Iron phosphinimide and phosphinimine complexes: Catalyst precursors for ethylene polymerization

Article abstract of DOI:10.1021/om011041m

Reaction of Li[NPt-Bu₃] with FeCl₂ affords [Cl₃Fe₂(μ-NPt-Bu₃)₂] 1 in 71% yield. This mixed valent Fe(III)-Fe(II) undergoes reversibly one-electron oxidation to generate [Cl₃Fe₂(μ-NPt-Bu₃)₂]⁺. Chemical oxidation with [Cp₂Fe]PF₆ yields [Cl₂Fe(μ-NPt-Bu₃)]₂ 2. The reaction of Li[NPt-Bu₃] with FeBr₃ affords [Br₄Fe₂(μ-NPt-Bu₃)₂] 3, while the reaction of FeCl₃ with Me₃-SiNPCy₃ gives [Cl₂Fe(μ-NPCy₃)]₂ 4. Hydrolysis of 3 yields the species [(t-Bu₃PNH)Br₂Fe]₂-(μ-O) 5. These species have also been evaluated as catalysts for the polymerization of ethylene and copolymerization of ethylene/octene. These species were found to be single-site catalysts even under rather demanding conditions (50-160 °C, 100-300 psig ethylene), although the activities are generally low. Compound 5 affords polymer similar to that produced by 3, suggesting that MAO dehydrates 5 generating a catalyst similar to that derived from 3. Compounds 1, 2, 4, and 5 have been crystallographically characterized.

Full text of DOI:10.1021/om011041m

1362
Organometallics 2002, 21, 1362-1366
Ir on P h osp h in im id e a n d P h osp h in im in e Com p lexes:
Ca ta lyst P r ecu r sor s for Eth ylen e P olym er iza tion
Luc LePichon,† Douglas W. Stephan,*,† Xiaoliang Gao,‡ and Qinyan Wang‡
School of Physical Sciences, Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4, and NOVA Chemicals Corporation,
Research & Technology Center, 2928 16 Street N.E, Calgary, Alberta, Canada T2E 7K7
Received December 6, 2001
Reaction of Li[NPt-Bu3] with FeCl2 affords [Cl3Fe2(µ-NPt-Bu3)2] 1 in 71% yield. This mixed
valent Fe(III)-Fe(II) undergoes reversibly one-electron oxidation to generate [Cl3Fe2(µ-NPt-
Bu3)2]+. Chemical oxidation with [Cp2Fe]PF6 yields [Cl2Fe(µ-NPt-Bu3)]2 2. The reaction of
Li[NPt-Bu3] with FeBr3 affords [Br4Fe2(µ-NPt-Bu3)2] 3, while the reaction of FeCl3 with Me3-
SiNPCy3 gives [Cl2Fe(µ-NPCy3)]2 4. Hydrolysis of 3 yields the species [(t-Bu3PNH)Br2Fe]2-
(µ-O) 5. These species have also been evaluated as catalysts for the polymerization of ethylene
and copolymerization of ethylene/octene. These species were found to be single-site catalysts
even under rather demanding conditions (50-160 °C, 100-300 psig ethylene), although the
activities are generally low. Compound 5 affords polymer similar to that produced by 3,
suggesting that MAO dehydrates 5 generating a catalyst similar to that derived from 3.
Compounds 1, 2, 4, and 5 have been crystallographically characterized.
The impact of plastics and polymers on modern
Grubbs.11 Such systems are extremely interesting, as
they offer a unique approach to a variety of branched
polyolefins. While such catalysts are thought to be
deactivated by moisture and oxygen, they do offer the
potential of greater functional group tolerance than
group IV systems. In continuing our efforts, we are
exploring late metal complexes of both phosphinimide
and phosphinimine ligands. In this work we explore the
utility of Fe-phosphinimide complexes as precursors for
olefin polymerization catalysts.
society continues to spur the exploration of transition
metal complexes for single-site olefin polymerization
catalysts. These efforts have resulted in the evolution
from early metal metallocenes1,2 to early metal non-
metallocenes3 and Schiff base-late metal catalyst
systems.4-12 In our work, we have recently reported the
use of sterically demanding phosphinimide ligands in
the development of nonmetallocene, titanium-based
ethylene polymerization catalysts.13,14 In this regard, we
have developed remarkably active polymerization cata-
lysts derived from the species (t-Bu3PN)2TiR2.13 Of
particular recent interest are developments of late metal
olefin polymerization catalysts by the research groups
of Brookhart,5,6,15 Gibson,7-9,16 and most recently
Exp er im en ta l Section
Gen er a l Da ta . All preparations were done under an
atmosphere of dry, O2-free N2 employing both Schlenk line
techniques and an Innovative Technologies or Vacuum Atmo-
spheres inert atmosphere glovebox. Solvents were purified
employing a Grubb’s type column system manufactured by
Innovative Technology. All organic reagents were purified by
conventional methods. Guelph Chemical Laboratories, Guelph,
Ontario, performed combustion analyses.
Syn th esis of [Cl3F e2(µ-NP t-Bu 3)2] 1. Li[NPt-Bu3] (446 mg,
2.00 mM) in THF solution (40 mL) was added to a suspension
of FeCl2 (254 mg, 2.00 mM) in 10 mL of THF. The reaction
mixture was stirred for 2 h at 25 °C, resulting in a gray
powdery precipitate. The solvent was removed in vacuo, and
15 mL of CH2Cl2 was added. The dark red solution was stirred
for 20 min and filtered through Celite, and the filtrate was
concentrated. Dark red crystals of 1 crystallized from solution
upon standing (71% yield). Anal. Calcd for C24H54Cl3Fe2N2P2:
C, 44.30; H, 8.36; N, 4.30; Found: C, 43.36; H, 8.45; N, 4.21.
* Corresponding author. E-mail: stephan@uwindsor.ca.
† University of Windsor.
‡ NOVA Chemicals Corporation.
(1) Kaminsky, W. J . Chem. Soc. (D) 1998, 1413-1418.
(2) Hlatky, G. G. Coord. Chem. Rev. 1999, 181, 243-296.
(3) Hlatky, G. G. Coord. Chem. Rev. 2000, 199, 235-329.
(4) Brookhart, M. Organometallics 2000, 19, 2125-2129.
(5) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049-4050.
(6) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 11664-11665.
(7) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428-447.
(8) Gibson, V. C.; Newton, C.; Redshaw, C.; Solan, G. A.; White, A.
J . P.; Williams, D. J . J . Chem. Soc. (D) 1999, 827-829.
(9) Britovsek, G. J . P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P.
J .; McTavish, S. J .; Solan, G. A.; White, A. J . P.; Williams, D. J . Chem.
Commun. 1998, 007, 849-850.
(10) Coles, M. P.; Dalby, C. I.; Gibson, V. C.; Clegg, W.; Elsegood,
M. R. J . Chem. Commun. 1995, 1709-1712.
(11) Younkin, T. R.; Connor, E. F.; Henerson, J . I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460-462.
(12) Theopold, K. H. Eur. J . Inorg. Chem. 1998, 15-24.
(13) Stephan, D. W.; Guerin, F.; Spence, R. E. V. H.; Koch, L.; Gao,
X.; Brown, S. J .; Swabey, J . W.; Wang, Q.; Xu, W.; Zoricak, P.; Harrison,
D. G. Organometallics 1999, 18, 2046-2048.
(14) Stephan, D. W.; Stewart, J . C.; Guerin, F.; Spence, R. E. V. H.;
Xu, W.; Harrison, D. G. Organometallics 1999, 18, 1116-1118.
(15) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414-6415.
Syn th esis of [Cl2F e(µ-NP t-Bu 3)]2 2. [Cp2Fe]PF6 (66 mg,
0.20 mM) was added to a solution of 1 (130 mg, 0.20 mM) in
10 mL of CH2Cl2. The solution was stirred 2 h at 25 °C. After
filtration through Celite the solution was evaporated and the
resulting red-brown powder washed with hexane. Recrystal-
lization in CH2Cl2 afforded red-brown crystals of 2 in 90% yield
(16) Gibson, V. C.; Marshall, E. L.; Redshaw, C.; Clegg, W.; Elsegood,
M. R. J . J . Chem. Soc. (D) 1996, 4197-4200.
10.1021/om011041m CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/08/2002

Iron Phosphinimide and Phosphinimine Complexes
Organometallics, Vol. 21, No. 7, 2002 1363
Ta ble 1. Cr ysta llogr a p h ic P a r a m eter s
1
2
4
5
formula
fw
a (Å)
b (Å)
c (Å)
C
24H54Cl3Fe2N2P2
C24H54Cl4Fe2N2P2
686.16
13.3445(3)
16.4624(4)
15.1202(3)
C36H66Cl4Fe2N2P2
842.34
9.3084(3)
16.2308(2)
14.3609(4)
C24H56Br4Fe2N2OP2
881.98
19.104(4)
15.719(2)
25.267(6)
650.68
11.7067(15)
12.7469(15)
12.8426(17)
65.577(2)
76.774(2)
69.131(3)
triclinic
P1h
1623.0(4)
1.331
2
1.255
3754
R (deg)
â (deg)
γ (deg)
cryst syst
space group
vol (Å3)
105.082(2)
orthorhombic
Pbcm
3321.64(13)
1.372
monoclinic
P21/c
2094.95(9)
1. 335
2
1.051
10 149
3636
orthorhombic
Pbca
7588(2)
1.544
8
5.080
34 911
6678
D
Z
calcd (g cm-1
)
4
abs coeff, µ (mm-1
)
1.308
16 631
3043
166
7.19
no. of data collected
no. of data Fo2>3σ(Fo
no. of variables
R (%)
2
)
2297
298
10.79
208
6.24
315
8.45
Rw (%)
goodness of fit
25.69
1.012
17.89
1.091
10.39
0.979
17.93
1.065
All data collected at 24 °C with Mo KR radiation (λ ) 0.71069 Å), R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) [∑[w(Fo - Fc2)2]/∑[wFo2)2]]0.5
.
a
2
(123 mg). Anal. Calcd for C24H54Cl4Fe2N2P2 + 0.50CH2Cl2: C,
30 °C. The temperature was controlled (to ca. (2 °C) with an
40.39; H, 7.61; N, 3.84. Found: C, 40.49; H, 8.05; N, 3.83.
Syn th esis of [Br 2F e(µ-NP t-Bu 3)]2 3. A solution of Li[NPt-
Bu3] (2.86 mg, 1.3 mmol) in hexane was added to a suspension
of FeBr3 (385 mg, 1.3 mmol) in toluene (40 mL) at -30 °C.
The mixture was slowly warmed to room temperature with
stirring for 12 h. The brownish-orange solution was filtered
and concentrated, heptane was added, and the reaction
mixture was allowed to stand at -35 °C to give an orange
crystalline product, 1 (540 mg, 96% yield). Anal. Calcd for
external heating/cooling bath and was monitored by a ther-
mocouple that extended into the polymerization vessel. Solu-
tions of MAO (500 equiv) and catalyst precursor in toluene
were sequentially injected. The mixture was stirred for 3 min
at a rate of 150 rpm after each addition. The rate of stirring
was increased to 1000 rpm, and the vessel was vented of N2
and pressurized with ethylene (33 psi). Any exotherm was
within the allowed temperature differential of the heating/
cooling system. The solution was stirred for 1 h, after which
time the reaction was quenched with 1 M HCl in MeOH. The
precipitated polymer was subsequently washed with MeOH
and dried at 100 °C for at least 24 h prior to weighing.
C
24H54Br4Fe2N2P2: C, 33.36; H, 6.30; N, 3.24. Found: C, 33.09;
H, 6.00; N, 2.97.
Syn th esis of [Cl2F e(µ-NP Cy3)]2 4. A solution of FeCl3 (91
mg, 0.56 mM) and Cy3PNSiMe3 (620 mg, 1.69 mM) in 10 mL
of dichloroethane was stirred at reflux during 4 h. After
evaporation of the solution the resulting red-brown powder was
washed with hexane. Recrystallization in CH2Cl2 afforded red-
brown crystals of 4 in relatively low yield (20%). Anal. Calcd
for C36H66Cl4Fe2N2P2: C, 51.33; H, 7.90; N, 3.33. Found: C,
51.01; H, 7.30; N, 2.92.
Syn th esis of [Br F e(HNP t-Bu 3)]2(µ-O) 5. A solution of
LiNPt-Bu3 (406 mg, 1.9 mmol) was suspended in anhydrous
heptane (20 mL). FeBr3 (552 mg, 1.9 mmol) was dissolved in
toluene (30 mL) and added to the heptane solution at -100
°C. The solution was stirred and warmed to room temperature
and H2O (16 mg, 0.88 mmol) was added dropwise in a toluene
(60 mL) solution. The mixture was stirred for 12 h, the solution
filtered, and the solvent removed. The light green product was
washed with heptanes, affording 5 in 34% yield. Anal. Calcd
for C24H56Br4Fe2N2P2O: C, 32.68; H, 6.40; N, 3.18. Found: C,
32.21; H, 6.30; N, 2.97.
X-r a y Da ta Collection a n d Red u ction . X-ray quality
crystals were obtained as described above. The crystals were
manipulated and mounted in capillaries in a glovebox, thus
maintaining a dry, O2-free environment for each crystal.
Diffraction experiments were performed on a Siemens SMART
System CCD diffractometer. In the later case the data were
collect in a hemisphere of data in 1329 frames with 10 s
exposure times. Crystal data are summarized in Table 1. The
observed extinctions were consistent with the space groups in
each case. The data sets were collected (4.5° < 2θ < 45-50.0°).
A measure of decay was obtained by re-collecting the first 50
frames of each data set. The intensities of reflections within
these frames showed no statistically significant change over
the duration of the data collections. The data were processed
using the SAINT and XPREP processing package. An empiri-
cal absorption correction based on redundant data was applied
to each data set. Subsequent solution and refinement was
performed using the SHELXTL solution package operating on
a Pentium computer.
Eth ylen e P olym er iza tion . These experiments were done
in one of two ways. Each are described below. (i) A solution of
6-10 µmol of catalyst precursor in 2.0 mL of dry toluene was
added to a flask containing 2.0 mL of dry toluene. Five
hundred equivalents of a 10 wt % toluene solution of methyl-
aluminoxane (MAO) was added to the flask. Alternatively, a
catalyst precursor was combined with [Ph3C][B(C6F5)4] under
an ethylene atmosphere. The flask was attached to a Schlenk
line with a cold trap, a stopwatch was started, and the flask
was three times evacuated for 5 s and refilled with predried
99.9% ethylene gas. The solution was rapidly stirred under 1
atm of ethylene at room temperature. The polymerization was
stopped by the injection of a 1.0 N HCl/methanol solution, total
reaction time was noted, and the polymer was isolated. (ii) A
1 L autoclave was dried under vacuum (10-2 mmHg) for
several hours. Dried toluene (500 mL) was transferred into
the vessel under a positive pressure of N2 and was heated to
St r u ct u r e Solu t ion a n d R efin em en t . Non-hydrogen
atomic scattering factors were taken from the literature tabu-
lations.17 The heavy atom positions were determined using
direct methods employing either the SHELXTL or direct
methods routines. The remaining non-hydrogen atoms were
located from successive difference Fourier map calculations.
The refinements were carried out by using full-matrix least
squares techniques on F, minimizing the function w(|Fo| -
|Fc|)2, where the weight w is defined as 4Fo2/2σ(Fo2) and Fo and
Fc are the observed and calculated structure factor amplitudes.
In the final cycles of each refinement, all non-hydrogen atoms
were assigned anisotropic temperature factors. Carbon-bound
hydrogen atom positions were calculated and allowed to ride
(17) Cromer, D. T.; Mann, J . B. Acta Crystallogr. A 1968, A24, 321-
324.

1364 Organometallics, Vol. 21, No. 7, 2002
LePichon et al.
Ta ble 2. P olym er iza tion Da ta a
temp
(°C)
time
(min)
activity
(g PE/mmol‚h‚bar)
Mw
e
catalyst/cocatalyst
(×10-3
)
PDIe
mp
slurry polymerization
3/MAO/Ph3C[B(C6F5)4]b
2/MAO
83.1
51.5
24
30
55
2
139.6
480.3
1.7
136.2
132.1
11.3
slurry copolymerization
3/MAOc
51.2
50.0
15
30
5
0.3
509.9
468.8
7.0
16.7
106.7
125.3
5/MAOc
solution polymerization
3/MAO/Ph3C[B(C6F5)4]d
5/MAO/Ph3C[B(C6F5)4]d
158.5
159.2
10
10
49
13
451.1
547.1
1.82
1.71
133.9
141.5
a
General polymerization conditions: 300 psig C2; 300 umol/L of catalyst; Al/Fe ) 60; 216 mL of toluene; MAO at 1 mmol/L as a
scavenger. Al/Fe ) 20; B/Al ) 1.05. c As above with 100 psig C2; 30 mL of 1-octene; 216 mL of toluene. 200 psig C2; 200 umol/L of
catalyst; Al/Fe ) 20; B/Al ) 1.05; PMAO at 1 mmol/L as a scavenger; 216 mL of toluene. e Molecular weights and PDI were measured by
GPC at 140 °C in 1,2,4-trichlorobenzene calibrated using polyethylene standards.
b
d
F igu r e 1. ORTEP drawing of 1; 20% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Fe(1)-
F igu r e 2. Cyclic voltammetry of 1 in CH2Cl2 with [Bu4N]-
PF6 as the supporting electrolyte. The vertical axis denotes
0.0 V relative to SCE.
N(1) 1.912(9), Fe(1)-N(2) 1.927(8), Fe(1)-Cl(1) 2.242(4),
Fe(1)-Cl(2) 2.244(4), Fe(1)-Fe(2) 2.523(2), Fe(2)-N(1)
1.933(8), Fe(2)-N(2) 1.948(10), Fe(2)-Cl(3) 2.211(3), P(1)-
N(1) 1.626(9), N(1)-Fe(1)-N(2) 99.0(4), N(1)-Fe(1)-Cl-
(1) 110.1(3), N(2)-Fe(1)-Cl(1) 110.1(3), N(1)-Fe(1)-Cl(2)
113.6(3), N(2)-Fe(1)-Cl(2) 110.5(3), Cl(1)-Fe(1)-Cl(2)
112.78(16), N(1)-Fe(2)-N(2) 97.5(4), N(1)-Fe(2)-Cl(3)
130.7(3), N(2)-Fe(2)-Cl(3) 131.7(3), P(1)-N(1)-Fe(1) 142.5-
(5), P(1)-N(1)-Fe(2) 135.4(5), Fe(1)-N(1)-Fe(2) 82.0(3),
P(2)-N(2)-Fe(1) 142.8(6), P(2)-N(2)-Fe(2) 136.0(5), Fe-
(1)-N(2)-Fe(2) 81.3(3).
trigonal planar coordination sphere comprised of the two
phosphinimide nitrogens and a single chloride ion. The
Fe-Cl distance in this case is 2.211(3) Å. This structure
confirms a mixed valent Fe(III)-Fe(II) formulation
consistent with the intermediate effective magnetic
moment of 2.60 µB.
It is noteworthy that all efforts to isolate a purely Fe-
(II) species were unsuccessful. In contrast, Dehnicke and
co-workers have described the Fe(II) tetrameric ag-
gregate [ClFe(µ-NPEt3)]4 with a cubane type structure.
Dehnicke et al.18 have also reported that use of the more
sterically demanding phosphinimide ligand [(Me2N)3PN]-
precludes tetramer formation, affording instead the
mixed-valent trimetallic species [Fe3Cl4(NP(NMe2)3)3].18
In the present work, the even greater steric demand of
the phosphinimide ligand [t-Bu3PN]- presumably pre-
cludes aggregation to analogous tetramers or trimers,
prompting disproportionation and formation of the
mixed valent dimeric species 1.
on the carbon to which they are bonded assuming a C-H bond
length of 0.95 Å. Hydrogen atom temperature factors were
fixed at 1.10 times the isotropic temperature factor of the
carbon atom to which they are bonded. The hydrogen atom
contributions were calculated, but not refined. The final values
of refinement parameters are given in Table 1. The locations
of the largest peaks in the final difference Fourier map
calculation as well as the magnitude of the residual electron
densities in each case were of no chemical significance.
Crystallographic information files have been deposited as
Supporting Information.
Resu lts a n d Discu ssion
The presence of a coordinatively unsaturated Fe
center in the Fe(III)/Fe(II) dimer 1 prompted attempts
to bind other ancillary donors such as olefins, nitriles,
isonitriles, and phosphines to the tricoordinate Fe
center. No evidence of ligand coordination was observed.
The redox properties of 1 were probed via cyclic volta-
mmetry in CH2Cl2 employing [Bu4N]PF6 as the sup-
porting electrolyte and a Pt electrode. A reversible one-
electron redox process is observed centered at 90 mV
versus the SCE, consistent with a one-electron oxidation
of 1 to [Cl3Fe2(µ-NPt-Bu3)2]+ (Figure 2, Scheme 1).
Application of reducing potentials showed no evidence
of the reduction of 1 prior to the reduction of the solvent.
A solution of Li[NPt-Bu3] in THF was added to a
suspension of FeCl2 in THF and allowed to react for 2
h at room temperature, affording a dark solution with
a gray-colored precipitate. Removal of the solvent under
vacuum and replacement with CH2Cl2 resulted in the
subsequent isolation of red crystals of 1 in 71% yield.
X-ray crystallographic study of 1 established the for-
mulation as [Cl3Fe2(µ-NPt-Bu3)2] (Figure 1), in which
two phosphinimide ligands bridge two inequivalent iron
centers. The Fe2N2 core is planar with Fe-N distances
in the range 1.912(9)-1.948(10) Å, while the Fe-Fe
separation is 2.523(2) Å. One of the iron centers, Fe(1)
is pseudo-tetrahedral with two chloride ions completing
the coordination sphere with an average Fe-Cl distance
of 2.243(4) Å. The second iron center adopts a pseudo-
(18) Riese, U.; Harms, K.; Pebler, J .; Dehnicke, K. Z. Anorg. Allg.
Chem. 1999, 625, 746-754.

Iron Phosphinimide and Phosphinimine Complexes
Organometallics, Vol. 21, No. 7, 2002 1365
Sch em e 1
Sch em e 2
F igu r e 3. ORTEP drawings of (a) 2 and (b) 4; 20% thermal
ellipsoids are shown. Hydrogen atoms are omitted for
clarity. 2: Fe(1)-N(2) 1.927(4), Fe(1)-N(1) 1.940(4), Fe-
(1)-Cl(1) 2.2260(17), Fe(1)-Cl(2) 2.2421(18), Fe(1)-Fe(1)′
2.5659(13), P(1)-N(1) 1.642(5), N(2)-Fe(1)-N(1) 96.71(15),
N(2)-Fe(1)-Cl(1) 115.60(16), N(1)-Fe(1)-Cl(1) 115.38(15),
N(2)-Fe(1)-Cl(2) 108.34(17), N(1)-Fe(1)-Cl(2) 111.00(17),
Cl(1)-Fe(1)-Cl(2) 109.19(9). P(1)-N(1)-Fe(1) 138.56(10),
P(1)-N(1)-Fe(1) 138.56(10), Fe(1)-N(1)-Fe(1) 82.8(2),
P(2)-N(2)-Fe(1) 138.24(11), P(2)-N(2)-Fe(1) 138.24(11),
Fe(1)-N(2)-Fe(1) 83.5(2). 4: Fe(1)-N(1) 1.909(4), Fe(1)-
N(1)′ 1.922(4), Fe(1)-Cl(1) 2.2227(16), Fe(1)-Cl(2) 2.2281-
(16), Fe(1)-Fe(1)′ 2.6133(15), P(1)-N(1) 1.619(4), N(1)-
Fe(1)-N(1)′ 93.98(16), N(1)-Fe(1)-Cl(1) 113.81(14), N(1)′-
Fe(1)-Cl(1) 112.14(14), N(1)-Fe(1)-Cl(2) 115.49(13), N(1)′-
Fe(1) Cl(2) 110.09(13), Cl(1)-Fe(1)-Cl(2) 110.35(7), P(1)-
N(1)-Fe(1) 141.8(3), P(1)-N(1)′-Fe(1) 131.7(2), Fe(1)-
N(1)-Fe(1) 86.02(16).
This infers that CH2Cl2 would act to oxidize an Fe(II)-
Fe(II) species, an observation that may account for the
isolation of partial oxidation product 1 from the prepa-
ration described above. Attempts to intercept the cat-
ionic Fe(III)/Fe(III) dimer with donor ligands also proved
unsuccessful.
Reaction of 1 with [Cp2Fe]PF6 was performed in CH2-
Cl2. Stirring for 2 h resulted in the generation of a red-
brown solution. The solvent was removed, and the
residue washed with hexane and crystallized from CH2-
Cl2 to give a new species, 2, in 90% yield. X-ray
crystallographic characterization of 2 established the
formulation as [Cl2Fe(µ-NPt-Bu3)]2 (Figure 3a). Crystal-
lographic symmetry imposes mirror symmetry on the
dimeric structure. Thus, one of the tert-butyl groups and
the P and N atoms sit precisely on the mirror plane.
Two chloride ions complete each of the coordination
spheres of the symmetry-related Fe centers. The Fe-N
and Fe-Cl distances average 1.933(4) and 2.2340(18)
Å respectively. The Fe2N2 core is similar to that seen
in 1 with a slightly larger Fe-Fe separation of 2.5659-
(13) Å. The compound 2 was found to have an effective
magnetic moment of 4.11 µB, consistent with the Fe-
(III)/Fe(III) formulation.
On the basis of the electrochemical properties of 1 and
the characterization of 2, it appears that [Cl3Fe2(µ-NPt-
Bu3)2]+ abstracts a chloride from CH2Cl2, resulting in
the formation of 2. Attempts to develop a direct syn-
thesis of 2 via reaction of FeCl3 with either Li[NPt-Bu3]
or Me3SiNPt-Bu3 proved unsuccessful, yielding only oily,
uncharacterized products. In contrast, reaction of Li-
[NPt-Bu3] in hexane with FeBr3 in toluene gave an
orange crystalline product 3 in 96% yield. The product
was formulated as [Br2Fe(µ-NPt-Bu3)]2 3 by analogy
with the crystallographically characterized species 2.
The analogous reaction of FeCl3 with Me3SiNPCy3
affords the red-brown species 4 in modest yields. The
compound 4 was also shown to be a crystallographically
centrosymmetric dimer, generally analogous to 3 (Fig-
ure 3b). It is noteworthy that the Fe-N distance in 4 is
significantly longer than those found in 2 and the
analogous species [Cl2Fe(µ-NPR3)]2 (R ) Ph, Et) previ-
ously described by groups of Roesky and Dehnicke.19,20
This, again reflects the greater steric demands of the
phosphinimide ligand [t-Bu3PN]-.
In some attempts to prepare 4 it was uncovered that
inferior quality (i.e., slightly wet) commercial-grade
FeBr3 led to the formation of a light green powder 5.
This same green material could be deliberately synthe-
sized directly from 4 via addition of an equivalent of
H2O. This product of hydrolysis 5 was identified by
single-crystal X-ray crystallography as species [(t-Bu3-
(19) Roesky, H. W.; Seseke, U.; Noltemeyer, M.; Sheldrick, G. M. Z.
Naturforsch. 1988, 43b, 1138.
(20) Mai, H. J .; Wocadlo, S.; Kang, H. C.; Massa, W.; Dehnicke, K.;
Maichle-Moessmer, C.; Straehle, J .; Fenske, D. Z. Anorg. Allg. Chem.
1995, 621, 705-712.

1366 Organometallics, Vol. 21, No. 7, 2002
LePichon et al.
single-site ethylene polymerization catalyst (55 g PE/
mmol Fe‚h/bar). The resulting polymer has a Mw of
139 000 with a polydispersity index of 1.7. Activation
of compound 2 by MAO alone results in much lower
activity and a polymer with much higher polydispersity,
suggesting the generation of multiple low-activity sites.
Analogous slurry copolymerization of ethylene/1-octene
using 3/MAO generated polymer with octene incorpora-
tion with 1.7 branches/1000 carbons, as evidenced by
13C{1H} NMR data.
Solution polymerization was also performed at 160
°C and 200 psig of ethylene. Consistent with the best
results in slurry polymerizations, a combination of MAO
and Ph3C[B(C6F5)4] was used to effect activation. The
ratios of Al/Fe and B/Fe were 20 and 1.05, respectively.
Compound 3 yields an active single-site catalyst for the
polymerization of ethylene giving 49 g PE/mmol Fe‚h/
bar. The resulting polymer had a Mw of 451 000 with a
PDI of 1.82, consistent with single-site character. It is
noteworthy that the Fe-catalyst derived from [(C5H3N)-
(CRdNC6H3i-Pr2)2]FeBr2/MAO5,9 degrades under these
conditions. Although it generates 53 g PE/mmol Fe‚h/
bar (287 psig, 140 °C, Mw 457 000), the polydispersity
is very broad (PDI ) 48) under these more demanding
conditions.
In what is perhaps a surprising observation, com-
pound 5 also affords an active single-site catalyst in
solution polymerization, producing 13 g PE//mmol Fe‚
h/bar. The resulting polymer is similar to that produced
from 3 with a Mw of 547 100 and a polydispersity index
of 1.71. Although the nature of the active species derived
from these two precursors has not been unambiguously
identified, the similarity of the products derived from 3
and 5 and the single site behavior suggest the possibility
that MAO dehydrates 5, generating a catalyst similar
to that derived from 3. This suggests that compounds
thought to be products of deactivation may be worthy
of further study. The development of related but more
active catalyst precursors is the target of ongoing efforts.
F igu r e 4. ORTEP drawings of 5; 20% thermal ellipsoids
are shown. Hydrogen atoms are omitted for clarity. Fe(1)-
O(1) 1.768(7), Fe(1)-N(1) 1.908(9), Fe(1)-Br(1) 2.3698(18),
Fe(1)-Br(2) 2.3704(17), P(1)-N(1) 1.630(9), O(1)-Fe(2)
1.760(7), Fe(2)-N(2) 1.950(7), Fe(2)-Br(4) 2.3548(18), Fe-
(2)-Br(3) 2.363(2), P(2)-N(2) 1.604(8), O(1)-Fe(1)-N(1)
101.9(4), O(1)-Fe(1)-Br(1) 109.2(3), N(1)-Fe(1)-Br(1)
114.7(3), O(1)-Fe(1)-Br(2) 105.7(2), N(1)-Fe(1)-Br(2)
113.4(3), Br(1)-Fe(1)-Br(2) 111.02(7), P(1)-N(1)-Fe(1)
150.3(6), O(1)-Fe(2)-N(2) 104.8(3), O(1)-Fe(2)-Br(4) 105.8-
(3), N(2)-Fe(2)-Br(4) 112.5(2), O(1)-Fe(2)-Br(3) 107.5-
(3), N(2)-Fe(2)-Br(3) 113.4(3), Br(4)-Fe(2)-Br(3) 112.17-
(8), P(2)-N(2)-Fe(2) 148.9(5).
PNH)Br2Fe]2(µ-O) 5 (Figure 4). The Fe-O distances in
this oxo-bridged diiron complexes average 1.764(7) Å,
while the Fe-O-Fe′ angle is 148.1(5)°. The Fe-N
distances average 1.929(9) Å, and the Fe-Br distances
range from 2.3548(18) to 2.3704(17) Å. The angles about
both Fe centers are consistent with slightly distorted
tetrahedral coordination spheres.
Eth ylen e P olym er iza tion . The ability of these Fe
species to effect ethylene polymerization catalysis in
solution and slurry phase was probed using a 500 mL
Autoclave reactor equipped with an air-driven stirrer
and an automatic temperature control system. All
solvent, catalyst (200 umol/L), and cocatalyst were fed
into the reactor batchwise except ethylene, which was
fed on demand at 200 psig. Reactions were terminated
by the addition of methanol (5 mL), and the polymer
was recovered by solvent removal. Results of prelimi-
nary screening of these species in slurry polymerization
at 50 °C revealed that activation of compound 3 with a
combination of MAO and Ph3C[B(C6F5)4] afforded a
Ack n ow led gm en t. Financial support from NSERC
of Canada and NOVA Chemicals is gratefully acknowl-
edged.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM011041M