Synthesis and structural characterization of new chiral (biscarbene)platinum(II) complexes

Article abstract of DOI:10.1002/ejic.201000939

New chiral bis(triazolium) salts have been prepared in good yields. The corresponding mononuclear platinum(II) complexes [Pt{bis(NHC)}X₂] (X = Br, I) have been synthesized and spectroscopically characterized. One of the synthesized biscarbene c

Full text of DOI:10.1002/ejic.201000939

FULL PAPER
DOI: 10.1002/ejic.201000939
Synthesis and Structural Characterization of New Chiral
(Biscarbene)platinum(II) Complexes
Stephanie K. U. Riederer,[a,b] Bettina Bechlars,[b] Wolfgang A. Herrmann,*[a,b] and
Fritz E. Kühn*[a,b,c]
Keywords: Chiral N-heterocyclic carbene metal complexes / Carbene ligands / 1,2,4-Triazole / Platinum / Hydrosilylation
New chiral bis(triazolium) salts have been prepared in good
yields. The corresponding mononuclear platinum(II) com-
plexes [Pt{bis(NHC)}X2] (X = Br, I) have been synthesized
and spectroscopically characterized. One of the synthesized
biscarbene complexes has also been characterised by X-ray
crystallography. These complexes are efficient catalyst pre-
cursors for the hydrosilylation of 1-octene.
within the past few years, focussing on both successful chi-
rality transfer, and on the limits of strategies designed to
extend this very valuable research field into industry.[3,19–23]
Previously, we have focussed on the synthesis of novel
chelating bidentate bis(NHC) ligands based on 1,2,4-tri-
azoles and have reported some of their rhodium(I) com-
plexes.[24]
On the basis of our experience in the coordination of
chelating bis(triazol-2-ylidenes), we have extended this work
to platinum. Herein, we describe the synthesis of the first
chiral platinum(II) complexes with chelating bis(NHC) li-
gands and discuss their application in hydrosilylation reac-
tions. The crystal structure of one of the complexes is also
described.
Introduction
An important aspect of organometallic chemistry is com-
plex stability, particularly if such compounds may find syn-
thetic or catalytic applications. As observed for phosphanes,
the introduction of chelating ability to carbenes confers ad-
ditional stabilizing character to the ligand.[1–3] Over the past
two decades, N-heterocyclic carbenes (NHCs) have emerged
as a new class of ancillary ligands for a broad range of
transition-metal-mediated catalytic reactions.[4–8] NHCs are
excellent σ-donors and form strong M–C bonds, often giv-
ing rise to complexes with a higher stability compared to
complexes containing phosphanes. Thus, as a logical exten-
sion of this work, the development of chiral versions of
NHC, e.g. as ligands for stereoselective catalysis, is of inter-
est. The quest for chiral NHC ligands began in 1996 with
the pioneering efforts of Herrmann et al.[9] and Enders et
al.[10] Since then, the impact of these ligands in enantio-
selective catalysis has been significant. A wide range of
stereoselective catalytic transformations catalyzed by chiral
di-NHC complexes has been reported, e.g., hydro-
silylation,[11–14] hydrogenation,[15] enantioselective 1,4-con-
jugate addition[16–17] and transfer hydrogenation.[18] As chi-
rality transfer is a topic of continuously increasing interest,
a number of review articles have been published in this field
Results and Discussion
Synthesis of Chiral (Biscarbene)platinum(II) Complexes
The chiral bis(triazolium) salts 2 and 4 were prepared
from (–)-(R,R)-1,2-diaminocyclohexane and (+)-(R,R)-1,2-
diphenylethane-1,2-diamine (see Scheme 1).
The neutral bis(triazoles) 1 and 3 are readily formed by
treating triethyl orthoformate and formylhydrazine with
commercially available amines in methanol at 90 °C. The
bis(triazolium) salts 2 and 4 are generated by alkylation
with the corresponding alkyl halide in acetonitrile at
100 °C.
[a] WACKER-Institut für Siliciumchemie, Department of
Chemistry, Technische Universität München,
Lichtenbergstr. 4, 85747 Garching bei München, Germany
E-mail: wolfgangherrmann@ch.tum.de
1H and 13C{1H} NMR spectra of compounds 2 and 4
fritz.kuehn@ch.tum.de
1
reflect the C2 symmetry of the complexes. The H NMR
[b] Department of Chemistry, Technische Universität München,
Lichtenbergstr. 4, 85747 Garching bei München, Germany
[c] Molecular Catalysis, Catalysis Research Center, Department of
Chemistry, Technische Universität München,
spectra display two signals between δ = 9.18 (NNCHN) and
10.57 (NCHN) ppm, which are characteristic of triazolium
cations.
Lichtenbergstr. 4, 85747 Garching bei München, Germany
Eur. J. Inorg. Chem. 2011, 249–254
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249

S. K. U. Riederer, B. Bechlars, W. A. Herrmann, F. E. Kühn
FULL PAPER
Scheme 1. Preparation of the chiral bis(triazolium) salts.[24]
The chiral complexes 5 and 6 (Scheme 2) have been syn-
1H and 13C{1H} NMR patterns of all complexes are di-
thesized according to a slightly modified literature pro- agnostic of the C1 symmetry of the structures. The assign-
cedure, by treating the platinum precursor with the triazol- ment of the proton and carbon atoms is also confirmed
ium salt in the presence of NaOAc as external base in di- by COSY and heteronuclear multiple quantum coherence
[25]
methyl sulfoxide at 90 °C.
In order to avoid halogen (HMQC) spectroscopy. As a representative example of the
scrambling during the reaction, the platinum(II) halides PtII complexes, the spectra of complex 5CH2Naphthyl are dis-
were treated with triazolium salts bearing the same halide cussed herein. The 13C{1H} NMR spectrum of this com-
counter anions. In contrast to other reports in the litera- plex shows carbene carbon atom signals at δ = 152.1 and
ture,[26] all complexes show optical activity in dimethyl sulf- 145.7 ppm, indicating bidentate coordination of the ligand.
1
oxide, indicating that no racemisation took place. The com- A distinct multiplet in the H NMR spectrum, attributed
plexes are air- and moisture-stable and can be stored for a to one of the c-hexCH protons of the cyclohexylene bridge,
prolonged period of time without apparent decomposition, is observed downfield at δ = 6.21 ppm and the other
as confirmed by NMR spectroscopy.
c-hexCH proton gives rise to a multiplet at δ = 4.60 ppm (see
Figure 1). The close proximity of the platinum metal centre
to one of the protons is most likely the reason for the down-
field shift observed for one of the signals.
Structure Determination of 5iPr
Single crystals of 5iPr suitable for X-ray diffraction were
grown by diffusion of diethyl ether into a solution of 5iPr
in acetonitrile. The molecular structure of the complex is
depicted in Figure 2.
The platinum(II) centre is coordinated to the two carb-
ene moieties of the chiral bidentate bis(NHC) ligand. The
complex adopts a distorted square-planar geometry, with
C–Pt–C angles slightly deviating from 90°, in particular the
C1–Pt1–C3 angle is 85.3(2)°. The Pt–Ccarbene bond lengths
are 1.963(5) and 1.974(6) Å, which fall within the range of
bond lengths reported for other PtII{bis(NHC)} complexes.
[28] The Flack parameter was used to determine the absolute
configuration of the complex, which was found to contain
two chiral centres, C5 and C6 with (R) configuration. To
ensure that the same configuration is valid for all molecules
in the sample, the angle of rotation was determined for the
whole sample by polarimetry.
Scheme 2. Preparation of the chiral (biscarbene)PtII complexes.
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Chiral (Biscarbene)platinum(II) Complexes
1
Figure 1. H NMR spectrum of 5CH2Naphthyl in [D6]dmso.
Table 1. Hydrosilylation of 1-octene with bis(trimethylsiloxy)meth-
ylsilane catalyzed by 5 and 6.
Entry
Complex
Yield of 7 [%][a]
1
2
3
4
5
6
5nBu
75
81
71
77
71
72
5iPr
5Bz
5CH2Naphthyl
Figure 2. The structure of 5iPr as determined from XRD. The ther-
mal ellipsoids are drawn at the 50% probability level. [27] Hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Pt1–C1 1.963(5), Pt1–C3 1.974(6), Pt1–I1 2.6588(5), Pt1–I2
2.6503(4), C1–Pt1–C3 85.3(2), I1–Pt1–I2 93.44(2), C1–Pt1–I2
91.8(2), C3–Pt1–I1 89.3(2), C1–Pt1–I1 174.6(2), C3–Pt1–I2
172.8(2).
6Me
6iPr
1
[a] Yield determined with H NMR spectroscopy; averaged over 3
runs.
All complexes show good activity in the hydrosilylation
reaction, even at a catalyst loading of only 200 ppm
(0.034 mol-%). The best results are obtained with the com-
Catalytic Application in the Hydrosilylation Reaction
The hydrosilylation of alkynes with platinum compounds plex bearing an isopropyl moiety as the N-substituent and
as catalysts is a versatile reaction in organosilicon chemis- a cyclohexylene bridge (Table 1, Entry 2); the complex with
try. The classical systems such as the Karstedt[29] and the same substituent but a different bridge type shows a
Speier[30] catalysts are well established as they display high lower activity (Table 1, Entry 6). Similar to other platinum
activity even at very low catalyst loadings. However, some complexes, complete regiocontrol is observed, and only the
drawbacks to these catalysts, such as the precipitation of anti-Markovnikov adduct is obtained.[31–32] No formation
black inactive colloidal platinum, have led to the search for of platinum black was observed at any time. The catalysts
new catalysts. Thus, the catalytic activities of the new com- were isolated after a catalytic run, and shown to still be
plexes 5 and 6 were tested in a model reaction, namely the intact. All attempts to use prochiral alkenes such as α-meth-
hydrosilylation reaction of 1-octene with bis(trimethylsil- ylstyrene or 2-methyl-1-pentene did not lead to the forma-
oxy)methylsilane, with a catalyst loading of 200 ppm at tion of the corresponding hydrosilylated product, even
120 °C. This silane was chosen as it mimics a polysiloxane when the siloxane was changed to Et3SiH; steric reasons
backbone (Table 1).
are most likely to be responsible for this behaviour.
Eur. J. Inorg. Chem. 2011, 249–254
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251

S. K. U. Riederer, B. Bechlars, W. A. Herrmann, F. E. Kühn
FULL PAPER
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_requ-
est/cif.
Conclusions
New chiral platinum(II) complexes have been synthesized
in good yields by a simple synthetic route. One of the
square-planar complexes has also been crystallographically
characterized. These moisture- and air-stable compounds
are efficient catalysts for the hydrosilylation of 1-octene at
very low catalyst loadings. However, the use of prochiral
General Procedure for the Synthesis of 3: Formylhydrazine (1.13 g,
18.8 mmol) and triethyl orthoformate (6.28 mL, 37.7 mmol) were
dissolved in methanol (20 mL) and heated at 90 °C in an ACE pres-
sure tube® (V = 35 mL) for 3 h. Then (+)-(R,R)-1,2-diphenyl-
ethane-1,2-diamine (1.00 g, 4.71 mmol) was added. The reaction
alkenes in the reaction did not lead to the formation of the mixture was kept at 110 °C for 72 h, before the resulting white solid
was filtered off, washed with thf and pentane and dried in vacuo.
Yield: 0.89 g (60%). [α]2D0 = –8.9 (c = 0.0071, dmso). 1H NMR
(400 MHz, [D6]dmso): δ = 6.91 (s, 2 H, CHPh), 7.23 (t, 2 H,
CHpara), 7.31 (t, 4 H, CHmeta), 7.54 (d, 4 H, CHortho), 8.74 (s, 4 H,
NCHN) ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ = 60.6
(CHPh), 127.7 (CHmeta), 128.8 (CHpara), 129.0 (CHortho), 136.1
(Cquat), 141.6 (NCHN) ppm. C18H16N6 (316.36): calcd. C 68.34, H
5.10, N 26.56; found C 68.35, H 5.09, N 26.35. MS-ESI: m/z =
971.1 [3 M + Na]+, 655.1 [2 M + Na]+, 317.0 [M + H]+.
desired products. Further work is currently underway in our
laboratories to elucidate the reaction mechanism and to de-
termine the ligand or complex modifications necessary to
allow for chirality transfer.
Experimental Section
General: The syntheses of the metal complexes were carried out
with standard Schlenk techniques under argon. All reagents were
purchased from commercial sources and used without further puri-
fication. All solvents were dried and degassed by standard methods
prior to use.[33] The term filtration refers to filtration by cannula
and a Whatman GF/B filter. Elemental analyses were carried out
by the Microanalytical Laboratory of the Technische Universität
München. FAB mass spectra were acquired by the Technische Uni-
versität München Mass Spectrometry Laboratory with a Finnigan
MAT 90 spectrometer equipped with an FAB ionization chamber.
ESI mass spectra were measured with an LCQ Finnigan instru-
General Procedure for the Synthesis of 2: Compound 1 (400 mg,
1.83 mmol), alkyl halide (4.58 mmol) and MeCN (1.0 mL) were
heated in an ACE pressure tube® (V = 35 mL) at 100 °C for 48 h.
The precipitate was isolated by filtration, washed three times with
thf (5 mL) and pentane and dried under reduced pressure to obtain
the solid.
2nBu: Yield: 903 mg (84%). [α]2D0 = –12.7 (c = 0.011, CH2Cl2). 1H
3
NMR (400 MHz, [D6]dmso): δ = 0.89 (t, J = 7.4 Hz, 6 H, CH3),
1.26 (sext, 3J = 7.4 Hz, 4 H, CH3CH2), 1.50 (m, 2 H, c-hexCH2),
1.82 (quint, 3J = 7.4 Hz, 4 H, CH3CH2CH2), 1.93 (m, 2 H,
c-hexCH2), 2.16 (m, 2 H, c-hexCH2), 2.41 (m, 2 H, c-hexCH2), 4.33 (t,
3J = 7.4 Hz, 4 H, NCH2), 5.02 (m, 2 H, c-hexCH), 9.27 (s, 2 H,
NCHN), 10.34 (s, 2 H, NCHN) ppm. 13C{1H} NMR (100.5 MHz,
[D6]dmso): δ = 13.1 (CH3), 18.6 (CH3CH2), 23.3 (c-hexCH2), 29.5
ment. NMR spectra were recorded with
a JEOL-JMX-GX
400 MHz or a Bruker Avance DPX 400 spectrometer. NMR multi-
plicities are abbreviated as follows: s, singlet; d, doublet; t, triplet;
sept, septet; m, multiplet. Coupling constants J are given in Hz.
The spectra were referenced to the residual 1H and 13C{1H} signals
of the solvents.
(
c-hexCH2), 30.9 (CH3CH2CH2), 51.7 (NCH2), 60.4 (c-hexCH), 141.8
(NCHN), 143.3 (NCHN) ppm. C18H32I2N6 (586.08): calcd. C
Single-Crystal X-ray Structure Determination of Compound 5iPr [34]
:
36.87, H 5.50, N 14.33; found C 36.69, H 5.54, N 14.18. MS-FAB:
Crystal data and details of the structure determination are as fol-
lows: C16H26I2N6Pt; Mr = 1502.6; crystal colour and shape: colour-
less fragment; crystal dimensions = 0.32ϫ0.15ϫ0.05 mm; crystal
system: monoclinic; space group: P21 (no. 14); a = 9.8275(5), b =
8.7788(6), c = 13.0436(8) Å; β = 100.325(2)°, V = 1107.10(12) Å3;
Z = 2; μ(Mo-Kα) = 9.137 mm–1; ρcalcd. = 2.254 gcm–3; θ range =
2.81–25.24°; data collected: 14673; independent data [Io Ͻ 2σ(Io)/
all data/Rint]: 3678/3812/0.0386; data/restraints/parameters: 3679/1/
230; R1 [Io Ͻ 2σ(Io)/all data]: 0.0193/0.0205; wR2 [Io Ͻ 2σ(Io)/
all data]: 0.0453/0.0458; GOF = 0.909; Δρmax/min: 0.81/–0.98 eÅ–3.
Suitable single crystals for the X-ray diffraction study were grown
from a mixture of diethyl ether and acetonitrile. Preliminary exami-
nation and data collection were carried out with an area detecting
system (APEX II, κ-CCD) at the window of a rotating anode
(Bruker AXS, FR591) and with graphite-monochromated Mo-Kα
radiation (λ = 0.71073 Å). Data collection was performed at 173 K
(Oxford Cryosystems). Raw data were corrected for Lorentz polar-
ization and, arising from the scaling procedure, for latent decay
and absorption effects. All non-hydrogen atoms were refined with
anisotropic displacement parameters. All hydrogen atoms were as-
signed to ideal positions and refined by using the riding model.
Matrix least-squares refinements were carried out by minimizing
m/z (%) = 458.8 (12.96) [M + I]+, 330.9 (100) [M]2+
.
2iPr: Yield: 963 mg (94%). [α]2D0 = –17.0 (c = 0.0034, dmso). 1H
3
NMR (400 MHz, [D6]dmso): δ = 1.49 (d, J = 6.6 Hz, 14 H, 12 H,
CH3, 2 H, c-hexCH2), 1.96 (m, 2 H, c-hexCH2), 2.19 (m, 2 H,
c-hexCH2), 2.39 (m, 2 H, c-hexCH2), 4.76 (sept, 3J = 6.6 Hz, 2 H,
CHCH3), 4.89 (m, 2 H, c-hexCH), 9.18 (s, 2 H, NCHN), 10.28 (s, 2
H, NCHN) ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ = 20.9
(CH3), 21.0 (CH3), 23.4 (c-hexCH2), 30.6 (c-hexCH2), 55.7 (CHCH3),
60.8 (c-hexCH), 140.7 (NCHN), 143.4 (NCHN) ppm. C16H28I2N6
(558.05): calcd. C 34.42, H 5.06, N 15.05; found C 32.98, H 5.04,
N 14.44. MS-FAB: m/z (%) = 430.0 (25) [M + I]+, 302.6 (100)
[M]2+
.
1
2Bz: Yield: 791 mg (78%). [α]2D0 = –39.2 (c = 0.0036, CH2Cl2). H
NMR (400 MHz, [D6]dmso): δ = 1.49 (m, 2 H, c-hexCH2), 1.93 (m,
2 H, c-hexCH2), 2.15 (m, 2 H, c-hexCH2), 2.40 (m, 2 H, c-hexCH2),
5.12 (m, 2 H, c-hexCH), 5.60 (m, 4 H, NCH2), 7.42 (s, 10 H, aryl),
9.32 (s, 2 H, NCHN), 10.57 (s, 2 H, NCHN) ppm. 13C{1H} NMR
(100.5 MHz, [D6]dmso): δ = 23.5 (c-hexCH2), 31.1 (c-hexCH2), 55.1
(NCH2), 60.6 (c-hexCH), 128.8 (aryl), 129.0 (aryl), 132.7 (Cquat.),
142.4 (NCHN), 143.9 (NCHN) ppm. C24H28Br2N6 (560.33): calcd.
C 51.44, H 5.04, N 15.00; found C 51.11, H 5.04, N 14.80. MS-
2
2 2
Σw(Fo – Fc ) with the SHELXL-97 weighting scheme. The final
residual electron density maps showed no remarkable features.
Neutral atom scattering factors for all atoms and anomalous dis-
persion corrections for the non-hydrogen atoms were taken from
FAB: m/z (%) = 479.1 (9) [M + Br]+, 399.2 (100) [M]2+
.
General Procedure for the Synthesis of 4: Compound 3 (0.47 mmol),
alkyl halide (1.2 mmol) and MeCN (1.0 mL) were heated in an
ACE pressure tube® (V = 35 mL) for the times reported below. The
solvent was removed under vacuum, and the precipitate washed
the International Tables for Crystallography. CCDC-785511 (5iPr
)
contains the supplementary crystallographic data for this paper.
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Chiral (Biscarbene)platinum(II) Complexes
three times with diethyl ether (2 mL) and pentane and dried under
reduced pressure to obtain the solid.
2 H, c-hexCH2), 1.94 (m, 2 H, c-hexCH2), 2.21 (m, 1 H, c-hexCH2),
2.37 (m, 2 H, c-hexCH2), 4.56 (m, 1 H, c-hexCH), 5.01 (d, 2J =
14.8 Hz, 1 H, NCH2), 5.45 (d, J = 14.8 Hz, 1 H, NCH2), 5.56 (d,
2
4Me: Required reaction time: 24 h. Yield: 228 mg (80%). [α]2D0
=
2J = 14.8 Hz, 1 H, NCH2), 5.62 (d, 2J = 14.8 Hz, 1 H, NCH2), 6.19
(m, 1 H, c-hexCH), 7.24 (m, 2 H, Haryl), 7.33 (m, 8 H, Haryl), 8.81
(s, 1 H, NCHN), 8.87 (s, 1 H, NCHN) ppm. 13C{1H} NMR
(100.5 MHz, [D6]dmso): δ = 23.96 (c-hexCH2), 24.04 (c-hexCH2), 28.9
–25.8 (c = 0.0042, dmso). 1H NMR (400 MHz, [D6]dmso): δ = 4.06
(s, 6 H, CH3), 7.32 (t, 2 H, CHpara), 7.37 (t, 4 H, CHmeta), 7.43 (s,
2 H, CHPh), 7.60 (d, 4 H, CHortho), 9.50 (s, 2 H, NCHN), 10.30
(s, 2 H, NCHN) ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ =
30.7 (CH3), 62.7 (CHPh), 128.4 (CHmeta), 129.4 (CHortho), 130.0
(CHpara), 132.8 (Cquat), 142.4 (NCHN), 142.9 (NCHN) ppm.
C20H22I2N6 (600.24): calcd. C 40.02, H 3.69, N 14.00; found C
39.83, H 3.76, N 13.89. MS-FAB: m/z (%) = 473.1 (41) [M + I]+,
(
(
c-hexCH2), 35.1 (c-hexCH2), 53.8 (NCH2), 55.6 (NCH2), 58.0
c-hexCH), 62.3 (c-hexCH), 127.9 (Caryl), 128.32 (Caryl), 128.38 (Caryl),
128.42 (Caryl), 128.44 (Caryl), 134.8 (Cquat), 135.4 (Cquat), 141.6
(NCHN), 145.5 (carbene), 145.6 (NCHN), 151.9 (carbene) ppm.
MS-FAB: m/z (%) = 672.9 (100) [M + Br]+, 592.0 (37) [M]2+
.
345.3 (100) [M]2+
.
C24H26Br2N6Pt (753.39): calcd. C 38.26, H 3.48, N 11.15; found C
37.82, H 3.39, N 10.80.
4iPr: Required reaction time: 4 d. Yield: 266 mg (86%). [α]2D0 = –41.0
(c = 0.0051, CH2Cl2). 1H NMR (400 MHz, [D6]dmso): δ = 1.48
5CH2-Naphthyl: Yield: 116.9 mg (81%). [α]2D0 = +9.6 (c = 1.9ϫ10–3,
dmso). 1H NMR (400 MHz, [D6]dmso): δ = 1.54 (m, 1 H,
c-hexCH2), 1.74 (m, 2 H, c-hexCH2), 1.95 (m, 2 H, c-hexCH2), 2.25
(m, 1 H, c-hexCH2), 2.40 (m, 2 H, c-hexCH2), 4.60 (m, 1 H, c-hexCH),
4.88 (d, 2J = 15.2 Hz, 1 H, NCH2), 5.32 (d, 2J = 14.8 Hz, 1 H,
3
3
(pseudo-t, J = 6.4 Hz, 12 H, CH3), 4.87 (sept, J = 6.4 Hz, 2 H,
CHCH3), 7.30 (s, 2 H, CHPh), 7.38 (m, 6 H, CHpara, CHmeta), 7.62
(d, 4 H, CHortho), 9.48 (s, 2 H, NCHN), 10.40 (s, 2 H, NCHN)
ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ = 21.0 (CH3), 55.9
(CHCH3), 63.2 (CHPh), 128.6 (CHmeta), 129.4 (CHortho), 130.1
(CHpara), 132.1 (Cquat), 140.8 (NCHN), 143.3 (NCHN) ppm.
C24H30I2N6 (656.34): calcd. C 43.92, H 4.61, N 12.80; found C
44.16, H 4.92, N 12.51. MS-FAB: m/z (%) = 529.2 (86) [M + I]+,
2
2
NCH2), 5.45 (d, J = 15.2 Hz, 1 H, NCH2), 5.71 (d, J = 14.8 Hz,
1 H, NCH2), 6.21 (m, 1 H, c-hexCH), 7.16 (m, 1 H, Haryl), 7.33 (m,
2 H, Haryl), 7.50–7.60 (m, 5 H, Haryl), 7.73–7.83 (m, 5 H, Haryl),
7.91 (m, 1 H, Haryl), 8.84 (s, 1 H, NCHN), 8.90 (s, 1 H, NCHN)
ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ = 23.95, 24.04
401.3 (100) [M]2+
.
(
c-hexCH2), 28.9 (c-hexCH2), 35.1 (c-hexCH2), 53.8 (NCH2), 55.6
Synthesis of 5 and 6: PtI2 (60 mg, 0.13 mmol) or PtBr2 (47.4 mg,
0.13 mmol), the corresponding ligand salt (0.13 mmol), and sodium
acetate (21.9 mg, 0.27 mmol) were suspended in dimethyl sulfoxide
(5 mL). The reaction mixture was heated at 90 °C for 12 h. The
resulting solution was filtered before the solvent was removed at
reduced pressure. The crude product was washed three times with
water and pentane and then dried under reduced pressure.
(NCH2), 58.0 (c-hexCH), 62.3 (c-hexCH), 125.5 (Caryl), 126.1 (Caryl),
126.3 (Caryl), 126.41 (Caryl), 126.43, (Caryl), 126.6 (Caryl), 127.5
(Caryl), 127.55 (2ϫCaryl), 127.57 (2ϫCaryl), 127.6 (Caryl), 127.8
(Caryl), 128.0 (Caryl), 132.3 (Cquat), 132.38 (Cquat), 132.40 (Cquat),
132.48 (Cquat), 132.53 (Cquat), 132.8 (Cquat), 141.6 (NCHN), 145.5
(NCHN), 145.7 (carbene), 152.1 (carbene) ppm. MS-FAB: m/z (%)
= 773.0 (100) [M – Br]+. C32H30Br2N6Pt·dmso (853.51 + 78.13):
calcd. C 43.83, H 3.89, N 9.02; found C 43.96, H 3.60, N 9.24.
5iPr: Yield: 85.4 mg (85%). [α]2D0 = +13.0 (c = 1.9ϫ10–3, dmso). 1H
3
NMR (400 MHz, [D6]dmso): δ = 1.27 (m, 6 H, CH3), 1.45 (d, J
6Me: Yield: 76.4 mg (72%). [α]2D0 = +39.3 (c = 2.1ϫ10–3, dmso). 1H
NMR (400 MHz, [D6]dmso): δ = 3.90 (s, 3 H, CH3), 4.04 (s, 3 H,
CH3), 6.75 (d, 2J = 11.6 Hz, 1 H, CHPh), 7.25 (m, 3 H, CHaryl),
7.48 (m, 3 H, CHaryl), 7.64–7.76 (m, 5 H, CHPh, CHaryl), 8.39 (s,
1 H, NCHN), 8.71 (s, 1 H, NCHN) ppm. 13C{1H} NMR
(100.5 MHz, [D6]dmso): δ = 41.6 (CH3), 63.3 (CHPh), 63.7
(CHPh), 128.0 (2ϫCaryl), 128.9 (2ϫCaryl), 129.1 (Caryl), 129.7
(2ϫCaryl), 129.8 (2ϫCaryl), 130.3 (Caryl), 130.9 (Cquat), 136.8
(Cquat), 141.8 (NCHN), 145.4 (NCHN), 150.1 (carbene), 155.2
(carbene) ppm. C20H20I2N6Pt (793.30): calcd. C 30.28, H 2.54, N
10.59; found C 29.98, H 2.69, N 10.06. MS-ESI: m/z = 1459.0 (2
M – I)+, 706.9 [M – I + CH3CN]+.
= 6.7 Hz, 6 H, CH3), 1.60 (m, 3 H, c-hexCH2), 1.93 (m, 2 H,
c-hexCH2), 2.19 (m, 1 H, c-hexCH2), 2.33 (m, 2 H, c-hexCH2), 4.48
(m, 1 H, c-hexCH), 5.19 [sept, 3J = 6.7 Hz, 1 H, CH(CH3)2], 5.61
[sept, 3J = 6.7 Hz, 1 H, CH(CH3)2], 6.16 (m, 1 H, c-hexCH), 8.80
(s, 1 H, NCHN), 8.88 (s, 1 H, NCHN) ppm. 13C{1H} NMR
(100.5 MHz, [D6]dmso): δ = 20.7 (CH3), 21.2 (CH3), 21.9 (CH3),
22.1 (CH3), 24.0 (c-hexCH2), 24.2 (c-hexCH2), 28.9 (c-hexCH2), 34.9
(
(
c-hexCH2), 53.3 [CH(CH3)2], 55.0 [CH(CH3)2], 57.6 (c-hexCH), 62.0
c-hexCH), 141.5 (NCHN), 145.6 (NCHN), 147.9 (carbene), 152.7
(carbene) ppm. MS-FAB: m/z (%) = 624.0 (100) [M – I]+.
C16H26I2N6Pt (753.32): calcd. C 25.58, H 3.49, N 11.19; found C
25.52, H 3.69, N 11.05.
6iPr: Yield: 73.9 mg (65%). [α]2D0 = +25.3 (c = 2.1ϫ10–3, dmso). 1H
NMR (400 MHz, [D6]dmso): δ = 1.33 (d, 3J = 6.6 Hz, 3 H,
CHCH3), 1.36 (d, 3J = 6.6 Hz, 3 H, CHCH3), 5.28 (sept, 3J =
5nBu: Yield: 64.6 mg (62%). [α]2D0 = +11.2 (c = 2.2ϫ10–3, dmso).
1H NMR (400 MHz, [D6]dmso): δ = 0.88 (t, 3J = 7.4 Hz, 3 H,
CH3), 0.91 (t, J = 7.4 Hz, 3 H, CH3), 1.23–1.43 (m, 4 H, CH3CH2),
1.58 (m, 1 H, c-hexCH2), 1.68–2.05 (m, 9 H, CH3CH2CH2,
c-hexCH2), 2.21 (m, 1 H, c-hexCH2), 2.44 (m, 1 H, c-hexCH2), 4.05
(m, 1 H, c-hexCH), 4.24–4.42 (m, 3 H, NCH2), 4.64 (m, 1 H, 1 H,
NCH2), 6.49 (m, 1 H, c-hexCH), 7.86 (s, 1 H, NCHN), 7.98 (s, 1 H,
NCHN) ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ = 13.4
(CH3), 13.5 (CH3), 19.07 (CH3CH2), 19.13 (CH3CH2), 24.0
3
6.4 Hz, 1 H, CHCH3), 5.69 (sept, J = 6.6 Hz, 1 H, CHCH3), 6.67
3
3
(d, J = 11.6 Hz, 1 H, CHPh), 7.23 (t, J = 7.4 Hz, 1 H, CHaryl),
7.27 (t, 3J = 7.4 Hz, 2 H, CHaryl), 7.34 (t, 3J = 7.4 Hz, 1 H, CHaryl),
7.43 (t, 3J = 7.4 Hz, 2 H, CHaryl), 7.61 (d, 3J = 7.4 Hz, 2 H, CHaryl),
7.69 (d, 3J = 7.4 Hz, 2 H, CHaryl), 7.69 (d, 3J = 11.6 Hz, 1 H,
CHPh), 7.75 (m, 2 H, CHaryl), 8.39 (s, 1 H, NCHN), 8.77 (s, 1 H,
NCHN) ppm. 13C{1H} NMR (100.5 MHz, [D6]dmso): δ = 20.8
(CH3), 21.2 (CH3), 21.9 (CH3), 22.0 (CH3), 53.5 [CH(CH3)2], 55.1
[CH(CH3)2], 63.6 (CHPh), 63.8 (CHPh), 128.0 (2ϫCaryl), 128.9
(2ϫCaryl), 129.1 (Caryl), 129.8 (4ϫCaryl), 130.3 (Caryl), 131.0
(Cquat), 136.8 (Cquat), 142.5 (NCHN), 146.2 (NCHN), 149.3 (carb-
ene), 154.1 (carbene) ppm. C24H28I2N6Pt (849.41): calcd. C 33.94,
H 3.32, N 9.89; found C 33.54, H 2.94, N 9.88. MS-ESI: m/z =
762.9 [M – I + CH3CN]+, 635.0 [M – 2 I – CH3CN]+, 594.3 [M –
(
c-hexCH2), 24.2 (c-hexCH2), 28.8 (c-hexCH2), 30.4 (CH3CH2CH2),
30.5 (CH3CH2CH2), 34.9 (c-hexCH2), 51.2 (NCH2), 53.3 (NCH2),
57.6 (c-hexCH), 61.9 (c-hexCH), 141.2 (NCHN), 145.2 (NCHN),
148.5 (carbene), 153.6 (carbene) ppm. C18H30I2N6Pt (779.36):
calcd. C 27.74, H 3.88, N 10.78; found C 28.13, H 3.73, N 10.32.
MS-FAB: m/z (%) = 652.0 (100) [M + I]+, 521.1 (64) [M]2+
5Bz: Yield: 92.9 mg (73%). [α]2D0 = 24.5 (c = 2.9ϫ10–3, dmso). H
NMR (400 MHz, [D6]dmso): δ = 1.52 (m, 1 H, c-hexCH2), 1.70 (m, 2 I]+.
.
1
Eur. J. Inorg. Chem. 2011, 249–254
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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253

S. K. U. Riederer, B. Bechlars, W. A. Herrmann, F. E. Kühn
FULL PAPER
[18]
[19]
C. Diez, U. Nagel, Appl. Organomet. Chem. 2010, 24, 509–516.
L. H. Gade, S. Bellemin-Laponnaz, Coord. Chem. Rev. 2007,
251, 718–725.
L. H. Gade, S. Bellemin-Laponnaz, Top. Organomet. Chem.
2007, 21, 117–157.
V. Cesar, S. Bellemin-Laponnaz, L. H. Gade, Chem. Soc. Rev.
2004, 33, 619–636.
X. Bantreil, J. Broggi, S. P. Nolan, Annu. Rep. Sect. B: Org.
Chem. 2009, 105, 232–263.
General Procedure for Hydrosilylation Catalysis Reactions: An ACE
pressure tube® was charged with methylbis(trimethylsilyloxy)silane
(4.00 g, 0.018 mol) and n-octene (2.02 g, 0.018 mol). Then the cata-
lyst (200 ppm Pt in relation to the total weight, 0.0062 mmol) was
added, and the reaction mixture was heated at 120 °C. After 24 h,
the reaction mixture was cooled, and the product yield was deter-
[20]
[21]
[22]
[23]
[24]
[25]
[26]
1
mined by H NMR spectroscopy.
M. C. Perry, K. Burgess, Tetrahedron: Asymmetry 2003, 14,
951–961.
Acknowledgments
S. K. U. Riederer, B. Bechlars, W. A. Herrmann, F. E. Kühn,
Dalton Trans. 2010, DOI: 10.1039/c0dt00724b.
M. Mühlhofer, T. Strassner, E. Herdtweck, W. A. Herrmann,
J. Organomet. Chem. 2002, 660, 121–126.
A. Meyer, M. A. Taige, T. Strassner, J. Organomet. Chem. 2009,
694, 1861–1868.
This work was generously supported by the Margarete Ammon
Stiftung (Ph. D. grant for S. K. U. R).
[1] J. A. Mata, M. Poyatos, E. Peris, Coord. Chem. Rev. 2007, 251,
841–859.
[2] S. K. U. Riederer, P. Gigler, M. P. Högerl, E. Herdtweck, B.
Bechlars, W. A. Herrmann, F. E. Kühn, Organometallics 2010,
in press.
[3] R. J. Lowry, M. K. Veige, O. Clement, K. A. Abboud, I. Ghivi-
riga, A. S. Veige, Organometallics 2008, 27, 5184–5195.
[4] F. E. Hahn, M. C. Jahnke, Angew. Chem. Int. Ed. 2008, 47,
3122–3172.
[27] K. Brandenburg, DIAMOND Version 3.1, Crystal and Molec-
ular Structure Visualaization, Bonn, 2005.
[28] J. J. Hu, F. Li, T. S. A. Hor, Organometallics 2009, 28, 1212–
1220.
[29] B. D. Karstedt, US Patent 226928, 1972.
[30] J. L. Speier, J. A. Webster, G. H. Barnes, J. Am. Chem. Soc.
1957, 79, 974–979.
[5] F. Glorius, N-Heterocyclic Carbenes in Transition Metal Catal-
ysis, Springer, Berlin/Heidelberg, 2007.
[6] W. A. Herrmann, Angew. Chem. Int. Ed. 2002, 41, 1290–1309.
[7] W. A. Herrmann, M. Elison, J. Fischer, C. Köcher, G. R. J.
Artus, Angew. Chem. Int. Ed. Engl. 1995, 34, 2371–2374.
[8] S. P. Nolan, N-Heterocyclic Carbenes in Synthesis, Wiley-VCH,
Weinheim, 2006.
[9] W. A. Herrmann, L. J. Goossen, C. Köcher, G. R. J. Artus, An-
gew. Chem. Int. Ed. Engl. 1996, 35, 2805–2807.
[10] D. Enders, H. Gielen, K. Breuer, Tetrahedron: Asymmetry
1997, 8, 3571–3574.
[11] W.-L. Duan, M. Shi, G.-B. Rong, Chem. Commun. 2003, 2916–
2917.
[31] G. Berthon-Gelloz, O. Buisine, J.-F. Brière, G. Michaud, S.
Stérin, G. Mignani, B. Tinant, J.-P. Declercq, D. Chapon, I. E.
Markó, J. Organomet. Chem. 2005, 690, 6156–6168.
[32] I. E. Markó, S. Stérin, O. Buisine, G. Berthon, G. Michaud, B.
Tinant, J.-P. Declercq, Adv. Synth. Catal. 2004, 346, 1429–1434.
[33] A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen,
F. J. Timmers, Organometallics 1996, 15, 1518–1520.
[34] a) SMART Software Users Guide, Version 5.1, Bruker Analyti-
cal X-ray Systems, Inc., Madison, WI, 1999; b) SAINT Soft-
ware Users Guide, Version 7.0, Bruker Analytical X-ray Sys-
tems, Inc., Madison, WI, 1999; c) G. M. Sheldrick, SADABS,
Version 2.03, Bruker Analytical X-ray Systems, Inc., Madison,
WI, 2000; d) WinGX, Version 1.70.01 (January 2005): L. J. Far-
rugia, J. Appl. Crystallogr. 1999, 32, 837–838; e) SIR92: A. Al-
tomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994, 27,
435–436; f) G. M. Sheldrick, SHELXL-97, Program for Crystal
Structure Refinement, Göttingen, 1997; g) International Tables
for Crystallography (Ed.: A. J. C. Wilson), Kluwer Academic
Publishers, Dordrecht, The Netherlands, 1992, vol. C, Tables
6.1.1.4 (pp. 500–502), 4.2.6.8 (pp. 219–222), and 4.2.4.2 (pp.
193–199); h) A. L. Spek, PLATON, A Multipurpose Crystallo-
graphic Tool, Utrecht University, Utrecht, The Netherlands,
2008.
[12] A. R. Chianese, R. H. Crabtree, Organometallics 2005, 24,
4432–4436.
[13] L.-j. Liu, F. Wang, M. Shi, Organometallics 2009, 28, 4416–
4420.
[14] Q. Xu, X. Gu, S. Liu, Q. Dou, M. Shi, J. Org. Chem. 2007, 72,
2240–2242.
[15] A. Arnanz, C. Gonzalez-Arellano, A. Juan, G. Villaverde, A.
Corma, M. Iglesias, F. Sanchez, Chem. Commun. 2010, 46,
3001–3003.
[16] P. L. Arnold, M. Rodden, K. M. Davis, A. C. Scarisbrick, A. J.
Blake, C. Wilson, Chem. Commun. 2004, 1612–1613.
[17] H. Clavier, J.-C. Guillemin, M. Mauduit, Chirality 2007, 19,
471–476.
Received: September 2, 2010
Published Online: November 29, 2010
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Eur. J. Inorg. Chem. 2011, 249–254