N-tripodal ligands to generate copper catalysts for the syndiotactic polymerization of methyl-methacrylate: Crystal structures of copper complexes

Article abstract of DOI:10.1016/j.jorganchem.2007.11.010

A library of N-tripodal ligands, based on a central nitrogen atom connected to three different functionalized arms, was investigated via a parallel approach for the polymerization of methyl-methacrylate (MMA) in presence of late transition metal salts. Copper salts CuCl₂ and Cu(OAc)₂ in combination with N-(2-furanylmethyl)-N-(1-3,5-dimethyl-1H-pyrazolylmethyl)-N- (phenylmethyl)amine were detected as efficient catalysts for the syndiotactic polymerization of MMA ([rr] up to 78%). Kinetic studies and X-ray structures of the best catalysts were reported.

Full text of DOI:10.1016/j.jorganchem.2007.11.010

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 393–398
www.elsevier.com/locate/jorganchem
N-tripodal ligands to generate copper catalysts for the
syndiotactic polymerization of methyl-methacrylate: Crystal
structures of copper complexes
*
´
Clement Lansalot-Matras, Fabien Bonnette, Emmanuel Mignard, Olivier Lavastre
ˆ
CNRS UMR 6226, Universite´ de Rennes 1, Campus Beaulieu, Batiment 24, CS 7420, 35042 Rennes, Cedex, France
Received 4 September 2007; received in revised form 6 November 2007; accepted 6 November 2007
Available online 13 November 2007
Abstract
A library of N-tripodal ligands, based on a central nitrogen atom connected to three different functionalized arms, was investigated
via a parallel approach for the polymerization of methyl-methacrylate (MMA) in presence of late transition metal salts. Copper salts
CuCl2 and Cu(OAc)2 in combination with N-(2-furanylmethyl)-N-(1-3,5-dimethyl-1H-pyrazolylmethyl)-N- (phenylmethyl)amine were
detected as efficient catalysts for the syndiotactic polymerization of MMA ([rr] up to 78%). Kinetic studies and X-ray structures of
the best catalysts were reported.
Ó 2007 Published by Elsevier B.V.
Keywords: Polymerization; MMA; Syndiotacticity; Tripodal ligands; Copper based-catalyst
1. Introduction
([Cp*2SmH]2) to produce highly syndiotactic PMMA
([rr] = 95%) with high yield [3]. Collins et al. achieved the
controlled polymerization of MMA with a two-component
system consisting of a cationic zirconocenium complex
Polymethyl-methacrylate (PMMA) is almost exclusively
produced in industry via radical polymerization with an
annual world production greater than two million tons.
This PMMA is generally atactic. The glass transition tem-
perature (Tg) and others properties are very dependent on
tacticity. Tg of isotactic PMMA is about 65 °C, whereas
syndiotactic PMMA exhibits a higher Tg, about 140 °C.
The advantage of the high optical quality of PMMA is
far improved when the Tg is raised. That is why many
attempts aiming to increase the syndiotacticity of PMMA
were planned [1,2]. Non radical metal-mediated polymeri-
zation of methyl-methacrylate (MMA) was first described
at the beginning of the 1990s when two groups indepen-
dently reported the living syndiospecific polymerization
of MMA with d0/fn metallocene catalysts: Yasuda et al.
used a neutral single-component lanthanide-based catalyst
À
Cp2ZrMe(THF)+BPh4
and
a
neutral zirconocene
Cp2ZrMe2 with a lower amount of syndiotactic dyads
([rr] = 80%) [4]. Since then, important research has been
conducted with late transition metal-mediated polymeriza-
tion, especially nickel-based catalysts: Ni(acac)2–MAO was
first found to be an effective catalyst for the atactic poly-
merization of MMA [5,6]. Syndiotactic PMMA
([rr] = 72%) produced via late transition metal catalysts
was first described with Cp2Ni–MAO [7]. Late transition
metal complexes such as (a-diimine)nickel(II), (pyridyl
bis-imine)iron(II) and (pyridyl bis-imine)cobalt(II), which
are widely used for the polymerization of olefins, were also
reported to polymerize MMA in combination with MAO
to give slightly syndiotactic PMMA ([rr] = 62–71%) [8].
Recently, Carlini et al. reported that salicylaldiminatenick-
el (II) complexes could polymerize MMA to give syndio-
tactic rich PMMA ([rr] = 77%) with a relatively wide
molecular weight distributions after activation with MAO
*
Corresponding author. Tel.: +33(0) 22 323 5630; fax: +33(0) 22 323
6939.
E-mail address: lavastre@univ-rennes1.fr (O. Lavastre).
0022-328X/$ - see front matter Ó 2007 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2007.11.010

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C. Lansalot-Matras et al. / Journal of Organometallic Chemistry 693 (2008) 393–398
[9–11]. Nickel(II) bearing b-ketimino ligands [N,O] were
recently reported to polymerize MMA to give syndiotactic
rich PMMA ([rr] = 82%) with a relatively broad molecular
weight distribution after activation with MAO [12,13].
However, very few examples of copper-based catalysts acti-
vated by MAO are reported in the literature. The Cu(D-
MOX)Cl2/MAO [14] and Cu-bis(benzimidazole) [15,16]
systems were described as efficient catalysts for the poly-
merization of methacrylates but the resulting polymers
were atactic. Here, we report new and highly active cop-
per-based catalysts based on N-tripodal ligands for the syn-
diospecific polymerization of MMA. Precatalysts were
isolated and described by X-ray diffractometry.
ligands 1a–g and different metal salts is very high depend-
ing on the metal centers, the counteranion and the nature
and position of heteroatoms within these molecules. Thus,
we have used a parallel approach to test catalytic systems
for the polymerization of MMA. The synthesis of the
library of potential catalysts with a combination of differ-
ent metal salts (M) and tripodal ligands 1a–g (L) using a
96 well-plate format was then achieved. The complexation
reactions were performed in tetrahydrofuran (THF) at
room temperature for 2 h with usual and unusual metallic
precursors having a potential in catalysis (CrCl3, CoCl2,
FeCl2, FeCl3, (COD)PdCl2, Cu(OAC)2, CuCl2, (DME)-
NiBr2, [Ni(p-allyl)Cl]2, [(p-cym)RuCl2]2, [(nbd)RhCl]2).
After drying the solutions, polymerizations of MMA in tol-
uene were carried out at room temperature for 4 h under
argon atmosphere. No activity was observed without acti-
vation with MAO. When they were activated with MAO,
ligands 1a, 1b, 1f and 1g in conjunction with copper dichlo-
ride or copper acetate gave a gel, whereas cobalt, iron, pal-
ladium, nickel, ruthenium and rhodium catalysts gave little
or no activity. Since copper precursors CuCl2 and
Cu(OAC)2 alone do not provide any polymer after activa-
tion with MAO, the tree component mixture [copper(II)/
ligands/MAO] is thus essential to obtain PMMA. These
systems were then evaluated in a SCHLENK scale (Table 1).
With the experimental conditions used, Cu(OAc)2-based
catalysts give yields from 23% to 40% and produce a
PMMA with a high degree of syndiotacticity ([rr] = 73–
78%). CuCl2 associated with ligands 1b and 1g gives higher
yields up to 60% and produces a polymer with a high
degree of syndiotacticity ([rr] = 72–75%). The ligands 1b
and 1g are very similar with the same dimethyl-pyrazole
group, and with a furan or thiophen group. Nevertheless,
CuCl2/1b with furan moiety produces a PMMA with num-
ber average molecular weight (Mn) measured at 73400 g/
mol whereas CuCl2/1g with thiophen moiety produces a
2. Results and discussions
The design of new ligands able to give selective mono, bi
or tridentate coordination with transition metals is a cur-
rent challenge in the field of controlled polymerization.
In previous papers, we have reported new heterocyclic mul-
tidentate molecules as promising ligands in coordination
chemistry and organometallic catalysis [17]. These N-tripo-
dal molecules are easily accessible and are based on a cen-
tral nitrogen connected with three different functionalized
arms. Tripodal ligands can be obtained via the condensa-
tion of 1-hydroxymethyl pyrazoles or 1-hydroxymethyl tri-
azoles with heterocyclic secondary amines using
microwaves [18]. All derivatives 1a–g (Fig. 1) were
obtained with very high yield and purity without any puri-
fication process. It was considered that, due to the diversity
of the arms, this class of molecules would present a high
potential for polymerization as they can potentially coordi-
nate transition metals in different ways, i.e. mono, bi or tri-
dentate fashion. In addition, they have never been used in
conjunction with late transition metals to polymerize meth-
acrylates. The number of possible coordination between
OEt
O
N
N
N
O
O
N
N
N
S
N
N
N
N
N
N
N
N
N
1d
1c
1a
1b
EtO
O
N
N
N
N
N
N
N
N
S
O
N
N
1e
1g
1f
Fig. 1. Library of N-tripodal ligands.

C. Lansalot-Matras et al. / Journal of Organometallic Chemistry 693 (2008) 393–398
395
Table 1
Polymerization of MMA with active M/L catalysts
Catalysts M/La
Temp. (°C)
Cu/MAO (mol/mol)
Yield (%)b
Mnc
Ipc
Tacticity (%)d
Tg (°C)e
rr
mr
mm
CuCl2/1b
CuCl2/1g
Cu(OAc)2/1b
Cu(OAc)2/1d
Cu(OAc)2/1f
Cu(OAc)2/1g
30
30
30
30
30
30
1/20
1/20
1/20
1/20
1/20
1/20
64
57
31
23
27
40
73 400
1.85
1.95
3.16
1.84
1.95
4.86
72
75
78
77
75
73
20
18
15
16
16
17
8
7
7
7
9
128
126
124
125
123
122
149 300
339 200
725 650
53 120
47 820
10
CuCl2/1b
0
30
50
30
1/20
1/20
1/20
1/100
12
64
74
34
58 300
73 400
2.07
1.85
2.13
f
62
72
72
55
23
20
21
29
15
8
7
119
128
127
114
114 602
f
16
a
Complexation M/L = 1/2, RT, 2 h, THF, [M] = 0.1 M.
Polymerization condition: M/MAO/MMA = 1/20/1000, 30 °C, 4 h, MMA:toluene = 1:2 in vol., yield defined as mass of dry polymer recovered/mass
b
of monomer used.
c
Determined by means of GPC.
d
Determined by 1H NMR analysis.
e
Determined by means of DSC.
Trimodal distribution of molecular weights Mp = 86600, 7130 and 540.
f
PMMA with a Mn two times higher, 149300 g/mol. In both
cases broad molecular weight distribution were observed
(Ip = 1.85–1.95). Table 1 gives lots of information. How-
ever, it is not easy to explain the difference of activity
and selectivity induced by ligands 1a–g as they are differen-
tiated by at least two different arms. In addition, the count-
eranion (OAcÀ/ClÀ) seems to have the largest effect.
Catalyst CuCl2/1b was evaluated more in detail for the
polymerization of MMA by changing the temperature of
polymerization and the amount of MAO. No significant
improvement in syndiotacticity could be achieved: The
same degree of syndiotacticity is obtained at 50 °C,
whereas a decrease in the temperature to 0 °C leads to a
decrease in syndiotacticity ([rr] = 62%). A kinetic study
was also carried out with these catalytic systems based on
CuCl2. For such systems the rate of polymerization could
be expressed as Rp = Àd[MMA]/dt = kp[MMA]a Á [active
center]b, where kp is the propagation rate constant, and a
and b are the kinetic orders of the monomer and the active
centers, respectively [6]. Fig. 2 (left) shows the semi-loga-
rithmic plot of the conversion of MMA as a function of
time at 0 and 20 °C. As expected, the rate of consumption
of MMA increases at higher temperature. Interestingly, a
linear regime is observed for both traces which indicates
(a) a first-order MMA conversion and (b) the concentra-
tion of the active centers was constant during the first
30–40% of the conversion, which is in good agreement with
the quasi steady-state approximation. One can see at 20 °C
a deviation from linearity of the semi-logarithmic trace
after 30% of conversion. Changes in Mn and the polydis-
persity index (Ip) in function of MMA conversion are also
plotted in Fig. 2 (right). With the same M/MAO/MMA
ratios, Mn remains the same about 60000–70000 g/mol
while the Ip remains quite high in both cases (>2). Repo
et al. also observed no evolution of Mn during the polymer-
ization of tert-butyl acrylate with iron(II) bearing
80 000
70 000
60 000
50 000
40 000
30 000
20 000
10 000
0
10
9
0.25
0.2
8
Mn @ 0 C
˚
Mn @ 20 C
7
˚
0.15
Ip @ 0 C
˚
6
20 C
˚
Ip @ 20 C
˚
0 C
5
˚
0.1
0.05
0
4
3
2
1
0
10
20
30
40
50
0
1
2
3
4
5
6
7
yields (%)
time (h)
Fig. 2. Semi-logarithmic plots as a function of time at 0 °C and 20 °C (left), molecular weight and polydispersity index obtained by GPC from aliquots
withdrawn during the polymerization as a function of MMA conversion (right). Conditions [CuCl2/1b] /MAO/MMA = 1/20/1000, MMA:toluene = 1:2
in vol.

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C. Lansalot-Matras et al. / Journal of Organometallic Chemistry 693 (2008) 393–398
bis(imido)pyridyl or phosphine ligands activated with
MAO [19]. Such characteristics indicate there is no control
of molecular weight. From these initial rates of polymeriza-
tion, one can plot the Arrhenius trace and calculate the
overall activation energy, about 50 kJ/mol. This value
could not be directly compared with another one from a
copper-based catalyst, but it is much higher than the one
published by Endo et al. (15.0 kJ/mol with Ni(acac)2–
MAO catalyst for the polymerization of MMA) [6].
Interestingly, CuCl2 and Cu(OAc)2 in conjunction with
ligand 1b give different results from the point of view of
Mn and Ip. Cu(OAc)2/1b give higher Mn than CuCl2/1b
(339200 and 73400 respectively), but higher Ip (Ip = 3.16
and 1.85, respectively). Moreover, syndiotacticity observed
with Cu(OAc)2/1b is the highest ([rr] = 78%). Single crys-
tals suitable for X-ray structure determination of copper
complexes CuCl2/1b and Cu(OAc)2/1b, were obtained from
recrystallisation in THF/heptane (1/2 in vol.). As depicted
in Fig. 3, the air-stable compound CuCl2/1b is a distorted
tetrahedral complex, where ligand 1b is bidentate. Coordi-
nation of copper occurred via the sp2 nitrogen of the pyra-
zole and the central sp3 nitrogen, and two chlorine atoms
acting as monodentate ligands. The furan unit does not
participate to the coordination. Distance between central
Fig. 4. Molecular structure of pre-catalyst Cu(OAc)2/1b; Selected bond
lengths (A) and angles (°): Cu1–N11 2.234, Cu1–Cu1* 2.679, Cu1–O1 1.980,
˚
*
Cu1–O2 1.973, Cu1–O3 1.984; Cu1–O4 1.976, N11–Cu1–Cu1 176.64, N11
–
Cu1–O1 92.66, N11–Cu1–O2 97.09, N11–Cu1–O3 99.64, and N11–Cu1–O4
95.48.
to the formation of a completely different coordination
mode. As depicted in Fig. 3, X-ray analysis revealed that
four acetate ligands bridge copper centers in a l-mode
leading to a paddle wheel type copper acetate. Two tripo-
dal ligands acting as monodentate ligands bind the axial
sites of the copper centre through the sp2 nitrogen atom
˚
nitrogen and the copper center is 2.089 A which is common
for copper dichloride complexes with N,N-bichelating
˚
ligands for instance Cu(DMOx)Cl2 (d(Cu–N) = 1.994 A)
˚
[14]. Distance between the pyrazole unit and copper center
of the pyrazole unit with a Cu1N11 distance of 2.234 A.
˚
is 1.959 A for complex CuCl2/1b. This is a little shorter
An inversion centre lies on the midpoint of the copper cen-
than other complexes with tripodal ligand containing pyr-
azol unit [20–22]. However, tri or tridentate coordination
mode were observed for these latter complexes, which is
different from the bidentate fashion observed for complex
CuCl2/1b. When associated with Cu(OAc)2, ligand 1b leads
tre then the complex Cu(OAc)2/1b is centrosymetric. The
*
˚
distance of Cu1–Cu1 is 2.679 A and the angle N11–Cu1–
Cu1* is 176.64° and is nearly linear. This copper dimer con-
formation was already obtained from Cu(OAc)2 salt and N
containing ligands such as pyrazine [23] or triazol based
˚
ligand (d(Cu–N) = 2.167 A) [24]. It is interesting to note
that acetate (OAc) are able to induce an anion-templating
effect (paddle wheel lmode) in the solid state (see Fig. 4).
This effect should be destroyed in solution in the presence
of MAO to induce a different coordination mode (di- or tri-
dentate) than the monodentate fashion to explain the syn-
diospecific polymerization observed.
In conclusion, we have reported a new class of ligands
for the syndiotactic polymerization of MMA in presence
of copper salts. Further research is currently being con-
ducted in order to determine the polymerization mecha-
nism and correlate the structure of active catalysts and
high syndiotacticity.
3. Experimental
All experiments were carried out under controlled atmo-
sphere using standard SCHLENK techniques or glove box.
Solvents were distilled over standard drying agents under
nitrogen and degassed directly before used. MMA from
Aldrich (99%) was distillated over CaH2 under reduced
pressure. Compounds 1a–g were prepared with high purity
according to published methods [16]. Crystallographic data
Fig. 3. Molecular structure of pre-catalyst CuCl2/1b; Selected bond
lengths (A) and angles (°): Cu1–N1 1.962, Cu1–N11 2.084, Cu1–Cl2 2.227,
Cu–Cl1 2.219; N1–Cu1–N11 82.43, N1–Cu1–Cl1 94.55, N11–Cu1–Cl2 99.17,
and Cl1–Cu1–Cl2 96.16.
˚

C. Lansalot-Matras et al. / Journal of Organometallic Chemistry 693 (2008) 393–398
397
collection, unit cell constant and space group determina-
tion were carried out on an automatic ‘Enraf Nonius
FR590’ NONIUS Kappa CCD diffractometer with graph-
ite monochromatized Mo Ka radiation at 120 K. The cell
parameters are obtained with Denzo and Scalepack with
10 frames (psi rotation: 1° per frame). The structure is
solved with SIR-97. The whole structure is refined with
SHELXL97 by the full-matrix least-square techniques.
sis was performed on a TA-Instrument DSC2010. NMR
spectra were recorded using Bruker Advance 300 MHz or
Bruker DPX 200 MHz spectrometers. Chemical shifts are
reported in d (ppm) using CDCl3 as the reference solvent
unless otherwise stated. The triad tacticity of the polymers
was determined by using the area ratios of the splitting a-
methyl protons in the 1H NMR spectra recorded at
300 MHz. HRMS were obtained with
a VARIAN
MAT311 and microanalysis with a Microanalyseur Flash
´
3.1. Screening test
EA1112 CHNS/O (Centre Regional de Mesures Physiques
de l’Ouest, Rennes, France).
10 l moles of each metal salt were added in 2.5 ml of
THF and stirred until complete dissolution, then 24 l
moles of each ligand were added in 3 mL of THF. 1 mL-
tubes were disposed in a 96 well-plate. The metal salts were
disposed in columns 1–11 and the ligands in rows B–H.
Each tube (from column 1 to 11) was charged first with
100 lL of the appropriate metal salt solution (0.4 lmol).
Then, each tube (from rows A to G) was charged with
3.4. Synthesis of complex [CuCl2] (1b)
CuCl2 (110 mg, 0.82 mmol) and ligand 1b (484 mg,
1.64 mmol) were dissolved in 10 mL of THF under stirring
for 2 h at room temperature. THF was partially evaporated
until the complex precipitated with 20 mL heptane. A green
apple-like colored solid was filtered, washed twice with
20 mL heptane and dried under vacuum overnight.
(348 mg, 99%). Anal. Calc. for C18H21Cl2CuN3O: C,
50.30; H, 4.92; N, 9.78. Found: C, 50.83; H, 5.54; N,
8.51%. Green crystals suitable for X-ray analysis were
obtained from recrystallisation in THF-heptane (1:2, v/v).
Crystal data: C18H21Cl2CuN3O; Mw 429.82; crystal size:
0.25 Â 0.15 Â 0.1 mm; temperature 100(2) K; wavelength
100 lL of
a solution of the corresponding ligand
(0.8 lmol). The cell in A-12 was kept empty. The mixtures
were let to react during 2 h at room temperature. Then, the
solvent was evaporated under reduced pressure and the cat-
alysts were used without further purification for the poly-
merization. 1.8 lL of MAO (30% wt in toluene) were
added in all tubes, and after 25 min at room temperature,
100 lL of toluene and 43 lL of MMA were added in each
tubes. Then, the tubes were sealed and carefully stirred by
hand. After 4 h at 30 °C, active catalysts were detected
when a gel was formed in the reaction mixture.
˚
0.71073 A; crystal system: monoclinic; space group: C2=c;
˚
˚
unit cell dimensions: a = 22.1397(7) A; b = 13.4559(4) A;
˚
c = 14.5198(4) A, a = 90°; b = 90.556(2)°; c = 90°;
3
3
˚
V = 4325.4(2) A ; Z = 8; Dc = 1.320 Mg/m ; absorption
coefficient: 1.266 mmÀ1; F(000)=1768; h-range for data
collection: 3.03–27.48°; reflections collected/unique:
3.2. Typical polymerization of MMA
38485/4935
[R(int) = 0.0298];
limiting
indices:
In a Schlenk tube under argon, 9.35 lmoles of metals
and 18.7 lmol of ligand were introduced with 100 lL of
THF. The solution was stirred 2 h at 30 °C. The solvent
was eliminated by reduced pressure. 41 lL of MAO solu-
tion (30% wt in toluene) were added and after 30 min at
30 °C, 2 mL of toluene was added. The MMA (1 mL,
9.35 mmol) was then added and the mixture was stirred
4 h at 30 °C. Finally, the polymerization experiment was
stopped by pouring the content of the Schlenk tube in a
large excess of methanol containing a small amount of
hydrochloric acid. The coagulated polymer was washed
with methanol, filtered and finally dried under vacuum.
The polymer yield was determined by gravimetry.
À28 6 h 6 28, À17 6 k 6 17, À18 6 l 6 18; completeness
to h = 27.48 (99.5%); max. and min. transmission: 0.881
and 0.715; data/restraints/parameters: 4935/0/226; good-
ness-of-fit on F2 = 1.112; final R indices [I > 2r(I)]:
R1 = 0.0584, wR2 = 0.1532;
R
indices (all data):
R1 = 0.0624, wR2 = 0.1553; largest diffraction peak and
hole: 1.362 and À1.074 e AÀ3
.
3.5. Synthesis of complex [Cu(OAc)2] (1b)
Cu(OAc)2 Á 6H2O (200 mg, 1.00 mmol) was first dehy-
drated under vacuum at 90 °C overnight and then dissolved
in 10 mL of THF with ligand 1b (591.6 mg, 2.00 mmol)
under stirring for 2 h at room temperature. THF was par-
tially evaporated until the complex precipitated with
20 mL heptane. The blue solid was filtered, washed twice
with 20 mL heptane and dried under vacuum one night
(180 mg, 37%). Blue crystals were obtained from recrystalli-
sation in THF-heptane (1:2, v/v). Crystal data: C22
H27CuN3O5; Mw 477.01; crystal size: 0.3 Â 0.15 Â 0.1 mm;
3.3. Polymer characterization
Molecular weights and molecular weight distributions of
the polymers were determined by size exclusion chromatog-
raphy (SEC) at 40 °C in chloroform. A Dionex P680 HPLC
pump equipped with the PL-ELS 1000 from Polymer Lab-
oratories was used and connected to a PLgel 10 lm
MIXED-B column. PMMA standards were used for cali-
bration (ꢀ1 mg/mL; injection volume 20 lL; flow rate
1 mL/min). Differential scanning calorimetry (DSC) analy-
˚
temperature: 120(2) K; wavelength: 0.71069 A; crystal sys-
ꢀ
tem: triclinic; space group: P1; unit cell dimensions:
˚
˚
˚
a = 8.397(5) A; b = 11.074(5) A; c = 13.132(5) A; a =
100.469(5)°; b = 104.559(5)°; c = 99.805(5)°; V =

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C. Lansalot-Matras et al. / Journal of Organometallic Chemistry 693 (2008) 393–398
3
3
˚
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1131.9(9) A ; Z = 2; Dc = 1.400 Mg/m ; adsorption coeffi-
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tion: 2.57–27.44°; limiting indices: À10 6 h 6 10,
À14 6 k 6 14, À16 6 l 6 17; reflections/collected/unique:
9274/5131 [R(int)=0.0491]; completeness to h = 27.44
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wR2 = 0.159;
R
indices (all data) R1 = 0.0735,
wR2 = 0.1695; largest diffraction peak and hole: 1.359 and
À1.350 e AÀ3
.
4. Supplementary material
CCDC 658502 and 658503 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_re-
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Acknowledgements
Acknowledgment is made to the CNRS, the MENRT
and the Regional Council of Bretagne. The authors are
grateful for Thierry Roisnel for the assistance in the X-
ray data handling. O.L. is grateful to the company TOTAL
for fruitful discussions and funding.
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