N, N′-bis(diphenylphosphino)diaminophenylphosphine ligands for chromium-catalyzed selective ethylene oligomerization reactions

Article abstract of DOI:10.1021/om100912y

Reaction of 1 or 2 equiv of Ph₂PCl with PhP(N(H)R)₂ (R = n-propyl) yields Ph₂PN(R)P(Ph)N(R)H (1) or Ph ₂PN(R)P(Ph)N(R)PPh₂ (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph₂PCl with PhP(N(H)R)₂ (R = isopropyl) yields exclusively Ph₂PN(R)P(Ph)N(R)H (3), even under more forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph₂PN(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N-H???P interaction of 2.95 A, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)₆] yields [Cr(3)(CO)₄] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its conversion to Ph₂PN(iPr)P(Ph)N(iPr)PPh₂ (4) while bound to chromium, yielding the complex [Cr(4)(CO)₄] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ with [Cr(acac)₃] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when activated with Ag[Al(OC₄F ₉)₄] and triethylaluminum, are moderately active and selective catalysts for the selective oligomerization of ethene to 1-hexene and 1-octene.

Full text of DOI:10.1021/om100912y

Organometallics 2011, 30, 935–941 935
DOI: 10.1021/om100912y
N,N0-Bis(diphenylphosphino)diaminophenylphosphine Ligands for
Chromium-Catalyzed Selective Ethylene Oligomerization Reactions
Arminderjit Dulai,† Claire L. McMullin,† Kenny Tenza,‡ and Duncan F. Wass*,†
†School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K., and ‡R&D Division,
Sasol Technology (Pty) Ltd., 1 Klasie Havenga Road, Sasolburg 1947, South Africa
Received September 22, 2010
Reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = n-propyl) yields Ph2PN(R)P(Ph)N-
(R)H (1) or Ph2PN(R)P(Ph)N(R)PPh2 (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph2PCl
with PhP(N(H)R)2 (R = isopropyl) yields exclusively Ph2PN(R)P(Ph)N(R)H (3), even under more
forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph2PN-
(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N-H P interaction of 2.95
A, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)6] yields
3 3 3
˚
[Cr(3)(CO)4] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its
conversion to Ph2PN(iPr)P(Ph)N(iPr)PPh2 (4) while bound to chromium, yielding the complex
[Cr(4)(CO)4] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ
with [Cr(acac)3] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when
activated with Ag[Al(OC4F9)4] and triethylaluminum, are moderately active and selective catalysts for
the selective oligomerization of ethene to 1-hexene and 1-octene.
Introduction
that relatively minor changes to ligand structure and reaction
conditions can lead to ethylene tetramerization rather than tri-
merization.4 A wider variety of diphosphine ligands has subse-
quently been investigated for these reactions with mixed results.
Carbon-backboned diphosphines of the type 1,2-bis(diphenyl-
phosphino)benzene5 and Ph2PCH(R)PPh2 (R = alkyl group)
have shown some promise.6 However, in general, nitrogen-
based backbone groups give the best results, including deriva-
tives of the original N,N-bis(diarylphosphino)amines (“PNP”)
and N,N0-bis(diarylphosphino)hydrazines (“PNNP”). The rea-
sons for this are yet to be fully defined, although in the case of
PNP ligands delocalization of the nitrogen lone pair over the
entire PNP chelate could be significant. We were interested in
extending this series, not least to explore the role of increasing
bite angle on catalysis. Longer chain phosphazane ligands
such as N,N0-bis(diarylphosphino)diaminoarylphosphine
(“PNPNP”) are known and show some interesting coordina-
tion chemistry,7 but their application in chromium-catalyzed
ethylene oligomerization has been unexplored.8 The synthesis
and catalytic screening of such complexes are reported here.
Catalysts capable of the selective trimerization or tetra-
merization of ethylene to 1-hexene or 1-octene via a distinctive
metallacyclic mechanism have revolutionized olefin oliogmeri-
zation.1 In 2002, we reported catalysts based on chromium
complexes of ligands of the type Ar2PN(Me)PAr2 (Ar =
o-methoxy-substituted aryl group) with productivity figures
over 1 order of magnitude better than for previous systems for
selective ethylene trimerization.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 which demonstrated
*To whom correspondence should be addressed. 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) McGuinness,
D. S.; Overett, M.; Tooze, R. P.; Blann, K.; Dixon, J. T.; Slawin, A. M. Z.
Organometallics 2007, 26, 1108. Hey, T. W.; Wass, D. F. Organometallics
2010, 29 (16), 3676. Bowen, L. E.; Charernsuk, M.; Hey, T. W.; McMullin,
C. L.; Orpen, A. G.; Wass, D. F. Dalton Trans. 2010, 39, 560.
(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) Dulai, A.; de Bod, H.; Hanton, M. J.; Smith, D. M.; Downing, S.;
Mansell, S. M.; Wass, D. F. Organometallics 2009, 28, 4613.
(7) Appleby, T.; Woollins, J. D. Coord. Chem. Rev. 2002, 235, 121.
€
(8) Ligands with a “PNPN” framework have been disclosed: Muller,
€
€
€
B. H., Fritz, P. M.; Bolt, H.; Wohl, A.; Muller, W.; Winkler, F.;
Wellenhofer, A.; Rosenthal, U.; Hapke, M.; Peulecke, N.; Al-Hazmi,
M. H.; Aliyev, O. V.; Mosa, M. F. PCT Pat. Appl. WO09006979, 2009.
Peitz, S.; Peulecke, N.; Aluri, B. R.; Hansen, S.; M€uller, B. H.; Spannenberg,
€
(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.
A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.; Wohl, A.; M€uller, W. Eur.
J. Inorg. Chem. 2010, 1167. Peitz, S.; Peulecke, N.; Aluri, B. R.; Mueller,
B. H.; Spannenberg, A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.;
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r
2011 American Chemical Society
Published on Web 02/16/2011
pubs.acs.org/Organometallics

936 Organometallics, Vol. 30, No. 5, 2011
Dulai et al.
Scheme 1. Synthesis of 1-3 and Attempted Synthesis of 4
Figure 1. Variable-temperature 31P NMR spectra of 3.
Results and Discussion
energy unique structures from this conformer search were then
optimized using density functional theory calculations (B3LYP/
6-31G*)11 to improve the predicted energetic ranking for each
isomer. Two of the eight optimized conformer geometries were
identical; the remaining seven geometries were labeled 3a-g
and evaluated further; we focus here on the three lowest energy
conformers, and structural data for all are available in the
Supporting Information.
We focused on the synthesis of Ph2PN(R)P(Ph)N(R)PPh2
(R = n-propyl, isopropyl), using a methodology based on
that reported by Keat and co-workers9 for other derivatives
(R=methyl, ethyl). This involves the initial synthesis of PhP-
(N(H)R)2 from PhPCl2 and 2 equiv of the desired primary
amine, followed by further reaction with 1 equiv of Ph2PCl
in the presence of triethylamine to yield Ph2PN(R)P(Ph)N-
(R)H or further reaction with 2 equiv of Ph2PCl in the
presence of triethylamine to yield Ph2PN(R)P(Ph)N(R)PPh2
(Scheme 1).
The two lowest energy conformers (3a,b) are not preor-
ganized for transition-metal complexation and have the lone
pairs of the phosphorus atoms (P1 and P2) pointing in
opposite directions; coordination as a chelate would require
rotation about the P1-N1 bond. In conformer 3a, the
terminal nitrogen atom, N2, has a very planar geometry,
with the angles around N2 totaling 349.5°. Inversion of this
planar N2 and subsequent rotation of the isopropyl group
about the N2-C1 bond gives rise to conformer 3b, which has
a slightly more pyramidal geometry around N2, with a
smaller sum of angles around N2 at 344.0°. The extra
stabilization of 3a might arise from an anomeric effect,12
where the lone pair (from a p orbital) of N2 delocalizes into
the antibonding σ* (P1-N1) orbital, while in 3b the lone pair
(sp3 hybridized orbital) of N2 has poorer overlap with the
antibonding orbital and a higher relative energy (by 2.5 kcal
mol-1). Due to the different N2 hybridization environments
and energy differences between conformers 3a,b, we suggest
that these might be seen as two distinct conformers, which
would give rise to different peak splittings in a 31P NMR
spectrum.
This sequence proceeded smoothly when R = n-propyl to
give 1 and 2, albeit in poor to moderate (12 and 30%) yields.
In contrast, when R = isopropyl, reaction with 1 or 2 equiv
of Ph2PCl gives only 3 in both cases. We reasoned that more
forcing conditions might be needed to obtain the more bulky
PNPNP compound 4 in this case, but 3 persists as the only
product even with a 10-fold excess of Ph2PCl, with more
n
potent bases (MeLi, BuLi, DBU), over extended reaction
times (72 h), or at higher temperature (reflux in 1,1,2,2-
tetrachloroethane). 31P NMR spectroscopy also revealed
differences between these derivatives; whereas 1 gives the
expected pattern of two sets of sharp doublets (at 48.6 and
88.6 ppm) at room temperature, 3 gives a rather broad
spectrum with two singlets (at 41.2 and 68.4 ppm). This is
presumably due to the bulkier isopropyl groups causing
restricted rotation about the P-N bonds, and in order to
examine this further, the 31P NMR spectra of 3 at lower
temperatures were recorded (Figure 1).
To our surprise, when the sample is cooled, the expected
pattern of two doublets is not observed; six doublets are
observed, suggesting that there are three species present,
each with two inequivalent phosphorus atoms. We specu-
lated that these three species originate from different con-
formers of 3, which interconvert on the NMR time scale at
room temperature. Similar behavior is known for related
systems; in a study of bis(isopropylamino)phenylphosphine,
Eichorn and co-workers used ab initio calculations to deter-
mine its four lowest energy conformers.10 In order to further
examine the results of the variable-temperature NMR experi-
ment, a molecular mechanics conformer search was carried out
on the free ligand with geometry taken from the crystal structure
of the chromium(0) complex 5 (see Figure 3). The eight lowest
Conformer 3c (also seen in Figure 2) has the same geo-
metry as seen in the crystal structure for the complexed
ligand (5 0.5CH2Cl2), with the lone pairs of each phos-
3
phorus atom pointing toward one another, ready for
complexation.
An interesting feature of conformations 3a,b is the close
˚
proximity of H1 to P2. The distances (2.95 and 2.82 A) are
significantly shorter for these conformers compared to those
˚
for the conformers 3c-g (∼4.5 A). As can be seen in Figure 2,
the orientation of conformers 3a,b suggests the amine proton
(11) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (b) Lee, C.;
Yang, W.; Parr, B. G. Phys. Rev. B 1988, 37, 785–789. (c) Vosko, S. H.;
Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200–1211. (d) Stephens,
P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem.
1994, 98, 11623–11627.
(9) Keat, R.; Sim, W.; Payne, D. S. J. Chem. Soc. A 1970, 2715.
€
(10) Eichhorn, B.; Noth, H.; Seifert, T. Eur. J. Inorg. Chem. 1999,
2355.
(12) Belyakov, A. V.; Haaland, A.; Shorokhov, D. J.; Sokolov, V. I.;
Swang, O. J. Mol. Struct. 1998, 445, 303–309.

Article
Organometallics, Vol. 30, No. 5, 2011 937
Figure 2. Geometries of ligand 3 suggested by conformer analysis as the three observed isomers at low temperature NMR, with
hydrogens (except for H1 and H2) omitted for clarity. Relative energies are given in kcal mol-1
.
Scheme 2. Synthesis of 5 and 6
Figure 3. Thermal ellipsoid plot of 5 0.5 CH2Cl2. Ellipsoids are
3
drawn at the 50% probability level. All hydrogen atoms and the
solvate have been omitted for clarity.
˚
Table 1. Key Bond Lengths (A) and Angles (deg) for 5 0.5CH2Cl2
3
H1 is sterically shielded by the neighboring isopropyl group
and the phenyl ring of the adjacent phosphorus atom,
potentially making it less accessible. This may help to explain
why reaction of 3 with another 1 equiv of Ph2PCl to yield 4
proved so difficult.
Cr1-P1
Cr1-P2
2.3592(6)
2.3380(7)
P1-N2
P1-N1
P2-N1
1.648(2)
1.719(2)
1.6932(19)
P1-Cr1-P2
67.95(2)
P1-N1-P2
100.57(10)
A potential solution to these synthetic challenges pre-
sented itself by exploiting a metal templating strategy. We
hypothesized that coordination of 3 in a chelating fashion to
a transition metal would not allow a conformation in this ligand
akin to that of 3a,b but rather would reduce the steric shield-
ing of H1, making it potentially reactive. We have previously
used coordination of diphosphines to [Cr(CO)4] fragments
as a “protection” strategy in the synthesis of C-substituted
bis(diphenylphosphino)methane derivatives;6 this has a number
of advantages, including ease of synthesis of the complexes, the
utility of [(diphosphine)Cr(CO)4] complexes as model com-
pounds in which steric and electronic factors can be probed,
and, perhaps most importantly, the fact that such complexes
are precatalysts for selective oligomerization catalysis via a one-
electron-oxidation method.13
concentrated CH2Cl2 solution of the complex at -20 °C, and
the complex crystallized in the space group Pbca. The molecular
structure of 5 is shown in Figure 3, with key bond lengths and
angles being given in Table 1. Ligand 3 coordinates through the
two phosphorus atoms to the octahedral chromium(0) metal
center in a fashion similar to that for known PNP chelates. It
has a bite angle, P1-Cr1-P2, of 67.95(2)°; the bite angle in the
complex [Cr(CO)4(Ar2PN(Me)PAr2)] is 68.44(3)°, where Ar
is C6H4(o-OMe).11b In this sense the ligand can be seen as a
simple asymmetric PNP ligand. The fold angle between the
P1-Cr1-P2 plane and the P1-N1-P2 plane is 8.11(1)°,
making the P1-Cr1-P2-N1 ring close to planar. The central
carbon (C1) of the isopropyl substituent at N1 lies close to this
˚
plane; C1 is only 0.196(4) A above the P1-N1-P2 plane. The
˚
P-N bonds in the chelate ring (P1-N1 = 1.719(2) A and
i
Complex 5 was obtained by the reaction of 3 with chro-
mium hexacarbonyl (Scheme 2).14 The expected 31P NMR
spectrum is obtained with two sharp doublets, both shifted
downfield compared to the free ligand, indicating rotation
around the P-N bond is now frozen on the NMR time scale.
˚
P2-N1 = 1.6932(19) A) are slightly longer than the P1-NH Pr
bond (P1-N2 = 1.648(2) A) due to the more planar nature of
the bridging nitrogen atom (N1).
˚
With compound 5 in hand, we were satisfied to observe
that reaction with Ph2PCl in the presence of MeLi
base proceeded smoothly to give the PNPNP ligand
complex [(4)Cr(CO)4] (6) in good yield (51%) (Scheme 2).
Simultaneous rearrangement gives a product in which the
newly formed PNPNP ligand 4 coordinates through its
terminal phosphorus atoms, as determined from its 31P
NMR spectrum, which displays the expected doublet and
triplet.
Crystals of complex 5 0.5CH2Cl2 suitable for X-ray dif-
3
fraction study were grown by slow diffusion of hexane into a
(13) (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.
(14) (a) Balakrishna, M. S.; Prakasha, T. K.; Krishnamurthy, S. S.;
Siriwardane, U.; Hosmane, N. S. J. Organomet. Chem. 1990, 390, 203.
(b) Compound 5 was recently independently reported: Aluri, B. R.;
Peulecke, N.; Peitz, S.; Spannenberg, A.; Mueller, B. H.; Schulz, S.;
Drexler, H.-J.; Heller, D.; Al-Hazmi, M. H.; Mosa, F. M.; Woehl, A.;
Mueller, W.; Rosenthal, U. Dalton Trans. 2010, 39, 7911.
Crystals of complex 6 2.5CH2Cl2 suitable for X-ray dif-
3
fraction study were grown by slow diffusion of hexane into a
concentrated CH2Cl2 solution of the complex at -20 °C, and
the complex crystallized in space group P21/c. The molecular

938 Organometallics, Vol. 30, No. 5, 2011
Dulai et al.
structure of complex 6 is shown in Figure 4. Key bond
lengths and angles are summarized in Table 2.
(pressure, temperature, activation method), and we attribute
this surprising difference to the slightly different conditions
employed. Comparison of runs 3 and 4, in which the same
ligand 3 is tested using different activation methods, shows
that MMAO activation of an in situ formed chromium
complex (run 3) gives a higher productivity value; a similar
trend is observed for PNP complex activation.13 Within
error, the selectivity is not influenced, suggesting that the
same active species is formed with either method. The
PNPNP ligand 2 and complex 6 (runs 2 and 5) yield catalysts
with productivity values similar to those for these other
systems. However, there is a marked influence on selectivity
with the N-n-propyl substituted system 2 (run 2) favoring
1-hexene over 1-octene (60.0% to 31.3%) and the N-isopro-
pyl-substituted system 6 (run 5) favoring 1-octene over
1-hexene (57.1% to 28.6%). Although we necessarily need
to use different activation methods for these derivatives and
cannot completely rule this out as the source of the observed
difference in selectivity, the previous comparison of runs 3
and 4 in terms of selectivity gives us confidence this is a
ligand-based structure-property relationship. The perfor-
mance of these PNPNP ligands does not match that of the
related PNP ligands (for example, Ph2PN(iPr)PPh2 tested
under similar conditions3g gives a productivity of 139 800
g/((g of Cr) h) and over 70% selectivity to octene), suggesting
that smaller bite angles are to be preferred. However, it is
perhaps surprising that PNPNP still outperforms many
carbon-backboned diphosphine ligands which initially seem
to be closer analogues of the PNP ligands (for example, bis-
(diphenylphosphino)methane or bis(diphenylphosphino)-
ethane).6
The structure of 6 has approximate mirror symmetry
through the Cr1-P2 plane and bisecting the six-membered
chelate ring, with a bite angle of 93.20(4)°. The chelate ring
has a “boat-like” conformation, with Cr1 and P2 sitting
˚
above the P1-N1-N2-P3 plane by 0.530(4) and 0.687(6) A,
respectively.
Complexes 5 and 6 were investigated by cyclic voltamme-
try to ensure that the chromium(I) analogues of these com-
plexes could be accessed using Ag[Al(OC(CF3)3)4]. Values
for E1/2 of 0.75 and 0.72 V, respectively, at a scan rate of 250
mV s-1 versus a saturated calomel electrode (SCE) indicate
that this is the case.
Ligands 1-3 and complexes 5 and 6 were all screened for
ethylene oligomerization using established methods. The
ligands were tested in conjunction with chromium tris-
(acetylacetonate) as the chromium source and MMAO as
the activator;2-5 the complexes were used in conjunction
with Ag[Al(OC(CF3)3)4] as an in situ oxidizing agent and
TEA as a carbonyl scavenger.13 Results of the screening are
summarized in Table 3.
Ligands 1 and 3 (runs 1 and 3), with a PNPN structure,
give moderately productive catalysts that have good selec-
tivity to 1-hexene and 1-octene.8 Interestingly, for ligand 3
we observed more octene than hexene, in contrast to litera-
ture reports of high 1-hexene selectivity for this particular
derivative. Selective olefin oligomerization catalysts are
known to be highly sensitive to reaction conditions
Conclusions
We have synthesized Ph2PN(R)P(Ph)N(R)H (R = nPr, iPr)
and Ph2PN(R)P(Ph)N(R)PPh2 (R = nPr). Low-temperature
NMR spectroscopy and a conformational analysis of the latter
compound revealed the lowest energy conformer to have a close
˚
N-H P interaction of 2.95 A, which may explain the lack of
3 3 3
further reactivity of this molecule. This problem was overcome
by coordination of the ligand to chromium, allowing its con-
version to Ph2PN(iPr)P(Ph)N(iPr)PPh2 while bound to the
metal. The ligands and complexes are moderately active and
selective catalysts for the selective oligomerization of ethene to
1-hexene and 1-octene.
Figure 4. Thermal ellipsoid plot of 6 2.5CH2Cl2. Ellipsoids are
3
drawn at the 50% probability level. All hydrogen atoms and the
solvate have been omitted for clarity.
˚
Table 2. Key Bond Lengths (A) and Angles (deg) for 6 2.5CH2Cl2
3
Experimental Section
Cr1-P1
Cr1-P3
N1-C13
N2-C22
2.3792(12)
2.3797(13)
1.522(6)
P1-N1
P2-N1
P2-N2
P3-N2
1.710(4)
1.721(4)
1.715(4)
1.710(3)
General Considerations. 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
1.517(5)
P1-Cr1-P3
N1-P2-N2
P1-N1-P2
93.20(4)
107.50(16)
125.8(2)
P2-N2-P3
N1-P1-Cr1
N2-P3-Cr1
126.2(2)
119.15(13)
119.58(13)
Table 3. Ethylene Oligomerization Results
oligomers (wt % of total products)
run
cat.
productivity (g/((g of Cr) h))
polymer (%)
C4
C6 (1-C6)
C8 (1-C8)
C10þ
1a
2a
3a
4b
5b
1
2
3
5
6
6 460
34 100
78 930
45 060
37 850
2.7
2.9
2.2
2.0
1.0
6.2
3.1
5.4
4.7
6.1
34.6 (89.9)
60.0 (89.6)
34.3 (96.7)
37.2 (96.4)
28.6 (91.9)
54.1 (99.2)
31.3 (98.2)
44.9 (99.5)
47.1 (99.8)
57.1 (99.4)
2.2
2.9
13.2
9.0
7.2
aRun conditions: 10 μmol of [Cr(acac)3], 20 μmol of ligand, chlorobenzene diluent, 20 bar of ethylene, 60 °C, 500 equiv of MMAO. bRun conditions:
10 μmol of complex, 20 μmol of Ag[AlO{OC(CF3)3)4], 300 equiv of TEA, chlorobenzene diluent, 20 bar of ethylene, 60 °C.

Article
Organometallics, Vol. 30, No. 5, 2011 939
methylaluminoxane (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. Infra-
red 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 121
MHz (31P{1H}), a JEOL Delta 400 at 200.6 MHz (13C{1H}), and
a JEOL Lambda 300 at 282 MHz (19F), in deuterated solvent.
1H and 13C{1H} NMR spectra are referenced with chemical
shifts relative to the high frequency of residual solvent, 31P
NMR spectra are referenced relative to the high frequency of
85% H3PO4, and 19F NMR spectra are referenced relative to
the high frequency of CCl3F. Mass spectrometry was carried
out by the Mass Spectrometry Service at the School of Chem-
istry at the University of Bristol. Microanalyses were carried
out by the Microanalytical Laboratory of the School of
Chemistry at the University of Bristol. Electrochemical studies
were carried out using an EG&G Model 273A potentiostat
linked to a computer using EG&G Model 270 Research
Electrochemistry software in conjunction with a three-elec-
trode cell. The working electrode was a platinum disk (1.6 mm
diameter) and the auxiliary electrode a platinum wire. The refer-
ence was an aqueous saturated calomel electrode separated from
the test solution by a fine-porosity frit and an agar bridge saturated
with KCl. Solutions were 1.0 mM in the test compound and 0.1 M
in [nBu4N][PF6] as the supporting electrolyte. The solvent used was
CH2Cl2. Under these conditions, E1/2 values for the one-electron
oxidation of [Fe(η5-C5H5)2] and [Fe(η5-C5(CH3)5)2] are 0.47 and
-0.08 V, respectively. In each experiment, one of these was added
to the test solutions as an internal calibrant.
Bis(isopropylamino)phenylphosphine. This was prepared using
a modification of the method of Eichhorn et al.10 Isopropylamine
(9.45 mL;6.50 g; 0.11 mol) was dissolved indiethylether (100 mL)
and cooled to 0 °C. Phenyldichlorophosphine (3.00 mL; 4.00 g;
0.02 mol) indiethyl ether (20mL) was added tothisdropwise over
10 min with stirring. A white precipitate formed almost immedi-
ately. The mixture was warmed to room temperature and stirred
for 16 h. It was then filtered and the solid washed with diethyl
ether (2 ꢀ 50 mL). The filtrate and washings were combined and
the solvents removed under reduced pressure to give the desired
compound as a viscous cream-colored liquid (3.70 g; 74%). 1H
NMR (CDCl3, 400 MHz): δ 1.17 (d, 6H, 3JH-H = 6.4 Hz, CH3),
1.21 (d, 6H, 3JH-H = 6.2 Hz, CH3), 2.01 (d, 2H, 2JP-H = 7.7 Hz,
NH), 3.30 (m, 2H, CH), 7.28 (m, 1H, ArH), 7.35 (m, 2H, ArH),
7.63 (m, 2H, ArH). 13C NMR (CDCl3, 100.5 MHz): δ 26.6
(d, 3JC-P = 5.8 Hz, CH3), 26.9 (d, 3JC-P = 2.9 Hz, CH3), 46.2
(d, 2JC-P =16.7Hz, CH), 127.7(s, CH), 128.0(d, JC-P = 3.5 Hz,
CH), 130.7 (d, 1JC-P = 15.6 Hz, CP), 141. Six (d, JC-P = 7.5 Hz,
CH). 31P NMR (CDCl3, 121 MHz): δ 58.5 (s). Anal. Calcd for
C12H21N2P: C, 64.26; H, 9.44; N, 12.49. Found: C, 65.78; H,
10.01; N, 12.23.
in CH2Cl2 (60 mL) and cooled to 0 °C. To this was added
dropwise a solution of bis(n-propylamino)phenylphosphine
(1.50 g; 6.70 mmol) and triethylamine (0.94 mL; 0.68 g; 6.7
mmol) over 10 min with stirring. The mixture was warmed to
room temperature and stirred for 3 h. The volatiles were
removed under reduced pressure, and diethyl ether (80 mL)
was added. The solution was then filtered, and the remaining
solid was washed with diethyl ether (2 ꢀ 30 mL). The washings
and filtrate were combined, and the solvent was removed under
reduced pressure to give a tacky, cream-colored solid. The solid
was triturated with hexane (50 mL), and the resulting cloudy
solution was passed through a column of neutral alumina. Re-
crystallization from hot ethanol afforded 1 as a white solid (0.32 g;
12%). 1H NMR (CDCl3, 400 MHz): δ 0.59 (t, 3H, 3JH-H = 7.3
Hz, CH3), 0.97 (t, 3H, 3JH-H = 7.4 Hz, CH3), 1.20 (m, 2H, CH2),
1.60 (m, 2H, CH2), 2.62 (m, 1H, NH), 3.09 (m, 2H, NCH2), 3.20
(m, 2H, NCH2), 7.37 (m, 10H, ArH), 7.46 (m, 3H, ArH), 7.55 (m,
2H, ArH). 13C NMR (CDCl3, 100.5 MHz): δ 11.4, 11.6 (s, CH3),
25.8 (d, 3JC-P = 4.6 Hz CH2), 26.5 (d, 3JC-P = 8.5 Hz, CH2), 48.5
(d, 2JC-P = 26.2 Hz, NCH2), 52.9 (d, 2JC-P = 21.3 Hz, NCH2),
129.1 (s, CH), 130.7 (d, JC-P = 16.9 Hz, CP), 131.8 (d, JC-P
=
=
19.2 Hz, CH), 133.6 (d, 1JC-P = 22.2 Hz, CP), 139.4 (d, JC-P
2.3 Hz, CH), 139. Six (d, JC-P = 2.3 Hz, CH), 140.4 (d, JC-P =4.6
Hz), 144.2 (d, 1JC-P = 7.9Hz, CH). 31PNMR(CDCl3, 121 MHz):
δ 88.6 (d, 2JP-P = 50.2 Hz, PPh), 48.6 (d, 2JP-P = 50.2 Hz, PPh2).
Anal. Calcd for C24H30N2P2: C, 70.57; H, 7.40; N, 6.86. Found: C,
70.32; H, 7.37; N, 6.82.
Ph2PN(nPr)PPhN(nPr)PPh2 (2). Chlorodiphenylphosphine
(2.78 mL; 3.39 g; 15.00 mmol) was dissolved in CH2Cl2 (60 mL)
and cooled to 0 °C. To this was added a solution of bis(n-propyl-
amino)phenylphosphine (1.68 g; 7.50 mmol) and triethylamine
(2.62 mL; 1.90 g; 19.00 mmol) in CH2Cl2 (20 mL). The solution
was warmed to room temperature and stirred for 3 h. After this time,
the volatiles were removed under reduced pressure and diethyl ether
(80 mL) was added. The mixture was filtered and the solid washed
with diethyl ether (2 ꢀ 30 mL). The filtrate and washings were
combined, and the solvent was removed under reduced pressure to
give a tacky, pale pink solid. This was triturated with hexane (40 mL)
and filtered. When the filtrate was cooled, a white solid was obtained
(1.30g;30%). 1HNMR(CDCl3, 400MHz):δ0.47 (t, 6H, 3JH-H
=
7.3 Hz, CH3), 1.07 (m, 2H, CH2), 1.41 (m, 2H, CH2), 2.83 (m, 2H,
NCH2), 3.23 (m, 2H, NCH2), 7.32 (m, 10H, ArH), 7.43 (m, 12H,
ArH), 7.59(m, 3H, ArH). 13CNMR(CDCl3, 100.5 MHz): δ11.1(s,
CH3),22.8(d,3JC-P =3.8HzCH2),25.3(d,3JC-P =3.6Hz,CH2),
53.2 (t, 2JC-P = 5 Hz, CH2), 53.4 (t, 2JC-P = 5 Hz, CH2), 128.0 (t,
JC-P=2.9 Hz, CH), 128.1 (t, JC-P=3.1 Hz, CH), 128.3 (d, JC-P
=
1.5 Hz, CH), 131.5 (d, 1JC-P=18.5 Hz, CP), 132.9 (t, JC-P=15.6
Hz, CH), 133.4 (t, JC-P=16.1 Hz, CP), 139.9 (d, JC-P=2.3 Hz,
CH), 140.6 (d, JC-P = 5.4 Hz, CH). 31P NMR (CDCl3, 121 MHz):
δ 106.3 (t, 2JP-P=24.2 Hz, PPh), 53.8 (d, 2JP-P = 24.5 Hz, PPh2).
Anal. Calcd for C36H39N2P3: C, 72.96; H, 6.63; N, 4.73. Found:
C, 72.74; H, 6.83; N, 4.67.
Bis(n-propylamino)phenylphosphine. This compound was pre-
pared as above using n-propylamine (11.20 mL; 8.00 g; 0.14 mol)
and phenyldichlorophosphine (4.10 mL; 5.40 g; 0.03 mol) to give
a viscous colorless liquid (3.20 g; 48%). 1H NMR (CDCl3, 400
Ph2PN(iPr)PPhN(iPr)H (3). This compound was synthesized
by the same method as for 1 using chlorodiphenylphosphine (1.29
mL; 1.58 g; 7.20 mmol), bis(isopropylamino)phenylphosphine (1.53
g; 6.8 mmol), and triethylamine (1.00 mL; 0.73 g; 7.20 mmol) in
CH2Cl2, The solvent was removed under reduced pressure to give a
colorless, highly viscous liquid. Recrystallization from hot ethanol
afforded 3 as a waxy, white solid (0.64 g; 23%). 1H NMR (CDCl3,
3
MHz): δ 0.95 (t, 6H, JH-H = 7.4 Hz, CH3), 1.55 (m, 4H,
CH2CH3), 2.22 (br, m, 2H, NH), 2.88 (m, 4H, NCH2), 7.29 (m,
1H, ArH), 7.37 (m, 2H, ArH), 7.63 (m, 2H, ArH). 13C NMR
(CDCl3, 100.5 MHz): δ 11.7 (s, CH3), 26.4 (d, 3JC-P = 5.4 Hz,
CH2CH3), 45.8 (d, 2JC-P = 11.5 Hz, NCH2), 128.1 (d, JC-P
=
3
400 MHz): δ 1.21 (d, 3H, JH-H = 6.6 Hz, CH3), 1.23 (d, 3H,
4.6, CH), 127.8 (s, CH), 130.7 (d, 1JC-P = 14.6 Hz, CP), 142.0
(d, JC-P = 6.2 Hz, CH). 31P NMR (CDCl3, 121 MHz): δ 65.7
(s); Anal. Calcd for C12H21N2P: C, 64.26; H, 9.44; N, 12.49.
Found: C, 64.70; H, 9.03; N, 11.88.
3JH-H =6.5Hz, CH3), 1.25(d, 3H, 3JH-H =6.5Hz, CH3), 1.29(d,
3H, 3JH-H = 6.4 Hz, CH3), 2.59 (br, dd, 1H, 2JP-H = 10.9 Hz,
3JH-H = 6.1 Hz, NH), 3.25 (m, 1H, CH), 3.58 (m, 1H, CH), 7.34
(m, 5H, ArH), 7.42 (m, 10H, ArH). 13C NMR (CDCl3, 100.5
MHz): δ25.2 (dd, 3JC-P=11.2 Hz, 3.5 Hz, CH3), 25.4(t, 3JC-P=6.1
Hz, CH3), 26.1 (d, 3JC-P=5.4 Hz, CH3), 26.2 (d, 3JC-P=6.2 Hz,
CH3), 46.9 (d, 2JC-P=28.4 Hz, CH), 50.2 (dd, 2JC-P=15.0 Hz, 5.0
Hz, CH), 130.7 (d, JC-P=17.7 Hz, CH), 132.8 (d, JC-P=19.9 Hz,
CP), 133.2 (d, JC-P = 2.3 Hz, CH), 133.4 (d, JC-P=1.5 Hz, CH),
139.7 (d, 1JC-P=16.9 Hz, CP), 141.2 (d, JC-P = 4.3 Hz, CH), 141.5
Ph2PN(nPr)PPhN(nPr)H (1). This compound was prepared
using a modification of the method of Maumela et al.15 Chloro-
diphenylphosphine (1.21 mL; 1.49 g; 6.70 mmol) was dissolved
(15) Maumela, M. C.; Blann, K.; de Bod, H.; Dixon, J. T.; Gabrielli,
W. F.; Williams, D. B. G. Synthesis 2007, 24, 3863.

940 Organometallics, Vol. 30, No. 5, 2011
Dulai et al.
(d, JC-P=3.8 Hz, CH), 144.9 (d, 1JC-P=6.9 Hz, CH). 31P NMR
(CDCl3,121MHz):δ68.4(brs,PPh),41.7(brs, PPh2). Anal. Calcd
for C24H30N2P2: C, 70.57; H, 7.40; N, 6.86. Found: C, 70.49; H,
7.25; N, 6.80.
Table 4. Crystallographic Data
5 0.5CH2Cl2
3
6 2.5CH2Cl2
3
color, habit
size/mm
empirical formula
Mr
cryst syst
yellow, plate
yellow, needle
0.08 ꢀ 0.05 ꢀ 0.01 0.20 ꢀ 0.06 ꢀ 0.02
[Cr(CO)4(3)] (5). Compound 3 (0.20 g; 0.34 mmol) and chro-
mium hexacarbonyl (0.15 g; 0.68 mmol) were dissolved in toluene
(30 mL). The mixture was heated at reflux for 72 h. It was then
cooled to room temperature and filtered, and the solvents were
removed under reduced pressure. The resulting crude product was
recrystallized from CH2Cl2 and hexane to give 5 as yellow plates
(0.14 g; 74%). 1H NMR (CDCl3, 400 MHz): δ 0.60 (d, 3H,
3JH-H = 6.6 Hz, CH3), 1.19 (d, 3H, 3JH-H = 6.8 Hz, CH3), 1.43
(d, 3H, 3JH-H = 6.2 Hz, CH3), 1.49 (d, 3H, 3JH-H =6.4 Hz, CH3),
3.64 (d, 1H, 2JP-H = 9.3 Hz, NH), 3.64 (m, 1H, CH), 4.12 (m, 1H,
CH), 7.41 (m, 3H, ArH), 7.48 (m, 3H, ArH), 7.58 (m, 5H, ArH),
7.64 (m, 2H, ArH), 7.89 (m, 2H, ArH). 13C NMR (CDCl3, 100.5
MHz): δ 20.9, 24.5 (s, CH3), 26.2 (d, 3JC-P = 3.8 Hz, CH3), 26.8 (d,
C28.5H31ClCrN2O4P2 C43H45Cl6CrN2O4P3
1229.89
orthorhombic
Pbca
1011.42
monoclinic
P21/c
space group
˚
a/A
15.4028(2)
17.6693(2)
21.5230(3)
90.0
9.5183(9)
26.520(2)
20.3442(19)
115.659(6)
4629.0(7)
4
˚
b/A
˚
c/A
β/deg
V/A3
Z
5857.63(1)
8
0.627
μ/mm-1
T/K
no. of rflns: total/indep 36 563/6725
6.553
100
74 266/7325
100
a
Rint
final R1
0.0582
0.0404
1.005, -0.450
1.395
2
3JC-P = 3.8 Hz, CH3), 47.7 (d, JC-P = 11.5 Hz, CH), 55.0
0.0516
0.659, -0.783
1.451
(t, 2JC-P = 6.3 Hz, CH), 128.3 (d, JC-P = 9.9 Hz, CH), 128.5 (d,
JC-P = 9.2 Hz, CH), 128.7 (d, JC-P = 10.0 Hz, CP), 130.0
(d, JC-P = 1.5 Hz, CH), 130.2 (d, JC-P = 2.3 Hz, CH), 130.7 (d,
-3
˚
largest peak, hole/e A
1
F
calcd/g cm-3
a Rσ = 0.0389.
JC-P = 3.1 Hz, CH), 131.23 (d, JC-P = 2.4 Hz, CH), 133.32 (d,
1JC-P = 14.6 Hz, CP). 31P NMR (CDCl3, 121 MHz): δ 102.2 (d,
2JP-P = 42.7 Hz, PPh), 121.2 (d, 2JP-P = 42.7 Hz, PPh2); Mass
spectrometry (EI, CH2Cl2): m/z 572.1 (Mþ). Anal. Calcd for
C28H32CrNO4P2: C, 58.33; H, 5.94; N, 4.86. Found: C, 58.65; H,
5.37; N, 4.65; IR (toluene): ν 1893 (CtO), 1919 (CtO), 1969
(CtO), 2006 cm-1 (CtO). E1/2 = 0.75 V vs SCE.
Crystallographic Details. X-ray diffraction experiments were
carried out at 100 K on a Bruker Kappa Apex II CCD
˚
diffractometer using Mo KR radiation (λ = 0.710 73 A) for
5 0.5CH2Cl2 and on a Bruker Microstar CCD diffractometer
˚
3
using Cu KR radiation (λ = 1.541 78 A) for 6 2.5CH2Cl2. Single
3
crystals were coated in inert oil and mounted on a glass fiber.
Intensities were integrated18 from several series of exposures in j
and ω calculated by the Apex II19 or Proteum II20 program after
unit cell determination. Absorption corrections were based on
equivalent reflections using SADABS,21 and structures were re-
fined against all Fo2 data with hydrogen atoms riding in calculated
positions using SHELXTL.22 Crystal structure and refinement
[Cr(CO)4(Ph2PN(iPr)P(Ph)N(iPr)PPh2)] (6). Compound 5
(0.06 g; 0.11 mmol) was dissolved in benzene (5 mL) to give a
clear yellow solution. To this was added dropwise MeLi (1.6 M in
diethyl ether; 0.07 mL; 0.11 mmol) over 10 min and the solution
stirred at room temperature for 30 min. Chlorodiphenylphosphine
(0.02 mL; 0.03 g; 0.11 mmol) was added and the solution stirred
at 60 °C for 4 h. The solution was then cooled to room temperature
and filtered, and the solvents were removed under reduced pressure.
The crude product was recrystallized from a 1:1 mixture of CH2Cl2
data are given in Table 4. The crystal used for 6 2.5CH2Cl2 was
3
nonmerohedrally twinned. The twin components of the diffraction
data were assigned using the Bruker program CELL_NOW23 and
corrected for absorption with TWINABS.24 Data completeness is
at 92% for this 1:1 twinned structure.
1
and hexane to give 6 as a yellow solid (0.04 g; 51%). H NMR
(CDCl3, 400 MHz): δ 0.80 (d, 6H, 3JH-H = 6.1 Hz, CH3), 1.78 (d,
6H, 3JH-H = 6.2 Hz, CH3), 4.18 (m, 2H, CH), 7.23 (m, 2H, ArH),
7.35 (m, 10H, ArH), 7.54 (m, 8H, ArH), 7.94 (m, 5H, ArH). 13
C
Both solvate structures exhibit static disorder for the half-
occupancy dichloromethane molecule to be 50%. For the dis-
ordered solvent in 6 2.5CH2Cl2 further restraints were applied
NMR (CDCl3, 100.5 MHz): δ 25.1 (d, 3JC-P = 6.2 Hz, CH3), 25.3
3
2
(d, JC-P = 22.2 Hz, CH3), 54.6 (t, JC-P = 3.8 Hz, CH), 54.9
(t, 2JC-P = 3.8 Hz, CH), 127.9 (t, JC-P = 4.6 Hz, CH), 128.4 (d,
JC-P = 3.8 Hz, CH), 128.5 (d, JC-P = 3.3 Hz, CH), 128.7 (d,
3
to the thermal ellipsoid parameters of the disordered central
carbon atom (C43a and C43b), to mimic the other dichloro-
methane carbons present in the model (C41 and C42). Nine low-
J
C-P = 3.1 Hz, CH), 128.8, 129.0 (s, CH), 130.1 (d, 1JC-P = 19.2
Hz, CP), 130.9(s, CH), 134.8 (br s, CH), 137.8 (d, 1JC-P =14.3Hz,
CP), 142.3 (t, JC-P = 6.5 Hz, CH), 145.9 (d, 1JC-P = 21.1 Hz, CP).
31P NMR (CDCl3, 121 MHz): δ 82.3 (t, 2JP-P = 31.4 Hz, PPh),
108.8 (d, 2JP-P = 33.4 Hz, PPh2). Anal. Calcd for C40H39CrN2-
angle reflections were omitted from 5 0.5CH2Cl2 and one from
6 2.5CH2Cl2.
3
3
Ethylene Oligomerization. Runs were carried out in a 300 mL
stainless steel Parr reactor with magnetic stirring. The oven-
dried vessel was purged with nitrogen, charged with chloro-
benzene (20 mL), and heated to the required temperature. The
catalyst solution was prepared by dissolving the required
amount of catalyst in chlorobenzene (5 mL) and adding the
required amount of triethylaluminum (AlEt3) in toluene or
MMAO in heptanes. The catalyst solution was injected into
the prepared autoclave, and the reactor was immediately
charged with the required pressure of ethylene and maintained
at this pressure for the duration of the reaction. After the run
O4P3 0.25CH2Cl2: C, 61.82; H, 5.45; N, 3.99. Found: C, 61.83; H,
3
5.61; N, 3.58. IR (toluene): ν 1837 (CtO), 1901 (CtO), 1925
(CtO), 2014 cm-1 (CtO). E1/2 = 0.72 V vs SCE.
Conformational Analysis of Ligand 3. A molecular mechanics
conformer search was carried out on the free ligand, using
geometry taken from the crystal structure of 5 0.5CH2Cl2, by
3
the PCModel program and forcefield MMX.16 The eight lowest
energy unique structures were taken from this search and
optimized using DFT calculations to improve the relative energy
ranking of each conformer, with the Jaguar program17 using the
standard hybridized functional B3LYP11 and basis-set combi-
nation 6-31G*. We note that the computational methodology
we have used here is quite simple, neglecting e.g. solvation and
dispersion effects, and that this may affect the relative energies
of the conformers of 3, but since we are mainly interested in
supporting the interpretation of NMR spectra here, we have not
pursued further method improvements.
(18) SAINT v7.34A; Bruker-AXS, Madison, WI, 2007.
(19) Apex2; Bruker-AXS, Madison, WI, 2007.
(20) Proteum2; Bruker-AXS, Madison, WI, 2007.
(21) Sheldrick, G. M. SADABS V2008/1; Bruker AXS, Madison,
WI, 2008.
(22) SHELXTL program system version V6.14; Bruker AXS, Madi-
son, WI, 2003.
(23) Sheldrick, G. M. CELL NOW V2008/2; Bruker AXS, Madison,
WI, 2008.
(24) Sheldrick, G. M. TWINABS V2008/2, Bruker AXS, Madison,
(16) PCModel v9.0; Serena Software, Bloomington, IN, 2004.
€
€
(17) Schrodinger, L. Jaguar 6.0; Schrodinger, LLC, New York, 2005.
WI, 2008.

Article
Organometallics, Vol. 30, No. 5, 2011 941
time, the reactor was cooled in an ice bath, the excess ethylene
was vented, and an internal standard was added (mesitylene,
50 μL). After quenching with 10% HCl, the organic phase was
separated, dried (MgSO4), and analyzed by GC. The white
solids were filtered, washed, dried, and weighed.
Supporting Information Available: CIF files, text, tables,
and a figure giving crystallographic data for 5 0.5CH2Cl2 and
3
6 2.5CH2Cl2 and Cartesian coordinates of the seven conformers
3
of 3. This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. We thank Sasol Technology (Pty)
Ltd, the CCDC, and the University of Bristol for funding.
Natalie Fey, Guy Orpen, and Paul Pringle (University of
Bristol) and Martin Hanton (Sasol) are thanked for
useful discussions.
Note Added after ASAP Publication. This paper was pub-
lished on the Web on Feb 16, 2011, and a pair of references to
work by Rosenthal et al. were omitted. These have now been
added to refs 8 and 14. The corrected version was reposted on
Mar 7, 2011.