin-
Laponnaz, S. Chem. Commun. 2011, 47, 5864. (c) Roland, S.; Jolivalt,
C.; Cresteil, T.; Eloy, L.; Bouhours, P.; Hequet, A.; Mansuy, V.;
Vanucci, C.; Paris, J. M. Chem. Eur. J. 2011, 17, 1442.
(7) (a) Hsu, T. H. T.; Naidu, J. J.; Yang, B. J.; Jang, M. Y.; Lin, I. J. B.
Inorg. Chem. 2012, 51, 98. (b) Azua, A.; Sanz, S.; Peris, E. Chem. Eur. J.
2011, 17, 3963. (c) Li, G.; Yang, H. Q.; Li, W.; Zhang, G. L. Green
Chem. 2011, 13, 2939. (d) Velazquez, H. D.; Verpoort, F. Chem. Soc.
Rev. 2012, 41, 7032. (e) Schaper, L.; Hock, S. J.; Herrmann, W. A.;
Kuhn, F. E. Angew. Chem., Int. Ed. 2013, 52, 270.
̈
(8) (a) Cure, J.; Poteau, R.; Gerber, I. C.; Gornitzka, H.; Hemmert,
C. Organometallics 2012, 31, 619. (b) Penafiel, I.; Pastor, I. M.; Yus,
̃
́
M.; Esteruelas, M. A.; Olivan, M.; Onate, E. Eur. J. Org. Chem. 2011,
̃
7174. (c) Yuan, D.; Huynh, H. V. Dalton Trans. 2011, 40, 11698.
(9) Herrmann, W. A.; Gooβen, L. J.; Spiegler, M. J. Organomet. Chem.
1997, 547, 357.
(10) (a) Yuan, D.; Huynh, H. V. Organometallics 2010, 29, 6020.
(b) Yuan, D.; Huynh, H. V. Dalton Trans. 2011, 40, 11698.
(11) Huynh, H. V.; Teng, Q. Chem. Commun. 2013, 49, 4244.
(12) (a) Zhang, D.; Zhou, S.; Li, Z. M.; Wang, Q. R.; Weng, L. H.
̈
Dalton Trans. 2013, 42, 12020. (b) Ozdemir, I.; Gurbuz, N.; Kalog
N.; Dog
Chem. 2013, 9, 303.
̆
̈
̈
̈
̆ ̆
an, O.; Kalogl
(13) Han, Y.; Huynh, H. V.; Koh, L. L. J. Organomet. Chem. 2007,
692, 3606.
(14) Huynh, H. V.; Wu, J. J. Organomet. Chem. 2009, 694, 323.
(15) Leadbeater, N. E.; Marco, M. Angew. Chem., Int. Ed. 2003, 42,
1407.
(16) (a) Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus,
̈
G. R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 2371. (b) Magill, A. M.;
McGuinness, D. S.; Cavell, K. J.; Britovsek, G. J. P.; Gibson, V. C.;
White, A. J. P.; Williams, D. J.; White, A. H.; Skelton, B. W. J.
Organomet. Chem. 2001, 617−618, 546.
(17) Amadio, E.; Scrivanti, A.; Bortoluzzi, M.; Bertoldini, M.;
Beghetto, V.; Matteoli, U.; Chessa, G. Inorg. Chim. Acta 2013, 405, 188
and references cited therein.
(18) Peh, G. R.; Kantchev, E. A. B.; Zhang, C.; Ying, J. Y. Org. Biomol.
Chem. 2009, 7, 2011.
(19) Bull, S. D.; Davies, S. G.; Smith, A. D. J. Chem. Soc., Perkin Trans.
1 2001, 22, 2931.
(20) (a) McGuinness, D. S.; Cavell, K. J. Organometallics 1999, 18,
1596. (b) Arnold, P. L.; Cloke, F. G. N.; Geldbach, T.; Hitchcock, P.
B. Organometallics 1999, 18, 3228. (c) Bohm, V. P. W.; Gstottmayr, C.
̈
̈
W. K.; Weskamp, T.; Herrmann, W. A. J. Organomet. Chem. 2000, 595,
186. (d) Lee, E.; Yandulov, D. V. J. Organomet. Chem. 2011, 696, 4095.
(21) Huynh, H. V.; Ho, J. H. H.; Neo, T. C.; Koh, L. L. J. Organomet.
Chem. 2005, 690, 3854.
(22) (a) Xu, X. Y.; Kim, S. H.; Zhang, X.; Das, A. K.; Hirao, H.;
Hong, S. H. Organometallics 2013, 32, 164. (b) Ghdhayeb, M. Z.;
Haque, R. A.; Budagumpi, S. J. Organomet. Chem. 2014, 757, 42.
(c) Adhikary, S. D.; Jhulki, L.; Seth, S.; Kundu, A.; Bertolasi, V.; Mitra,
L
dx.doi.org/10.1021/om500274c | Organometallics XXXX, XXX, XXX−XXX