C-substituted bis(diphenylphosphino)methane-type ligands for chromium-catalyzed selective ethylene oligomerization reactions

Article abstract of DOI:10.1021/om900285e

Ligand backbone alkylation of the complex [Cr(CO)₄(dppm)] (dppm = bis(diphenylphosphino)methane) with alkyl iodides yields the C-substituted dppm ligand complexes [Cr(CO)₄{Ph₂PCH(R)PPh₂}] (R = methyl, n-hexyl, b

Full text of DOI:10.1021/om900285e

Organometallics 2009, 28, 4613–4616 4613
DOI: 10.1021/om900285e
C-Substituted Bis(diphenylphosphino)methane-Type Ligands for
Chromium-Catalyzed Selective Ethylene Oligomerization Reactions
Arminderjit Dulai,† Henriette de Bod,‡ Martin J. Hanton,§ David M. Smith,§
Stephen Downing,§ Stephen M. Mansell,† and Duncan F. Wass*,†
†School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K., ‡R&D Division, Sasol
Technology (Pty) Ltd., 1 Klasie Havenga Road, Sasolburg 1947, South Africa, and §Sasol Technology U.K.
Ltd., Purdie Building, North Haugh, St. Andrews KY16 9ST, U.K.
Received April 15, 2009
Summary: Ligand backbone alkylation of the complex
[Cr(CO)4(dppm)] (dppm = bis(diphenylphosphino)methane)
with alkyl iodides yields the C-substituted dppm ligand com-
plexes [Cr(CO)4{Ph2PCH(R)PPh2}] (R = methyl, n-hexyl,
benzyl). Activation of these complexes via one-electron oxida-
tion with Ag[(Al(OC4F9)4] and CO removal with triethylalu-
minium, or (in the case of R=methyl) by in situ treatment of
the free ligand with a chromium salt and modified methyl
alumoxane (MMAO), leads to catalysts showing some selec-
tivity for ethylene trimerization and tetramerization. NMR
spectroscopic studies of the parent dppm or [Cr(CO)4(dppm)]
compounds suggest that ligand deprotonation and decom-
plexation may be the cause of the surprisingly poor catalytic
performance of these specific derivatives.
demonstrated that relatively minor changes to ligand struc-
ture and reaction conditions can lead to ethene tetrameriza-
tion rather than trimerization.4 More recently, a wider
variety of carbon-bridged diphosphine ligands has been
investigated for these reactions, with 1,2-bis(diphenylphos-
phino)benzene, in particular, showing promise.5 Sur-
prisingly, bis(diphenylphosphino)methane ligands, despite
being very similar to the highly active and selective
N,N-bis(diphenylphosphino)amine in terms of bite angle,
steric constraints, and donor strength,6 proved to be very
poor ligands for catalysis. Indeed, the direct analogue dppm
showed no evidence of selective oligomerization, producing
only a Schulz-Flory distribution of oligomers.5 This result is
in line with our earlier findings for P-anisyl-substituted
derivatives.2 It was postulated that the unsubstituted nature
of the backbone made the ligand susceptible to deprotona-
tion during catalysis, leading to the observed disappointing
results. With this hypotheses in mind, and to access ligands
sterically equivalent to the successful N-alkyl-substituted N,
N-bis(diphenylphosphino)amines, it was reasoned that li-
gands of the type Ph2PCH(R)PPh2 (R = alkyl) may give
improved performance. The synthesis and catalytic screen-
ing of such complexes are reported here.
Introduction
In recent years, catalysts have emerged that are capable of
the selective trimerization of ethene to 1-hexene via a dis-
tinctive metallacyclic mechanism.1 In 2002, we reported
catalysts based on chromium complexes of ligands of the
type Ar2PN(Me)PAr2 (Ar=ortho-methoxy-substituted aryl
group) with productivity figures over an order of magnitude
better than previous systems.2 This unprecedented perfor-
mance led to interest both from a mechanistic viewpoint and
in extending the range of substrates used in these reactions;3
however, the most significant subsequent development
has been the report from Bollmann and co-workers that
Results and Discussion
Shaw and co-workers reported the synthesis of backbone-
substituted dppm ligands via deprotonation and alkylation
of various simple dppm complexes, in which complexation
acts to protect phosphorus from substitution.7 Of particular
interest for this study is the report of chromium carbonyl
complexes, such species being useful precatalysts that can be
activated via one-electron oxidation.8 Following Shaw’s
method, complexes 2-4 were synthesized in 38-63% yield
from [Cr(CO4)(dppm)] 1 (Scheme 1). IR spectroscopy re-
veals the carbonyl stretching bands for these complexes to be
very similar (1877, 1894, 1917, 2007 cm-1 for 2, 1876, 1892,
*Corresponding author. E-mail: duncan.wass@bristol.ac.uk.
(1) (a) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H.
J. Organomet. Chem. 2004, 689, 3641. (b) Wass, D. F. Dalton Trans. 2007,
816.
(2) Carter, A.; Cohen, S. A.; Cooley, N. A.; Murphy, A.; Scutt, J.;
Wass, D. F. Chem. Commun. 2002, 858.
(3) (a) Agapie, T.; Schofer, S. J.; Labinger, J. A.; Bercaw, J. E. J. Am.
Chem. Soc. 2004, 126, 1304. (b) Blann, K.; Bollmann, A.; Dixon, J. T.; Hess,
F. M.; Killian, E.; Maumela, H; Morgan, D. H.; Neveling, A.; Otto, S.;
Overett, M. J. Chem. Commun. 2005, 620. (c) Overett, M. J.; Blann, K.;
Bollmann, A.; Dixon, J. T.; Hess, F.; Killian, E.; Maumela, H.; Morgan, D. H.;
Neveling, A.; Otto, S. Chem. Commun. 2005, 622. (d) Bowen, L. E.; Wass,
D. F. Organometallics 2006, 25, 555. (e) Bowen, L. E.; Charernsuk, M.;
Wass, D. F. Chem. Commun. 2007, 2835. (f) Blann, K.; Bollmann, A.; De
Bod, H.; Dixon, J. T.; Killian, E.; Nongodlwana, P.; Maumela, M. C.;
Maumela, H.; McConnell, A. E.; Morgan, D. H.; Overett, M. J.; Pretorius,
M.; Kuhlmann, S.; Wasserscheid, P. J. Catal. 2007, 249, 244. (g) McGuin-
ness, D. S.; Overett, M.; Tooze, R. P.; Blann, K.; Dixon, J. T.; Slawin, A. M. Z.
Organometallics 2007, 26, 1108.
(5) Overett, M. J.; Blann, K.; Bollmann, A.; de Villiers, R.; Dixon, J.
T.; Killian, E.; Maumela, M. C.; Maumela, H.; McGuinness, D. S.;
Morgan, D. H.; Rucklidge, A.; Slawin, A. M. Z. J. Mol. Catal. A: Chem.
2008, 283, 114.
(6) Dennett, J. N. L.; Gillon, A. L.; Heslop, K.; Hyett, D. J.; Fleming,
J. S.; Lloyd-Jones, C. E.; Orpen, A. G.; Pringle, P. G.; Wass, D. F.; Scutt,
J. N.; Weatherhead, R. H. Organometallics 2004, 23, 6077.
(7) Al-Jibori, S.; Shaw, B. L. Inorg. Chim. Acta 1983, 74, 235.
(8) (a) Rucklidge, A. J.; McGuinness, D. S.; Tooze, R. P.; Slawin, A.
M. Z.; Pelletier, J. D. A.; Hanton, M. J.; Webb, P. B. Organometallics
2007, 26, 2782. (b) Bowen, L. E.; Haddow, M.; Orpen, A. G.; Wass, D. F.
Dalton Trans. 2007, 1160.
(4) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H; McGuiness, D. S.; Morgan, D. H.; Neveling, A.; Otto, S.;
Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J. Am.
Chem. Soc. 2004, 126, 14712.
r
2009 American Chemical Society
Published on Web 07/17/2009
pubs.acs.org/Organometallics

4614 Organometallics, Vol. 28, No. 15, 2009
Dulai et al.
Scheme 1. Synthesis of Complexes
1917, 2005 cm-1 for 3, and 1877, 1894, 1918, 2006 cm-1 for 4)
and close to the values for the related N,N-bis-
(diphenylphosphino)amine complexes8 (for [Cr(CO)4-
(Ar2PN(Me)PAr2)], Ar=2-C6H4(MeO), 1869, 1888, 1907,
2002 cm-1). This suggests the effect of the less electronega-
tive carbon backbone is offset by the potential for delocali-
zation of the lone pair into the P-N-P chelate. It also
suggests on simple electronic grounds these ligands may be
expected to have similar performance in catalysis. Crystals of
compound 2, suitable for X-ray diffraction study, were
obtained by dichloromethane at -30 °C; the structure is
illustrated in Figure 1.
Figure 1. Molecular structure and numbering scheme for 2. All
hydrogen atoms are omitted for clarity; thermal ellipsoids are set
˚
to 50% probability. Selected bond lengths (A) and angles (deg):
Cr(1)-C(28) 1.846(3), Cr(1)-C(30) 1.850(3), Cr(1)-C(29)
1.877(3), Cr(1)-C(27) 1.880(3), Cr(1)-P(2) 2.3535(7), Cr(1)-
P(1) 2.3593(7), P(1)-C(1) 1.813(2), P(1)-C(7) 1.815(3), P(1)-
C(25) 1.852(2), P(2)-C(19) 1.817(2), P(2)-C(13) 1.819(2),
P(2)-C(25) 1.852(2), C(27)-O(1) 1.144(3), C(28)-O(2)
1.149(3), C(29)-O(3) 1.143(3), C(30)-O(4) 1.152(3), P(2)-Cr-
(1)-P(1) 70.58(2), P(2)-C(25)-P(1) 94.62(11).
Compound 2 shows the expected octahedral coordination
at chromium with a nonplanar Cr-P-C-P ring (deviation
of C25 from planarity=0.513 A) with a methyl substituent
˚
pseudoequatorial on the carbon backbone. The P-Cr-P
bite angle is 70.58(2)°, very similar to the related
[Cr(CO)4(Ar2PCH2PAr2)], Ar = 2-C6H4(MeO), with an
angle of 71.52(5)° and the trimerization-active precatalyst
[Cr(CO)4(Ar2PN(Me)PAr2)] with an angle of 68.44(3)°.8b
The Cr-C bond lengths for the CO ligands trans to the
The activation method of choice has previously been
shown to have a profound effect on oligomerization activity
and selectivity, and to benchmark our results against pre-
vious studies, which often rely on in situ activation of a
chromium salt and ligand with MAO or MMAO,1-5 we
synthesized the free methyl-substituted ligand 9 using the
recent method of Hogarth and co-workers.9 Screening of this
ligand with [Cr(acac)3] and MMAO gave an approximate
order of magnitude increase in productivity and a reduction
in polymer levels compared to the previous activation route.
Comparison of these new ligands with dppm shows that
backbone substitution leads to an increase in productivity in
every case; selectivity is also influenced with dppm giving
what is best described as a Schulz-Flory distribution (R=
0.55).5 It has been previously reported that attempts to
prepare the complex [Cr(dppm)(CO)4][Al(OC4F9)4] were
met with decomposition;8a thus no direct comparison of
the catalysis with complexes 5-7 can be made with the dppm
analogue. Clearly, our approach has led to an improvement
in catalysis results, although it is sobering to compare these
results to the N,N-bis(diphenylphosphino)isopentylamine
ligand complex 10, which gives higher activity and signifi-
cantly better selectivity.
˚
˚
diphosphine are 1.846(3) A for C(28) and 1.850(3) A for
C(30) and are slightly shorter than the other Cr-C bonds at
1.880(3) A for C(27) and 1.877(3) A.
˚
˚
Treatment of 5-7 with Ag[Al(OC4F9)4] leads to smooth
one-electron oxidation and generates complexes 5-7 with
carbonyl stretching bands shifted to higher wavenumber (for
example 1966, 2011, 2043, and 2088 cm-1 for 5) as expected.
Cyclic voltammetry of 2-4 reveals reversible oxidation in
each case with E1/2 of 0.68, 0.69, and 0.79 V vs SCE,
respectively. Complexes 5-7 may be activated using triethy-
laluminum as a CO scavenger;7 oligomerization results are
presented in Table 1.
Complexes 5-7 all exhibit modest activity and some
selectivity to C6 and C8 products above that expected for a
Schulz-Flory distribution. Unfortunately, significant
amounts of polymeric product are also observed, especially
in runs 1 and 3. Increasing the chain length of the ligand C-
substituent from methyl to n-hexyl approximately doubles
activity and significantly reduces the amount of polymer
byproduct; a modest increase in the selectivity to octene over
hexane is also observed. The benzyl derivative retains much
of this activity but has extremely poor selectivity: it is
noteworthy that N,N-bis(diphenylphosphino)benzylamine
ligands also have poor performance. For comparison com-
plex 10 was prepared and tested; this variant with the P-N-
P ligand framework showed the activity and productivity
associated with the amine backbone ligand, the selectivity
toward tetramerization being as expected, with a low poly-
mer formation level.
In an attempt to understand the poor performance of
dppm and the possibility of ligand deprotonation during
catalysis, an NMR-scale reaction in which dppm was treated
with 300 equiv of MMAO in toluene was performed. The
ligand is remarkable robust in the presence of this cocatalyst,
the 31P NMR resonance at δ -22.6 remaining the only signal
at room temperature for 30 min. Repeating this experiment
at the catalytic reaction temperature of 60 °C still only leads
(9) Hogarth, G.; Kilmartin, J. J. Organomet. Chem. 2007, 692, 5655.

Note
Organometallics, Vol. 28, No. 15, 2009 4615
Table 1. Ethylene Oligomerization Results
oligomers/wt % of liquid fractionb
runa
catalyst
activity (g/g Cr/h)
productivity (g/g Cr)
polymer (wt %)
C4
C6 (1 - C6)
C8 (1 - C8)
C10
C12
C14
1
2
3
5
6
7
10
9
44 080
82 820
70 150
1 920 775
790 180
21 000
8130
23 010
19 490
733 096
219 490
53.7
17.0
64.3
0.9
6.5
3.8
5.3
1.8
3.7
23.9 (70.4)
18.8 (48.0)
21.9 (50.0)
28.8 (81.6)
16.2 (49.8)
34.6 (91.3)
38.4 (95.2)
30.8 (91.3)
63.0 (99.4)
34.1 (95.9)
5.3
6.5
7.8
4.0
5.4
6.3
5.4e
6.1
3.4
4.6
5.3
4
5c
6d
29.6
6.5
5.3
8
Schulz-Flory distribution of LAOs (R = 0.55)
a Conditions unless stated otherwise: 2.5 μmol of compound, 150 equiv of triethylaluminium, chlorobenzene diluent, 55 bar of ethene, 60 °C.
b Determined by GC; remainder is C16-20+. c Conditions as run 1 except 9 added to [Cr(acac)3] (2.5 μmol), then MMAO (960 equiv) added. d Taken from
ref 5. e Total C10-14
.
to slow decomposition (30% decomposition after 30 min) to
a species with a 31P NMR resonance at δ -7.1. These NMR
data are consistent with previously reported alkyl aluminum
bis(diphenylphosphino)methide compounds,10 the expected
ligand deprotonation products, but the slow rate of forma-
tion at this temperature is surprising. Clearly, coordination
of the ligand to a metal center will influence this reactivity,
but observation of such species is frustrated by the para-
magnetism of the Cr(I) or Cr(III) precatalysts. As a model
reaction, treatment of [Cr(CO)4(dppm)] with 300 equiv of
MAO in toluene was carried out. Again, the ligand of the
complex is remarkably robust, and only after 30 min at 60 °C
is any decomposition observed, interestingly to the same
species at δ -7.1, suggesting ligand decomplexation. These
studies, although not conclusive, point to deprotonation
under catalytic conditions being surprisingly difficult; a
simple steric influence from backbone substitution may be
a better explanation for the improved performance of these
new catalysts.
121 MHz (31P{1H}), a JEOL delta 400 at 200.6 MHz
(13C{1H}), and a JEOL lambda 300 at 282 MHz (19F), in
1
deuterated solvent. H and 13C{1H} NMR spectra are refer-
enced with chemical shifts relative to high frequency of residual
solvent, 31P NMR spectra are referenced relative to high fre-
quency of 85% H3PO4 and 19F NMR spectra are referenced
relative to high frequency of CCl3F. Mass spectrometry was
carried out by the Mass Spectrometry Service at the School
of Chemistry at the University of Bristol. Microanalyses were
carried out by the Microanalytical Laboratory of the
School of Chemistry at the University of Bristol. Complex 10
was synthesized in an analogous method to that previously
reported.8a
Synthesis of 2-4. The same general method was followed in
each case and is described here for 2.
[Cr(CO)4(dppm)] (0.50 g; 0.91 mmol) and N,N,N0,N0-tetra-
methylethylenediamine (0.21 mL; 1.37 mmol) were stirred in
benzene (20 mL), giving a clear yellow solution. To this stirred
solution was added dropwise nBuLi (1.6 M in hexanes; 0.86 mL;
1.37 mmol) at ambient temperature. After 1 h, methyl iodide
(0.11 mL; 1.82 mmol) was added and the solution was stirred for
4 h at 60 °C. On cooling, degassed water (20 mL) was added and
the solution stirred, then left to separate. The organic layer was
collected and dried (MgSO4) and the solvent removed in vacuo to
give a yellow solid (0.21 g; 0.37 mmol; 41%). Crystals suitable
for X-ray diffraction study were obtained from a concentrated
dichloromethane solution cooled to -30 °C.
Conclusions
We have synthesized new ethene trimerization- and tetra-
merization-active catalysts based on chromium complexes of
C-substituted dppm ligands. Our synthetic route can be
thought of as a particularly efficient protecting group strat-
egy in which potentially reactive phosphorus(III) centers are
protected by complexation to the oligomerization-active
metal, chromium. Performance is enhanced compared to
unsubstituted dppm catalysts, tentatively attributed to in-
creased stability against deprotonation and decomplexation
during catalysis, but still falls well short of the outstanding
performance demonstrated by N,N-bis(diarylphosphino)-
amine catalysts.
Characterizing data for 2: 1H NMR (CDCl3, 300 MHz) δ
1.11-1.24 (td, 3H, JP-H=13.8 Hz, JH-H=7.8 Hz, CH3), 4.75
(m, 1H, CH), 7.33 - 7.60 (m, 20H, ArH); 31P NMR (CDCl3) δ
46.95; 13C NMR (CDCl3) δ 15.57 (s, CH3), 53.94 (t, JCP=16.4
Hz, CH), 128.48 (d, JCP =4.6 Hz), 128.85, 130.14, 130.52 (s,
CH), 131.33 (t, JCP=5.7 Hz, CH), 134.14 (t, JCP=6.7 Hz, CP);
IR (CH2Cl2) ν 1877 (CtO), 1894 (CtO), 1917 (CtO), 2007
(CtO) cm-1; MS (ESI, CH2Cl2) m/z 562.0 (Mþ). Anal. Calcd
for C30H24CrO4P2: C 64.06, H 4.30. Found: C 63.98, H 4.84.
E
1/2: 0.68 V vs SCE.
Characterizing data for 3: 1H NMR (CDCl3, 300 MHz) δ 0.76
(t, 3H, J=6.99 Hz, CH3), 0.96 (m, 4H, CH2CH2CH3), 1.10 (m,
4H, CH(CH2CH2CH2-CH2CH2CH3)), 1.51 (dt, 2H, J=6.48,
21.36 Hz, CH(CH2)), 4.60 (m, 1H, CH(n-hexyl)), 7.33-7.58 (m,
20H, ArH) ; 31P NMR (CDCl3) δ 48.84; 13C NMR (CDCl3) δ
1.12 (s, CH3), 14.01, 22.46, 28.82, 29.35, 31.34 (s, CH2), 60.31 (t,
Experimental Section
General Procedures. All procedures were carried out under an
inert (N2) atmosphere using standard Schlenk line techniques or
in an inert atmosphere (Ar) glovebox. Chemicals were obtained
from Sigma Aldrich or Fisher Scientific and used without
further purification unless otherwise stated. Modified methyl
aluminoxane (MMAO) was obtained from Akzo-Nobel as a 7
wt % solution in hexane. All solvents were purified using an
Anhydrous Engineering Grubbs-type solvent system. Infrared
spectra were recorded on a Perkin-Elmer 1600 series FTIR
spectrometer in dichloromethane. NMR spectra were recorded
on a JEOL ECP 300 spectrometer at 300 MHz (1H) and
J
CP = 16.5 Hz CH), 128.65 (d, JCP = 21.3 Hz, CH), 130.06,
130.52, 131.36, (s, CH) 132.81 (t, JCP=11 Hz CH), 134.08 (s,
CP); IR (CH2Cl2) ν 1876 (CtO), 1892 (CtO), 1917 (CtO),
2005 (CtO) cm-1; MS (ESI, CH2Cl2) m/z 632.0 (Mþ). Anal.
Calcd for C35H34CrO4P2: C 66.45, H 5.42. Found: C 66.56, H
4.87. E1/2: 0.69 V vs SCE.
Characterizing data for 4: 1H NMR (CDCl3, 300 MHz) δ 2.87
(m, 2H, CH2), 4.96 (m, 1H, CH), 6.60 (m, 2H, o-BzH), 7.12 (m,
3H, m/p-BzH), 7.29-7.55 (m, 20H, ArH); 31P NMR (CDCl3) δ
51.62; 13C NMR (CDCl3) δ 36.00 (s, CH2), 61.98 (t, JCP=12.7
Hz, CH), 126.91, 128.44, 128.48, 128.53, 128.57, 128.68 (s, Bz
CH), 128.75 (d, JCP=4.6 Hz, CH), 128.83 (d, JCP=4.6 Hz, CH),
€
(10) Schmidbaur, H; Laureschlager, S; Muller, G. J. Organomet.
€
Chem. 1985, 281, 33.

4616 Organometallics, Vol. 28, No. 15, 2009
Dulai et al.
130.10, 130.60 (s, CH), 131.78 (t, JCP=6.1 Hz, CH), 134.19, (d,
SMART CCD three-circle diffractometer with Mo KR
˚
J
CP=12.1 Hz, CP); IR (CH2Cl2) ν 1877 (CtO), 1894 (CtO),
radiation (λ = 0.71073 A). The hydrogen atom on C25 was
1918 (CtO), 2006 (CtO) cm-1; MS (ESI, CH2Cl2) m/z 638.0
(Mþ). Anal. Calcd for C36H28CrO4P2: C 67.71, H 4.42. Found:
C 67.70, H 4.62. E1/2: 0.79 V vs SCE.
located in the electron density difference map and refined
isotropically, whereas all others were assigned ideal geometries.
Crystal data for 2: C30H24CrO4P2, M=562.43, orthorhombic
˚
˚
Synthesis of 5-7. The same general method was followed in
each case and is described here for 5.
space group Pbca, a = 15.8426(9) A, b = 16.7783(10) A, c =
3
˚
˚
20.2915(12) A, U=5393.7(5) A , T=173(2) K, Z=8, μ(Mo
KR) = 1.385 mm-1, 55 001 reflections measured, 6227 unique
(Rint=0.0932), which were used in all calculations. The final R1
[I > 2σ(I)] was 0.0453.
A Schlenk flask was charged with 2 (0.12 g, 0.213 mmol), and
dichloromethane (15 mL) was added. Ag[Al(OC4F9)4] (0.23 g,
0.213 mmol) was added to the solution, and an immediate color
change to deep purple was observed. The mixture was stirred at
ambient temperature for 1 h, after which a second equivalent of
Ag[Al(OC4F9)4] was added and the mixture stirred overnight.
The solution was then filtered, and the solvent was removed in
vacuo. The resultant purple solid was washed with hexane (2 ꢀ
10 mL) and dried in vacuo (0.26 g; 0.170 mmol; 79.8%).
Characterizing Data for 5: 19F NMR (CDCl3, 282 MHz) δ -
75.2 (s, ν1/2 = 16.5 Hz); IR (CH2Cl2) ν = 1966 (CtO), 2011
(CtO), 2043 (CtO), 2088 (CtO) cm-1; MS (ESI nanospray,
positive and negative mode, CH2Cl2) m/z 562.0 (Mþ), 966.9
(A-); trace amounts of residual silver salts meant that satisfac-
tory elemental analysis could not be obtained.
Ethene Oligomerization Runs. Ethene oligomerization was
carried out in a 300 mL stainless steel reactor with mechanical
stirring. The oven-dried vessel was purged with N2 followed by
ethene, charged with diluent (90 mL), and heated to the required
run temperature. The catalyst solution was prepared by dissol-
ving the required amount of catalyst in diluent (10 mL) and
adding the required amount of trialkylaluminum (AlR3) or
MMAO. The solution was injected into the prepared autoclave,
and the reactor was immediately charged with the required
pressue of ethene and maintained at this pressure for the
duration of the reaction. After the run time, the reactor was
cooled in an ice bath, the excess ethene was bled, and an internal
standard was added (nonane, 1000 μL). After quenching with
MeOH followed by 10% HCl, the organic phase was analyzed
by GC, and the white solids were filtered, washed, dried, and
weighed.
Characterizing data for 6: 19F NMR (CDCl3, 282 MHz) δ -
75.2 (s, ν1/2=15.5 Hz); IR (CH2Cl2) ν 1964 (CtO), 2010 (CtO),
2043 (CtO), 2088 (CtO) cm-1; MS (ESI nanospray, positive
and negative mode, CH2Cl2) m/z 632.0 (Mþ), 966.9 (A-). Anal.
Calcd for C51H34AlCrF36O8P2: C 38.29, H 2.14. Found: C
38.22, H 2.85.
Acknowledgment. We would like to thank Sasol Tech-
nology (Pty) Ltd and the Univeristy of Bristol for fund-
ing. Paul Pringle (University of Bristol), Kevin Blann and
Johntho Dixon (both Sasol) are thanked for useful dis-
cussions.
Characterizing data for 7: 19F NMR (CDCl3 282 MHz) δ -
75.2 (s, ν1/2=17.1 Hz); IR (CH2Cl2) ν 1966 (CtO), 2011 (CtO),
2043 (CtO), 2089 (CtO) cm-1; MS (ESI nanospray, positive
and negative mode, CH2Cl2) m/z 638.0 (Mþ), 966.8 (A-); trace
amounts of residual silver salts meant that satisfactory elemen-
tal analysis could not be obtained.
Crystallographic Details. A single crystal of 2 was mounted in
inert oil and transferred to the cold gas stream of the diffract-
ometer. X-ray measurements were made for 2 using a Bruker
Supporting Information Available: Crystallographic data as a
CIF file. This material is available free of charge via the Internet
at http://pubs.acs.org.