Polymerization of ethylene with cationic palladium and nickel catalysts containing bulky nonenolizable imine-phosphine ligands

Article abstract of DOI:10.1021/om0206305

A number of bulky, nonenolizable Pd(II) and Ni(II) imine-phosphine complexes have been synthesized and tested in the ethylene polymerization. These catalysts show improved temperature stability with respect to the corresponding diimine complexes. Nickel imine-phosphine precatalysts containing gem-dimethyl substituent a to phosphorus display moderate activity and produce substantially higher molecular weight polyethylene compared to the corresponding enolizable complexes.

Full text of DOI:10.1021/om0206305

5926
Organometallics 2002, 21, 5926-5934
P olym er iza tion of Eth ylen e w ith Ca tion ic P a lla d iu m a n d
Nick el Ca ta lysts Con ta in in g Bu lk y Non en oliza ble
Im in e-P h osp h in e Liga n d s
Olafs Daugulis and Maurice Brookhart*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
Received August 2, 2002
A number of bulky, nonenolizable Pd(II) and Ni(II) imine-phosphine complexes have been
synthesized and tested in the ethylene polymerization. These catalysts show improved
temperature stability with respect to the corresponding diimine complexes. Nickel imine-
phosphine precatalysts containing gem-dimethyl substituent R to phosphorus display
moderate activity and produce substantially higher molecular weight polyethylene compared
to the corresponding enolizable complexes.
In tr od u ction
metal along the polymer backbone (chain-running) in
competition with monomer insertion. A limited set of
polar monomers can be copolymerized with ethylene and
R-olefins.1e,2g,h
In the late 70’s and 80’s several Ni(II) catalysts
capable of polymerizing ethylene were described.1 The
report in 1995 of versatile, highly active Pd(II) and
Ni(II) aryl-substituted R-diimine catalysts 1 sparked
Considerable effort has been expended to identify
other Ni(II) and Pd(II) complexes bearing bulky biden-
tate ligands which can be similarly employed in olefin
polymerizations and which expand the scope of utility
of such catalysts.1e-g,2 A particularly important goal is
to identify catalysts with increased activity, lifetime,
and thermal stability while maintaining the feature of
chain-running that gives rise to polymers with unique
microstructures. Recognizing the high stability of
Pd(II) and Ni(II) phosphine complexes and the fact that
bidentate complexes containing a single aryl imine arm
function much like diimine systems,3 complexes con-
taining bidentate phosphine-imine ligands are obvious
and attractive targets.
Several phosphine-imine nickel complexes have re-
cently been described in the patent literature. In a
contribution from Eastman, complexes of general type
2 were reported together with their ethylene polymer-
ization properties upon MAO activation.4 At 0-23 °C
and 1 atm of ethylene a small amount of high molecular
weight (Mw up to 400 000) polyethylene was obtained,
suggesting incomplete precatalyst activation. In contri-
butions by Guan, precatalysts of type 3 were shown to
renewed interest in developing late metal catalysts for
olefin polymerization.2a The key to producing high
molecular weight polymers is clearly the incorporation
of substituents in the ortho-positions of the aryl rings
which provide bulk in the axial sites of the square plane
and retard the rate of chain transfer.2a These R-diimine
catalysts have been demonstrated to convert ethylene,2a-c
R-olefins,2a,b,d cyclopentene,2e and trans-1,2-disubsti-
tuted olefins2f to high molecular weight polymers with
unique microstructures as a result of migration of the
(1) (a) Wilke, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 185. (b)
Keim, W.; Kowaldt, F. H.; Goddard, R.; Kru¨ger, C. Angew. Chem., Int.
Ed. Engl. 1978, 17, 466. (c) Klabunde, U.; Ittel, S. D. J . Mol. Catal.
1987, 41, 123. (d) Ostoja Starzewski, K. A.; Witte, J . Angew. Chem.,
Int. Ed. Engl. 1985, 24, 599. For recent reviews, see: (e) Ittel, S. D.;
J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169. (f)
Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed.
1999, 38, 428. (g) Mecking, S. Coord. Chem. Rev. 2000, 203, 325.
(2) (a) J ohnson, L. K.; Killian, C. K.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414. (b) Brookhart, M. S.; J ohnson, L. K.; Killian, C.
M.; Arthur, S. D.; Feldman, J .; McCord, E. F.; McLain, S. J .; Kreutzer,
K. A.; Bennett, M. A.; Coughlin, E. B.; Ittel, S. D.; Parthasarathy, A.;
Tempel, D. J . WO 9623010, 1996. (c) Gates, D. P.; Svejda, S. A.; On˜ate,
E.; Killian, C. M.; J ohnson, L. K.; White, P. S.; Brookhart, M.
Macromolecules 2000, 33, 2320. (d) Killian, C. M.; Tempel, D. J .;
J ohnson, L. K.; Brookhart, M. J . Am. Chem. Soc. 1996, 118, 11664. (e)
McLain, S. J .; Feldman, J .; McCord, E. F.; Gardner, K. H.; Teasley,
M. F.; Coughlin, E. B.; Sweetman, K. J .; J ohnson, L. K.; Brookhart,
M. Macromolecules 1998, 31, 6705. (f) Leatherman, M. D.; Brookhart,
M. Macromolecules 2001, 34, 2748. (g) J ohnson, L. K.; Mecking, S.;
Brookhart, M. J . Am. Chem. Soc. 1996, 118, 267. (h) Mecking, S.;
J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120,
888.
polymerize ethylene at high temperatures (70-100 °C)
to give polyethylene with a bimodal molecular weight
10.1021/om0206305 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/23/2002

Nonenolizable Pd(II) and Ni(II) Imine-Phosphine Complexes
Sch em e 1
Organometallics, Vol. 21, No. 26, 2002 5927
distribution if activated by PMAO-IP or MAO.5 The
major fraction of the polyethylene generally had Mw in
the range of a few thousands, but the minor fraction
consisted of very high molecular weight polymer (Mw
up to 106). One possible explanation of these data is that
while at low pressures and temperatures used by Killian
et al. the precatalyst is not completely activated, at
higher temperatures used by Guan the catalyst is
partially chemically modified, and this modification is
responsible for the low molecular weight fraction in the
polymer. Since the catalyst backbone is easily enolizable
(e.g. ligands 5 and 6 exist either as enamines or imine-
enamine mixtures in solution),5,6 and complexation to
a metal is expected to increase the acidity, the enoliza-
tion of the catalyst backbone by the MAO activator is
possible. Feringa and co-workers have described non-
enolizable palladium phosphine-imine catalysts 4 that
oligomerize ethylene at 100 °C.7a
The aim of the work reported here was to prepare
Pd(II) and Ni(II) complexes from bulky phosphine-
imine bidentate ligands which are nonenolizable in the
hope of obtaining thermally stable polymerization cata-
lysts which would produce high molecular weight,
branched polyethylene. Since ethylene polymerization
catalysts containing smaller chelate rings seem gener-
ally to be more productive,8 the focus of this work has
been on the complexes of general type 7 containing five-
ways. If the bulky mesityl (Mes) substituent was
introduced on phosphorus, the azaenolate was reacted
with MesPCl2 followed by MeMgBr to introduce the
other substituent on phosphorus yielding 9a ,b. Use of
MesP(Me)Cl gave rise to mixtures of products presum-
ably arising from the reaction at both carbon and
nitrogen of the azaenolate.6a,b In the case of less
hindered phenyl- and methyl-substituted compounds it
was possible to react the azaenolate directly with
Ph2PCl and Me2PCl affording 11a ,b. We observed that
the amount of reaction at the N-terminus of the aza-
enolate increased with steric hindrance and decreased
with increasing electrophilicity of the phosphorus elec-
trophile. The purity and yield of the ligands was
estimated from the 31P NMR spectra, and after the
addition of (cod)PdMeCl to crude iminophosphines the
corresponding ligand-palladium methyl chloride com-
plexes were isolated. Chloride abstraction was effected
by reaction with NaB(ArF)4 in acetonitrile/dichlo-
romethane affording cationic acetonitrile complexes
10a ,b and 12a ,b (Scheme 1).
A single-crystal X-ray analysis confirmed the struc-
ture of 13 (Figure 1). As expected on electronic grounds,
chloride is trans to the better donor phosphorus while
methyl is trans to the poorer donor nitrogen.9 The fact
(3) (a) J ohnson, L. K.; Bennett, A. M. A.; Ittel, S. D.; Wang, L.;
Parthasarathy, A.; Hauptman, E.; Simpson, R. D.; Feldman, J .;
Coughlin, E. B. WO 9830609, 1998. (b) Wang, C.; Friedrich, S.;
Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, T. A.; Day, M. W.
Organometallics 1998, 17, 3149. (c) Hicks, F. A.; Brookhart, M.
Organometallics 2001, 20, 3217.
(4) Killian, C. M.; McDevitt, J . P.; Mackenzie, P. B.; Moody, L. S.;
Ponasik, J . A., J r. WO 9840420, 1998.
(5) (a) Guan, Z. WO 0059956, 2000. (b) Guan, Z.; Marshall, W. J .
Organometallics 2002, 21, 3580.
(6) (a) Novikova, Z. S.; Kabachnik, M. M.; Chadnaya, I. A.; Borisen-
ko, A. A.; Beletskaya, I. P. Zh. Org. Khim. 1993, 29, 461. (b) Novikova,
Z. S.; Kabachnik, M. M.; Chadnaya, I. A.; Lutsenko, I. F. Zh. Obsch.
Khim. 1988, 58, 1663. (c) Coleman, K. S.; Green, M. L. H.; Pascu, S.
I.; Rees, N. H.; Cowley, A. R.; Rees, L. H. J . Chem. Soc., Dalton Trans.
2001, 3384. (d) Liu, X.; Mok, K. F.; Leung, P.-H. Organometallics 2001,
20, 3918. In refs 6c and 6d enolizable phosphine-imine palladium
complexes have been described.
membered rather than six-membered chelate rings and
a gem-dimethyl group R to phosphorus, which renders
these phosphine-imine chelate ligands rigid, bulky, and
nonenolizable.
(7) (a) van den Beuken, E. K.; Smeets, W. J . J .; Spek, A. L.; Feringa,
Resu lts a n d Discu ssion
B. L. Chem. Commun. 1998, 223. For
a report of nonenolizable
phosphine-imine cobalt dichloride complexes and their ethylene
polymerization properties, see: (b) Tsukahara, T.; Kanno, T. J P
2000128922, 2000. Oligomerization of norbornene using palladium
phosphine-imine palladium catalysts has also been reported. See: (c)
Chen, Y.-C.; Chen, C.-L.; Chen, J .-T.; Liu, S.-T. Organometallics 2001,
20, 1285. Dimerization and trimerization of ethylene using phosphine-
imine palladium catalysts has been described. (d) Chen, J .-T.; Liu, S.-
L.; Zhao, K.-Q. J . Chin. Chem. Soc. 2000, 47, 279.
1. Syn th esis of P h osp h in e-Im in e P a lla d iu m
Com p lexes a n d Th eir Use a s Eth ylen e P olym er i-
za t ion Ca t a lyst s. Phosphine-imine ligands bearing
gem-dimethyl groups adjacent to phosphorus were
prepared using precedented procedures.4-6 The imines
8a ,b were deprotonated using t-BuLi or LDA to form
the corresponding lithium azaenolates. The reactions
with phosphorus electrophiles were carried out in two
(8) Keim, W.; Schulz, R. P. J . Mol. Catal. 1994, 92, 21.
(9) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.

5928 Organometallics, Vol. 21, No. 26, 2002
Daugulis and Brookhart
reaction of 13 with NaB(ArF)4 in the presence of ethyl-
ene and the barrier to migratory insertion was deter-
mined. The loss of the methyl resonance in the 1H NMR
spectrum of 14a was measured with respect to time in
the presence of 20 equiv of ethylene yielding k ) 3 ×
10-6 s-1 at 23 °C, corresponding to ∆Gq ) 24.8(3) kcal/
mol. For comparison, a typical ethylene insertion barrier
into a diimine-palladium methyl bond is ca. 17 kcal/
mol,2a and the insertion barriers into diphosphine-
palladium methyl bonds are 16.3-17.9 kcal/mol.11
Clearly, complexes containing diphosphine and diimine
ligands are substantially more reactive than the ones
containing imine-phosphine ligands. In the imine-
phosphine palladium complexes the situation is unfa-
vorable for migratory insertion since in the more stable
isomer 14a the Pd-CH3 bond is expected to be stronger
than the Pd-CH3 bond in 14b while the Pd-ethylene
interaction is stronger than that in 14c (see Figure 2).
Thus the stability of the methyl ethylene “unit” is
greatest in 14a . In the transition state where the
Pd-CH3 bond is largely broken and the ethylene unit
is transforming to a σ bond, the unsymmetrical ligand
will likely provide less stabilization than either sym-
metrical ligand, thus a larger ground state/transition
state energy difference can be expected for the unsym-
metrical bidentate ligand. A simpler but equivalent
explanation arises if the migratory insertion is regarded
as an attack of the nucleophilic methyl group on the
electrophilic ethylene ligand. The methyl group in 14a
(trans to N) is less nucleophilic than the methyl group
in 14b (trans to P), while the ethylene unit in 14a (trans
to P) is less electrophilic than ethylene in 14c (trans to
N). This point is illustrated quantitatively in Figure 2
below. Vrieze et al. have used similar arguments to
rationalize varying rates of CO insertion into pal-
ladium-methyl bonds.12
F igu r e 1. ORTEP view of 13. Selected interatomic dis-
tances (Å) and angles (deg): Pd(1)-N(4) ) 2.176(12),
Pd(1)-P(1) ) 2.206(4), Pd(1)-C(1) ) 2.012(16), P(1)-C(2)
) 1.880(12), N(4)-C(3) ) 1.282(21); N(4)-Pd(1)-P(1)-C(2)
) -25.1(8), Pd(1)-N(4)-C(24)-C(25) ) 84.5(16).
Ta ble 1. Oligom er iza tion /P olym er iza tion of
Eth ylen e by 10a ,b a n d 12a ,b
time,
h
g of
polymer
TOF,
h-1
Br/1000
Cc
b
entry
catalysta
Mn
1
2
3
4
5
6
10a
10a
3
15
3
3
3
0.43
0.97
0.06
0.09
∼0
510
230
70
350
350
660
620
89
90
116
113
10bd
10bd,e
12a
110
∼0
12bd,e
3
∼0
∼0
a
0.01 mmol of catalyst in 100 mL of toluene used, 400 psi
ethylene, 80 °C. Mn determined by 1H NMR spectroscopy (see
b
Experimental Section for details). c Branching per 1000 C deter-
mined by 1H NMR spectroscopy (see Experimental Section for
d
details). Small amount of polyethylene obtained may cause errors
in Mn and branching determination due to adventitious alkane
impurities. e Reaction in chlorobenzene (100 mL).
that the methyl group is cis to the phosphorus is
demonstrated also by the magnitude of Me-P coupling
1
constants (J (Me-P), H 2.3 Hz and 13C 0 Hz; similar
2. Syn th eses a n d Eth ylen e P olym er iza tion P r op -
er ties of P h osp h in e-Im in e Nick el Com p lexes.
Nickel dibromide complexes of the phosphine-imines
were produced by the reaction of crude imines (synthe-
sized as above, see Scheme 1) with NiBr2(DME) (Scheme
2). The precatalysts 16 were isolated as highly colored
solids, insoluble in most organic solvents but moderately
soluble in chlorinated hydrocarbons. For comparison the
closest analogous enolizable complex 18 was also syn-
thesized.
values were observed also for 10a ,b, 12a ,b, and the
intermediate palladium methyl chloride complexes).6c
The bond lengths in 13 are typical for palladium-
diimine complexes (C(3)-N(4) 1.282(21) Å, Pd(1)-N(4)
2.176(12) Å).10 The five-membered chelate ring adopts
an envelope conformation with P(1) forming the flap
of the envelope (torsion angle N(4)-Pd(1)-P(1)-C(2)
) -25.1(8)°). The mesityl group is positioned almost
perpendicular to the chelate ring (torsion angle
Pd(1)-N(4)-C(24)-C(25) 84.5(16)°) providing efficient
blocking of the axial sites on palladium from one side.
Ethylene oligomerizations with catalysts 10a ,b and
12a ,b were carried out at 400 psi and 80 °C (Table 1).
Aldimine-derived catalyst 10a was substantially more
active than ketimine-containing 10b but produced
lower Mn oligomers (entry 1 vs entry 3). Catalyst 10a
has a substantial lifetime at 80 °C (entries 1 and 2).
Unexpectedly, diphenyl- and dimethyl-substituted com-
plexes 12a ,b produced only negligible amounts of oli-
gomer at 80 °C. The activities of these phosphine-imine
systems are low compared with those of diimine-Pd
catalysts.
The dimethyl-substituted complex 16a was used to
screen the behavior and efficiency of several aluminum
alkyl derived activators (Table 2). Use of ethylaluminum
dichloride led to the production of butenes with >106
TO/h in a very exothermic reaction (the reactor was
cooled with a -78 °C bath to maintain 19-26 °C).13
Activation using diethylaluminum chloride resulted in
the production of butenes and a trace of polymer (1H
analysis of crude reaction mixture). PMAO-IP afforded
both butenes and polymer. Gratifyingly, use of MMAO-
3A under 400 psi of ethylene at room temperature gave
exclusively polymer with Mn 2 400 and 13 500 TO/h.
To further explore the surprising inactivity of 12b,
the methyl ethylene complex 14a was prepared in the
(11) Ledford, J .; Shultz, C. S.; Gates, D. P.; White, P. S.; DeSimone,
J . M.; Brookhart, M. Organometallics 2001, 20, 5266.
(12) Dekker, G. P. C. M.; Buijs, A.; Elsevier: C. J .; Vrieze, K.; van
Leeuwen, P. W. N. M.; Smeets, W. J . J .; Spek, A. L.; Wang, Y. F.; Stam,
C. H. Organometallics 1992, 11, 1937.
(10) (a) van Asselt, R.; Elsevier, C. J .; Smeets, W. J . J .; Spek, A. L.;
Benedix, R. Recl. Trav. Chim. Pays-Bas 1994, 113, 88. (b) Tempel, D.
J .; J ohnson, L. K.; Huff, R. L.; White, P. S.; Brookhart, M. J . Am. Chem.
Soc. 2000, 122, 6686.
(13) This behavior is reminiscent of Wilke-type systems R3PNi-
(allyl)+. See ref 1a.

Nonenolizable Pd(II) and Ni(II) Imine-Phosphine Complexes
Organometallics, Vol. 21, No. 26, 2002 5929
F igu r e 2. Comparison of migratory insertion barriers.
Sch em e 2
catalyst at room temperature). A control experiment
using the closest analogous enolizable precatalyst at 60
°C revealed that the nonenolizable backbone is essential
for obtaining high molecular weight polymer. Precata-
lyst 18, lacking one methyl group in the backbone,
produced polymer with Mw ) 2 400 compared to Mw
)
50 000 for the nonenolizable complex 16b containing a
gem-dimethyl group. Additionally, a small amount (ca.
0.15 g) of polymer precipitated from the reaction mix-
ture, and a fraction of this precipitate was insoluble in
bromobenzene at 130 °C, suggesting the possibility of a
minor very high molecular weight fraction as observed
by Guan.5
Analysis of the nature of the branching was carried
out using 13C spectroscopy (Table 4).14 The polymer
formed by 16b at 29 °C has almost exclusively methyl
branches, while 80 °C material contains a substantial
amount of higher branches. Polymer formed by 16d at
60 °C contains an abnormal amount of higher branches.
In general, polyethylenes obtained using catalysts 16
are substantially more branched than polymers ob-
tained by diimine-nickel catalysts under similar
conditons.2c The total number of branches calculated
from 13C spectral analysis agrees with the branching
Given the molecular weight and reactivity depend-
ences observed in the case of palladium complexes it
was hoped that mesityl-substituted precatalyst 16c
would be more reactive than dimethyl-substituted com-
plex 16a and give high molecular weight product.
Unexpectedly, only a small amount of polymer with a
bimodal molecular weight distribution (Mp ) 37 200;
3 100) was obtained (Table 3). On the other hand,
diphenyl-substituted precatalyst 16b was found to be
more effective - in 1 h at 29 °C and 400 psi of ethylene
with MMAO-3A activation 4.1 g (29 ,300 TO/h) of a
clear, extremely tough, elastomeric material with Mn
) 72 000, Mw ) 133 000 was obtained (0.005 mmol of
precatalyst was used). No significant amount of lower
molecular weight material was observed in the reaction
and the GPC trace showed a single monomodal peak.
In a 3-h run under similar conditions 10.0 g (24 000 TO/
h) of polymer was obtained. Lower productivity in this
case is clearly due to mass-transport problems: the
contents of the reactor had gelled due to polymer
occluding all solvent. At 100 psi of ethylene, the TOF
dropped to 14 000 h-1. Interestingly, also tetraethyl-
dialumoxane could be used as an activator, albeit with
some loss of activity (15 000 TO/h vs 29 000 TO/h using
MMAO-3A). At 60 °C (MMAO-3A activator) no signifi-
cant difference of activity between 30 min and 1.5 h was
observed, suggesting long catalyst lifetime under these
conditions. For comparison, diimine-Ni catalysts have
a half-life of less than 1 h at that temperature.2c At 80
°C catalyst starts to decompose, but it still has a
reasonable lifetime. A trace of butenes was observed in
the crude NMR of the 80 °C polymerization mixture.
As expected, the molecular weight decreases with
increasing temperature (Mw ) 290 000 at 0 °C, 140 000
at 29 °C, 52 000 at 60 °C, 19 000 at 80 °C), while
branching slightly increases (56 br/1000 C at 0 °C to 74
br/1000 C at 80 °C). Increase of steric bulk at phospho-
rus (16d ) gave rise to lower molecular weight material
(Mw ) 75 000 vs 140 000 for diphenyl-substituted pre-
1
number obtained from the H spectra.
Su m m a r y
A number of Pd and Ni imine-phosphine catalysts
possessing nonenolizable ligand backbone have been
synthesized and tested in the polymerization of ethyl-
ene. These catalysts show improved temperature stabil-
ity with respect to the corresponding diimine complexes.
At 80 °C the palladium catalysts oligomerize ethylene
giving branched oligomers with Mn up to 660. The
ethylene insertion barrier into the palladium-methyl
bond of 14a was shown to be 24.8(3) kcal/mol, which is
ca. 8 kcal/mol higher than the corresponding insertion
barriers in palladium-diimine and palladium-diphos-
phine complexes.15 This shows a possible disadvantage
(14) Cotts, M. P.; Guan, Z.; McCord, E.; McLain, S. Macromolecules
2000, 19, 6945.
(15) For diimine-palladium and nickel alkyl ethylene complexes,
the difference in migratory insertion barriers is 4-5 kcal/mol. In the
case of phosphine-imine complexes, the difference is >8 kcal/mol
between 14a and its Ni cogener (TOF of 30 000 at 29 °C corresponds
to ∆Gq ) 16.4 kcal/mol assuming the alkyl olefin resting state for
precatalyst 16b). One possible explanation for the unexpectedly low
barrier in the Ni complex is that cis/trans isomerization occurs from
the more stable isomer (Ni cogener of 14a ) to the less stable isomer
with ethylene trans to nitrogen and the migrating alkyl group trans
to phosphorus. In the less stable isomer the migratory insertion is
expected to proceed with a much lower barrier. Provided cis/trans
isomerization is fast relative to insertion, the observed rate constant
for insertion via minor isomer will be Keqkins(minor), which may exceed
kins(major). A computational study in the salicylaldiminato Ni(II) system
has predicted a similar behavior. See: Chan, M. S. W.; Deng, L.;
Ziegler, T. Organometallics 2000, 19, 2741.

5930 Organometallics, Vol. 21, No. 26, 2002
Daugulis and Brookhart
Ta ble 2. Activa tor Stu d ies Usin g 16a (0.018 m m ol) in Ch lor oben zen e (100 m L) a t 30-35 °C, 400 p si of
Eth ylen e P r essu r e
a
entry
activator/equiv
time, h
product
TOF, h-1
Mn
Br/1000 Ca
1b
2
3
4
5
EtAlCl2/400
Et2AlCl/300
PMAO-IP/750
MMAO-3A/370
MMAO-3A/370
0.3
0.5
1
1
5
butenes
butenes
butenes + PE
PE, 6.8 g
106
nd
nd
13500
7100
nd
2400
2800
nd
65
66
PE, 18.0 g
a
b
Branching/1000 C and Mn determined by 1H NMR spectroscopy (see Experimental Section for details). 0.0046 mmol of catalyst
used, 19-26 °C, 200 psi of ethylene; TON determined by 1H NMR analysis of crude reaction mixture.
Ta ble 3. P olym er iza tion of Eth ylen e by 16a -d a n d 17 in Ch lor oben zen ea a t 400 p si
entry
catalyst
time, h
temp, °C
g of PE
TOF, h-1
Mw
290 000
133 000
140 000
52 000
52 000
19 000
19 000
143 000
104 000
37 000; 3 100h
75 000
17 000
2 400
Br/1000 Cb
PDI
1c
2
3
4
5
16b
16b
16b
16b
16b
16b
16b
16b
16b
16c
16d
16d
18
4
1
3
0.5
1.5
0.5
1.5
1
0
29
29
60
60
80
80
29
29
60
29
60
60
1.9
4.1
10.0
2.4
6.6
2.6
4.4
2.1
2.0
0.24
6.3
7.4
7.0
3 400
29 000
24 000
34 000
31 000
37 000
21 000
15 000
14 000
1 700
56
62
64
69
70
71
74
63
65
57
67
71
94
2.2
1.9
1.9
1.9
2.0
1.5
1.6
1.9
2.0
ND
1.8
2.2
2.1
6
7
8d
9e
1
10c,f,g
11f,g
12c,f
13
0.5
1.1
0.6
1.5
20 000
44 000
33 000
a
b
0.005 mmol of precatalyst in 200 mL of chlorobenzene, MMAO-3A activator, Al/Ni ratio 1800. Branching/1000 C determined by 1H
NMR spectroscopy (see Experimental Section for details). c 100 mL of solvent used. Tetraethyldialumoxane activator (1800 equiv). e 100
d
psi of ethylene pressure. f 0.01 mmol of precatalyst used. Al/Ni ratio 660. Bimodal molecular weight distribution; Mp (peak molecular
g
h
weights) reported.
atmosphere using standard Schlenk techniques. The H, 31P,
and 13C spectra were recorded using Bruker 300 or 400 MHz
spectrometers and referenced against residual solvent peaks
(1H, 13C) or H3PO4 (31P). Flash chromatography was performed
using 60 Å silica gel (SAI). Room-temperature GPC measure-
ments were performed on a Waters Alliance HPLC Separations
Module equipped with Waters Styragel HR2, HR4, and HR5
columns in series and a Waters 2410 Differential Refracto-
meter RI (refractive index) detector relative to polystyrene
standards. Samples consisted of ∼1 mg of polymer in 1 mL of
degassed THF. High-temperature (135 °C) GPC was performed
by DuPont Analytical (Wilmington, DE) in 1,2,4-trichloroben-
zene using a Waters HPLC equipped with Shodex columns. A
calibration curve was established with polystyrene standards
and universal calibration was applied using Mark-Houwink
constants for polyethylene (k ) 4.34 × 10-4; R ) 0.724).
Differential scanning calorimetry was recorded on a Seiko
Instruments DSC 220 calibrated with the melting transition
of indium. Elemental analyses were performed by Atlantic
Microlab Inc. of Norcross, GA. 13C NMR analyses of polymers
were carried out under the conditions reported by the DuPont
group.14
1
Ta ble 4. An a lysis of P olyeth ylen e Br a n ch in g
Usin g 13C Sp ectr oscop y
catalyst Mea Et
16bd
55.5 2.4 >1
% Mee 95.9 4.1
16bf
50.2 7.1
% Mee 67.1 9.5
Pr
nBu sBub Am higher br/1000 Cc
>1
>1
>1
>1
58
75
67
3.9
5.2
1.6
2.4
4.1
1.5
3.1
2.1
2.3
9.6
1.7 17.1
7.2
5.5
4.9
7.3
16d g
33.9 7.5
% Mee 50.6 11.2
2.5 25.5
Number of corresponding branches per 1000 C. b A sBu branch
a
is counted as one Me and one Et branch. c Total number of methyl
d
branches per 1000 C. Entry 3 from Table 3. e Percent of the
methyl groups in the given branch with respect to total Me. f Entry
g
6 from Table 3. Entry 12 from Table 3.
in using chelating ligands with two electronically in-
equivalent groups, whereby a reaction intermediate is
sufficiently stabilized in the ground state to substan-
tially retard the rate of migratory insertion.
Nickel imine-phosphine precatalysts containing gem-
dimethyl substituent R to phosphorus display moderate
activity and produce substantially higher molecular
weight polyethylene compared to the corresponding
enolizable complexes. A control experiment using non-
enolizable precatalyst 16b and enolizable precatalyst 18
revealed that under the same conditions the former
produces more than 20 times higher molecular weight
polyethylene than the latter, even though they differ
only by a single methyl group in the backbone. Future
studies will focus on copolymerizations of ethylene with
R-olefins and polar comonomers using catalyst 16b, as
well as the variations in reactivity through the modi-
fication of imine moiety. Mechanistic studies of the
nickel phosphine-imine catalysts are underway.
Ma ter ia ls. Anhydrous solvents were used in the reactions.
Solvents were distilled from drying agents or passed through
alumina columns under an argon or nitrogen atmosphere.
NMR solvents were vacuum transferred from P2O5 and de-
gassed by repeated freeze-pump-thaw cycles. The following
starting materials were made using literature procedures:
mesityldichlorophosphine,16 NiBr2(DME),17 and (cod)PdMeCl.18
NaB(ArF)4 was purchased from Boulder Scientific. PMAO-IP
and MMAO-3A were purchased from Akzo Nobel. Alkylalu-
minum chlorides and tetraethyldialumoxane were purchased
from Aldrich.
An a lysis of P olym er Molecu la r Weigh t a n d Br a n ch in g
by H NMR Sp ectr oscop y. The following labels are used for
1
(16) Sakaki, J .-i.; Schweizer, W. B.; Seebach, D. Helv. Chim. Acta
1993, 76, 2654.
Exp er im en ta l Section
(17) Ward, L. G. L. Inorg. Synth. 1971, 13, 154.
(18) 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.
Gen er a l Con sid er a tion s. All the operations related to
catalysts or phosphines were carried out under an argon

Nonenolizable Pd(II) and Ni(II) Imine-Phosphine Complexes
Organometallics, Vol. 21, No. 26, 2002 5931
denoting different types of hydrogen signals in the polymer
spectrum (CDCl3 solvent): H1 (vinylidene end group, CdCH2,
br s, 4.7 ppm); H2 (1,2-disubstituted olefin, CHdCH, m, 5.3-
5.4 ppm); H3 (trisubstituted olefin CdCH, m, 5.18 ppm); H4
(R-olefin, H2CdCH, m, 5.85, 5.0, 4.9 ppm); H5 (alkyl methyl,
alk-CH3, m, 0.77-0.95 ppm); H6 (allylic methyl, CdC-CH3,
m, 1.6 ppm); H7 (alkyl methylene and methine, alk-CH and
alk-CH2, m, ca. 1.0-1.45 ppm); H8 (allylic methylene or
methine, CdC-CH2 and CdC-CH, m, 1.85-2.05 ppm). In the
following formulas Hn values refer to integral values.
were acquired to check for butenes. Higher molecular weight
polymers were dried in a vacuum oven at 75 °C.
The following polymer Tm values were determined (entry
number in Table 3; Tm, °C): 1, 74; 3, 64; 4, 59 (shoulder at
43); 8, 69; 9, 59; and 12, 11 (shoulder at 38).
Isobu tyr a ld eh yd e 2,4,6-Tr im eth ylp h en ylim in e (8a ).
2,4,6-Trimethylaniline (4.2 mL, 30 mmol, Aldrich) was mixed
with isobutyric aldehyde (5.5 mL, 60 mmol, Aldrich), chloro-
form (50 mL), p-toluenesulfonic acid (0.29 g, 1.5 mmol, Ald-
rich), and MgSO4 (ca. 10 g). The reaction mixture was stirred
at room temperature for 22 h. After filtration and washing of
MgSO4 with chloroform (20 mL) molecular sieves (3 Å) were
added and stirring was continued for an additional 24 h. The
solvent and excess aldehyde were evaporated and the residue
was distilled at reduced pressure collecting three fractions: (1)
68-74 °C/0.5 mm, mixture of product/amine; (2) 74-76 °C/
0.5 mm, product; and (3) 76-78 °C/0.5 mm, product. Fractions
2 and 3 were combined to give 3.0 g (52.9%) of the imine. The
compound is unstable at room temperature and has to be
Nav ) (2/V) × (A) + 2
where Nav ) average number of carbons in polymer chain
V ) H1 + H2 + 2H3 + (2/3)H4
and
1
stored at -30 °C. H NMR (CDCl3) 7.52 (d, 1H, J ) 4.8 Hz),
A ) (H5 + H6 + H7 + H8 - H1 - H2 - 3H3 - (1/3)H4)/2
Mn ) Nav × 14.01
6.84 (br s, 2H), 2.70 (d of septets, 1H, J ) 4.8, 6.9 Hz), 2.26 (s,
3H), 2.05 (s, 6H), 1.22 (d, 6 H, J ) 6.9 Hz). 13C{1H} NMR
(CDCl3): 172.7, 148.7, 132.6, 128.7, 126.8, 35.0, 20.8, 19.2, 18.1.
Isob u t yr op h en on e 2,4,6-Tr im et h ylp h en ylim in e (8b ).
2,4,6-Trimethylaniline (16.9 mL, 120 mmol, Aldrich) was
mixed with isobutyrophenone (12.0 mL, 80 mmol, Acros) and
p-TsOH (1.5 g, 8.0 mmol, Aldrich). The resulting mixture was
heated for 10 h at 220 °C in a flask equipped with a Dean-
Stark trap. Vacuum distillation afforded two fractions: (1)
unreacted starting materials, 40-48 °C/0.3 mm; and (2)
Nbr ) (1000/Nav) × (Y - X)
where Nbr ) number of methyl branches per 1000 C, Y ) ((H5
+ H6)/3) × (2/V), X ) ((H1/2) + H2 + 2H3 + (H4/3)) × (2/V).
The formula is not exact since the signal of secondary homoal-
lylic hydrogen overlaps with the signal of H6.
Sp ectr a l Da ta for th e B(Ar F )4 Cou n ter ion . The following
1H and 13C spectroscopic assignments of the B(ArF)4 counterion
were invariant for different complexes and temperatures and
are not reported in the spectroscopic data for each of the
1
product as a yellow oil, 98-108 °C/0.1 mm (6.2 g, 29.2%). H
NMR (tetrachloroethane-d2, 383 K) 7.29 (s, 5H), 6.77 (s, 2H),
3.13 (septet, 1H, J ) 6.8 Hz), 2.26 (s, 3H), 2.05 (s, 6H), 1.34
(d, 6 H, J ) 6.8 Hz). 13C{1H} NMR (tetrachloroethane-d2, 403
K): 174.1 (br), 145.6 (br), 138.8 (br), 130.9 (br), 128.1, 128.0,
127.4, 126.6, 124.8 (br), 36.3 (br), 20.3, 20.1, 17.6. Anal. Calcd
for C19H23N: C 85.98, H 8.74, N 5.28. Found: C 85.95, H 8.87,
N 5.42.
-
1
cationic complexes. B[3,5-C6H3(CF 3)2]4 (B(Ar F )4). H NMR
(CD2Cl2): 7.74 (br s, 8H), 7.57 (s, 4H). 13C{1H} NMR (CD2Cl2)
162.2 (q, J C-B ) 37.4 Hz), 135.2, 129.3 (q, J C-F ) 31.3 Hz),
125.0 (q, J C-F ) 272.5 Hz), 117.9.
Gen er a l P olym er iza tion P r oced u r e. Polymerizations
using Pd catalysts and 16a were carried out in a mechanically
stirred 300-mL Parr reactor equipped with an electric heating
mantle controlled by a thermocouple in the reaction mixture.
The reactor was charged with toluene or chlorobenzene (100
mL) and heated for 1 h at 150 °C. After cooling to room
temperature the solvent was poured out and the reactor heated
under vacuum at 150 °C for 1 h. The reactor was filled with
Ar, cooled to room temperature, pressurized to 200 psi of
ethylene, and vented three times. A solution of the catalyst in
100 mL of the appropriate solvent was added to the reactor
via cannula followed by activator if applicable. After that the
reactor was pressurized with ethylene and the reaction
mixture stirred for the appropriate time. Polymerizations using
Ni catalysts other than 16a and entries 10 and 12 in Table 3
(100 mL of solvent used in these cases) were carried out in a
600-mL Parr reactor equipped with water cooling and an
electric heating mantle controlled by a thermocouple in the
reaction mixture in 200 mL of solvent. After venting, the
reaction mixture was worked up in one of three ways: (A) the
reaction mixture was evaporated and the distillate checked
for oligomers by GC (no oligomers up to C10 were observed;
used for polymerizations catalyzed by palladium complexes);
(B) the reaction mixture was extracted with 10% HCl (oc-
casionally chloroform was added to make the separations
better) and evaporated (used for polymerizations catalyzed by
16a , 16b at 60 and 80 °C, 16c, 16d , 18); and (C) the reaction
mixture was poured into methanol and stirred for 1 h and the
precipitate washed with a 1:1 mixture of methanol and 10%
aqueous HCl, and then with methanol (used for 0 and 29 °C
polymerizations catalyzed by 16b). On some occasions, the
methanol/water layer was evaporated and the residue checked
by NMR. No significant quantity of oligomers was detected.
In all cases 1H NMR spectra of the crude reaction mixtures
-
[(MesNdCH CMe2P MesMe)P d (NCMe)Me]+ B(Ar F )4
(10a ). To a solution of isobutyraldehyde 2,4,6-trimethylphen-
ylimine (0.378 g, 2.0 mmol) in diethyl ether (5 mL) was added
t-BuLi (1.25 mL of a 1.7 M solution in pentane, 2.1 mmol,
Aldrich) at -78 °C. The solution was stirred for 10 min at -78
°C, warmed to room temperature, and stirred for 20 min. The
yellow solution of azaenolate was added dropwise to a solution
of mesityldichlorophosphine (0.37 mL, 2.1 mmol) in THF (5
mL) at -78 °C. The mixture was stirred at -78 °C for 10 min,
warmed to room temperature, and stirred for an additional
30 min. Assay by 31P NMR (crude reaction mixture) showed
the presence of a single major product (+101.5 ppm). The
reaction mixture was recooled to -78 °C and MeMgBr (0.71
mL of a 3.1 M solution in ether, 2.2 mmol, Strem) was added
in one portion. After warming to room temperature the
mixture was stirred for 30 min. Assay by 31P NMR (crude
reaction mixture) showed the presence of a single major
product (-18.0 ppm) together with starting material (+101.5
ppm). The reaction mixture was recooled to -78 °C and
additional MeMgBr (1 mL, 3.1 mmol) was added. After
warming to room temperature the mixture was stirred for 12
h. 31P NMR (crude reaction mixture) showed the complete
consumption of the starting material. TMSCl (0.5 mL) was
added to quench the excess MeMgBr, the solution was stirred
for 30 min at room temperature and evaporated, and the
residue was extracted with hexanes (4 × 10 mL). The hexane
extracts were evaporated to give the iminephosphine ligand
as a yellowish oil. To the crude ligand was added (cod)PdMeCl
(0.26 g, 0.98 mmol) and CH2Cl2 (5 mL). The reaction mixture
was stirred for 30 min at room temperature and evaporated,
and the residue was purified by extraction with hexanes (3 ×
10 mL). 9a *PdMeCl was obtained as a light yellow, hexane-
insoluble powder, 0.37 g (36.3%). 1H NMR (CDCl3, 330 K) 7.40

5932 Organometallics, Vol. 21, No. 26, 2002
Daugulis and Brookhart
(d, 1H, J ) 26.0 Hz), 6.95 (d, 2H, J ) 3.2 Hz), 6.85 (s, 2H),
2.91 (br s, 6H), 2.30 (s, 3H), 2.26 (s, 3H), 2.23 (d, 3H, J ) 9.1
Hz), 2.21 (s, 6H), 1.66 (d, 3H, J ) 10.1 Hz), 1.19 (d, 3H,
J ) 11.9 Hz), 0.54 (Pd-Me, d, 3H, J ) 3.1 Hz). 31P{1H} NMR
(CD2Cl2): +31.2 ppm (s).
additional 30 min. Assay by 31P NMR (crude reaction mixture)
showed the presence of a single major product (-27.9 ppm).
The reaction mixture was evaporated and the residue ex-
tracted with toluene and filtered through a plug of Celite to
remove inorganic salts. After evaporation of the solvent crude
ligand was obtained as a yellowish oil. To the crude ligand
was added (cod)PdMeCl (0.195 g, 0.74 mmol) and CH2Cl2 (5
mL). The reaction mixture was stirred for 30 min at room
temperature, filtered, and evaporated. The residue was puri-
fied by flash chromatography on silica gel (3.3 × 2.3 cm) in
CH2Cl2 followed by ethyl acetate. Fractions containing the
product were evaporated and triturated with ethyl acetate (10
mL) to give 11a *PdMeCl (0.202 g, 41.9%) as a white powder.
1H NMR (CDCl3) 7.29-7.19 (m, 3H), 7.04-6.96 (m, 2H), 6.60
(s, 2H), 2.22 (s, 6H), 2.08 (s, 3H), 1.56 (d, 6H, J ) 9.9 Hz),
1.49 (d, 6H, J ) 12.6 Hz), 0.67 (Pd-Me, d, 3H, J ) 3.1 Hz).
To the mixture of 9a *PdMeCl (0.10 g, 0.196 mmol) and NaB-
(ArF)4 (0.174 g, 0.196 mmol) was added dry acetonitrile (1 mL)
and CH2Cl2 (2 mL). The mixture was stirred for 12 h at room
temperature, cannula filtered to remove NaCl, evaporated, and
coevaporated with hexanes (3 mL). The product was obtained
as a light yellow foam (0.240 g, 88.8%). 1H NMR (CD2Cl2) 7.54
(d, 1H, J ) 27.1 Hz), 7.03 (d, 2H, J ) 3.7 Hz), 6.96 (s, 2H),
3.10 (br s, 3H), 2.55 (br s, 3H), 2.31 (s, 3H), 2.28 (s, 3H), 2.24
(d, 3H, J ) 9.9 Hz), 2.19 (s, 6H), 1.74 (br s, 3H), 1.70 (d, 3H,
J ) 11.3 Hz), 1.21 (d, 3H, J ) 13.1 Hz), 0.32 (Pd-Me, d, 3H,
J ) 2.1 Hz). 31P{1H} NMR (CD2Cl2): +34.4 ppm (s). Anal.
Calcd for C58H50BF24N2PPd: C 50.50, H 3.65, N 2.03. Found:
C 50.75, H 3.85, N 1.90.
31P{1H} NMR (CDCl3): +45.6 ppm (s). Anal. Calcd for C22H31
-
ClNPPd: C 54.78, H 6.48, N 2.90. Found: C 54.67, H 6.48, N
2.84.
-
[(MesNdCP h CMe2P MesMe)P d (NCMe)Me]+ B(Ar F )4
The synthesis of the cationic acetonitrile complex 12a was
performed as in the case of 10a , using 11a *PdMeCl (0.08 g,
0.166 mmol) and NaB(ArF)4 (0.147 g, 0.166 mmol), and a
reaction time of 2 h. Product was obtained as a white powder,
(10b). To a solution of isobutyrophenone 2,4,6-trimethylphen-
ylimine (0.53 g, 2.0 mmol) in diethyl ether (5 mL) was added
t-BuLi (1.25 mL of a 1.7 M solution in pentane, 2.1 mmol,
Aldrich) at -78 °C. The solution was stirred for 10 min at -78
°C, warmed to room temperature, and stirred for 20 min. The
red-brown solution of azaenolate was added dropwise to a
solution of mesityldichlorophosphine (0.37 mL, 2.1 mmol) in
THF (5 mL) at -78 °C. The mixture was stirred at -78 °C for
10 min, warmed to room temperature, and stirred for an
additional 30 min. Assay by 31P NMR (crude reaction mixture)
showed the presence of a single major product (+103.7 ppm).
The reaction mixture was recooled to -78 °C and MeMgBr
(1.4 mL of a 3.1 M solution in ether, 4.3 mmol, Strem) was
added in one portion. After warming to room temperature the
mixture was stirred for 30 min. Assay by 31P NMR (crude
reaction mixture) showed the presence of a single major
product (-20.3 ppm). TMSCl (0.5 mL) was added to decompose
the excess MeMgBr, and the solution was stirred for 30 min
at room temperature and evaporated. The residue was ex-
tracted with hexanes (4 × 10 mL). The hexane extracts were
evaporated to give crude ligand as a yellow oil. To the crude
ligand was added (cod)PdMeCl (0.416 g, 1.57 mmol) and
CH2Cl2 (5 mL). The reaction mixture was stirred for 30 min
at room temperature and evaporated, and the residue was
purified by extraction with hexanes (3 × 10 mL). 9b*PdMeCl
was obtained as a white, hexane-insoluble powder, 0.94 g
(80.2%). 1H NMR (CDCl3) 7.25-7.14 (m, 3H), 7.02-6.91 (m,
4H), 6.58 (s, 2H), 2.95 (br s, 6H), 2.37 (d, 3H, J ) 8.9 Hz), 2.30
(s, 3H), 2.27 (s, 3H), 2.22 (s, 3H), 2.07 (s, 3H), 1.42 (d, 3H, J )
10.2 J ), 1.37 (d, 3H, J ) 13.5 Hz), 0.54 (Pd-Me; d, 3H, J ) 2.9
Hz). 31P{1H} NMR (CD2Cl2): +41.6 ppm (s).
1
0.211 g (94.1%). H NMR (CD2Cl2) 7.40-7.27 (m, 3H), 7.07-
7.00 (m, 2H), 6.74 (s, 2H), 2.19 (s, 6H), 2.14 (s, 3H), 1.68 (s,
3H), 1.60 (d, 6H, J ) 10.7 Hz), 1.49 (d, 6H, J ) 13.5 Hz), 0.44
(Pd-Me, d, 3H, J ) 2.0 Hz). 31P{1H} NMR (CD2Cl2): +48.8
ppm (s). Anal. Calcd for C56H46BF24N2PPd: C 49.78, H 3.43,
N 2.07. Found: C 50.11, H 3.44, N 2.11.
[MesNdCP h CMe2P P h 2]P d MeCl (13). The reaction was
carried out as in the case of 12a on a 2 mmol scale using
chlorodiphenylphosphine (0.38 mL, 2.1 mmol, Aldrich) instead
of chlorodimethylphosphine. Assay by 31P NMR (crude reaction
mixture) showed the presence of the product (+13.4 ppm). The
reaction mixture was evaporated and the residue extracted
with toluene and filtered through a plug of Celite to remove
inorganic salts. After evaporation of the solvent crude ligand
was obtained as a yellowish oil. To the crude ligand was added
(cod)PdMeCl (0.270 g, 1.02 mmol) and CH2Cl2 (5 mL). The
reaction mixture was stirred for 12 h at room temperature.
After evaporation the residue was extracted with hexanes (2
× 10 mL) and dried to give 13 (0.202 g, 41.9%) as a light
yellow, hexane-insoluble powder. X-ray quality crystals were
1
obtained by recrystallization from acetonitrile at -30 °C. H
NMR (CD2Cl2): 7.86-7.74 (m, 4H), 7.67-7.50 (m, 6H), 7.36-
7.24 (m, 3H), 7.18-7.07 (m, 2H), 6.64 (s, 2H), 2.14 (s, 9H),
1.43 (d, 6H, J ) 12.8 Hz), 0.65 (Pd-Me, d, 3H, J ) 2.3 Hz).
13C{1H} NMR (CD2Cl2): 185.1 (d, J C-P ) 8.9 Hz), 144.5, 135.4
(d, J C-P ) 6.9 Hz), 135.0 (d, J C-P ) 11.2 Hz), 134.9, 132.0 (d,
J C-P ) 2.5 Hz), 130.1, 129.4 (d, J C-P ) 10.5 Hz), 128.8, 128.7,
128.6, 127.5 (d, J C-P ) 44.9 Hz), 125.8, 53.6 (d, J C-P
25.8 Hz), 26.1 (d, J C-P ) 1.7 Hz), 21.0, 19.8, -3.8 (Pd-Me).
31P{1H} NMR (CD2Cl2): +71.2 ppm (s). Anal. Calcd for C32H35
)
The synthesis of cationic acetonitrile complex 10b was
performed as in the case of 10a , using 9b*PdMeCl (0.10 g,
0.171 mmol) and NaB(ArF)4 (0.151 g, 0.171 mmol), and a
reaction time of 14 h. Product was obtained as a white powder,
-
ClNPPd: C 63.37, H 5.82, N 2.31. Found: C 63.62, H 5.97, N
2.31.
1
0.228 g (91.6%). H NMR (CD2Cl2) 7.37-7.25 (m, 3H), 7.07-
[(MesNdCP h CMe2P P h 2)P d (NCMe)Me]+ B(Ar F)4- (12b).
The synthesis of the cationic acetonitrile complex 12b was
performed as in the case of 10a , using 13 (0.10 g, 0.165 mmol)
and NaB(ArF)4 (0.146 g, 0.165 mmol), and a reaction time of
12 h. Product was obtained as a white powder, 0.210 g (94.1%).
1H NMR (CD2Cl2): 7.75-7.59 (m, 10H), 7.41-7.32 (m, 3H),
7.22-7.15 (m, 2H), 6.75 (s, 2H), 2.19 (s, 6H), 2.15 (s, 3H), 1.66
(s, 3H), 1.47 (d, 6H, J ) 13.7 Hz), 0.59 (Pd-Me, d, 3H, J ) 1.1
Hz). 13C{1H} NMR (CD2Cl2): 187.2 (d, J C-P ) 7.5 Hz), 143.7,
136.6, 134.8 (d, J C-P ) 10.8 Hz), 133.8 (d, J C-P ) 7.0 Hz), 133.2
(d, J C-P ) 2.8 Hz), 131.2, 130.0 (d, J C-P ) 11.1 Hz), 129.5,
129.4, 128.6, 126.0, 125.2 (d, J C-P ) 51.4 Hz), 118.7, 55.4 (d,
J C-P ) 29.1 Hz), 26.1 (d, J C-P ) 1.0 Hz), 20.7, 19.5, 1.8, -2.6
(Pd-Me). 31P{1H} NMR (CD2Cl2): +71.5 ppm (s). Anal. Calcd
6.99 (m, 4H), 6.74 (s, 2H), 2.88 (br s, 6H), 2.37 (d, 3H, J ) 9.7
Hz), 2.32 (s, 3H), 2.28 (s, 3H), 2.22 (s, 3H), 2.14 (s, 3H), 1.72
(s, 3H), 1.67 (s, 3H), 1.48 (d, 3H, J ) 11.5 Hz), 1.37 (d, 3H, J
) 14.4 Hz), 0.32 (Pd-Me, d, 3H, J ) 1.8 Hz).31P{1H} NMR
(CD2Cl2): +42.2 ppm (s). Anal. Calcd for C64H54BF24N2PPd:
C 52.82, H 3.74, N 1.92. Found: C 52.81, H 3.95, N 1.82.
[(MesNdCP h CMe2P Me2)P d (NCMe)Me]+ B(Ar F)4- (12a ).
To a solution of isobutyrophenone 2,4,6-trimethylphenylimine
(0.265 g, 1.0 mmol) in diethyl ether (3 mL) was added t-BuLi
(0.62 mL of a 1.7 M solution in pentane, 1.05 mmol, Aldrich)
at -78 °C. The solution was stirred for 10 min at -78 °C,
warmed to room temperature, and stirred for 30 min. The red-
brown solution of azaenolate was added dropwise to a solution
of dimethylchlorophosphine (0.083 mL, 1.05 mmol, Strem) in
THF (2 mL) at -78 °C. The mixture was stirred at -78 °C for
10 min, warmed to room temperature, and stirred for an
for C66H50BF24N2PPd: C 53.73, H 3.42, N 1.90. Found:
53.77, H 3.49, N 1.84.
C

Nonenolizable Pd(II) and Ni(II) Imine-Phosphine Complexes
Organometallics, Vol. 21, No. 26, 2002 5933
Gen er a tion of [(MesNdCP h CMe2P P h 2)P d (eth ylen e)-
Me]+ B(Ar F )4- (14a ), Mea su r em en t of Eth ylen e In ser tion
Ba r r ier . Solid 13 (0.0068 g, 0.01 mmol) was mixed with NaB-
(ArF)4 (0.012 g, 0.014 mmol) in a Teflon-lined screw-cap NMR
tube. After cooling to -78 °C ethylene gas (1 mL, 0.045 mmol)
was added, followed by CD2Cl2 (0.7 mL) and more ethylene (4
mL, 0.18 mmol). After that, the NMR tube was shaken a few
times and kept at -30 °C for 48 h. Then the NMR tube was
warmed to room temperature (+23 °C) and the disappearance
of methyl peak (0.69 ppm, d, J ) 2.2 Hz at +23 °C) of the
formed methyl ethylene complex was observed vs. time by
NMR, affording k ) 3 × 10-6 s-1, corresponding to ∆Gq ) 24.8-
(3) kcal/mol.
Spectral data for 14: 1H NMR (CD2Cl2, 233 K, 1 equiv of
free ethylene present): 7.69-7.49 (m, 10H), 7.44-7.30 (m, 3H),
7.23-7.11 (m, 2H), 6.74 (s, 2H), 4.98 (s, 4H; complexed
ethylene; free ethylene appears at 5.38 ppm), 2.11 (s, 3H), 2.04
(s, 6H), 1.50 (d, 6H, J ) 13.9 Hz), 0.64 (Pd-Me s, 3H).
13C{1H} NMR (CD2Cl2, 233 K): 188.3 (d, J C-P ) 7.6 Hz), 141.7,
137.0, 134.3 (d, J C-P ) 10.7 Hz), 133.5 (d, J C-P ) 6.7 Hz), 132.9
(d, J C-P ) 2.1 Hz), 131.0, 129.9 (d, J C-P ) 10.7 Hz), 129.8,
129.1, 127.4, 125.4, 123.6 (d, J C-P ) 48.3 Hz), 111.9, 111.8,
54.0 (d, J C-P ) 26.5 Hz), 25.9, 20.6, 19.1, 2.6 (Pd-Me).
31P{1H} NMR (233 K, CD2Cl2) +67.5.
remove excess MePCl2 and THF (5 mL) was added. The
reaction mixture was recooled to -78 °C and mesitylmagne-
sium bromide (4 mL of a 1 M solution in ether, 4 mmol,
Aldrich) was added in one portion. After warming to room
temperature the mixture was stirred for 30 min. Assay by 31P
NMR (crude reaction mixture) showed the presence of a single
major product (-20.1 ppm). Acetic acid (3 drops) was added
to decompose the excess Grignard reagent and the solvent was
removed under vacuum. The residue was dissolved in CH2Cl2
and filtered through a 3 × 2.2 cm plug of silica gel under Ar,
eluting with CH2Cl2 (30 mL) followed by diethyl ether (20 mL).
The solvent was evaporated to give crude ligand as a yellow
oil. To the crude ligand was added NiBr2(DME) (0.124 g, 0.40
mmol) and CH2Cl2 (10 mL). The dark purple solution was
stirred for 1 h at room temperature and evaporated and the
residue was washed with diethyl ether (2 × 20 mL) and
hexanes (20 mL). A violet solid (0.26 g, quantitative based on
Ni) was obtained. No signal in the 31P spectrum was observed.
1H NMR (CD2Cl2): 7.29-7.14 (m, 5H), 6.97 (br d, 1H, J ) 6.0
Hz), 6.82 (br d, 1H, J ) 6.0 Hz), 6.75 (s, 1H), 6.56 (s, 1H), 4.65
(br s, 6 H), 3.18 (s, 3 H), 3.16 (s, 3 H), 2.37 (s, 3H), 2.26 (s,
3H), 2.22 (s, 3H), 1.37 (s, 6H). Anal. Calcd for C29H36Br2-
NNiP: C 53.74, H 5.60, N 2.16. Found: C 53.90, H 5.89, N
2.21.
Di(2-m eth ylp h en yl)h a lop h osp h in e.19 A solution of ZnCl2
(7.0 g, 101 mmol, Aldrich; fused under vacuum) in THF (70
mL) was added to o-tolylmagnesium bromide (50 mL of a 2.0
M solution in diethyl ether; 100 mmol, Aldrich) at 0 °C. The
solution was warmed to room temperature and added dropwise
to a solution of PCl3 (4.3 mL, 49 mmol, Aldrich) in THF (30
mL) at -78 °C. The solution was stirred for 10 min at -78 °C,
warmed to room temperature, and stirred for 30 min. Assay
by 31P NMR (crude reaction mixture) showed the presence of
di(2-methylphenyl)chlorophosphine and di(2-methylphenyl)-
bromophosphine (+74.1; +66.3 ppm, 1/0.75 ratio). The solvent
was evaporated, hexanes (200 mL) was added to the residue,
and the solution was filtered through Celite followed by
washing of the precipitate with toluene (50 mL) and hexanes
(4 × 50 mL). Evaporation of the solvent followed by distillation
under reduced pressure afforded the product (bp 125-131
°C/0.2 mm, 8.3 g, 62.0%) as a yellowish solid, 1/0.75 ratio of
P-Cl/P-Br.
[MesNdCP h CMe2P (o-Tol)2]NiBr 2 (16d ). Lithium azaeno-
late was prepared as in the case of 12a using 2 mmol of the
imine. The red-brown solution of azaenolate was added drop-
wise to a solution of di(2-methylphenyl)halophosphine (0.56
g, 2.1 mmol; 1/0.75 R2PCl/R2PBr) in THF (5 mL) at -78 °C.
The mixture was stirred at -78 °C for 30 min, warmed to room
temperature, and stirred for an additional 30 min. Assay by
31P NMR (crude reaction mixture) showed the presence of a
major product (-11.5 ppm) in addition to several impurities.
The solvent was evaporated under reduced pressure. The
residue was dissolved in CH2Cl2 and filtered through a 3 ×
2.2 cm plug of silica gel under Ar, eluting with toluene (30
mL) followed by CH2Cl2 (20 mL). The solvent was evaporated
to give crude ligand as a yellow oil. To the crude ligand was
added NiBr2(DME) (0.123 g, 0.4 mmol) and CH2Cl2 (7 mL).
The dark brown-violet solution was stirred for 2.5 h at room
temperature and evaporated and the residue was washed with
diethyl ether (3 × 10 mL) and hexanes (10 mL). A brown solid
(0.196 g, 70.4% based on Ni) was obtained. Anal. Calcd for
[MesNdCP h CMe2P Me2]NiBr 2 (16a ). To crude ligand
(obtained as in the case of 12a using 1 mmol of imine) was
added NiBr2(DME) (0.240 g, 0.78 mmol) and CH2Cl2 (5 mL).
The dark purple solution was stirred for 1 h at room temper-
ature, the solution was evaporated, and the residue was
washed with hexanes (3 × 10 mL). A purple solid (0.42 g,
99.0% based on Ni) was obtained.
[MesNdCP h CMe2P P h 2]NiBr 2 (16b). To a solution of di-
isopropylamine (0.34 mL, 2.4 mmol, Aldrich) in diethyl ether
(7 mL) was added n-BuLi (1.4 mL of a 1.6 M solution in
hexanes, 2.2 mmol, Aldrich) at 0 °C. The reaction mixture was
stirred at room temperature for 10 min. The solution of LDA
was added to the solution of 8b (0.53 g, 2.0 mmol) in diethyl
ether (10 mL) at -78 °C. The solution was stirred at -78 °C
for 30 min, warmed to room temperature, and stirred for 1.5
h. After recooling to -78 °C Ph2PCl (0.40 mL, 2.2 mmol, Acros)
was added to the solution of the azaenolate at -78 °C. The
yellow solution was stirred for 30 min at -78 °C, warmed to
room temperature, and stirred for an additional 30 min. Assay
by 31P NMR (crude reaction mixture) showed the presence of
one major product (+13.5) and residual chlorodiphenylphos-
phine (+88.1 ppm). The residue was filtered through a 3 ×
2.2 cm pad of silica gel in diethyl ether (40 mL) followed by
THF (20 mL). The solvent was evaporated to give crude ligand
as a yellow oil. To crude ligand was added NiBr2(DME) (0.310
g, 1.0 mmol) and CH2Cl2 (10 mL). The dark purple-brown
solution was stirred for 2 h at room temperature, the solution
was evaporated, and the residue was washed with diethyl
ether (2 × 20 mL) and hexanes (3 × 10 mL). A dark red-brown
solid (0.650 g, quantitative based on Ni) was obtained. The
reaction is cleaner and higher yielding if LDA instead of t-BuLi
is used to deprotonate the imine. No signal in the 31P spectrum
was observed. 1H NMR (CD2Cl2): 8.71 (br s, 4H), 7.80 (s, 2H),
7.39-7.18 (m, 7H), 7.10 (br d, 2H, J ) 7.3 Hz), 6.39 (br t, 2H,
J ) 7.3 Hz), 4.76 (s, 3 H), 4.30 (s, 6 H), 2.53 (s, 6 H). Anal.
Calcd for C31H32Br2NNiP: C 55.73, H 4.83, N 2.10. Found: C
55.81, H 4.93, N 2.15.
C
33H36Br2NNiP: C 56.93, H 5.21, N 2.01. Found: C 56.95, H
[MesNdCP h CMe2P MesMe]NiBr 2 (16c). Lithium azaeno-
late was prepared as in the case of 12a using 2 mmol of the
imine. The red-brown solution of azaenolate was added drop-
wise to a solution of dichloromethylphosphine (0.2 mL, 2.2
mmol, Strem) in THF (5 mL) at -78 °C. The mixture was
stirred at -78 °C for 10 min, warmed to room temperature,
and stirred for an additional 30 min. Assay by 31P NMR (crude
reaction mixture) showed the presence of a single major
product (+101.5 ppm) in addition to starting materials (+194.5,
+190.7 ppm). The solvent was evaporated under vacuum to
5.49, N 1.92.
P r op iop h en on e 2,4,6-Tr im eth ylp h en ylim in e (17). 2,4,6-
Trimethylaniline (11.5 mL, 82 mmol, Aldrich) was mixed with
propiophenone (10 mL, 74.5 mmol, Aldrich) and p-TsOH (1.4
g, 7.3 mmol, Aldrich). The resulting mixture was heated for 2
h at 200 °C under a weak stream of Ar to remove formed H2O.
(19) Dang, T. P.; Poulin, J .-C.; Kagan, H. B. J . Organomet. Chem.
1975, 91, 105.

5934 Organometallics, Vol. 21, No. 26, 2002
Daugulis and Brookhart
Ta ble 5. Cr ysta llogr a p h ic Da ta Collection
P a r a m eter s for 13
(5 mL) was added n-BuLi (0.7 mL of a 1.6 M solution in
hexanes, 1.1 mmol, Aldrich) at 0 °C. The reaction mixture was
stirred at room temperature for 10 min. The solution of LDA
was added to the solution of 17 (0.251 g, 1.0 mmol) in diethyl
ether (5 mL) at -78 °C. The solution was stirred at -78 °C
for 20 min, warmed to room temperature, and stirred for 1 h.
After recooling to -78 °C Ph2PCl (0.25 mL, 1.4 mmol, Acros)
was added to the solution of the azaenolate at -78 °C. The
yellow solution was stirred for 15 min at -78 °C, warmed to
room temperature, and stirred for an additional hour. Assay
by 31P NMR (crude reaction mixture) showed the presence of
one major product (-1.3 ppm) and residual chlorodiphen-
ylphosphine (+83.1 ppm). The residue was filtered through a
3 × 2.2 cm pad of silica gel in diethyl ether (40 mL) followed
by THF (20 mL). The solvent was evaporated to give crude
ligand as a yellow oil. To the crude ligand was added NiBr2-
(DME) (0.155 g, 0.5 mmol) and CH2Cl2 (5 mL). The dark
purple-brown solution was stirred for 2 h at room temperature,
solution was evaporated, and the residue was washed with
diethyl ether (2 × 20 mL) and hexanes (3 × 10 mL). A gray-
brown solid (0.263 g, 80.4% based on Ni) was obtained. Anal.
Calcd for C30H30Br2NNiP: C 55.09, H 4.62, N 2.14. Found: C
55.36, H 4.72, N 2.08.
formula
mol wt
C34H38PN2PdCl
647.51
cryst syst
space group
a, Å
orthorhombic
Pc21n
9.5956(9)
13.1193(13)
25.1307(25)
3163.6(5)
4
b, Å
c, Å
V, Å3
Z
density calcd, Mg/m3
F(000)
1.359
1333.55
0.30 × 0.25 × 0.10
-100
cryst dimens, mm
temp, °C
radiation (λ, Å)
2θ range, deg
µ, mm-1
total no. of reflns
total no. of unique reflns
no. of obsd data
(I > 3.0σ(I))
no. of refined params
RF, %
0.71073
5.00-50.00
0.75
5673
3892
2971
352
0.061
0.078
1.2490
R
W, %
GOF
X-r a y Cr ysta l Str u ctu r e (13). Diffraction data were
collected on a Bruker SMART diffractometer using the ω-scan
mode. Refinement was carried out with the full-matrix least-
After cooling to room temperature the reaction mixture was
poured into hexanes (100 mL) and filtered, and the precipitate
was washed with additional hexanes (2 × 100 mL) followed
by the evaporation of the filtrate. The residue was filtered
through a 9 × 4.1 cm plug of silica gel in hexanes/ether 10/1
(300 mL collected). After evaporation of the solvent the
unreacted starting materials were distilled off under vacuum
(45-50 °C/0.4 mm). The residue was crystallized from metha-
nol at -30 °C. Product was isolated as large orange-yellow
squares method based on
F (NCRVAX) with anisotropic
thermal parameters for all non-hydrogen atoms. Hydrogen
atoms were inserted in calculated positions and refined riding
with the corresponding atom. Complete details of X-ray data
collection are given in Table 5.
Ack n ow led gm en t. We are grateful to DuPont for
support of this research, to DuPont Analytical for GPC
analyses, to Dr. Peter S. White for X-ray analysis of 13,
and to Prof. A. Goldman for a helpful discussion.
1
crystals, 4.8 g, (25.6%). H NMR (CDCl3): 8.00-7.94 (m, 2H),
7.51-7.45 (m, 3H), 6.89 (s, 2H), 2.50 (q, 2H, J ) 7.7 Hz), 2.31
(s, 3H), 2.04 (s, 6 H), 0.98 (t, 3 H, J ) 7.7 Hz). 13C NMR
(CDCl3): 170.8, 146.4, 138.2, 131.9, 130.3, 128.7, 128.6, 127.7,
125.6, 23.9, 20.9, 18.2, 11.6. Anal. Calcd for C18H21N: C 86.00,
H 8.42, N 5.57. Found: C 85.79, H 8.41, N 5.56.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallogra-
phy data for 13 and a graph for the determination of the rate
of migratory insertion. This material is available free of charge
via the Internet at http://pubs.acs.org.
[MesNdCP h CHMeP P h 2]NiBr 2 (18). To a solution of di-
isopropylamine (0.17 mL, 1.2 mmol, Aldrich) in diethyl ether
OM0206305