New Bulky Phosphino-Pyridine Ligands. Palladium and Nickel Complexes for the Catalytic Polymerization and Oligomerization of Ethylene

Article abstract of DOI:10.1021/om030242i

Two bulky phosphino-pyridine ligands (6-mesityl-2-((diarylphosphino)methyl)pyridine, P～N) were successfully prepared by means of Suzuki coupling of mesitylboronic acid with 6-bromo-2-picoline followed by phosphinylation. These ligands readily form the pal

Full text of DOI:10.1021/om030242i

Organometallics 2003, 22, 4893-4899
4893
New Bu lk y P h osp h in o-P yr id in e Liga n d s. P a lla d iu m a n d
Nick el Com p lexes for th e Ca ta lytic P olym er iza tion a n d
Oligom er iza tion of Eth ylen e
Hsin-Pei Chen, Yi-Hung Liu, Shie-Ming Peng, and Shiuh-Tzung Liu*
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
Received April 2, 2003
Two bulky phosphino-pyridine ligands (6-mesityl-2-((diarylphosphino)methyl)pyridine,
P ∼N) were successfully prepared by means of Suzuki coupling of mesitylboronic acid with
6-bromo-2-picoline followed by phosphinylation. These ligands readily form the palladium
and nickel complexes upon treatment with (COD)PdMeCl and (DME)NiBr2, respectively.
These P ∼N chelating Pd(II) and Ni(II) complexes were characterized by both spectral data
and X-ray crystallography. The coordination geometry around the metal center is square
planar for the Pd(II) complexes and tetrahedral for the Ni(II) complexes. The cationic
methylpalladium(II) complexes showed poor activity in the catalytic polymerization of
ethylene, but the nickel complexes were highly active with the activation of MAO. The nickel
complexes catalyzed the polymerization of ethylene with an Al/Ni ratio of 150, whereas di-
and trimerization was observed when the Al/Ni ratio is 500. The obtained polyethylenes are
highly crystalline.
Ch a r t 1
In tr od u ction
Due to the different properties of the phosphorus and
nitrogen donors, the study of phosphine-imine (P ∼N)
ligands in coordination chemistry and catalysis has
received much attention.1-10 Recently, we demonstrated
that palladium complexes 1 (Chart 1) can stabilize
(1) (a) Dario, D.; Felice, F.; Giancarlo,Belletti, D.; Graiff, C.; Tirip-
icchio, A. Organometallics 2002, 21, 761. (b) Crociani, B.; Antonaroli,
S.; Di Vona, M. L.; Licoccia, S. J . Organomet. Chem. 2001, 631, 117.
(c) Polosukhin, A. I.; Bondarev, O. G.; Lyubimov, S. E.; Korostylev, A.
V.; Lyssenko, K. A.; Davankov, V. A.; Gavrilov, K. N. Tetrahedron:
Asymmetry 2001, 12, 2197. (d) Ru¨ther, T.; Done, M. C.; Cavell, K. J .;
Peacock, E. J .; Skelton, B. W.; White, A. H. Organometallics 2001, 20,
5522. (e) Green, M. J .; Cavell, K. J .; Edwards, P. G. J . Chem. Soc.,
Dalton Trans. 2000, 853. (f) Bachechi, F.; Burini, A.; Fontani, M.;
Galassi, R.; Macchioni, A.; Pietroni, B. R.; Zanello, P.; Zuccaccia, C.
Inorg. Chim. Acta 2001, 323, 45.
(2) (a) Bhattacharyya, P.; Loza, M. L.; Parr, J .; Slawin, A. M. Z. J .
Chem. Soc., Dalton Trans. 1999, 2917. (b) Faller, J . W.; Mason, J .;
Parr, J . J . Organomet. Chem. 2001, 626, 181. (d) Parr, J .; Slawin,
A. M. Z. Inorg. Chim. Acta 2000, 303, 116. (e) Yang, H.; Alvarez-
Gressier, M.; Lugan, N.; Mathieu, R. Organometallics 1997, 16, 1401.
(f) van den Beuken, E. K.; Smeets, W. J . J .; Spek, A. L.; Feringa, B. L.
Chem. Commun, 1998, 223. (g) Gsponer, A.; Schmid, T. M.; Consiglio,
G. Helv. Chim. Acta 2001, 84, 2986 (h) Romeo, R.; Scolaro, L. M.;
Plutino, M. R.; Romeo, A.; Nicolo, F.; Del Zotto, A. Eur. J . Inorg. Chem.
2002, 629.
(3) (a) Dahan, F.; Dyer, P. W.; Hanton, M. J .; J ones, M.; Mingos, D.
M. P.; White, A. J . P.; Williams, D. J .; Williamson, A.-M. Eur. J . Inorg.
Chem. 2002, 732. (b) Deng, W.-P.; Hou, X.-L.; Dai, L.-X.; Dong, X.-W.
Chem. Commun. 2000, 1483. (c) Yang, H.; Gao, H.; Angelici, R.
Organometallics 2000, 19, 622. (d) Liu, X.; Mok, K. F.; Leung, P. H.
Organometallics 2001, 20, 3918. (e) Mikoluk, M. D.; McDonald, R.;
Cavell, R. G. Inorg. Chem. 1999, 38, 2791. (f) Manzano, B. R.; J alo´n,
F. A.; Go´mez-de la Torre, F.; Lo´pez-Agenjo, A. M.; Rodriguez, A. M.;
Mereiter, K.; Weissensteiner, W.; Sturm, T. Organometallics 2002, 21,
789 and references therein.
(4) (a) Braunstein, P.; Naud, F.; Rettig, S. J . New J . Chem. 2001,
25, 32, (b) Sauthier, M.; Leca, F.; Toupet, L.; Re´au, R. Organometallics
2002, 21, 1591. (c) Coleman, K. S.; Green, M. L. H.; Pascu, S. I.; Rees,
N. H.; Cowley, A. R.; Rees, L. H. Dalton Trans. 2001, 3384 and
references therein.
(5) References involving diimine ligands: (a) J ohnson, L. K.; Killian,
C. M.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 6414. (b) Ittel, S.
D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169 and
references therein.
various insertion intermediates such as CO and olefins/
alkynes.10 However, complex 1 can only catalyze the di-
and trimerization of ethylene.11 In comparison with the
complex 2 developed by Guan8 and 3 by Brookhart,9 the
substituents on the P ∼N donor in 1 are less bulky. This
might be attributed to result in the oligomerization of
ethylene. In a continuation of this work, we have
(6) For phenanthroline ligands: (a) Rix, F. C.; Brookhart, M.; White,
P. S. J . Am. Chem. Soc. 1996, 118, 4746. (b) Milani, B.; Scarel, A.;
Mestroni, G.; Gladiali, S.; Taras, R.; Carfagna, C.; Mosca, L. Organo-
metallics 2002, 21, 1323. (c) Sen, A.; J iang, Z. Macromolecules 1993,
26, 911 and references therein.
(7) Mu¨ller, G.; Klinga, M.; Osswald, P.; Leskela, M.; Rieger, B. Z.
Naturforsch., B: Chem. Sci. 2002, 57, 803.
(8) Guan, Z. B.; Marshall, W. J . Organometallics 2002, 21, 3580.
(9) Daugulis, O.; Brookhart, M. Organometallics 2002, 21, 5926.
(10) (a) Chen, Y.-C.; Chen, C.-L.; Chen, J .-T.; Liu, S.-T. Organome-
tallics 2001, 20, 1285. (b) Reddy, K. R.; Surekha, K.; Lee, G.-H.; Peng,
S.-M.; Chen, J .-T.; Liu, S.-T. Organometallics 2000, 19, 2637 and
references therein.
(11) Chen, J .-T.; Liu, S.-T.; Zhao, K.-Q. J . Chin. Chem. Soc. 2000,
47, 279.
10.1021/om030242i CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/22/2003

4894 Organometallics, Vol. 22, No. 24, 2003
Sch em e 1. P r ep a r a tion of P ∼N Liga n d s
Chen et al.
a
Sch em e 2
F igu r e 1. ORTEP plot of 5b (30% probability ellipsoids).
a
Legend: (i) (COD)PdMeCl, CH2Cl2, room temperature; (ii)
AgBF4, MeCN, room temperature.
designed new bulky P ∼N ligands 4a -d by introducing
substituents at the 6-position of pyridine and a mesityl
or tolyl group on the phosphorus atom. The two donors
are linked by a nonenolizable rigid carbon framework.
In this report, the synthesis of nickel and palladium
complexes containing 4a ,b and the catalytic activities
of these complexes in the polymerization and oligomer-
ization of ethylene are described.
Resu lts a n d Discu ssion
P r ep a r a tion of Liga n d a n d Com p lexes. Starting
with chloropicoline, the mesityl group was introduced
via a Suzuki coupling reaction to give 2-methyl-6-
mesitylpyridine, which was converted into the desired
P ∼N ligand by diarylphosphinylation at the R-position
(Scheme 1). Compound 4a was obtained as a white solid,
whereas 4b is a viscous, air-sensitive liquid. 31P NMR
showed the chemical shifts for both ligands in the range
of -20 to -30 ppm, a typical range for diarylalkylphos-
phine. Other spectroscopic data are also consistent with
the expected structure. Due to the air-sensitive nature
of these two ligands, we were not able to obtain the
analytically pure compounds, but the corresponding
palladium complexes were isolated upon the treatment
of crude ligands with [(COD)PdMeCl] (COD ) 1,5-
cyclooctadiene).
The desired palladium complexes could be obtained
quantitatively by the substitution reaction of (COD)-
PdMeCl with the corresponding ligand in dichlo-
romethane at room temperature. Subsequent reaction
of the complexes with AgBF4 in the presence of aceto-
nitrile resulted in the formation of the cationic solvento
palladium complexes [(P ∼N)PdMeL]BF4 (Scheme 2).
However, the cationic palladium complex 6a was ob-
tained as an aqua complex, which presumably was due
to the substitution of water during the recrystallization.
All 31P NMR signals of Pd(II) complexes are shifted
F igu r e 2. Molecular structure of the cationic part of 6b
(30% probability ellipsoids).
downfield relative to the free ligand, indicating the co-
ordination of phosphine toward the metal center. As
for the stereochemistry around the metal center, the
small magnitude of the coupling constants J P-Me
(2-4.5 Hz) suggest that the methyl group is cis to
the phosphine, which is in agreement with data for
other complexes with the formula (P ∼N)PdMeCl.4c,9,10
In addition to the spectroscopic analysis, the struc-
tures of complexes 5b and 6a ,b were further con-
firmed by their X-ray single-crystal structural deter-
mination (Figures 1 and 2; drawings for 6a are depos-
ited as Supporting Information). Selected bond dis-
tances and bond angles of palladium and nickel com-
plexes are collected in Tables 1 and 2, respectively.
There are no significant differences observed in the
bond lengths of Pd-P(1), Pd-N(1), and Pd-C(1) for
5b and 6a ,b, which are also in agreement with the
values for complex 3 and related species.7,9,10 The
mesityl ring at the 2-position is seated nearly perpen-
dicularly to the pyridine ring, as evidenced by the
torsion angle N(1)-C(6)-C(11)-C(12) (71.8° for 5b ;

New Bulky Phosphino-Pyridine Ligands
Organometallics, Vol. 22, No. 24, 2003 4895
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 5b, 6a , a n d 6b
5b (X dCl(1))
6a (X ) O)
6b (X ) N(2))
Pd-P(1)
Pd-N(1)
Pd-C(1)
Pd-X
N(1)-C(2)
C(2)-C(7)
C(7)-P(1)
2.2092(8)
2.226(3)
2.043(4)
2.3760(8)
1.354(4)
1.499(4)
1.841(3)
2.2045(9)
2.212(3)
2.030(4)
2.166(3)
1.344(5)
1.505(5)
1.862(4)
2.216(1)
2.224(3)
2.027(4)
2.083(3)
1.361(5)
1.512(6)
1.828(4)
N(1)-Pd-P(1)
N(1)-Pd-C(1)
P(1)-Pd-C(1)
P(1)-Pd-X
P(1)-C(7)-C(2)
Pd-P(1)-C(7)
80.20(7)
174.1(1)
94.6(1)
162.77(3)
108.9(2)
96.7(1)
84.44(8)
175.1(2)
90.7(1)
102.0(1)
109.9(3)
98.3(1)
80.55(9)
174.5(1)
94.5(1)
174.8(1)
109.6(3)
97.7(1)
F igu r e 3. ORTEP plot of nickel complex 10a (30%
probability ellipsoids).
Ta ble 2. Im p or ta n t Bon d Dista n ces (Å) a n d An gles
(d eg) for Nick el Com p lexes
Sch em e 3
10a
10b
Ni-P(1)
2.320(1)
2.029(3)
2.3461(7)
2.3458(7)
1.362(4)
1.495(5)
1.831(4)
2.357(1)
2.015(4)
2.3887(8)
2.3287(7)
1.345(6)
1.502(7)
1.848(5)
Ni-N(1)
Ni-Br(1)
Ni-Br(2)
N(1)-C(2)
C(2)-C(7)
C(7)-P(1)
N(1)-Ni(1)-P(1)
N(1)-Ni(1)-Br(1)
P(1)-Ni(1)-Br(1)
Br(1)-Ni(1)-Br(2)
N(1)-Ni(1)-Br(2)
P(1)-Ni(1)-Br(2)
86.46(9)
106.08(9)
99.83(3)
125.5(3)
120.47(9)
112.45(3)
84.9(1)
98.4(1)
95.90(4)
115.01(3)
134.0(1)
119.76(4)
84.2° for 6a ; 70.4° for 6b).In contrast to our previous
findings,12 the bulky P ∼N ligand 7 behaves as a
monodentate ligand toward (COD)PdMeCl. Further-
more, C-H activation takes place to form the P∼N∼C
palladium complex 9 upon the reaction of 8 with silver
tetrafluoroborate (Scheme 3).12 However, the P ∼N
ligands (4a ,b) behave as chelating bidentate ligands,
because the aromatic ring of the bulky mesityl group is
seated almost perpendicularly to the pyridine plane,
which allows the metal ion to enter the ligand pocket.
For the nickel complexes, treatment of (DME)NiBr2
(DME ) 1,2-dimethoxyethane) with the corresponding
ligand readily provided the dibromide species [(P ∼N)-
NiBr2] (10a , P ∼N ) 4a ; 10b, P ∼N ) 4b). These
complexes were isolated as brown solids and were
soluble in most polar organic solvents. Unlike the
palladium complexes, these nickel complexes are para-
magnetic, suggesting that the nickel species have a
tetrahedral geometry. The tetrahedral geometry was
confirmed by X-ray single-crystal analysis. For the
nickel species 10a (Figure 3) and 10b (drawings for 10b
are deposited as Supporting Information), the geom-
etries of both complexes are distorted tetrahedral, as
evidenced by the bond angles around the metal center.
In our previous study, the P ∼N ligand in complex 1 can
readily form the bis ligand complex 11,13 suggesting that
the bulky size of 4a ,b and 7 prevents complexation of
more than one ligand per metal.
gave negligible amounts of oligomers, which is different
from the catalytic activity of 13 reported by Rieger and
co-workers.7 In fact, palladium black was obtained in
most instances, indicating the instability of these pal-
ladium complexes under the reaction conditions. To
understand the relative migratory insertion of ethylene
for the present system, equimolar amounts of 5a and
NaBAr4 were dissolved in 0.5 mL of CDCl3 (with 5%
CD3CN) under an ethylene atmosphere. The relative
intensity of Pd-CH3 (5a ) in the 1H NMR spectrum
disappeared very slowly, accompanied by the formation
of propene and palladium black. This might explain the
different activities between 6b and 13.7
These activities are poor compared to those of the
palladium complexes 2 and 3 developed by Guan8 and
Brookhart,9 respectively. As addressed by Brookhart,
the migratory insertion of ethylene into Pd-CH3 is
disfavored by the methyl group trans to the nitrogen
donor in palladium complexes containing a P ∼N type
ligand due to the trans influence of that donor.9 This
might explain the low activity of 6a ,b in polymerization.
In addition, the space-filling model of 6a (Figure 4)
P olym er iza tion . Complexes developed in this work
were tested for polymerization of ethylene. However, the
reaction of 6a or 6b with ethylene (200 psi, 30-60 °C)
(12) Chen, H.-P.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Dalton 2003,
1419
(13) Reddy, K. R.; Liu, S.-T. Unpublished results.

4896 Organometallics, Vol. 22, No. 24, 2003
Chen et al.
F igu r e 4. Space-filling model of palladium complex 6a :
(a) top view; (b) bottom view.
Ta ble 3. P olym er iza tion of Eth ylen e Ca ta lyzed by
Nick el Com p lexesa
insoluble PEd
yield Tm
entry Nib (mL) (°C) (mg) (°C) (mg) Mn PDIf 1000g
soluble PEe
Al/ solvc
T
yield
Br/
1
2
3
150
150
50 30
50
710 115.4
810 117.3
980 121.3
670 117.3
390 113.6
490 114.1
0
39 4000 2.13
66 4300 3.14
46 2100 2.08
23 2300 2.67
20 1900 2.09 101
94 2300 2.25
76
98
54
75
0
150 100 30
4h
5i
6j
7
75
150
150
500
50 30
50 30
50 30
67
50
k
l
8m 500
50 30 2010 110.2
71 3500 2.90
88
a
Conditions: complex 10a (0.0115 mmol) in autoclave with
ethylene (500 psi) for 4 h. Mole ratio Al/Ni. c Toluene as the
b
d
solvent. PE obtained is in the solid form and is not soluble in
F igu r e 5. XRD pattern (a) and SEM photograph (b) of
polyethylene.
most organic solvents and chlorinated benzenes. e PE obtained is
soluble in toluene and most organic solvents. f Mw/Mn. g Branching
per 1000 C determined by 1H NMR spectroscopy. Complex 10a
h
(5.8 × 10-3 mmol) as the catalyst. Complex 10b (0.0115 mmol)
i
two kinds of polyethylene are directed from the same
active metal center or from two independent pathways
at this moment.
j
k
as the catalyst. 4a + Ni(acac)2 as the catalyst. Exothermic
l
m
reaction. Butanes and hexenes. CO2 (850 psi) was added.
Instead of polyethylene, butenes and hexenes were
obtained in high conversions when a larger quantity of
MAO (Al/Ni ) 500) was used (Table 3, entry 7). It was
illustrated by Brookhart’s group that nickel complex
12b catalyzed the dimerization of ethylene with a high
turnover frequency (>106) in a very exothermic man-
ner.9 In our investigation, the reaction was extremely
exothermic as well, but the product formation was
different from that obtained by complex 12b. Both
butenes and hexenes were formed from these reaction
conditions (see below). Another interesting observation
about this catalysis was that a considerable amount of
polymer was obtained by running the reaction in the
presence of carbon dioxide under high-pressure condi-
tions (Table 3, entry 8).
indicates that the metal center is readily accessible
along the axis. Accordingly, the bulky substituents on
either the pyridine ring or phosphorus appear not to
interfere with the axial orientation of the palladium
center.
The activity of nickel complexes in oligo- or polymer-
ization of ethylene is quite different from that of the
palladium species. With a molar ratio of MAO to com-
plex of 150:1, complex 10a catalyzed the polymerization
of ethylene to form PE in poor yields with a bimodal
molecular weight distribution (Table 3). As shown in the
table, all reactions gave a mixture of solid and low-
molecular-weight polyethylene. The obtained solid PE
was insoluble in most organic solvents but was soluble
in trichlorobenzenes. Upon heating in chlorobenzene,
the obtained PE sample melted and formed a two-phase
solution. Tm values of all samples (Table 3) were in the
range of 110-122 °C, which is typical for linear poly-
ethylene. The XRD pattern of the solid PE from entry
3 shows that the sample has a highly orthorhombic
structure (Figure 5a), with a molecular weight esti-
mated by its viscosity in the range of ∼106. In addition,
the SEM of the sample (Figure 5b) is consistent with
the observed diffraction pattern.
Di- a n d Tr im er iza tion . In an attempt to better
understand the activity of nickel complexes in oligo-
merization, complex 10a and the mixture of 4a and
Ni(acac)2 were used as precatalysts to study. The re-
sults are summarized in Table 4. All reactions were
extremely exothermic, and the reaction temperature
reached 70-80 °C even when the mixture was cooled
with an ice bath. It was found that the nickel dibromide
10a had an activity similar to that of the nickel complex
prepared in situ (entries 1 and 5), but with a slightly
different product distribution. From entries 1, 3, and 4
(Table 4), it appears that a longer reaction time provides
a better yield, indicating a substantial lifetime of the
catalyst. Unlike the precatalyst 12b,9 the nickel complex
with ligand 4a did provide the formation of hexenes with
a negligible amount of oligomers. Reaction proceeded
In addition to the solid product, there was a small
amount of low-molecular-weight (Mn ) 1900-4000)
polyethylenes in the reaction mixture (Table 3). With
the exception of entry 3, these soluble PEs obtained in
this work were slightly more branched than those
polymers catalyzed by 12a reported by Brookhart and
co-workers.9 However, we do not know whether these

New Bulky Phosphino-Pyridine Ligands
Organometallics, Vol. 22, No. 24, 2003 4897
Ta ble 4. Di- a n d Tr im er iza tion of Eth ylen e Ca ta lyzed by Nick el Com p lexesa ,b
butanes (g)
hexenes (g)
entry
C2H4 (psi)
t (h)
1-butene
2-butenec
1-hexene
2-ethyl-1-butene
othersd
TOFe × 105
1
2
3
500
300
500
500
500
14.5
500
3
3
7
10
3
12
3
14.6
4.6
43.0
53.6
18.8
1.7
16.8
9.7
26.3
28.9
8.4
3.4
0
3.9
0.9
11.9
18.5
1.9
0
1.4
0.6
2.5
1.8
1.3
0.2
0
11.7
2.9
15.2
10.9
8.2
9.5
3.6
8.4
6.0
4.8
4
5f
6
7g
0
0
a
b
Conditions: ligand 4a + Ni(acac)2 (1:1 mole ratio) in toluene (50 mL) at 80 °C. Product analysis was based on 1H NMR. c Cis and
trans forms. 2- and 3-hexenes in both cis and trans forms. e Overall turnover frequency (C4+ C6), in units of g mol-1 h-1
precatalyst. Ni(acac)2 as the catalyst.
.
f 10a as the
d
g
boronic acid,15 NiBr2‚DME,16 and (COD)PdMeCl17 were pre-
pared according to the procedures described in the literature.
2-Meth yl-6-(2,4,6-tr im eth ylp h en yl)p yr id in e. A mixture
of 2-chloro-6-methylpyridine (2.5 mL, 22.75 mmol), (2,4,6-
trimethylphenyl)boronic acid (4.44 g. 27.1 mmol), triphen-
ylphosphine (0.6 g, 2.3 mmol), Pd(OAc)2 (0.127 g, 0.48 mmol),
sodium bicarbonate (8.5 g, 61.6 mmol), degassed water (30
mL), and 1,2-dimethoxyethane (25 mL) in a 250 mL round-
bottom flask was heated to reflux for 18 h. The resulting
reaction mixture was extracted with ethyl acetate (50 mL ×
3). All extracts were combined, dried over MgSO4, and
concentrated. The crude product was distilled under vacuum
(bp 80 °C (0.1 Torr)) to give the desired compound as a clear,
colorless liquid (yield 4.12 g, 86%): 1H NMR (d6-acetone, 400
MHz): δ 7.71 (dd, J ) 7.7, 7.7 Hz, 1H, py H4), 7.18 (d, J ) 7.7
Hz, 1H, py H3), 7.03 (d, J ) 7.7 Hz, 1H, py H5), 6.9 (s, 2H, Ar
H), 2.50 (s, 3H, CH3), 2.28 (s, 3H, CH3), 1.96 (s, 3H, CH3). 13C
NMR (CDCl3, 100 MHz): δ 159.2, 158.0, 137.8, 137.1, 136.2,
135.5, 128.2, 121.4, 120.8, 24.5 (py-CH3), 20.9, 20.0. HR-
FABMS (C15H17N): m/z calcd, 211.1361; found, 212.1434 (M
+ 1). Anal. Calcd for C15H17N: C, 85.26; H, 8.11; N, 6.63.
Found: C, 85.10; H, 8.13; N, 6.40.
selectively at atmospheric pressure of ethylene to yield
butenes, but with lower turnover frequency (Table 4,
entry 6).
For the product distribution, the butenes were the
major component of the reactions with a C4 to C6 mole
ratio of ∼3.5. It appears that more butenes form under
a lower pressure of ethylene (entries 1, 2, and 6),
indicating that a higher concentration of ethylene favors
the chain growth. All three isomeric forms (1-butene,
cis- and trans-2-butene) of butenes were found and
identified by their 1H NMR spectroscopic data. In
contrast, several isomeric forms of hexenes were ob-
tained, including 1-, 2-, and 3-hexenes as well as 2-ethyl-
1-butene. The formation of these isomeric products is
possibly due to the chain “walking” and/or metal-
catalyzed isomerization. In agreement with this obser-
vation, these nickel complexes catalyze the isomeriza-
tion of R-olefins. The reaction of 1-hexene with 10a
yielded 2- and 3-hexenes.
2-[(Dim esit ylp h osp h in yl)m et h yl]-6-(2,4,6-t r im et h yl-
p h en yl)p yr id in e (4a ). To a solution of 2-methyl-6-(2,4,6-
trimethylphenyl)pyridine (0.7 g, 3.3 mmol) in THF (25 mL)
was added a 1.6 M hexane solution of n-butyllithium (2.07 mL,
3.3 mmol) at -78 °C. After the above reaction mixture was
stirred for 3 h, a THF solution (1.67 M) of dimesitylchloro-
phosphine (2.09 mL, 3.3 mmol) was added. The resulting
mixture was slowly warmed to room temperature and stirred
for 12 h. Water was added to quench the reaction. Upon
concentration, the hexane extracts of the residue were passed
through Celite to remove the insoluble materials. The filtrate
was concentrated and chromatographed on silica gel using
dichloromethane as eluant. The desired product was obtained
as white solids upon concentration (yield 0.98 g, 62%): mp
75-76 °C. 1H NMR (d6-acetone, 400 MHz): δ 7.53 (dd, J )
7.7, 7.7 Hz, 1H, py H4), 6.98 (d, 1H, J ) 7.7 Hz, py H3), 6.86
(s, 2H, Ar H), 6.77 (d, 1H, J ) 7.7 Hz, py H5), 6.75 (d, J ) 2.4
Hz, 4H, Ar H), 4.11 (s, 2H, py-CH2), 2.26 (s, 3H, Ar-CH3),
2.18-2.17 (18H, Ar-CH3), 1.88 (s, 6H, Ar-CH3). 31P NMR
(161.9 MHz): δ -19.6. HRFABMS: m/z calcd for C33H38NP,
479.2742; found, 479.2748.
Su m m a r y
Pyridine-based bulky phosphine ligands and their
palladium and nickel complexes were successfully pre-
pared and characterized. The cationic methyl palladium-
(II) complexes showed poor activity toward ethylene, but
the nickel(II) dibromo complexes were highly active in
the presence of MAO. With a lower Al/Ni ratio, the
nickel complexes catalyzed the polymerization of eth-
ylene, yielding an orthorhombic form. On the other
hand, the same nickel species with a high Al/Ni ratio
shows a high activity in the catalysis of the di- and
trimerization of ethylene.
Exp er im en ta l Section
Gen er a l In for m a tion . Nuclear magnetic resonance spectra
were recorded in CDCl3 or acetone-d6 on either a Bruker AC-E
200, AM-300, or AVANCE 400 spectrometer. Chemical shifts
are given in parts per million relative to tetramethylsilane for
1H and 13C NMR and relative 85% H3PO4 for 31P NMR.
Infrared spectra were measured on a Nicolet Magna-IR 550
spectrometer (Series-II) as KBr pellets, unless otherwise noted.
Gel permeation chromatography (GPC) data were obtained
from a Waters Model 590 liquid chromatograph installed with
a Lab Allience RI 2000 detector using THF as eluant at room
temperature and polystyrene calibration curve for analyses.
All reactions, manipulations, and purification steps were
performed under a dry nitrogen atmosphere. Tetrahydrofuran
was distilled under nitrogen from sodium benzophenone ketyl.
Dichloromethane and acetonitrile were dried with CaH2 and
distilled under nitrogen. Other chemicals and solvents were
of analytical grade and were used as received unless otherwise
stated. Dimesitylchlorophosphine,14 (2,4,6-trimethylphenyl)-
2-[(Di-o-t olylp h osp h in yl)m et h yl]-6-(2,4,6-t r im et h yl-
p h en yl)p yr id in e (4b). The procedure for the preparation of
4b is similar to that for 4a . 4b was obtained as an air-sensi-
1
tive yellow viscous liquid. H NMR (CDCl3, 200 MHz): δ 7.54
(dd, J ) 7.7, 7.7 Hz, 1H, py H4), 7.47-7.40 (m, 2H, Ar-H),
7.28-7.21 (m, 7H, Ar-H), 7.03 (s, 1H, Ar-H), 7.00-6.98 (m,
1H, Ar-H), 6.96 (s, 2H, Ar-H), 3.69 (s,, 2H, py-CH2), 2.36
(14) Howthorne, M. F. J . Org. Chem. 1958, 23, 1579.
(15) Beswick, M. A.; Cromhout, N. L.; Harmer, C. N.; Palmer, J . S.;
Raithby, P. R.; Steiner, A.; Verhorevoort, K. L.; Wright, D. S. Chem.
Commun. 1997, 583.
(16) Ward, L. G. L. Inorg. Synth. 1971, 13, 154.
(17) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

4898 Organometallics, Vol. 22, No. 24, 2003
Ta ble 5. Selected Cr ysta llogr a p h ic Da ta of Com p lexes 5b, 6a , 6b, 10a , a n d 10b
Chen et al.
5b
6a
6b
10a
10b
formula
fw
cryst syst
Space group
a, Å
b, Å
c, Å
C
30H33ClNPPd
C34H41BF4NOPPd
703.86
monoclinic
P21/n
10.5380(1)
25.3380(3)
12.5570(1)
90
92.428(1)
90
C33H38BCl2F4N2PPd
757.73
triclinic
C34.5H41Br2Cl3NNiP
825.53
monoclinic
P21/n
12.1420(1)
23.9220(3)
13.3490(1)
90
106.777(1)
90
C29H30Br2NNiP
642.04
580.39
monoclinic
P21/c
20.1850(1)
15.7450(2)
8.6630(2)
90
90.178(1)
90
monoclinic
P21/c
17.4120(2)
10.2430(1)
16.2910(3)
90
106.735(1)
90
2782.46(7)
4
P1h
12.5590(1)
12.6630(2)
13.2780(2)
83.092(1)
61.840(1)
74.268(1)
1791.90(4)
2
R, deg
â, deg
γ, deg
V, Å3
2753.20(7)
4
1.400
3349.86(6)
4
1.396
3712.32(6)
4
1.477
Z
Dcalcd, Mg/m3
F(000)
1.404
772
1.533
1296
1192
1446
1676
cryst size, mm
θ range
no. of rflns collected
no. of indep rflns
0.30 × 0.25 × 0.20
2.02-25.00
16 611
0.25 × 0.20 × 0.10
2.09-25.00
19 581
0.30 × 0.25 × 0.20
2.20-25.00
11 551
0.20 × 0.15 × 0.15
2.63-25.00
41 428
0.15 × 0.10 × 0.10
2.84-25.00
20 876
6373 (Rint )
0.0544)
4849 (Rint
)
5883 (Rint
0.0354)
)
6285 (Rint
)
6532 (Rint
)
0.0286)
0.0193)
0.0578)
refinement method
full-matrix least squares on F2
R (I > 2σ(I))
R1 ) 0.0379
wR2 ) 0.1052
1.172
R1 ) 0.0426
wR2 ) 0.1160
1.097
R1 ) 0.0467
wR2 ) 0.1567
1.278
R1 ) 0.0504
wR2 ) 0.1506
1.033
R1 ) 0.0454
wR2 ) 0.1049
1.017
goodness of fit on F2
(s, 3H, Ar-CH3), 2.30 (s, 6H, Ar-CH3), 2.01 (s, 6H, Ar-CH3).
31P NMR (161.9 MHz): δ -29.6. HRFABMS: m/z calcd for
Ar-CH3), 2.23 (s, 6H, Ar-CH3), 2.0 (s, 2H, H2O), 1.98 (s, 6H,
Ar-CH3), 0.35 (d, J ) 2.5 Hz, 3H, PdCH3). 31P NMR (161.9
MHz): δ 11.9. 13C NMR (100 MHz): δ 160.9, 156.9, 142.4 (d,
J ) 10.8 Hz), 139.8, 136.5, 133.1 (d, J ) 19.4 Hz), 132.4, 132.3,
128.5, 126.8 (d, J ) 10.4 Hz), 125.7, 123.6 (d, J ) 8.4 Hz),38.4
(d, J ) 8.8 Hz, py-CH2), 22.3 (d, J ) 8.8 Hz), 21.1, 2.7 (PdCH3).
Anal. Calcd for C36H44N2PPdBF4: C, 57.85; H, 6.14; N, 1.98.
Found: C, 57.48; H, 6.14; N, 2.33.
C
29H30PN, 423.2116; found, 423.2121.
Com p lex 5a . A mixture of 3a (0.355 g, 0.74 mmol) and
(COD)PdMeCl (0.19 g, 0.73 mmol) in dichloromethane (10 mL)
was stirred for 2 h at ambient temperature. Upon concentra-
tion to a small volume of reaction mixture, hexane was added
and the desired complex was precipitated out from the solu-
tion. The yellow solids were collected and washed with ether
(yield 462 mg, 98%): mp 196-197 °C dec. 1H NMR (CDCl3,
400 MHz): δ 7.51 (dd, J ) 7.7, 7.7 Hz, 1H, py H4), 6.97-6.95
(m, 2H, py H3,5), 6.89 (s, 2H, Ar H), 6.78 (s, 4H, Ar H), 4.50 (d,
J ) 10.4 Hz, 2H, CH2), 2.49 (s, 12H, Ar-CH3), 2.31 (s, 3H,
Ar-CH3), 2.18 (s, 6H, Ar-CH3), 1.99 (s, 6H, Ar-CH3), 0.69
(d, J ) 4.4 Hz, 3H, PdCH3). 31P NMR (161.9 MHz): δ 13.3.
13C NMR (CDCl3, 100 MHz): δ 163.4, 158.3, 141.6 (d, J ) 8.9
Hz), 140.3 (d, J ) 2.1 Hz), 137.8, 137.4, 136.3, 136.2, 130.9 (d,
J ) 8.3 Hz), 127.9, 126.0, 125.9, 125.6, 43.2 (d, J ) 28.1 Hz,
py-CH2), 24.9 (d, J ) 28.1 Hz), 21.3, 21.0, 20.8, 1.01 (PdCH3).
Anal. Calcd for C34H41ClNPPd: C, 64.15; H, 6.49; N, 2.20.
Found: C, 64.02; H, 6.22; N, 1.99.
Com p lex 6b. The procedure for the preparation of this
compound is similar to that for 6a : yellow solids (yield 97%);
1
mp 174-175 °C dec. H NMR (CDCl3, 400 MHz): δ 7.91 (dd,
J ) 7.7, 7.6 Hz, 1H, py H4), 7.81 (d, J ) 7.7 Hz, 1H, py H3),
7.43-7.17 (m, 8H, Ar H), 7.07 (d, J ) 7.6 Hz, 1H, py H5),
6.81 (s, 2H, Ar H), 4.43 (d, J ) 11.1 Hz, 2H, CH2), 2.62 (s, 6H,
Ar-CH3), 2.30 (s, 3H, Ar-CH3), 2.01 (s, 3H, CH3CN), 1.76 (s,
6H, Ar-CH3), 0.48 (d, J ) 2.1 Hz, 3H, PdCH3). 31P NMR (161.9
MHz): δ 32.9. 13C NMR (100 MHz): δ 161.0, 156.9, 142.4 (d,
J ) 14.9 Hz), 139.9, 138.9, 136.5, 133.1 (d, J ) 9.7 Hz), 132.3
(d, J ) 5.4 Hz), 128.4, 126.8 (d, J ) 10.4 Hz), 125.7, 123.7 (d,
J ) 9.0 Hz), 38.4 (d, J ) 32.3 Hz, py-CH2), 22.3 (d, J ) 8.9
Hz), 21.1, 19.9, 2.6 (CH3CN), 1.5 (PdCH3). Anal. Calcd for
C
32H36PN2PdBF4: C, 57.12; H, 5.39; N, 4.16. Found: C, 57.54;
Com p lex 5b. This complex was prepared according to a
procedure similar to that for 5a : light yellow solids (yield
94.6%); mp 220-221 °C dec. 1H NMR (CDCl3, 400 MHz): δ
7.13 (dd, J ) 7.7, 7.7 Hz, 1H, py H4), 7.41-7.28 (m, 5H, Ar H,
py H), 7.09-7.00 (m, 5H, Ar H, py H), 6.81 (s, 2H, Ar H3,5),
4.29 (d, J ) 9.8 Hz, 2H, CH2), 2.70 (s, 6H, Ar-CH3), 2.26 (s,
3H, Ar-CH3), 1.74 (s, 6H, Ar-CH3), 0.80 (d, J ) 3.2 Hz, 3H,
PdCH3). 31P NMR (161.9 MHz): δ 29.4. 13C NMR (100 MHz):
δ 163.2, 156.4, 143.2 (d, J ) 12.7 Hz), 137.8 (d, J ) 5.7 Hz),
136.1, 132.0 (d, J ) 8.6 Hz), 131.8 (d, J ) 6.5 Hz), 131.2 (d, J
) 2.2 Hz), 128.1, 126.4, 126.3 (d, J ) 8.6 Hz), 125.3, 124.8,
38.0 (d, J ) 30.0 Hz, py-CH2), 22.2 (d, J ) 9.6 Hz), 21.3, 20.3,
1.2 (PdCH3). Anal. Calcd for C30H33PNClPd: C, 62.08; H, 5.73;
N, 2.41. Found: C, 62.29; H, 5.75; N, 2.30.
Com p lex 6a . To a mixture of 5a (0.16 g, 0.25 mmol) and
AgBF4 (0.049 g, 0.25 mmol) in a 25 mL flask was added
dichloromethane (10 mL) and acetonitrile (0.5 mL) with
stirring. The reaction mixture was filtrated through Celite to
remove the silver salt, and the filtrate was concentrated. The
residue was dissolved in ether for crystallization. Complex 6a
was obtained as an aqua complex as light yellow crystalline
solids (yield 0.18 g, 98%): mp 166-168 °C dec. 1H NMR
(CDCl3, 400 MHz): δ 7.74 (d, J ) 7.6, 7.6 Hz, 1H, py H4), 7.32
(d, J ) 7.6 Hz, 1H, py H3), 7.05 (d, J ) 7.6 Hz, 1H, py
H5), 6.95 (s, 2H, Ar H), 6.84 (d, J ) 3.8 Hz, 4H, Ar H), 4.49 (d,
J ) 11.4 Hz, 2H, CH2), 2.46 (s, 12H, Ar-CH3), 2.33 (s, 3H,
H, 5.46; N, 4.00.
Complex 10a . A mixture of 3a (0.10 g, 0.208 mmol) and
(DME)NiBr2 in CH2Cl2 (5 mL) was stirred at room temperature
for 14 h. Upon concentration, the crude product was recrystal-
lized from dichloromethane/ether to give the desired complex
as light brown solids (yield 133 mg, 92%): mp 190-192 °C
dec. λmax ) 498.5 nm (ꢀ ) 138). 1H NMR (CDCl3, 400 MHz): δ
7.23 (br), 4.98 (br), 2.14 (br), 1.6-0.84 (br). 31P NMR (CDCl3,
161.9 MHz): δ -8.9 (br). Anal. Calcd for C33H38Br2NNiP‚
3/2CH2Cl2: C, 50.20; H, 5.01. Found: C, 50.05; H, 5.00.
Com p lex 10b. Procedures for preparation of this compound
are similar to those for 10a : dark-brown solids (yield 88%);
mp 182-184 °C. Unlike 7a , no NMR data were recorded due
to the paramagnetic nature of 10b. λmax ) 498.5 nm (ꢀ ) 100).
Anal. Calcd for C29H30Br2NNiP: C, 54.25; H, 4.71. Found: C,
54.05; H, 4.62.
Cr ysta llogr a p h y. Crystals suitable for X-ray determina-
tion were obtained for 5b, 6a , 6b, 10a ‚3/2CH2Cl2, and 10b by
slow diffusion of hexane into a dichloromethane solution at
room temperature. Cell parameters were determined on a
Siemens SMART CCD diffractometer. Crystal data of these
complexes are listed in Table 5, and ORTEP plots of 5b, 6b,
and 10a are shown in Figures 1-3, respectively (labels of
phenyl groups are omitted for clarity). Other crystallographic
data are deposited as Supporting Information.

New Bulky Phosphino-Pyridine Ligands
Organometallics, Vol. 22, No. 24, 2003 4899
5b, 6a , 6b, 10a ‚3/2CH2Cl2, and 10b, including ORTEP plots of
6a and 10b and tables of atomic coordinates, isotropic and
anisotropic thermal parameters, and bond distances and
angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank the National Science
Council for financial support (Grant No. NSC92-2113-
M-002-040).
Su p p or tin g In for m a tion Ava ila ble: Complete descrip-
tion of the X-ray crystallographic structure determinations of
OM030242I