Synthesis, structure and butadiene polymerization behavior of CoCl 2(PRxPh3 - X)2 (R = methyl, ethyl, propyl, allyl, isopropyl, cyclohexyl; X = 1, 2). Influence of the phosphorous ligand on polymerization stereo

Article abstract of DOI:10.1016/j.jorganchem.2005.02.012

Several cobalt(II) phosphine complexes have been synthesized by reacting cobalt(II) chloride with various mono- and diphenylalkylphosphines (PR _xPh_{3 - x}; R = methyl, ethyl, allyl, propyl, isopropyl, cyclohexyl; x = 1, 2). For some of

Full text of DOI:10.1016/j.jorganchem.2005.02.012

Journal of Organometallic Chemistry 690 (2005) 1845–1854
www.elsevier.com/locate/jorganchem
Synthesis, structure and butadiene polymerization behavior
of CoCl2(PRxPh3 ꢀ x)2 (R = methyl, ethyl, propyl, allyl,
isopropyl, cyclohexyl; x = 1, 2). Influence of the phosphorous
ligand on polymerization stereoselectivity
a,
b
a
c
Giovanni Ricci *, Alessandra Forni , Aldo Boglia , Anna Sommazzi ,
d
Francesco Masi
a
CNR-Istituto per lo Studio delle Macromolecole (ISMAC), via E. Bassini 15, 20133 Milano, Italy
CNR-Istituto di Scienze e Tecnologie Molecolari (ISTM), via C. Golgi 19, 20133 Milano, Italy
b
c
Polimeri Europa S.p.A. – Centro Ricerche di Novara, ‘‘Ist. Guido Donegani’’; via Fauser 4, 28100 Novara, Italy
d
Polimeri Europa S.p.A. – Divisione Politene, via Jannozzi 1, 20097 San Donato Milanese, Italy
Received 17 December 2004; accepted 10 February 2005
Available online 17 March 2005
Dedicated to the memory of Roberto Santi, who was an irreplaceable teacher and friend for all of us
Abstract
Several cobalt(II) phosphine complexes have been synthesized by reacting cobalt(II) chloride with various mono- and diph-
enylalkylphosphines (PRxPh3 ꢀ x; R = methyl, ethyl, allyl, propyl, isopropyl, cyclohexyl; x = 1, 2). For some of these complexes sin-
gle crystals were obtained and their molecular structures were determined by X-ray diffraction method. All the complexes were then
used in association with MAO for the polymerization of 1,3-butadiene and they were found to be extremely active. Predominantly
1,2 polymers having different tacticity (predominantly iso- or syndiotactic), depending on the type of phosphine ligand bonded to
the cobalt atom, were obtained. An interpretation of this particular behavior, based on the diene polymerization mechanism pre-
viously proposed, is reported.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Phosphine cobalt complexes; X-ray structure; Cobalt catalysts; Butadiene polymerization; 1,2 Syndiotactic polybutadiene; Polymeri-
zation stereoselectivity
1. Introduction
Predominantly 1,2 polybutadienes having an atactic
structure were obtained with systems using less hindered
phosphines (e.g., PEt3, PnPr3), while essentially cis-1,4
polybutadienes were prepared by using more hindered
phosphines (e.g., PtBu2Me). We have also reported on
the synthesis of CoCl2(PiPrPh2)2 and its behavior in
the polymerization of butadiene [2]; when used in asso-
ciation with MAO, it was found to be extremely active
and stereospecific, giving a highly syndiotactic 1,2 poly-
butadiene. If we consider that, as cited above, the sys-
We have recently found that the systems CoCl2
(PR3)2–MAO (R = alkyl group) give, from butadiene,
polymers with different structure (cis-1,4; mixed cis-
1,4/1,2; predominantly 1,2) depending on the type of
phosphine ligand [1], meaning that the ligand has a
strong influence on the polymerization chemoselectivity.
*
Corresponding author. Tel.: +390223699376; fax: +39022362946.
E-mail address: giovanni.ricci@ismac.cnr.it (G. Ricci).
tem CoCl2(PEt3)2–MAO gives from butadiene a
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.012

1846
G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
predominantly 1,2 polymer having an atactic structure,
it follows that the type of phosphorous
ligand may influence the polymerization stereoselectiv-
ity, too.
We thought to check this experimental indication by
synthesizing some new cobalt complexes using different
mono- and diphenylalkyl phosphines [3] (PMePh2,
PMe2Ph, PEtPh2, PEt2Ph, P(allyl)Ph2, P(allyl)2Ph,
PnPrPh2, PCyPh2, PCy2Ph; Me = methyl, Et = ethyl,
nPr = normal-propyl, Cy = cyclohexyl) in which the ste-
ric demand of the alkyl group is varied with respect to
CoCl2(PiPrPh2)2: it is well known that steric and elec-
tronic properties of the phosphines are strongly influ-
enced by the nature of substituents on the
C3
C4
Cl2
C2
C17
Cl1
C16
C22
C1
Co1
C5
C10
C18
P1
C6
C15
P2
C11
C12
C9
C19
C8
C21
C20
C7
C24
C14
C23
C13
C25
Cl3
C28
C32
C31
C30
C26
C27
C33
Co2
C29
C34
C39
P3
C38
C37
C40
C41
C36
C35
C42
Fig. 1. ORTEP plot of CoCl2(PEtPh2)2 [13] with atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability. Hydrogen
atoms are omitted for clarity.
C43
C42
C44
C41
C40
P3
C45
C14
C13
C15
C10
Cl2
P2
Cl1
Cl3
C12
C31
Co1
Co2
C11
C33
C6
C29
C37
C30
C32
P1
C28
C27
C36
C8
C25
C17
C38
C39
C34
C35
C7
C23
C9
C1
C5
C26
C18
C16
C22
C21
C24
C2
C4
C19
C3
C20
Fig. 2. ORTEP plot of CoCl2(PnPrPh2)2 [13] with atom numbering scheme. Displacement ellipsoids are drawn at the 20% probability. Hydrogen
atoms are omitted for clarity.

G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
1847
Table 2
Selected bond lengths (A) and angles (ꢁ) for CoCl2(P PrPh2)2
n
˚
Cl1
Cl2
C23
Co1–Cl1
Co1–Cl2
Co2–Cl3
Co1–P1
Co1–P2
Co2–P3
P1–C1
2.2118(9)
2.1960(9)
2.2090(8)
2.3691(8)
2.3640(10)
2.3940(9)
1.811(2)
1.827(2)
1.815(3)
1.814(2)
1.826(2)
1.816(2)
1.820(3)
1.827(2)
1.810(3)
C24
C22
C10
C7
Co
C9
P2
P1
C1
C18
C8
C19
C11
C2
C12
C13
C17
P1–C7
C3
P1–C10
P2–C16
P2–C22
P2–C25
P3–C31
P3–C37
P3–C40
C20B
C6
C14
C21B
C16
C4
C15
C5
Fig. 3. ORTEP plot of CoCl2(P(allyl)2Ph)2 [13] with atom numbering
scheme. Displacement ellipsoids are drawn at the 20% probability.
Cl1–Co1–Cl2
Cl3–Co2–Cl30
P1–Co1–P2
P3–Co2–P30
Cl1–Co1–P1
Cl1–Co1–P2
Cl2–Co1–P1
Cl2–Co1–P2
Cl3–Co2–P3
Cl3–Co2–P30
C1–P1–C7
112.60(3)
113.49(6)
103.73(3)
105.97(4)
108.36(4)
111.46(4)
111.11(3)
109.23(3)
107.82(3)
110.75(3)
105.16(11)
105.98(11)
103.12(12)
106.24(11)
105.73(11)
102.02(11)
102.32(11)
105.27(12)
105.04(12)
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) for CoCl2(PEtPh2)2
Co1–Cl1
Co1–Cl2
Co2–Cl3
Co1–P1
Co1–P2
Co2–P3
P1–C1
2.2276(7)
2.2201(7)
2.2145(6)
2.3747(6)
2.3760(6)
2.3654(6)
1.8134(18)
1.8304(19)
1.8179(18)
1.8097(19)
1.8319(19)
1.8131(19)
1.8173(18)
1.8262(19)
1.8127(19)
C1–P1–C10
C7–P1–C10
C16–P2–C22
C16–P2–C25
C22–P2–C25
C31–P3–C37
C31–P3–C40
C37–P3–C40
P1–C7
P1–C9
P2–C15
P2–C21
P2–C23
P3–C29
P3–C35
P3–C37
Cl1–Co1–Cl2
Cl3–Co2–Cl30
P1–Co1–P2
P3–Co2–P30
Cl1–Co1–P1
Cl1–Co1–P2
Cl2–Co1–P1
Cl2–Co1–P2
Cl3–Co2–P3
Cl3–Co2–P30
C1–P1–C7
110.57(2)
115.07(4)
100.63(2)
105.15(3)
111.85(2)
109.92(2)
111.01(2)
112.52(2)
106.94(2)
111.17(2)
103.22(8)
105.85(8)
104.37(8)
104.69(9)
104.87(8)
104.22(8)
104.00(9)
105.11(8)
104.67(9)
Table 3
˚
Selected bond lengths (A) and angles (ꢁ) for CoCl2(P(allyl)2Ph)2
Co–Cl1
Co–Cl2
Co–P1
Co–P2
P1–C1
2.2095(7)
2.2092(7)
2.3565(7)
2.3490(7)
1.816(2)
1.826(2)
1.839(2)
1.810(2)
1.831(2)
1.826(2)
P1–C7
P1–C10
P2–C13
P2–C19
P2–C22
C1–P1–C9
C7–P1–C9
C15–P2–C21
C15–P2–C23
C21–P2–C23
C29–P3–C35
C29–P3–C37
C35–P3–C37
Cl1–Co–Cl2
P1–Co–P2
117.29(3)
106.58(2)
114.46(2)
100.28(2)
104.59(2)
113.43(2)
103.75(9)
105.63(9)
104.86(10)
105.97(9)
106.82(11)
104.76(11)
Cl1–Co–P1
Cl1–Co–P2
Cl2–Co–P1
Cl2–Co–P2
C1–P1–C10
C1–P1–C7
phosphorous atom [4]. The crystalline structures of
some of these complexes were determined and then they
were used in combination with MAO for the polymeri-
zation of 1,3-butadiene [5]. The results obtained are re-
ported in the present paper.
C10–P1–C7
C13–P2–C22
C13–P2–C19
C22–P2–C19

1848
G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
2. Results and discussion
centre. The largest deviations from the ideal tetrahedral
geometry, 117.29(3)ꢁ and 100.28(2)ꢁ, are observed in
CoCl2[P(allyl)2Ph]2 for the angles Cl1–Co–Cl2 and
Cl1–Co–P2, respectively. In all cases, the Cl–Co–Cl an-
gles are found systematically larger than the tetrahedral
value, while the opposite trend is observed for the P–
Co–P angles.
The crystal structures of CoCl2(PEtPh2)2 and
CoCl2(PnPrPh2)2 are very similar, as it appears by com-
paring not only the geometrical parameters of Tables 1
and 2, but also the structural data reported in Table 4.
In both cases the space group is C2/c, with one and a half
molecules in the asymmetric unit and a very long (up to
2.1. Synthesis and characterization of cobalt complexes
The complexes were prepared following a general
experimental procedure already reported in the litera-
ture [6]. CoCl2 was reacted with an excess of phosphine
using ethanol as solvent. Crystalline products were ob-
tained by continuous extraction of the reaction products
with boiling pentane or toluene. Single crystals were ob-
tained in the case of CoCl2(PEtPh2)2, CoCl2(PnPrPh2)2
and CoCl2[P(allyl)2Ph]2, and their structures determined
by X-ray diffraction. For CoCl2(PMePh2)2 and CoCl2-
(PCyPh2)2, structure determination was not possible
owing to large disorder affecting both structures. No
monocrystals have been obtained for all the other
complexes.
˚
47 A) a cell side. By averaging on all the chemically
equivalent bond lengths, the values Co–Cl = 2.221 and
˚
˚
2.206 A, Co–P = 2.372 and 2.376 A, P–Caromatic
=
1.814 A (in both structures), P–Calyphatic = 1.830 and
˚
˚
The molecular structures of CoCl2(PEtPh2)2,
CoCl2(PnPrPh2)2 and CoCl2[P(allyl)2Ph]2 are shown in
Figs. 1–3, respectively, and selected bond lengths and
angles are reported in Tables 1–3. The complexes show
a distorted tetrahedral coordination around the Co(II)
1.827 A are obtained in CoCl2(PEtPh2)2 and
CoCl2(PnPrPh2)2, respectively. When comparing these
two systems with the previously studied CoCl2(PiPrPh2)2
complex, [2] we observe only slight differences, the larger
˚
one being a longer P–Calyphatic average distance (1.850 A)
Table 4
Crystal data, details of data collection and results of the refinement for CoCl2(PEtPh2)2, CoCl2(PnPrPh2)2 and CoCl2(P(allyl)2Ph)2
Compound
Formula
Mr
CoCl2(PEtPh2)2
C28H30Cl2CoP2
558.29
CoCl2(PnPrPh2)2
C30H34Cl2CoP2
586.34
CoCl2(P(allyl)2Ph)2
C24H30Cl2CoP2
510.25
Crystal system
Space group
Z
Monoclinic
C2/c
12
Monoclinic
C2/c
12
Triclinic
ꢀ
P1
2
1.292
Dcalc (g cmꢀ3
)
Unit cell dimensions
1.400
1.331
˚
a (A)
46.361(9)
9.863(2)
47.058(9)
10.169(2)
9.377(2)
10.336(2)
13.654(3)
˚
b (A)
˚
c (A)
18.645(4)
90
19.538(4)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
87.235(10)
86.248(10)
83.913(10)
1312.0(5)
111.28(1)
90
7944(3)
110.12(3)
90
8779(3)
3
˚
V (A )
Crystal size (mm)
Color, habit
0.52 · 0.32 · 0.10
Light blue, prism
0.986
0.25 · 0.17 · 0.10
Light blue, prism
0.896
0.30 · 0.24 · 0.08
Light blue, prism
0.988
l (mmꢀ1
Radiation
T (K)
)
Mo Ka
90(2)
Mo Ka
293(2)
Mo Ka
293(2)
2hmax (ꢁ)
h, k, l ranges
56.5
ꢀ61 ! 60; ꢀ12 ! 12; ꢀ24 ! 24
53.7
ꢀ59 ! 59; ꢀ12 ! 12; ꢀ24 ! 24
66.2
ꢀ14 ! 14; ꢀ15 ! 15; ꢀ20 ! 20
0.00
Intensity decay,%
Absorption correction
Tmin, Tmax
0.00
0.00
None
Multi-scan (Bruker SADABS)
0.899, 1.000
52731
Multi-scan (Bruker SADABS)
0.908, 1.000
19647
–
53660
Number of measured reflections
Rint
0.0298
9433
0.0580
9060
5619
0.0257
9105
Number of independent reflections
Number of reflections with I > 2r(I)
Number of parameters, restraints
R(F2), wR(F2)
R[F2 > 2r(F2)], wR[F2 > 2(F2)]
Goodness-of-fit
8701
447, 0
4753
281, 3
474, 0
0.0396, 0.0898
0.0365, 0.0882
1.058
0.0671, 0.0847
0.0375, 0.0799
0.867
0.0884, 0.1146
0.0423, 0.1026
0.897
(D/r)max
Dqmax,qmin (e A
0.001
0.968, ꢀ0.397
0.001
0.285, ꢀ0.217
0.001
0.374, ꢀ0.194
ꢀ3
˚
)

G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
1849
in CoCl2(PiPrPh2)2, which can be ascribed to the larger
2.2. Polymerization of 1,3-butadiene
bulkiness of the isopropyl group with respect to the ethyl
and the n-propyl groups.
The results obtained in the polymerization of butadi-
ene with the various cobalt complexes are shown in
Table 5 and can be summarized as follows; the results
obtained with the system CoCl2(PiPrPh2)2–MAO, al-
ready reported in the literature [2], are added for
comparison.
Complex CoCl2[P(allyl)2Ph]2 is very similar to the
previously discussed ones, as far as the relevant struc-
tural parameters are concerned. The only remarkable
difference, in agreement with the reduced bulkiness of
the phosphine ligands, is observed in the Co–P distances
˚
(2.353 A on average), which are slightly shorter than
the corresponding ones in CoCl2(PEtPh2)2 and
CoCl2(PnPrPh2)2.
(i) The systems CoCl2(PRPh2)2–MAO (R = methyl,
normal-propyl, ethyl, allyl, iso-propyl, cyclohexyl)
were found to be extremely active in the polymer-
ization of butadiene; in general complete conver-
sions were reached in a few minutes. The
polymers obtained are essentially 1,2, as indicated
Analysis of crystal packing reveals the presence of C–
Hꢁ ꢁ ꢁCl intermolecular hydrogen bonds in all structures,
the stronger ones being C12–H12Aꢁ ꢁ ꢁCl1
and
ꢀx, ꢀy, 1 ꢀ z
C15–H15ꢁ ꢁ ꢁCl21 + x, y, z in complex CoCl2 [P(allyl)2Ph]2
1
˚
(Hꢁ ꢁ ꢁCl distances 2.80(1) and 2.90(1) A, C–Hꢁ ꢁ ꢁCl an-
by their H NMR spectra (Fig. 4); the 1,2 content
gles 150(1)ꢁ and 167(1)ꢁ, respectively). Moreover, in
CoCl2(PEtPh2)2 and CoCl2(PnPrPh2)2 the presence of
several p–p interactions between phenyl rings arranged
in T-shape configuration can be detected on the basis
of geometrical considerations. The dihedral angles be-
tween the least-square planes through the interacting
rings fall in the range 85(1)–90(1)ꢁ, and one or two H
atom of a phenyl ring point towards the centre or a
bond of the other ring. The shortest approaching dis-
tance is observed in CoCl2(PEtPh2)2, where the atom
is in the range 70–88%, and varies with varying the
type of catalyst and the polymerization conditions.
The remaining units are essentially cis-1,4; the
band at 967 cmꢀ1 in the IR spectra of the poly-
mers, indicative of the presence of trans-1,4 units,
is almost negligible.
(ii) The polymer tacticity strongly depends on the type
of catalyst, i.e., the type of phosphine bonded to
the cobalt atom. The syndiotactic index (expressed
as percentage of sydiotactic triads rr) of the poly-
mers, determined by their 13C NMR spectra
(Fig. 5), increases with increasing the hindrance
of the phosphorous ligand, i.e., the steric demand
˚
H25x, 1 ꢀ y, 1/2 + z is placed at 2.54(1) A from the plane of
the ring C29–C34, pointing approximately towards its
centre.
Table 5
Polymerization of butadiene with different cobalt systemsa
Run
Catalyst
Polymerization
Time (min)
Polymer microstructureb
m.p. (ꢁC)
Co-compound
CoCl2(PMePh2)2
Al/Co (molar ratio)
Conv (%)
cis (%)
1,2 (%)
rr::mr::mm (molar fraction)
1
2
1000
500
100
50
5
5
58.0
59.2
64.7
26.0
15.2
93.7
100
29.9
27
70.1
73.0
76.1
73.0
74.0
77.7
78.7
80.2
85.4
82.7
88.0
80.0
84.5
88.0
84.0
73.0
75.3
74.0
79.4
23/47/30
23/51/26
24/52/24
24/52/24
25/52/23
42/45/13
44/43/13
41/44/15
74/26/0
–
–
3
5
23.9
27.0
26.0
22.3
21.3
19.8
14.6
17.3
12
–
4
60
60
5
–
5
20
–
6
CoCl2(PEtPh2)2
CoCl2(PnPrPh2)2
CoCl2[P(allyl)Ph2]2
CoCl2(PiPrPh2)2
CoCl2(PCyPh2)2
100
100
100
100
1000
1000
500
100
100
20
–
7
5
–
8
5
76
100
–
9
5
126
117
132
106
109
139
115
–
10
11c
12
13
14c
15
16
17
18
19
a
5
72
100
71/25/4
76/22/2
2
5
70.8
75.0
100
20
68/28/4
69/27/4
5
15.5
12
3
78/20/2
70/27/3
60
5
33.4
39.8
55.4
40.1
55.1
16
CoCl2(PMe2Ph)2
CoCl2(PEt2Ph)2
CoCl2[P(allyl)2Ph]2
CoCl2(PCy2Ph)2
100
100
100
100
27.0
24.7
26.0
20.6
15/51/34
19/49/32
22/49/29
44/41/15
5
–
5
–
5
–
Polymerization conditions: butadiene, 2 ml; toluene, total volume 16 ml; MAO; 5 · 10ꢀ6 mol of Co (1 · 10ꢀ5 mol in runs 4,5 and 15); +20 ꢁC. The
molecular weight (MW) and molecular weight distribution (MWD) of the amorphous 1,2 polybutadienes are in the range 250–300000 g/mol and 2–
2.5, respectively. The predominantly syndiotactic 1,2 polybutadienes (runs 9–15) were not soluble in the GPC conditions used.
b
Determined by 1H and 13C NMR analysis; trans-1,4 units were found to be negligible, as indicated by the extremely low intensity of the band at
967 cmꢀ1 in the IR spectra of the polymers.
c
Heptane as solvent was used instead of toluene.

1850
G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
Fig. 4. 1H NMR spectrum (C2D2Cl4, HMDS as internal standard,
103 ꢁC) of the polybutadiene obtained with the system CoCl2(P-
CyPh2)2–MAO (Table 5, run 13).
of the alkyl group bonded to the phosphorous
atom (compare, for instance, runs 3, 6–9, and 13
in Table 5).
(iii) The 1,2 polybutadienes obtained with the cobalt
systems using less hindered ligands (e.g., PMePh2;
PEtPh2; PnPrPh2) are amorphous and no melting
point could be detected; the Tg values of these
polymers were found to be in the range ꢀ10 to
ꢀ15 ꢁC. The polymers obtained with systems using
more hindered ligands (e.g., PiPrPh2 and PCyPh2)
are crystalline by X-ray with a melting point rang-
ing from 109 to 139 ꢁC, depending on the polymer-
ization conditions. They exhibited Tg values
around 3–5 ꢁC and crystallization enthalpies rang-
ing from ꢀ10 to ꢀ20 J/g.
(iv) In general the Al/Co molar ratio does not affect the
stereospecificity, but it has some influence on
the catalyst activity. When the Al/Co ratio is in
the range 100–1000, the activity is extremely high
and complete conversions can be reached in a
few minutes, nevertheless a quite good activity is
also obtained at very low Al/Co molar ratio (20–
50).
(v) The polymerization rate is higher and more stereo-
regular polymers (higher 1,2 content and higher
syndiotacticity) are obtained when heptane instead
of toluene is used as polymerization solvent, indi-
cating that the aromatic solvent can in some way
coordinate to the metal atom affecting the catalyst
geometry and competing with the incoming mono-
mer. This phenomenon is not however surprising
because a similar solvent effect was already
observed for instance in the polymerization of
1,3-dienes with neodymium catalysts [7].
Fig. 5. 13C NMR spectrum (olefinic region, C4 signal; C2D2Cl4,
HMDS as internal standard, 103 ꢁC) of the polybutadienes obtained
with (a) CoCl2(PMePh2)2–MAO (Table 5, run 3); (b) CoCl2-
(PnPrPh2)2–MAO (Table 5, run 7); (c) CoCl2(PCyPh2)2–MAO (Table
5, run 13).
(vi) We have also examined the polymerization of
butadiene with the systems CoCl2(PR2Ph)2–
MAO (Table 5, runs 16–19); essentially 1,2 poly-
mers were obtained also in this case but the
syndiotactic index of the polymers, at the same
polymerization conditions, was in general slightly
lower with respect to that of the 1,2 polybutadi-
enes obtained with CoCl2(PRPh2)2–MAO.

G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
1851
sible to obtain 1,2 polybutadienes having different melt-
ing point, crystallinity degree and tacticity, the
syndiotacticity increasing with increasing the steric hin-
drance of the alkyl group.
Finally, the results obtained have also some mecha-
nistic implications; they can be interpreted on the basis
of the diene polymerization mechanism proposed by
Porri, confirming, if still necessary, its validity and sup-
porting some aspects of the same mechanism, in partic-
ular the influence of the ligand on the stereoselectivity.
4. Experimental
Fig. 6. Possible reciprocal orientation ((a) exo–exo; (b) exo–endo) of
the butadiene of the allylic unit of the polymer growing chain and of
the butadiene entering monomer.
4.1. General procedures and materials
Methyldiphenylphosphine (Strem, 99% pure),
dimethylphenylphosphine (Strem, 99% pure), normal-
The formation of 1,2 polymers having different tactic-
ity depending on the type of phosphine ligand, in the
polymerization of butadiene with the cobalt systems of
this paper, is not an absolute novelty. A similar behavior
has already been observed in the polymerization of
butadiene with CrCl2(L)2–MAO systems (L = bidentate
phosphine ligand) [8]. The interpretation given at that
time for such a behavior, based on the diene polymeriza-
tion mechanism proposed by Porri et al. [9], is still valid
and can also be applied to the cobalt catalysts described
in this paper. The incoming butadiene monomer and the
allylic unit of the growing polymer chain can assume the
two different orientations shown in Fig. 6. Depending
on the type of phosphine ligand the exo–exo or the
exo–endo orientation can be favored and syndiotactic
or isotactic sequences can be formed; when the steric de-
mand of the ligand is higher (e.g., PiPrPh2, PCyPh2, and
PCy2Ph), the exo–exo orientation is the favored one and
predominantly syndiotactic polymers are obtained.
propyldiphenylphosphine
(Aldrich,
98%
pure),
ethyldiphenylphosphine (Aldrich, 98% pure), diethyl-
phenylphosphine (Aldrich, 96% pure), allyldiphenyl-
phosphine (Aldrich, 95% pure), diallylphenylphosphine
(Aldrich, 95% pure), iso-propyldiphenylphosphine (Al-
drich, 97% pure), cyclohexyldiphenylphosphine (Strem,
98% pure), dicyclohexylphenyphosphine (Aldrich, 95%
pure), anhydrous cobalt dichloride (Aldrich, 99.9%
pure), and methylaluminoxane (MAO) (Crompton,
10 wt% solution in toluene) were used as received. Ethyl
alcohol (Carlo Erba, 96ꢁ) was degassed under vacuum,
then by bubbling dry dinitrogen and kept over molecular
sieves; pentane (Carlo Erba, >99% pure) was refluxed
over Na/K alloy for ca. 8 h, then distilled and stored over
molecular sieves under dry dinitrogen; toluene (Carlo
Erba, 99.5% pure) was refluxed over Na for ca. 8 h, then
distilled and stored over molecular sieves under dry dini-
trogen. 1,3-Butadiene (Air Liquide, >99.5% pure) was
evaporated from the container before each run, dried
by passing through a column packed with molecular
sieves and condensed into the reactor which had been
precooled to ꢀ20 ꢁC. All the phosphine cobalt complexes
were synthesized as indicated below, following a general
procedure already reported in the literature [6]. Infrared
spectra of the cobalt complexes were recorded as KBr
disks with a Bruker IFS 48 instrument.
3. Conclusion
New cobalt phosphine complexes have been synthe-
sized by reacting cobalt (II) chloride with various diph-
enylalkylphosphines. In the case of CoCl2(PEtPh2)2,
CoCl2(PnPrPh2)2 and CoCl2[P(allyl)2Ph]2, single crystals
have been obtained allowing us to determine their
molecular structure.
4.2. Synthesis of cobalt phosphine complexes
All these complexes were then used in association
with MAO for the polymerization of 1,3 butadiene; they
were found to be highly active catalysts giving polymers
having an essentially 1,2 structure. This result is quite
interesting, since it is known that 1,2 polybutadiene
plays an important role in the field of butadiene poly-
mers, being the only polymer together with cis-1,4 poly-
butadiene industrially produced.
4.2.1. CoCl2(PMePh2)2
Methyldiphenylphosphine (4.00 g, 1.82 · 10ꢀ2 mol)
was added to
a
solution of CoCl2 (1.06 g,
8.20 · 10ꢀ3 mol) in ethanol (100 ml). A blue precipitate
is immediately formed; after 20 h it was filtered, washed
with ethyl alcohol (2 · 10 ml) and pentane (2 · 10 ml),
then dried in vacuum at room temperature. The blue so-
lid isolated was transferred on the filter of a Soxhlet for
solids and extracted in continuous with boiling toluene.
Moreover by varying the alkyl group bonded to the
phosphorous atom, i.e., the ligand hindrance, it was pos-

1852
G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
The extraction was practically complete in two days; at
the end a crystalline blue product is formed on the bot-
tom of the extraction Schlenck-tube. The blue superna-
tant solution was removed, concentrated and cooled at
ꢀ30 ꢁC, causing the precipitation of a crystalline prod-
uct. Further crops of crystals were obtained by repeating
this work-up operation several times. Yield: 3.49 g (80%
based on CoCl2).
Anal. Calc. for C26H26CoCl2P2: Co, 11.11; Cl, 13.37;
P, 11.68. Found: Co, 10.9; Cl, 13.2; P, 11.3%.
Spectroscopic data: IR (KBr) m (cmꢀ1) 3053m,
3009w, 2988w, 1484m, 1437s, 1416m, 1332w, 1314w,
1289w, 1186w, 1100m, 1073w, 1026w, 999w, 888s,
844w, 757m, 739s, 694s, 507s, 472m, 436w, 419w.
4.2.4. CoCl2(PEt2Ph)2
Diethylphenylphosphine (2.1 g, 9.75 · 10ꢀ3 mol) was
added to a solution of CoCl2 (0.26 g, 2 · 10ꢀ3 mol) in
ethyl alcohol (60 ml).The dark blue solution formed
was stirred at room temperature for 24 h, then the sol-
vent was removed under vacuum. The residue obtained
was washed with pentane (3 · 20 ml), dried under vac-
uum and then extracted in continuous with boiling tolu-
ene for ca. 24 h. The blue solution obtained was
concentrated, and a large excess of pentane was added
causing the formation of a blue precipitate which was fil-
tered off and dried under vacuum. Yield, 0.66 g (69%
based on CoCl2).
Anal. Calc. for C20H30Cl2CoP2: Co, 12.75; Cl, 15.34;
P, 13.4. Found: Co, 12.4; Cl, 15.5; P, 13.0%.
4.2.2. CoCl2(PMe2Ph)2
Dimethylphenylphosphine (2.2 g; 1.65 · 10ꢀ3 mol)
Spectroscopic data: IR (KBr) m (cmꢀ1) 2961m,
2934m, 2873m, 2855m, 1462s, 1435ms, 1378m,
1102ms, 1072w, 1043m, 1032m, 856w, 777m, 748m,
732m, 722m, 713m, 694m, 639m, 513s.
was added to
a
solution of CoCl2 (1.07 g,
8.2 · 10ꢀ3 mol) in ethanol (60 ml). A dark-blue solution
is immediately formed; it was kept under stirring at
room temperature for 24 h, then the solvent was re-
moved under vacuum. The residue was washed with eth-
anol (2 · 10 ml) at low temperature and with pentane
(3 · 20 ml) and then dried under vacuum at room tem-
perature. Yield: 2.6 g (80% based on CoCl2).
Anal. Calc. for C16H22Cl2CoP2: Co, 14.51; Cl, 17.46;
P, 15.25. Found: Co, 14.2; Cl, 17.7; P, 15.4%.
Spectroscopic data: IR (KBr) m (cmꢀ1) 3076w,
2971m, 2907m, 1489m, 1435s, 1420s, 1322w, 1305m,
1288w, 1136m, 1107ms, 1029w, 1001w, 953s, 906s,
873m, 837w, 747s, 717m, 690s, 677m, 484s.
4.2.5. CoCl2(PnPrPh2)2
Propyldiphenylphosphine (4 g, 1.75 · 10ꢀ2 mol) was
introduced on an ethanol solution (60 ml) of CoCl2
(1.06 g, 8.16 · 10ꢀ3 mol). The reaction was stirred for
about 24 h, then the blue precipitate formed was sepa-
rated by filtration, washed with ethyl alcohol and dried
under vacuum. The blue solid was then transferred on
the filter of a Soxhlet for solids and extracted in contin-
uous with boiling pentane. The solubility is not very
high, so the extraction was continued for several days.
A crystalline product is formed during the extraction,
which was separated by removing the supernatant and
dried under vacuum. Yield: 4.09 g (85% based on CoCl2).
Anal. Calc. for C30H34CoCl2P2: Co, 10.05; Cl, 12.09;
P, 10.56. Found: Co, 10.0; Cl, 12 4; P, 10.2%.
4.2.3. CoCl2(PEtPh2)2
Ethyldiphenylphosphine (2.1 g; 9.75 · 10ꢀ3 mol) was
added to a solution of CoCl2 (0.55 g, 4.24 · 10ꢀ3 mol)
in 60 ml of ethyl alcohol. A blue precipitate is immedi-
ately formed; it was kept under stirring for 20 h then it
was filtered. The residue was washed with ethyl alcohol
(2 · 10 ml), then dried under vacuum. The blue solid
isolated was then transferred on the filter of a Soxhlet
for solids and extracted in continuous with boiling tol-
uene. The solubility in toluene is very high and the
extraction was practically completed in a few hours.
At the end a crystalline blue product is present on
the bottom of the extraction Schlenck, and further
crops of crystals can be isolated by concentration and
cooling of the supernatant. Yield: 2.2 g (94% based
on CoCl2).
Spectroscopic data: IR (KBr) m (cmꢀ1) 3051w,
2964m, 2938m, 2894w, 2873w, 1484m, 1450w, 1434s,
1408w, 1376w, 1332w, 1313w, 1187w, 1101s, 1080m,
1029m, 853w, 837m, 755s, 730ms, 696s, 513s, 482ms,
459w, 417w.
4.2.6. CoCl2[P(allyl)Ph2]2
A solution of CoCl2 (0.191 g, 1.4 · 10ꢀ3 mol) in ethyl
alcohol (10 ml) was added to an ethanol solution (40 ml)
of allyldiphenylphosphine (1 g, 4.42 · 10ꢀ3 mol). The
solution became dark blue; it was stirred for ca. 24 h,
then the solvent was removed under vacuum. The blue
residue was washed with small amounts of ethanol at
low temperature and with pentane (2 · 10 ml) and final-
ly dried in vacuum. Yield: 0.582 g (68% based on
CoCl2).
Anal. Calc. for C28H30CoCl2P2: Co, 10.56; Cl, 12.70;
P, 11.10. Found: Co, 10.6; Cl, 13.0; P, 11.2%.
Spectroscopic data: IR (KBr) m (cmꢀ1) 3050m,
2978m, 2965m, 2932m, 2907m, 2877m, 1484ms,
1457ms, 1435s, 1411m, 1385m, 1336w, 1313w, 1275w,
1251w, 1185m, 1161w, 1126w, 1102s, 1072w, 1028w,
1000s, 854w, 769ms, 742s, 695s, 674m, 512s, 480s,
461m, 418w.
Anal. Calc. for C24H30CoCl2P2: Co, 10.12; Cl, 12.18;
P, 10.64. Found: Co, 9.9; Cl, 12.3; P, 10.3%.
Spectroscopic data: IR (KBr) m (cmꢀ1) 1635m,
1484w, 1464m, 1435s, 1377m, 1099m, 988m, 923m,
839m, 740s, 691s.

G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
1853
4.2.7. CoCl2[P(allyl)2Ph]2
Anal. Calc. for C36H54Cl2CoP2: Co, 8.68; Cl, 10.45;
P, 9.13. Found: Co, 8.4; Cl, 10.6; P, 9.0%.
Bis-allylphenylphosphine (2 g, 1.05 · 10ꢀ2 mol) was
added to an ethanol solution (35 ml) of CoCl2 (0.55 g,
4.21 · 10ꢀ3 mol). The dark blue solution immediately
formed was stirred for one night at room temperature,
then the solvent was removed under vacuum. The resi-
due was washed several times with pentane; at the end
a blue solid is isolated. It was dissolved in toluene and
a crystalline product was obtained by cooling the solu-
tion at ꢀ30 ꢁC. Further crops of crystals were obtained
by concentration and cooling of the supernatant. Yield:
1.32 g (69% based on CoCl2).
Spectroscopic data: IR (KBr) m (cmꢀ1), 2954w, 2919s,
2853mw, 1626s, 1462s, 1377m, 1342w, 1268w, 1182mw,
999mw, 887w, 749s, 727m, 698s, 523s.
4.3. X-ray crystallographic studies
A summary of the experimental details concerning
the X-ray diffraction study of CoCl2(PEtPh2)2,
CoCl2(PnPrPh2)2 and CoCl2[P(allyl)2Ph]2 is reported in
Table 4. The crystals used for data collection were en-
tirely covered with perfluorinated oil to reduce crystal
decay. X-ray data were collected on a Bruker Smart
Apex CCD area detector equipped with fine-focus sealed
tube operating at 50 kV and 30 mA. The first 100 frames
were collected also at the end of the data collection to
monitor crystal decay. Data reduction was made using
SAINT programs; absorption corrections based on multi-
scan were obtained by SADABS [10]. The structures were
solved by SIR 92 [11] and refined on F2 by full-matrix
least-squares using SHELX 97 [12]. The program ORTEP-
III [13] was used for molecular graphics.
Anal. Calc. for C24H30Cl2CoP2: Co, 11.55; Cl, 13.90;
P, 12.14. Found: Co, 11.4; Cl, 13.8; P, 11.9%.
Spectroscopic data: IR (KBr) m (cmꢀ1) 3083w, 3057w,
3013w, 2978w, 2942w, 2899w, 1637ms, 1592w, 1487w,
1437s, 1421m, 1397m, 1262w, 1205m, 1152s, 1114s,
1074m, 996m, 932s, 852m, 833m, 748s, 694s, 631ms,
593m, 491m.
4.2.8. CoCl2(PCyPh2)2
Cyclohexyldiphenylphosphine (4.85 g, 1.81 · 10ꢀ2 mol)
dissolved in ethanol (60 ml) was added to an ethanol
solution (60 ml) of CoCl2 (1.065 g, 8.2 · 10ꢀ3 mol). A
blue precipitate is rapidly formed; the suspension was
stirred for ca. 20 h, then filtered. The blue residue on
the filter was washed with ethanol (2 · 10 ml) and
pentane (2 · 10 ml), then dried under vacuum. The blue
solid was then transferred on the filter of a Soxhlet for
solids and extracted in continuous with boiling pentane.
The solubility is moderate and the extraction was con-
tinued for several days. A crystalline product increasing
with time is formed during the extraction. At the end the
pentane solution is removed and the crystals are dried
under vacuum. Yield: 4.74 g (87% based on CoCl2).
Anal. Calc. for C36H42CoCl2P2: Co, 8.84; Cl, 10.64;
P, 9.29. Found: Co, 9.0; Cl, 10.5; P, 9.4%.
4.4. Polymerization
All operations were carried out under an atmosphere
of dry dinitrogen. A standard procedure is reported.
1,3-Butadiene was condensed into a 25 mL dried glass
reactor kept at ꢀ20 ꢁC, then toluene was added and
the solution so obtained was brought to the desired
polymerization
temperature.
Methylaluminoxane
(MAO) and the cobalt compound were then added, as
toluene solutions, in the order. The polymerization
was terminated with methanol containing a small
amount of hydrochloric acid, the polymer was coagu-
lated and repeatedly washed with methanol, then dried
in vacuum at room temperature.
Spectroscopic data: IR (KBr) m (cmꢀ1) 3056w, 2934s,
2853m, 1626s, 1482m, 1453s, 1372w, 1336w, 1264w,
1185mw, 1100ms, 1027mw, 999mw, 889w, 802mw,
745s, 694s, 618w, 527s, 516s, 499ms, 460mw.
4.5. Polymer characterization
13C NMR and 1H NMR measurements were per-
formed with a Bruker AM 270 instrument. The spectra
were obtained in C2D2Cl4 at 103 ꢁC (hexamethyldisilox-
ane, HMDS, as internal standard). The concentration of
polymer solutions was about 10 wt%. Differential scan-
ning calorimetry (DSC) scans were carried out on a Per-
kin Elmer Pyris 1 instrument. Typically, ca. 10 mg of
polymer were analyzed in each run, while scan speed
was ca. 20 K/min under a dinitrogen atmosphere.
X-ray diffraction powder spectra of the polymers were
recorded on an Italstructure h/h diffractometer. The
infrared spectra were performed with a Bruker IFS 48
instrument, using polymer films on KBr disks. The films
were obtained by deposition from solutions in benzene
or hot (ca.100 ꢁC) solutions in 1,2,4-trichlorobenzene.
4.2.9. CoCl2(PCy2Ph)2
Dicyclohexylphenylphosphine (1 g, 3.64 · 10ꢀ3 mol)
dissolved in ethanol (50 ml) was added to an ethanol
solution (20 ml) of CoCl2 (0.19 g, 1.46 · 10ꢀ3 mol). After
a few minutes, a blue-turquoise suspension is formed. It
was kept under stirring for one night, then the solvent
was partially removed and the blue precipitate filtered
off. The residue on the filter was washed with ethanol
(3 · 10 ml) and pentane (3 · 10 ml), then dried under
vacuum. The residue was successively extracted in con-
tinuous with boiling toluene for a few days; the blue
extraction solution was concentrated and a large excess
of pentane was added causing the precipitation of a blue
powder. Yield, 0.85 g (86% conversion based on CoCl2).

1854
G. Ricci et al. / Journal of Organometallic Chemistry 690 (2005) 1845–1854
The molecular weight averages (MW) and the molecular
weight distribution (MWD) were obtained by a high
temperature GPCV 2000 system (from Waters) using
two on-line detectors: a differential viscometer and a
refractometer. The experimental conditions consisted
of three Olefi columns from PSS, o-dichlorobenzene as
mobile phase, 0.8 mL/min of flow rate and 145 ꢁC of
temperature. The calibration of the GPC system was
constructed by eighteen narrow MWD polystyrene stan-
dards with the molar mass ranging from 162 to
3.3 · 106 g/mol.
References
[1] G. Ricci, A. Forni, A. Boglia, T. Motta, J. Mol. Cat. A: Chem.
226 (2005) 235.
[2] G. Ricci, A. Forni, A. Boglia, T. Motta, G. Zannoni, M. Canetti,
F. Bertini, Macromolecules 38 (2005) 1064.
[3] G. Ricci, A. Boglia, A. Forni, R. Santi, A. Sommazzi, F. Masi,
Italian Patent MI03A 001808, 23/09/2003.
[4] C.A. Tolman, Chem. Rev. 77 (1977) 313.
[5] (a) G. Ricci, A. Boglia, R. Santi, A. Sommazzi, F. Masi, Italian
Patent MI03A 001807, 23/09/2003;
(b) G. Ricci, A. Boglia, R. Santi, A. Sommazzi, F. Masi, Italian
Patent MI03A 001809, 23/09/2003.
[6] J. Chatt, B.L. Shaw, J. Chem. Soc. (1961) 285.
[7] G. Ricci, G. Boffa, L. Porri, Makromol. Chem., Rapid Commun.
7 (1986) 355.
5. Supplementary material
[8] (a) G. Ricci, M. Battistella, L. Porri, Macromolecules 34 (2001)
5766;
Tables of atomic coordinates, anisotropic thermal
parameters, bond lengths and angles of CoCl2(PEtPh2)2,
CoCl2(PnPrPh2)2 and CoCl2(P(allyl)2Ph)2 may be ob-
tained free of charge from The Director CCDC, 12 Union
Road, Cambridge CB2 1 EZ, UK, on quoting the deposi-
tion numbers CCDC 258333, 258334 and 258335, respec-
tively, the names of the authors and the journal citation
(fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk; web site: http://www.ccdc.cam.ac.uk).
(b) G. Ricci, A. Forni, A. Boglia, M. Sonzogni, Organometallics
23 (2004) 3727.
[9] (a) L. Porri, in: F. Ciardelli, P. Giusti (Eds.), Structural Order in
Polymers, Pergamon Press Ltd., Oxford, 1981, p. 51;
(b) L. Porri, A. Giarrusso, G. Ricci, Prog. Polym. Sci. 16 (1991)
405;
(c) L. Porri, A. Giarrusso, G. Ricci, Makromol. Chem., Macro-
mol. Symp. 48/48 (1991) 239;
(d) L. Porri, A. Giarrusso, G. Ricci, Macromol. Symp. 178 (2002)
55.
[10] Bruker, SMART, SAINT and SADABS; Bruker AXS Inc.: Madison
Wisconsin, USA, 1997.
[11] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C.
Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994)
435.
Acknowledgments
[12] G.M. Sheldrick, SHELX-97. Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Go¨ttingen Germany,
1997.
We thank Mr. Giulio Zannoni and Mr. Alberto Gia-
cometti Schieroni for their assistance in NMR and GPC
analyses of the polymers, respectively. The work has
been carried out with the financial support of Polimeri
Europa.
[13] M.N. Burnett, C.K. Johnson, ORTEP-III: Oak ridge thermal
ellipsoid plot program for crystal structure illustrations, Oak
Ridge National Laboratory Report ORNL-6895, 1996.