New constrained geometry catalysts-type yttrium, samarium and neodymium derivatives in olefin polymerization

Article abstract of DOI:10.1016/j.molcata.2007.03.017

A straightforward synthetic methodology to prepare ansa-monocyclopentadienyl-imino-pyridine dichloro metal derivatives of the type MLCl₂(THF) {M = Y, Sm, Nd} has been developed. Here, we report the syntheses and characterizations of both the ligand and the complexes and the results of some catalytic tests towards olefin polymerization. The most astonishing data come from the influence of both the metal fragments and the co-catalysts used towards the selectivity in butadiene polymerization: in fact, changing these parameters it is possible to range from >99% 1,4 cis-polybutadiene to >99% 1,4 trans-polybutadiene.

Full text of DOI:10.1016/j.molcata.2007.03.017

Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
New constrained geometry catalysts-type yttrium, samarium
and neodymium derivatives in olefin polymerization
Gino Paoluccia,∗, Alessandra Zanellaa, Marco Bortoluzzia,
Silvana Sosterob, Pasquale Longoc,∗∗, Mariagrazia Napolic
a Dipartimento di Chimica, Universita` Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy
b Dipartimento di Chimica, Universita` di Ferrara, Via L. Borsari 35, 44100 Ferrara, Italy
c Dipartimento di Chimica, Universita` di Salerno, Via Ponte don Melillo, 84084 Fisciano (SA), Italy
Received 30 January 2007; received in revised form 2 March 2007; accepted 6 March 2007
Available online 12 March 2007
Abstract
A straightforward synthetic methodology to prepare ansa-monocyclopentadienyl-imino-pyridine dichloro metal derivatives of the type
MLCl2(THF) {M = Y, Sm, Nd} has been developed. Here, we report the syntheses and characterizations of both the ligand and the complexes and
the results of some catalytic tests towards olefin polymerization. The most astonishing data come from the influence of both the metal fragments
and the co-catalysts used towards the selectivity in butadiene polymerization: in fact, changing these parameters it is possible to range from >99%
1,4 cis-polybutadiene to >99% 1,4 trans-polybutadiene.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Yttrium; Samarium; Neodymium; Constrained geometry catalysts; Polybutadiene
1. Introduction
yttrium complexes [12,13]. Herein, we report a straightforward
synthetic approach to prepare cyclopentadienyl-imino-pyridine
dichloro complexes of yttrium, samarium and neodimium (see
Chart 1).
The Y (5), Sm (6) and Nd (7) complexes, activated by a
suitable co-catalyst, showed some activity in the polymerization
of ethylene and butadiene. Both the activity and the selectivity
strongly depend upon the metal ion and the co-catalyst used.
Cationiccomplexesofgroup4metals, e.g. alkylzirconocenes
or titanocenes, are highly active catalysts in homogeneous ethy-
lene polymerization [1–3]. Polyethylene can be also obtained
in the presence of neutral scandocene alkyl compounds, as
well as in the presence of a number of cationic alkyl com-
plexes of the rare-earth metals, stabilized by anionic ancillary
non-cyclopentadienyl ligands, such as amido functionalized tri-
azacyclononanes, ␤-diketiminates or benzoamidinate [4–10].
The synthesis of monocyclopentadienyl derivatives of
rare-earth metals usually is not easy, therefore cationic half-
metallocenes group 3 metals are not very widespread, although
the expected electrophilicity, and consequently the predictable
catalytic ability in the olefins polymerization, makes them
attractive [11]. In past years, we developed the synthesis and
characterization of monocyclopentadienyl-based zirconium and
2. Experimental
2.1. Materials and methods
All inorganic manipulations were carried out under oxygen-
and moisture-free atmosphere in a Braun MB 200 G-II
glove-box. All reaction and NMR solvents were thoroughly
deoxygenated and dehydrated under argon by refluxing over
suitable drying agents. The salts YCl3, SmCl3 and NdCl3
(Strem) were used as received, like 2,6-dihydroxymethyl-
pyridine (Aldrich). 2,6-Diisopropyl-aniline (Aldrich) was
distilled at reduced pressure over KOH and kept in the dark,
while dicyclopentadiene (Aldrich) was distilled immediately
before use. Microanalyses were performed at the Istituto di
∗
∗∗
Corresponding author. Tel.: +39 0412348563; fax: +39 0412348684.
Corresponding author. Tel.: +39 089969564; fax: +39 089969603.
E-mail addresses: paolucci@unive.it (G. Paolucci), plongo@unisa.it
(P. Longo).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.03.017

G. Paolucci et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
259
of the solvent, water (20 mL) was added and the by-product
2,6-dichloromethyl-pyridine was removed by extraction with
diethylether (2 mL × 30 mL). The pKa of the aqueous solu-
tion was adjusted to about 7 by addition of aqueous NH3
andthe2-hydroxymethyl-6-chloromethylpyridinewasextracted
with diethylether (3 mL × 20 mL). The resulting organic solu-
tion was dried with MgSO4 and the product was isolated by
in vacuo removal of the solvent, giving 1.84 g of white solid
(55% yield).
Elemental analysis, found (%): C 53.25, H 5.20, N 8.75, Cl
22.60.
Calcd for C7H8ONCl (%): C 53.35, H 5.12, N 8.89, Cl 22.50.
3
1H NMR (CDCl3, 298 K): 7.67 (t, 1H, JHH = 7.5 Hz, H4);
7.32 (d, 1H, 3JHH = 7.5 Hz, H3); 7.23 (d, 1H, 3JHH = 7.5 Hz, H5);
4.71 (s, 2H, CH2OH); 4.60 (s, 2H, CH2Cl); 4.45 (s, br, 1H, OH).
1
13C { H} NMR (CDCl3, 298 K): 159.3 C6, 155.3 C2, 137.7
C4, 121.2 C3, 119.9 C5, 64.0 CH2OH, 46.2 CH2Cl.
Chart 1. Y (5), Sm (6) and Nd (7) monocyclopentadienyl-imino-pyridine
dichloro derivatives.
2.3. Synthesis of 6-chloromethyl-pyridine-2-carbaldehyde
(2) (C7H6ClNO, Mw = 155.58)
Chimica Inorganica e delle Superfici, CNR, Padova. IR spec-
tra (KBr disks) were recorded from 4000 to 450 cm−1 on a
To a solution of oxalyl chloride (1.7 mL, 19.5 mmol) in
CH2Cl2 (25 mL) cooled to −60 ◦C dimethylsulphoxide (2.9 mL,
40.8 mmol) was added dropwise [12]. After 5 min, a solution of
2-hydroxymethyl-6-chloromethylpyridine (3.00 g, 19.0 mmol)
in CH2Cl2 (20 mL) was slowly added. The resulting solution
was stirred at −60 ◦C until the formation of a milky suspension
(about 15–20 min), then triethylamine (12 mL, 86.1 mmol) was
added dropwise by maintaining the temperature under −50 ◦C.
The colour of the reaction mixture turned to red, then the reac-
tor was allowed to warm to room temperature and the reaction
mixture was quenched with cold water (about 50 mL). The prod-
uct was extracted with dichloromethane (3 mL × 50 mL) and the
resulting organic fraction was dried over Na2SO4. The solvent
and volatiles were removed under vacuum and the resulting red
oil was purified by filtration on a silica gel column, using a 1:1
mixture of hexane–ethyl acetate as eluent. After the evaporation
of the solvents, pentane (5 mL) was added to the resulting oil.
After 2 h of vigorous stirring, the product was collected as a very
pale yellow solid (2.571 g, 87% yield).
1
Perkin-Elmer Spectrum One. 1H NMR, 13C{ H} NMR, COSY,
NOESY, APT, HMQC spectra were obtained as CDCl3 or
CD2Cl2 solutions on a Bruker Avance 300 spectrometer operat-
ing at 300 and 75 MHz, respectively. Mass spectra (E.I., 70 eV)
were recorded on a Finnigan Trace GC–MS equipped with a
probe controller for the sample direct inlet.
All the polymerization operations were performed under
nitrogen atmosphere by using conventional Schlenk-line tech-
niques. Toluene was refluxed over sodium diphenylketyl for 48 h
and distilled before use. Methylaluminoxane (10% in toluene,
Witco) was used as a solid after distillation of solvent. Ethy-
lene (>98%), 1,3-butadiene (>99%), Mg(Bu)2, Al(i-Bu)3, BuLi
and AlH(i-Bu)2, were purchased from Aldrich, B(C6F5)3 and
[C(C6H5)3][B(C6F5)4]werepurchasedfromBoulder. 13CNMR
spectra of the polymers were recorded on an AX 400 Bruker
spectrometer operating at 100 MHz at 298 K. The samples
were prepared by dissolving 20 mg of polymer in 0.5 mL of
CDCl3. TMS was used as internal chemical shift reference. The
structures of the polymers were determined by NMR analysis
comparing the chemical shifts of the resonances observed in the
spectra with the data reported in the literature [14,15]. Melting
points were measured by using a Du Pont 9900 DSC calorime-
ter with a heating rate of 10 K/min, on previously melted and
re-crystallized samples.
Elemental analysis: found (%): C 54.15, H 3.85, N 9.15, Cl
22.50.
Calcd per C7H6ClNO (%): C 54.04, H 3.89, N 9.00, Cl 22.79.
IR (KBr disk) (cm−1): 1713 νCO
.
1H NMR (CDCl3, 298 K): 10.03 (s, 1H, CHO); 7.95–7.65
(m, 3H, H3, H4, H5), 4.75 (s, 2H, CH2).
1
13C{ H}NMR(CDCl3, 298 K):192.8CHO, 157.4C6, 152.2
2.2. Synthesis of 2-hydroxymethyl-6-chloromethyl-
C2, 138.1 C4, 126.0 C5, 120.8 C3, 46.0 CH2.
Mass data (E.I., 70 eV. Tprobe: 100 ◦C, m/z): 155.1[M]•+, 127
[M•+−CHO]+, 91.1 [M•+−Cl−CHO]+.
pyridine[10] (1) (C7H8ONCl, Mw = 157.60)
To a solution of 2,6-dihydroxymethyl-pyridine (3.00 g,
21.6 mmol) in liquid SO2 (75 mL) cooled at −70 ◦C a slight
excess of thionyl chloride (1.8 mL, 24.7 mmol) dissolved in
CH2Cl2 (10 mL) was slowly added under vigorous magnetic
stirring. Once the addition was ended the temperature was
left to slowly (8 h) increase to room temperature, then the
reaction mixture was left to react overnight. After removal
2.4. Synthesis of (6-chloromethyl-pyridin-2-ylmethylene)-
(2,6-diisopropyl-phenyl)-amine (3) (C19H23N2Cl,
Mw = 314.85)
To a solution of the aldehyde (2) (1.18 g, 7.6 mmol) in anhy-
drous CH2Cl2 (50 mL), in the presence of molecular sieves 4 A
˚

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G. Paolucci et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
(10 g) and anhydrous MgSO4 or Na2SO4 (10 g), freshly dis-
tilled 2,6-diisopropylaniline (1.43 mL, 7.6 mmol) in anhydrous
CH2Cl2 (30 mL) at room temperature and under magnetic stir-
ring was added. The reaction mixture was left to react overnight.
Then molecular sieves and the salt were filtered off and the sol-
venteliminatedundervacuumtogiveananalyticallypureyellow
solid (2.338 g, 98% yield).
mixture was quenched with cold water (30 mL) and the crude
product was extracted with dichloromethane (3 mL × 50 mL).
The resulting organic fraction was dried over Na2SO4, the sol-
vent was removed by evaporation under reduced pressure and
the resulting yellow oil was purified by flash cromatography on
silica gel, using a 9:1 mixture of hexane–ethyl acetate as eluent.
The product was isolated as yellow oil by in vacuo removal of
the solvent (1.51 g, 60% yield).
Elemental analysis: found (%): C 72.65, H 7.10, N 9.05, Cl
11.15.
Elemental analysis: found (%): C 83.50, H 8.05, N 8.25.
Calcd (%) for C24H28N2: C 83.68, H 8.19, N 8.13.
Calcd for C19H23N2Cl (%): C 72.48, H 7.36, N 8.90, Cl
11.26.
1H NMR (CDCl3, 298 K): 8.33 (s, 2H, CH = N); ABC
spin system (6H, δA = 8.15 ppm, δB = 7.77 ppm, δC = 7.31 ppm,
JAB = JBC = 7.6 Hz, JAC = 0.0 Hz, pyridine rings); 7.25–7.15 (m,
6H, phenyl rings); 6.56–6.15 (m, 6H, vinilyc Cp protons); 4.04
(s, 2H, CH2); 4.01 (s, 2H, CH2); 3.51 (sept, 4H, 3JHH = 7.0 Hz,
CH); 3.05–3.00 (m, 4H, aliphatic Cp protons); 1.21 (d, 24H,
3JHH = 7.0 Hz, CH3).
1H NMR (CDCl3, 298 K): 8.30 (s, 1H, CH = N); 8.24 (d,
1H, 3JHH = 6.0 Hz, H3); 7.90 (t, 1H, 3JHH = 6.0 Hz, H4); 7.64 (d,
3
1H, JHH = 6.0 Hz, H5); A2B spin system (3H, δA = 7.19 ppm,
3
δB = 7.15 ppm, JHH = 7.9 Hz, phenyl); 4.77 (s, 2H, CH2Cl);
2.97 (sept, 2H, 3JHH = 6.0 Hz, CH); 1.19 (d, 12H, 3JHH = 6.0 Hz,
CH3).
1
1
13C { H} NMR (CDCl3, 298 K): 162.6 CH = N, 156.7 C6,
13C{ H}NMR(CDCl3, 298 K):163.8 CH = N, 137.7, 125.0,
154.0 C2, 148.2 phenyl-C1, 137.7 C4, 137.1 phenyl-C2, 124.5,
124.4 C5, phenyl-C4, 123.0 phenyl-C3, 120.5 C3, 46.4 CH2Cl,
27.9 CH, 23.4 CH3.
119.3 pyridine primary carbons, 137.5, 134.7, 132.8, 132.4,
129.5, 129.1 Cp primary carbons, 124.8, 123.4 phenyl primary
carbons, 44.0, 42.0 Cp secondary carbons, 40.3, 39.4 CH2, 28.4
CH, 23.8 CH3.
Mass data (E.I., 70 eV. Tprobe: 120 ◦C, m/z): 314.4 [M]•+
299.3 [M•+−CH3]+.
,
Mass data (E.I., 70 eV. Tprobe: 120 ◦C, m/z): 344 [M]•+, 329.4
[M•+−CH3]+.
2.5. Synthesis of (6-cyclopentadiendemethyl-pyridin-2-
ylmethylene)-(2,6-diisopropyl-phenyl)-amine, sodium salt
(4) (C24H27N2Na, Mw = 366.47)
2.7. Synthesis of YLCl2(THF)(5) (C28H35Cl2N2OY,
Mw = 575.40)
To a solution of (3) (0.500 g, 1.6 mmol) in anhydrous THF
(25 mL) at −80 ◦C a THF solution of sodium cyclopentadienide
NaCp (0.87 M, 3.65 mL, 3.2 mmol) was slowly added. The reac-
tion mixture was allowed to gradually reach room temperature
and then left to react overnight. The NaCl was eliminated by
centrifugation and the solution was evaporated under vacuum to
dryness, affording a red solid (0.565 g, 96% yield).
2.7.1.1. Method 1
To a suspension of YCl3 (0.215 g, 1.1 mmol) in anhydrous
THF (50 mL) a THF solution (20 mL) of 4 (0.403 g, 1.1 mmol)
at room temperature and under magnetic stirring was dropwise
added. At the end of the addition the yellow-gold suspension
obtained was left to react overnight. After elimination of NaCl
by centrifugation, the yellow solution was concentrated to 10 mL
under vacuum and by addition of n-hexane (20 mL) afforded
yellow microcrystals (0.415 g, 66% yield).
Elemental analysis: found (%): C 78.45, H 7.55, N 7.80.
Calcd for C24H27N2Na (%): C 78.66, H 7.43, N 7.64.
1H NMR (d5-pyridine, 298 K): 8.51 (s, 1H, CH = N); ABC
spin system (3H, δA = 7.87 ppm, δB = 7.68 ppm, δC = 7.57 ppm,
JAB = JBC = 7.6 Hz, JAC = 0.0 Hz, pyridine ring); 7.20–7.06 (m,
3H, phenyl); 6.48, 6.30 (A2B2 spin system, JAB = 2.5 Hz, Cp
2.7.1.2. Method 2
To a solution of 4H (0.379 g, 1.1 mmol) in THF a stoichiomet-
ric amount of potassium tert-butoxide (0.123 g, 1.1 mmol) was
slowly added at room temperature. After 15 min under stirring,
solid YCl3 (0.215 g, 1.1 mmol) was added and the resulting mix-
turewasallowedtoreactfor12 h. AftereliminationoftheKClby
centrifugation, the yellow solution was concentrated to 10 mL
under vacuum and by addition of n-hexane (20 mL) afforded
yellow microcrystals (0.432 g, 68% yield).
3
ring); 4.59 (s, 2H, CH2); 2.91 (sept, 2H, JHH = 7.0 Hz, CH);
0.98 (d, 12H, 3JHH = 7.0 Hz, CH3).
2.6. Synthesis of (6-cyclopenta-1,3-dienylmethyl-pyridin-2-
ylmethylene)-(2,6-diisopropyl-phenyl)-amine and
(6-cyclopenta-1,4-dienylmethyl-pyridin-2-ylmethylene)-
(2,6-diisopropyl-phenyl)-amine (4H) (C24H28N2,
Mw = 344.49)
Elemental analysis: found (%): C 58.15, H 6.20, N 4.80, Cl
12.40.
Calcd for C28H35Cl2N2OY (%): C 58.45, H 6.13, N 4.87, Cl
12.32.
To a solution of the Schiff base (3) (2.31 g, 7.3 mmol)
in anhydrous THF (20 mL) at −80 ◦C a solution of sodium
cyclopentadienide (19.00 mL, 0.86 M, 16.3 mmol) in anhydrous
THF (50 mL) was added under vigorous agitation. Once the
addition was completed the reaction mixture was allowed to
gradually warm to room temperature, then the resulting solu-
tion was left overnight under stirring. Subsequently, the reaction
1H NMR (CD2Cl2, 298 K): 8.15 (s, 1H, CH = N); ABC
spin system (3H, δA = 8.07 ppm, δB = 7.70 ppm, δC = 7.59 ppm,
JAB = JAC = 8.2 Hz, JBC = 0.0 Hz, pyridine ring); 7.42–7.05 (m,
3H, phenyl); 6.43, 6.18 (A2B2 spin system, 4H, JAB = 2.0 Hz, Cp
ring); 4.51 (s, 2H, CH2); 3.84 (m, br, 4H, THF); 3.51 (sept, 1H,
3JHH = 6.7 Hz, CH); 2.96 (m, br, 1H, CH); 1.85 (m, br, 4H, THF);

G. Paolucci et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
261
Table 1
Calcd for C28H35Cl2N2OSm (%): C 52.81, H 5.54, N 4.40,
Polymerization of ethylene in the presence of (5), (6) and (7) based catalytic
systems
Cl 11.13.
Mass data (E.I., 70 eV. Tprobe: 110 ◦C, m/z): 564 [M•+
−THF]+, 529 [M•+−THF−Cl]+.
Runa Catalyst Co-catalysta
Activityb m.p. (◦C)
1c
2d
3e
4g
5d
6d
5
5
5
5
6
7
BuLi/AlH(i-Bu)2
MAO
Mg(Bu)2/B(C6F5)3
[C(C6H5)3][B(C6F5)4]/Al(i-Bu)3
MAO
MAO
150
1400
310
90
60
250
132
135
–
132
133
132
2.9. Synthesis of NdLCl2(THF) (7) (C28H35Cl2N2NdO,
Mw = 630.74)
f
To a suspension of NdCl3 (0.276 g, 1.1 mmol) in anhydrous
THF (50 mL) at −20 ◦C and under vigorous stirring a THF solu-
tion (30 mL) of 4 (0403 g, 1.1 mmol) was dropwise added during
a period of half one hour. Once ended the addition, the green
suspension obtained was left to reach room temperature and left
to react overnight. After elimination of NaCl by centrifugation,
the light green solution was concentrated to 10 mL under vac-
uum and by addition of n-hexane (20 mL) afforded light green
microcrystals (0.522 g, 75% yield).
a
All the run were performed by dissolving, in 125 mL of toluene,
2.0 × 10−5 mol of catalyst, the proper amount of co-catalyst, under pressure
of 6 bar of ethene for 20 h.
b
Activity in g of polymer/(mol of catalyst)(h)(mol L−1 of ethylene).
(1)/BuLi/HAl(i-Bu)2 = 1/10/10; temperature = 20 ◦C [ethene] = 1.34 mol
c
L−1
.
d
(catalyst)/MAO = 1/1000 (based on Al); temperature = 50 ◦C [ethene] = 0.87
mol L−1
.
e
(1)/Mg(Bu)2 /B(C6F5)3 = 1/10/10; temperature = 50 ◦C [ethene] = 0.87 mol
.
L−1
Elemental analysis: found (%): C 53.20, H 5.50, N 4.50, Cl
11.35.
f
oligomers.
g
(1)/Al(i-Bu)3 /(C6H5)3C B(C6F5)4, = 1/5/1; temperature = 50 ◦C [ethene] =
Calcd for C28H35Cl2N2NdO (%): C 53.32, H 5.59, N 4.44,
Cl 11.24.
0.87 mol L−1
.
Mass data (E.I., 70 eV. Tprobe: 120 ◦C, m/z): 558 [M•+
−THF]+, 523 [M•+−THF−Cl]+.
3
3
1.27 (d, 6H, JHH = 6.7 Hz, CH3); 1.01 (d, 6H, JHH = 6.7 Hz,
CH3).
13C{ H}NMR(CD2Cl2, 298 K):166.7CH N, 140.5, 127.8,
1
2.10. Polymerization
127.4, 127.3, 124.1 phenyl and pyridine primary aromatic car-
bons; 116.4, 114.0 cyclopentadienil primary carbons, 67.7 THF;
37.6 CH2, 28.6 CH, 25.7 THF, 23.6 CH, 26.7, 23.3 CH3.
2.10.1. Run 1–6
Polymerizations of ethylene were performed in a 250 mL
glass-autoclave introducing the amount of catalyst and co-
catalyst dissolved in 125 mL of toluene, as reported in Table 1.
The mixtures was fed with the monomer and kept under mag-
netic stirring over the runs. The autoclave was vented and the
polymerization mixture was poured in acidified ethanol, the
polymers were recovered by filtration, washed with fresh ethanol
and dried in vacuo at 60 ◦C.
Mass data (E.I., 70 eV. Tprobe: 120 ◦C, m/z): 503 [M•+
−
THF]+.
2.8. Synthesis of SmLCl2(THF) (6) (C28H35Cl2N2OSm,
PM = 636.86)
ToasolutionofSmCl3 (0.282 g, 1.1 mmol) inanhydrous THF
(25 mL) at −20 ◦C and under vigorous stirring a THF solution
(30 mL) of 4 (0403 g, 1.1 mmol) was dropwise added. At the end
of the addition, the yellow-gold suspension obtained was left to
reach room temperature and to react overnight. After elimination
of NaCl by centrifugation, the yellow solution was concentrated
to 10 mL under vacuum and by addition of n-hexane (20 mL)
afforded yellow microcrystals (0.470 g, 67% yield).
Elemental analysis: found (%): C 52.90, H 5.50, N 4.45, Cl
11.20.
2.10.2. Runs 7–12
Polymerizations of 1,3-butadiene were performed by intro-
ducing 19 mL of dry toluene and the co-catalysts into 100 mL
glass flasks equipped with magnetic stirrer. The flasks were
cooled with liquid nitrogen and the inert gas was evacuated. 1,3-
Butadiene (the amount are reported in Table 2) was condensed
into the flasks, then the reactors were quickly thermostated at
the reaction temperature and polymerizations were started by
Table 2
Polymerization of butadiene in the presence of (5), (6) and (7) based catalytic systems
Runa
Catalyst (mol)
Co-catalystb
[Butadiene] (mol/L)
Activityc
Microstructure
7
8
9
10
11
12
5 (5.96 × 10−6
5 (3.97 × 10−5
6 (8.95 × 10−6
6 (8.95 × 10−6
7 (8.85 × 10−6
7 (3.54 × 10−5
)
)
)
)
)
)
MAO
Mg(Bu)2/B(C6F5)3
MAO
Mg(Bu)2/B(C6F5)3
MAO
Mg(Bu)2/B(C6F5)3
0.31
1.79
2.3
1.79
1.2
320
8
17
0.4
22
0.5
>99% 1,4 cis
20% 1,4 cis; 80% 1,4 trans
76% 1,4 cis; 17% 1,4 trans, 7% 1,2
30% 1,4 cis; 70% 1,4trans
65% 1,4 cis; 35% 1,4 trans
>99% 1,4 trans
1.79
a
All the run were performed by dissolving, in 20 mL of toluene, the butadiene, the catalyst, the co-catalyst. Temperature 25 ◦C.
(Catalyst)/MAO = 1/1000 (based on Al); (catalyst/Mg(Bu)2/B(C6F5)3 = 1/5/1.
b
c
Activity in g of polymer/(mol of catalyst)(h)(mol L−1 of butadiene).

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G. Paolucci et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
injecting 1 mL of a toluene solution of 5,6 or 7. Polymerizations
were stopped by introducing a few amount of ethanol. Then,
the polymers were coagulated in an excess of acidified ethanol,
washed several times with fresh ethanol and dried in vacuo at
room temperature.
The reaction 1 was carried out by using SOCl2 in liq-
uid SO2. The use of liquid SO2 as solvent increases the
yield of (1) by solubilizing the pyridinium salt of the start-
ing material due to the presence of HCl formed during the
reaction: in fact the high solvating power of the liquid SO2
allows the complete solubilization of all the species in the
reaction mixture. The reaction was carried out with the stoi-
chiometric ratio diol/thionyl chloride 1:1.2 at low temperature.
All the products of the reaction, i.e. the 2,6-dichloromethyl-
pyridine, the 2-hydroxymethyl-6-chloromethylpyridine (1) and
the unreacted 2,6-dihydroxymethyl-pyridine can be eas-
ily isolated by successive selective extractions. The first
extraction by diethylether from the acid aqueous solution
allowed the isolation of the 2,6-dichloromethyl-pyridine, while
after the neutralization by diluted ammonia solution the
2-hydroxymethyl-6-chloromethylpyridine (1) is isolated by suc-
cessive extractions with diethylether. The small amount of
unreacted 2,6-dihydroxymethyl-pyridine can be recovered from
the aqueous fraction.
3. Results and discussion
3.1. Ligand syntheses
The ansa-imino-cyclopentadienyl-pyridine ligand (4) was
synthesized according to the following successive reactions (see
Scheme 1):
(1) monochloruration of 2,6-dihydroxymethyl-pyridine;
(2) oxidation of the alcoholic group of (1) to aldehyde;
(3) condensation of the aldehyde group of (2) with 2,6-
diisopropyl-aniline;
(4) nucleophilic substitution of the Cl atom of (3) with
cyclopentadienide ion.
The oxidation of the 2-hydroxymethyl-6-chloromethyl-
pyridine (1) was carried out with oxalyl chloride and
Scheme 1. Reaction pathway for the synthesis of (4).

G. Paolucci et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
263
dimethylsulphoxide [16] at low temperature (−60 ◦C) to give
a reactive intermediate of the type [Me2SCl]Cl, which reacts
with the alcoholic group by oxydazing it to aldehyde. The crude
product was purified by filtration on silica gel giving the product
(2) in good yields (>80%).
Analogous complexes LnLCl2(THF) {Ln = Sm(III) (6),
Nd(III) (7)} were prepared according to the synthetic method
applied for the yttrium derivative. Due to the strong paramag-
netism of the Nd(III) and Sm(III) the NMR spectra did not allow
precise assignments. In addition to the elemental analyses, the
complexes were characterized by mass spectrometry. In the case
of the samarium complex (6) meaningful signals were observed
at 564 m/z, assignable to the molecular ion without THF, and at
529 m/z assignable to the [M•+ −Cl −THF]+ fragment formed
by the loss of a chlorine atom from the previous ion. Both the
assignments were done by comparison between the theoretical
and experimental isotopic clusters. Analogously, the mass spec-
trum of the neodymium complex (7) showed a signal at 558 m/z
attributable to the molecular ion without THF and another at
523 m/z due to the [M•+−Cl−THF]+ ion.
The condensation reaction with 2,6-diisopropylaniline was
˚
carried out by adding to the reagents molecular sieves 4 A and
anhydrous MgSO4 or Na2SO4 to shift the reaction equilibrium
towards the imine product (3) in almost quantitative yields.
The introduction of the cyclopentadienyl group was made as
the final step 4 as we have observed that, if the reaction 4 is made
before the reaction 3, a mixture of hardly separable product was
obtained, probably due to the reaction of the cyclopentadienyl
ion with the aldehyde group. The reaction is carried out in THF
at low temperature (−80 ◦C). By using a stoichiometry 1:2.2 in
the final reaction the product 4 was obtained as the monosodium
salt. Usually the purity of the sodium salt of 4 sometimes was
satisfactory to be directly used in the syntheses of the com-
plexes. Moreover, if necessary, a purification of the species 4
after protonation with water of its sodium salt could be done
by flash chromatography (4H). The neutral tautomeric mixture
can be quantitatively deprotonated with bases like potassium
tert-butoxide. The whole reaction pathway is summarized in
Scheme 1.
3.3. Polymerization reactions
Yttrium compound (5) was tested in the polymeriza-
tion of ethylene in the presence of several co-catalysts,
i.e. BuLi/AlH(i-Bu)2, MAO, Mg(Bu)2/B(C6F5)3 and
[C(C6H5)3][B(C6F5)4]/Al(i-Bu)3. The polymerization condi-
tions and the corresponding results are summarized in Table 1.
On inspection of the data the following can be observed:
The presence of two tautomers for 4H is confirmed by NMR
spectroscopy: in fact, even if the downfield and the aliphatic
regions of the 1H NMR spectrum does not give any information
about the presence of the two species, two groups of signals are
present both for the vinyl and allyl groups of the cyclopentadiene
(i) All the systems produce linear polyethylene, presenting a
melting point of the polymers, always higher than 130 ◦C.
(ii) (5) Mixed with MAO affords the most active system.
(iii) Activation of (5) with Mg(Bu)2 and B(C6F5)3 only gives
oligomerization of ethylene.
and for the methylenic group in the 1H NMR and 13C { H} NMR
1
spectra.
3.2. Syntheses of the Y (5), Sm (6) and Nd(7)
chloro-complexes MLCl2(THF)
In Table 1, the polymerization data relative to samarium (6)
and neodymium (7) based catalysts are also reported. Complex
(5) always showed higher reactivity, although derivatives (6) and
(7) were used in the same conditions.
The yttrium complex 5 was prepared by the very slow addi-
tion of the ligand sodium salt 4 to a suspension of YCl3 in THF
at room temperature. Many attempts to carry out the reaction
at low temperatures afforded lower yields of the final prod-
uct. Alternatively, the protonated ligand 4H was reacted with
potassium tert-butoxide in THF at room temperature and subse-
quently solid YCl3 was slowly added. In both cases the mixtures
obtained were allowed to react for 12 h. After separation of
NaCl or KCl the complex YLCl2(THF) (5) was obtained as
yellow microcrystals and was fully characterized by NMR and
Complexes (5), (6) and (7) activated with MAO or
with Mg(Bu)2 and B(C6F5)3 were tested in the poly-
merization of butadiene. The catalysts showed very low
activities affording polybutadiene with low molecular weight
(Mw = 103–104 g/mol−1) but with MWD unimodal and narrow
(Mw/Mn = 1.4–2). However, unexpected results relative to poly-
mer microstructure (showed in Table 2) were obtained. In fact,
polymerization performed by using MAO as activator of group
3 metal compounds produced prevailingly a 1,4-cis polybutadi-
ene (e.g. yttrium based catalyst give exclusively 1,4-cis units).
Instead, by using as co-catalyst Mg(Bu)2 and B(C6F5)3, pre-
vailingly 1,4-trans polybutadiene was obtained (e.g. samarium
based catalyst give exclusively 1,4-trans units).
It is well known from the literature, that the formation of a
1,4-cis or a 1,4-trans unit arise from an ␲-allyl terminal grow-
ing chain anti or syn, respectively. Anti-allyl group is generated
by a s-cis monomer coordination and insertion. Syn-allyl group
can be both obtained by a trans monomer insertion and by iso-
merization of less thermodynamically stable anti-group [17,18].
The two mechanisms are depicted in Scheme 2. Generally, η4-
cis coordination of butadiene is possible when the catalytic site
1
1
Mass Spectrometry. Its H NMR and 13C { H} NMR spectra
showed, downfield, the signals of the imine group, the pyri-
dine and phenyl rings. The Cp ring appears as a pseudo-A2B2
spin system. The aliphatic region showed the co-ordinated THF
molecule, the methylenic and isopropylic groups: these last ones
were non-equivalent, since the co-ordination to the metal frag-
ment does not allow the free rotation of the phenyl ring around
the C(phenyl)-N(imine) single bond. The MS spectrum of the
complex showed the presence of the signal at 503 m/z assignable
to the molecular ion after the loss of the co-ordinated THF
molecule, which is immediately lost because of the relatively
high temperature (about 300 ◦C) of the sample injection system.

264
G. Paolucci et al. / Journal of Molecular Catalysis A: Chemical 272 (2007) 258–264
4. Conclusions
In conclusion, it is interesting to observe how both the nature
of the metal ion and the co-catalyst play a fundamental role
not only in catalytic activity, but also in selectivity of the
MLCl2(THF)-based systems. In fact, as discussed before, the
change in selectivity can be really tremendous, ranging from
>99% 1,4 cis-polybutadiene to >99% 1,4 trans-polybutadiene.
Further studies will be carried out in order to improve the activity
of the catalytic systems here presented.
Acknowledgements
The authors are indebted with MIUR (Italian Minister of Uni-
versity and Research) for the financial support (PRIN 2004 prot
2004030307 003).
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