Syntheses of a 2,6-bis-(methylphospholyl)pyridine ligand and its cationic Pd(II) and Ni(II) complexes - Application in the palladium-catalyzed synthesis of arylboronic esters

Article abstract of DOI:10.1016/j.jorganchem.2004.06.035

2,6-Bis(2,5-diphenylphospholyl-1-methyl)pyridine (2) was prepared from the reaction of 2,5-diphenylphospholide anion with 2,6-bis(chloromethyl)pyridine. The X-ray crystal structure of 2 was recorded. Reaction of 2 with [Pd(COD)Cl₂] in the presence of AgBF₄ yields the cationic complex [Pd(2)Cl][BF₄] (3). The analogous Ni complex [Ni(2)Br][BF₄] (4) was prepared in a similar way by reacting ligand 2 with [NiBr₂(DME)] in the presence of AgBF₄ and its formulation was confirmed by an X-ray crystal structure study. Complex 3 efficiently catalyzes the coupling between pinacolborane and iodo and bromoarenes with good TON (up to 1 × 10⁵ with iodo derivatives and 8.9 × 1 0³ with bromo derivatives).

Full text of DOI:10.1016/j.jorganchem.2004.06.035

Journal of Organometallic Chemistry 689 (2004) 2988–2994
www.elsevier.com/locate/jorganchem
Syntheses of a 2,6-bis-(methylphospholyl)pyridine ligand and
its cationic Pd(II) and Ni(II) complexes – application in
the palladium-catalyzed synthesis of arylboronic esters
*
Mohand Melaimi, Claire Thoumazet, Louis Ricard, Pascal Le Floch
´ ´ ´ ´
Laboratoire ‘‘heteroelements et Coordination’’, UMR CNRS 7653, Ecole Polytechnique, 91128 Palaiseau cedex, France
Received 3 May 2004; accepted 21 June 2004
Available online 31 July 2004
Abstract
2,6-Bis(2,5-diphenylphospholyl-1-methyl)pyridine (2) was prepared from the reaction of 2,5-diphenylphospholide anion with 2,6-
bis(chloromethyl)pyridine. The X-ray crystal structure of 2 was recorded. Reaction of 2 with [Pd(COD)Cl2] in the presence of
AgBF4 yields the cationic complex [Pd(2)Cl][BF4] (3). The analogous Ni complex [Ni(2)Br][BF4] (4) was prepared in a similar
way by reacting ligand 2 with [NiBr2(DME)] in the presence of AgBF4 and its formulation was confirmed by an X-ray crystal struc-
ture study. Complex 3 efficiently catalyzes the coupling between pinacolborane and iodo and bromoarenes with good TON (up to
1 · 105 with iodo derivatives and 8.9 · 103 with bromo derivatives).
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Arylboronic esters; Catalysis; Complexes; Phosphorus heterocycles; Nickel; Palladium
1. Introduction
applications in catalysis of heteroditopic chelates and
multidentate ligands incorporating phospholes, we
recently reported the synthesis of an easily available bi-
dentate PN ligand featuring a pyridine and the 2,5-diphe-
nylphosphole ring connected by a methylene group. The
low sensitivity towards oxidation and the high thermal
resistance of this phosphole are two important factors
that make it very attractive for the elaboration of robust
catalysts. Thus, we recently showed that the chlororuthe-
nium-cymene complex of this 2-(2,5-diphenyl-1-
methylphospholy)pyridine ligand exhibited a remarkable
In recent years, tridentate ligands of the type PXP
(X = C, N) have found numerous applications in coordi-
nation chemistry and are now increasingly implicated in
homogeneous catalysis [1]. It is now well established that
the role of ancillary phosphine groups is crucial and a fine
tuning of the electronic and stereochemical properties of
transition metal complexes can be achieved by adjusting
the substitution scheme around phosphorus. However,
most systems reported so far incorporate acyclic tertiary
phosphine groups and only little attention has been paid
to the synthesis and reactivity of mixed PXP ligands fea-
turing phosphorus heterocycles [2]. As part of a large pro-
gram aimed at exploring the synthesis and potential
activity
in
the
ruthenium-catalyzed
transfer
hydrogenation of ketones with TON up to 20 · 106
(Scheme 1) [3].
This preliminary result encouraged us in pursuing our
investigation on such systems and we logically extended
our studies to the synthesis of PNP derivatives featuring
a central pyridine unit as ligand. Herein we report
the synthesis of the 2,6-bis-(methylphospholyl)pyridine
*
Corresponding author. Tel.: +33-1-69334570; fax: +33-1-
69333990.
E-mail address: lefloch@poly.polytechnique.fr (P.L. Floch).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.06.035

M. Melaimi et al. / Journal of Organometallic Chemistry 689 (2004) 2988–2994
2989
Ph
Ph
P
N
N
P
Ru
Cl
Ph
Ph
Scheme 1.
ligand and its PdCl and NiBr complexes as well as their
catalytic activity in the Miyaura coupling reaction which
allows the synthesis of arylboronic esters.
Fig. 1. ORTEP drawing of one molecule of ligand 2. Ellipsoids are
scaled to enclose 50% of the electron density. The numbering is
arbitrary and different from that used in the 13C NMR spectrum.
2. Results and discussion
Table 1
˚
Selected interatomic distances (A) and angles (ꢁ) (with e.s.d.s in
parentheses) in compound 2
2.1. Synthesis
P1–C1
C1–C2
C2–C3
C3–C4
C4–P1
1.815(2)
1.358(3)
1.442(3)
1.809(2)
1.809(2)
P1–C5
C5–C6
C6–C7
C7–C8
C6–N1
1.867(2)
1.509(2)
1.392(3)
1.386(2)
1.344(2)
The synthetic scheme followed for the synthesis of
ligand 2 relies on the reactivity of the phospholide anion
1 towards halogenoalkyls. Reaction of two equivalents
of phospholide anion 1, prepared by cleavage of PP
bond of the corresponding 1,10-biphosphole [4], with
2,6-bis-(chloromethyl)pyridine in THF at room temper-
ature cleanly afforded ligand 2 in good yield (86%)
(Scheme 2). The formulation of 2 was unambiguously
C4–P1–C1
C4–P1–C5
C1–P1–C5
C1–C1–P1
C4–C3–C2
91.1(1)
C1–C2–C3
C3–C4–P1
C6–C5–P1
N1–C5–C6
C7–C6–C5
115.2(2)
109.5(2)
106.9(1)
116.2(2)
121.0(2)
101.9(1)
104.0(1)
108.9(2)
114.8(2)
1
established on the basis of H, 31P and 13C NMR data
and elemental analyses. Additional evidence was also
given by X-ray crystal structure analysis. An ORTEP
view of one molecule of 2 is presented in Fig. 1. Selected
bond distances and bond angles are listed in Table 1 and
crystal data are summarized in Table 2. As can be seen,
in the solid state 2 adopts a conformation that minimizes
the steric congestion between the two pendant methyl-
enephosphole arms, one phenyl ring of each phosphole
subunit partially overlapping with the central pyridine
chloromethane at room temperature. Complex 3 was
isolated with a very good yield (95%) as an air stable
orange solid after purification (Scheme 3). Though the
structure of the intermediary complex was not investi-
gated in details, the singlet observed in the 31P NMR
spectrum of the crude reaction mixture suggests that a
symmetrical complex is formed and that the ancillary
phosphole ligands are coordinated (d = 29.5 ppm).
However, on the simple basis of this 31P NMR spec-
trum, we could not conclude whether this intermediate
is a cationic tetracoordinated or a neutral pentacoordi-
nated specie. Indeed, Nelson and Dahlhoff [6] have
showed that neutral pentacoordinated complexes can al-
so be formed when 2,6-bis(diphenylphosphinomethyl)-
pyridine is used as ligand with Fe, Co and Ni(II)
salts. All NMR data and elemental analyzes support
the formulation proposed for 3. Its 31P NMR signal ap-
pears as a singlet thus confirming that the two phospho-
rus atoms are magnetically equivalent and that the
structure is symmetric (trans arrangement of the phosp-
˚
ring (shorter interatomic distance of 3.2 A). The two
phospholyl units are roughly planar, the phosphorus
atoms escaping from the plane defined by the four carbon-
ring atoms only from 5ꢁ. Examination of metric data
within the phosphole ring do not deserve further com-
ment and compare with those recorded for the 1,2,5-
triphenylphosphole derivative [5].
The synthesis of the cationic palladium complex 3
was achieved by reacting ligand 2 with [Pd(COD)Cl2]
in the presence of AgBF4 as chloride abstractor in di-
1
hole ligands). On the other hand in the H NMR spec-
1/2
trum, coordination of the pyridine moiety is evidenced
by a significant downfield shift of the H aromatic signals
(doublet at 7.68 and triplet at 8.07 ppm with a
3JHH = 7.8 Hz). In the 13C NMR spectrum, the CH2
group and Ca and Cb carbon atoms at phosphorus in
the phosphole moieties appear as a AXX0 spin-system
pattern, as expected. Unfortunately, despite many
Ph
P
Ph
P
N
N
Cl
Cl
Ph
Ph
P
Li
THF, RT
Ph
Ph
2
1
Scheme 2.

2990
M. Melaimi et al. / Journal of Organometallic Chemistry 689 (2004) 2988–2994
Table 2
Crystallographic data for compound 2
BF4
Ph
P
Ph
P
Molecular formula
Molecular weight
Crystal habit
C41H33Cl6NP2
814.32
Colorless plate
1) [NiBr2(DME)]
N
2
Ni
2) AgBF4
Crystal dimensions (mm)
Crystal system
Space group
0.20 · 0.20 · 0.06
Monoclinic
Br
Ph
Ph
MeCN/CH2Cl2, RT
4
C2/c
27.206(5)
˚
a (A)
Scheme 4.
˚
b (A)
6.223(5)
22.443(5)
˚
c (A)
b (ꢁ)
94.820(5)
3786(3)
3
˚
V (A )
dium complex 3, an intermediate which adopts a sym-
metrical structure (tetra or pentacoordinated)
is transiently formed (broad signal at 30.2 ppm in
31P NMR).
Z
4
1.429
d (g cmꢀ3
F(000)
)
1672
0.570
l (cmꢀ1
Absorption corrections
)
Multiple scans; 0.8945 min,
0.9666 max
KappaCCD
All NMR data of complex 4 are very similar to those
of the palladium derivative 3 and the magnetic equiva-
lence of the two coordinated pendant methylphosphole
ancillary ligands is evidenced in 1H NMR and 13C
NMR by the presence of second order spin-system pat-
terns. Fortunately, single crystals of 4 could be grown by
slow evaporation of a dichloromethane solution of the
complex at room temperature. An ORTEP view of
one molecule of 4 is presented in Fig. 2. The most signif-
icant bond lengths and bond angles are listed in Table 3
and crystal data are summarized in Table 4. As can be
seen, the complex adopts a square planar geometry,
the two phosphole ligands lying in a mutually trans con-
figuration. Intramolecular bond distances and bond an-
gles compare with those of dicationic Ni(II) complexes
of the (diphenylphosphinomethyl)pyridine ligand [7].
Apart from the spatial arrangement of the four phenyl
groups that seem to hinder the access to the metal
centre, the structure of 4 deserves no special comments.
Diffractometer
X-ray source
Mo Ka
0.71069
˚
k (A)
Monochromator
Graphite
150.0(10)
T (K)
Scan mode
/ and x scans
27.47
Maximum h
hkl ranges
ꢀ35 35; ꢀ7 8; ꢀ29 29
Reflections measured
Unique data
Rint
7134
4314
0.0202
3451
Reflections used
Criterion
>2r(I)
Refinement type
Hydrogen atoms
Parameters refined
Reflections/parameter
wR2
F2
Mixed
231
14
0.1201
R1
0.0436
0.0490; 5.9725
1.045
Weights a, b
Goodness-of-fit
Difference peak/hole (e A
ꢀ3
˚
)
0.762(0.061)/ꢀ0.706(0.061)
BF4
Ph
1) [Pd(COD)Cl2]
CH2Cl2, RT
Ph
P
N
2
P
Pd
2) AgBF4, RT
Cl
Ph
Ph
3
Scheme 3.
attempts using different solvents or crystallization tech-
niques, no suitable single crystals of complex 3 could
be obtained. The synthesis of the nickel complex 4 was
achieved following a similar procedure. Reaction of
ligand 2 with [NiBr2(DME)] in a mixture of CH3CN/di-
chloromethane (1:1) at room temperature followed by a
treatment with AgBF4 furnished 4 in a very good yield
Fig. 2. ORTEP drawing of one molecule of complex 4. Ellipsoids are
scaled to enclose 50% of the electron density. The numbering is
arbitrary and different from that used in the 13C NMR spectrum.
(95%) as
(Scheme 4). Note that, like in the synthesis of the palla-
a
brownish solid after purification

M. Melaimi et al. / Journal of Organometallic Chemistry 689 (2004) 2988–2994
2991
Table 3
Table 5
Cross-coupling reaction between iodo and bromoarenes with pina-
colborane using complex 3 as catalyst (yields given by GC)
˚
Selected interatomic distances (A) and angles (ꢁ) (with e.s.d.s in
parentheses) in complex 4
P1–C1
C1–C2
C2–C3
C3–C4
C4–C15
C1–C9
P1–C5
1.806(3)
1.349(5)
1.447(5)
1.349(5)
1.452(5)
1.466(5)
1.829(3)
C5–C6
C6–N1
C6–C7
C7–C8
P1–Ni1
N1–Ni1
Ni1–Br1
1.487(4)
1.368(3)
1.379(4)
1.369(4)
2.1571(7)
1.911(3)
2.2709(7)
Ar–X (X = I, Br)
T (h)
% cat
Yield (%)
TON (%)
C6H5I
48
48
48
48
40
40
40
40
0.001
0.001
0.001
0.001
0.01
100
100
93
100 · 103
100 · 103
93 · 103
91 · 103
86 · 102
55 · 102
89 · 102
81 · 102
p-IC6H5Ome
o-IC6H5Ome
o-IC6H4Me
C6H5Br
91
86
p-BrC6H4COMe
p-BrC6H4Ome
p-BrC6H4Me
0.01
0.01
55
89
C4–P1–C1
C1–C2–C3
C3–C4–P1
C6–N1–Ni1
P1–Ni1–P10
94.3(2)
P1–C1–C2
C2–C3–C4
C5–C6–N1
N1–Ni1-Br1
N1–Ni1–P1
106.5(3)
116.5(3)
119.1(3)
180.0
0.01
81
116.4(3)
106.3(3)
120.9(2)
176.35(5)
3 (0.001%/mol, X = I)
(0.01%/mol, X = Br)
88.18(2)
R
R
O
B
O
O
X
H
B
+
O
Et3N, dioxane, 80˚C
Table 4
Crystallographic data for compound 4
Scheme 5.
Molecular formula
Molecular weight
Crystal habit
C39H31BBrF4NNiP2
801.02
acetophenone with phenylboronic acid to yield biphenyl
(Suzuki coupling) [8], no complete conversion was ob-
served (51%) using 0.001% of catalyst after 2 h in
toluene under reflux (TON = 51 · 103). A modest con-
version yield (42%) was also obtained in the coupling
of bromobenzene with styrene (Heck reaction) [9] after
15 h heating in dioxane at 80 ꢁC (TON = 42 · 103) and
triethylamine as base. Additional experiments using
other solvents such as NMP, MeCN, yielded compara-
ble results. Interestingly, much more significant
performances were obtained in the Miyaura cross-
coupling process that allows the preparation of arylbo-
ronic esters[10] from pinacolborane and halogenoarenes
[11]. We found that iodoaromatics are easily converted
at 80 ꢁC in dioxanne using 0.001% of catalyst and triethyl-
amine as base (TON about 100 · 103, see Table 5). The
conversion of bromoarenes proved to be more difficult
to achieve and 0.01% of catalyst was needed to achieve
a partial conversion after 40 h of heating (see Scheme 5)
(TON between 55 and 89 · 102, see Table 5). However,
to the best of our knowledge, the TON obtained with
complex 3 as catalyst are the highest reported so far in
this Miyaura cross-coupling process.
Red cube
0.20 · 0.20 · 0.16
Rhombohedral
Crystal dimensions (mm)
Crystal system
Space group
ꢀ
R3c
˚
a (A)
29.2369(4)
21.3678(5)
15818.0(5)
18
˚
c (A)
3
˚
V (A )
Z
d (g cmꢀ3
F(000)
)
1.514
7308
l (cmꢀ1
)
1.831
Multiple scans; 0.7109 min, 0.7583 max
KappaCCD
Absorption corrections
Diffractometer
X-ray source
Mo Ka
0.71073
˚
k (A)
Monochromator
T (K)
Scan mode
Graphite
150.0(10)
/ and x scans
27.50
Maximum h
hkl ranges
ꢀ27 30; ꢀ37 26; ꢀ18 27
Reflections measured
Unique data
Rint
18844
4018
0.0387
3093
Reflections used
Criterion
>2r(I)
Refinement type
Hydrogen atoms
Parameters refined
Reflections/parameter
wR2
F2
Mixed
224
To summarize, we reported here the first example of a
PNP pincer ligand featuring ancillary phosphole as
ligands. Further studies aimed at exploring the catalytic
activity of this new type of ligands and their functional
derivatives are under progress in our laboratories and
will be reported in due course.
13
0.1226
R1
0.0402
0.0562; 83.345
1.060
Weights a, b
Goodness-of-fit
Difference peak/hole (e A
ꢀ3
˚
)
1.960(0.088)/ꢀ0.384(0.088)
2.2. Catalysis
3. Experimental
The catalytic activities of complexes 3 and 4 were in-
vestigated in three cross-coupling processes using low
loading of catalyst. In all our experiments, the nickel
complex 4 showed no activity. Its palladium analogue
3 yielded better results. Thus, in the reaction of 4-bromo-
3.1. General procedure
All reactions were routinely performed under an inert
atmosphere of argon or nitrogen by using Schlenk and

2992
M. Melaimi et al. / Journal of Organometallic Chemistry 689 (2004) 2988–2994
glove-box techniques and dry deoxygenated solvents.
Dry THF, ether, dioxane and hexanes were obtained
by distillation from Na/benzophenone and dry CH2Cl2
and CDCl3 from P2O5. Dry CD2Cl2 was distilled and
and the reaction mixture was stirred at room tempera-
ture for one hour. Then, filtration on celite allowed
the elimination of AgCl salt and the solvent was evapo-
rated yielding a viscous orange oil which was washed
with hexanes (3 · 20 mL) to remove 1,5-cyclooctadiene.
Complex 3 was obtained as an orange solid. Yield: 152
mg (95%). 31P NMR (CD2Cl2, 25 ꢁC): d = 33.2; 1H
˚
stored, like CDCl3, on 4 A Linde molecular sieves. Nu-
clear magnetic resonance spectra were recorded on a
Bruker Avance 300 spectrometer operating at 300
MHz for H, 75.5 MHz for 13C and 121.5 MHz for
NMR (CD2Cl2, 25 ꢁC):
d
4.34 (vt, A2A02XX0,
1
P
31P. Solvent peaks are used as internal reference relative
to Me4Si for 1H and 13C chemical shifts (ppm); 31P
chemical shifts are relative to a 85% H3PO4 external
reference and coupling constants are expressed in Hertz.
The following abbreviations are used: b, broad; s, sin-
glet; d, doublet; t, triplet; m, multiplet; p, pentuplet;
sext, sextuplet; sept, septuplet; v, virtual. Mass spectra
were obtained at 70 eV with a HP 5989B spectrometer
coupled to a HP 5980 chromatograph by the direct inlet
method. Elemental analyses were performed by the
‘‘Service dÕanalyse du CNRS’’, at Gif sur Yvette,
France. [NiBr2(DME)] [12], [Pd(COD)Cl2] [13], 2,6-bis-
(chloromethyl)pyridine [14] and triphenylphosphole[15]
were prepared according to literature procedures. All
other reagents and chemicals were obtained commer-
cially and used as received.
JPH = 10.8 Hz, 4 H, CH2), 7.32–7.40 (m, 12 H, H
meta and H para of phenyls), 7.47 (vt, A2A02XX0,
P
JPH = 30.9 Hz, 4H, Hb of phosphole), 7.68 (d,
3JHH = 7.8 Hz, 2 H, H meta of pyridine), 7.77 (m, 8
3
H, H ortho of phenyl groups), 8.07 (t, JHH = 7.8 Hz,
1 H, H para of pyridine); 13C NMR (CD2Cl2, 25 ꢁC):
P
d 39.1 (vt, AXX0, JPC = 21.6 Hz, PCH2), 125.4 (vt,
P
AXX0,
JPC = 13.8 Hz, C meta pyridine), 127.4 (vt,
P
AXX0, JPC = 7.6 Hz, C ortho phenyl), 130.0 (s, C meta
or para of phenyl), 130.1 (s, C meta or para of phenyl),
P
132.1 (vt, AXX0,
JPC = 14.8 Hz, Cipso of phenyl),
P
138.2 (vt, AXX0, JPC = 20.53 Hz, Cb of phosphole),
P
138.8 (vt, AXX0,
JPC = 50.3 Hz, Ca of phosphole),
142.6 (s, C para of pyridine), 162.8 (vt, AXX0,
P
JPC = 9.1 Hz, C ortho pyridine); Anal. Calc. for
C39H31BClF4NP2Pd: C, 58.24; H, 3.88. Found: C,
58.11; H, 3.76%.
3.2. Synthesis of ligand (2)
To a freshly prepared solution of phospholide anion
1 (6 mmol) in THF (50 mL) at room temperature was
added 2,6-bis(chloromethyl)pyridine (528 mg, 3 mmol).
After stirring for 20 min at this temperature, the com-
plete formation of 2 was attested by 31P NMR spectros-
copy. After evaporation of the solvent, hexanes (100
mL) was added and the resulting mixture was filtered.
After evaporation of hexanes, compound 2 was ob-
tained as a yellow powder which was re-crystallized in
MeOH. Yield: 1.482 g (86%). 31P NMR (CDCl3, 25
3.4. Synthesis of complex (4)
Ligand 2 (161 mg, 0.2 mmol) was added to a mixture
of [NiBr2(DME)] (61 mg, 0.2 mmol) in dichlorometh-
ane/acetonitrile (2 mL/2 mL) at room temperature.
After stirring for 10 min, AgBF4 (39 mg, 0.2 mmol)
was added and the reaction mixture was stirred at room
temperature for one hour. After filtration on celite, the
solvents were evaporated yielding complex 4 as a brown
powder. Crystallization of 4 was achieved in dichloro-
methane at room temperature. Yield: 152 mg (95%).
1
ꢁC): d ꢀ1.9; H NMR (CDCl3, 25 ꢁC): d 3.02 (s, 4 H,
PCH2), 5.93 (d, 3JHH = 7.7 Hz, 2H, H meta of pyridine),
6.67 (t, 3JHH = 7.7 Hz, 1H, H para of pyridine), 6.98 (d,
3JPH = 9.5 Hz, 4H, Hb of phosphole), 7.18–7.51 (m,
20H, CH of phenyl groups); 13C NMR (CDCl3, 25
31P NMR (CD3CN, 25 ꢁC): d = 32.3. 1H NMR
P
(CD3CN, 25 ꢁC): d 4.35 (vt, A2A0 XX0,
Hz, 4 H, CH2), 7.40–7.46 (m, 12 H, H meta and H para
JPH = 8.4
2
P
of phenyls), 7.59 (vt, A2A02XX0, JPH = 30.6 Hz, 4H,
3
3
ꢁC): d 33.4 (d, JPC = 20.3 Hz, CH2), 118.7, (s, C meta
of pyridine); 125.1–133.4 (phenyl groups and C para of
Hb of phosphole), 7.62 (d, JHH = 7.8 Hz, 2 H, H meta
of pyridine), 7.96 (m, JHH = 7.5 Hz; 8 H, H ortho of
3
3
3
phenyl groups), 8.10 (t, JHH = 7.8 Hz, 1 H, H para of
pyridine), 137.7 (d, JPC = 13.6 Hz, Ca of phosphole),
152.4 (d, JPC = 4.5 Hz, Cb of phosphole); 153.7 (s, C
pyridine); 13C NMR (CD3CN, 25 ꢁC): d 35.2 (vt, AXX0,
2
P
P
ortho of pyridine); MS, m/z (relative intensity): 575
(M+, 90%). Anal. Calc. for C39H31NP2: C, 81.38; H,
5.43. Found: C, 81.31; H, 5.37%.
JPC = 20.4 Hz, PCH2), 122.7 (vt, AXX0, JPC = 11.5
Hz, C meta pyridine), 124.62 (s, C ortho phenyl), 127.25
(s, C meta or para of phenyl), 127.47 (s, C meta or para
P
of phenyl), 129.8 (vt, AXX0, JPC = 13.5 Hz, Cipso of
P
3.3. Synthesis of complex (3)
phenyl), 135.97 (vt, AXX0,
phosphole), 137.4 (vt, AXX0,
JPC = 16.6 Hz, Cb of
JPC = 50.7 Hz, Ca of
P
Ligand 2 (161 mg, 0.2 mmol) was added to a solution
of [Pd(COD)Cl2] (57 mg, 0.2 mmol) in dichloromethane
(3 mL) at room temperature. After 10 min of stirring at
this temperature, AgBF4 (39 mg, 0.2 mmol) was added
phosphole), 139.7 (s, C para of pyridine), 161.8 (vt,
P
AXX0, JPC = 23.6 Hz, C ortho pyridine). Anal. Calc.
for C39H31BBrF4NP2Ni: C, 58.48; H, 3.90. Found: C,
58.51; H, 3.81%.

M. Melaimi et al. / Journal of Organometallic Chemistry 689 (2004) 2988–2994
2993
3.5. General procedure for the coupling of bromoaceto-
phenone with phenylboronic acid and bromobenzene with
styrene
Yield (after chromatography): 335 mg (85%). For char-
acterizations, see [11k].
4,4,5,5-Tetramethyl-2-o-tolyl-[1,3,2]dioxaborolane
(from o-bromotoluene): Yield (after chromatography):
273 mg (78%). For characterizations, see [11k].
4-bromoacetophenone (10 mmol) and phenylboronic
acid (15 mmol) were added to a solution of catalyst 3
(0.001%) with potassium carbonate (20 mmol) in tolu-
ene (20 mL). Then the mixture was heated at 110 ꢁC
for 2 h and the progress of the reaction was monitored
by GC.
Styrene (2.4 mmol) and bromobenzene (1.6 mmol)
were added to a solution of catalyst 3 (0.001%) in dioxane
(4 mL). Triethylamine (3.2 mmol) was then added and
the mixture was allowed to heat at 110 ꢁC for 15 h. The
progress of the reaction was monitored by GC.
3.7. X-ray crystal structures of compounds 2 and 4
Single crystals of compound 2 were obtained by slow
evaporation of a chloroform solution of the compound
at room temperature. Single crystals of 4 were grown
by slow evaporation of a dichloromethane solution of
the complex at room temperature. Data were collected
on a Nonius Kappa CCD diffractometer using a Mo
˚
Ka (k = 0.71073 A) X-ray source and a graphite mono-
chromator. Experimental details are described in Tables
1 and 3. The crystal structure was solved using SIR97
[16] and SHELXL-97 [17]. ORTEP drawings were made
using ORTEP III for Windows [18].
3.6. General procedure for the coupling of pinacolborane
with iodo and bromoaromatics and characterizations of
arylboronic esters
Pinacolborane (2.4 mmol), the halogenoaromatic
(iodo or bromo derivative) (1.6 mmol) and triethylamine
(4.8 mmol) were successively added to a solution of
catalyst 3 (0.001% for iodo- and 0.01% for bromo
derivatives) in distilled dioxane (10 mL). The reaction
mixture was heated at 80 ꢁC and the progress of the
reaction was monitored by GC. At the end of the reac-
tion, the solvent was evaporated and diethylether (10
mL) was added. After filtration and washing of the
ammonium salts with ether (2 · 10 mL), the solvent
was evaporated. Then, the oily residue obtained was
purified by column chromatography using silicagel
(important: the silicagel must be previously treated
with a mixture of hexanes Et3N (95/5) to avoid any
acidic promoted decomposition of the boronic esters).
The boronic ester was eluted with hexanes as solvent.
Formulations of boronic esters were confirmed by
4. Supplementary material
Crystallographic (excluding structure factors) have
been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications Nos. CCDC
235565 for compound 2 and CCDC 235565 for com-
pound 4. Copies of the data can be obtained free of
charge, on application to the CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk).
Acknowledgements
The authors thank the CNRS (Centre National de la
Recherche Scientifique) and the Ecole Polytechnique for
the financial support of this work.
1
comparison of H and 13C NMR data with literature
values.
4,4,5,5-Tetramethyl-2-phenyl-[1,3,2]dioxaborolane (from
iodobenzene): Yield (after chromatography): 313 mg
(96%). For characterizations, see T. Ishiyama, M. Mura-
ta, N. Miyaura, J. Org. Chem. 60 (1995) 7508.
2-(4-Methoxy-phenyl)-4,4,5,5-tetramethyl-[1,3,2]di-
oxaborolane (from p-methoxy-iodobenzene): Yield (after
chromatography): 359 mg (96%). For characterizations,
see [11j].
2-(2-Methoxy-phenyl)-4,4,5,5-tetramethyl-[1,3,2]di-
oxaborolane (from o-methoxy-iodobenzene): Yield (after
chromatography): 318 mg (85%). For characterizations,
see [11d].
4,4,5,5-Tetramethyl-2-p-tolyl-[1,3,2]dioxaborolane
(from p-tolyl-iodobenzene): Yield (after chromatogra-
phy): 315 mg (90%). For characterizations, see [11d].
1-[4-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolane-2-
yl)-phenyl]-ethanone (from p-bromo-acetophenone):
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