Square-planar diacetatopalladium complexes with trans-configured secondary amine ligands that avoid orthometalation: Ligand synthesis, coordination, molecular structure and catalytic potential for Suzuki cross-coupling reactions

Article abstract of DOI:10.1002/ejic.200700518

The trans-configured square-planar palladium complexes [Pd(OAc) ₂(LNtBu)₂] (1), [Pd(OAc)₂(η²- LN∩NtBu)] (2), [Pd(OAc)₂(LNPh)₂] (3), and [Pd(OAc)₂(η²-LN∩NPh)] (4), have been synthesized by treating palladium acetate with the amines NHtBuCH₂-2,4,6-Me ₃C₆H₂ (LNtBu) or NHPhCH₂-2,4,6- Me₃C₆H₂ (LNPh) or with the diamines NHtBuCH₂-2,4,6-Me₃C₆H-CH₂-2,4,6- Me₃C₆H-CH₂-NHtBu (LN∩NtBu) or NHPh-CH ₂-2,4,6-Me₃C₆H-CH₂-2,4,6-Me ₃C₆H-CH₂-NHPh (LN∩NPh). The single-crystal X-ray structure analysis of complexes 1-3 confirms a trans arrangement of the two acetato groups and of the two nitrogen atoms. Orthometalation leading to palladacycles is impossible in all cases as the ortho positions in the benzylic rings are blocked by methyl substituents. All complexes are found to catalyze Suzuki cross-coupling reactions of deactivated and even sterically hindered arene substrates. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700518

FULL PAPER
DOI: 10.1002/ejic.200700518
Square-Planar Diacetatopalladium Complexes with trans-Configured
Secondary Amine Ligands that Avoid Orthometalation: Ligand Synthesis,
Coordination, Molecular Structure and Catalytic Potential for Suzuki
Cross-Coupling Reactions
Ludovic Chahen,[a] Bruno Therrien,[a] and Georg Süss-Fink*[a]
Keywords: Cross-coupling / Palladium / N ligands / Amines / Homogeneous catalysis
The trans-configured square-planar palladium complexes
[Pd(OAc)2(LNtBu)2] (1), [Pd(OAc)2(η2-LNʝNtBu)] (2),
[Pd(OAc)2(LNPh)2] (3), and [Pd(OAc)2(η2-LNʝNPh)] (4),
have been synthesized by treating palladium acetate with
the amines NHtBuCH2-2,4,6-Me3C6H2 (LNtBu) or NHPhCH2-
2,4,6-Me3C6H2 (LNPh) or with the diamines NHtBuCH2-
2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-CH2-NHtBu (LNʝNtBu)
complexes 1–3 confirms a trans arrangement of the two acet-
ato groups and of the two nitrogen atoms. Orthometalation
leading to palladacycles is impossible in all cases as the ortho
positions in the benzylic rings are blocked by methyl substi-
tuents. All complexes are found to catalyze Suzuki cross-
coupling reactions of deactivated and even sterically hin-
dered arene substrates.
or NHPh-CH2-2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-CH2-NHPh (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
(LNʝNPh). The single-crystal X-ray structure analysis of
Germany, 2007)
efficient at low temperature and under aerobic conditions,
a significantly higher amount of palladium acetate (2 mol-
%) is needed compared to the molar ratio generally required
with phosphane ligands (0.01 mol-%) in order to afford
similar turnover numbers.
Introduction
The Suzuki cross-coupling reaction is one of the most
important methods for the selective assembly of biaryls in
the synthesis of natural products, pharmaceuticals, and ad-
vanced materials.[1] Although many palladium(II) or palla-
dium(0) complexes catalyze this coupling reaction, signifi-
cant efforts have been made to design ligands that can in-
crease the catalytic activity of the palladium center. Some
of the most widely studied Suzuki catalysts are palladium
phosphane complexes that are susceptible to orthomet-
alation or palladacycle formation.[2] However, the most ef-
ficient catalysts so far reported are palladium phosphane
complexes that cannot undergo orthometalation.[3] These
very active phosphane complexes require rigorous exclusion
of air and water, however, due to the air sensitivity of the
phosphane ligands, which is the main reason for the grow-
ing interest in Ncoordinating ligands for Suzuki catalysts.
Indeed, many N-based ligands have been reported to be
efficient for the Suzuki cross-coupling reactions, especially
tertiary amines and imines.[4] These ligands are air-stable
and are therefore easier to synthesize and handle. Boykin et
al. have screened several simple and commercially available
amines as ligands with palladium acetate in the Suzuki
cross-coupling reaction and found that bulky primary and
secondary amines appear to be better ligands than compar-
able tertiary amines that do not form stable complexes with
palladium acetate.[5] Although these catalytic systems are
Our laboratory has recently designed new ligands that
impose a trans geometry at the metal center, thereby pre-
venting orthometalation.[6] As the palladium complex trans-
[PdCl2(PʝP)], which contains the diphosphane li-
gand PPh2CH2-2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-CH2-
PPh2 (PʝP) is an active Suzuki catalyst for the cross-coup-
ling of deactivated or hindered aryl bromides, we decided to
synthesize the analogous amine ligands NHtBu-CH2-2,4,6-
Me3C6H2 (LNtBu), NHPh-CH2-2,4,6-Me3C6H2 (LNPh),
NHtBu-CH2-2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-CH2-
NHtBu (LNʝNtBu), and NHPh-CH2-2,4,6-Me3C6H-CH2-
2,4,6-Me3-C6H-CH2-NHPh (LNʝNPh) in order to study
their coordination to palladium acetate as well as the cata-
lytic potential of these complexes for Suzuki reactions.
Results and Discussion
Synthesis and Characterization of New Secondary Amine
Ligands
The secondary amines NHtBu-CH2-2,4,6-Me3C6H2
(LNtBu), NHtBu-CH2-2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-
CH2-NHtBu (LNʝNtBu), and NHPh-CH2-2,4,6-Me3C6H-
CH2-2,4,6-Me3C6H-CH2-NHPh (LNʝNPh) are accessible
in one step from the corresponding bromide and the corre-
[a] Institut de Chimie, Université de Neuchâtel,
Case Postale 158, 2009 Neuchâtel, Switzerland
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L. Chahen, B. Therrien, G. Süss-Fink
FULL PAPER
sponding amine (Scheme 1). The synthesis of (2,4,6-tri- by NMR spectroscopy and X-ray crystallography for com-
methylbenzyl)aniline (LNPh) has been described pre- plexes 1–4.
viously.[7]
The two asymmetric nitrogen centers in the bis-amine
complexes 1 and 3 give rise, in principle, to three isomers
Ϫ a pair of enantiomers (R,R and S,S) and a meso isomer
(R,S), as shown in Scheme 3. In both cases, all three iso-
mers are indeed formed upon coordination of LNtBu or
LNPh to [Pd(OAc)2] as the NMR spectra show the ex-
pected signals of both diastereoisomers.
Scheme 1. Synthesis of the secondary amines LNtBu, LNPh,
LNʝNtBu, and LNʝNPh.
All new compounds were characterized by NMR (1H,
13C) spectroscopy, mass spectrometry, and elemental analy-
sis.
Scheme 3. Representation of the stereoisomeric configurations of
complexes 1 and 3.
Synthesis and Molecular Structure of trans-Palladium
Complexes
While it did not prove possible to separate the three iso-
mers of complex 3, we succeeded in separating the dia-
stereoisomers of 1 by extraction with diethyl ether. How-
ever, the separated diastereoisomers (R,R)/(S,S)-1 and
(R,S)-1 were found to isomerize in solution over a period
of several minutes so it was only possible to record 1H
NMR spectra of diastereomerically pure 1a and 1b, but not
the 13C{1H} NMR spectra. Crystallization from chloro-
form gave only the meso isomer (R,S) for both complexes 1
and 3.
The trans-palladium complexes [Pd(OAc)2(LNtBu)2] (1),
[Pd(OAc)2(η2-LNʝNtBu)] (2), [Pd(OAc)2(LNPh)2] (3), and
[Pd(OAc)2(η2-LNʝNPh)] (4) were synthesized by treating
[Pd(OAc)2] with the corresponding amines or diamines in
toluene at 50 °C and simple workup of the reaction mixture
(Scheme 2).
The single-crystal X-ray structure analysis of 1 and 3 re-
vealed that, in contrast to solutions of these complexes,
which contain all isomers, the crystals isolated in both cases
represent only the meso isomer. The molecular structures of
1 and 3 show the palladium atom to be in a square-planar
geometry surrounded by two acetato ligands and two nitro-
gen atoms in a trans coordination geometry (Figures 1 and
2, respectively).
There are intramolecular hydrogen bonds in the crystal
structures of 1 and 3 between the NH of the amino function
and the C=O group of the acetato ligands [N–O 2.846(5) Å,
N–H···O 141.7° in 1 and N–O 2.714(3) Å, N–H···O 150.4°
in 3; Figure 3]. The N···O distances and N–H···O angles are
similar to those observed in analogous trans acetato(amino)-
palladium complexes.[5a,8]
Scheme 2. Synthesis of the palladium complexes trans-[Pd(OAc)2-
(LNtBu)2](1),trans-[Pd(OAc)2(η2-LNʝNtBu)](2),trans-[Pd(OAc)2-
(LNPh)2] (3), and trans-[Pd(OAc)2(η2-LNʝNPh)] (4).
The rigid diamine backbone in the diamine complexes 2
and 4 generates an additional chirality upon coordination,
The question of stereochemistry needs to be addressed with two enantiomers (P and M) being generated de-
for complexes containing secondary amine ligands with pending on the sense of helicity. Complexes 2 and 4 there-
three different substituents as the nitrogen atom is fore possess three chiral elements (two chiral nitrogen atoms
stereogenic (asymmetric tetrahedral geometry) due to coor- and a helical chirality element) and thus eight stereoiso-
dination to the metal center. This problem has been solved meric species can theoretically be obtained (Scheme 4).
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Square-Planar Diacetatopalladium Complexes
1
However, as suggested by H NMR spectroscopy and con-
firmed by the X-ray structure analysis of 2, only one pair
of enantiomers is observed for 2 and 4.
Figure 1. ORTEP drawing of 1 showing ellipsoids at the 50% prob-
ability level with hydrogen atoms omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–O(1) 2.038(4), Pd(1)–N(1)
2.097(5), O(1)–C(1) 1.239(7), O(2)–C(1) 1.236(9), C(2)–C(1)
1.506(11), N(1)–C(3) 1.501(5), N(1)–C(13) 1.509(9), C(3)–C(4)
1.497(10); O(1)–Pd(1)–O(1)i 180.0(4), N(1)–Pd(1)–O(1) 87.3(2),
N(1)–Pd(1)–N(1)i 180.0(1). (i = –x, –y, –z).
Scheme 4. Representation of the possible stereoconfigurations of
complexes 2 and 4.
Despite the high number of theoretically possible iso-
1
mers, the H NMR spectra of complexes 2 and 4 are not
complex and show only the expected signals for the ligands,
thereby suggesting that only one isomer or pair of enantio-
mers is present in solution. As neither 2 nor 4 shows a sig-
nal in its CD spectrum, it can be assumed that both com-
plexes exist as a pair of enantiomers. The single-crystal X-
ray structure analysis of 2 confirmed this hypothesis since
it reveals a racemic crystal containing two enantiomers,
with the square-planar palladium center being trans coordi-
nated to two acetato ligands and to the two nitrogen atoms
of the diamine ligand (Figure 4).
Figure 2. ORTEP drawing of 3 showing ellipsoids at the 50% prob-
ability level with hydrogen atoms omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–O(1) 2.013(2), Pd(1)–N(1)
2.079(2), O(1)–C(1) 1.280(3), O(2)–C(1) 1.230(3), C(2)–C(1)
1.504(4), N(1)–C(3) 1.500(3), N(1)–C(13) 1.446(3), C(3)–C(4)
1.506(3); O(1)–Pd(1)–O(1)i 180.0(1), N(1)–Pd(1)–O(1) 96.14(8),
N(1)–Pd(1)–N(1)i 180.0. (i = –x, –y, 1 – z).
The coordination of the chelating diamino ligand in 2
imposes a slight distortion of the planar geometry. Thus,
unlike in 1 and 3, where the O–Pd–O and N–Pd–N axes are
perfectly linear by symmetry, the corresponding angles in 2
are 179.1(4)° and 178.8(4)°, respectively. A strong distortion
is imposed on the diphenylmethane spacer such that the
angle between the two planes of the phenyl rings is much
more acute (56.4°; Figure 5) than the corresponding angle
in diphenylmethane[9] (80.5°), the analogous trans-diphos-
phane complex [PdCl2(PʝP)][6] (65.9°), and in the structur-
ally constrained dinuclear chromium complex [(µ2-η6,η6-di-
Figure 3. Intramolecular hydrogen-bonded systems in 1 (left) and
3 (right).
Eur. J. Inorg. Chem. 2007, 5045–5051
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L. Chahen, B. Therrien, G. Süss-Fink
FULL PAPER
is a deactivated bromo derivative, and the cross-coupling of
phenylboronic acid with 1-bromo-2,4,6-trimethylbenzene,
which is both deactivated and sterically hindered. The
cross-coupling of phenylboronic acid with aliphatic bro-
mides, which was recently reported to occur with
[Pd(OAc)2] in the presence of sterically hindered phos-
phanes,[12,13] does not work with our complexes [Ͻ5% of
product formation with CH3(CH2)11Br; catalyst/substrate
ratio: 1:20; dioxane, tBuOK, 30–90 °C].
The results summarized in Table 1 show that the effi-
ciency of the catalysts depends mainly on the temperature.
Thus, at 90 °C the highest catalytic turnover number
(86000) is achieved with [Pd(OAc)2], which is not surprising
given that recent work has shown [Pd(OAc)2] to be an excel-
lent source of highly active palladium nanoparticles during
cross-coupling reactions.[14] However, at 60 °C complexes 1
and 2 are more efficient than [Pd(OAc)2] and the other
complexes, thereby indicating that the ligands have a strong
influence on the catalytic performance Ϫ the electronic and
steric effect of the tert-butyl groups on secondary amines is
stronger than that of phenyl groups. Finally, this sequence
changes again at 30 °C, since complex 2 becomes the least
efficient one. This is due to the rigidity of the ligand, which
means that the complex requires more energy to perform
the catalytic reaction.
Figure 4. ORTEP drawing of 2 showing ellipsoids at the 50% prob-
ability level with hydrogen atoms omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–O(1) 1.999(9), Pd(1)–O(3)
2.012(9), Pd(1)–N(1) 2.112(11), Pd(1)–N(2) 2.102(10), O(1)–C(1)
1.260(16), O(3)–C(21) 1.268(18), N(1)–C(3) 1.504(16), N(1)–C(13)
1.552(17), N(2)–C(23) 1.528(16), N(2)–C(33) 1.531(16), C(3)–C(4)
1.537(19), C(23)–C(24) 1.517(16); O(1)–Pd(1)–O(3) 179.1(4), N(1)–
Pd(1)–O(1) 83.9(4), N(1)–Pd(1)–O(3) 95.5(4), N(1)–Pd(1)–N(2)
178.8(4), C(6)–C(18)–C(26) 111.4(12).
phenylmethane)-(µ2-1,1,2,2-tetramethyldiphosphane-P,PЈ)-
bis(dicarbonylchromium)] (71.9°).[10] Intramolecular hydro-
gen bonds are observed between the N–H amino function
and the C=O oxygen of an acetato group in the crystal
structure of 2, as in 1 and 3 (Figure 5). The N···O distances
are 2.801(16) and 2.765(15) Å with N–H···O angles of
149.0° and 150.3°, respectively.
Table 1. Catalytic turnover numbers (TON), indicating the mol of
product formed per mol of catalyst used after 18 h, for the Suzuki
cross-coupling of 4-bromotoluene and phenylboronic acid cata-
lyzed by 1–4 and [Pd(OAc)2]. Solvent: toluene; base: K2CO3; reac-
tion time: 18 h. Average of two runs.
Catalyst/
substrate
T [°C]
1
2
3
4
[Pd(OAc)2]
30
30
60
60
60
90
90
90
1:1000
1:10000
1:1000
1:10000
1:100000
1:1000
1:10000
1:100000
410
2700
620
250
0
960
130
600
360
230
900
390
2200
12000 21000
710
240
460
1000
3800
4800 6200 2300
36000 38000 7000
800
6200 9100 4000
45000 58000 28000 29000 86000
1000 710
1000
9600
4900
Figure 5. Intramolecular hydrogen-bonded system in 2 (left) and
axial view in 2 (right).
Nevertheless, as the TONs of the four complexes have
the same order of magnitude as that of [Pd(OAc)2], we com-
pared complex 2 and [Pd(OAc)2] kinetically at 60 °C with a
catalyst/substrate ratio of 1:10000.
Catalytic Activity of Complexes 1–4 for Suzuki Cross-
Coupling Reactions
The trans-palladium complexes 1–4 were studied as cata-
Figure 6 shows that the two precursors behave differently
lyst precursors for Suzuki cross-coupling reactions. As we during the catalytic reaction. Thus, whereas [Pd(OAc)2]
wanted to study the real influence of the ligands and the shows a relatively constant activity, complex 2 undergoes
geometry they impose, we decided to compare the results an induction period of almost one hour, thereby indicating
of these four complexes with the ligand-free compound that it is also only a precatalyst. As we cannot exclude nan-
[Pd(OAc)2], which is suspected to catalyze the Suzuki cross- oparticle formation in the case of 2, we performed poison-
coupling due to nanoparticle formation, depending on the ing tests with metallic mercury using a catalyst/substrate
catalyst concentration.[11]
ratio of 1:1000. At 60 °C, 2 attains a TON of 300 after 1 h,
We studied two Suzuki-type reactions, namely the cross- while it is 960 after 18 h. When 400 equiv. of mercury is
coupling of phenylboronic acid with 4-bromotoluene, which added at the beginning of the reaction, the TON falls to
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Square-Planar Diacetatopalladium Complexes
480 after 18 h, and if mercury is added after one hour of ents in the ortho-positions, catalyze the Suzuki cross-coup-
reaction the TON is 660 after 18 h. Under the same condi- ling of 4-bromotoluene and even of 2,4,6-trimethylphenyl
tions, the catalytic turnover of [Pd(OAc)2] drops to 84 or bromide with phenylboronic acid. Whereas the TONs of
267 if 400 equiv. of mercury is added at the beginning or the four complexes show the same order of magnitude as
after 1 h, respectively. Since the catalytic activity of metallic [Pd(OAc)2] in both reactions, it seems that the new ligands
palladium nanoparticles should be suppressed completely give rise to the formation of catalytically active molecular
by metallic mercury, we can conclude that the molecular species rather than to metallic nanoparticles. Furthermore,
catalysis pathway dominates for complex 2 while in the case we have shown that, at temperatures above 60 °C, the rigid-
of palladium acetate the nanoparticle pathway is dominant. ity of the ligand backbone and the tert-butyl substituents
increase the catalytic performance in the Suzuki cross-coup-
ling of sterically hindered and deactivated bromides.
Experimental Section
General: All reactions were carried out under argon using standard
Schlenk techniques. Thf was distilled from sodium benzophenone
under N2 to avoid water and oxygen contamination. Toluene, n-
hexane, and diethyl ether were purchased from Merck (puriss., pro
analysi) and, along with distilled water, were saturated with argon
prior to use. Dichloromethane was distilled from CaH2 and satu-
rated with N2. [Pd(OAc)2] was purchased from Aldrich and used
as received. Deuterated chloroform was used as received, and all
NMR spectra were performed with
a Bruker spectrometer
[400 MHz for 1H and 100 MHz for 13C{1H}]. All GC analyses were
performed using a GC DANI 86.10 equipped with a fused-silica
capillary column OPTIMA δ-3 (0.5 µm, 30 mϫ0.25 mm) and an
SP-4400 integrator.
Figure 6. Kinetic comparison of complex 2 and [Pd(OAc)2] at 60 °C
with a ratio of 1:10000.
Synthesis of NHtBu-CH2-2,4,6-Me3C6H2 (LNtBu): tert-Butylamine
(2.11 mL, 20 mmol) was added to
a suspension of 1-(bro-
momethyl)-2,4,6-trimethylbenzene (1.278 g, 6 mmol) and K2CO3
(2.76 g, 20 mmol) in toluene (20 mL). The mixture was refluxed for
15 h, then cooled to room temperature, and filtered through filter
pulp. The filtrate was evaporated to dryness to give 793 mg of an
oil (yield 64%). 1H NMR (400 MHz, CDCl3, 25 °C): δ = 6.91 (s, 2
H), 3.75 (s, 2 H), 2.44 (s, 6 H), 2.32 (s, 3 H), 1.27 (s, 9 H) ppm.
13C{1H} NMR (100 MHz, CDCl3, 25 °C): δ = 136.74, 136.09,
134.25, 128.95, 50.43, 40.37, 28.89, 20.84, 19.21 ppm. EI-MS: m/z
The results of the Suzuki cross-coupling of 1-bromo-
2,4,6-trimethylbenzene with phenylboronic acid are summa-
rized in Table 2. As expected with a sterically hindered and
deactivated bromide, the TONs are lower than those ob-
served for the previous reaction. Complex 2 is less active 206 [M + H]+. C14H23N (205.34): calcd. C 81.89, H 11.29, N 6.82;
found C 81.95, H 11.34, N 6.75.
than 1 at 30 °C because of the rigidity of the ligand back-
bone. However, at temperatures above 60 °C complex 2
shows the best catalytic performance for sterically hindered
substrates.
Synthesis of NHtBu-CH2-2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-CH2-
NHtBu (LNʝNtBu): tert-Butylamine (2.11 mL, 20 mmol) was
added to
a suspension of bis[3-(bromomethyl)-2,4,6-trimeth-
ylphenyl]methane (1.313 g, 3 mmol) and K2CO3 (2.76 g, 20 mmol)
in toluene (20 mL) and the mixture refluxed for 15 h. The solution
was then filtered through filter pulp at room temperature and the
filtrate dried in vacuo (yield 80%). 1H NMR (400 MHz, CDCl3,
25 °C): δ = 6.78 (s, 2 H), 4.02 (s, 2 H), 3.63 (s, 4 H), 2.32 (s, 6 H),
2.08 (s, 12 H), 1.15 (s, 18 H) ppm. 13C{1H} NMR (100 MHz,
CDCl3, 25 °C): δ = 136.41, 135.87, 135.15, 135.13, 133.99, 130.54,
50.46, 41.07, 32.39, 28.90, 21.07, 19.37, 15.74 ppm. C29H46N2
(422.69): calcd. C 82.40, H 10.97, N 6.63; found C 82.56, H 11.04,
N 6.57.
Table 2. Catalytic turnover numbers (TON) indicating the mol of
product formed per mol of catalyst used after 18 h for the Suzuki
cross-coupling of 2,4,6-trimethylphenyl bromide and phenylboronic
acid catalyzed by 1–4 and [Pd(OAc)2]. Solvent: toluene; base:
K2CO3; reaction time: 18 h. Average of two runs.
Catalyst/
substrate
T [°C]
1
2
3
4
[Pd(OAc)2]
86
30
60
60
90
90
1:1000
1:1000
1:10000
1:1000
1:10000
297 66
430 620 80
2790 2900 300 900 420
550 730 140 140 270
3200 4900 800 1000 1300
18
60
160 200
Synthesis of NHPh-CH2-2,4,6-Me3C6H-CH2-2,4,6-Me3C6H-CH2-
NHPh (LNʝNPh): Phenylamine (2 mL, 20 mmol) was added to a
suspension of bis[3-(bromomethyl)-2,4,6-trimethylphenyl]methane
(1.313 g, 3 mmol) and K2CO3 (2.76 g, 20 mmol) in toluene (20 mL)
and the mixture refluxed for 24 h. The solution was then filtered
through filter pulp at room temperature and the filtrate dried in
vacuo. The white residue was washed with n-hexane (20 mL) to
remove an excess of phenylamine (yield 968 mg, 70%). 1H NMR
Conclusions
The trans-secondary amino complexes 1–4, in which or-
thometalation is impossible because of the methyl substitu- (400 MHz, CDCl3, 25 °C): δ = 7.35–7.24 (m, 4 H), 6.91 (s, 2 H),
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6.88–6.69 (m, 6 H), 4.22 (s, 4 H), 4.15 (s, 2 H), 2.38 (s, 6 H), 2.19
(s, 6 H), 2.16 (s, 6 H) ppm. 13C{1H} NMR (100 MHz, CDCl3,
25 °C): δ = 148.20, 136.48, 136.22, 134.77, 133.09, 130.68, 129.25,
and the mixture stirred at 50 °C for 15 h. The red solution became
clear after 20 min. After 15 h the solvent was evaporated to dryness
to give a yellow powder, which was washed with diethyl ether
129.01, 128.20, 125.28, 117.42, 115.16, 112.62, 43.15, 32.36, 21.09, (10 mL). Yield 80%. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 7.71
19.53, 16.12 ppm. EI-MS: m/z 463 [M + H]+. C33H38N2 (462.67):
calcd. C 85.67, H 8.28, N 6.05; found C 85.89, H 8.46, N 5.90.
(d, JH,H = 10.6 Hz, 2 H), 6.86 (s, 2 H), 4.16 (s, 2 H), 3.61 (dd,
3
3
3JH,H = 12.3, 10.6 Hz, 2 H), 2.93 (d, JH,H = 12.6 Hz, 2 H), 2.51
(s, 6 H), 3.32 (s, 6 H), 1.72 (s, 6 H), 1.67 (s, 18 H), 1.66 (s, 6 H)
ppm. 13C{1H} NMR (100 MHz, CDCl3, 25 °C): δ = 180.16, 140.47,
138.95, 136.26, 135.70, 132.40, 129.94, 59.47, 42.90, 32.39, 28.85,
24.80, 21.48, 20.59, 18.46 ppm. C33H52N2O4Pd (647.20): calcd. C
61.24, H 8.10, N 4.33; found C 61.48, H 8.28, N 4.28.
Synthesis of [Pd(OAc)2(LNtBu)2] (1):
A solution of LNtBu
(102.5 mg, 0.5 mmol) in toluene (40 mL) was added to a suspension
of [Pd(OAc)2] (56 mg, 0.25 mmol) in toluene (40 mL) and the mix-
ture stirred at 50 °C for 3 h. The red solution became clear after
20 min, although towards the end of the reaction it became slightly
cloudy again. After 3 h the cloudy solution was concentrated in
vacuo to 40 mL and then filtered through filter pulp to remove the
solid precipitate. The filtrate was evaporated to dryness and the
residue washed with n-hexane (40 mL) to give analytically pure 1
as a mixture of isomers (total yield 65%). Complex 1 was separated
into two diastereoisomers by extraction with diethyl ether (40 mL).
After stirring at room temperature for 10 min, the diethyl ether
extract was filtered through a cannula equipped with filter paper
and the solvents evaporated to dryness to give isomer 1a; dia-
stereoisomer 1b remained as a solid.
Synthesis of [Pd(OAc)2(LNPh)2] (3): A solution of LNPh (225 mg,
1 mmol) in toluene (50 mL) was added to a suspension of
[Pd(OAc)2] (112 mg, 0.5 mmol) in toluene (50 mL) and the mixture
stirred at 50 °C for 3 h. The red solution became clear after 20 min,
although towards the end of the reaction the solution became
slightly cloudy again. After 3 h the cloudy solution was concen-
trated in vacuo to 50 mL and then filtered through filter pulp to
remove the solid precipitate. The filtrate was evaporated to dryness
and the residue washed with diethyl ether (20 mL) to give analyti-
cally pure 3 as a mixture of isomers (total yield 60%). 1H NMR
(400 MHz, CDCl3, 25 °C): δ = 9.35 (m), 9.06 (m), 7.22–7.07 (m),
1
3
1a: H NMR (400 MHz, CDCl3, 25 °C): δ = 7.60 (br. d, JH,H
=
3
6.82 (s), 6.78 (s), 4.41–4.20 (m), 3.79 (dd, JH,H = 13.4, 4.6 Hz),
3
9.6 Hz, 2 H, NH), 6.87 (s, 4 H), 3.69 (dd, JH,H = 12.8, 9.6 Hz, 2
3
3.63 (dd, JH,H = 13.4, 4.7 Hz), 2.37 (s), 2.33 (s), 2.28 (s), 1.81 (s),
3
H), 3.05 (dd, JH,H = 12.8, 2.2 Hz, 2 H), 2.40 (s, 6 H), 2.19 (s, 12
1.76 (s) ppm. 13C{1H} NMR (100 MHz, CDCl3, 25 °C): δ = 180.78,
147.21, 138.35, 137.87, 129.52, 129.42, 129.20, 129.08, 128.90,
125.61, 122.96, 122.26, 50.78, 49.84, 29.32, 24.22, 23.15, 21.27,
20.39, 20.26 ppm. C36H44N2O4Pd (675.17): calcd. C 61.20, H 6.10,
N 4.46; found C 61.48, H 6.12, N 4.42.
H), 1.80 (s, 6 H), 1.63 (s, 18 H) ppm. C32H52N2O4Pd (635.19):
calcd. C 63.72, H 8.69, N 4.64; found C 63.96, H 8.85, N 4.44.
1
3
1b: H NMR (400 MHz, CDCl3, 25 °C): δ = 7.11 (br. d, JH,H
=
3
10.6 Hz, 2 H, NH), 6.90 (s, 4 H), 3.64 (t, JH,H = 10.6 Hz, 2 H),
3
3.00 (dd, JH,H = 12.8, 2.0 Hz, 2 H), 2.45 (s, 12 H), 2.32 (s, 6 H),
Synthesis of [Pd(OAc)2(η2-LNʝNPh)] (4): A solution of LNʝNPh
(230 mg, 0.5 mmol) in toluene (50 mL) was added to a suspension
of [Pd(OAc)2] (112 mg, 0.5 mmol) in toluene (50 mL) and the mix-
ture stirred at 50 °C for 15 h. The red solution became clear after
20 min, although towards the end of the reaction the solution be-
came slightly cloudy again. After 15 h the cloudy solution was con-
1.70 (s, 6 H), 1.41 (s, 18 H) ppm. C32H52N2O4Pd (635.19): calcd.
C 63.72, H 8.69, N 4.64; found C 63.88, H 8.78, N 4.50.
Synthesis of [Pd(OAc)2(η2-LNʝNtBu)] (2):
LNʝNtBu (105 mg, 0.25 mmol) in toluene (50 mL) was added to
a suspension of [Pd(OAc)2] (56 mg, 0.25 mmol) in toluene (50 mL)
A solution of
Table 3. Crystallographic and selected experimental data for 1–3.
1
2
3
Chemical formula
Formula weight
Crystal system
Space group
Crystal color and shape
Crystal size [mm]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C32H52N2O4Pd
635.16
C33H52N2O4Pd
647.17
C36H44N2O4Pd
675.13
triclinic
monoclinic
P21/c
yellow block
0.18ϫ0.15ϫ0.13
12.5014(12)
14.5192(10)
19.354(3)
triclinic
¯
¯
P1
P1
yellow block
0.35ϫ0.22ϫ0.20
9.095(3)
yellow block
0.23ϫ0.22ϫ0.18
8.8590(9)
9.1797(10)
11.2241(12)
66.176(12)
71.855(12)
75.525(12)
785.34(14)
1
9.113(2)
10.093(2)
107.71(3)
99.14(3)
91.95(3)
783.8(3)
110.856(10)
γ [°]
V [Å3]
3282.8(6)
4
Z
1
T [K]
173(2)
1.346
0.629
173(2)
1.309
0.602
173(2)
1.428
0.633
Dc [gcm–3]
µ [mm–1]
Scan range [°]
Unique reflections
Reflections used [I Ͼ 2σ(I)]
Rint
4.30 Ͻ 2θ Ͻ 51.80
1552
1494
4.42 Ͻ 2θ Ͻ 51.90
6379
3759
4.90 Ͻ 2θ Ͻ 51.92
2852
2745
0.0166
0.1243
0.0287
R indices [I Ͼ 2σ(I)][a]
R indices (all data)
Goodness-of-fit
Max, min ∆ρ [eÅ–3]
0.0364, wR2 0.0739
0.0302, wR2 0.0898
1.224
0.1587, wR2 0.4129
0.1927, wR2 0.4256
1.518
0.0253, wR2 0.0630
0.0287, wR2 0.0739
1.151
0.535, –0.686
13.775, –2.481
0.575, –0.998
[a] Structures were refined on Fo : wR2 = {Σ[w(Fo – Fc2)2]/Σw(Fo ) }1/2, where w–1 = [Σ(Fo ) + (aP)2 + bP] and P = [max(Fo , 0) + 2Fc2]/3.
2
2
2 2
2
2
5050 Eur. J. Inorg. Chem. 2007, 5045–5051
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Square-Planar Diacetatopalladium Complexes
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centrated in vacuo to 50 mL and then filtered through filter pulp
to remove the solid precipitate. The filtrate was evaporated to dry-
ness and the residue washed with diethyl ether (20 mL) to give 4
(yield 60%). 1H NMR (400 MHz, CDCl3, 25 °C): δ = 10.34 (d,
3JH,H = 10.0 Hz, 2 H, NH), 7.35–7.31 (m, 4 H), 7.27–7.15 (m, 6
3
H), 6.98 (s, 2 H), 4.39 (dd, JH,H = 12.1, 10.0 Hz, 2 H), 4.23 (s, 2
H), 3.08 (d, 3JH,H = 12.1 Hz, 2 H), 2.56 (s, 6 H), 2.28 (s, 6 H), 1.90
(s, 6 H), 1.79 (s, 6 H) ppm. 13C{1H} NMR (100 MHz, CDCl3,
25 °C): δ = 181.20, 148.43, 140.28, 138.23, 136.90, 136.23, 131.37,
130.18, 129.44, 125.37, 121.29, 49.00, 32.38, 25.34, 21.62, 19.67,
18.59 ppm. C37H44N2O4Pd (687.18): calcd. C 64.67, H 6.45, N
4.08; found C 64.90, H 6.59, N 3.99.
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X-ray Crystallographic Study: Crystals of 1–3 were mounted on
a Stoe Image Plate Diffraction system equipped with a φ circle
goniometer and
a Mo-Kα graphite-monochromated radiation
source (λ = 0.71073 Å). Data were collected in the φ range 0–200°,
in increments of 1.0°, 1.2°, and 1.0°, respectively, with the 2θ range
2.0–26° and Dmax–Dmin = 12.45–0.81 Å. The structures were solved
by direct methods using the program SHELXS-97.[15] Refinement
and all further calculations were carried out using SHELXL-97.[16]
The H-atoms were included in calculated positions in all complexes
and treated as riding atoms using the SHELXL default parameters.
The non-H atoms were refined anisotropically using weighted full-
matrix least-squares on F2. Crystallographic details are summa-
rized in Table 3. Figures 1, 2, and 4 were drawn with ORTEP[17]
and Figures 3 and 5 with MERCURY.[18]
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de Vries, Adv. Synth. Catal. 2004, 346, 1812.
CCDC-647487 (for 1), -647488 (for 2), and -647489 (for 3) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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many, 1999.
Catalytic Reactions: The catalyst was added (in the molar ratio
given in Tables 1 and 2) to a solution of K2CO3·1.5H2O (138 mg,
0.8 mmol), phenylboronic acid (91 mg, 0.75 mmol), and the aryl
bromide (0.5 mmol) in toluene (5 mL) in a Schlenk tube and the
mixture heated to the desired temperature (Tables 1 and 2) and
stirred for 18 h. After cooling, the solution was filtered through a
small silica gel column then the silica gel was eluted with diethyl
ether (20 mL). The filtrate was combined with the ether washings
and the solution obtained analyzed by GC.
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Received: May 16, 2007
Published Online: September 12, 2007
Eur. J. Inorg. Chem. 2007, 5045–5051
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5051