Synthesis of new phosphine imine ligands and their effects on the thermal stability of late-transition-metal olefin polymerization catalysts

Article abstract of DOI:10.1021/om020240i

A series of α-phosphine imine hybrid ligands was successfully synthesized by nucleophilic substitution of di-tert-butylchlorophosphine or diphenylchlorophosphine on imine anions. These ligands exist as α-phosphine enamines before complexation, which tautomerize to α-phosphine imines upon coordination to Ni(II) or Pd(II). The Ni(II) and Pd(II) complexes with these P∧N ligands were prepared and fully characterized by NMR, elemental analysis, and single-crystal X-ray crystallography. While all the Ni(II)-P∧N complexes assume tetrahedral coordination geometry, the Pd(II)-P∧N complexes are square planar. Upon activation with MAO, the Ni(II) complexes were active for ethylene polymerization. Whereas the Ni(II)-P∧N complexes are less productive than the Brookhart Ni(II)-α-bis(imine) complexes and form polyethylenes with relatively low molecular weight, the thermal stabilities of these complexes upon activation are significantly higher than those of the corresponding Ni(II)-α-bis(imine) complexes. ¹³C NMR shows that the polyethylenes are highly branched and have branch-on-branches. In contrast, the Pd(II)-P∧N complexes were inactive for ethylene polymerization.

Full text of DOI:10.1021/om020240i

3580
Organometallics 2002, 21, 3580-3586
Syn th esis of New P h osp h in e Im in e Liga n d s a n d Th eir
Effects on th e Th er m a l Sta bility of La te-Tr a n sition -Meta l
Olefin P olym er iza tion Ca ta lysts
Zhibin Guan* and William J . Marshall†
Department of Chemistry, University of California, Irvine, California 92697-2025
Received March 28, 2002
A series of R-phosphine imine hybrid ligands was successfully synthesized by nucleophilic
substitution of di-tert-butylchlorophosphine or diphenylchlorophosphine on imine anions.
These ligands exist as R-phosphine enamines before complexation, which tautomerize to
R-phosphine imines upon coordination to Ni(II) or Pd(II). The Ni(II) and Pd(II) complexes
with these P∧N ligands were prepared and fully characterized by NMR, elemental analysis,
and single-crystal X-ray crystallography. While all the Ni(II)-P∧N complexes assume
tetrahedral coordination geometry, the Pd(II)-P∧N complexes are square planar. Upon
activation with MAO, the Ni(II) complexes were active for ethylene polymerization. Whereas
the Ni(II)-P∧N complexes are less productive than the Brookhart Ni(II)-R-bis(imine)
complexes and form polyethylenes with relatively low molecular weight, the thermal
stabilities of these complexes upon activation are significantly higher than those of the
corresponding Ni(II)-R-bis(imine) complexes. 13C NMR shows that the polyethylenes are
highly branched and have branch-on-branches. In contrast, the Pd(II)-P∧N complexes were
inactive for ethylene polymerization.
Ch a r t 1
In tr od u ction
Transition-metal catalysts have played and will con-
tinue to play crucial roles in making important poly-
meric materials.1,2 Whereas early-transition-metal cata-
lysts such as the Ziegler-Natta and single-site metallo-
cene catalysts3 remain as the workhorse in olefin
polymerization industry, significant advances have been
made recently in late-transition-metal polymerization
catalysts.4-6 Some exciting examples are the Ni(II)- and
Pd(II)-R-bis(imine) complexes (Chart 1) reported by
Brookhart and co-workers.7,8 These catalysts show
activities comparable to those of the early-metal cata-
lysts in polymerizing ethylene into high-molecular-
weight polymers.9 The polyethylenes formed have
branched microstructures in which the branching was
proposed to be introduced by catalyst isomerization or
“walking” along the polyethylene backbone during the
migratory insertion polymerization.7,8,10 By exploitation
of this chain-walking feature, it was shown that poly-
ethylenes with a broad spectrum of topology ranging
from linear to hyperbranched to dendritic can be
obtained from polymerization of ethylene by simply
varying ethylene pressure.11-14
Whereas the Ni(II)- and Pd(II)-R-bis(imine) cata-
lysts exhibit excellent activity and good functional group
tolerance, one severe limitation is their relatively low
thermal stability. The catalysts decompose rapidly at
temperatures about 50 °C for Pd(II)-R-bis(imine) and
70 °C for Ni(II)-R-bis(imine) catalysts,15 which is
significantly lower than the decomposition temperatures
of early-transition-metal species such as Ziegler-Natta
and single-site metallocene catalysts.3 For practical
* To whom correspondence should be addressed. Fax: 949-824-2210.
E-mail: zguan@uci.edu.
† X-ray crystal structure determination of complexes 3a ,b and
4b,c. Address: Experimental Station, DuPont Central Research and
Development, Wilmington, DE 19880-0328.
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10.1021/om020240i CCC: $22.00 © 2002 American Chemical Society
Publication on Web 07/25/2002

New Phosphine Imine Ligands
Organometallics, Vol. 21, No. 17, 2002 3581
Sch em e 1. Syn th esis of P ∧N Liga n d s a n d Th eir Ni(II) a n d P d (II) Com p lexes
nosulfonamide,27 and R-iminocarboxamidato28 ligands
have been reported for various studies.
Ch a r t 2
Resu lts a n d Discu ssion
Liga n d a n d Com p lex Syn th eses. Previous studies
by Brookhart and co-workers on the Ni(II)- and Pd-
(II)-R-bis(imine) complexes have shown that the bulky
ortho substituents on the aniline moieties and their
orientation toward the axial positions of the square-
planar complexes are crucial for obtaining high poly-
mers (Chart 1). To maintain this steric requirement,
bulky phosphines and aniline were used in the ligand
synthesis. Monocyclic and bicyclic backbones were used
to enhance the conformational rigidity of the P∧N
ligands to improve the chelation with the metal center
(Chart 2). A series of P∧N ligands with the structures
shown in Scheme 1 were synthesized. Following stan-
dard procedures for imine preparation, imine precursors
1a ,b were synthesized by heating to reflux in toluene.
A disubstituted phosphine was installed by nucleophilic
substitution of the imine anion with a disubstituted
chlorophosphine. The formation of 2a -c was monitored
by 31P NMR, and the products were analyzed by NMR,
GC/MS, and elemental analysis. Solid products were
purified by recrystallization, and liquid products were
purified by flash column chromatography.
applications, significantly higher thermal stability is
desired for process and economic considerations. We
have been attempting to determine how ligand structure
affects the thermal stability of the Ni(II) and Pd(II)
complexes. In this paper, we wish to report the synthe-
sis, structural characterization, and ethylene polymer-
ization studies of a family of nickel and palladium
complexes with a new class of phosphine imine (P∧N)
ligands (Chart 2).16 In these P∧N ligands, we used a
better σ-donating phosphine to replace one imine site
of the bis(imine) ligands with the purpose of increasing
the binding strength of the ligand to the metal center.
The stronger binding ability of the phosphine may lead
to an improvement of the catalyst thermal stability.
Other complexes of late transition metals with various
phosphine nitrogen,17-25 diphosphaalkene,26 phosphi-
31P NMR showed single peaks for all the ligands,
indicating that they are pure compounds. 1H NMR
showed that the products exist in the enamine tau-
tomers (Scheme 2), which isomerize back to the imine
tautomers upon coordination with Ni(II) or Pd(II) metal
ions.
(16) Guan, Z. (E. I. Du Pont de Nemours and Co.). PCT Int. Appl.,
2000; 44 pp.
(17) Kapteijn, G. M.; Spee, M. P. R.; Grove, D. M.; Kooijman, H.;
Spek, A. L.; van Koten, G. Organometallics 1996, 15, 1405-1413.
(18) Ruelke, R. E.; Kaasjager, V. E.; Wehman, P.; Elsevier, C. J .;
van Leeuwen, P. W. N. M.; Vrieze, K.; Fraanje, J .; Goubitz, K.; Spek,
A. L. Organometallics 1996, 15, 3022-3031.
Pd(II) complexes 3a -c and Ni(II) complexes 4a -c
were prepared by mixing the corresponding ligands with
(19) Crociani, L.; Bandoli, G.; Dolmella, A.; Basato, M.; Corain, B.
Eur. J . Inorg. Chem. 1998, 1811-1820.
(20) Crociani, L.; Tisato, F.; Refosco, F.; Bandoli, G.; Corain, B. Eur.
J . Inorg. Chem. 1998, 1689-1697.
(21) Reddy, K. R.; Surekha, K.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T.
Organometallics 2001, 20, 5557-5563.
(25) Mueller, C.; Iverson, C. N.; Lachicotte, R. J .; J ones, W. D. J .
Am. Chem. Soc. 2001, 123, 9718-9719.
(22) Reddy, K. R.; Chen, C.-L.; Liu, Y.-H.; Peng, S.-M.; Chen, J .-T.;
Liu, S.-T. Organometallics 1999, 18, 2574-2576.
(26) Ikeda, S.; Ohhata, F.; Miyoshi, M.; Tanaka, R.; Minami, T.;
Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2000, 39, 4512-4513.
(27) Rachita, M. J .; Huff, R. L.; Bennett, J . L.; Brookhart, M. J .
Polym. Sci., Part A: Polym. Chem. 2000, 38, 4627-4640.
(28) Lee, B. Y.; Bazan, G. C.; Vela, J .; Komon, Z. J . A.; Bu, X. J .
Am. Chem. Soc. 2001, 123, 5352-5353.
(23) Reddy, K. R.; Surekha, K.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T.
Organometallics 2000, 19, 2637-2639.
(24) Reddy, K. R.; Surekha, K.; Lee, G.-H.; Peng, S.-M.; Chen, J .-
T.; Liu, S.-T. Organometallics 2001, 20, 1292-1299.

3582 Organometallics, Vol. 21, No. 17, 2002
Guan and Marshall
Sch em e 2. Ta u tom er iza tion betw een Im in e a n d
En a m in e
(COD)PdCl2 or (DME)NiBr2 in dichloromethane and
purified by recrystallization in dichloromethane.
Sin gle-Cr ysta l X-r a y Str u ctu r e An a lysis. Single
crystals were grown from a dichloromethane solution
for single-crystal X-ray crystallographic analysis. X-ray
structures were obtained for the complexes 3a ,b and
4b,c. As representative examples, the ORTEP plots for
3a and 4b are shown in Figure 1 and Figure 2,
respectively.
F igu r e 1. ORTEP drawing for 3a .
Although some P∧N ligands were reported to form
polynuclear complexes with Ni(II) or Pd(II),29,30 all our
complexes between Ni(II) and Pd(II) and the P∧N
ligands are mononuclear. Presumably the bulky sub-
stituents on the phosphine and on the aniline moiety
prevent the polynuclear complexes from forming. The
coordination geometry is tetrahedral for all the Ni(II)
complexes and is square planar for all the Pd(II)
complexes. The crystal, intensity collection, and refine-
ment data for complexes 3a ,b and 4b,c are presented
in Table 1. The most relevant bond parameters for
complexes 3a and 4b are summarized in Table 2.
The C1-N1 bond distances in complexes 3a and 4b
are 1.276(4) and 1.274(9) Å, respectively, which agree
with that of a carbon-nitrogen double bond, indicating
that the enamines tautomerize to imines after coordi-
nating to Ni(II) or Pd(II). The bond distances and bond
angles in 3a and 4b are comparable to those in relevant
complexes reported previously.17-25 Both 3a and 4b are
chiral molecules, with the C5 carbon in 3a and the C6
carbon in 4b being chiral centers. Both enantiomers of
3a were observed in the X-ray crystal analysis, which
cocrystallize in the same unit cell (see Supporting
Information). For 4b, however, X-ray crystal analysis
showed that the C6 carbon only exists in the S config-
uration (Figure 2), presumably because this is the
thermodynamically more stable stereoisomer.
Since the active cationic catalytic species during
polymerization adopt square-planar geometry at the
metal center for both Ni(II) and Pd(II) complexes, it
would be interesting to examine the square-planar
palladium complex 3a more carefully. Similar to the
Brookhart Pd(II)-R-bis(imine) complexes,7,15 the aniline
phenyl ring in 3a is almost perpendicular to the
coordination plane. The angle between the coordination
mean plane defined by P1-N1-Pd-Cl1-Cl2 and the
phenyl ring is 78.75°. This orients the two o-isopropyl
substituents on the aniline moiety to the axial positions
of the complex. The two tert-butyl groups on the phos-
phine are also oriented toward the axial positions of the
coordination center. The angle between the same coor-
F igu r e 2. ORTEP drawing for 4b.
dination mean plane and the plane defined by C23-
P1-C27 is 83.35°. As shown by Brookhart and co-
workers7,15 in previous studies of Ni(II)- and Pd(II)-
R-bis(imine) complexes, blocking axial faces of the
coordination site with bulky substituents of the aniline
moieties is critical for shutting off the associative chain
transfer process in order to obtain polymers with high
molecular weight. In complex 3a , the orientation of both
the tert-butyl groups from phosphine and the isopropyl
groups from aniline to the axial positions should par-
tially reduce the chain transfer process. However, the
steric bulkiness for 3a is unsymmetrical for the axial
faces above and below the coordination plane. This can
be better viewed in the space-filling model of 3a . Figure
3 shows the space-filling models of the complex 3a
viewed from the front, the top, and the bottom. The top
axial face is much more open than the bottom one. The
openness at the top axial face makes the metal center
susceptible to ethylene associative chain transfer, which
is presumably the cause for the formation of polyeth-
ylenes with relatively low molecular weight in the
ethylene polymerization catalyzed by the Ni(II)-P∧N
complexes (vide infra).
E t h ylen e P olym er iza t ion by t h e Com p lexes.
Surprisingly, all the Pd(II)-P∧N complexes (3a -c)
upon activation with MAO were inactive to polymerize
ethylene. We are not exactly sure why the Pd(II)-P∧N
complexes are inactive in ethylene polymerization but
(29) Deeming, A. J .; Rothwell, I. P.; Hursthouse, M. B.; Malik, K.
M. A. J . Chem. Soc., Dalton Trans. 1980, 1974-1982.
(30) Deeming, A. J .; Rothwell, I. P.; Hursthouse, M. B.; Malik, K.
M. A. J . Chem. Soc., Dalton Trans. 1979, 1899-1911.

New Phosphine Imine Ligands
Organometallics, Vol. 21, No. 17, 2002 3583
Ta ble 1. Su m m a r y of Cr ysta l Da ta , Da ta Collection , a n d Str u ctu r e Refin em en t P a r a m eter s for Com p lexes
3a ,b a n d 4b,c
3a
3b
4b
4c
formula
fw
C
26H44PdCl4PN
C29H48PdCl6PN
760.80
C27H44Br2NiPN
632.16
C31H36Br2NiPN
672.14
649.83
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
173
173
173
173
monoclinic
P21/n (No. 14)
20.556(2)
14.819(1)
21.382(2)
109.31(1)
6147.1
monoclinic
P21/c (No. 14)
9.996(1)
19.452(1)
19.352(1)
110.96(1)
3513.9
monoclinic
P21 (No. 4)
9.053(1)
14.751(2)
11.194(1)
104.49(1)
1447.3
orthorhombic
Pbca (No. 61)
16.939(1)
32.804(1)
10.554(1)
â (deg)
V, Å3
5864.5
8
34.38
Z
8
4
2
µ(Mo KR), cm-1
10.13
1.404
10.46
1.438
34.77
1.450
Fcalcd (g cm-3
)
1.522
cryst size (mm)
2θ range (deg)
total no. of rflns
no. of unique data, I ) 3.0σ(I)
Rmerge
0.35 × 0.39 × 0.43
3.4-48.2
32 097
7603
0.018
0.28 × 0.37 × 0.41
3.1-48.2
18 571
3821
0.019
0.08 × 0.28 × 0.38
5.2-48.2
7884
3080
0.021
0.02 × 0.44 × 0.50
4.6-48.2
21 820
2741
0.044
no. of params
R1
595
0.032
338
0.076
288
0.054
325
0.036
wR2
0.037
0.089
0.062
0.035
goodness of fit
1.89
4.58
3.20
1.43
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3a a n d 4b
striking feature of the Ni(II)-P∧N complexes is their
relatively high thermal stability. The catalysts remained
active to polymerize ethylene after polymerization at 70
°C for many hours. Comparison of polymerization with
4b for 3 and 7 h (runs 2 and 3) indicates that the
catalyst remains active after polymerizing ethylene for
up to 7 h. For comparison, the Ni(II)-R-bis(imine)
catalysts usually decompose within 1/2 h for ethylene
polymerization at 70 °C. The enhanced thermal stability
is ascribed to the stronger binding ability of the phos-
phine site introduced into the ligands.
3a
4b
Bond Lengths
Pd1-N1
Pd1-P1
Pd1-Cl1
Pd1-Cl2
N1-C1
2.056(2)
Ni1-N1
Ni1-P1
Br1-Ni1
Br2-Ni1
N1-C1
2.043(6)
2.338(2)
2.359(1)
2.341(1)
1.274(9)
1.861(8)
1.470(9)
1.896(8)
1.870(9)
2.2545(8)
2.2934(7)
2.3615(8)
1.276(4)
1.856(3)
1.464(4)
1.866(3)
1.863(3)
P1-C5
P1-C6
N1-C11
P1-C23
P1-C27
N1-C11
P1-C23
P1-C27
The ligand structure influences both the catalyst
activity and the molecular weight of the polymer formed
(comparing runs 1, 2, and 6). Complex 4c is much more
active than 4a ,b. This is presumably due to the differ-
ence of electronic structure between 4c and 4a ,b. The
phosphine in 4a ,b is much more electron rich than the
phosphine in 4c because the tert-butyl group has a
stronger electron donating ability than the phenyl group
has. The lower molecular weight for polyethylene ob-
tained with complex 4c is attributed to the decreased
steric bulkiness of the diphenylphosphine in 4c as
compared to the di-tert-butylphosphine in 4a ,b. To
examine the influence of polymerization conditions on
the catalyst performance, complex 4b was studied for
ethylene polymerization at different temperatures and
pressures. Polymerization at lower ethylene pressure
(comparing runs 3 and 4) resulted in a lower turnover
rate and lower molecular weight for the polymer. The
catalyst was more active at higher temperature but
afforded short oligomers as the major product (run 5,
at 110 °C).
Bond Angles
P1-Pd1-N1
85.07(7)
177.7(1)
91.78(7)
93.72(3)
176.25(7)
89.49(3)
119.3(2)
123.9(2)
99.1(1)
P1-Ni1-N1
87.4(2)
N1-Pd1-Cl1
N1-Pd1-Cl2
Cl1-Pd1-P1
Cl2-Pd1-P1
Cl1-Pd1-Cl2
Pd1-N1-C1
Pd1-N1-C11
Pd1-P1-C5
Pd1-P1-C23
Pd1-P1-C27
Br1-Ni1-Br2
Br1-Ni1-N1
Br2-Ni1-N1
Br1-Ni1-P1
Br2-Ni1-P1
Ni1-N1-C1
Ni1-N1-C11
Ni1-P1-C6
Ni1-P1-C23
Ni1-P1-C27
119.01(5)
100.6(2)
124.3(2)
110.08(7)
110.91(6)
116.4(5)
119.7(4)
92.8(2)
112.0(1)
117.2(1)
114.5(2)
116.7(2)
tentatively attribute this to the electronic structure of
the Pd(II)-P∧N complexes.31 Low activity was also
observed by Rieger and co-workers for ethylene polym-
erization catalyzed by Pd(II) complexes with some
special bis(imine) ligands in which the catalysts decom-
posed rapidly.32
All the Ni complexes are active to polymerize ethylene
upon activation with MAO. Some of the ethylene po-
lymerization results are summarized in Table 3. Whereas
the activities of these catalysts are less than those of
the Ni(II)-R-bis(imine) complexes and the molecular
weights of the polyethylenes are generally low, one
The molecular weights of the polyethylenes obtained
with these three complexes are generally low compared
to those obtained with the Ni(II)-R-bis(imine) catalysts.
Whereas the exact cause for this warrants further
investigation, it is tentatively attributed to the unsym-
metrical geometry of the complexes, which causes one
side of the axial face to be susceptible to ethylene
associative chain transfer (vide supra).
(31) Pd black was observed for some polymerization of Pd(II)-P∧N
complexes activated with MAO. Presumably, this could be either due
to the low thermal stability of the activated catalysts or due to
reduction of the Pd(II) by MAO to Pd(0). P∧N-Pd(Me)Cl complexes
were also prepared and tested for ethylene polymerization. Upon
activation with 2 equiv of Na+BAF- (where BAF- ) [B{3,5-C6H3-
(CF3)2}4]-), the complexes were also inactive in polymerizing ethylene.
(32) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskelae, M.; Rieger,
B. Organometallics 2001, 20, 2321-2330.
Another unusual feature of ethylene polymerization
by the Ni(II)-P∧N complexes is that the polyethylenes

3584 Organometallics, Vol. 21, No. 17, 2002
Guan and Marshall
F igu r e 3. Space-filling models of the complex 3a based on its X-ray structure: (a) front view; (b) top view; (c) bottom
view.
of the branches being simple methyl and ethyl branches.9
Ta ble 3. Eth ylen e P olym er iza tion Resu lts w ith th e
NiII-P ∧N Com p lexesa
The short-chain branches in Ni(II)-P∧N catalyzed
ethylene polymerization is presumably formed by the
chain-walking mechanism proposed by Brookhart7 and
Fink10 for the Ni(II)- and Pd(II)-R-bis(imine) catalyst
systems. The observed higher branching density, longer
short-chain branches, and significant amount of branch-
on-branches for polyethylenes made by our Ni(II)-P∧N
complexes suggest that chain walking is more competi-
tive in our system than in the Ni(II)-R-bis(imine)
system.
run
temp pressure time
d
no. catalyst (°C)
(psi)
(h)
TOb TO/hc Mn Mw/Mn
1
2
3
4
5
6
4a
4b
4b
4b
4b
4c
70
70
70
70
110
70
500
500
500
350
500
500
7
3
7
5
4
6700
960 2000
1.4
1.2
1.2
1.3
e
5020 1670 1450
10800 1540 1400
5880 1180 1290
13390 3350 e
2.7 46500 17200 800
1.3
a
Polymerizations were run with 20 mg of catalyst loading in
100 mL chlorobenzene. b TO ) turnover, which is the ratio of moles
of ethylene polymerized by 1 mol of catalyst. c TO/h is the average
turnover per hour. In units of g/mol. e The GPC trace of the
d
Con clu sion s
product showed bimodal distribution with the major peak with
peak molecular weight of 430 and a very small peak at very high
mass (Mn ) 59 500, Mw/Mn ) 2.8).
A series of new phosphine imine hybrid ligands were
successfully synthesized. Ni(II) and Pd(II) complexes
with these P∧N ligands were prepared and fully char-
acterized by NMR, elemental analysis, and single
crystal X-ray crystallography. Whereas the Ni(II)-P∧N
complexes assume a tetrahedral coordination geometry,
the Pd(II)-P∧N complexes are all square planar. Upon
activation with MAO, the Ni(II) complexes were active
for ethylene polymerization. The Ni(II)-P∧N complexes
are significantly more stable than the corresponding Ni-
(II)-R-bis(imine) complexes, which is ascribed to the
stronger binding ability of the phosphine binding site.
The molecular weights of the polyethylenes are rela-
tively low, which is presumably caused by facile chain
transfer at one axial face that is relatively open. 13C
NMR shows that the polyethylenes are highly branched
and have branch-on-branches. In contrast, the Pd(II)-
P∧N complexes were inactive for ethylene polymeriza-
tion.
Ta ble 4. Sh or t-Ch a in Br a n ch in g Distr ibu tion
Obta in ed fr om Qu a n tita tive 13C NMRa
catalyst total Me Me Et
Pr Bu Am Hex+ 1B2%
4a
4b
4c
55
58
65
23 3.2 0.5 1.1
22 3.0 0.6 1.6
22 4.5 1.1 3.7 11.9
7.0
8.9
20.3
22
22
53
58
55
a
The data are for polyethylenes obtained at 500 psi and 70 °C
with different complexes. The data are expressed as the number
of branches per 1000 CH2 units. The abbreviations used in the
table are as follows: total Me ) total branches including chain
ends, Me ) methyl branches, Et ) ethyl branches, Pr ) propyl
branches, Bu ) butyl branches, Am ) amyl branches, Hex+ )
hexyl and longer branches, 1B2% ) percentage of ethyl branches
existing in isobutyl branches.
formed are much more branched than the polyethylenes
made by the Ni(II)-R-bis(imine) complexes at similar
polymerization conditions. The short-chain branches
measured by quantitative 13C NMR analyses33,34 were
summarized in Table 4, which indicates that the poly-
mers formed were highly branched with branching
densities in the range of 50-60 total branches per 1000
methylenes. Significant amounts of the branches are
relatively long (such as amyl and hexyl). Short branch-
on-branches also exist in the polyethylenes, as evidenced
by the presence of ethyl in isobutyl groups. This is in
great contrast to the polyethylenes formed by Ni(II)-
R-bis(imine) complexes. The polyethylenes obtained by
the Brookhart Ni(II)-R-bis(imine) complexes under
similar polymerization conditions usually only have
about 20 total branches per 1000 methylenes, with most
Exp er im en ta l Section
Ma ter ia ls. All the starting materials and reagents were
purchased from Aldrich and Strem and used without further
purification. Ethylene (99.9%) was purchased from MG In-
dustries. All dry solvents were purified by passing through
solvent purification columns following the method introduced
by Grubbs.35 Deuterated solvents were dried using standard
procedures and stored over freshly calcined molecular sieves
(4 Å) in the glovebox. Methyl aluminoxane (MAO) was
purchased from Aldrich as a 10 wt % solution in toluene.
Gen er a l Con sid er a tion s. Manipulation of organometallic
compounds was performed in a nitrogen-filled Vacuum Atmo-
spheres drybox. NMR spectra were obtained with a Bruker
Avance 500 spectrometer. Quantitative 13C NMR spectra were
obtained in a 10 mm probe on 10-20 wt % solutions of the
polymers and 0.05 M CrAcAc in 1,2,4-trichlorobenzene (TCB)
(33) McLain, S. J .; McCord, E. F.; J ohnson, L. K.; Ittel, S. D.;
Nelwson, L. T. J .; Arthur, S. D.; Halfhill, M. J .; Teasley, M. F. Polym.
Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1997, 38, 772-773.
(34) McCord, E. F.; McLain, S. J .; Nelson, L. T. J .; Arthur, S. D.;
Coughlin, E. B.; Ittel, S. D.; J ohnson, L. K.; Tempel, D.; Killian, C. M.;
Brookhart, M. Macromolecules 2001, 34, 362-371.
(35) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518-1520.

New Phosphine Imine Ligands
Organometallics, Vol. 21, No. 17, 2002 3585
unlocked at 120-140 °C using a 90° pulse of 17.8 µs, a spectral
width of 35 kHz, a relaxation delay of 5 s, an acquisition time
of 0.64 s, and inverse gated decoupling.33,34 Spectra are
referenced to the solvent TCB high-field resonance at 127.9
ppm. GC-MS analysis was carried out with a Hewlett-Packard
6890 series instrument. Molecular weights of polyethylenes
were measured by gel permeation chromatography (GPC)
using trichlorobenzene as eluent on an Agilent GPC equipped
with a polystyryl gel mixed bed column. The molecular weight
was obtained by calibration using polystyrene as standard.
THF (10 mL), -50 °C overnight and 35 °C for 18 h, flash
column separation (basic alumina, 40:1 hexane/chloroform),
1
yield 0.40 g white powder (26%). H NMR (CDCl3): δ 1.02 (d,
J ) 6.8 Hz, 6H, CHMe2), 1.11 (d, J ) 6.8, 6H, C′HMe2), 1.19
(d, J P-H ) 13.0, 18H, But), 1.66 (quint, J ) 7.0, 2H, CH2CH2-
CH2), 1.90 (t, J ) 7.0, 2H, CH2CH2CH2), 2.62 (t, J ) 7.0, 2H,
CH2CH2CH2), 3.21 (sep, J ) 6.8, 2H, CHMe2 and C′HMe2), 6.23
(b, 1H, NH), 7.02 (d, J ) 8.6, 2H, Ar m-H), 7.12 (t, J ) 8.6,
1H, Ar p-H). 31P NMR (CDCl3): δ 6.08 (s). Anal. Calcd for
C
25H42NP: C, 77.47; H, 10.92; N, 3.61. Found: C, 77.36; H,
10.78; N, 3.63.
Sin gle-Cr ysta l X-r a y Str u ctu r e An a lysis. X-ray diffrac-
tion data for all of the structures, 3a ,b and 4b,c, were collected
using Mo KR radiation on a Rigaku RU300 diffractometer
modified with an R-AXIS image plate area detector. For each
structure 45 frames of data were collected, each having an ω
oscillation of 4° and exposure times of 8-20 min. All structures
were solved by direct methods using teXsan36 (SIR-92) and
were refined using the Z program suite (Calabrese).37 Refine-
ment was by full-matrix least squares on F. Scattering factors,
including anomalous terms for Pd, Br, Cl, and P, were taken
from refs 38 and 39. All of the hydrogen atoms have been
idealized close to their previously refined positions. The
enantiomeric setting for noncentrosymmetric 4b was chosen
on the basis of the r factors. Inverting to the opposite
enantiomer raised the R1 value significantly from 5.47 to 6.57.
Table 1 provides information on the data collection and
refinement parameters for complexes 3a ,b and 4b,c reported
in this paper. The pertinent bond parameters for complexes
3a and 4b are summarized in Table 2.
Gen er a l P r oced u r e for th e Syn th esis of P ∧N Liga n d s.
Step 1. An appropriate amount of cyclopentanone or norcam-
phor was mixed with 1.5 equiv of 2,6-diisopropylaniline in
toluene followed by addition of a small amount of p-toluene-
sulfonic acid as the catalyst. The solution was heated to reflux
for 2 days, and a Dean-Stark trap was used to remove water
constantly. After the completion of the reaction as monitored
by GC, the solvent was removed by vacuum to leave an oily
mixture. The imine intermediate was obtained by recrystal-
lization or flash column separation.
Step 2. To a solution of of lithium diisopropylamide (LDA,
1.15 equiv) in THF at 0 °C, one of the imine intermediates
from the first step dissolved in THF was added dropwise. After
being stirred at 0 °C for 4 h, the mixture was cooled to -100
°C by using an ether/dry ice cold bath. Di-tert-butylchloro-
phosphine or diphenylchlorophosphine (1.0 equiv) in THF was
syringed into the reaction mixture dropwise. After addition
was completed, the mixture was stirred at -50 °C overnight
and then at room temperature and finally heated if necessary
until the reaction was completed, as monitored by 31P NMR.
After removal of solvent, the residue was dissolved in diethyl
ether, and this solution was subsequently poured into 1 N NH4-
Cl aqueous solution. The organic layer was collected, and the
aqueous layer was extracted with diethyl ether. The organic
phases were combined, washed with water, and dried with
MgSO4, and finally the solvent was removed. The final product
was purified either by recrystallization or flash column
separation.
Syn th esis of 2b. Step 1: norcamphor (8.00 g, 0.073 mol),
2,6-diisopropylaniline (21.6 g, 0.12 mol), 60.0 mL of toluene,
recrystallized from Et2O, yield 11.0 g (56%). Step 2: imine 1b
(2.0 g, 7.42 mmol) in THF (10 mL), LDA (1.5 M in cyclohexane,
5.5 mL, 8.25 mmol), di-tert-butylchlorophosphine (1.34 g, 7.42
mmol) in THF (20 mL), -50 °C overnight and room temper-
ature for 2 days, recrystallized from hexane twice, yield 0.75
g (24%). 1H NMR (CDCl3): δ 1.00 (d, J ) 6.8 Hz, 3H,
CHMeMe′), 1.03 (d, J ) 6.8, 3H, CHMeMe′), 1.11 (d, J ) 6.8,
3H, C′HMeMe′), 1.15 (d, J ) 6.8, 3H, C′HMeMe′), 1.27 (d, J P-H
) 13.0, 18H, But), 1.35-1.47 (b, 3H), 1.66-1.73 (b, 1H), 1.88
(b, 1H), 2.45 (b, 1H), 2.54 (b, 1H), 2.67 (sep, J ) 6.8, 1H,
CHMeMe′), 2.79 (b, 1H), 2.85 (sep, J ) 6.8, 1H, C′HMeMe′),
6.94 (t, J ) 8.6, 1H, Ar p-H), 6.99 (d, J ) 8.6, 1H, Ar m-H),
7.02 (d, J ) 8.6, 1H, Ar m′-H). 13C NMR (CDCl3): δ 21.88,
22.92, 23.91, 24.48, 24.75, 24.51, 28.45, 30.84, 30.89, 30.99,
31.10, 31.12, 31.24, 33.22, 37.03, 41.88, 42.92, 43.03, 48.94,
49.26, 122.30, 122.82, 122.96, 135.90, 137.03, 147.34, 181.44.
31P NMR (CDCl3): δ 53.47 (s). Anal. Calcd for C27H44NP: C,
78.40; H, 10.72; N, 3.39. Found: C, 78.29; H, 10.70; N, 3.35.
Syn th esis of 2c. Step 1: same as above. Step 2: imine 1b
(2.0 g, 7.42 mmol) in THF (10 mL), LDA (1.5 M in cyclohexane,
5.5 mL, 8.25 mmol), diphenylchlorophosphine (1.65 g, 7.42
mmol) in THF (20 mL), -50 °C overnight and 45 °C for 6 h,
1
recrystallized from hexane twice, yield 1.15 g (35%). H NMR
(CDCl3): δ 0.89 (d, J ) 6.8 Hz, 3H, CHMeMe′), 1.04 (d, J )
6.8, 3H, CHMeMe′), 1.10-1.20 (m, 6H, C′HMe2), 1.29-1.51 (m,
3H), 1.58-1.74 (m, 1H), 1.99 (b, 1H), 2.18 (m, 1H), 2.60 (b,
1H), 2.73 (sep, J ) 6.8, 1H, CHMeMe′), 2.82 (sep, J ) 6.8, 1H,
C′HMe2), 3.15 (m, 1H), 6.84-7.05 (m, 3H, Ar H), 7.15 (m, 3H,
Ar′ H), 7.30 (m, 3H, Ar′ H), 7.49 (m, 2H, Ar′ H), 7.67 (m, 2H,
Ar′ H). 31P NMR (CDCl3): δ -7.44 (s). Anal. Calcd for C31H36
NP: C, 82.08; H, 8.00; N, 3.09. Found: C, 82.02; H, 7.94; N,
3.11.
-
Gen er a l P r oced u r es for th e Syn th esis of P d a n d Ni
Com p lexes. Into a suspension of dichloro(1,5-cyclooctadiene)-
palladium ((COD)PdCl2) or dibromo(1,2-dimethoxyethane)-
nickel ((DME)NiBr2) in dichloromethane was added one of the
P∧N ligands. The mixture was stirred at room temperature
for 2-3 days. The solution was passed through Celite to
remove any insoluble materials. After the solution was con-
centrated, a large excess of hexane was added to precipitate
the complex. The complex was filtered, washed with hexane,
and recrystallized from dichloromethane or a mixture of
dichloromethane and hexane.
Syn th esis of 3a : (COD)PdCl2 (60 mg, 0.21 mmol), 2a (87
mg, 0.22 mmol), 10 mL of CH2Cl2, 2 days, recrystallized from
dichloromethane, yield 59 mg (50%). 1H NMR (CDCl3): δ 1.12
(d, J ) 6.8 Hz, 3H, CHMeMe′), 1.20 (d, J ) 6.8, 3H, CHMeMe′),
1.44 (d, J ) 6.8, 3H, C′HMeMe′), 1.51 (d, J ) 6.8, 3H,
C′HMeMe′), 1.70 (d, J P-H ) 13.0, 9H, But), 1.79 (d, J P-H ) 13.0,
9H, Bu′t), 1.85-2.5 (m, 6H, CH2CH2CH2), 3.04 (sep, J ) 6.8,
1H, CHMeMe′), 3.23 (sep, J ) 6.8, 1H, C′HMeMe′), 3.68 (dt,
Syn th esis of 2a . Step 1: cyclopentanone (8.00 g, 0.095 mol),
2,6-diisopropylaniline (25.29 g, 0.14 mol), 50.0 mL of toluene,
flash column separation (basic alumina, 40:1 hexane/chloro-
form), yield 13.8 g (60%). Step 2: imine 1a (1.0 g, 4.12 mmol)
in THF (10 mL), LDA (1.5 M in cyclohexane, 3.1 mL, 4.65
mmol), di-tert-butylchlorophosphine (0.744 g, 4.12 mmol) in
J P ) 14.0, J H-H ) 7.0, 1H, CHP), 7.13 (d, J ) 8.6, 2H, Ar
-H
(36) teXsan; Molecular Structure Corp., The Woodlands, TX.
(37) Z-Program Suite,; J CC, DuPont Co., 1994.
(38) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. 4,
pp 71-147.
(39) Cromer, D. T.; Ibers, J . A. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. 4,
pp 148-151.
m-H), 7.25 (t, J ) 8.6, 1H, Ar p-H). 31P NMR (CDCl3): δ 77.17
(s). Anal. Calcd for C25H42NPPdCl2: C, 53.15; H, 7.49; N, 2.48.
Found: C, 53.06; H, 7.44; N, 2.43.
Syn th esis of 3b: (COD)PdCl2 (70 mg, 0.25 mmol), 2b (111
mg, 0.27 mmol), 10 mL of CH2Cl2, 3 days, recrystallized from
CH2Cl2/hexane, yield 85 mg (58%). H NMR (CDCl3): δ 1.04
1

3586 Organometallics, Vol. 21, No. 17, 2002
Guan and Marshall
(d, J ) 6.8 Hz, 3H, CHMeMe′), 1.16 (d, J ) 6.8, 3H, CHMeMe′),
1.37 (d, J ) 6.8, 3H, C′HMeMe′), 1.42 (d, J ) 6.8, 3H,
C′HMeMe′), 1.60 (d, J P-H ) 13.0, 9H, But), 1.65 (d, J P-H ) 13.0,
9H, Bu′t), 1.69-1.93 (b, 4H), 2.05 (b, 1H), 2.58 (sep, J ) 6.8,
1H, CHMeMe′), 2.71-2.87 (b, 2H), 3.02 (b, 2H), 3.34 (sep, J )
6.8, 1H, C′HMeMe′), 7.00-7.20 (m, 3H, Ar H). 31P NMR
(CDCl3): δ 97.73 (s). Anal. Calcd for C27H44NPPdCl2: C, 54.88;
H, 7.50; N, 2.37. Found: C, 54.81; H, 7.46; N, 2.35.
P r oced u r e for Eth ylen e P olym er iza tion . An evacuated
600 mL Parr pressure reactor was charged with a solution of
one of the complexes (20 mg) in 100 mL of chlorobenzene under
nitrogen. After the reactor was flushed with ethylene, methyl
aluminoxane (MAO) (4 mL in 4.14 M toluene solution, 16
mmol) was charged to the above solution under 100 psi of
ethylene. The resulting mixture was stirred under 500 psi of
ethylene at 70 °C for 2-7 h. Ethylene pressure was vented
and the reaction mixture quenched by the addition of 50 mL
of 2-propanol. Water (200 mL) was added into the mixture,
and the organic layer was separated. The aqueous layer was
extracted with hexane (4 × 40 mL), and all the organic phases
were combined and dried with MgSO4. Polyethylene oils were
obtained by solvent removal.
Syn th esis of 3c: (COD)PdCl2 (70 mg, 0.25 mmol), 2c (122
mg, 0.27 mmol), 10 mL of CH2Cl2, 2 days, recrystallized from
1
CH2Cl2/hexane, yield 95 mg (60%). H NMR (CDCl3): δ 0.73
(d, J ) 6.8 Hz, 3H, CHMeMe′), 0.90 (b, 1H), 1.09 (d, J ) 6.8,
3H, CHMeMe′), 1.29-1.35 (m, 1H), 1.38 (d, J ) 6.8, 3H,
C′HMeMe′), 1.55 (d, J ) 6.8, 3H, C′HMeMe′), 1.55-1.65 (m,
1H), 1.63-1.77 (m, 2H), 1.80-1.92 (m, 1H), 2.49 (b, 1H), 2.72
(sep, J ) 6.8, 1H, CHMeMe′), 2.91 (b, 1H), 3.15 (sep, J ) 6.8,
1H, C′HMeMe′), 3.86 (dd, J P-H ) 14.0, J H-H ) 3.2, 1H, CHP),
7.00-7.22 (m, 3H, Ar H), 7.38-7.78 (m, 8H, Ar′ H), 8.20-8.31
(m, 2H, Ar′ H). 31P NMR (CDCl3): δ 49.69 (s). Anal. Calcd for
Ack n ow led gm en t. This work was generously sup-
ported by the DuPont Co., the Army Research Office
(Contract No. 42395-CH-H), the donors of the Petroleum
Research Fund, administered by the American Chemi-
cal Society, and the startup fund of the University of
California, Irvine, CA. Technical support by J iazhong
Chen at DuPont is greatly appreciated. Z.G. gratefully
acknowledges a National Science Foundation Career
Award, an Arnold and Mabel Beckman Foundation
Young Investigator Award, a DuPont Young Professor
Award, and a 3M Non-Tenured Faculty Award.
C
31H36NPPdCl2: C, 59.01; H, 5.75; N, 2.22. Found: C, 58.92;
H, 5.69; N, 2.24.
Syn th esis of 4a : (DME)NiBr2 (110 mg, 0.36 mmol), 2a (87
mg, 0.38 mmol), 10 mL of CH2Cl2, overnight, recrystallized
from CH2Cl2/hexane, yield 98 mg (45%). Anal. Calcd for C25H42
-
NPNiBr2: C, 49.54; H, 6.98; N, 2.31. Found: C, 49.46; H, 6.88;
N, 2.30.
Syn th esis of 4b: (DME)NiBr2 (90 mg, 0.29 mmol), 2b (121
mg, 0.29 mmol), 10 mL of CH2Cl2, 3 days, recrystallized from
CH2Cl2/hexane, yield 85 mg (46%). Anal. Calcd for C27H44
-
NPNiBr2: C, 51.30; H, 7.02; N, 2.22. Found: C, 51.23; H, 6.94;
N, 2.19.
Syn th esis of 4c: (DME)NiBr2 (90 mg, 0.29 mmol), 2c (136
mg, 0.30 mmol), 10 mL of CH2Cl2, overnight, recrystallized
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, bond distances, bond angles, anisotropic dis-
placement parameters, and all atom coordinates and thermal
parameters. This material is available free of charge via the
Internet at http://pubs.acs.org.
from CH2Cl2/hexane, yield 81 mg (44%). Anal. Calcd for C31H36
-
NPNiBr2: C, 55.40; H, 5.40; N, 2.08. Found: C, 55.30; H, 5.32;
N, 2.04.
OM020240I