Platinum(II) complexes with thioether-functionalized benzimidazolin-2- ylidene ligands: Synthesis, structural characterization, and application in hydroelementation reactions

Article abstract of DOI:10.1021/om400929t

A series of six benzimidazolium salts with an alkyl-alkyl thioether moiety in the side chain has been synthesized. While it was impossible to obtain the platinum(II) complexes by direct reaction between ligand precursors and basic platinum salts, the mild

Full text of DOI:10.1021/om400929t

Article
pubs.acs.org/Organometallics
Platinum(II) Complexes with Thioether-Functionalized
Benzimidazolin-2-ylidene Ligands: Synthesis, Structural
Characterization, and Application in Hydroelementation Reactions
Jan C. Bernhammer and Han Vinh Huynh*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
S
* Supporting Information
ABSTRACT: A series of six benzimidazolium salts with an alkyl−
alkyl thioether moiety in the side chain has been synthesized.
While it was impossible to obtain the platinum(II) complexes by
direct reaction between ligand precursors and basic platinum salts,
the mild silver carbene transfer reaction gave the desired complexes
in all cases. X-ray crystallography confirmed the expected κ2C,S
coordination mode of the benzimidazolin-2-ylidene ligands, with a
cis arrangement of the carbene and the hemilabile thioether
moieties in all complexes. Preliminary studies of the catalytic
activity of these complexes showed them to be active catalysts for
the intermolecular hydroamination of alkynes with sterically hindered anilines in conjunction with silver triflate. Additionally, the
complexes catalyzed the hydrosilylation of alkenes with excellent yields and good regioselectivity.
frequent incidence of sulfur-bound coligands.9 In light of the
INTRODUCTION
■
favorable previous experiences with sulfur-functionalized NHC
Late-transition-metal complexes with N-heterocyclic carbene
ligands and their coordination chemistry with palladium(II),10
(NHC) ligands have been extensively studied, with particular
interest in their catalytic activities.1 Notable examples of
it is of considerable interest to extend this chemistry to
platinum(II).
commercially successful catalysts incorporating NHC ligands
are the second-generation Grubbs catalyst2 and its derivatives as
well as Organ’s PEPPSI complexes.3 The popularity of NHC
RESULTS AND DISCUSSION
■
complexes is related to their easy synthesis, the possibilities for
electronic and steric fine tuning of the ligands, and their
chemical properties, which are similar to and sometimes
Ligand Precursor Synthesis. Thioether-functionalized
benzimidazolium salts are accessible in three steps starting
from benzimidazole, as outlined in Scheme 1. Monoalkylated
benzimidazoles 1a−c can be obtained in good yields by a
superior to the properties of the ubiquitously used phosphine
ligands.4
straightforward reaction between alkyl bromides and benzimi-
Especially, NHC complexes of group 10 metals have been
dazole in the presence of sodium hydroxide following a
widely investigated as potential catalysts. Palladium(II)
previously described procedure.6g,11 The subsequent introduc-
complexes have been found to catalyze C−C cross-coupling
tion of a bromoalkyl side chain is plagued by chemoselectivity
reactions such as the Suzuki−Miyaura and Mizoroki−Heck
problems, since the desired reaction is competing with the
reactions as well as olefin polymerizations, Hartwig−Buchwald
linkage of two benzimidazole moieties. This problem was
aminations, and the α-arylation of ketones.5 In recent years,
controlled by using a large excess of alkylating agent, which also
nickel(II) NHC complexes have received increasing attention
acted as the solvent in the reaction.12 The recovery of surplus
as well, due to the similarities in reactivity with their
1,2-dibromoethane and 1,3-dibromopropane by distillation
palladium(II) counterparts and the lower costs associated
from the crude mixture is possible, rendering the alkylation
with this metal.6 In contrast to complexes of the lighter
reaction more economical.
homologues, platinum(II) NHC complexes have been less well
studied.
Separation of the desired bromoalkyl-functionalized benzi-
midazolium salts from the linked, dicationic byproducts was
The rise of cisplatin as a chemotherapeutic agent has sparked
achieved by exploiting the higher solubility of the monocationic
increased interest in metal-based drugs, and consequently a
salts in dichloromethane. The benzimidazolium salts 2a−c,
number of platinum(II) NHC complexes have been examined
for their cytotoxic properties.7 In the field of catalysis,
which contain a bromoethyl side chain, as well as their
bromopropyl-functionalized counterparts 3a−c, were obtained
platinum(II) and platinum(0) complexes bearing NHC ligands
have shown promising activities in various transformations,
notably hydroelementation reactions of carbon−carbon multi-
Received: September 16, 2013
Published: December 11, 2013
ple bonds.8 A striking feature of platinum(II) complexes is the
© 2013 American Chemical Society
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Scheme 1. Synthesis of Thioether-Functionalized Ligand Precursors
in moderate yields. All compounds were obtained as colorless
Scheme 2. Preparation of Platinum(II) NHC Complexes
with Tethered S-Donors
solids with relatively poor solubility in chlorinated solvents,
while being insoluble in hydrocarbons and ethereal solvents.
In the final step, nucleophilic substitution of bromine by in
situ generated sodium propane-2-thiolate in degassed acetoni-
trile at ambient temperature yielded the desired thioether-
containing benzimidazolium salts 4a−c and 5a−c as colorless
solids, with the exception of 5b, which was obtained as a highly
viscous oil. The yields were moderate to excellent. Upon
introduction of the isopropyl thioether, the solubility in
chlorinated solvents increased markedly, while the solubility
in ethereal solvents as well as in hydrocarbons remained low.
Synthesis of Platinum(II) Complexes. Several pathways
for the formation of the desired chelating mono-NHC
complexes were explored. No reaction was observed with 4a,
platinum(II) acetylacetonate, and potassium bromide as the
external bromide source in acetonitrile, even after prolonged
heating.8c,13 Platinum(II) bromide and sodium acetate as
external base reacted with 4a, although yields were low and
the reaction was accompanied by significant decomposition
reactions, leading to hard to purify crude mixtures. A more
convenient and high-yielding route was found utilizing the mild
yet efficient silver carbene transfer protocol.14
protons in the thioether side chain diastereotopic. In 6b and 7b,
diastereotopic behavior is observed for the NCH2 protons in
the nonfunctionalized side chain as well.
In the 13C NMR spectra of the complexes, the resonance of
the carbene carbon is observed between 150.6 and 156.0 ppm.
These chemical shifts are in good agreement with literature
values.9a,15 No satellites due to carbon−platinum coupling are
observed, which is common in platinum mono-NHC
complexes, due to the low signal intensity of the carbene
carbon resonance and the often poor solubility of the
complexes.
All benzimidazolium salts reacted with silver(I) oxide to yield
the corresponding carbene complexes. No attempts were made
to isolate the intermediate silver NHC complexes, which were
instead directly reacted with freshly prepared [PtBr2(dmso)2].
Transmetalation from silver to platinum occurred rapidly, and
the desired platinum complexes could be isolated in moderate
to good yields from the reaction mixture (Scheme 2).
All complexes were obtained as almost white to pale yellow
microcrystalline solids, which were insoluble in hydrocarbons
and ethereal solvents. Their solubility in chlorinated solvents is
low, and they are only moderately soluble in polar solvents such
as DMSO. The 1H NMR spectra of all complexes are markedly
different from those of the corresponding ligand precursors. In
all cases, the disappearance of the singlet resonance observed
between 10.42 and 11.70 ppm in the spectra of the ligand
precursors, which can be attributed to H-2, indicates the
success of the transformation. Pronounced changes are
observed in the signals of the thioether side chains. In most
instances, the resonances are found to be more downfield in the
complexes, and in all cases, the complexity of coupling patterns
has increased dramatically. The latter observation indicates that
the ligands indeed bind in a chelating fashion, rendering the
Complexes 7a and 7c were isolated as inseparable mixtures
of multiple species, as evidenced by their NMR spectra. It
occurs frequently that palladium complexes of thioether-
functionalized NHC ligands exhibit dynamic hemilabile
behavior with multiple species coexisting in solution.10a,b,16
While platinum has a higher affinity for sulfur donors than
palladium, it is still plausible that subtle influences such as the
higher ring strain in the monomeric chelates featuring a seven-
membered metallacycle can lead to the formation of one of the
species A−C shown in Figure 1.
Molecular Structures. Single crystals suitable for X-ray
diffraction analysis of 6b, 7a and 7b were obtained by slow
evaporation of concentrated solutions in dichloromethane. In
the case of 6a, 6c and 7c, single crystals were obtained by slow
evaporation of concentrated solutions in dichloromethane/
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group 9−12 metals are able to catalyze hydroamination
reactions with good yield.18 Notable NHC-based catalysts
include complexes of rhodium, palladium, iridium, and gold.19
Platinum salts and complexes are also well-known to be
catalysts for hydroamination reactions,20 and indeed a number
of platinum NHC complexes have been employed for this kind
of transformation.8i,j The mechanism has been studied in detail
both by experimental methods and by DFT calculations by Poli
et al.21
To gauge the performance of 6a−c and 7a−c in
intermolecular hydroaminations, the reaction between phenyl-
acetylene (8) and 2,6-dimethylaniline (9) was studied (Scheme
3). The initial hydroamination of the triple bond followed by a
rapid enamine−imine tautomerization would yield 10. It was
found that all six complexes were active catalysts in the
presence of silver triflate, while in the absence of an additive
only trace amounts of product were observed in the reaction
mixture (Table 2). Silver triflate alone showed only minor
catalytic activity; thus, the dramatic enhancement of catalytic
performance can be attributed with near-certainty to the
abstraction of the bromido coligands from the complexes and
their formal replacement with very labile triflato groups,
generating readily available coordination sites for the incoming
substrate.
In all cases, the reaction proceeded with perfect Markovnikov
selectivity, with the enamine tautomerizing to the correspond-
ing imine rapidly. The observed yields were in the range from
moderate to good, with the best performance being observed
for complexes 6c and 7c (Table 2, entries 4 and 7). It is likely
that the bulky benzhydryl side chain present in these two
complexes favors the elimination of the product after the attack
of the amine on the activated alkyne, thus enhancing catalytic
turnover. On average, to some extent better results were
obtained with complexes 6a−c. A possible reason could be the
higher stability of the six-membered metallacycles in these
complexes, which hampers catalyst decomposition. In terms of
reaction conditions, required time, and catalyst loading, 6c
compares favorably to other catalytic systems described for this
particular transformation.19g,h,22
Figure 1. Possible dimeric species coexisting with the monomeric
forms of 7a and 7c.
THF, dichloromethane/hexane, and dichloromethane/toluene,
respectively. The molecular structures of all complexes reveal
the expected monomeric species with distorted-square-planar
coordination geometries at the platinum center (Figures 2−4).
1
As anticipated from the analysis of the H NMR spectra, the
thioether is coordinated to the metal in all cases, with a cis
arrangement of the two bromido coligands. The metallacycles
adopt a slightly distorted boat conformation irrespective of ring
size.
The planes defined by the NHC ring and the coordination
plane are twisted by 55.0(5)−71.5(5)° with respect to each
other. Larger dihedral angles are observed for 7a−c, reflecting
the higher degree of conformational freedom conferred by the
longer propyl side chain. All bond lengths fall within the
expected range (Table 1).9a,15 Interestingly, the platinum−
ligand bond lengths are very similar in all complexes.
This is especially pronounced in the case of the platinum−
carbon bonds, which are identical within experimental error
with an average length of 1.972 Å. The bond lengths between
platinum and the two distinct bromido ligands are markedly
different; a longer bond is found between platinum and Br2 due
to the stronger trans influence of the NHC donor. The
bromido ligand in a position trans to the more weakly donating
thioether moiety is located significantly closer to the platinum
center.
Hydroamination of Phenylacetylene. Hydroamination
reactions of carbon−carbon multiple bonds are an excellent
way of introducing carbon−nitrogen bonds due to the
complete atom economy with which the transformation
proceeds.17 The avoidance of waste makes the reaction
potentially more environmentally benign than other alter-
natives. It has been shown that salts and simple complexes of
Hydrosilylation of Styrene. Other types of atom-
economical transformations are the hydrosilylation reactions
of carbon−carbon double and triple bonds.23 These reactions
provide some of the most important ways to synthesize
alkylsilanes and alkenylsilanes. Since in industrial synthesis the
Figure 2. Molecular structures of 6a (left) and 7a (right). Thermal ellipsoids are shown at the 50% probability level; hydrogen atoms have been
omitted for clarity.
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Figure 3. Molecular structures of 6b (left) and 7b (right). Thermal ellipsoids are shown at the 50% probability level; hydrogen atoms and solvent
molecules have been omitted for clarity.
Figure 4. Molecular structures of 6c (left) and 7c (right). Thermal ellipsoids are shown at the 50% probability level; hydrogen atoms and solvent
molecules have been omitted for clarity.
Table 1. Bond Distances (Å) and Angles (deg) in Complexes 6a−c and 7a−c
bond param
6a
6b
6c
7a
7b
7c
Pt1−C1
Pt1−S1
Pt1−Br1
Pt1−Br2
C1−Pt1−S1
C1−Pt1−Br1
S1−Pt1−Br2
Br1−Pt1−Br2
C1−Pt1−Br2
S1−Pt1−Br1
1.972(8)
2.267(2)
2.4478(9)
2.4819(9)
92.0(3)
1.972(6)
2.271(1)
2.4410(7)
2.4765(7)
90.6(2)
1.972(5)
2.279(2)
2.4546(7)
2.4845(5)
91.5(2)
1.970(5)
2.267(1)
2.4580(6)
2.4824(6)
93.1(2)
1.975(9)
2.277(3)
2.444(1)
2.492(1)
94.5(3)
1.971(6)
2.277(1)
2.4496(7)
2.4886(8)
94.2(4)
89.5(3)
93.3(2)
91.8(2)
89.4(1)
91.1(3)
91.4(2)
88.23(6)
90.48(3)
179.0(3)
171.21(6)
84.99(4)
91.45(2)
174.7(2)
171.86(4)
87.28(4)
89.90(2)
176.7(2)
169.18(4)
84.83(4)
92.70(2)
177.9(1)
174.83(4)
85.11(7)
89.00(4)
178.0(3)
171.44(7)
83.21(4)
91.08(2)
177.0(2)
173.03(4)
reaction conditions, which is one of the major drawbacks of the
commercially used systems.26,8a,b,g,h
Scheme 3. Hydroamination of Phenylacetylene with 2,6-
Dimethylaniline
As a benchmark reaction, the hydrosilylation of styrene (11)
using the relatively reactive bis(trimethylsilyloxy)methylsilane
(12) was studied under the conditions employed by Strassner
et al.8h Because of the fast formation of the catalytic species in
the presence of silanes, no additives were explored.27 All six
platinum(II) complexes were found to be efficient catalysts for
this reaction under mild conditions (Scheme 4). After 5 h at 70
°C, quantitative yields of hydrosilylation products were
obtained when complexes 7a−c were used as catalysts, while
complexes 6a−c gave somewhat lower yields. A likely
explanation for the better performance of 7a−c in comparison
to their counterparts with a shorter thioether side chain could
most commonly employed catalysts, i.e. the Speier catalyst24
and the more active Karstedt catalyst,25 are platinum species,
research interest in the catalytic properties of alternative
platinum compounds has been considerable. Especially, NHC
complexes of platinum(0) as well as platinum(II) have shown
promise to circumvent the formation of platinum black under
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a
a
Table 2. Catalyst Performance for Hydroaminations
Table 3. Catalyst Performance for Hydrosilylations
b
b
yield (%)
entry
catalyst
yield (%)
13a/13b
1
2
3
4
5
6
7
0
79
entry
catalyst
no additive
+2% AgOTf
6a
6b
6c
7a
7b
7c
87/13
87/13
88/12
89/11
88/12
88/12
1
2
3
4
5
6
7
0
0
3
1
0
0
0
8
34
75
87
38
31
61
75
6a
6b
6c
7a
7b
7c
86
>99
>99
>99
a
Reaction conditions: 0.5 mol % of precatalyst, styrene (4.0 mmol),
silane 12 (1.1 equiv), 70 °C, 5 h. Yields determined by GC-MC with
decane as internal standard; average of two runs.
b
a
Reaction conditions: 1 mol % of precatalyst, phenylacetylene (2.0
equiv), 2,6-dimethylaniline (1.0 mmol), toluene (3 mL), 80 °C, 3 h.
Yields determined by GC-MS with decane as internal standard;
b
average of two runs.
and the absence of catalyst decomposition to platinum black
make this reaction an interesting candidate for further
optimization.
be the higher solubility of these complexes in the relatively
nonpolar starting materials, which were used neat. This is in
line with the observations of Strassner et al., who found that the
reaction temperature could not be lowered below 50 °C due to
the poor solubility of their platinum(II) bis(NHC) complexes
in the mixture of starting materials at lower temperatures.8h For
6a−c, an influence of the noncoordinating side chain can be
discerned. A benzyl substituent is more beneficial than the
isobutyl substituent, and both are outperformed by the more
bulky benzhydryl group. Whether this effect can be attributed
to solubility effects or the increasing steric demand of the side
chain remains unclear.
In contrast to the hydroamination reaction, which proceeds
with perfect regioselectivity, regioisomers are frequently
observed for hydrosilylation reactions. While there was a
good selectivity for the linear alkylsilane 13a, neither the length
of the thioether side chain nor the bulk of the noncoordinating
side chain had any discernible influence on the observed
product distribution within the margin of error of analysis. The
regioselectivity observed for both series of complexes is
marginally better than the values reported by Strassner et
al.8h It should be noted that no formation of platinum black or
any other indication of catalyst decomposition was observed
under reaction conditions, making this reaction a good
candidate for further optimization.
EXPERIMENTAL SECTION
■
General Considerations. All reactions were carried out without
precautions to exclude air and moisture, unless stated otherwise. All
solvents and chemicals were used as received or dried using standard
procedures when appropriate. NMR spectra were recorded on a
Bruker AV 300 spectrometer. The chemical shifts (δ) were internally
referenced to the residual solvent signals relative to tetramethylsilane
(1H, 13C). ESI mass spectra were measured using a Finnigan LCQ
spectrometer (ESI). Melting points were determined in open
capillaries using a Buchi B-540 apparatus. Elemental analyses were
̈
performed on an Elementar Vario Micro Cube elemental analyzer at
the Department of Chemistry, National University of Singapore. 1a−
c,6g,11 2a,12a and 3a12b were prepared according to known procedures.
1-Isobutyl-3-(2-bromoethyl)benzimidazolium Bromide (2b).
Compound 1b (8.00 g, 46.0 mmol) was dissolved in 1,2-dibromo-
ethane (50 mL) and heated to 85 °C for 15 h. Then the volatiles were
distilled off under reduced pressure, and the solid residue was
extracted with dichloromethane (150 mL). The resulting suspension
was filtered, and the solvent of the filtrate was evaporated. The residue
was washed with acetone (50 mL). An off-white solid was obtained
(8.52 g, 23.5 mmol, 51%). 1H NMR (300 MHz, CDCl3): δ 11.14 (s, 1
H, NCHN), 8.00−7.91 (m, 1 H, Ar-H), 7.76−7.60 (m 3 H, Ar-H),
3
3
5.25 (t, JH−H = 6 Hz, 2 H, NCH2), 4.41 (d, JH−H = 7 Hz, 2 H,
NCH2), 4.07 (t, 3JH−H = 6 Hz, 2 H, CH2Br), 2.41 (sept, 3JH−H = 7 Hz,
1 H, CH), 1.03 (d, 3JH−H = 7 Hz, 6 H, CH3). 13C{1H} NMR (75 MHz,
CDCl3): δ 143.8 (NCHN), 132.0, 131.9, 128.1, 128.0, 114.3, 113.8
(Ar-C), 55.2 (NCH2), 49.4 (NCH2), 30.9 (CH), 29.5 (CH2Br), 20.5
(CH3). Mp: 158 °C. Anal. Calcd for C13H18Br2N2·H2O: C, 41.08; H,
5.30; N, 7.37. Found: C, 40.77; H, 4.98; N, 7.66. MS (ESI): m/z 281
[M − Br]+.
CONCLUSION
■
Two series of platinum(II) NHC complexes featuring a
hemilabile thioether side chain have been developed and fully
characterized. X-ray crystallography shows unambiguously that
in all complexes the thioether side chains coordinate to the
metal center in a chelating fashion, forming six- and seven-
membered rings. In the presence of silver triflate, all complexes
were able to catalyze the hydroamination of carbon−carbon
triple bonds in moderate to good yields, while in the absence of
an additive virtually no reaction was observed. The hydro-
silylation of carbon−carbon double bonds was promoted by all
complexes in good to excellent yields. The good performance
1-Benzhydryl-3-(2-bromoethyl)benzimidazolium Bromide
(2c). 2c was prepared in analogy to 2b from 1c (1.80 g, 6.34
mmol) and 1,2-dibromoethane (10 mL). A white solid was obtained
(1.09 g, 2.31 mmol, 37%). 1H NMR (300 MHz, CDCl3): δ 10.21 (s, 1
H, NCHN), 7.96 (d, 3JH−H = 8 Hz, 2 H, Ar−H), 7.62 (t, 3JH−H = 8 Hz,
1 H, Ar-H), 7.49−7.33 (m, 12 H, Ar-H), 7.21 (s, 1 H, NCHPh2), 5.28
3
3
(t, JH−H = 5 Hz, 2 H, NCH2), 4.00 (t, JH−H = 5 Hz, 2 H, CH2Br).
13C{1H} NMR (75 MHz, DMSO-d6): δ 143.7 (NCHN), 136.2, 132.0,
131.1, 129.5, 129.5, 128.8, 127.3, 114.0 (Ar-C), 65.3 (NCHPh2), 48.6
(NCH2), 31.4 (CH2Br). Mp: 199 °C. Anal. Calcd for C22H20Br2N2: C,
Scheme 4. Hydrosilylation of Styrene
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55.96; H, 4.27; N, 5.93. Found: C, 56.03; H, 4.36; N, 5.73. MS (ESI):
m/z 391 [M − Br]+.
(391 mg, 9.78 mmol, 1.50 equiv), and 2c (3.08 g, 6.52 mmol, 1.00
1
equiv). A white solid was obtained (2.03 g, 4.34 mmol, 67%). H
1-Isobutyl-3-(3-bromopropyl)benzimidazolium Bromide
(3b). 1b (8.00 g, 46.0 mmol) was dissolved in 1,3-dibromopropane
(50 mL) and heated to 85 °C for 15 h. Then the volatiles were
distilled off under reduced pressure, and the solid residue was
extracted with dichloromethane (150 mL). The resulting suspension
was filtered, and the solvent of the filtrate was evaporated. The residue
was washed with acetone (50 mL) to yield a white solid (8.57 g, 22.8
mmol, 50%). 1H NMR (300 MHz, CDCl3): δ 11.25 (s, 1 H, NCHN),
NMR (300 MHz, CDCl3): δ 10.42 (s, 1 H, NCHN), 7.80 (d, 3JH−H
=
4
3
9 Hz, 1 H, Ar-H), 7.58 (dt, JH−H = 1 Hz, JH−H = 8 Hz, 1 H, Ar-H),
7.50−7.35 (m, 12 H, Ar-H), 7.27 (s, 1 H, NCHPh2), 4.99 (t, 3JH−H = 6
Hz, 2 H, NCH2), 3.10 (t, 3JH−H = 6 Hz, 2 H, SCH2), 3.09 (sept, 3JH−H
= 7 Hz, 1 H, SCH), 1.16 (d, 3JH−H = 7 Hz, 6 H, CH3). 13C{1H} NMR
(75 MHz, CDCl3): δ 144.0 (NCHN), 135.7, 132.5, 131.7, 130.3,
129.2, 127.9, 127.7, 115.4, 114.0 (Ar-C), 67.4 (NCHPh2), 47.9
(NCH2), 35.6 (SCH), 30.5 (SCH2), 24.0 (CH3). Mp: 214 °C. Anal.
Calcd for C25H27BrN2S: C, 64.23; H, 5.82; N, 5.99. Found: C, 64.25;
H, 5.58; N, 5.90. MS (ESI): m/z 387 [M − Br]+.
7.88−7.83 (m, 1 H, Ar-H), 7.74−7.63 (m 3 H, Ar-H), 4.90 (t, 3JH−H
=
7 Hz, 2 H, NCH2), 4.41 (d, 3JH−H = 7 Hz, 2 H, NCH2), 3.56 (t, 3JH−H
= 6 Hz, 2 H, CH2Br), 2.71 (tt, 3JH−H = 6 Hz, 3JH−H = 7 Hz, 2 H, CH2),
2.41 (sept, 3JH−H = 7 Hz, 1 H, CH), 1.01 (d, 3JH−H = 7 Hz, 6 H, CH3).
13C{1H} NMR (75 MHz, CDCl3): δ 143.7 (NCHN), 132.1, 132.0,
1-Benzyl-3-(3-(isopropylthio)propyl)benzimidazolium Bro-
mide (5a). 5a was prepared in analogy to 4a from 2-mercaptopropane
(3.05 mL, 33.0 mmol, 1.50 equiv), sodium hydroxide (1.32 g, 33.0
mmol, 1.50 equiv), and 3a (9.02 g, 22.0 mmol, 1.00 equiv). An off-
128.0, 127.9, 113.9, 113.8 (Ar-C), 55.2 (NCH2), 46.5 (NCH2), 32.8
(CH2), 30.4 (CH2), 29.6 (CH2Br), 20.6 (CH3). Mp: 192 °C. Anal.
Calcd for C14H20Br2N2·CH2Cl2: C, 43.07; H, 5.20; N, 7.05. Found: C,
42.76; H, 5.15; N, 7.45. MS (ESI): m/z 295 [M − Br]+.
1
white solid was obtained (5.24 g, 12.9 mmol, 58%). H NMR (300
MHz, CDCl3): δ 11.70 (s, 1 H, NCHN), 7.81−7.75 (m, 1 H, Ar-H),
7.63−7.47 (m, 5 H, Ar-H), 7.39−7.30 (m, 3 H, Ar-H), 5.87 (s, 2 H,
3
3
NCH2Ph), 4.77 (t, JH−H = 8 Hz, 2 H, NCH2), 2.90 (sept, JH−H = 7
Hz, 1 H, SCH), 2.67 (t, 3JH−H = 7 Hz, 2 H, SCH2), 2.40 (tt, 3JH−H = 7
1-Benzhydryl-3-(3-bromopropyl)benzimidazolium Bromide
(3c). 3c was prepared in analogy to 3b from 1c (1.80 g, 6.34 mmol)
and 1,3-dibromopropane (10 mL). A white solid was obtained (1.74 g,
3
3
Hz, JH−H = 8 Hz, 2 H, CH2), 1.21 (d, JH−H = 7 Hz, 6 H, CH3).
3.58 mmol, 57%). H NMR (300 MHz, CDCl3): δ 10.82 (s, 1 H,
13C{1H} NMR (75 MHz, CDCl3): δ 143.9 (NCHN), 133.3, 132.3,
1
3
NCHN), 7.86 (d, JH−H = 8 Hz, 1 H, Ar-H), 7.68−7.59 (m, 1 H, Ar-
131.8, 130.0, 129.9, 129.1, 127.9, 127.8, 114.4, 113.8 (Ar-C), 52.1
(NCH2Ph), 46.9 (NCH2), 36.0 (SCH), 29.8 (SCH2), 27.9 (CH2),
24.0 (CH3). Mp: 90 °C. Anal. Calcd for C20H25BrN2S·1/4CH2Cl2: C,
57.01; H, 6.02; N, 6.57. Found: C, 57.03; H, 5.95; N, 6.82. MS (ESI):
m/z 325 [M − Br]+.
H), 7.51−7.27 (m, 12 H, Ar-H) 7.30 (s, 1 H, NCHPh2), 4.95 (t, 3JH−H
3
= 7 Hz, 2 H, NCH2), 3.58 (t, JH−H = 6 Hz, 2 H, CH2Br), 2.77−2.65
(m, 2 H, CH2). 13C{1H} NMR (75 MHz, CDCl3): δ 143.6 (NCHN),
135.9, 135.7, 132.6, 130.2, 130.1, 129.1, 128.1, 127.9, 115.7, 114.0 (Ar-
C), 67.6 (NCHPh2), 47.0 (NCH2), 32.6 (CH2Br), 30.5 (CH2). Mp:
206 °C. Anal. Calcd for C23H22Br2N2: C, 56.81; H, 4.56; N, 5.76.
Found: C, 56.44; H, 4.33; N, 5.58. MS (ESI): m/z 405 [M − Br]+.
1-Benzyl-3-(2-(isopropylthio)ethyl)benzimidazolium Bro-
mide (4a). 2-Mercaptopropane (351 μL, 3.78 mmol, 1.50 equiv)
was dissolved in degassed acetonitrile (30 mL). Sodium hydroxide
(151 mg, 3.78 mmol, 1.50 equiv) in water (1 mL) was added, and the
resulting mixture was stirred for 30 min at ambient temperature. Then,
2a (1.00 g, 2.52 mmol, 1.00 equiv) was added, and stirring was
continued for 15 h at ambient temperature. After this time, the
volatiles were removed under reduced pressure. The solid residue was
suspended in dichloromethane (10 mL) and filtered. The solvent was
removed under reduced pressure, and the residue was washed with
diethyl ether (5 mL). A white solid was obtained (978 mg, 2.50 mmol,
99%). 1H NMR (300 MHz, CDCl3): δ 11.60 (s, 1 H, NCHN), 7.69−
7.74 (m, 1 H, Ar-H), 7.46−7.65 (m, 6 H, Ar-H), 7.36−7.40 (m, 2 H,
1-Isobutyl-3-(3-(isopropylthio)propyl)benzimidazolium Bro-
mide (5b). 5b was prepared in analogy to 4a from 2-
mercaptopropane (849 μL, 9.20 mmol, 1.50 equiv), sodium hydroxide
(369 mg, 9.20 mmol, 1.50 equiv), and 3b (2.31 g, 6.10 mmol, 1.00
equiv). A brown oil was obtained (1.76 g, 4.74 mmol, 78%). 1H NMR
(300 MHz, CDCl3): δ 11.49 (s, 1 H, NCHN), 7.84−7.78 (m, 1 H, Ar-
3
H), 7.72−7.60 (m, 3 H, Ar-H), 4.80 (t, JH−H = 7 Hz, 2 H, NCH2),
3
3
4.41 (d, JH−H = 8 Hz, 2 H, NCH2), 2.89 (sept, JH−H = 7 Hz, 1 H,
3
SCH), 2.66 (t, JH−H = 7 Hz, 2 H, SCH2), 2.43−2.30 (m, 3 H, CH,
CH2), 1.21 (d, 3JH−H = 7 Hz, 6 H, CH3), 1.02 (d, JH−H = 7 Hz, 6 H,
3
CH3). 13C{1H} NMR (75 MHz, CDCl3): δ 143.9 (NCHN), 132.1,
132.0, 127.8, 113.8 (Ar-C), 55.0 (NCH2), 46.8 (NCH2), 36.0 (SCH);
29.9 (CH), 29.6 (SCH2), 27.8 (CH2), 24.0 (CH3), 20.5 (CH3). No
correct elemental analysis could be obtained for this compound,
despite several attempts. MS (ESI): m/z 291 [M − Br]+.
1-Benzhydryl-3-(3-(isopropylthio)propyl)benzimidazolium
Bromide (5c). 5c was prepared in analogy to 4a from 2-
mercaptopropane (1.48 mL, 16.1 mmol, 1.50 equiv), sodium
hydroxide (644 mg, 16.1 mmol, 1.50 equiv), and 3c (5.21 g, 10.7
mmol, 1.00 equiv). A white solid was obtained (3.09 g, 6.42 mmol,
3
Ar-H), 5.84 (s, 2 H, NCH2Ph), 4.87 (t, JH−H = 7 Hz, 2 H, NCH2),
3
3
3.19 (t, JH−H = 7 Hz, 2 H, SCH2), 3.17 (sept, JH−H = 7 Hz, 1 H,
SCH), 1.26 (d, JH−H = 7 Hz, 6 H, CH3). 13C{1H} NMR (75 MHz,
3
CDCl3): δ 144.0 (NCHN), 133.3, 132.1, 131.7, 130.0, 129.9, 128.9,
127.8, 114.4, 113.8 (Ar-C), 52.1 (NCH2Ph), 47.8 (NCH2), 35.9
(SCH), 30.5 (SCH2), 24.0 (CH3). Mp: 165 °C. Anal. Calcd for
C19H23BrN2S·H2O: C, 55.74; H, 6.16; N, 6.84. Found: C, 56.11; H,
5.80; N, 6.88. MS (ESI): m/z 311 [M − Br]+.
1
60%). H NMR (300 MHz, CDCl3): δ 10.88 (s, 1 H, NCHN), 7.82
(d, 3JH−H = 8 Hz, 1 H, Ar-H), 7.58 (dt, 4JH−H = 1 Hz, 3JH−H = 7 Hz, 1
H, Ar-H), 7.47−7.33 (m, 12 H, Ar-H), 7.29 (s, 1 H, NCHPh2), 4.87
3
3
(t, JH−H = 7 Hz, 2 H, NCH2), 2.85 (sept, JH−H = 7 Hz, 1 H, SCH),
3
3
2.65 (t, JH−H = 7 Hz, 2 H, SCH2), 2.34 (quint, JH−H = 7 Hz, 2 H,
1-Isobutyl-3-(2-(isopropylthio)ethyl)benzimidazolium Bro-
mide (4b). 4b was prepared in analogy to 4a from 2-
mercaptopropane (628 μL, 6.80 mmol, 1.51 equiv), sodium hydroxide
(272 mg, 6.80 mmol, 1.51 equiv), and 2b (1.63 g, 4.50 mmol, 1.00
CH2), 1.18 (d, JH−H = 7 Hz, 6 H, CH3). 13C{1H} NMR (75 MHz,
3
CDCl3): δ 143.8 (NCHN), 135.8, 132.6, 131.7, 130.1, 129.2, 127.8,
127.7, 115.7, 114.0 (Ar-C), 67.4 (NCHPh2), 47.3 (NCH2), 36.0
(SCH), 29.6 (SCH2), 27.9 (CH2), 24.0 (CH3). Mp: 200 °C. Anal.
Calcd for C26H29BrN2S: C, 64.86; H, 6.07; N, 5.84. Found: C, 64.80;
H, 5.73; N, 5.88. MS (ESI): m/z 401 [M − Br]+.
cis-Dibromido(1-benzyl-3-(2-(isopropylthio)ethyl)-
benzimidazolin-2-ylidene-κ2C,S)platinum(II) (6a). 4a (117 mg,
0.30 mmol, 1.00 equiv) and silver(I) oxide (35 mg, 0.15 mmol, 0.50
equiv) were suspended in dichloromethane (15 mL) and stirred at
ambient temperature for 15 h shielded from light. Platinum(II)
bromide (106 mg, 0.30 mmol, 1.00 equiv) was dissolved in DMSO (5
mL) by stirring for 10 min at 80 °C. After the [PtBr2(dmso)2] solution
had cooled to ambient temperature, the silver complex solution was
added by filtration over a short plug of Celite, and the resulting
mixture was stirred for 1 h at ambient temperature. Then the solution
was filtered over Celite. The solution was extracted with water (2 × 50
1
equiv). A white solid was obtained (1.26 g, 3.53 mmol, 78%). H
NMR (300 MHz, CDCl3): δ 11.33 (s, 1 H, NCHN), 7.79−7.59 (m, 4
H, Ar-H), 4.91 (t, 3JH−H = 7 Hz, 2 H, NCH2), 4.40 (d, 3JH−H = 7 Hz, 2
3
3
H, NCH2), 3.19 (sept, JH−H = 7 Hz, 1 H, SCH), 3.17 (t, JH−H = 7
3
Hz, 2 H, SCH23), 2.41 (m, 1 H, CH), 1.24 (d, JH−H = 7 Hz, 6 H,
CH3), 1.05 (d, JH−H = 7 Hz, 6 H, CH3). 13C{1H} NMR (75 MHz,
CDCl3): δ 144.3 (NCHN), 132.1, 131.9, 127.8, 113.8 (Ar-C), 55.1
(NCH2), 47.6 (NCH2), 35.7 (SCH), 30.6 (CH), 29.6 (SCH2), 24.0
(CH3), 20.5 (CH3). Mp: 122 °C. Anal. Calcd for C16H25BrN2S·1/
5CH2Cl2: C, 51.98; H, 6.84; N, 7.48. Found: C, 52.37; H, 6.68; N,
7.67. MS (ESI): m/z 277 [M − Br]+.
1-Benzhydryl-3-(2-(isopropylthio)ethyl)benzimidazolium
Bromide (4c). 4c was prepared in analogy to 4a from 2-
mercaptopropane (903 μL, 9.78 mmol, 1.50 equiv), sodium hydroxide
177
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Organometallics
Article
mL), dried over sodium sulfate, and filtered, and the solvent was
removed under reduced pressure. The residue was washed with small
quantities of dichloromethane. The product was obtained as an off-
white solid (176 mg, 0.26 mmol, 88%). 1H NMR (300 MHz, DMSO-
d6): δ 7.93 (d, 3JH−H = 8 Hz, 1 H, Ar-H), 7.61 (d, 3JH−H = 8 Hz, 1 H,
Ar-H), 7.49−7.23 (m, 9 H, Ar-H, NCH2Ph), 6.45 (d, 2JH−H = 16 Hz, 1
H, NCH2), 5.82 (d, 2JH−H = 16 Hz, 1 H, NCH2), 5.04 (d, 2JH−H = 15
Hz, 1 H, SCH2), 4.35 (t, 2JH−H = 13 Hz, 1 H, SCH2), 2.69−2.52 (m, 1
H, SCH), 1.04 (d, 3JH−H = 6 Hz, 3 H, CH3), 0.87 (d, 3JH−H = 6 Hz, 3
H, CH3). 13C{1H} NMR (75 MHz, DMSO-d6): δ 152.3 (Ccarbene),
136.1, 133.8, 132.7, 128.6, 127.8, 127.4, 124.1, 123.9, 112.0, 111.7 (Ar-
C), 50.4 (NCH2Ph), 45.9 (NCH2), 45.0 (SCH), 30.1 (SCH2), 22.3
(CH3), 21.1 (CH3). Mp: 252 °C dec. Anal. Calcd for C19H22Br2N2PtS·
1.5CH2Cl2: C, 31.06; H, 3.18; N, 3.53. Found: C, 31.43; H, 3.53; N,
3.71. MS (ESI): m/z 585 [M − Br]+.
0.99 (m, 6 H, CH3). 13C{1H} NMR (75 MHz, DMSO-d6) (two signal
sets observed): δ 156.0 (Ccarbene), 135.6, 135.5, 134.1, 133.3, 133.2,
132.6, 128.7, 128.6, 127.9, 127.7, 127.4, 127.0, 124.0, 124.0, 112.4,
112.0, 111.8, 111.3 (Ar-C), 51.2, 51.1 (NCH2Ph), 46.8, 42.8 (NCH2),
42.6, 33.8 (SCH), 29.1, 28.5 (SCH2), 26.7, 24.3 (CH2), 23.3, 23.2
(CH3), 21.7, 20.9 (CH3). Mp: 225 °C dec. Anal. Calcd for
C20H24Br2N2PtS: C, 35.36; H, 3.56; N, 4.12. Found: C, 35.73; H,
3.72; N, 4.16. MS (ESI): m/z 599 [M − Br]+.
cis-Dibromido(1-isobutyl-3-(3-(isopropylthio)propyl)-
benzimidazolin-2-ylidene-κ2C,S)platinum(II) (7b). 7b was pre-
pared in analogy to 6c from 5b (371 mg, 1.00 mmol, 1.00 equiv),
silver(I) oxide (116 mg, 0.50 mmol, 0.50 equiv), and platinum(II)
bromide (355 mg, 1.00 mmol, 1.00 equiv). The product was obtained
as an off-white solid (283 mg, 0.44 mmol, 44%). 1H NMR (300 MHz,
DMSO-d6): δ 7.94−7.70 (m, 2 H, Ar-H), 7.55−7.25 (m, 2 H, Ar-H),
5.39−5.12 (m, 1 H, NCH2), 5.00−4.60 (m, 2 H, NCH2), 4.55−4.04
(m, 1 H, NCH2), 2.98−2.58 (m, 2 H, SCH2), 2.48−1.60 (m, 4 H,
SCH, CH, CH2), 1.47−1.13 (m, 6 H, CH3), 1.06−0.82 (m, 6 H,
CH3). 13C{1H} NMR (75 MHz, DMSO-d6): δ 154.9 (Ccarbene), 134.0,
132.8, 123.9, 112.1, 111.0 (Ar-C), 54.9 (NCH2), 46.7 (NCH2), 33.8
(SCH), 28.6 (SCH2), 28.4 (CH), 26.7 (CH2), 23.3 (CH3), 23.2
(CH3), 19.9 (CH3), 19.8 (CH3). Mp: 148 °C. Anal. Calcd for
C17H26Br2N2PtS: C, 31.64; H, 4.06; N, 4.34. Found: C, 31.44; H, 3.90;
N, 4.27. MS (ESI): m/z 1210 [2 M − Br]+.
cis-Dibromido(1-isobutyl-3-(2-(isopropylthio)ethyl)-
benzimidazolin-2-ylidene-κ2C,S)platinum(II) (6b). 6b was pre-
pared in analogy to 6a from 4b (107 mg, 0.30 mmol, 1.00 equiv),
silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and platinum(II)
bromide (106 mg, 0.30 mmol, 1.00 equiv). The product was obtained
as an off-white solid (102 mg, 0.16 mmol, 54%). 1H NMR (300 MHz,
DMSO-d6): δ 7.96−7.77 (m, 2 H, Ar-H), 7.46−7.30 (m, 2 H, Ar-H),
5.19 (dd, 3JH−H = 7 Hz, 2JH−H = 14 Hz, 1 H, NCH2), 5.01 (d, 2JH−H
=
15 Hz, 1 H, NCH2), 4.45−4.24 (m, 1 H, NCH2), 4.09 (dd, 3JH−H = 9,
4JH−H = 13 Hz, 1 H, NCH2), 2.83−2.60 (m, 2 H, SCH2), 1.33 (d,
3JH−H = 7 Hz, 3 H, CH3), 1.31−1.23 (m, 1 H, CH), 1.18 (d, 3JH−H = 6
cis-Dibromido(1-benzhydryl-3-(3-(isopropylthio)propyl)-
benzimidazolin-2-ylidene-κ2C,S)platinum(II) (7c). 7c was pre-
pared in analogy to 6c from 5c (482 mg, 1.00 mmol, 1.00 equiv),
silver(I) oxide (116 mg, 0.50 mmol, 0.50 equiv), and platinum(II)
bromide (355 mg, 1.00 mmol, 1.00 equiv). The product was obtained
as an off-white solid (405 mg, 0.54 mmol, 54%). 1H NMR (300 MHz,
DMSO-d6) (two signal sets observed, ratio 1/0.6): δ (major) 8.35 (s, 1
H, Ar-H), 7.92−7.85 (m, 1 H, Ar-H), 7.47−7.33 (m, 7 H, Ar-H),
3
Hz, 3 H, CH3), 1.00 (d, JH−H = 6 Hz, 3 H, CH3), 0.83 (d, 3JH−H = 6
Hz, 3 H, CH3), (SCH not observed due to overlap with solvent peak).
13C{1H} NMR (75 MHz, DMSO-d6): δ 150.6 (Ccarbene), 134.4, 132.4,
123.8, 123.7, 111.9, 111.5 (Ar-C), 53.8 (NCH2), 45.7 (NCH2), 45.2
(SCH), 30.4 (SCH2), 28.7 (CH), 22.8, 21.3, 19.8, 19.6 (CH3). Mp:
239 °C dec. Anal. Calcd for C16H24Br2N2PtS: C, 30.44; H, 3.83; N,
4.44. Found: C, 30.31; H, 3.83; N, 4.49. MS (ESI): m/z 550 [M −
Br]+.
3
7.31−7.21 (m, 4 H, Ar-H, NCHPh2), 7.10 (t, JH−H = 8 Hz, 1 H, Ar-
3
H), 6.48 (d, JH−H = 8 Hz, 1 H, Ar-H), 5.55−5.38 (m, 1 H, NCH2),
4.86 (dd, 3JH−H = 8 Hz, 4JH−H = 15 Hz, 1 H, NCH2), 3.31−2.59 (m, 2
H, SCH2/SCH/CH2), 2.45−2.10 (m, 2 H, SCH2/SCH/CH2), 1.53−
cis-Dibromido(1-benzhydryl-3-(2-(isopropylthio)ethyl)-
benzimidazolin-2-ylidene-κ2C,S)platinum(II) (6c). 4c (468 mg,
1.00 mmol, 1.00 equiv) and silver(I) oxide (116 mg, 0.50 mmol, 0.50
equiv) were suspended in dichloromethane (50 mL) and stirred at
ambient temperature for 15 h shielded from light. Platinum(II)
bromide (355 mg, 1.00 mmol, 1.00 equiv) was dissolved in DMSO (5
mL) by stirring for 10 min at 80 °C. After the [PtBr2(dmso)2] solution
had cooled to ambient temperature, the silver complex solution was
added by filtration, and the resulting mixture was stirred for 1 h at
ambient temperature. Then the solution was filtered and the solvent
was removed under reduced pressure. The residue was washed with
methanol (40 mL) and diethyl ether (40 mL). The product was
3
1.31 (m, 1 H, SCH2/SCH/CH2), 1.00 (d, JH−H = 7 Hz, 3 H, CH3),
0.59 (3JH−H = 6 Hz, 3 H, CH3); (minor) 8.42 (s, 1 H, Ar-H), 7.92−
7.85 (m, 1 H, Ar-H), 7.47−7.33 (m, 7 H, Ar-H), 7.31−7.21 (m, 4 H,
Ar-H, NCHPh2), 7.10 (t, 3JH−H = 8 Hz, 1 H, Ar-H), 6.57 (d, JH−H = 8
Hz, 1 H, Ar-H), 5.02−4.90 (m, 1 H, NCH2), 4.72−4.55 (m, 1 H,
NCH2), 3.31−2.59 (m, 2 H, SCH2/SCH/CH2), 2.45−2.10 (m, 2 H,
SCH2/SCH/CH2), 1.53−1.31 (m, 1 H, SCH2/SCH/CH2), 1.23 (d,
3JH−H = 7 Hz, 3 H, CH3), 1.22 (d, 3JH−H = 7 Hz, 3 H, CH3). Because
of the low solubility of this compound, no 13C NMR spectrum could
be obtained. Mp: 187 °C dec. Anal. Calcd for C26H28Br2N2PtS: C,
41.34; H, 3.74; N, 3.71. Found: C, 41.71; H, 3.54; N, 3.74. MS (ESI)
m/z 675 [M − Br]+.
1
obtained as an off-white solid (529 mg, 0.71 mmol, 71%). H NMR
(300 MHz, DMSO-d6): δ 8.60 (s, 1 H, Ar-H), 7.94 (d, 3JH−H = 8 Hz, 1
H, Ar-H), 7.48−7.33 (m, 7 H, Ar-H), 7.31−7.21 (m, 4 H, Ar-H,
NCHPh2), 7.17−7.06 (m, 1 H, Ar-H), 6.53 (d, 3JH−H = 8 Hz, 1 H, Ar-
H), 5.07 (t, 2JH−H = 15 Hz, 1 H, NCH2), 4.45 (t, 2JH−H = 13 Hz, 1 H,
NCH2), 2.63−2.52 (m, 1 H, SCH2), 2.13−1.96 (m, 1 H, SCH), 1.32−
1.22 (m, 1 H, SCH2), 0.89 (d, 3JH−H = 6 Hz, 3 H, CH3), 0.48 (d, 3JH−H
= 7 Hz, 3 H, CH3). 13C{1H} NMR (75 MHz, DMSO-d6): δ 154.3
(Ccarbene), 137.8, 133.3, 133.2, 129.1, 128.6, 128.4, 127.6, 123.8, 123.7,
113.6, 112.2 (Ar-C), 65.6 (NCHPh2), 46.3 (NCH2), 45.5 (SCH), 30.4
(SCH2), 21.9 (CH3), 20.9 (CH3). Mp: 201 °C dec. Anal. Calcd for
C25H26Br2N2PtS: C, 40.50; H, 3.53; N, 3.78. Found: C, 40.62; H, 3.53;
N, 3.78. MS (ESI): m/z 661 [M − Br]+.
General Procedure for Catalytic Hydroaminations. A Schlenk
tube was charged with precatalyst (10 μmol, 1.0 mol %) under an
atmosphere of dry nitrogen. Anhydrous toluene (3 mL) andin some
casessilver triflate (5.1 mg, 20 μmol, 2.0 mol %) were added, and
the resulting suspension was stirred for 5 min at ambient temperature.
Then phenylacetylene (219 μL, 2.00 mmol, 2.00 equiv) and 2,6-
dimethylaniline (123 μL, 1.00 mmol, 1.00 equiv) were added, and the
Schlenk tube was immersed in an oil bath preheated to 80 °C. The
mixture was allowed to react for 3 h. After this time, the Schlenk tube
was taken out of the oil bath, the suspension was diluted with diethyl
ether (10 mL), and decane as an internal standard was added. Samples
were analyzed by GC-MS.
General Procedure for Catalytic Hydrosilylations. A Schlenk
tube was charged with precatalyst (20 μmol, 0.5 mol %) under an
atmosphere of dry nitrogen. Styrene (459 μL, 4.00 mmol, 1.00 equiv)
and bis(trimethylsilyloxy)methylsilane (1.20 mL, 4.40 mmol, 1.10
equiv) were added, and the Schlenk tube was immersed in an oil bath
preheated to 70 °C. After a reaction time of 5 h, the Schlenk tube was
taken out of the oil bath. Diethyl ether (10 mL) and decane as an
internal standard were added, and samples were analyzed by GC-MS.
X-ray Diffraction Studies. X-ray data were collected with a
Bruker AXS SMART APEX diffractometer, using Mo Kα radiation at
cis-Dibromido(1-benzyl-3-(3-(isopropylthio)propyl)-
benzimidazolin-2-ylidene-κ2C,S)platinum(II) (7a). 7a was pre-
pared in analogy to 6a from 5a (122 mg, 0.30 mmol, 1.00 equiv),
silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and platinum(II)
bromide (106 mg, 0.30 mmol, 1.00 equiv). The product was obtained
as an off-white solid (205 mg, 0.30 mmol >99%). 1H NMR (300 MHz,
DMSO-d6) (two overlapping sets of signals, ratio ∼1/1): δ 7.78 (d,
3JH−H = 8.0 Hz, 1 H, Ar-H), 7.56−7.13 (m, 10 H, Ar-H, NCH2Ph),
6.20−6.06 (m, 1 H, NCH2), 6.06−5.91 (m, 1 H, NCH2), 5.42−5.22
(m, 1 H, SCH2), 4.89−4.70 (m, 1 H, SCH2), 2.86−2.63 (m, 0.5 H,
SCH), 2.46−2.16 (m, 2 H, CH2), 1.95−1.78 (m, 0.5 H, SCH), 1.28−
178
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100(2) K, with the SMART suite of programs.28 Data were processed
and corrected for Lorentz and polarization effects with SAINT29 and
for absorption effects with SADABS.30 Structural solution and
refinement were carried out with the SHELXTL suite of programs.31
The structure was solved by direct methods to locate the heavy atoms,
followed by difference maps for the light, non-hydrogen atoms. All
hydrogen atoms were placed at calculated positions. All non-hydrogen
atoms were generally given anisotropic displacement parameters in the
final model. A summary of crystallographic data is given in Table 1 and
the Supporting Information.
Wasserscheid, P.; Cavell, K. J.; Skelton, B. W.; White, A. H.; Englert,
U. Organometallics 2002, 21, 175. (d) Kuhl, S.; Schneider, R.; Fort, Y.
Organometallics 2003, 22, 4184. (e) Matsubara, K.; Ueno, K.; Shibata,
Y. Organometallics 2006, 25, 3422. (f) Schaub, T.; Backes, M.; Radius,
U. Organometallics 2006, 25, 4196. (g) Huynh, H. V.; Wong, L. R.; Ng,
P. S. Organometallics 2008, 27, 2231. (h) Huynh, H. V.; Jothibasu, R.
Eur. J. Inorg. Chem. 2009, 1926. (i) Bheeter, L. P.; Henrion, M.; Brelot,
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ASSOCIATED CONTENT
■
S
* Supporting Information
Figures giving 1H and 13C NMR spectra, CIF files for 6a−c and
7a−c, and tables giving crystallographic data. This material is
available free of charge via the Internet at http://pubs.acs.org.
Marinetti, A. J. Med. Chem. 2013, 56, 2074.
AUTHOR INFORMATION
Corresponding Author
*E-mail for H.V.H.: chmhhv@nus.edu.sg.
Notes
■
(8) (a) Berthon-Gelloz, G.; Buisine, O.; Brier
Sterin, S.; Mignani, G.; Tinant, B.; Declercq, J.-P.; Chapon, D.; Marko,
I. E. J. Organomet. Chem. 2005, 690, 6156. (b) De Bo, G.; Berthon-
Gelloz, G.; Tinant, B.; Marko, I. E. Organometallics 2006, 25, 1881.
(c) Ahrens, S.; Strassner, T. Inorg. Chim. Acta 2006, 359, 4789.
(d) Lillo, V.; Mata, J. A.; Segarra, A. M.; Peris, E.; Fernandez, E. Chem.
̀
e, J.-F.; Michaud, G.;
́
́
́
The authors declare no competing financial interest.
́
ACKNOWLEDGMENTS
Commun. 2007, 2184. (e) Brissy, D.; Skander, M.; Retailleau, P.;
Frison, G.; Marinetti, A. Organometallics 2009, 28, 140. (f) Pubill-
Ulldemolins, C.; Bo, C.; Mata, J. A.; Fernandez, E. Chem. Asian J.
́
■
We thank the National University of Singapore and the
Singapore Ministry of Education for financial support (WBS R
143-000-483-112 and SINGA scholarship) and the CMMAC
staff of the department of chemistry for technical assistance.
2010, 5, 261. (g) Dunsford, J. J.; Cavell, K. J.; Kariuki, B. J. Organomet.
Chem. 2011, 696, 188. (h) Taige, M. A.; Ahrens, S.; Strassner, T. J.
Organomet. Chem. 2011, 696, 2918. (i) Cao, P.; Cabrera, J.; Padilla, R.;
Serra, D.; Rominger, F.; Limbach, M. Organometallics 2012, 31, 921.
(j) Zhang, R.; Xu, Q.; Mei, L.-Y.; Li, S.-K.; Shi, M. Tetrahedron 2012,
68, 3172.
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4612. (b) Newman, C. P.; Deeth, R. J.; Clarkson, G. J.; Rourke, J. P.
Organometallics 2007, 26, 6225. (c) Petretto, G. L.; Wang, M.; Zucca,
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(e) Marshall, P.; Jenkins, R. L.; Clegg, W.; Harrington, R. W.;
Callear, S. K.; Coles, S. J.; Fallis, I. A.; Dervisi, A. Dalton Trans. 2012,
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3833. (b) Huynh, H. V.; Yeo, C. H.; Chew, Y. X. Organometallics 2010,
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