Synthesis and structural characterization of palladium dicarbene complexes bearing labile co-ligands

Article abstract of DOI:10.1071/CH09143

Dicarbene complexes [Pd(OAc)₂(diNHC)] (2), [Pd(O ₂CCF₃)₂(diNHC)] (3), and [Pd(CNCH ₃)₂(diNHC)](SO₃CF₃)₂ (4) bearing labile acetato, fluoroacetato, and aceto

Full text of DOI:10.1071/CH09143

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2009, 62, 983–987
Synthesis and Structural Characterization of Palladium
Dicarbene Complexes Bearing Labile Co-Ligands
Han Vinh HuynhA,B and Hui Xian SeowA
ADepartment of Chemistry, National University of Singapore, 3 Science Drive 3,
Singapore 117543, Singapore.
BCorresponding author. Email: chmhhv@nus.edu.sg
Dicarbene complexes [Pd(OAc)2(diNHC)] (2), [Pd(O2CCF3)2(diNHC)] (3), and [Pd(CNCH3)2(diNHC)](SO3CF3)2 (4)
bearing labile acetato, fluoroacetato, and acetonitrile co-ligands have been synthesized via metathesis reaction of the
respective precursor [PdBr2(diNHC)] (1) with Ag-salts. All complexes are stable towards air and moisture and have been
fully characterized by spectroscopic and spectrometric methods. Notably and in comparison to diphosphine analogues,
they resist ligand disproportionation in solution. Their molecular structures have also been determined by single crystal
X-ray diffraction. A preliminary catalytic study showed low activity in the hydroamination reaction, but revealed an
interesting co-ligand influence.
Manuscript received: 11 March 2009.
Manuscript accepted: 8 April 2009.
Introduction
structural characterizations of cis-chelating dibenzimidazolin-
2-ylidene complexes bearing weakly coordinating carboxylato
and acetonitrile co-ligands.
Transition metal complexes of N-heterocyclic carbenes (NHCs)
have been investigated in recent years with great intensity due to
their unique properties especially in the field of organometallic
chemistry and catalysis.[1,2] In particular, mono and bis(carbene)
complexes of transition metals with chloro, bromo, and iodo
ligands have been studied in more detail, while other anionic
co-ligands remain relatively rare in NHC chemistry. Notably,
NHC research is also commonly centred on imidazolium- and
imidazolinium-based systems and less attention has been paid
on complexes with benzannulated carbenes, although these may
exhibit interesting properties due to their intermediate position
between saturated and unsaturated NHCs.[3,4] Besides via in-
situ deprotonation of benzimidazolium salts with basic metal
precursors, such complexes can also be obtained by less com-
mon, but interesting routes, such as metal insertion into the
C=C bond of dibenzotetraazafulvalenes[5] or template-assisted
synthesis through intramolecular, nucleophilic attack on coor-
dinated ortho-functionalized phenyl isocyanides.[6–8] Recently,
we have reported the straightforward synthesis of carboxylato-
Pd(II) complexes stabilized by two monodentate benzannulated
carbenes and their application as catalyst precursors for the
Mizoroki-Heck reaction.[9,10] These complexes also showed an
interesting trans-cis isomerism.A detailed comparison of related
cis and trans-complexes revealed that a cis-arrangement of
NHC ligands in such complexes translates into a faster catalyst-
initiation due to their strong trans-effect.[11] In addition, it is
expected that the presence of labile co-ligands also contributes
to a faster initiation. However, it has also been reported that
related diphosphine complexes especially with labile co-ligands
are unstable and tend to undergo ligand disproportionation
(autoionization) to give cationic bis(chelate) complexes.[12,13]
In search for cis-NHC complexes with labile co-ligands that
resist autoionization, we herein describe the synthesis and
Results and Discussion
Syntheses and Characterizations
The syntheses of all compounds are summarized in Scheme 1.
The reaction of dicarbene precursor diNHC·2HBr (A)[14] with
one equiv of Pd(OAc)2 in DMSO at 90◦C afforded the respec-
tive dibromo-dicarbene complex [PdBr2(diNHC)] (1) in 82%
yield.[15] Successful coordination of the dicarbene ligand to
Pd(II) was corroborated by the absence of the downfield sig-
1
nal for the NCHN proton characteristic for A in the H NMR
spectrum of 1. In addition, the protons for the methylene bridge
become diastereotopic upon coordination and split into two
slightly broad doublets at 7.35 and 6.78 ppm with a geminal,
2
homonuclear coupling constant of J(H,H) = 14.1 Hz. Its for-
mation is also supported by a base peak at m/z = 503 for the
[M − Br + MeCN]+ fragment in the positive mode electrospray
ionization (ESI) mass spectrum.
The introduction of labile co-ligands can be straight-
forwardly achieved by metathesis reactions of complex 1
with various Ag salts in hot acetonitrile. Hence, the mixed
carboxylato-dicarbene complexes [Pd(OAc)2(diNHC)] (2) and
[Pd(O2CCF3)2(diNHC)] (3) as well as the acetonitrile-dicarbene
complex [Pd(diNHC)(NCCH3)2](O3SCF3)2 (4) were prepared
by reacting precursor-complex 1 with AgO2CCH3, AgO2CCF3,
and AgO3SCF3, respectively, as depicted in Scheme 1. The
complexes were isolated as white and air-stable solids. Even
in solution, the complexes are unusually stable and no palla-
dium black was observed upon prolonged standing, even in polar
solvents such as DMSO.
In general, the substitution of both bromo-ligands in 1 by car-
boxylato and acetonitrile ligands leads to an improved solubility.
© CSIRO 2009
10.1071/CH09143
0004-9425/09/090983

RESEARCH FRONT
984
H. V. Huynh and H. X. Seow
N
N
ϩ
ϩ
N
N
2BrϪ
A
Pd(OAc)2
DMSO
90ЊC
N
N
N
N
N
N
N
N
Br
Br
N
N
O2CCH3
O2CCH3
O2CCF3
2AgO2CCF3
2AgO2CCH3
Pd
Pd
Pd
CH3CN
80ЊC
CH3CN
80ЊC
O2CCF3
N
N
1
3
2
2AgO3SCF3
CH3CN
80ЊC
2ϩ
N
N
N
N
NCCH3
NCCH3
Pd
4
2CF3SO3Ϫ
Scheme 1. Synthesis of dicarbene complexes 1–4 bearing various co-ligands.
All novel complexes 2–4 are soluble in acetone, CH3CN, DMSO,
DMF and insoluble in non-polar solvents such as diethyl ether,
hexane, or toluene. However, their solubility is still inferior com-
pared with their analogues which contain monodentate carbene
in a dicationic bis(chelate) complex with the same dicarbene
ligand.[17] 1H NMR spectroscopy also showed no indication for
a bridging or bidentate coordination mode of the carboxylato
ligands in 2 and 3.
1
ligands.[9] The H NMR resonances recorded in d6-DMSO of
Molecular Structures
the chelating dibenzimidazolin-2-ylidene ligand in 2–4 remain
largely unaffected upon ligand exchange. The only difference
noted is the broadness of the resonances for the diastereotopic
protons of the methylene bridge indicating a different rate of
fluxionality due to different co-ligands. For example, only two
very broad singlets are observed for complex 2, whereas the
spectra of 3 and 4 show two defined doublets for these methy-
lene protons. However, the influence of the various co-ligands
has more impact on the 13C NMR chemical shift of the car-
bene carbon. The coordination of the acetato ligand leads to a
slight upfield shift from 171.4 ppm in 1[15] to 169.8 ppm in 2.
This shielding effect is even greater when the weaker coordi-
nating anions such as fluoroacetates and triflates are employed,
where upfield shifts of the carbenoid signal to 159.4 ppm and
159.1 ppm, respectively, are observed. We have observed a sim-
ilar but much more pronounced upfield shift in methylene
Single crystals of complexes 2–4 suitable for X-ray diffrac-
tion studies were obtained by slow diffusion of dichloromethane
(2·CH2Cl2·H2O) or diethyl ether (3, 4·2CH3CN) into concen-
trated acetonitrile solutions at ambient temperature. For the
purpose of comparison, X-ray analysis was also carried out
for single crystals of the dibenzimidazolium salt A obtained
as solvate A·2H2O by slow evaporation of a concentrated
methanol/ethyl acetate solution at ambient temperature.
The molecular structures of salt A and complexes 2–4 are
depicted in Figs 1–4 along with selected bond parameters.
Selected crystallographic data are listed in Table 1. All three
complexes crystallized as mononuclear complexes, in which the
palladium centre is coordinated by the chelating dicarbene and
two monodentate co-ligands in a nearly perfect square-planar
geometry. Upon coordination, the NCN angle of the heterocyclic
ring decreases from 110.55◦ inA to ∼107◦ in all complexes 2–4.
This change is accompanied by a slight lengthening of the aver-
age N-Ccarbene bond from 1.327 Å in A (N-Cprecarbene) to 1.348,
1.347, and 1.345 Å in the complexes 2–4, respectively. The sim-
ilarity of these bond distances in the three complexes indicates
the absence of any co-ligand influence. The short methylene
bridge of the dicarbene ligand prevents the favourable perpen-
dicular orientation of the carbene ring planes with respect to
the PdC2L2-coordination plane, which results in small dihedral
angles ranging from 39◦ to 47◦. More importantly, a compar-
ison of the average Pd-C bonds in 2–4 reveals that those in 2
and 4 are almost identical (∼1.9645 Å), whereas those in 3 are
bridged imidazolin-2-ylidene analogues previously.[16] The 13
C
NMR signals for the CF3 groups of the fluoroacetato ligand
in 3 (116.4 ppm, q) and the triflate anions in 4 (120.7 ppm, q)
show the expected splitting pattern due to 13C-19F heteronuclear
1
couplings with J(C,F) = 290 and 323 Hz, respectively. In the
19F NMR spectra, broad singlets are observed at 2.55 ppm (3)
and −1.80 ppm (4) for these CF3 groups. More importantly, even
inthepolarsolventd6-DMSOwedidnotfindanyNMRevidence
for the formation of bis(chelates) due to possible autoioniza-
tion processes as observed for diphosphine analogues.[12,13] To
this point, it is worth noting that we have recently reported
such autoionization behaviour in a Ni(II) system, which resulted

RESEARCH FRONT
Characterization of Palladium Dicarbene Complexes
985
C17
N4
N2
N3
C9
C1
N1
N1
C8
Pd1
O2
O4
C24
N2
C1
C22
Br1
O3
O1
Fig. 1. Molecular structure of salt A showing 50% probability ellipsoids
with the crystallographic numbering scheme; solvent molecules and hydro-
gen atoms are omitted for clarity; selected bond lengths [Å] and angles [◦]:
N1-C1 1.343(3), N2-C1 1.311(3), N1-C8 1.455(2); N1-C1-N2 110.55(19),
N1-C8-N1A 113.2(2).
Fig. 3. Molecular structure of [Pd(O2CCF3)2(diNHC)] (3) showing 50%
probability ellipsoids with the crystallographic numbering scheme; hydro-
gen atoms are omitted for clarity; selected bond lengths [Å] and angles [◦]:
Pd1-C11.956(3), Pd1-C91.951(3), Pd1-O12.0614(19), Pd1-O32.0721(18),
N1-C1 1.339(3), N2-C1 1.355(3), N2-C17 1.446(3), N4-C17 1.451(3),
N4-C9 1.362(3), N3-C9 1.333(3); C9-Pd1-C1 85.42(11), N1-C1-N2
107.1(2), N2-C17-N4 108.8(2), N3-C9-N4 106.5(2); PdC2O2/carbene di-
hedral angles 41.49 and 42.49.
C17
N2
N4
C1
N1
C9
N3
C17
Pd1
O1
O4
N2
N3
O2
O3
C9
C20
C1
N4
N1
C18
Pd1
Fig. 2. Molecular structure of [Pd(OAc)2(diNHC)] (2) showing 50%
probability ellipsoids with the crystallographic numbering scheme; sol-
vent molecules and hydrogen atoms are omitted for clarity; selected
bond lengths [Å] and angles [◦]: Pd1-C1 1.972(3), Pd1-C9 1.958(2),
Pd1-O1 2.0685(19), Pd1-O3 2.0668(19), N1-C1 1.343(3), N2-C1 1.354(3),
N2-C17 1.449(3), N4-C17 1.450(3), N4-C9 1.354(3), N3-C9 1.341(3);
C9-Pd1-C1 85.32(10), N1-C1-N2 106.4(2), N2-C17-N4 108.86(19),
N3-C9-N4 106.4(2); PdC2O2/carbene dihedral angles 39.15 and 42.96.
N6
N5
Fig. 4. Molecular structure of [Pd(diNHC)(NCCH3)2](SO3CF3)2 (4)
showing 50% probability ellipsoids with the crystallographic numbering
scheme; a solvent molecule, counter anions and hydrogen atoms are omit-
ted for clarity; selected bond lengths [Å] and angles [◦]: Pd1-C1 1.971(6),
Pd1-C9 1.958(5), Pd1-N5 2.076(5), Pd1-N6 2.066(5), N1-C1 1.317(7),
N2-C1 1.370(3), N2-C17 1.452(7), N3-C17 1.456(7), N4-C9 1.337(7),
N3-C9 1.356(7); C9-Pd1-C1 83.5(2), N1-C1-N2 107.3(5), N2-C17-N3
109.0(5), N3-C9-N4 107.1(5); PdC2N2/carbene dihedral angles 46.39 and
46.94.
markedly shorter (1.9535 Å). This observation indicates that the
donor ability of acetato and acetonitrile ligands is comparable
regardless of the overall charge of the resulting complex. The
trifluoroacetato ligands in 3, however, are expected to be less
basic, thus leading to a more Lewis acidic metal centre, which in
turn results in shorter and supposedly stronger Pd-C bonds. The
bite angles for the two carboxylato complexes 2 and 3 amount-
ing to 85.32◦ and 85.42◦ are very similar. The angle for the
complex-cation 4 is with 83.5◦, surprisingly smaller.
For both complexes 2 and 3, the two carboxylato ligands
coordinate in a monodentate fashion with their pendant oxygen
atoms found in syn conformation. However, this does not indi-
cate the preference of syn over anti conformation, because both
have been observed in related complexes previously.[10] Fur-
ther structural parameters are unexceptional and do not require
further comments.
[Pd]
CF3COOH
HN
NH2
ϩ
Toluene
100ЊC, 24 h
Scheme 2. Pd-catalyzed hydroamination of styrene with aniline.
hydroamination reaction of styrene with aniline in the presence
of CF3CO2H as activator (Scheme 2).
Disappointingly, only complex 3 showed low activity giv-
ing the desired addition product in 15% yield after 24 h at
2 mol-% catalyst loading and under non-optimized conditions.
Complexes 2 and 4, however, showed no activity at all, although
very different observations were made for these two complexes.
Preliminary Catalytic Test for the Hydroamination
Reaction
In a preliminary study, the catalytic activity of the title com-
plexes 2–4 has been tested in the challenging intermolecular

RESEARCH FRONT
986
H. V. Huynh and H. X. Seow
Table 1. Selected crystallographic data for salt A and complexes 2–4
A·2H2O
2·CH2Cl2·H2O
3
4·2CH3CN
Formula
Formula weight
Crystal system
Space group
a [Å]
C17H22Br2N4O2
474.21
Monoclinic
C2/c
C22H26Cl2N4O5Pd
603.77
Orthorhombic
Pccn
C21H16F6N4O4Pd
608.78
Triclinic
P-1
9.3832(5)
C25H25F6N7O6PdS2
804.04
Monoclinic
P2(1)/n
20.822(5)
15.7032(17)
8.6202(6)
b [Å]
8.2040(18)
13.855(4)
90
126.080(8)
90
1912.8(8)
17.4546(19)
18.665(2)
90
90
11.1193(6)
11.7971(6)
68.4750(10)
81.2280(10)
78.6820(10)
1118.36
13.4411(10)
27.9130(18)
90
97.264(2)
90
3208.2(4)
c [Å]
α [◦]
β [◦]
γ [◦]
90
V [Å3]
5116.0(10)
Z
4
8
2
4
Dc [g cm−3
]
1.647
4.256
2.76 to 27.47
0.4832 and 0.3820
R1 = 0.0268, wR2 = 0.0661
R1 = 0.0335, wR2 = 0.0675
0.973
1.568
0.974
1.74 to 27.50
0.7999 and 0.6968
R1 = 0.0355, wR2 = 0.0861
R1 = 0.0477, wR2 = 0.0916
1.055
1.808
0.917
1.665
0.794
1.68 to 25.00
0.9320 and 0.7418
R1 = 0.0636, wR2 = 0.1431
R1 = 0.0821, wR2 = 0.1520
1.117
µ [mm−1
θ range [◦]
]
1.86 to 27.50
0.8823 and 0.7833
R1 = 0.0359, wR2 = 0.0891
R1 = 0.0389, wR2 = 0.0907
1.084
Max., min. transmission
Final R indices [I > 2σ(I)]
R indices (all data)
Goodness-of-fit on F2
Large diff. peak and hole
0.658 and −0.371
0.588 and −0.452
0.834 and −0.421
0.852 and −0.855
[e Å−3
]
Complex 2 did not show any sign of decomposition, whereas
complex 4 led to a black mixture upon heating to 100◦C most
likely due to the formation of palladium black. The same obser-
vation was made in the absence of co-acid. This leads to the
assumption that the acetato ligands in 2 are too stabilizing,
whereas the acetonitrile ligands in 4 are too labile despite having
similar donor strengths (vide supra).As mentioned above, the tri-
fluoroacetato ligands in 3 give rise to the most Lewis acidic metal
centre and, at the same time, seem to have the best properties in
terms of donor strength and lability in this series.
Dibromo-1,1ꢀ-methylene-(3,3ꢀ-dimethyldibenzimidazolin-
2-ylidene)palladium(II) 1
A mixture of A (0.656 g, 1.5 mmol) and Pd(OAc)2 (0.336 g,
1.5 mmol) was dissolved in DMSO (5 mL). The suspension was
stirred overnight at 90◦C. The solvent was then removed by
vacuum distillation. Deionized water was added to the residue
and the mixture was stirred overnight and then filtered. The
residue was washed with ethanol followed by diethyl ether
and dried under vacuum to yield the title compound as an
1
orange amorphous solid. Yield: 0.669 g (1.23 mmol, 82%). H
NMR (300 MHz, d6-DMSO, ppm): δ 8.48 (d, 3J(H,H) = 7.6 Hz,
2H, Ar-H), 8.23 (d, 3J(H,H) = 7.4 Hz, 2H, Ar-H), 7.51–7.40
(m, 4H), 7.35 (d, 2J(H,H) = 14.1 Hz, 1H, CHH), 6.78 (d,
2J(H,H) = 14.1 Hz, 1H, CHH), 4.13 (s, 6H, CH3). MS (ESI,
positive ions) m/z [%]: 503 (100) [M − Br + MeCN]+.
Conclusions
In conclusion, we have presented a straightforward and high
yielding synthesis of benzannulated dicarbene complexes bear-
ing labile acetato, fluoroacetato, and acetonitrile co-ligands,
which are unusually stable in solution and resist ligand dispro-
portionation. All complexes have been fully characterized and
their molecular structures established by X-ray single crystal
diffraction. A preliminary catalytic study using the hydroami-
nation reaction of styrene with aniline revealed that complex 3
bearing trifluoroacetato ligands showed some activity, whereas
theacetatoandacetonitrilecomplexes 2and 4wereeithertoosta-
ble or too labile under the reaction conditions. Further research in
our laboratory is underway to optimize the reaction time and con-
ditions and to find more suitable catalysts with trifluoroacetato
ligands for the highly challenging hydroamination reaction.
Di(acetato)-1,1ꢀ-methylene-(3,3ꢀ-dimethyldibenzimidazolin-
2-ylidene)palladium(II) 2
A mixture of 1 (0.185 g, 0.340 mmol) and AgOAc (0.114 g,
0.680 mmol) was suspended in acetonitrile (10 mL). The reac-
tion mixture was shielded from light and heated under reflux
overnight. The resulting yellow suspension was filtered through
celite to remove yellow-green solids of AgI and the solvent of
the filtrate removed under vacuum. The residue was then sus-
pended in dichloromethane, filtered, and washed with diethyl
ether. The title compound was obtained as a white amorphous
solid after drying. Single crystals of 2 suitable for X-ray diffrac-
tion studies were obtained from a concentrated acetonitrile/
dichloromethane solution at ambient temperature.Yield: 116 mg
(0.232 mmol, 68%). 1H NMR (300 MHz, d6-DMSO): δ 8.20 (d,
3J(H,H) = 7.8 Hz, 2H,Ar-H), 7.67 (d, 3J(H,H) = 7.8 Hz, 2H,Ar-
H), 7.50–7.38 (m, 4H, Ar-H), 7.32 (s, br, 1H, CHH), 6.58 (s, br,
1H, CHH), 3.99 (s, 6H, NCH3), 1.78 (s, 6H, O2CCH3). 13C{1H}
NMR (75.48 MHz, d6-DMSO): δ 174.4 (s, COO), 169.8 (s,
NCN), 133.7, 132.2, 124.0, 123.8, 111.6, 110.8 (s,Ar-C), 56.6 (s,
CH2), 33.6(s, NCH3), 23.6(s, O2CCH3). MS(ESI, positiveions)
m/z [%]: 441 (100) [M − O2CCH3]+. Calc. for C21H22N4O4Pd
Experimental
Methods and Materials
All manipulations were carried out in air unless otherwise stated.
All solvents were used as received. Dicarbene precursor A was
synthesized according to a literature report.[14] 1H, 13C, and
19F NMR spectra were recorded on Bruker 300 MHz FT-NMR
spectrometers using Me4Si as an internal and CF3CO2H as an
external standard at ambient temperature. ESI mass spectra were
obtained using a Finnigan MAT LCQ spectrometer. Elemental
analyses were performed on a Perkin–Elmer PE 2400 elemental
analyzer.

RESEARCH FRONT
Characterization of Palladium Dicarbene Complexes
987
(500.84): C, 50.36; H, 4.43; N, 11.19%. Anal. Found: C, 50.54;
H, 4.39; N, 10.99%.
atoms. All hydrogen atoms were put at calculated positions.
All non-hydrogen atoms were generally given anisotropic dis-
placement parameters in the final model. A summary of the
most important crystallographic data is given in Table 1.
CCDC723157(A·2H2O), 723158(2·CH2Cl2·H2O), 723159(3),
and 723160 (4·2CH3CN) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
1,1ꢀ-Methylene-(3,3ꢀ-dimethyldibenzimidazolin-
2-ylidene)di(trifluoroacetato)palladium(II) 3
Complex 3 was synthesized in analogy to 2 from 1 (0.127 g,
0.234 mmol) and AgO2CCF3 (0.103 g, 0.468 mmol) and iso-
lated as a white amorphous solid after drying. Transparent
cubic crystals of 3 suitable for X-ray diffraction studies
were obtained by diffusion of diethyl ether into a concen-
trated acetonitrile solution at ambient temperature.Yield: 80 mg
(0.132 mmol, 56%). 1H NMR (300 MHz, d6-DMSO): δ 8.26 (d,
3J(H,H) = 7.7 Hz, 2H,Ar-H), 7.79 (d, 3J(H,H) = 7.7 Hz, 2H,Ar-
Acknowledgements
The authors thank the National University of Singapore for financial support
(Grant no. R 143–000–327–133) and especially Ms Geok Kheng Tan and
Professor Lip Lin Koh for determining the X-ray molecular structures.
2
H), 7.57–7.46 (m, 4H, Ar-H), 7.39 (d, J(H,H) = 12.3 Hz, 1H,
CHH), 6.79 (d, 2J(H,H) = 12.3 Hz, 1H, CHH), 4.04 (s, 6H, CH3).
13C{1H} NMR (75.48 MHz, d6-DMSO): δ 161.7 (s, COO),
159.4 (s, NCN), 133.6, 132.6, 124.6, 124.4 (s, Ar-C), 116.4
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1
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3773(20000204)39:3<541::AID-ANIE541>3.0.CO;2-B
[5] F. E. Hahn, T. von Fehren, T. Lügger, Inorg. Chim. Acta 2005, 358,
4137. doi:10.1016/J.ICA.2004.11.053
[6] F. E. Hahn, V. Langenhahn, T. Lügger, T. Pape, D. Le Van, Angew.
Chem. Int. Ed. 2005, 44, 3759. doi:10.1002/ANIE.200462690
[7] F. E. Hahn, V. Langenhahn, N. Meier, T. Lügger, W. P. Fehlhammer,
Chem. Eur. J. 2003, 9, 704. doi:10.1002/CHEM.200390079
[8] F. E. Hahn, C. G. Plumed, M. Münder, T. Lügger, Chem. Eur. J. 2004,
10, 6285. doi:10.1002/CHEM.200400576
[9] Y. Han, H.V. Huynh, L. L. Koh, J. Organomet. Chem. 2007, 692, 3606.
doi:10.1016/J.JORGANCHEM.2007.04.037
[10] H. V. Huynh, T. C. Neo, G. K. Tan, Organometallics 2006, 25, 1298.
doi:10.1021/OM0510369
[11] H. V. Huynh, J. H. H. Ho, T. C. Neo, L. L. Koh, J. Organomet. Chem.
2005, 690, 3854. doi:10.1016/J.JORGANCHEM.2005.04.053
[12] A. Marson, A. B. van Oort, W. P. Mul, Eur. J. Inorg. Chem.
2002, 3028. doi:10.1002/1099-0682(200211)2002:11<3028::AID-
EJIC3028>3.0.CO;2-8
Bis(acetonitrile)-1,1ꢀ-methylene-(3,3ꢀ-
dimethyldibenzimidazolin-2-ylidene)
palladium(II) Ditriflate 4
Complex 4 was synthesized in analogy to 2, from 1 (0.197 g,
0.364 mmol) andAgO3SCF3 (0.211 g, 0.820 mmol) and isolated
as a white solid. Transparent cubic crystals suitable for X-ray
diffraction studies were obtained by diffusion of diethyl ether
into a concentrated acetonitrile solution at ambient tempera-
1
ture. Yield: 0.136 g (0.200 mmol, 55%). H NMR (300 MHz,
3
d6-DMSO): δ 8.25 (d, J(H,H) = 7.7 Hz, 2H, Ar-H), 7.81 (d,
3J(H,H) = 7.9 Hz, 2H, Ar-H), 7.59–7.49 (m, 4H, Ar-H), 7.36
2
2
(d, J(H,H) = 13.1 Hz, 1H, CHH), 6.92 (d, J(H,H) = 13.1 Hz,
1H, CHH), 4.10 (s, 6H, CH3), 1.75 (CH3CN). 13C{1H} NMR
(75.48 MHz, d6-DMSO): δ 159.1 (s, NCN) 133.8, 132.4, 127.1,
124.8, 124.6 (s, Ar-C), 120.7 (q, 1J(C,F) = 322.8 Hz, CF3),
112.1, 111.3 (s, Ar-C), 57.0 (s, CH2), 34.5 (s, CH3). 19F{1H}
NMR (282 MHz, d6-DMSO): −1.80 (br s, 6F, CF3). MS (ESI,
positive ions) m/z [%]: 531 (44) [M − O3SCF3]+.
[13] C. Bianchini, A. Meli, W. Oberhauser, Organometallics 2003, 22,
4281. doi:10.1021/OM030132B
[14] T. Scherg, S. K. Schneider, G. D. Frey, J. Schwarz, E. Herdtweck,
W. A. Herrmann, Synlett 2006, 2894.
General Procedure for Pd-catalyzed Hydroamination
of Styrene Using Aniline
[15] (a) The preparation of complex 1 by a different route with a lower
yield of 58% has recently been reported: A. Biffis, C. Tubaro,
G. Buscemi, M. Basato, Adv. Synth. Catal. 2008, 350, 189.
doi:10.1002/ADSC.200700271
Complex 3 (0.02 mmol) was weighed into a Schlenk tube. The
flask was evacuated and filled with nitrogen. Toluene (0.5 mL),
styrene (0.17 mL, 1.5 mmol), and aniline (0.09 mL, 1 mmol)
were added stepwise. The mixture was heated and stirred at
100◦C for 30 min and CF3CO2H (0.015 mL, 0.20 mmol) was
added. The mixture was left to stir for 24 h at 100◦C. The
reaction mixture was adsorbed onto silica gel and eluted with
hexane/ethyl acetate (1:0.15).
(b) The diiodo analogue of 1 has also been reported: F. E. Hahn,
M. Foth, J. Organomet. Chem. 1999, 585, 241. doi:10.1016/S0022-
328X(99)00219-3
[16] H. V. Huynh, D. LeVan, F. E. Hahn, T. S. A. Hor, J. Organomet. Chem.
2004, 689, 1766. doi:10.1016/J.JORGANCHEM.2004.02.033
[17] H. V. Huynh, R. Jothibasu, Eur. J. Inorg. Chem. 2009, 1926.
doi:10.1002/EJIC.200801149
X-Ray Diffraction Studies
[18] SMART version 5.628 2001 (Bruker AXS Inc.: Madison, Wisconsin,
USA).
X-ray data were collected with a Bruker AXS SMART APEX
diffractometer, using MoKα radiation at 223 K with the SMART
suite of programs.[18] Data were processed and corrected for
Lorentz and polarization effects with SAINT,[19] and for absorp-
tion effect with SADABS.[20] Structural solution and refinement
were carried out with the SHELXTL suite of programs.[21] The
structure was solved by direct methods to locate the heavy
atoms, followed by difference maps for the light, non-hydrogen
[19] SAINT+ version 6.22a 2001 (Bruker AXS Inc.: Madison, Wisconsin,
USA).
[20] G. W. Sheldrick, SADABS version 2.10 2001 (University of Göttin-
gen).
[21] SHELXTL version 6.14 2000 Bruker AXS Inc.: Madison, Wisconsin,
USA.