Square-planar dichloro palladium complexes with trans-configurated phosphine ligands avoiding ortho-metallation: Ligand design, complex synthesis, molecular structure and catalytic potential for Suzuki cross-coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2006.06.020

The square-planar palladium complexes trans-[PdCl₂(PPh₂-CH₂-2,4,6-C₆H₂Me₃)₂] (1) and trans-[PdCl₂(η²-PPh₂-CH₂-2,4,6-C₆HMe₃-CH₂-2,4,6-C₆HMe₃-CH₂-PPh₂)] (2) have been synthesized from [PdCl₂(cod)] (cod = 1,5-cyclooctadiene) and the corresponding new phosphine or diphosphine ligands. The single-crystal X-ray structure analysis reveals for both complexes a trans arrangement of the two chlorine and of the two phosphorus atoms. In both cases, ortho-metallation leading to palladacycles is not possible, since all ortho positions in the benzylic rings of 1 and 2 are blocked by methyl substituents. Both complexes are found to catalyze Suzuki cross-coupling reactions of deactivated and even bulky arene substrates.

Full text of DOI:10.1016/j.jorganchem.2006.06.020

Journal of Organometallic Chemistry 691 (2006) 4257–4264
www.elsevier.com/locate/jorganchem
Square-planar dichloro palladium complexes with
trans-configurated phosphine ligands avoiding ortho-metallation:
Ligand design, complex synthesis, molecular structure and catalytic
potential for Suzuki cross-coupling reactions
*
Ludovic Chahen, Bruno Therrien, Georg Suss-Fink
¨
ˆ ˆ
Institut de Chimie, Universite´ de Neuchatel, Case Postale 158, CH-2009 Neuchatel, Switzerland
Received 8 May 2006; accepted 9 June 2006
Available online 23 June 2006
Abstract
The square-planar palladium complexes trans-[PdCl2(PPh2-CH2-2,4,6-C6H2Me3)2] (1) and trans-[PdCl2(g2-PPh2-CH2-2,4,6-C6HMe3-
CH2-2,4,6-C6HMe3-CH2-PPh2)] (2) have been synthesized from [PdCl2(cod)] (cod = 1,5-cyclooctadiene) and the corresponding new
phosphine or diphosphine ligands. The single-crystal X-ray structure analysis reveals for both complexes a trans arrangement of the
two chlorine and of the two phosphorus atoms. In both cases, ortho-metallation leading to palladacycles is not possible, since all ortho
positions in the benzylic rings of 1 and 2 are blocked by methyl substituents. Both complexes are found to catalyze Suzuki cross-coupling
reactions of deactivated and even bulky arene substrates.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Suzuki cross-coupling; Palladium complexes; Ligand rigidity; Ligand flexibility
1. Introduction
and a base to give a Pd(II) complex containing two aryl
ligands, and finally by a reductive elimination step to give
the product and a Pd(0) species [2].
The Suzuki cross-coupling (Suzuki-Miyaura reaction)
catalyzed by various palladium complexes, is among the
most powerful synthetic tools for the generation of car-
bon–carbon bonds [1]. Although many different palla-
dium(II) or palladium(0) complexes catalyze this coupling
reaction, significant efforts have been put on the design of
suitable ligands that can increase the catalytic activity of
the palladium center. Despite the still lacunary mechanistic
knowledge, a simplified catalytic cycle involving palla-
dium(0) or palladium(II) complexes according to Scheme 1
is generally accepted: The oxidative addition of the aryl
halide to a Pd(0) complex to give a Pd(II) species is fol-
lowed by a transmetallation step involving arylboronic acid
As the oxidative addition step is supposed to give rise to
a cis-Pd(II) complex [3], and as the reductive elimination
step seems to involve a cis-Pd(II) complex [4], it has been
assumed that palladium(II) complexes containing two
phosphine ligands would be more active in the cis than in
the trans form. Accordingly, diphosphine ligands that
impose a cis geometry on the palladium center, such as
diphenylphosphinomethane (dppm), diphenylphosphinoe-
thane (dppe) or diphenylphosphinoferrocene (dppf) have
been used as co-catalysts (ligands) in Suzuki cross-coupling
reactions [5]. Moreover, some of the most active Suzuki
catalysts are palladium complexes susceptible to ortho-met-
allation or palladacycle formation [6,7]. The influence of
the phosphine ligands on the catalytic activity used in
Suzuki cross-coupling reactions has been studied systemat-
ically by Buchwald and co-workers [8], which allowed a
*
Corresponding author. Tel.: +41 32 718 2405; fax: +41 32 718 2511.
E-mail address: georg.suess-fink@unine.ch (G. Suss-Fink).
¨
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.020

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L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
Scheme 1. Catalytic cycle of Suzuki cross-coupling adapted for the coupling of an arylbromide with phenylboronic acid.
rational design of a universal Suzuki catalyst [9]. However,
the precise geometries and possible isomerization processes
of the catalytically active species are not known.
in addition to the palladium-phosphorus bond. Carbon
atoms susceptible to reaction are the ortho-carbon atoms
of aryl substituents in b-position with respect to the phos-
phorus atom (e.g. benzyl), since in this case a stable five-
membered palladacycle can be formed. By contrast, a-aryl
substituents (e.g. phenyl) do not undergo ortho-metallation
at palladium [20].
For this reason we designed two new phosphine ligands,
the ortho-positions in the b-aryl substituents of which are
blocked by methyl groups: the monophosphine PPh2-
CH2-2,4,6-C6H2Me3 and the analogous diphosphine
PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2,
which can be expected to allow to bite angle (P–Pd–P) close
to 180ꢁ upon coordination to palladium (trans geometry).
Recently, several palladium(II) complexes containing
trans-spanning diphosphine ligands, that contain a rigid
ligand backbone, have been synthesized [10,11,16]. Thus,
trans-[PdCl2(SPANphos)] reported by van Leeuwen does
not show any tendency to cis-trans isomerization [10], the
complex trans-[PdCl2(diphos)] (diphos = 2,6-bis(2-((diph-
enylphosphino)methyl)phenyl)benzene) reported by Prot-
asiewicz [11] has been successfully used as Heck and
Suzuki catalyst, in spite of the rigid trans-geometry [12].
With the diphosphine Xantphos, developed by van Leeu-
wen [13] and used as a ligand for Suzuki reactions, palla-
dium complexes with trans-standing alkyl and chloro
ligands [14] and with trans-standing aryl and bromo
ligands [15] have been isolated and characterized by
X-ray crystallography.
In this paper we report two new trans-palladium(II)
complexes and their use as Suzuki catalysts. In both com-
plexes, the formation of palladacycles via ortho-metallation
is not possible thanks to two newly designed phosphine
ligands. However, the two complexes differ in the rigidity
of their structures: While trans-[PdCl2(PPh2-CH2-2,4,6-
C6H2Me3)2] (1) with two monophosphine ligands is more
flexible, the diphosphine ligand in trans-[PdCl2(g2-
PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2)]
(2) increases the steric bulk of the complex.
2.1. Synthesis of the new phosphines diphenyl-
(2,4,6-trimethylbenzyl)phosphine and
bis(3-((diphenylphosphino)methyl)-
2,4,6-trimethylphenyl)methane
The new aryl phosphines PPh2-CH2-2,4,6-C6H2Me3 and
PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2
are accessible in two steps (Scheme 2), the first step being
the bromomethylation of the mesityl group with hydrogen
bromide and paraformaldehyde in glacial acetic acid at
50 ꢁC as reported by Niehues et al. [17]; then the bromo
derivatives obtained are reacted with lithium diphenylphos-
phide in tetrahydrofurane at 0 ꢁC to give the target mole-
cules and lithium bromide.
2. Results and discussion
The synthesis and isolation of the products must be car-
ried out with rigorous exclusion of air, in order to avoid
oxidation of the phosphine groups. Both compounds have
been characterized by correct NMR (1H, 13C, 31P) and
One of the problems encountered in palladium phos-
phine coordination chemistry is the ortho-metallation,
which results in the formation of a palladium-carbon bond

L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
4259
Scheme 2. Synthesis of the new phosphines PPh2-CH2-2,4,6-C6H2Me3 and PPh2-CH2-2,4,6-C6HMe3-CH2–2,4,6-C6HMe3-CH2-PPh2.
mass-spectroscopic data as well as by satisfactory elemen-
tal analysis data.
2.2. Synthesis and molecular structure of the palladium
complexes trans-[PdCl2(PPh2-CH2-2,4,6-C6H2Me3)2] (1)
and trans-[PdCl2(g2-PPh2-CH2-2,4,6-C6HMe3-CH2-
2,4,6-C6HMe3-CH2-PPh2)] (2)
The palladium complexes trans-[PdCl2(PPh2-CH2-2,4,6-
C6H2Me3)2] (1) and trans-[PdCl2(g2-PPh2-CH2-2,4,6-
C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2)] (2) are obtained
by reacting [PdCl2(cod)] (cod = 1,5-cyclooctadiene) with
the new aryl phosphines PPh2-CH2-2,4,6-C6H2Me3 and
PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2 in
methylene chloride at room temperature. Both complexes
1 and 2, isolated as air stable yellow powders, have been
characterized by correct NMR (1H, 13C, 31P) and mass-spec-
troscopic data, by satisfactory elemental analysis data and
by single-crystal X-ray structure analysis (see Scheme 3).
The molecular structures of 1 and 2 show the palladium
atom to be in a square-planar geometry, surrounded by
two chlorine atoms and two phosphorus atoms in a trans
coordination geometry, see Figs. 1 and 2, respectively. In
2, the coordination of the chelating diphosphine ligand
imposes a significant distortion of the planar geometry:
Fig. 1. POV-ray view of 1, hydrogen atoms are omitted for clarity.
Scheme 3. Synthesis of the palladium complexes trans-[PdCl2(PPh2-CH2-
2,4,6-C6 H2Me3)2] (1) and trans-[PdCl2(g2-PPh2-CH2-2,4,6-C6HMe3-CH2-
2,4,6-C6HMe3-CH2-PPh2)] (2).
Fig. 2. POV-ray view of 2, CHCl3 molecules and hydrogen atoms are
omitted for clarity.

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L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
2.3. Molecular structure dynamics of complexes 1 and 2
studied by variable-temperature NMR
1
The H and 31P{1H} NMR spectra of 1 and of 2 were
studied in toluene-d8 over a temperature range of ꢀ40 ꢁC
to +90 ꢁC. In the case of 1, no significant spectral change
was observed except a slight shift of the signals. Thus, the
single 31P signal of 1 varies from 12.43 ppm (ꢀ40 ꢁC) via
13.50 (+25 ꢁC) and to 13.78 (+90 ꢁC). While the charac-
1
teristic H signal of the benzyl CH2 groups shows up as
a virtual triplet at 4.24 ppm (see above) at +25 ꢁC, this
signal is only slightly shifted to 4.22 ppm at ꢀ40 ꢁC and
to 4.25 ppm at +90 ꢁC, but in both cases it appears as a
broad signal without triplet structure, due to the loss of
resolution. No signal of another compound can be
detected over the whole temperature range, suggesting
that 1, which has a trans configuration in the solid state,
maintains this geometry in solution up to +90 ꢁC. This
interpretation is supported by the comparison with the
Fig. 3. Capped stick representations, along the -CH2–P–Pd–P-CH2– axis,
of the two enantiomers of 2.
Indeed, unlike 1, where the Cl–Pd–Cl and P–Pd–P axes are
perfectly linear, the corresponding angles in 2 are 167.4(1)
and 175.5(1)ꢁ, respectively.
It is noteworthy that in 2 the rigid diphosphine back-
bone generates chirality upon coordination. According to
the sense of the –CH2-P-Pd-P-CH2– torsion angle, two
enantiomers D-2 and K-2 can be distinguished in the same
crystal, see Fig. 3.
benzyl-diphenyl
phosphine
analogue
[(PhCH2-
PPh2)2PdCl2], for which the cis and trans isomers are
known: Whereas the 31P signal of the trans isomer is
observed at 20.06 ppm, this cis isomer gives rise to a sig-
nal at 30.27 ppm (CDCl3, +25 ꢁC), the shift difference
being 10 ppm [18].
In contrast to 1, the more rigid diphosphine complex 2
shows the appearance of a new species above +70 ꢁC.
The 1H NMR spectra of 1 and 2 are as expected, except
for the signals of the methylene groups bound to phospho-
rus, which are complicated by virtual coupling. In 1, the
two equivalent protons of the two equivalent CH2 groups,
for which a doublet (due to 31P-1H coupling) is expected,
show up as pseudo-triplet (a doublet of doublet) due to
the coupling not only with the a-P atom but also with
the c-P atom (through palladium). This type of virtual cou-
pling has also been observed in [{(Ph-CH2)Ph2P}2PdCl2]
[18] and in [(Me3P)2PdCl2] [19]. Accordingly, the methylene
triplet in the 1H NMR spectrum of 1 collapses to give a sin-
glet upon {31P} decoupling.
The situation is even more complex in 2, in which the
rigid diphosphine backbone causes the non-equivalence
1
of the two vicinal protons in both CH2 groups. The H
NMR spectrum shows for the methylene protons in CDCl3
(400 MHz) a doublet of triplets centered at 3.68 ppm and a
second doublet of triplets superimposed by a broad singlet
at 4.30 ppm, which is assigned to the methylene bridge
between the two aromatic rings. In C6D6 (400 MHz) it is
possible to resolve the three signals for the methylene pro-
tons: a doublet of triplets at 3.51 ppm [J(1H–1H) 13.0 Hz,
J(31P–1H) 4.2 Hz], a doublet of triplets at 4.45 ppm
[J(1H–1H) 13.0 Hz, J(31P–1H) 4.2 Hz] and a singlet at
2.76 ppm. Selective proton–proton decoupling as well as
COSY and NOESY experiments show that the vicinal pro-
tons of the two phosphorus-bound CH2 groups couple with
each other and that there is no other 1H–1H coupling.
Accordingly, upon {31P} decoupling, the two doublets of
triplets signals collapse to the two expected doublets, con-
Fig. 4. Variable-temperature 31P{1H} NMR spectra of 2 in C6D6 over
temperature range from 25 ꢁC to 70 ꢁC and back to 25 ꢁC.
1
firming a H–1H coupling of 13 Hz.

L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
4261
The 31P signal of 2 at 19.71 ppm (+25 ꢁC) shifts to
19.34 ppm at ꢀ40 ꢁC and to 20.02 ppm at +90 ꢁC, a second
31P resonance emerging above +70 ꢁC is observed at
14.16 ppm (+90 ꢁC), representing 5–10% of signal inten-
sity. The 31P NMR signals are better resolved in benzene-
d6, even if the temperature range is more restricted in this
case. Fig. 4 displays the variable-temperature 31P{1H}
NMR spectra of 2 in C6D6 over the temperature range
from +25 ꢁC to +70 ꢁC and back to +25 ꢁC. The cooling
experiment shows that the species formed above +70 ꢁC
disappears again upon cooling down. In the 1H NMR spec-
tra, the temperature dependant shift of the benzylic CH2
signals at 4.35 and 3.48 ppm (+25 ꢁC) to 4.29 and 3.39
(ꢀ40 ꢁC) and to 4.33 and 3.53 (+90 ꢁC) is clearly visible,
however, the new species formed above +70 ꢁC (seen in
the 31P spectrum) cannot be detected unambiguously in
The most significant results for the cross-coupling of 4-
bromotoluene and phenyl boronic acid are summarized in
Table 1. As the catalytic turnover numbers after 18 h indi-
cate, there is no significant difference in the catalytic pro-
ductivity at 90 ꢁC. The two complexes are less active at
lower temperatures: At 30 ꢁC, a catalyst/substrate ratio
of 1:1000 is required to observe catalytic activity, the direct
comparison of 1 and 2 shows that the more flexible com-
plex trans-[PdCl2(PPh2-CH2-2,4,6-C6H2Me3)2] (1) is 15
times more active that the analogous rigid complex trans-
[PdCl2(g2-PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-
CH2-PPh2)] (2).
For the cross-coupling of phenyl boronic acid with the
sterically hindered 2,4,6-trimethylphenyl bromide, the
results are summarized in Table 2. At 90 ꢁC, both com-
plexes 1 and 2 are highly active, the turnover numbers
(36500 and 38700 for a catalyst/substrate ratio of
1:100000) being comparable. By contrast, at lower temper-
atures, the rigid diphosphine complex 2 is less active than
1
the H NMR spectrum, due to the low concentration of
5–10% and the complexity of the 1H NMR spectrum.
Given the reversibility of the reaction, the species formed
in low concentration from trans-[PdCl2(g2-PPh2-CH2-
2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2)] (2) may
either be the cis isomer or a trans dimer, see Scheme 4.
The 31P resonance of 14.16 ppm (90 ꢁC) does not allow dis-
crimination between the two possibilities.
Table 1
Catalytic turnover numbers (TON), indicating the moles of product
formed per mol of catalyst used after 18 h, for the Suzuki cross-coupling
of 4-bromotoluene and phenyl boronic acid, catalyzed by 1 and 2
Br
+
(HO)2B
2.4. Catalytic activity of complexes 1 and 2 for Suzuki
cross-coupling reactions
T (ꢁC)
Catalyst/substrate
1
2
The two trans-complexes trans-[PdCl2(PPh2-CH2-2,4,6-
C6H2Me3)2] (1) and trans-[PdCl2(g2-PPh2-CH2-2,4,6-
C6HMe3-CH2-2,4,6-C6HMe3-CH2-PPh2)] (2) have been
studied as catalyst precursors for Suzuki coupling
reactions.
30
30
30
60
60
60
90
90
90
1:1000
300
0
0
1000
9400
44500
1000
21
0
0
1:10000
1:100000
1:1000
1:10000
1:100000
1:1000
1000
8900
1000
1000
10000
98700
Two Suzuki-type reactions have been studied with com-
plexes 1 and 2: On the one hand, the cross-coupling of phe-
1:10000
1:100000
10000
99000
nyl boronic acid with 4-bromotoluene, which is
a
Solvent toluene, base K2CO3, reaction time 18 h.
deactivated bromo derivative, and on the other hand, the
cross-coupling phenyl boronic acid with 2,4,6-trimethyl-
phenyl bromide, which is both, deactivated and sterically
hindered.
Table 2
Catalytic turnover numbers (TON), indicating the moles of product
formed per mol of catalyst used after 18 h, for the Suzuki cross-coupling
of 2,4,6-trimethyl-phenyl bromide and phenyl boronic acid, catalyzed by 1
and 2
Br
+
(HO)2B
T (ꢁC)
Catalyst/substrate
1
2
30
30
30
60
60
60
90
90
90
1:1000
283
0
0
960
4235
15000
926
0
0
0
1:10000
1:100000
1:1000
1:10000
1:100000
1:1000
872
5200
0
1000
8770
1:10000
1:100000
6330
36500
38700
Scheme 4. Possible structures of the high-temperature species formed
reversibly from 2 above 70 ꢁC.
Solvent toluene, base K2CO3, reaction time 18 h.

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L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
the analogous bis(monophosphine) complex 1, which even
shows a turnover of 283 at 30 ꢁC for a catalyst/substrate
ratio of 1:1000.
mixture was added. After intense shaking, the organic layer
was separated, dried with MgSO4 and evaporated in vacuo.
n-Hexane (10 mL) was added, and the solution was fil-
trated though a canula equipped with filter paper. The fil-
trate was dried in vacuo to give a colorless oil (yield 80%).
1H NMR (200 MHz, CDCl3): d = 7.51–7.37(m, 10H),
6.88(s, 2H), 3.48(s, 2H), 2.36(s, 3H), 2.06(s, 6H). 31P
NMR (81 MHz, CDCl3): d = ꢀ15.96 (s). 13C NMR
(100 MHz, CDCl3): d = 133.60(Ar), 133.24(Ar), 129.27
(Ar), 129.23(Ar), 128.99(Ar), 128.70(Ar), 128.56(Ar),
31.95(C2), 21.21(C1), 20.53(C1). Anal. Calc.: C, 82.99; H,
7.28. Found: C, 82.65; H, 7.24%.
3. Conclusion
The trans-complexes 1 and 2, in which ortho-metallation
is impossible because of the methyl substituents in the
ortho-positions, show both a good catalytic performance,
but differ at low temperatures. In the range of 30–60 ꢁC,
with catalyst/substrate ratios between 1000 and 100,000,
1 is more active than 2 in each reaction, suggesting that
the rigidity of the ligand reduces the catalytic performance
at low temperature. Nevertheless, at 90 ꢁC, the catalytic
performance of 1 is similar to that of 2. The slightly supe-
rior performance of 2 for the cross-coupling of the steri-
cally hindered bromide at 90 ꢁC, may be explained by the
emergence of a high-temperature species, reversibly formed
from 2 above 70 ꢁC. This high-temperature species,
observed by variable-temperature 31P NMR spectros-
copy (see 2.3), may be either an isomer of 2, namely
cis-[PdCl2(g2-PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6H-
4.2. Synthesis of bis(3-(bromomethyl)-2,4,6-
trimethylphenyl)methane
A 33 wt.% HBr-AcOH solution (5 mL) was rapidly
added to
a mixture of bis(mesityl)methane (3.15 g,
12.5 mmol), paraformaldehyde (0.750 g, 25 mmol) and
20 mL of glacial acetic acid. The mixture was stirred at
50 ꢁC for one night and then poured into 50 mL of water.
The pH of the mixture was raised to 7 by addition of
K2CO3 (2M), and then 50 mL of dichloromethane were
added. The organic layer was extracted, dried with MgSO4
and evaporated in vacuo to give a white powder, which was
purified by recrystallization from diethyl ether (yield 80%).
1H NMR (400 MHz, CDCl3): d = 6.86(s, 2H), 4.58(s, 4H),
4.09(s, 2H), 2.39(s, 6H), 2.14(s, 6H), 2.13(s, 6H). 13C NMR
(100 MHz, CDCl3): d = 137.87(C4), 137.01(C4), 136.83
(C4), 135.26(C3), 131.31(C4), 32.61(C2), 31.33(C2), 21.67
(C1), 19.65(C1), 16.27(C1). Mass: EI-m/z = 358.1 [M–
Br]+ Anal. Calc.: C, 57.55 ; H, 5.98. Found: C, 57.67; H,
6.03%.
Me3-CH2-PPh2)], or
a dimer of 2, namely trans,
trans-[PdCl2(PPh2-CH2-2,4,6-C6HMe3-CH2-2,4,6-C6HMe3-
CH2-PPh2)]2 (Scheme 4). As this species converts back
to 2 at temperatures below 70 ꢁC, it is not possible to iso-
late this complex.
4. Experimental
All reactions were carried out by using standard Schlenk
techniques under argon atmosphere. The solvent tetrahy-
drofuran (thf) was distilled from sodium benzophenone
under N2 to avoid water and oxygen contaminations. Tol-
uene, n-hexane and diethyl ether were purchased from
Merck (puriss p.a.) and were as well as distilled water,
argon-saturated prior to use. Methylene chloride was dis-
tilled over CaH2 and saturated with N2. The [PdCl2(cod)]
(cod = 1,5-cyclooctadiene) was purchased from Strem
Chemicals. Deuterated chloroform was used as received,
and all NMR spectra were performed with a Bruker spec-
4.3. Synthesis of bis(3-((diphenylphosphino)methyl)-2,4,6-
trimethylphenyl)methane
To a solution of butyl-lithium (1.25 mL, 1.6 M in hex-
ane) in 30 mL of thf, diphenylphosphine (350 lL) was
added dropwise at 0 ꢁC. Then the solution, which turns
red, was stirred for 2 h. Bis((bromomethyl)-2,4,6-trimethyl-
benzene)methane (0.438 g, 1 mmol) was dissolved in a min-
imum of thf and then added dropwise to this solution. The
mixture, which became colorless, was stirred overnight at
room temperature. Then, 60 mL of an ether/water (1:1)
mixture was added. After intense shaking, the organic layer
was separated, dried with MgSO4 and evaporated in vacuo.
The crude product was washed with hot n-hexane (10 mL)
and dried (yield 50%). 1H NMR (400 MHz, CDCl3):
d = 7.45–7.25(m, 20H), 6.73(s, 2H), 3.96(s, 2H), 3.47(bs,
4H), 2.06(bs, 6H), 1.92(s, 6H), 1.82(s, 6H). 13C NMR
(100 MHz, CDCl3): d = 136.78, 136.01, 134.68, 134.64,
133.63, 133.44, 131.03, 129.06, 128.74, 128.67, 33.15,
30.34, 21.51, 20.78, 17.25. 31P NMR (81 MHz, CDCl3):
d = ꢀ14.80 (s). Mass: APCI-m/z = 681.1 [648 + O2 + H]+
(bisoxidation product). Anal. Calc.: C, 83.31; H, 7.15.
Found: C, 83.03; H, 7.12%.
1
trometer (400 MHz for H, 81 MHz for 31P, and 100 MHz
for 13C). All gas chromatography analyses were done on a
GC DANI 86.10, equipped with a fused silica capillary col-
umn OPTIMA d-3 (0.5 lm, 30 m · 0.25 mm) and an inte-
grator SP-4400.
4.1. Synthesis of diphenyl(2,4,6-trimethylbenzyl)phosphine
To a solution of butyl-lithium (2.86 mL, 1.4 M in hex-
ane) in 30 mL of thf, diphenylphosphine (796 lL, 4 mmol)
was added dropwise at 0 ꢁC. Then the solution, which turns
red, was stirred for 2 h. A solution of (bromomethyl)-2,4,6-
trimethylbenzene (0.852 g, 4 mmol), dissolved in a mini-
mum of thf, was then added dropwise to the solution.
The mixture, which became colorless, was stirred overnight
at room temperature. Then, 60 mL of an ether/water (1:1)

L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
4263
Table 3
J = 13.0 and 4.2 Hz, 2H), 2.48(s, 6H), 2.40(s, 6H), 1.17(s,
6H). 13C NMR (100 MHz, CDCl3): d = 138.02(C4),
136.67(C4), 135.37(C3), 134.94(C4), 134.20(C3), 130.91
(C4), 130.64(C3), 128.86(C4), 128.33(C4), 127.26(C3),
33.75(C2), 28.62(C2), 24.15(C1), 21.98(C1), 19.63(C1).
31P NMR (81 MHz, CDCl3): d = 20.56 (s). Mass: ESI-
m/z = 787.4 [M–Cl–H]. Anal. Calc.: C, 65.42; H, 5.61.
Found: C, 65.19; H, 5.58%.
Crystallographic and selected experimental data of complexes 1 and 2
1
2 Æ 2CHCl3
Chemical formula
Formula weight
Crystal system
C44H46Cl2P2Pd
814.05
Monoclinic
P21/a
Yellow plate
0.48 · 0.42 · 0.2
10.5553(8)
17.5232(14)
10.3940(9)
90
92.516(9)
90
1920.6(3)
2
203(2)
1.408
0.736
3.92 < 2h < 51.86
3661
2977
0.0791
0.0328, wR2 0.0816
0.0416, wR2 0.0847
0.985
0.801, ꢀ1.484
C47H48Cl8P2Pd
1064.79
Monoclinic
C2/c
Yellow rod
0.18 · 0.10 · 0.05
26.079(5)
13.993(3)
15.307(3)
90
120.98(3)
90
4789.0(17)
4
173(2)
1.477
0.933
3.96 < 2h < 51.96
4493
2631
0.0620
0.0554, wR2 0.1266
0.1044, wR2 0.1440
0.895
Space group
Crystal colour and shape
Crystal size
˚
a (A)
˚
b (A)
4.6. Catalytic reactions
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
In a Schlenk tube, the catalyst was added (in the molar
ratio given in Table 1 or 2) to a solution of 138 mg
(0.5 mmol) of K2CO3 Æ 1.5 H2O, 91 mg (0.75 mmol) of
phenylboronic acid and 0.5 mmol of the aryl bromide in
5 mL of toluene. Then, the mixture was heated to the
desired temperature (Table 1 or 2) and stirred for 18 h.
After cooling, the solution was filtrated over a small silica
gel column then eluted with ether (20 mL). The filtrate was
combined with the ether washings, and the solution was
analyzed by GC.
3
˚
V (A )
Z
T (K)
Dc (g cmꢀ3
)
l (mmꢀ1
)
Scan range (ꢁ)
Unique reflections
Reflections used [I > 2r(I)]
Rint
Final R indices [I > 2r(I)]a
R indices (all data)
Goodness-of-fit
4.7. X-ray crystallographic study
ꢀ3
˚
Max, Min Dq/e (A
)
1.615, ꢀ1.345
P
P
2
2 1=2
a
Crystals of 1 and 2 were mounted on a Stoe Image Plate
Diffraction system equipped with a / circle goniometer,
using Mo Ka graphite monochromated radiation (k =
Structures were refined on F 2o : wR2 ¼ ½ ½wðF o2 ꢀ F c2Þ ꢁ= wðF 2oÞ ꢁ
,
P
2
where wꢀ1 ¼ ½ ðF o2Þ þ ðaPÞ þ bPꢁ and P ¼ ½maxðF o2; 0Þ þ 2F 2c ꢁ=3.
˚
0.71073 A) with / range 0–200ꢁ, increment of 1.2 and 1
4.4. Synthesis of diphenyl(2,4,6-trimethylbenzyl)phosphine
palladium dichloride (1)
respectively, 2h range from 2.0 to 26ꢁ, Dmax ꢀ Dmin
=
˚
12.45–0.81 A. All the structures were solved by direct meth-
ods using the program SHELXS-97 [21]. Refinement and all
further calculations were carried out using SHELXL-97 [22].
In 1 and 2 the H-atoms were included in calculated posi-
tions and treated as riding atoms using the SHELXL default
parameters. In all cases the non-H atoms were refined
anisotropically, using weighted full-matrix least-square on
F2. Crystallographic details are summarized in Table 3.
Figures of 1 and 2 were drawn with POV-ray [23] and
Fig. 3 with MERCURY [24].
In 40 mL of dichloromethane, diphenyl(2,4,6-trimeth-
ylbenzyl)phosphine (1 mmol, 0.259 g) and PdCl2(cod)
(0.142 g, 0.5 mmol) were stirred at room temperature for
2 days. Then, the solvent was evaporated and the residue
was purified by column chromatography on silica gel with
dichloromethane (yield 80%). 1H NMR (400 MHz,
CDCl3): d = 7.55–7.50(m, 8H), 7.41(t, J = 7.4 Hz, 4H),
7.31–7.24(m, 8H), 6.65(s, 4H), 4.21(t, J = 3.6 Hz, 4H),
2.22(s, 6H), 2.02(s, 12H). 31P NMR (81 MHz, CDCl3):
d = 13.68(s). 13C NMR (100 MHz, CDCl3): d = 138.23,
134.87, 134.81, 134.75, 130.70, 129.22, 128.08, 128.04,
27.42(C2), 22.07(C1), 21.19(C1). Anal. Calc.: C, 64.91; H,
5.70. Found: C, 64.65; H, 5.67%.
Acknowledgements
Financial support of the Fond National Suisse de la
Recherche Scientifique is gratefully acknowledged (Grant
No. 200020-105’132). We thank Professor H. Stoeckli-
´
ˆ
4.5. Synthesis of bis(3-((diphenylphosphino)methyl)-2,4,6-
trimethylphenyl)methane palladium dichloride (2)
Evans (Universite de Neuchatel, Switzerland) for helpful
discussions.
In 100 mL of dichloromethane, bis(3-((diphenylphos-
phino)methyl)-2,4,6-trimethylphenyl)methane (0.4 mmol,
0.259 g) and PdCl2(cod) (0.12 g, 0.4 mmol) were stirred at
room temperature for 2 days. Then, solvent was evapo-
rated and the residue was purified by column chromatogra-
phy on silica gel with dichloromethane (yield 70%). 1H
NMR (400 MHz, CDCl3): d = 7.99–7.91(m, 4H), 7.55–
7.48(m, 6H), 7.32(t, J = 7.5 Hz, 2H), 7.13(t, J = 7.5 Hz,
4H), 6.78–6.71(m, 6H), 4.35–4.26(m, 4H), 3.68(dt,
Appendix A. Supplementary data
CCDC-602844 1 and 602845 2 contain the supplemen-
tary crystallographic data for this paper. These data can
be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ,
UK; fax: (internat.) +44 1223/336 033; E-mail: depos-
it@ccdc. cam.ac.uk]. Supplementary data associated with

4264
L. Chahen et al. / Journal of Organometallic Chemistry 691 (2006) 4257–4264
[9] S.D. Walker, T.E. Barder, J.R. Martinelli, S.L. Buchwald, Angew.
Chem. Int. Ed. 43 (2004) 1871–1876.
this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2006.06.020.
[10] Z. Freixa, M.S. Beentjes, G.D. Batema, C.B. Dieleman, G.P.F. van
Strijdonck, J.N.H. Reek, P.C.J. Kamer, J. Fraanje, K. Goubitz,
P.W.N.M. van Leeuwen, Angew. Chem. Int. Ed. 42 (2003) 1284–1287.
[11] R.C. Smith, J.D. Protasiewicz, Organometallics 23 (2004) 4215–
4222.
[12] R.C. Smith, C.R. Bodner, M.J. Earl, N.C. Sears, N.E. Hill, L.M.
Bishop, N. Sizemore, D.T. Hehemann, J.J. Bohn, J.D. Protasiewicz,
J. Organomet. Chem. 690 (2005) 477–481.
[13] M. Kranenburg, Y.E.M. van der Burgt, Organometallics 14 (1995)
3081–3089.
[14] P.C.J. Kramer, P.W.N.M. van Leeuwen, Acc. Chem. Res. 34 (2001)
895–904.
References
[1] (a) N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457–2483;
(b) S. Kotha, K. Lahiri, D. Kashinath, Tetrahedron 58 (2002) 9633–
9695;
(c) A. Suzuki, J. Organomet. Chem. 653 (2002) 83–90;
(d) F. Bellina, A. Carpita, R. Rossi, Synthesis 15 (2004) 2419–2440.
[2] S.R. Chemler, D. Trauner, S.J. Danishefsky, Angew. Chem. Int. Ed.
40 (2001) 4544–4568.
[3] P. Espinet, A.M. Echavarren, Angew. Chem. Int. Ed. 43 (2004) 4704–
4734.
[4] (a) A. Gillie, J.K. Stille, J. Am. Chem. Soc. 102 (1980) 4933–4941;
(b) A. Moravskiy, J.K. Stille, J. Am. Chem. Soc. 103 (1981) 4182–
4186.
[5] A. Zapf, M. Beller, Chem. Eur. J. 7 (2001) 2908–2915.
[6] M. Beller, H. Fischer, W.A. Herrmann, K. Ofele, C. Brossmer,
Angew. Chem. Int. Ed. 34 (1995) 1848–1849.
[7] R.B. Bedford, S.L. Hazelwood (ne´eWelch), M.E. Limmert, D.A.
Albisson, S.M. Draper, P.N. Scully, S.J. Coles, M.B. Hursthouse,
Chem. Eur. J. 9 (2003) 3216–3227.
[15] J. Yin, S.L. Buchwald, J. Am. Chem. Soc. 124 (2002) 6043–6048.
[16] S. Burger, B. Therrien, G. Suss-Fink, Eur. J. Inorg. Chem. (2003)
¨
3099–3103.
[17] M. Niehues, J. Organomet. Chem. 663 (2002) 192–203.
[18] A.W. Verstuyft, D.A. Redfield, L.W. Cary, J.H. Nelson, Inorg.
Chem. 16 (1977) 2776–2786.
[19] J.P. Facker Jr., J.A. Fetchin, J. Mayhew, W.C. Seidel, T.J. Swift, M.
Weeks, J. Am. Chem. Soc. 91 (1969) 1941–1947.
[20] R.B. Bedford, S.L. Hazelwood, P.N. Horton, M.B. Hursthouse,
Dalton Trans. (2003) 4164–4174.
[21] G.M. Sheldrick, Acta Cryst. A46 (1990) 467–473.
[22] G.M. Sheldrick, SHELXL-97, University of Go¨ttingen, Go¨ttingen,
Germany, 1999.
[23] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[24] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P.
McCabe, J. Pearson, R. Taylor, Acta Cryst. B58 (2002) 389–397.
[8] (a) T.E. Barder, S.D. Walker, J.R. Martinelli, S.L. Buchwald, J. Am.
Chem. Soc. 127 (2005) 4685–4696;
(b) J. Yin, M.P. Rainka, X. Zhang, S.L. Buchwald, J. Am. Chem.
Soc. 124 (2002) 1162–1163;
(c) J.P. Wolfe, R.A. Singer, B.H. Yang, S.L. Buchwald, J. Am.
Chem. Soc. 121 (1999) 9550–9561.