Preparation, structure, and olefin polymerization behavior of a picolyl-functionalized carborane nickel(II) complex

Article abstract of DOI:10.1021/om0493356

The picolyl-functionalized o-carborane ligand Cab^NH (1; Cab ^NH = 1-(2′-picolyl)-o-carborane) was prepared from the monolithium carborane LiHC²B¹⁰H¹⁰ (=LiCab) and picolyl chloride (2-CH₂ClC₅H₅N). 1 was lithiated with n-BuLi and then reacted with Ni(PPh₃) ₂Cl₂ to give the mononuclear Ni complex [(Cab ^N)₂]Ni (2). 2 was characterized by IR and NMR spectroscopy and elemental analysis. In addition, an X-ray structure analysis was performed on the complex, where the potential C,N-chelate ligand 1 was found to coordinate in a bidentate mode. The carborane complex 2 shows moderate catalytic activities of up to 3 × 10⁶ g of PNB (mol of Ni)^-1 h^-1 for the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities, molecular weights, and molecular weight distributions of polynorbornene (PNB) have been investigated under the various reaction conditions.

Full text of DOI:10.1021/om0493356

Organometallics 2004, 23, 6319-6322
6319
Notes
Preparation, Structure, and Olefin Polymerization
Behavior of a Picolyl-Functionalized Carborane
Nickel(II) Complex
Xin Wang and Guo-Xin Jin*
Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry,
Fudan University, Shanghai 200 433, China
Received August 25, 2004
Summary: The picolyl-functionalized o-carborane ligand
group strongly bound to a late transition metal and
another coordinatively labile group has been of consid-
erable interest.9
Derivatives of the icosahedral carboranes have at-
tracted considerable recent attention in both their
N
N
Cab H (1; Cab H ) 1-(2′-picolyl)-o-carborane) was
-14
prepared from the monolithium carborane LiHC2B10H10
(
)LiCab) and picolyl chloride (2-CH2ClC5H5N). 1 was
lithiated with n-BuLi and then reacted with Ni(PPh3)2-
N
Cl2 to give the mononuclear Ni complex [(Cab )2]Ni (2).
2
fundamental properties and their wide-ranging poten-
was characterized by IR and NMR spectroscopy and
15-17
tial applications.
N-functionalized carboranes are
elemental analysis. In addition, an X-ray structure
analysis was performed on the complex, where the
potential C,N-chelate ligand 1 was found to coordinate
in a bidentate mode. The carborane complex 2 shows
potential σ-bonded carboranyl ligands possessing a
18,19
pendant nitrogen donor group.
It was therefore of
interest to investigate the possibility of using such
intramolecularly coordinated complexes containing the
o-carboranyl C,N-chelating ligand system as catalysts
for olefin polymerization.
6
moderate catalytic activities of up to 3 × 10 g of PNB
-
1
-1
(mol of Ni)
h
for the addition polymerization of
norbornene in the presence of methylaluminoxane (MAO)
as cocatalyst. Catalytic activities, molecular weights, and
molecular weight distributions of polynorbornene (PNB)
have been investigated under the various reaction condi-
tions.
Here we report the synthesis and characterization of
an intramolecularly coordinated nickel complex. The
method of preparing this compound is generally based
on the addition of [picolyl-o-carboranyl]lithium to a
suitable nickel complex. Preliminary studies show that
N
the complex [Cab ]2Ni is active toward the polymeri-
Introduction
zation of norbornene.
In recent years, transition-metal complexes with
ligands containing dissimilar donor atoms have been
widely investigated, primarily for their applications in
Results and Discussion
Compound 1, 1-(2′-picolyl)-o-carborane, was obtained
1
-8
important homogeneous catalytic processes.
The co-
by treating monolithium carborane with picolyl chloride
1
ordinatively labile donor atom in such ligands is capable
of reversible dissociation from the metal center. Such
dynamic behavior will produce vacant coordination sites
that allow complexation of substrates during the cata-
lytic cycle; at the same time the strong donor moiety
remains connected to the metal center. Therefore, the
design of such ligand systems containing one functional
(Scheme 1). IR and H NMR spectroscopic data are
consistent with the described picolyl-o-carborane struc-
ture.
(
9) (a) Roundhill, D. M.; Bechtold, R. A.; Roundhill, S. G. N. Inorg.
Chem. 1980, 19, 284-289. (b) Rauchfuss, T. B.; Patino, F. T.; Roundhill,
D. M. Inorg. Chem. 1975, 14, 652-656.
(
10) (a) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.;
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Chem. Ber. 1959, 92, 3175.
*
To whom correspondence should be addressed. E-mail: gxjin@
fudan.edu.cn. Fax: +86-21-65641740. Tel: +86-21-65643776.
1) Takei, I.; Nishibayashi, Y.; Arikawa, Y.; Uemura, S.; Hidai, M.
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Organomet. Chem. 1999, 587, 244-251.
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748.
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5) Yang, H.; Alvarez-Gressier, M.; Lugan, N.; Mathieu, R. Orga-
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2197.
1
0.1021/om0493356 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 11/16/2004

6320 Organometallics, Vol. 23, No. 26, 2004
Notes
Scheme 1. Synthesis of Complex 2
Table 1. Addition Polymerization of Norbornene
with Nickel Complex 2 Activated by
Methylaluminoxane (MAO)a
run complex Al/Ni T (°C) activityb Mvc Mwd Mw/Mnd
Figure 1. Molecular structure of complex 2. The hydrogen
atoms are omitted for clarity. Selected distances (Å) and
angles (deg): Ni(1)-N(1) ) 1.887(4), Ni(1)-N(2) ) 1.892-
(
4), Ni(1)-C(11) ) 1.972(5), Ni(1)-C(2) ) 1.973(5), C(1)-
C(2) ) 1.660(6); N(1)-Ni(1)-N(2) ) 165.51(18), N(1)-
Ni(1)-C(11) ) 91.49(18), N(2)-Ni(1)-C(11) ) 91.11(19),
N(1)-Ni(1)-C(2) ) 90.14(18), N(2)-Ni(1)-C(2) ) 91.69-
1
2
3
4
5
6
7
8
9
2
2
2
2
2
2
2
2
2
3000
6000
8000
10000
8000
8000
8000
8000
30
30
30
30
20
50
60
80
30
30
0.19
0.62
1.12
0.93
0.9
2.0
3.0
2.3
0
0.9
4.4
5.6
(
18), C(11)-Ni(1)-C(2) ) 162.3(2), C(1)-C(2)-Ni(1) )
6.8
111.6(3), C(4)-N(1)-Ni(1) ) 125.1(3).
9.4
7.5 8.28
6.0
2.2
The intramolecularly stabilized tetracoordinated (o-
7.3
0
0
carboranyl)nickel complex 2 was synthesized in THF
from Ni(PPh3)2Cl2 and the (picolyl-o-carboranyl)lithium
compound LiCabN (Scheme 1). Complex 2 has been
isolated as yellow, transparent crystals. A detailed
e
0
0
0
0
f
10
0
a
Polymerization conditions: solvent, chlorobenzene; total vol-
ume, 10 mL; nickel complex (2), 0.4 µmol; norbornene, 1.88 g
1
11
b
analysis of the spectroscopic data ( H NMR, B NMR,
(norbornene/Ni (molar) ) 68 000); reaction time, 30 min. In units
6
-1
-1
c
-5
-1
13
of 10 g of PNB (mol of Ni ) h
.
v
M (10 g mol ) values were
C NMR, and IR spectra) showed that the 1-(2′-picolyl)-
d
measured by the Ubbelohde calibrated viscosimeter technique. Mw
o-carborane ligand 1 is coordinated to the nickel(II)
through the carbon and nitrogen atoms.
-
5
-1
(
10
g mol ) and Mw/Mn values were determined by GPC.
e
f
Without cocatalyst MAO. Without nickel complex.
The stabilization in complex 2 is due to the formation
of a six-membered chelate ring. The nickel complex 2
is soluble in THF and CH2Cl2 and sparingly soluble in
hexane. The complex 2 is moderately stable in air and
shows only slow decomposition when in contact with
moisture.
with the dihedral angle between the planes [Ni(1), C(2),
C(1), C(3)] and [Ni(1), N(1), C(4), C(3)] being 59.9° and
that between [Ni(1), C(11), C(12), C(13)] and [Ni(1),
N(2), C(14), C(13)] being 57.9°. The bond lengths and
angles associated with pyridine and o-carboranyl groups
are normal with respect to the other o-carboranyl
N
The ORTEP diagram of [Cab ]2Ni is presented in
Figure 1. Crystallographic data and processing param-
eters are given in Table 2. The molecular structure
reveals that the geometry at the nickel atom is distorted
14,19,22
substituted compounds.
Preliminary experiments indicated that the nickel
complex 2 can be activated for norbornene polymeriza-
tion by treatment with MAO to afford addition-type
N
square planar, the two chelates [Cab ] adopt a trans
arrangement around the nickel atom, and there is a C2
symmetry. The angles of C(1)-C(2)-Ni(1) and C(12)-
C(11)-Ni(1) within the two six-membered rings are
smaller (111.6(3) and 111.8(3)°, respectively) than the
expected 120°. The Ni-N distances in 2 (1.887(4) and
6
polynorbornene (PNB) with moderate activity (10 g of
-1 -1
PNB (mol of Ni)
1
h ), high molecular weight (Mw )
5
-1
0 g mol ), and moderate molecular weight distribu-
tion (Mw/Mn ) 2.2). Under the same conditions, however,
the complex itself and MAO did not produce polymers
1
.892(4) Å) are much smaller than that in the corre-
(
runs 9 and 10). The norbornene polymerization results
sponding pyridine-ligated system [{bpa(CH2)2O(CH2)2-
OH}Ni(NO3)](NO3) (bpa ) bis(2-picolyl)amine; 2.0708-
are collected in Table 1. It was revealed that MAO was
essential for this polymerization, and the catalytic
activity was dependent upon the Al/Ni molar ratio, as
shown in Table 1 (runs 1-4). The optimized Al/Ni molar
ratio for the activity was 8000, and the activity de-
creased for both lower and higher molar ratios. Intrinsic
(
13) and 2.0765(12) Å)20 and [Ni(2-{1′-(diphenylphos-
21
phanyl)-1′-methyl}ethylpyridine)Cl2] (1.950(3) Å). The
two six-membered Ni-C-C-C-C-N rings are folded
(
20) Kirin, S. I.; Happel, C. M.; Hrubanova, S.; Weybermueller, T.;
Metzler-Nolte, N. Dalton 2004, 1201-1207.
21) Speiser, F.; Braunstein, P.; Saussine, L. Organometallics 2004,
3, 2625-2632.
(
(22) Wang, H.; Wang, H. P.; Li, H. W.; Xie, Z. W. Organaometallics
2004, 23, 875-885.
2

Notes
Organometallics, Vol. 23, No. 26, 2004 6321
Table 2. Summary of Crystallographic Data for 2
high, indicating that the normal mode of chain transfer
(
â-hydride elimination) was not possible in PNB, given
chem formula
formula wt
temp (K)
C18H36B20Cl4N2Ni
697.20
the geometry of the active growing center. Therefore,
the polymerization took place in a vinyl addition man-
ner. The DSC study of obtained PNB did not give an
endothermic signal upon heating to the decomposition
temperature (above 450 °C).
293(2)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
0.710 73
monoclinic
P21/n
11.095(4)
b (Å)
21.883(8)
c (Å)
14.564(5)
Conclusion
â (deg)
90.213(5)
3
V (Å )
3536(2)
This report provides the first report of an intramo-
lecularly coordinated nickel complex containing an
o-carboranyl C,N-chelating ligand system. A combina-
tion of X-ray crystallographic and spectroscopic studies
confirms the nature of this nickel complex. A prelimi-
nary study shows that the new nickel complex 2 is
moderately active as a catalyst precursor in norbornene
polymerization. To the best of our knowledge, this is the
first report that this kind of N-functionalized o-carbo-
ranyl late-transition-metal complex exhibits activity
toward vinyl addition polymerization of norbornene.
Further investigations into the polymerization mecha-
nism are ongoing.
Z
4
3
Dcalcd (Mg/m )
1.310
abs coeff (mm-1)
F(000)
0.869
1416
cryst size (mm)
θ range for data collecn (deg)
limiting indices
0.40 × 0.25 × 0.20
1.68-25.01
-13 e h e 13, -22 e k e 26,
-
17 e l e 16
no. of rflns collected
no. of indep rflns
14 683
6214 (R(int) ) 0.0346)
25.01 (99.7%)
0.8454 and 0.7225
full-matrix least squares on F
6214/4/396
completeness to θ (deg)
max and min transmissn
refinement method
2
no. of data/restraints/params
viscosity molecular weights Mv of polymers increased
due to an increase in the Al/Ni molar ratio. We found
Experimental Section
that the complex 2 showed the highest activity at 60
6
General Procedures. All manipulations were performed
°
C (3 × 10 ). The activity of 2 increased when the
using standard Schlenk techniques under an atmosphere of
temperature of polymerization rose from 20 to 60 °C.
This is because the concentration of the active center
activated by MAO increases as the temperature rises.
At the same time 2 usually becomes unstable at high
temperature. The highest activity at 60 °C is the result
of the compromise of two factors. The decomposition of
the active center increased and the activity dropped at
2 2 2
argon. CH Cl and chlorobenzene were dried over CaH and
THF, diethyl ether, hexane, and norbornene over Na and then
distilled under nitrogen immediately prior to use. Methylalu-
minoxane (MAO) and 2-picolyl chloride hydrochloride were
purchased from Witco and Acros, respectively. Other solvents
3 2
were used as received as technical grade solvents. Ni(PPh ) -
2
6
1
13
Cl
2
was prepared according to the literature. H, C, and
B NMR spectra were recorded on a Bruker VAVCE-DMX 500
spectrometer in CDCl or o-dichlorobenzene-d . Elemental
analysis was performed on an Elementar Vario EL III ana-
lyzer. Average molecular weight (M ) and molecular weight
distribution (M /M ) values of PBN products were determined
11
8
0 °C. It is clear that the Mv value was lower at higher
5
3
4
temperature. A molecular weight of 9.4 × 10 was
obtained at a reaction time of 20 °C.
w
1
The polymers obtained were characterized by IR, H
w
n
1
3
NMR, C NMR, and GPC analyses. The resonances of
with a PL GPC-220 permeation chromatograph at 150 °C,
using a narrow standards calibration and equipped with three
PL gel columns (sets of PL gel 10m MIXED-BLS). Trichlo-
robenzene was employed as a solvent at a flow rate of 1.00
mL/min. IR (KBr) spectra were recorded on a Nicolet FT-IR
spectrophotometer.
PNB appear at 0.9-3.03 ppm (m, maxima at 1.52, 1.87,
1
2
.23, 2.59 ppm) in the H NMR, and the absence of
-
1
bands at 1680∼1620 cm in the IR spectra indicated
no double bonds, which was different from the polymers
23
of norbornene ring-opening metathesis polymerization.
The C NMR spectrum of PNB shows the main reso-
1
3
1-(2′-Picolyl)-o-carborane (1). To a solution of o-carborane
(
2
288 mg, 2 mmol) in dry Et
2
O (20 mL) at -78 °C was added
.5 M of n-BuLi in hexane (0.8 mL, 2 mmol), and the reaction
mixture was stirred for 1 h at -78 °C. Then 2-picolyl chloride
255 mg, 2 mmol; prepared by neutralizing picolyl chloride
nances at δ 30.0-48.8 ppm (m, maxima at 32.43, 39.12,
4
8.39, 48.77 ppm), attributed to the vinyl-addition
polymer structure of polynorbornene, bridge carbon,
bridgehead carbon, and the backbone carbon.24 Fur-
thermore, the product of cationic or free-radical polym-
erization of norbornene is usually formed with low
molecular weight (molecular weight <1000) and low
yield because of the rearrangements and transfer reac-
(
18
hydrochloride ) was added at -78 °C, and the stirred reaction
mixture was warmed to room temperature for 1 h. Addition
3
of water (30 cm ) dissolved the nascent LiCl, and the separated
Et
O layer was further washed with water (2 × 30 mL) before
being isolated and dried over Na SO . Filtration, followed by
2
2
4
2
5
tions. The GPC molecular weights Mw and intrinsic
viscosity molecular weights Mv of polymers were very
removal of the solvent in vacuo, gave a white solid. Unreacted
o-carborane was removed by slow vacuum sublimation (40 °C,
0
.01 mmHg) to give analytically pure 1 (250 mg, 57% yield).
-
1
IR (KBr, cm ): 3069, 3020 m (br) (carborane CH), 2916 w,
2848 w (pyridyl/CH str), 2596 vs, 2575 s (BH); 1593 s, 1570
(
23) (a) Sacchi, M. C.; Sonzogni, M.; Losio, S.; Forlin, F. Macromol.
Chem. Phys. 2001, 202, 2052-2058. (b) Barnes, D. A.; Benedikt, G.
M.; Goodall, B. L.; Huang, S. S. Macromolecules 2003, 36, 2623-2632.
2
m, 1476 s, 1438 s (pyridyl skel), 1095 m, 1063 m, 1017 m, 769
(
24) Huang, W. J.; Chang, F. C.; Chu, P. P. J. Polym. Sci. 2000, 38,
1
s, 751 m (CH oop and carborane skel), 719 s (br) (BH wag). H
2
3
554-2563. Mi, X.; Ma, Z.; Cui, N. J. Appl. Polym. Sci. 2003, 88, 3273-
NMR (500 MHz, CDCl
pyridyl), 7.26 (1H, m, pyridyl), 7.18 (1H, d, pyridyl), 4.08 (1H,
s, C2H), 3.66 (1H, m, CH ), 3.55 (1H, m, CH ).
3
): δ 8.56 (1H, d, pyridyl), 7.70 (1H, m,
278.
(
25) (a) Gaylord, N. G.; Deshpande, A. B.; Mandal, B. M.; Martan,
M. J. Macromol. Sci. Chem. 1977, A11(5), 1053-1070. (b) Gaylord, N.
G.; Mandal, B. M.; Martan, M. J. Polym. Sci., Polym. Lett. Ed. 1976,
2
2
1
4, 555-559. (c) Gaylord, N. G.; Deshpande, A. B. J. Polym. Sci., Polym.
Lett. Ed. 1976, 14, 613-617.
(26) Venanzi, L. M. J. Chem. Soc. 1958, 719-724.

6322 Organometallics, Vol. 23, No. 26, 2004
Notes
Bis[1-(2′-picolyl)-o-carborane]nickel (2). To a stirred
norbornene in 4.0 mL of chlorobenzene, and another 3.0 mL
of fresh chlorobenzene were added into a special polymeriza-
tion bottle (20 mL) with a strong stirrer under an Ar
atmosphere. After the mixture was kept at the desired
temperature for 10 min, the desired MAO (10%) was charged
into the polymerization system via syringe, and the reaction
solution of 1 (235 mg, 1 mmol) in 20 mL of THF, which was
cooled to -78 °C, was added 2.5 M n-BuLi (0.4 mL, 1 mmol)
via a syringe. The resulting pale yellow solution was stirred
at -78 °C for 1 h and then transferred through a cannula to
3 2 2
a suspension of Ni(PPh ) Cl (654 mg, 1 mmol) in 20 mL of
THF. After the mixture was stirred for 16 h, the solvent was
removed under vacuum, and the resulting residue was taken
up in a minimum of THF and then recrystallized by slow
diffusion of hexane into this solution. Yield: 163 mg (62%).
was started. Thirty minutes later, acidic ethanol (Vmethanol
:
Vconcd HCl ) 20:1) was added to terminate the reaction. The PNB
was isolated, washed with methanol, and dried at 80 °C for
48 h under vacuum. For all the polymerization procedures,
the total reaction volume was 10.0 mL, which can be achieved
-
1
IR (KBr, cm ): 3057 m (br) (carborane CH), 2924 w, 2850 w
(
(
pyridyl/CH
2
str), 2561 vs (BH), 1593 m, 1560 m, 1437 s
-1
by variation of chlorobenzene when necessary. IR (KBr, cm ):
2946 vs, 2869 vs, 1473 m, 1451 s, 1375 m, 1295 m, 1258 m,
pyridyl skel), 1119 vs, 1098 s, 1073 m, 1023 m, 749 m (CH
1
oop and carborane skel), 723 s, 694 s (br) (BH wag). H NMR
500 MHz, CDCl ): δ 9.64 (1H, d, pyridyl), 7.98 (1H, m,
pyridyl), 7.59 (2H, m, pyridyl), 4.33 (1H, d, CH ), 4.01 (1H, d,
): δ 156.6 (pyridyl, C ),
), 126.0 (pyridyl, C ), 123.5
), 71.3 (C1), 52.0 (C2) ppm. B NMR (500 MHz,
): δ -2.15, -5.71, -8.78, -9.62, -10.88 ppm. Anal.
Ni‚0.5C O: C, 38.39; H, 6.39; N, 4.97.
1
(
3
1222 m, 1148 m, 1108 m, 1040 w, 943 w, 893 m. H NMR (o-
dichlorobenzene-d
at 1.52, 1.87, 2.23, 2.59). C NMR (o-dichlorobenzene-d
4
, 500 MHz): δ 0.9-3.03 ppm (m, maxima
2
1
3
13
CH
51.9 (pyridyl, C
pyridyl, C
2
) ppm. C NMR (500 MHz, CDCl
3
2
4
, 500
1
(
6
), 139.1 (pyridyl, C
4
5
MHz): δ 30.0-48.8 ppm (m, maxima at 32.43, 39.12, 48.39,
48.77).
1
1
3
CDCl
Calcd for C16
3
B H N
20 32 2
4 8
H
Found: C, 38.62; H, 6.01; N, 4.69.
X-ray Crystallography. Suitable crystals for X-ray analy-
sis of 2 were obtained by slow diffusion of hexane into CH Cl
2 2
Acknowledgment. Financial support by the Na-
tional Nature Science Foundation of China for Distin-
guished Young Scholars (Grant Nos. 29925101 and
solutions of the corresponding compound. None showed signals
of decomposition during X-ray data collection, which was
carried out at room temperature. Details of the data collection
and refinement are summarized in Table 2. Selected bond
lengths and angles are given in Figure 1. The structure was
solved by direct methods using SHELX-97 and refined by full-
matrix least-squares calculations, using the program system
SHELXTL-97.
2
0274008) and by the special Funds for Major State
Basic Research Projects (G 1999064800) is gratefully
acknowledged.
Supporting Information Available: Crystallographic
data for 2 as a CIF file. This material is available free of charge
via the Internet at http://pubs.acs.org.
Norbornene Polymerization. In a typical procedure, 0.4
µmol of nickel complex 2 in 2.0 mL of chlorobenzene, 1.88 g of
OM0493356