Facile oxidative addition of organic halides to heteroleptic and homoleptic Pd0-N-heterocyclic carbene complexes

Article abstract of DOI:10.1002/ejic.201001257

Novel heteroleptic Pd⁰ complexes with an N-heterocyclic carbene (NHC) ligand [(Me₃P)Pd(NHC)] (NHC = IPr, 1; SIPr, 2) were obtained from [Pd(CH₂=CHPh)(PMe₃)₂] and an equivalent of NHC [NHC = 1,3-bis(2,

Full text of DOI:10.1002/ejic.201001257

FULL PAPER
DOI: 10.1002/ejic.201001257
Facile Oxidative Addition of Organic Halides to Heteroleptic and Homoleptic
Pd0–N-Heterocyclic Carbene Complexes
Jung-Hyun Lee,[a] Hyeong-Tak Jeon,[a] Yong-Joo Kim,*[a] Kyung-Eun Lee,[b]
Young Ok Jang,[b] and Soon W. Lee[b]
Keywords: Palladium / Oxidative addition / N-Heterocyclic carbenes / Halides / Heteroleptic complexes
Novel heteroleptic Pd0 complexes with an N-heterocyclic
carbene (NHC) ligand [(Me3P)Pd(NHC)] (NHC = IPr, 1; SIPr,
2) were obtained from [Pd(CH2=CHPh)(PMe3)2] and an
equivalent of NHC [NHC = 1,3-bis(2,6-diisopropylphenyl)-
imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)-
4,5-dihydroimidazol-2-ylidene (SIPr)]. Further treatments of
complexes 1 and 2 with an additional equimolar NHC
afforded the corresponding bis(NHC)–Pd0 complexes
[Pd(NHC)2] (NHC = IPr, 3; SIPr, 4). Complexes 1–4 readily
reacted with dichloromethane or chloroform to give C–Cl oxi-
dative addition products. In addition, the reactivity of com-
plex 2 toward other organic halides such as bromobenzene,
trans-1,2-dichloroethylene, and 5,5Ј-dibromo-2,2Ј-bithio-
phene to produce the corresponding oxidative addition prod-
ucts was investigated. Finally, the ligand replacement of
complex 1 with a chelating phosphane was examined.
as precursors for zero-valent Pd complexes. We here report
the preparation of several phosphane–NHC–Pd0 and
bis(NHC)–Pd0 complexes and demonstrate their oxidative
addition reactivity toward various organic halides including
halogenated solvents.
Introduction
Pd–NHC-catalyzed (NHC=N-heterocyclic carbene) C–C
or C–X (X = heteroatom) coupling reactions have been in-
creasingly studied during the past decade.[1–4] In the cata-
lytic cycles, the oxidative addition of organic halides is a
fundamental step to give organic products or Pd–σ-bonded
intermediates. Although many low-valent group 10 metal–
phosphane complexes undergo oxidative addition with or-
ganic halides,[5–9] quite a few Pd0–NHC complexes exhibit
such reactivity.[10–12] For example, Cavell’s[11] group as well
as the groups of Caddick and Cloke[12] reported the oxidat-
ive addition of aryl halides to Pd0–NHC complexes. In ad-
dition, the groups of Cavell[11b] and Radius[13] demonstrated
oxidative additions of organic halides and sulfides to Ni0–
NHC complexes. Theoretical and mechanistic studies on
the oxidative addition of aryl halides to Pd0–NHC com-
plexes were also reported.[14,15]
The NHC ligand is known to be an alternative group of
typical tertiary phosphanes in zero-valent Pd complexes. In
addition, the activity of the Pd–NHC-catalyzed cross-cou-
plings varies with the electronic or steric properties of ancil-
lary ligands, and it also depends on the stability or reactiv-
ity of the catalysts. To develop efficient catalysts other than
known Pd–NHC catalysts, we tried to prepare novel NHC–
Pd0 complexes from dialkyl–Pd complexes, which may serve
Results and Discussion
Preparation of PMe3–NHC–Pd0 Complexes
Room-temperature reactions of [Pd(CH2=CHPh)-
(PMe3)2],[16,17] which could be generated in situ from trans-
[PdEt2L2] and styrene, with IPr [IPr = 1,3-bis(2,6-diiso-
propylphenyl)imidazol-2-ylidene] or SIPr [1,3-bis(2,6-di-
isopropylphenyl)-4,5-dihydroimidazol-2-ylidene] in a 1:1
molarratiogavenovelPMe3–NHC–Pd0complexes[(Me3P)Pd-
(NHC)] (NHC = IPr, 1; SIPr, 2) (Scheme 1). As mentioned
in the Introduction, the above NHC ligands were adopted
as supporting ligands to the Pd center in our study.
[a] Department of Chemistry, Kangnung-Wonju National
University,
Gangneung 210-702, South Korea
Fax: +82-33-640-2264
E-mail: yjkim@ kangnung.ac.kr
[b] Department of Chemistry, Sungkyunkwan University, Natural
Science Campus,
Suwon 440-746, Korea
Scheme 1.
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Heteroleptic and Homoleptic Pd0–NHC Complexes
Complexes 1 and 2 were obtained as pale yellow solids, work, we could prepare unique NHC-stabilized bis(di-
which were moderately stable in the solid state at room tem- ethyl)–PdII complexes that are moderately stable both in the
perature but air sensitive in solution. In particular, these solid state and in solution at room temperature. We moni-
complexes slowly decomposed in polar solvents and readily tored the 1H NMR spectra of compounds 5 and 6 dissolved
reacted with halogenated solvents (see Scheme 4 below). in THF or toluene by heating the solutions from room tem-
1
The H and 31P{1H} NMR spectra of the final products perature to 70 °C. The solutions were thermally stable to
indicate that these contained a small amount of the bis- 50 °C. When the temperature was raised to 70 °C, decompo-
(carbene)–Pd0 complexes [Pd(NHC)2] [NHC = IPr (3) or sition of the compounds occurred. However, we could not
SIPr (4)],[17] which were presumably formed by the dissoci- identify PMe3–NHC–Pd0 compounds due to their compli-
ation of PMe3 during the reaction. As a result, an analyti- cated spectral patterns. These results strongly support the
cally pure product could not be obtained. Moreover, during known fact that NHC ligands behave as better stabilizing
the course of recrystallization in ditheyl ether or THF, com- ancillary ligands than tertiary phosphane ligands. Com-
plexes 1 and 2 partially dissociated the PMe3 ligand to give plexes 5 and 6 were isolated as white crystals, and the mo-
the bis(NHC)–Pd0 complexes 3 and 4 (Scheme 2). A similar lecular structure of complex 6 in Figure 1 was determined
phosphane dissociation was also previously observed in the by X-ray diffraction. The crystal and refinement data of 6
reactions between [Pd{P(o-tolyl)3}2] and IPr, SIPr, or 1,3- is summarized in Table 1. The coordination sphere of Pd
bis(adamantly)imidazolin-2-ylidene to give phosphane– can be described as a square plane that consists of one
NHC–Pd0 complexes [(R3P)Pd(NHC)] [NHC = IPr, SIPr; NHC, one PMe3, and two trans-Et ligands. The N1–C1
PR3 = P(o-tol)3] or bis(NHC)–Pd0 complexes.[18,19] Re- [1.345(2) Å] and N2–C1 [1.355(2) Å] bonds, in which C1 is
cently, Nolan and co-workers[20] reported a general syn- the carbene carbon, are significantly shorter than the other
thetic route to phosphane–NHC–Pd0 complexes, [(R3P)- N–C bonds [the average is 1.460(2) Å]. The shortening of
Pd(NHC)] [NHC = IPr, SIPr; PR3 = PPh3, PCy3, the N–C (carbene) bonds probably reflects the resonance of
P(Bu)(Ad)2], from [(NHC)Pd(η3-allyl)Cl] and tertiary phos- those bonds due to the lone pair of electrons on the carbene
phanes. The 13C{1H} NMR spectrum of 1 shows a doublet carbon. Terminal methyl groups on the ethyl ligands are
(JP,C = 16 Hz) at δ = 178.5 ppm due to the NCN carbene
carbon, which indicates that the PMe3 ligand in complex 1
exerts a stronger trans influence than other phosphanes
(JP,C = 83–94 Hz) in the above-mentioned phosphane–
NHC–Pd complexes.
Scheme 3.
Scheme 2.
To confirm the formation of bis(NHC)–Pd0 complexes,
complexes 1 and 2 were treated with one additional equiva-
lent of the NHC agent (Scheme 2), and complexes 3 and 4
were obtained as yellow (64%) and orange (46%) crystals,
respectively. Consistent with our expectation, the NMR
(1H, 13C{1H}, and 31P{1H} NMR) spectroscopic data of
complexes 3 and 4 agree well with those previously re-
ported.[18]
We also examined the reactivity of bis(phosphane)–di-
ethyl–PdII complexes toward NHC ligands, as shown in
Scheme 3. In these reactions, one PMe3 ligand was replaced
with the NHC ligand, and NHC–diethyl–PdII complexes
Figure 1. ORTEP drawing of 6. Selected bond lengths [Å] and
trans-[Pd(PMe3)Et2(IPr)] (5) and trans-[Pd(PMe3)Et2(SIPr)]
(6) were obtained. trans- or cis-diethyl–PdII complexes that
possess tertiary phosphanes are known to decompose by β-
H elimination or reductive elimination.[21] The starting ma-
terial, trans-[PdEt2(PMe3)2][16b] is thermally unstable in so-
angles [°]: Pd1–C1 2.027(2), Pd1–C31 2.135(2), Pd1–C33 2.144(2),
Pd1–P1 2.2533(7), N1–C1 1.345(2), N(1)–C4 1.446(2), N1–C2
1.478(3), N2–C1 1.355(2), N2–C16 1.439(2), N2–C3 1.475(3); C1–
Pd1–C31 90.44(8), C1–Pd1–C33 88.60(8), C31–Pd1–C33 179.01(9),
C1–Pd1–P1 176.22(6), C31–Pd1–P1 90.25(6), C33–Pd1–P1
90.73(7), N1–C1–N2 106.3(2), C1–N1–C2 112.8(2), C1–N2–C3
lid and in solution at room temperature. However, in this 112.5(2).
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Y.-J. Kim et al.
FULL PAPER
Table 1. Crystal data and structure refinements for complexes 6–8, 10, and 11–15.
6
7
8
10
11·Et2O
Formula
Mr
C34H57N2PPd
631.19
C31H47Cl2N2P1Pd C31H49Cl2N2PPd
C55H78Cl2N4Pd
972.51
C58H82Cl2N4OPd
1028.58
655.98
657.99
T [K]
296(2)
296(2)
296(2)
200(2)
200(2)
Crystal size [mm3]
0.42ϫ0.38ϫ0.32
orthorhombic
Pbca
0.40ϫ0.30ϫ0.20
monoclinic
P21/n
0.52ϫ0.44ϫ0.36
monoclinic
P21/n
0.32ϫ0.25ϫ0.22
triclinic
0.25ϫ0.20ϫ0.13
orthorhombic
P212121
Crystal system
Space group
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
18.9961(3)
15.7425(2)
23.3332(4)
11.3708(1)
20.5091(2)
14.3001(2)
11.3636(5)
20.7074(9)
14.2241(6)
12.3144(8)
12.3951(7)
17.2209(10)
82.391(1)
87.649(2)
88.439(1)
2602.6(3)
2
12.9601(7)
20.4366(11)
21.3284(11)
β [°]
91.596(1)
91.459(2)
γ [°]
V [Å3]
6977.7(2)
8
1.202
0.600
2688
3333.56(6)
4
1.307
0.786
1368
3346.0(3)
4
1.306
0.783
1376
5649.0(5)
4
1.209
0.463
2184
Z
dcalcd. [gcm–3]
1.241
0.498
1032
μ [mm–1]
F(000)
Tmin
Tmax
0.7866
0.8311
116702
8699
0.7439
0.8586
51129
8278
0.6862
0.7657
45489
8142
0.8570
0.8984
19369
12619
5657
0.8929
0.9422
42254
13825
7956
Measured reflections
Unique reflections
R(int) reflections [IϾ2σ(I)] 6937
6685
6807
Parameters refined
Max. Δρ [eÅ–3]
Min. Δρ [eÅ–3]
GoF on F2
343
334
335
559
2.022
595
0.421
–0.326
1.100
0.0318
0.0686
0.0468
0.0793
0.309
–0.268
1.012
0.0269
0.0632
0.0392
0.0694
0.399
–0.337
1.031
0.0251
0.0622
0.0344
0.0677
1.099
–1.866
0.985
0.0575
0.0804
0.1372
0.1099
–1.185
0.887
0.0678
0.1155
0.1568
0.1509
[a]
R1
wR2
[b]
R (all data)
[a]
wR2 (all data)
12
13
14·C6H14
15
Formula
Mr
C36H52BrN2PPd
631.19
C32H49Cl2N2PPd
670.00
C72H112Br2N4P2Pd2S2 C54H52P4Pd
1556.36
931.24
T [K]
296(2)
296(2)
200(2)
200(2)
Crystal size [mm3]
0.26ϫ0.16ϫ0.10
monoclinic
P21/c
0.20ϫ0.16ϫ0.12
monoclinic
P21/c
0.17ϫ0.15ϫ0.04
triclinic
0.21ϫ0.18ϫ0.17
monoclinic
C2/c
Crystal system
Space group
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
12.9802(7)
15.5482(8)
17.9521(8)
13.8695(5)
23.4601(8)
20.8522(7)
10.543(1)
10.875(1)
17.851(2)
84.535(3)
85.478(3)
69.365(3)
1904.4(4)
1
18.2610(7)
13.2898(6)
20.0819(8)
β [°]
100.257(2)
92.265(2)
109.419(1)
γ [°]
V [Å3]
3565.2(3)
4
1.360
1.712
1512
6779.6(4)
8
1.313
0.775
2800
4596.3(3)
4
1.346
0.579
1928
Z
dcalcd. [gcm–3]
1.357
1.660
808
μ [mm–1]
F(000)
Tmin
Tmax
0.6645
0.8475
32723
8510
0.8605
0.9128
100790
16421
7055
0.7656
0.9366
14201
9236
3505
0.8881
0.9080
16453
5582
Measured reflections
Unique reflections
R(int) reflections [IϾ2σ(I)] 5050
3736
Parameters refined
Max. Δρ [eÅ–3]
Min. Δρ [eÅ–3]
GoF on F2
371
685
373
0.653
267
0.409
–0.399
0.958
0.0407
0.0625
0.0998
0.0752
0.373
–0.612
0.943
0.0517
0.0877
0.1749
0.1187
0.623
–0.699
0.955
0.0405
0.0729
0.0811
0.0890
–1.141
0.761
0.0581
0.0789
0.1693
0.1106
[a]
R1
wR2
[b]
R (all data)
[a]
wR2 (all data)
[a] R1 = Σ||Fo| – |F||/Σ|Fo|. [b] wR2 = Σ[w(F2o – Fc2)2]/Σ[w(F2o)2]½.
oriented perpendicular to the square plane that contains the found for other Pd–dialkyl complexes: 2.089(3) and
NHC ligand. The Pd–C bond lengths [2.135(2) and 2.090(3) Å in cis-[PdMe2(PPh2Me)];[22] 2.026 and 2.029 Å
2.144(2) Å] in complex 6 are somewhat longer than those in [PdMe2(Me2NCH2CH2NMe2)];[23] and 2.087(4) Å in
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Heteroleptic and Homoleptic Pd0–NHC Complexes
[PdMe2(Me2PCH2CH2PMe2)].[23] However, we could not
provide a clear explanation due to the limited structural
data available for trans-dialkyl–Pd complexes.
Reactivity of PMe3–NHC–Pd0 Complexes toward
Halogenated Solvents (Dichloromethane and Chloroform)
Attempts to recrystallize PMe3–NHC–Pd0 complexes 1
and 2 from halogenated solvents such as CH2Cl2 or CHCl3
failed because these complexes reacted with those solvents
(Scheme 4).
Scheme 4.
When complex 1 or 2 was dissolved in CH2Cl2 at room
temperature, white solids of [(Me3P)ClPd(CH2Cl)(IPr)] (7,
84%) or [(Me3P)ClPd(CH2Cl)(SIPr)] (8, 69%) were ob-
tained. These reactions also occurred in the presence of
either a stoichiometric or an excess amount of CH2Cl2 in
organic solvents. However, in spite of several attempts in
1
CHCl3, pure products could not be obtained because they Figure 2. Variable-temperature H NMR (600 MHz) spectroscopic
signals for the alkyl substituents of 7 from –40 to 20 °C in CDCl3.
were thermally unstable and inseparable mixtures. Com-
plexes 7 and 8 were characterized by 1H, 13C{1H}, and
31P{1H} NMR spectroscopy, elemental analyses, as well as
X-ray diffraction.
At around 0 °C, the methine signals becme broad. At
The methylene signals (Pd–CH2Cl) in the 1H NMR spec- 20 °C, a complete broadening of the methine signals occurs,
tra of 7 and 8 in CDCl3 at –40 °C appeared at δ = 3.08 and and the signals can be hardly identified. This type of peak
3.14 ppm, respectively, as a doublet (JP,H = 7.3 Hz), which broadening is also observed for the methyl protons of the
are comparable to the typical CH2X signals; for example, iPr and iPrЈ groups. Two well-separated doublets (δ = 1.36
those in trans-[PdCl(CH2Cl){P(tBu)2H}2][24] (δ = 3.73 ppm and 1.47 ppm) due to the methyl protons colalesce at 0 °C.
1
in C6D6 at 298 K) and trans-[PdCl(CH2Cl)(PPh3)2][25] (δ = In the coalescence temperature range, H NMR spectra of
3.92 ppm in C6D6 at 298 K). A singlet in the 31P{1H} NMR 7 were carefully taken as a function of temperature at 2 °C
spectra of complexes 7 and 8 support the presence of one intervals to find out the exact coalescence temperature (Tc).
PMe3 ligand coordinated to the Pd center. The doublets As a result, we could determine the coalescence tempera-
(JP,C = 158 and 147 Hz) at 183.6 (7) and 209.8 ppm (8) due tures 22 °C for the methine (CH) and –1 °C for the methyl
to the carbene carbon (NCN) in the 13C NMR spectra indi- signals of CH(CH3)2 of the 2,6-diisopropylphenyl groups,
cate the trans orientation of the carbene (NHC) and the respectively. At these temperatures, the free energies for ac-
PMe3 ligands.
tivation barriers were calculated from the Eyring equation
As shown in Figure 2, the methine signals CH(CH3)2 of [ΔG‡ = 19.12Tc(10.32 + logTc – logkc); kc = πΔν/√2; Δν =
the 2,6-diisopropylphenyl groups on the imidazoline ring of the chemical shift difference in hertz between two separate
7 exhibit temperature dependence in the range of –40 to signals].[26] The ΔG‡ value for the rotation of the methine
20 °C in CDCl3. At –40 °C, the methine signals in the iPr2 groups in CDCl3 is (13.5Ϯ0.10) kJmol–1 and that of the
and iPrЈ2 groups split into two septets at δ = 2.78 and methyl groups is (13.2Ϯ0.10) kJmol–1.
3.26 ppm. This phenomenon arises because the iPr groups
The organic substituents of complex 7 were characterized
do not interchange by the phenyl-ring rotation at this tem- by heteronuclear multiple quantum coherence (HMQC),
perature.
COSY(H–H), NOESY, and distortionless enhancement by
Eur. J. Inorg. Chem. 2011, 1750–1761
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Y.-J. Kim et al.
FULL PAPER
polarization rransfer (DEPT) NMR spectroscopic tech-
niques.
X-ray crystal structures (see Figures 3 and 4) confirm the
formation of complexes 7 and 8. Because these complexes
are isostructural, only the structure of complex 7 is de-
scribed in detail. In Figure 3 (complex 7), the coordination
sphere Pd1 can be described as a square plane, with the Cl
and CH2Cl ligands being trans to each other. The imid-
azoline ring is significantly twisted from the two 2,6-bis(iso-
propyl)phenyl rings with the dihedral angle of 73.54(6) or
78.16(7)°, probably because of the two bulky isopropyl sub-
stituents on the phenyl rings. The Pd–C (Pd–CH2Cl) bond
lengths [Pd1–C31: 2.021(2) Å in 7; 2.018(2) Å in 8] are close
to that [2.031(2) Å] of trans-[PdCl(CH2Cl)(PPh3)2],[25]
which was prepared from [PdCl2(cod)] (cod = 1,2-cyclooc-
tadiene), excess amounts of diazomethane or bis(chlorome-
thyl)mercury, followed by the ligand replacement with
PPh3. Although many cases of the thermal or photoinduced
oxidative addition of dihalomethanes to low-valent Pt,[27–30]
Pd,[24,31–33] Rh,[34–43] Ru,[44] Ir,[45–47] Co,[48] and Au[49] com-
plexes were reported, only a few cases have been known to
date for zero-valent Pd complexes, including [Pd(PtBu2-
H)3],[24] [Pd(PCy3)2(dba)] (dba = dibenzylideneacetone; Cy
= cyclohexyl),[31] and [PdN(CH2CH2PPh2)3].[28] Further-
more, there have been no reports for the structural charac-
terization of the oxidative addition complex Cl–PdCH2Cl
by X-ray diffraction. Complexes 7 and 8 provide the first
examples of oxidative addition of dichloromethane to Pd0–
NHC complexes.
Figure 4. ORTEP drawing of 8. Selected bond lengths [Å] and
angles [°]: Pd1–C31 2.018(2), Pd1–C1 2.059(1), Pd1–P1 2.3112(4),
Pd1–Cl1 2.3828(5), Cl2–C31 1.822(2), N1–C1 1.341(2), N1–C2
1.475(2), N1–C4 1.441(2), N2–C1 1.346(2), N2–C16 1.441(2), N2–
C3 1.477(2), C2–C3 1.495(3); C31–Pd1–C1 91.38(7), C31–Pd1–P1
89.96(6), C1–Pd1–P1 177.78(4), C31–Pd1–Cl1 177.86(6), Cl2–C31–
Pd1 113.1(1).
1H NMR spectra of 9 and 10 appear at δ = 3.05 and
3.07 ppm as a singlet, respectively. In sharp contrast, com-
plex 3 reacted with chloroform to produce dichloro–NHC–
PdII species [Pd(IPr)2Cl2] (11) in 79% yield. In this reaction,
chloroform served as a chlorine source. Although we have
no concrete evidence about the side products, we speculate
that the product may have been formed by oxidative ad-
dition of CHCl3, followed by the C–Cl cleavage at some
stage. Molecular structures of 10 (Figure 5) and 11 (Fig-
ure 6) were determined by X-ray diffraction. The coordina-
tion sphere of 10 can be described as square planar, and
the Cl and CH2Cl ligands are trans to each other.
Figure 3. ORTEP drawing of 7. Selected bond lengths [Å] and
angles [°]: Pd1–C31 2.021(2), Pd1–C1 2.055(2), Pd1–P1 2.3031(5),
Pd1–Cl1 2.3831(5), Cl2–C31 1.817(2), N1–C1 1.362(2), N1–C2
1.382(2), N1–C4 1.448(2), N2–C1 1.360(2), N2–C3 1.383(2), N2–
C16 1.449(2); C31–Pd1–C1 91.23(7), C31–Pd1–P1 90.27(6), C1–
Pd1–P1 176.97(5), C31–Pd1–Cl1 179.08(7), Cl2–C31–Pd1
113.61(12).
Scheme 5.
The five-membered rings in the NHC ligands are signifi-
The bis(NHC)–Pd0 complexes (NHC = IPr, 3; SIPr, 4) cantly twisted from the molecular plane. The coordination
also react with halogenated solvents (Scheme 5). In the case sphere of 11 is also square-planar with a set of trans-
of CH2Cl2, rapid oxidative addition occurs to produce the chlorido ligands and a set of trans-NHC ligands.
corresponding addition products, [ClPd(CH2Cl)(IPr)2] (9)
Various organic halides readily undergo oxidative ad-
and [ClPd(CH2Cl)(SIPr)2] (10), the formation of which can dition to electronically unsaturated Pd0 complexes.[5] In this
readily be monitored by the color change from the initial study, small organic halogenated molecules such as dichlo-
orange to colorless. The methylene signals (CH2Cl) in the romethane or chloroform oxidatively add to the phos-
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Eur. J. Inorg. Chem. 2011, 1750–1761

Heteroleptic and Homoleptic Pd0–NHC Complexes
Under mild conditions, p-nitroiodobenzene readily un-
dergoes oxidative addition to the bis(NHC)–Pd0 complex
stabilized by maleic anhydride.[11] In addition, Caddick and
Cloke et al.[12] independently reported that the reaction of
the bis(NHC)–Pd0 complex (4) with aryl chloride does not
produce a four-coordinate complex at room temperature or
even under heating conditions, but an arylimidazolium
compound, a reductive-elimination product, is produced. In
contrast to the above-mentioned results, our bis(NHC)–Pd0
complexes 3 and 4 smoothly underwent oxidative addition
with organic halogenated solvents at room temperature
(Scheme 5). In our case, a small steric requirement of or-
ganic reagents (dichloromethane and chloroform) seemed
to be an important factor responsible for the observed oxi-
dative addition reactivity. The molecular structures of 10
and 11 clearly demonstrate the steric congestion around the
Pd metal, which may hinder organic halides from under-
going oxidative addition to NHC–Pd0 compounds.
Reactivity of PMe3–NHC–Pd0 Complexes toward Organic
Halides and a Chelated Phosphane
Figure 5. ORTEP drawing of 10. Selected bond lengths [Å] and
angles [°]: Pd1–C28 2.056(5), Pd1–C1 2.080(6), Pd1–C55 2.115(5),
Pd1–Cl1 2.393(2), Cl2–C55 1.554(6); C28–Pd1–C1 178.3(2), C28–
Pd1–C55 94.2(2), C1–Pd1–C55 86.6(2), C28–Pd1–Cl1 82.6(1), N2–
C1–N1 106.1(5), N3–C28–N4 106.2(4).
We further examined the reactivity of the PMe3–NHC–
Pd0 complex toward other organic halides, including bro-
mobenzene, trans-1,2-dichloroethylene, and 5,5Ј-dibromo-
2,2Ј-bithiophene (Scheme 6 and Scheme 7). Reactions of 2
with excess amounts of bromobenzene and trans-1,2-dichlo-
roethylene at room temperature proceeded to give the ex-
pected oxidative addition products, [(Me3P)Pd(C6H5)-
Br(SIPr)] (12, 65% yield) or [(Me3P)Pd(CH=CHCl)Cl-
(SIPr)] (13, 39% yield), respectively, which were charac-
terized by spectroscopy and elemental analyses. Unfortu-
nately, the similar reaction with cis-ClCH=CHCl could not
give pure products on account of its thermal instability in
solution. Grusin and co-workers[50] previously prepared a
similar Pd–(aryl) complex from IPr·HCl and [(Ph3P)2-
Pd2Ph2(μ-OH)2].
Figure 6. ORTEP drawing of 11·Et2O. Selected bond lengths [Å]
and angles [°]: Pd1–C52 2.040(4), Pd1–C25 2.043(4), Pd1–Cl1
2.230(1), Pd1–Cl2 2.303(1), N1–C25 1.363(6), N2–C25 1.358(5),
N3–C52 1.361(5), N4–C52 1.363(5); C52–Pd1–C25 179.1(2), C52–
Pd1–Cl1 87.9(1), C25–Pd1–Cl1 91.2(1), C52–Pd1–Cl2 92.1(1),
C25–Pd1–Cl2 88.8(1), Cl1–Pd1–Cl2 178.67(5).
Scheme 6.
phane–NHC–Pd0 and bis(NHC)–Pd0 complexes. To the
best of our knowledge, our results provide the first case
for the oxidative addition of small alkyl halides to NHC-
stabilized Pd0 complexes.
Scheme 7.
Eur. J. Inorg. Chem. 2011, 1750–1761
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Y.-J. Kim et al.
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A molecular structure of complexes 12 is presented in
Figure 7. The coordination sphere Pd1 can be described as
a square plane, and the Br and phenyl ligands are mutually
trans. The molecular plane (P1, Br1, C1, C28, Pd1) is
roughly planar with an average atomic displacement of
0.065(1) Å, and the phenyl ligands are essentially perpen-
dicular to this plane with the dihedral angle of 84.78(7)°.
Figure 7. ORTEP drawing of 12. Selected bond lengths [Å] and
angles [°]: Pd1–C28 2.022(3), Pd1–C1 2.074(3), Pd1–P1 2.3185(8),
Pd1–Br1 2.5178(4), N1–C1 1.351(3), N1–C16 1.445(3), N1–C2
1.480(3), N2–C1 1.342(3), N2–C4 1.433(3), N2–C3 1.473(3), C2–
C3 1.488(4); C28–Pd1–C1 97.65(10), C28–Pd1–P1 82.95(8); C1–
Pd1–P1 178.06(8), C28–Pd1–Br1 170.36(8).
The molecular structure of 13 in Figure 8 clearly reveals
that trans-ClCH=CHCl undergoes C–Cl trans addition to
the PMe3–NHC–Pd0 complex. The oxidative addition of
C–Cl bond of trans-1,2-dichloroethylene above and below
the molecular plane of the PMe3–NHC–Pd0 compound
might have led to the formation of enantiomers (13A and
13B). The ORTEP drawing of 13 exhibits an enantiomeric
pair. The enantiomers 13A (Figure 8, A) and 13B (Figure 8,
B) have practically the same bond lengths and angles, and
have the NHC ligand trans to the PMe3 ligand. The molecu-
lar plane in both enantiomers, defined by two C, one P, one
Cl, and one Pd atoms, is essentially planar [the average
atomic displacement is 0.0151(2) or 0.010(2) Å]. The car-
Figure 8. (A) ORTEP drawing of enantiomer A of complex 13. (B)
ORTEP drawing of enantiomer B of complex 13. Selected bond
lengths [Å] and angles [°]: Pd1–C28 2.014(6), Pd1–C1 2.041(4),
Pd1–P1 2.296(2), Pd1–Cl1 2.373(1), Pd2–C60 2.077(5), Pd2–C33
2.047(4), Pd2–P2 2.292(1), Pd2–Cl3 2.353(1), N1–C1 1.351(5), N1–
C2 1.468(5), N2–C1 1.342(5), N2–C3 1.451(5), N4–C33 1.349(5),
N4–C48 1.441(5), N4–C35 1.471(5), N3–C33 1.353(5), N3–C36
1.444(5), N3–C34 1.462(5); C1–Pd1–P1 177.2(1), C28–Pd1–Cl1
176.5(2), C33–Pd2–P2 179.0(1), C60–Pd2–Cl3 176.7(2), N1–C1–
N2 106.5(4), N4–C33–N3 106.3(4).
bene carbon atom (NCN) of the imidazoline ring appears crystal quality for X-ray diffraction analysis, we obtained
as a doublet (JP,C = 194 Hz) at δ = 201.9 ppm in the 13C very thin plate-shaped crystals. As a result, the number of
NMR spectra.
reflections with IϾ2σ(I) is small, and therefore the ratio of
Scheme 7 shows the oxidative addition of the C–Br bond the number of reflections to the number of parameters is
of 5,5Ј-dibromo-2,2Ј-bithiophene to two Pd centers of com- rather low (3505:373 in Table 1). However, the obtained
plex 2 to give a dinuclear PdII complex (14) with a bridging molecular structure of 14 shows a definite atom–atom con-
bithiophene group. The two singlets assignable to the CH nectivity to clearly confirm its 3D structure (Figure 9).
protons on the bridging thiophene rings spectra are ob-
We also attempted the ligand replacement of PMe3–
1
served at δ = 5.22 and 6.38 ppm in the H NMR spectra of NHC–Pd0 complex 1 with a chelating phosphane [dppp =
complex 14. In particular, the methine signals CH(CH3)2 of 1,3-bis(diphenylphosphanyl)propane],
as
shown
in
the 2,6-diisopropylphenyl groups appear as a normal septet Scheme 8.
(J = 6.4 Hz) at δ = 3.74 ppm and a broad signal at δ =
This reaction proceeds smoothly to produce the
3.42 ppm, strongly indicating the free rotation of one imid- bis(dppp)–Pd0 compound, [Pd(dppp)2], in 69% yield, which
azoline moiety. In spite of several attempts to improve the was characterized by elemental analysis, NMR spec-
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Eur. J. Inorg. Chem. 2011, 1750–1761

Heteroleptic and Homoleptic Pd0–NHC Complexes
PMe3 and NHC ligands compared to the dppp ligand,
which is expected to have chelating effects.
Conclusion
In summary, novel heteroleptic PMe3–NHC–Pd0 com-
plexes were prepared from a diethyl PdII compound, and
then homoleptic bis(NHC)–Pd0 complexes were prepared
by treating PMe3–NHC–Pd0 complexes with one additional
equivalent of NHC. Oxidative additions of various organic
halides to these NHC complexes were investigated. In par-
ticular, we observed the facile oxidative addition of small
alkyl halides such as dichloromethane and chloroform to
these NHC–Pd0 complexes. Complex 6, [(Me3P)ClPd-
(CH=CHCl)(SIPr)], exhibits enantiomerism.
Figure 9. ORTEP drawing of complex 14·C6H14. Unlabeled atoms
are related to labeled ones by inversion. The co-crystallized hexane
molecule is omitted for clarity. Selected bond lengths [Å] and angles
[°]: Pd1–C31 2.017(5), Pd1–C1 2.077(6), Pd1–P1 2.299(2), Pd1–Br1
2.4983(8), N1–C11.341(7), N1–C2 1.496(7), N2–C1 1.330(7), N2–
C3 1.474(8); C31–Pd1–C1 95.2(2), C31–Pd1–P1 87.4(2), C1–Pd1–
P1 176.5(2), C31–Pd1–Br1 172.1(2), C1–Pd1–Br1 90.8(1), N2–C1–
N1108.1(6).
Experimental Section
General: All manipulations of air-sensitive complexes were per-
formed under N2 or Ar by standard Schlenk-line techniques. Sol-
vents were distilled from Na–benzophenone. The analytical
laboratories at Kangnung-Wonju National University carried out
elemental analyses with a CE instruments EA1110. IR spectra were
recorded with a Perkin–Elmer BX spectrophotometer. NMR (1H,
13C{1H}, and 31P{1H}) spectra were obtained with a JEOL Lamda
300 and ECA 600 MHz spectrometer. Chemical shifts were refer-
enced to internal Me4Si or to external 85% H3PO4. Some of the
X-ray analysis was carried out at the Jeonju Center at the Basic
Science Institute of Korea. trans-[PdEt2(PMe3)2] was prepared by
the literature method.[16b] IPr [1,3-bis(2,6-diisopropylphenyl)imid-
azol-2-ylidene] and SIPr [1,3-bis(2,6-diisopropylphenyl)-4,5-dihy-
droimidazol-2-ylidene] were prepared by the literature method[51]
or purchased from Strem Chemical.
Scheme 8.
troscopy, and X-ray diffraction. The molecular structure of
15 (Figure 10) shows an extremely distorted tetrahedral
structure. This reaction may reflect the higher lability of the
Preparations
[(Me3P)Pd(IPr)] (1) and [(Me3P)Pd(SIPr)] (2): Styrene (0.604 g,
5.81 mmol) and THF (3 mL) were added sequentially to a Schlenk
flask that contained trans-[PdEt2(PMe3)2] (0.736 g, 2.32 mmol) at
0 °C. The mixture was heated at 55 °C for 1 h to give a yellow
solution. At room temperature, IPr (0.885 g, 2.28 mmol) was added
to the mixture, and then the initial colorless solution turned to an
orange solution. After stirring the reaction mixture for 3 h, the sol-
vent was removed completely under vacuum, and then the resulting
oily residue was solidified with hexane. The solids were filtered and
washed with hexane (2 mLϫ3) to give pale yellow solids of 1
1
(0.852 g, 65%). H NMR (600 MHz, C6D6, 10 °C): δ = 0.68 [br., 9
H, P(CH3)3], 1.12 [d, J = 6.8 Hz, 12 H, CH(CH3)2], 1.46 [br., 12
H, CH(CH3)2], 3.21 [br., 4 H, CH(CH3)2], 6.63 (br., 2 H, CH),
6.90–6.97 (m, 2 H, Ar–H), 7.05–7.10 (m, 2 H, Ar–H), 7.14–7.19
(m, 2 H, Ar–H), 7.22–7.29 (m, 2 H, Ar–H) ppm. 13C{1H} NMR
(151 MHz, [D6]acetone, –40 °C): δ = 17.9 [d, JP,C = 29 Hz,
P(CH3)3], 26.6, 26.9, 29.9, 30.0 [s, CH(CH3)2], 69.5 [s, CH(CH3)2],
107.6 (d, JP,C = 6.9 Hz, NCH=), 127.5, 128.5, 133.8, 139.7, 148.1,
152.4 (s, Ar–C), 178.5 (d, JP,C = 16 Hz, NCN) ppm. 31P{1H} NMR
(243 MHz, C6D6, 10 °C): δ = –28.6 (s) ppm.
Complex 2 (84%) was prepared in a similar way. 1H NMR
(600 MHz, C6D6, 10 °C): δ = 0.67 [d, J = 4.1 Hz, 9 H, P(CH3)3],
1.25 [d, J = 6.8 Hz, 12 H, CH(CH3)2], 1.60 [br., 12 H, CH(CH3)2],
3.42 [br., 8 H, CH2, CH(CH3)2], 6.96–7.22 (m, 6 H, aromatic) ppm.
13C{1H} NMR (151 MHz, C6D6, 10 °C): δ = 19.2 [d, JP,C = 14 Hz,
Figure 10. ORTEP drawing of 15. Selected bond lengths [Å] and
angles [°]: Pd1–P2 2.3239(7), Pd1–P1 2.3269(7); P2–Pd1–P2#1
121.62(4), P2–Pd1–P1#1 97.74(3).
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P(CH3)3], 24.9, 28.6 [s, CH(CH3)2], 53.1 [s, CH(CH3)2], 123.8, 146.6 (s, Ar–C), 220.8 (d, JP,C = 146 Hz, NCN) ppm. 31P{1H}
125.4, 138.4, 147.1 (s, Ar–C) . The 13C signal due to the NCN
for 2 could not be assigned due to the broadness. 31P{1H} NMR
(243 MHz, C6D6 at 10 °C): δ = –28.8 (s) ppm.
NMR (243 MHz, [D6]acetone, –40 °C): δ = –12.3 (s) ppm.
Reactivity of [(Me3P)Pd(IPr)], [(Me3P)Pd(SIPr)], [Pd(IPr)2], and
[Pd(SIPr)2] toward Organic Halides (Dichloromethane, Chloroform,
Bromobenzene, trans-1,2-Dichloroethylene, 5,5Ј-Dibromo-2,2Ј-bi-
thiophene) and dppp
[Pd(IRr)2] (3) and [Pd(SIPr)2] (4): At room temperature, a solution
of IPr (0.417 g, 1.05 mmol) in toluene (7 mL) was added to a solu-
tion of [(Me3P)Pd(IPr)] (0.547 g, 0.96 mmol) in toluene (5 mL).
The initial pale yellow solution slowly turned into an orange solu-
tion. After stirring for 3 h at room temperature, the solvent was
completely removed under vacuum, and then the resulting oily resi-
due was solidified with hexane. The solids were filtered and washed
with hexane (2 mLϫ3) to give yellow solids. Recrystallization from
toluene gave yellow crystals of 3 (0.541 g, 64%). C54H72N4Pd
(883.60): calcd. C 73.40, H 8.21, N 6.34; found C 73.52, H 8.73, N
1
6.24. H NMR (600 MHz, C6D6, 23 °C): δ = 1.11 [d, J = 6.0 Hz,
24 H, CH(CH3)3], 1.20 [d, J = 6.0 Hz, 24 H, CH(CH3)2], 2.88 [sept,
J = 6.0 Hz, 8 H, CH(CH3)2], 6.27 (s, 4 H, CH), 7.09 (d, J = 9.0 Hz,
8 H, Ar–H), 7.29 (t, J = 9.0 Hz, 4 H, Ar–H) ppm. 13C{1H} NMR
(151 MHz, C6D6, 23 °C): δ = 24.0, 25.1, 28.7 [s, CH(CH3)2], 121.2,
123.4, 128.6, 139.1, 146.0 (s, Ar–C), 198.8 (s, NCN) ppm.
[(Me3P)ClPd(CH2Cl)(IPr)] (7), [(Me3P)ClPd(CH2Cl)(SIPr)] (8),
[ClPd(CH2Cl)(IPr)2] (9), and [ClPd(CH2Cl)(SIPr)2] (10): Complex
1 (0.460 g, 0.81 mmol) was dissolved in CH2Cl2 (3 mL). After stir-
ring for 3 h at room temperature, the solvent was completely re-
moved under vacuum, and then the resulting oily residue was solid-
ified with hexane. The solids were filtered and dried to give gray
solids of crude products. The final products were recrystallized
from a diethyl ether/hexane mixture to give final product 7 (0.443 g,
84%). C31H47Cl2N2PPd (656.02): calcd. C 56.76, H 7.22, N 4.27;
found C 56.72, H 7.83, N 4.12. 1H NMR (600 MHz, CDCl3,
–40 °C): δ = 1.12 [d, J = 6.9 Hz, 6 H, CH(CH3c)2], 1.15 [d, J =
6.9 Hz, 6 H, CH(CH3a)2], 1.20 [d, J = 9.7 Hz, 9 H, P(CH3)3], 1.36
[d, J = 6.9 Hz, 6 H, CH(CH3b)2], 1.47 [d, J = 6.4 Hz, 6 H,
CH(CH3d)2], 2.79 [sept, J = 6.8 Hz, 2 H, CH(CH3)2e], 3.08 (d, J =
7.3 Hz, 2 H, CH2), 3.26 [sept, J = 6.8 Hz, 2 H, CH(CH3)2f], 7.15
(s, 2 H, CH=), 7.30 (d, J = 7.8 Hz, 2 H, Ar-H), 7.36 (d, J = 7.8 Hz,
2 H, Ar–H), 7.48 (t, J = 7.8 Hz, 2 H, Ar–H) ppm. 13C{1H} NMR
(151 MHz, CDCl3, –40 °C): δ = 12.9 [d, JP,C = 28 Hz, P(CH3)3],
23.0 [s, CH(CbH3)2], 23.8 [s, CH(CdH3)2], 26.4 [s, CH(Cc+aH3)2],
28.8 [s, CfH(CH3c)2], 28.9 [s, CeH(CH3c)2], 29.3 (s, CH2), 123.7 (s,
N–CH), 123.8, 123.9 (s, N–CH=), 124.5, 129.7, 135.5, 144.5, 146.9
(s, Ar–C), 183.6 (d, JP,C = 158 Hz, NCN) ppm. 31P{1H} NMR
(243 MHz in CDCl3, –40 °C): δ = –12.7 (s) ppm.
Complex 4 (46%) was prepared analogously. The analytical data
for 4 are identical to those in literature.[18]
Complexes 3 and 4 were previously prepared from [Pd{P(o-
tolyl)3}2] with IPr or SIPr by the groups of Caddick, Cloke,[18] and
Herrmann.[19]
trans-[Pd(PMe3)Et2(IPr)] (5) and trans-[Pd(PMe3)Et2(SIPr)] (6):
IPr (0.434 g, 1.12 mmol) solution dissolved in THF (4 mL) was
added to a Schlenk flask that contained trans-[PdEt2(PMe3)2]
(0.354 g, 1.12 mmol) at 0 °C. After stirring the reaction mixture
overnight at room temperature, the solvent was completely re-
moved under vacuum. A dithyl ether/n-hexane mixture (3:1) was
added to the resulting oily residue, and then it was stored in the
freezer to give crude solids. The solids were filtered, washed with
hexane (2 mLϫ2), and recrystallized from dithyl ether to give
white crystals of 5 (171 g, 24%). C34H55N2PPd (629.21): calcd. C
64.90, H 8.81, N 4.45; found C 64.83, H 9.32, N 4.38. 1H NMR
(600 MHz, [D6]acetone, –40 °C): δ = –0.11 (dq, J = 7.3 Hz, 4 H,
Pd–CH2), 0.40 (dt, J = 2.3, 7.8 Hz, 6 H, Pd–CH2CH3), 1.07 [d, J
= 7.8 Hz, 9 H, P(CH3)3], 1.11 [d, J = 6.8 Hz, 12 H, CH(CH3)2],
1.32 [d, J = 6.9 Hz, 12 H, CH(CH3)2], 3.31 [sept, J = 6.8 Hz, 4 H,
CH(CH3)2], 7.30 (d, J = 7.8 Hz, 4 H, Ar–H), 7.40 (t, J = 7.8 Hz,
2 H, Ar–H), 7.48 (s, 2 H, CH=) ppm. 13C{1H} NMR (151 MHz,
[D6]acetone, –40 °C): δ = 3.45 (d, JP,C = 10 Hz, Pd–CH2), 14.7 [d,
JP,C = 24 Hz, P(CH3)3], 17.4 (d, JP,C = 3.5 Hz, CH2CH3), 23.1 [s,
CH(CH3)2], 25.9 [s, CH(CH3)2], 29.7 [s, CH(CH3c)2], 122.9
Complex 8 (69%) was prepared analogously. C32H49Cl2N2PPd
(670.04): calcd. C 56.58, H 7.51, N 4.26; found C 56.54, H 8.19, N
4.06. 1H NMR (600 MHz, CDCl3, –40 °C): δ = 1.15 [d, J = 9.7 Hz,
9 H, P(CH3)3], 1.26 [d, J = 6.8 Hz, 6 H, CH(CH3c)2], 1.30 [d, J =
6.4 Hz, 6 H, CH(CH3a)2], 1.40 [d, J = 6.8 Hz, 6 H, CH(CH3b)2],
1.53 [d, J = 6.8 Hz, 6 H, CH(CH3d)2], 3.14 (d, J = 7.3 Hz, 2 H,
CH2), 3.16 [sept, J = 6.8 Hz, 2 H, CH(CH3)2e], 3.61 [sept, J =
6.8 Hz, 2 H, CH(CH3)2f], 3.95 (m, 2 H, NCH2g), 4.03 (m, 2 H,
NCH2h), 7.25 (dd, J = 1.4, 7.7 Hz, 2 H, Ar–H), 7.32 (dd, J = 1.4,
7.7 Hz, 2 H, Ar–H), 7.40 (t, J = 7.8 Hz, 2 H, Ar–H) ppm. 13C{1H}
NMR (151 MHz, CDCl3, –40 °C): δ = 12.5 [d, JP,C = 28 Hz,
P(CH3)3], 23.4 [s, CH(CbH3)2], 24.3 [s, CH(CdH3)2], 26.7 [s,
CH(CcH3)2], 26.8 [s, CH(CaH3)2], 28.4 [s, CfH(CH3c)2], 28.6 [s,
CeH(CH3c)2], 29.2 (s, CH2), 53.8 (s, N–CH2), 53.9 (s, N–CH2),
(NCH=), 124.3, 129.5, 137.9, 146.1 (s, Ar–C), 196.0 (d, JP,C
=
154 Hz, NCN) ppm. 31P{1H} NMR (243 MHz, [D6]acetone,
–40 °C): δ = –11.7 (s) ppm.
Complex
6 (33%) was prepared analogously. C34H57N2PPd
(631.22): calcd. C 64.69, H 9.10, N 4.44; found C 64.35, H 9.66, N
1
4.26. H NMR (600 MHz, [D6]acetone, –40 °C): δ = –0.03 (dq, J
= 7.3 Hz, 4 H, Pd–CH2), 0.35 (dt, J = 2.3, 7.3 Hz, 6 H, Pd–
CH2CH3), 1.04 [d, J = 7.3 Hz, 9 H, P(CH3)3], 1.23 [d, J = 6.8 Hz,
12 H, CH(CH3)2], 1.37 [d, J = 6.9 Hz, 12 H, CH(CH3)2], 3.59 [sept,
J = 6.9 Hz, 4 H, CH(CH3)2], 4.00 (s, 4 H, NCH2), 7.24 (d, J =
123.8, 124.6, 128.5, 135.5, 145.3, 147.7 (s, Ar–H), 209.8 (d, JP,C
=
147 Hz, NCN) ppm. 31P{1H} NMR (243 MHz, CDCl3, –40 °C): δ
= –12.7 (s) ppm.
7.3 Hz, 4 H, Ar–H), 7.30 (t, J = 7.5 Hz, 2 H, Ar–H) ppm. 13C{1H} Complex 3 (0.177 g, 0.20 mmol) was dissolved in CH2Cl2 (3 mL).
NMR (151 MHz, [D6]acetone, –40 °C): δ = 2.18 (d, JP,C = 10 Hz,
Pd–CH2), 14.0 [d, JP,C = 23 Hz, P(CH3)3], 16.8 (d, JP,C = 3.5 Hz,
Pd–CH2CH3), 23.4 [s, CH(CH3)2], 26.1 [s, CH(CH3)2], 28.4 [s,
CH(CH3c)2], 54.1 (d, JP,C = 5.2 Hz, NCH2), 124.0, 127.5, 137.8,
The initial orange mixture turned colorless. After stirring for 3 h
at room temperature, the solvent was completely removed under
vacuum, and then the resulting solids were crystallized from diethyl
ether to give final product 9 (0.183 g, 94%). C55H74Cl2N4Pd
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Heteroleptic and Homoleptic Pd0–NHC Complexes
(968.53): calcd. C 68.21, H 7.70, N 5.78; found C 68.57, H 7.99, N
5.32. 1H NMR (600 MHz, CD2Cl2, –40 °C): δ = 0.83 [d, J = 6.9 Hz,
12 H, CH(CH3)2], 0.89 [d, J = 7.3 Hz, 12 H, CH(CH3)2], 0.90 [d,
J = 7.3 Hz, 12 H, CH(CH3)2], 0.96 [d, J = 6.9 Hz, 12 H, CH-
[(Me3P)ClPd(CH=CHCl)(SIPr)] (13): trans-Dichloroethylene
(0.548 g, 5.7 mmol) and THF (4 mL) were sequentially added to a
Schlenk flask that contained 2 (0.325 g, 0.57 mmol) at room tem-
perature. After stirring for 3 h at room temperature, the solvent was
(CH3)2], 2.66 [sept, J = 6.8 Hz, 4 H, CH(CH3)2], 3.04 [sept, J = completely removed under vacuum, and then the resulting residue
6.8 Hz, 4 H, CH(CH3)2], 3.05 (s, 2 H, CH2), 6.83 (s, 4 H, CH=),
7.11, 7.13, 7.14, 7.15 (br., 8 H, Ar–H), 7.37 (t, J = 7.8 Hz, 4 H,
was extracted with an excess amount of n-hexane. The collected
filtrates were stored in the freezer to give white solids and then
Ar–H) ppm. 13C{1H} NMR (151 MHz, CD2Cl2, –40 °C): δ = 22.5 recrystallized from n-hexane to give white crystals of 13 (0.149 g,
[s, CH(CH3)2], 22.6 [s, CH(CH3)2], 26.2 [s, CH(CH3)2], 26.4 [s,
39%). C32H49Cl2N2PPd (670.04): calcd. C 57.36, H 7.37, N 4.18;
CH(CH3)2], 28.1 [s, CH(CH3)2], 28.1 [s, CH(CH3)2], 28.5 (s, CH2), found C 57.47, H 7.80, N 3.94. 1H NMR (600 MHz, CDCl3 at
123.4 (s, N–CH=), 123.5 (s, N–CH=), 124.1, 124.9, 124.2, 129.2,
129.3, 136.7, 145.3, 147.2 (s, Ar–C), 182.8 (s, NCN) ppm.
–40 °C): δ = 1.05 [d, J = 11 Hz, 9 H, P(CH3)3], 1.23 [d, J = 6.8 Hz,
12 H, CH(CH3)3], 1.48 [d, J = 6.4 Hz, 12 H, CH(CH3)3], 3.22 [sept,
J = 7.0 Hz, 2 H, CH(CH3)2], 3.65 [sept, J = 7.0 Hz, 2 H, CH-
(CH3)2], 3.81 (d, J = 14 Hz, Pd–CH=CH), 3.90 (s, 2 H, NCH2),
4.09 (s, 2 H, NCH2), 5.74 (dd, J = 5.5, 14 Hz, Pd–CH=CH), 7.25
(d, J = 7.8 Hz, 4 H, Ar–H), 7.37 (t, J = 7.8 Hz, 2 H, Ar-H) ppm.
Complex 4 analogously produced 10 (53%). C55H78Cl2N4Pd
(972.56): calcd. C 67.92, H 8.08, N 5.76; found C 67.83, H 8.47, N
5.73. 1H NMR (600 MHz, CDCl3, –30 °C): δ = 0.92 [d, J = 6.9 Hz,
12 H, CH(CH3)2], 0.97 [d, J = 6.4 Hz, 12 H, CH(CH3)2], 1.00 [d,
J = 6.9 Hz, 12 H, CH(CH3)2], 1.08 [d, J = 6.4 Hz, 12 H, CH-
(CH3)2], 3.07 (s, 2 H, CH2), 3.08 [sept, J = 6.4 Hz, 4 H, C-
H(CH3)2], 3.40 [sept, J = 6.9 Hz, 4 H, CH(CH3)2], 3.70 (m, 8 H,
NCH2), 7.06, 7.07, 7.08, 7.09 (br., 8 H, Ar–H), 7.27 (t, J = 7.3 Hz,
4 H, Ar–H) ppm. 13C{1H} NMR (151 MHz, CDCl3, –30 °C): δ =
23.4 [s, CH(CH3)2], 23.9 [s, CH(CH3)2], 26.8 [s, CH(CH3)2], 27.0 [s,
CH(CH3)2], 28.2 [s, CH(CH3)2], 28.6 [s, CH(CH3)2], 29.2 (s, CH2),
54.0 (s, N–CH2), 124.0, 124.9, 128.4, 137.4, 146.2, 148.2 (s, Ar–C),
209.0 (s, NCN) ppm.
13C{1H} NMR (151 MHz in CDCl3 at –40 °C): δ = 13.1 [d, JP,C
=
29 Hz, P(CH3)3], 23.2, 24.3, 26.7, 28.4 [s, CH(CH3)2], 54.0 (s,
NCH2), 104.1 (t, JP,C = 10 Hz, Pd–CH), 123.8, 128.4, 136.0, 145.9
(s, Ar–C), 207.5 (d, JP,C = 156 Hz, NCN) ppm. 31P{1H} NMR
(243 MHz in CDCl3 at –40 °C): δ = –12.6 (s) ppm.
[{(Me3P)(SIPr)BrPd}2(μ-C4H2S–C4H2S)] (14): 5,5Ј-Dibromo-2,2Ј-
bithiophene (0.066 g, 0.20 mmol) and THF (4 mL) were sequen-
tially added to
a Schlenk flask that contained 1 (0.239 g,
0.42 mmol) at room temperature. The initial insoluble material
slowly dissolved to give a yellow solution. After stirring for 3 h
at room temperature, the solvent was completely removed under
vacuum, and then the resulting oily residue was solidified with hex-
ane. The solids were filtered and washed with a diethyl ether (1 mL)
to give yellow solids and recrystallized from an excess amount of
diethyl ether to give yellow crystals of 14 (0.231 g, 77%).
C68H98Br2N4P2Pd2S2 (1470.26): calcd. C 55.55, H 6.72, N 3.81;
found C 55.94, H 7.27, N 3.57. 1H NMR (600 MHz, CDCl3,
25 °C): δ = 0.89 [d, J = 9.6 Hz, 18 H, P(CH3)3], 1.07 [d, J = 5.9 Hz,
12 H, CH(CH3)2], 1.16 [d, J = 6.9 Hz,12 H, CH(CH3)2], 1.26 [d, J
= 6.9 Hz,12 H, CH(CH3)2], 1.62 [d, J = 6.4 Hz, 12 H, CH(CH3)2],
3.42 [br., 4 H, CH(CH3)2], 3.74 [sept, J = 6.4 Hz, 4 H, CH-
(CH3)2], 3.90–3.96 (m, 8 H, NCH2), 5.38 (d, J = 3.2 Hz, 2 H,
SCH=), 6.42 (d, J = 3.2 Hz, 2 H, SCH=), 7.10 (d, J = 1.4 Hz, 2
H, Ar–H), 7.11 (d, J = 0.9 Hz, 2 H, Ar–H), 7.29 (d, J = 1.4 Hz, 2
H, Ar–H), 7.30 (d, J = 1.4 Hz, 2 H, Ar–H), 7.36 (d, J = 1.4 Hz, 2
H, Ar–H) ppm. 13C{1H} NMR (151 MHz, CDCl3, –20 °C): δ =
13.4 [d, JP,C = 29 Hz, P(CH3)3], 23.2 [s, CH(CH3)2], 25.1 [s,
CH(CH3)2], 26.7 [s, CH(CH3)2], 27.0 [s, CH(CH3)2], 28.6 [s,
CH(CH3)2], 28.9 [s, CH(CH3c)2], 54.3 (NCH2), 120.1, 122.0,
123.9,124.7, 128.6,129.5, 137.1, 138.4, 141.4, 146.3, 147.4 (s, Ar–
H), 206.0 (d, JP,C = 165 Hz, NCN) ppm. 31P{1H} NMR (243 MHz,
CDCl3, –20 °C): δ = –12.1 (s) ppm.
[Pd(IPr)2Cl2] (11): Complex 3 (0.152 g, 0.17 mmol) was dissolved
in CHCl3 (3 mL). The initial yellow mixture turned colorless. After
stirring for 3 h, the solvent was completely removed under vacuum,
and then the resulting solids were crystallized from a diethyl ether
to give white crystals of 11 (0.137 g, 79%). 1H NMR (600 MHz,
CD2Cl2, –40 °C): δ = 0.89 [d, J = 6.9 Hz, 24 H, CH(CH3)2], 0.93
[d, J = 6.8 Hz, 24 H, CH(CH3)2], 2.86 [sept, J = 6.8 Hz, 8 H,
CH(CH3)2], 6.83 (s, 4 H, NCH=), 7.12 (d, J = 7.7 Hz, 8 H, Ar–H),
7.42 (t, J = 7.8 Hz, 4 H, Ar–H) ppm. 13C{1H} NMR (151 MHz,
CD2Cl2, –40 °C): δ = 22.7 [s, CH(CH3)2], 26.0 [s, CH(CH3)2], 28.2
[s, CH(CH3)2], 123.8 (s, N–CH=), 124.3, 129.4, 136.7, 146.2 (s, Ar–
C), 171.7 (s, NCN) ppm. C54H72Cl2N4Pd (954.50): calcd. C 67.95,
H 7.60, N 5.87; found C 68.10, H 8.12, N 5.82.
[(Me3P)BrPd(C6H5)(SIPr)]
(12):
Bromobenzene
(0.095 g,
0.60 mmol) and THF (2 mL) were sequentially added to a Schlenk
flask that contained 2 (0.230 g, 0.40 mmol) at room temperature.
After stirring for 3 h at room temperature, the solvent was com-
pletely removed under vacuum, and then the resulting oily residue
was solidified with hexane. The solids were filtered and washed
with hexane (2 mLϫ3) to give yellow solids of 12 (0.189 g, 65%).
C36H52BrN2PPd (730.11): calcd. C 59.22, H 7.18, N 3.84; found C
59.57, H 7.50, N 3.74. 1H NMR (600 MHz, CDCl3, 23 °C): δ =
0.75 [d, J = 9.7 Hz, 9 H, P(CH3)3], 0.80 [d, J = 6.4 Hz, 6 H,
CH(CH3)3c], 1.07 [d, J = 6.4 Hz, 6 H, CH(CH3)3a], 1.25 [d, J =
6.4 Hz, 6 H, CH(CH3)3b], 1.58 [d, J = 6.4 Hz, 6 H, CH(CH3)3d],
3.12 [sept, J = 6.4 Hz, 2 H, CH(CH3)2e], 4.03 [sept, J = 6.4 Hz, 2
H, CH(CH3)2f], 3.88–3.91 (m, 2 H, NCH2), 4.09–4.12 (m, 2 H,
NCH2), 6.19 (m, 2 H, Ar–H), 6.56 (m, 3 H, Ar–H), 7.13 (d, J =
7.8 Hz, 2 H, Ar–H), 7.35 (d, J = 6.0 Hz, 2 H, Ar–H), 7.39 (t, J =
7.8 Hz, 2 H, Ar–H) ppm. 13C{1H} NMR (75 MHz, CDCl3, 23 °C):
δ = 14.0 [d, JP,C = 28 Hz, P(CH3)3], 22.6 [s, CH(CbH3)2], 25.1 [s,
CH(CdH3)2], 26.4 [s, CH(CcH3)2], 26.9 [s, CH(CaH3)2], 28.4 [s,
CfH(CH3c)2], 28.7 [s, CeH(CH3c)2], 53.8 (s, N–CH2), 53.9 (s, N–
CH2), 121.5, 123.7, 124.8, 126.6, 128.5, 137.7 (t, JP,C = 4.5 Hz),
146.5, 148.5, 152.1 (s, Ar–C), 210.3 (d, JP,C = 149 Hz, NCN) ppm.
31P{1H} NMR (243 MHz, CDCl3, 23 °C): δ = –14.8 (s) ppm.
[Pd(dppp)2] (15): A solution of dppp in THF (0.220 g, 0.53 mmol)
was added to a solution of 1 (0.304 g, 0.53 mmol) in THF (1 mL)
at –40 °C. The reaction mixture was slowly warmed up to room
temperature. After stirring the reaction mixture for 2 h, the yellow
solids gradually precipitated. The resulting suspension was com-
pletely evaporated to give crude solids, which was washed with n-
hexane and diethyl ether. The isolated solids were recrystallized
from THF/n-hexane to give yellow crystals of 15 (0.171 g, 69%).
C54H52P4Pd (931.30): calcd. C 69.64, H 5.62; found C 69.25, H
5.82. 1H NMR (600 MHz, C6D6, 23 °C): δ = 1.42 (br., 4 H, –CH2),
2.25 (br., 8 H, P–CH2), 6.90–7.01 (m, 24 H, Ar–H), 7.50 (br., 16
H, Ar–H) ppm. 31P{1H} NMR (243 MHz, C6D6, 23 °C): δ = 4.46
(s) ppm.
Complex 15 was independently prepared from [Pd(C2H4)(dppp)]
with dppp.[52]
Eur. J. Inorg. Chem. 2011, 1750–1761
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1759

Y.-J. Kim et al.
FULL PAPER
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