Synthesis, characterisation, and polymerisation studies of hexamethylindenyl zirconocenes and hafnocenes

Article abstract of DOI:10.1016/j.jorganchem.2015.01.019

Abstract A family of group 4 metallocene complexes based on the hexamethylindenyl ligand (C₉Me₆H; Ind^#) have been prepared and fully characterised. The complexes rac-Ind^#₂ZrCl₂ (rac-1), meso-Ind^#₂ZrCl₂ (meso-1), rac-Ind^#₂HfCl₂ (rac-2), meso-Ind^#₂HfCl₂ (meso-2) were prepared by the reaction of Ind^#Li with the corresponding MCl₄ (where M = Zr, Hf); and rac-Ind^#₂Zr(CH₂Ph)₂ (rac-3) was derived from rac-1 using two equivalents of potassium benzyl (KCH₂Ph). All five species were characterised by NMR spectroscopy, single crystal X-ray diffraction and studied using density functional theory. The zirconocenes were tested for their activity as solution-phase ethylene polymerisation catalysts and rac-1 was found to outperform the meso-1 at most temperatures. The benzyl analogue, rac-3, peaked at more than double the activity reported for the dihalide species.

Full text of DOI:10.1016/j.jorganchem.2015.01.019

Accepted Manuscript
Synthesis, Characterisation, and Polymerization Studies of Hexamethylindenyl
Zirconocenes and Hafnocenes
Thomas A.Q. Arnold, Jean-Charles Buffet, Zoë R. Turner, Dermot O’Hare
PII:
S0022-328X(15)00042-X
10.1016/j.jorganchem.2015.01.019
JOM 18884
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 31 December 2014
Revised Date: 21 January 2015
Accepted Date: 22 January 2015
Please cite this article as: T.A.Q. Arnold, J.-C. Buffet, Z.R. Turner, D. O’Hare, Synthesis,
Characterisation, and Polymerization Studies of Hexamethylindenyl Zirconocenes and Hafnocenes,
Journal of Organometallic Chemistry (2015), doi: 10.1016/j.jorganchem.2015.01.019.
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ACCEPTED MANUSCRIPT
A family of group 4 metallocene complexes based on the hexamethylindenyl ligand (C9Me6H; Ind#)
have been prepared and fully characterised.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis, Characterisation and Olefin Polymerisation Studies of
Hexamethylindenyl Zirconocenes and Hafnocenes
Thomas A. Q. Arnold, Jean-Charles Buffet, Zoë R. Turner and Dermot O’Hare*
Chemistry Research Laboratory, Department of Chemistry, University of Oxford,
Mansfield Road, Oxford, OX1 3TA, UK.
*Corresponding author: Tel: +44(0) 1865 272 686. Fax +44 1865 272690
E-mail address: dermot.ohare@chem.ox.ac.uk (Dermot O’Hare)
Abstract
A family of group 4 metallocene complexes based on the hexamethylindenyl ligand
(C9Me6H; Ind#) have been prepared and fully characterised. The complexes rac-Ind2#
ZrCl2 (rac-
meso-
) were prepared by the reaction of Ind#Li with the corresponding MCl4
(where M = Zr, Hf). rac-Ind2#Zr(CH2Ph)2 (rac-
) was obtained by treatment of rac-1
1 1 2
), meso-Ind#2ZrCl2 (meso- ), rac-Ind2#HfCl2 (rac- ), meso-Ind2#HfCl2
(
2
3
with two equivalents of potassium benzyl (KCH2Ph). All five metallocenes were
characterised by NMR spectroscopy, single crystal X-ray diffraction and density
functional theory. The zirconocenes were tested for their activity as solution-phase
ethylene polymerisation catalysts. In the presence of an aluminoxane (MAO)
activator, rac-Ind2#ZrCl2 (rac-
kgPE/molZr/h/bar. Rac-Ind#2Zr(CH2Ph)2 (rac-
1
) exhibited a peak catalytic activity at 50 °C of 433
) was found to be the most active
3
ethylene polymerisation catalyst in solution in the presence of MAO, a peak catalytic
activity of 1059 kgPE/molZr/h/bar was observed at 60 °C which was twice the
recorded activity of the dichloride precursor rac-Ind#2ZrCl2 (rac-
1).
Keywords
Metallocene, zirconium, hafnium, indenyl, benzyl, olefin polymerisation,
polyethylene.
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Introduction
Since the publication of zirconocene dichloride, Cp2ZrCl2, in 1954 by Wilkinson et
al.,1 the bis-cyclopentadienyl complexes of the group 4 metals have been much
studied. In 1965, novel ligand systems quickly developed to include Cp-based
variants including indene and fluorene.2 The indenyl ligand (Ind) was found to
demonstrate additional flexibility due to its ability to change its hapticity from η5 to
η3 which has been exploited for a variety of uses including increased rates of ligand
substitution.3 Methylation of π-ligands such as cyclopentadienyl (Cp) shifts the olefin
π-ligands ionisations making it a higher field ligand, more electron releasing and
more bulky. Methylation often can be used to stabilises a wider range of
organometallic complexes than Cp itself.
O’Hare and co-workers have developed the syntheses of a number of highly
methylated indenyl (Ind) ligands.4–7 In 1994, they reported the synthesis of the
8
*
permethylated indenyl (C9Me7; Ind*) group 4 derivative, Ind2 ZrCl2. These
zirconocenes exist as one isomeric form due to the symmetric nature of the ligands.
However, the incorporation of a linking group between the two indenyl rings
introduces stereocentres giving the ligand chirality and generates rac- and meso-
forms of the complexes which can have dramatically different properties. In 2011,
Ransom et al. published the synthesis of the ethylene bridged group 4 complexes,
rac/meso-ethylenebis(1-hexamethylindenyl)zirconium
dichloride,
rac/meso-
EBI*ZrCl2.9
Polyolefins and specifically polyethylene (PE) dominates the polymer market, with
total global production of over 75 million tonnes per annum.10 The development of
polymerisation catalysts have come a long way from the breakthrough discoveries of
Ziegler.11–13 The development of single-site metallocene catalysts14,15 still remains a
very active research field for both industry and academia.16–21 rac/meso-EBI*ZrCl2
exhibited very different ethylene polymerisation activities in solution phase in the
presence of an MAO activator. rac-EBI*ZrCl2 was found to be one of the most active
known metallocenes, with an activity of 32,000 kgPE/molZr/h/bar giving high
molecular weight HDPE. In contrast, meso-EBI*ZrCl2 exhibited activities
approximately 50% less than the rac-isomer.
2

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Here we report the synthesis, characterisation and polymerisation of a family of
group 4 metallocene complexes based on the hexamethylindenyl ligand (C9Me6H;
Ind#).
Results and Discussion
Synthesis of 2,3,4,5,6,7-hexamethylindene (Ind#H)
The synthesis of 2,3,4,5,6,7-hexamethylindene (Ind#H) was first reported by Alias et
al. in 1997 as a precursor in the synthesis of a dimethylsilylbis(1-
hexamethylindenyl).7 The complex was made in relatively high yield from the
previously reported 2,3,4,5,6,7-hexamethylindan-1-one,8 although the procedure
requires two steps and 24 hours to complete. We have now developed a new
optimised procedure which simplifies the synthesis of the methylated indene, Ind#H
and the precursor ketone, Scheme 1. Overall, these modifications improve the
previously reported yields and decreases the overall cost of the ligand synthesis.
Scheme 1: synthesis of hexamethylindene (Ind#H).
We mirror the original synthesis of chlorinating tiglic acid before combining it with
tetramethylbenzene using a Friedel-Crafts acylation and concomitant Nazarov
cyclisation. However, thionyl chloride has been replaced to increase the rate of
reaction, and allowing it to proceed in high yield at room temperature. The use of a
THF solution of lithium aluminium hydride shortens the reduction to only two hours,
the the H2O elimination step is now carried out using concentrated sulphuric acid, the
whole procedure now takes less than 24 hours to complete with an extremely high
overall yield on a large scale (using up to 50 g of tetramethylbenzene).
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Synthesis of Ind2#ZrCl2 and Ind2#HfCl2
Scheme 2: synthesis of meso- and rac- group 4 metallocenes, Ind#2MCl2.
Ind#Li was obtained in quantitative yield by treatment of the protio congener with BuLi in
pentane. Ind#Li was reacted in benzene with freshly dried zirconium tetrachloride and
allowed to stir at room temperature for 72 hours, Scheme 2. The slurry was allowed to settle
and the supernatant decanted, dried and recrystallized in hexane affording a mixture of the
rac- and meso-isomers in a moderate yield of 43%. The isomers were found to be inseparable
by fractional crystallisation in aliphatic and aromatic solvents. However, large dark orange
crystals were seen to form on cooling of a saturated acetone solution to −35 °C, and these
were identified as meso-Ind#2ZrCl2. The appearance of a pale orange microcrystalline solid
#
1
was also noted and this was identified as rac-Ind2ZrCl2 by H NMR spectroscopy. Both
isomers were characterised by single crystal X-ray analysis and their solid-state structures are
shown in Figs. 1 and 2.
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Fig. 1: solid-state molecular structure of rac-Ind#2ZrCl2, rac-1, with methyl protons omitted for clarity. Thermal
ellipsoids shown at 50%.
Fig. 2: solid-state molecular structure of meso-Ind#2ZrCl2, meso-1, with methyl protons omitted for clarity.
Thermal ellipsoids shown at 50%.
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The synthesis of the analogous Ti and Hf derivatives was attempted using HfCl4 and
.
TiCl4 2THF. No tractable products were identified for the titanium species while the hafnium
reaction proceeded as for zirconium. A clean mixture of rac/meso-Ind#2HfCl2 was obtained, in
moderate yield (34%). It was noted that the reaction proceeded more slowly, but reached
completion after 72 hours. The solid state structures for both isomers are shown in Fig. 3 and
4.
Fig. 3: solid-state molecular structure of rac-Ind#2HfCl2, rac-2, with methyl protons omitted for clarity. Thermal
ellipsoids shown at 50%.
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Fig. 4: solid-state molecular structure of meso-Ind#2HfCl2, meso-2, with methyl protons omitted for clarity.
Thermal ellipsoids shown at 50%.
The pairs rac-1/2 and meso-1/2 can be considered to be isomorphous with the rac-forms
crystallising in the spacegroup P21/c and the meso-isomers in P21/n. Z = 4 for both crystal
systems the volume of the unit cells, varies very little between all four complexes
(2594.3(4) Å3 - 2633.74(4) Å3). The a, b, c, and β lattice parameters are approximately 17 Å,
9 Å, 18 Å and 115° for rac-1, and 13 Å, 15 Å, 14 Å and 99° for meso-1 respectively.
Fig. 5. Schematic depictions defining various geometric parameters.
The rotation angle (RA) between the indenyl ligands (Fig 5) differs substantially between the
rac- and meso- forms and by conventional measurement (Fig. S14) the values for rac-1,
meso-1, rac-2, and meso-2 are 135.32°, 55.85°, 135.81°, and 57.25° respectively. However,
given that there is a large tilt angle between the rings, α, (41.84°, 53.28°, 51.58°, 53.50°) due
to the tetrahedral coordination at the metal centre, this calculation for RA will be noticeably
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distorted from that reported for a coplanar metallocene such as Ind#2Fe.7 A better measure of
the rotation angle might be a torsion angle taken between the C2 methyl group and C2 itself
and its opposite number, C18, and the C18 methyl group. This yields the following values of
RA: 175.82°, 37.16°, 175.29° and 37.82°. These parameters compare more favourably with
*
*
those reported for rac-EBI ZrCl2 and meso-EBI ZrCl2 at 152.88° and 18.97° although there
*
is clearly some constraining effects caused by the bridge. However, Ind2ZrCl2, does not have
any isomeric forms due to its symmetrical ring structure, it appears to be halfway position
with an RA of 91.27°,22 while the RA for Ind2ZrCl2 is 55.87°.23 The values of α, however,
compare more favourably with the unbridged analogues, falling within the range 41.02° to
*
59.31° as exemplified by Ind2ZrCl2 and Ind2ZrCl2 respectively. This might be expected on
increasing the permethylation in order to create more space for the bulkier ligands. It is
interesting to note that the orientation of the rings in all four rac/meso-Ind#2MCl2 (M = Zr, Hf)
structures leave the two cyclopentadienyl protons in alignment where one might expect to
find the bridge. It is postulated that this is because it allows the rings to tilt away from a
parallel conformation to create more space for the methyl groups but the larger values of α
seen for the ethylene bridged species (57.15°, 56.87°, 56.97° and 56.94°) suggests that the
constraining geometry of the ethylene bridge exacerbates that effect.
The average M-Cpcent distances observed for the rac-1, meso-1, rac-2, and meso-2 are 2.228,
2.250, 2.217 and 2.227 Å respectively and these compare very favourably with those reported
for the equivalent rac/meso-EBI*MCl2 (M = Zr, Hf) (2.240 Å, 2.248 Å, 2.222 Å and 2.226
Å). In all cases the Zr-Cpcent distances are longer than the hafnium equivalent, rationalised as
being caused by the lanthanide contraction and the meso-forms show longer bond lengths
than the rac- as the steric repulsion between the eclipsed indenyl ligands might be expected
to lengthen this bond. In addition the Zr-Cpcent distances agree well those reported for
Ind2ZrCl2 and Ind*2ZrCl2, at 2.231 Å and 2.257 Å respectively. The M-Cl distances were also
found to be in good agreement, with those for hafnium marginally shorter.
Synthesis of Ind#2ZrBz2
Treatment of rac-1 with two equivalents of potassium benzyl in benzene at 25 °C for 18 h
affording rac-Ind#2Zr(CH2Ph)2, rac-3, in 59% yield, Scheme 3.
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Scheme 3: synthesis of rac-Ind#2Zr(CH2Ph)2, rac-3.
rac-3 was found to crystallise as yellow blocks from toluene in the spacegroup P21/n. The
solid-state molecular structure of rac-3, is shown in Fig. 6.
Fig. 6: solid-state molecular structure of rac-Ind2#ZrCl2, rac-3, with methyl and CH2 protons omitted for clarity.
Thermal ellipsoids shown at 50%.
When comparing rac-3 to rac-1, the first striking feature is the dramatic increase in RA from
the benzyl complex, 95.93°, to its dichloride counterpart, 175.82°. The primary cause of this
must be down to the increase bulk of the σ-ligands; by twisting one of the indenyl rings by
approximately 90°, a whole face (out of the plane of the paper in Fig. 6) of the complex has
been opened up to accommodate the two benzyl groups. Both benzyl groups are seen to tilt in
the same direction, presumably to avoid close interactions with the methyl substituents on the
indenyl ring. This tilt is effected by the angles subtended at C33 and C40: 131.20(12)° and
127.57(12)° respectively. According to the investigation by Parkin et al. into a variety of
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benzyl compounds found in the CSD and Zr(CH2Ph)4 itself,24 these angles are far greater than
the 97° proposed for anything other than an η1 benzyl bonding motif. Moreover, a δipso
,
calculated as the difference between ipso distance (Zr1-C34/41) and the CH2 distance (Zr1-
C33/40), should not be greater than 0.5 Å. In the case of rac-3, this distance is 1.156 Å and
1.114 Å which exceeds the suggested limit allowing us to unequivocally assign the bonding
as η1 for both benzyl moieties and the formal valence electron count to 16. The values for the
zirconium-carbon σ-bonds, Zr1-C33/40, are 2.3021(16) Å and 2.3385(16) Å. Unsurprisingly,
these are shorter than the Zr-Cl distances reported for rac-1 (2.4286(14) Å and 2.4135(14) Å)
but fit well with those reported for similar species.24 The value for α is 52.32° which is
notably smaller than the values reported for the dichloride analogues. This is likely caused by
the changed to an intermediary RA of 95.93°, allowing the indenyl rings to flatten to reduce
their interactions with one another, while still creating space for the benzyl groups. The Zr-
Cpcent distances of 2.263 Å and 2.305 Å are longer than those of rac-1 (2.225 Å and 2.231 Å),
indicating a slightly weaker indenyl-zirconium interaction to counterbalance the increased σ-
donation of the benzyl ligands in comparison to chloride. A full comparison of structural
parameters for the five Ind# group 4 complexes is given in Table 1.
Table 1: Comparison of selected bond lengths and parameters
Complex
rac-1
2.228
2.532
175.82
41.84
meso-1
2.250
2.557
37.16
53.28
rac-2
2.217
meso-2
2.227
2.536
37.82
53.50
rac-3
2.284
2.5258
95.93
52.32
Avg. M-Cpcent (Å)
Avg. M-CCp (Å)
RA (°)†
2.5986
175.29
51.58
α (°)
2.4211
2.4277
2.4092
2.4084
2.3203*
Avg. M-Cl* (Å)
† calculated using the C2-C18 torsion angle * indicates the M-Cbenzyl distance where applicable
Density Functional Theory studies
Calculations at the B3LYP25–27 and BP8628,29 levels of DFT were performed in order better to
understand the bonding and structure of these metallocenes. In each case, the computed
optimised metrical parameters were found compare well with each other as well as with those
obtained by the single crystal X-ray diffraction studies. Illustrations of the DFT-computed
HOMO and LUMO for rac-3 are presented in Fig. 7 and for rac-1, meso-1, rac-2 and meso-2
in the Supporting Information (Figs. S1-9).
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Fig. 7: Illustration of the DFT-computed HOMO (left) and LUMO (right) calculated for rac-3.
All of the computations demonstrated similar frontier orbitals. For example, in rac-3, the
HOMO is predominantly based on one of the Ind# ligand fragments with 24.6% of the density
spread over the four pz orbitals of the benzene ring. The LUMO, however, is more localised
with 56.7% based on the Zr dxy orbital. A bonding interaction is noticed with the benzyl
moiety in MOs 174 and 175, three and two levels below the HOMO respectively, each
showing a significant amount of electron density between C33 and Zr1.
Variable temperature 1H NMR spectroscopy
1
The room temperature H NMR spectrum for meso-1 shows the methyl group protons
clustered together in a tight group of six resonances, each corresponding to six protons, in the
range 1.98 – 2.60 ppm (in toluene-d8 – Fig. 8 and in chloroform-d1 – Fig. S10). Typically,
rac-1, exhibits five methyl proton signals in the range 2.25 – 2.60 ppm with the sixth
appearing upfield at 1.60 ppm (in chloroform-d1 – Fig. S11). In both cases a single resonance,
of relative intensity two, was identified as the cyclopentadienyl proton at 5.73 and 6.16 ppm
for meso-1 and rac-1 respectively. The simplicity of these 1H NMR spectra suggest that both
species are fluxional in solution at room temperature and that the equivalent indenyl ring
protons on each ligand are chemically identical. Apart from some signal broadening, no
change was noted on cooling the sample to −80 °C (Fig. 8).
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Fig. 8: variable temperature 1H NMR spectra of meso-Ind2#ZrCl2 in the range 193 – 293 K. The NMR spectra
were obtained at 500 MHz in a solution of toluene-d8 and the residual protio solvent resonances, by which the
spectra were referenced, are indicated by asterisks.
Similarly, the spectrum of rac-3 showed symmetrical indenyl rings with the separation of the
most upfield methyl resonance from the others (1.80 and 2.02 – 2.39 ppm in benzene-d6). The
benzylic protons appear as diastereotopic doublets at 1.01 and 1.19 ppm and the lone Cp
proton resonates at 4.90 ppm. As expected the aromatic protons of the benzyl groups appear
in the region 6.92 – 7.21 ppm. Given the bulk of the ancillary ligands it was hoped that by
cooling the sample, the two indenyl rings might be distinguished on the NMR timescale
which was not observed for meso-1 (Fig. 9). The resonances corresponding to the methyl
protons around the rings were seen to broaden significantly on cooling to −95 °C. However,
the diastereotopic benzyl proton resonances and that of the proton at the 1-position were
observed to broaden into the baseline, it was not possible to cool the samples further.
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Fig. 9: variable temperature 1H NMR spectra of rac-Ind2#ZrBz2 in the range 178 – 293 K. The NMR spectra
were obtained at 500 MHz in a solution of toluene-d8 and referenced to the residual protio solvent resonances.
Ethylene polymerisation studies
Zirconocenes are some of the most widely studied single-site olefin polymerisation catalyst.
The permethylated indenyl complexes, rac- and meso-EBI*ZrCl2, have previously been
shown to be exceptional ethylene polymerisation catalysts.9 rac-1, meso-1 and rac-3 were
tested as ethylene polymerisation catalysts in solution in the presence of methylaluminoxane
activator (MAO) between 50-90 °C. A summary of their activities is shown in Figs. 10 and
11.
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Fig. 10: a plot of polymerisation activity (kgPE/molZr/h/bar) vs. temperature (°C) for the solution-phase
polymerisation of ethylene using rac-1 and meso-1. Polymerisations were carried out in duplicate under the
following conditions: 2 bar ethylene, 50 mL hexane, 30 minutes, 0.2 mg catalyst loading, 2000:1 [Al]:[Zr] ratio
(MAO). Errors bars indicate one standard deviation in either direction.
Fig. 11: a plot of polymerisation activity (kgPE/molZr/h/bar) vs. temperature (°C) for the solution-phase
polymerisation of ethylene using rac-1 and rac-3. Polymerisations were carried out in duplicate under the
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following conditions: 2 bar ethylene, 50 mL hexane, 30 minutes, 0.2 mg catalyst loading, 2000:1 [Al]:[Zr] ratio
(MAO). Errors bars indicate one standard deviation in either direction.
Figure 10 shows two contrasting trends in activity with varying temperature: meso-1 displays
a clear optimum activity at 70 °C while rac-1 shows a gradual decline in activity with
increasing temperature. The activities are very similar for both isomers from 70 – 90 °C but
the more active rac-isomer outperforms the meso- significantly below 70 °C (50 °C: 433 and
181 kgPE/molZr/h/bar respectively). Figure 11 illustrates the improved catalyst activity when
the chloride ligands are replaced by benzyl ligands at all temperatures studied. rac-3 is a
significantly more active then both dichloride congeners almost two fold under all conditions
tested, furthermore it displays an optimum activity at 60 °C (1059 kgPE/molZr/h/bar). The
activities for meso-1 and rac-1 are comparable to those reported by Lee et al. for Ind2ZrCl2
supported on silica with trimethylalumnium activator (400 kgPE/molZr/h/bar).30 However, rac-
3 exhibits almost the equivalent activity of 2-Me,4-PhSBI*ZrCl2 (1185 kgPE/molZr/h/bar), studied
by Napoli and co-workers in 2011.31 While rac-3 qualifies as a “very high” activity catalyst
on the Gibson scale,18 all three catalysts tested fall short of the 32,000 kgPE/molZr/h/bar
reported for the related ethylene bridged species, rac-EBI*ZrCl2, or the 14,000
kgPE/molZr/h/bar for Ind2ZrCl2.32
Conclusions
A family of group 4 metallocene complexes, rac/meso-Ind#2MX2 (M = Zr, Hf,; X = Cl,
CH2Ph) based on the hexamethylindenyl ligand (C9Me6H; Ind#) have been prepared and fully
characterised. Both the meso- and rac-Ind2#MCl2 (M = Zr, Hf,) were found to be isostructural.
All these novel zirconocenes, rac/meso-Ind#2ZrX2 (X = Cl, CH2Ph) were tested for their
activity as an ethylene polymerisation catalyst in solution. rac-Ind#2Zr(CH2Ph)2 was found to
be the most active ethylene polymerisation catalyst in solution in the presence of MAO, an
peak catalytic activity of 1059 kgPE/molZr/h/bar was observed at 60 °C which was twice the
recorded activity of the dichloride precursor rac-Ind#2ZrCl2.
Materials and methods
General procedure:
Air and moisture sensitive reactions were performed on a dual-manifold vacuum/N2
line using standard Schlenk techniques, or in a N2 filled MBraun Unilab glovebox.
Hexane and toluene were dried using a Braun SPS-800 solvent purification system.
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Et2O and THF were dried at reflux over Na/benzophenone and distilled under N2.
Hexane, toluene and Et2O were stored over K mirrors. THF was stored over activated
3 Å molecular sieves. Benzene-d6 (99.6%; Sigma Aldrich) and toluene-d8 (99.5%;
Goss Scientific) were dried over K. chloroform-d1 (99.5%; Sigma Aldrich) was dried
over CaH2. All NMR solvents were freeze-pump-thaw degassed three times before
being vacuum transferred prior to use. Solution NMR samples were prepared in the
glovebox under N2 atmosphere in Young’s tap NMR tubes. 1H, 13C{1H} and 2-D NMR
spectra were recorded on 400 MHz or 500 MHz Bruker spectrometers. All chemical
shifts were expressed as δ, in parts per million (ppm) relative to TMS (δ = 0). Crystals
were mounted on MiTeGen MicroMounts using perfluoropolyether oil, and cooled
rapidly to 150 K in a stream of cold nitrogen using an Oxford Cryosystems
CRYOSTREAM unit.33 Data collections were performed using an Enraf-Nonius
FR590 Kappa CCD diffractometer, utilising graphite-monochromated Mo Kα X-ray
radiation (λ = 0.71073 Å). Raw frame data were collected at 150(2) K using a Nonius
Kappa CCD diffractometer, reduced using DENZO-SMN34 and corrected for
absorption using SORTAV.35 The structure was solved using SuperFlip36 and refined
using full matrix least-squares using CRYSTALS.37,38 Interplanar distances and angles
were calculated using PLATON.39
Ind#H
Oxalyl chloride (52.9 g, 417 mmol, 1 eq.) was added to tiglic acid [trans-2-methylbutenoic
acid] (41.8 g, 417 mmol, 1 eq.) dissolved in 1 L DCM. Five drops of N,N-
dimethylformamide was pipetted into the vigorously stirred solution causing a large amount
of effervescence and the reaction was left stirring under nitrogen for 12 h before cooling to
8 °C. Aluminium trichloride (61.2 g, 459 mmol, 1.1 eq.) was quickly added under a flow of
N2, causing a small temperature rise and the resulting DCM slurry to become light orange.
1,2,3,4-tetramethylbenzene [TMB] (50 g, 372 mmol, 0.90 eq.) was mixed with 100 mL DCM
and transferred to a pressure-equalising dropping-funnel. The TMB solution was added to the
stirred reaction mixture in a fast-dropwise manner effecting a colour change through dark-
orange to red. After stirring for a further four hours at room temperature, a solution of
500 mL conc. HCl and 500 g ice was made-up and was transferred to the reaction mixture to
quench it, dropwise at first and then more quickly over 10 minutes. This caused the dark-red
slurry to decolourise to a light pink solution. The stirring was stopped and the DCM layer
was decanted before extracting the aqueous layer with 500 mL DCM twice more. The
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combined organic layer was washed with 500 mL deionised water, drying with magnesium
sulfate, filtering and reducing in vacuo (40 °C, 550 mbar). The product was obtained as a
light brown oil in 96 % yield (77.25 g, 357 mmol). 100 mL LiAlH4 (2.0 M in THF;
200 mmol, 0.5 eq.) was combined with 100 mL dry, degassed THF and the mixture was
cooled to 8 °C under N2. 86.53 g Ind#=O (400 mmol, 1 eq.) was dissolved in 150 mL dry,
degassed THF and this was added to the stirred reaction mixture in a fast dropwise manner
over the course of 10 minutes causing a small rise in temperature. The reaction was stirred for
four hours before careful, portionwise quenching with 14.4 mL H2O (800 mmol, 2 eq.) over
approximately 30 minutes. 113 mL conc. H2SO4 (>95 %; 2 mol, 5 eq.) was added, slowly at
first, causing the colour to change to a medium-dark grey over 30 minutes. The reaction was
quenched with an additional 500 mL H2O and extracted with DCM (3 x 500 mL). The
combined organic layer was washed with a further 500 mL H2O, dried over magnesium
sulphate and reduced in vacuo (40 °C, 250 mbar), affording the product as a dark brown oil in
98 % yield (78.51 g, 392 mmol).
Ind#2ZrCl2
Two equivalents of Ind#Li (4 g, 19.4 mmol) were added to one equivalent of ZrCl4 (2.26 g,
9.71 mmol) in a Schlenk tube inside a glove box, and were stirred in 100 mL benzene under
nitrogen for 72 h. The mixture was allowed to settle, and the solution decanted. The solid was
extracted with further benzene (2 x 50 mL) and the filtrates combined and reduced in vacuo.
The mixture was recrystallised from hot hexane affording an orange crystalline solid in 45 %
yield (2.43 g, 4.35 mmol). This solid comprised an equal mixture of both the rac- and meso-
isomeric forms which proved inseparable by fractional crystallisation from hexane. A further
recrystallisation from acetone yielded large dark orange crystals which were isolated and
found to contain only meso-Ind#2ZrCl2. On reduction in volume, the acetone solution
#
#
1
precipitated rac-Ind2ZrCl2 as a pale-orange microcrystalline solid. rac-Ind2ZrCl2 H NMR
(400 MHz, CDCl3): δ 1.60 (s, 6H, Cp-Me), 2.25 (s, 6H, Ar-Me), 2.26 (s, 6H, Ar-Me), 2.43
(s, 6H, Ar-Me), 2.54 (s, 6H, Cp-Me), 2.60 (s, 6H, Ar-Me), 6.26 (s, 2H, Cp-H). 1H NMR (400
MHz, C6D6): δ 1.55 (s, 6H, Cp-Me), 2.08 (s, 6H, Ar-Me), 2.15 (s, 6H, Ar-Me), 2.39 (s, 6H,
Ar-Me), 2.49 (s, 6H, Cp-Me), 2.57 (s, 6H, Ar-Me), 6.12 (s, 2H, Cp-H). 13C {1H} NMR (400
MHz, CDCl3): δ 14.06 (Cp-Me), 14.96 (Ar-Me), 16.47 (Ar-Me), 16.78 (Ar-Me), 17.42 (Cp-
Me), 17.63 (Ar-Me), 93.49 (Cp-H), 119.15 (Cp), 124.08 (Ar), 124.96 (Ar), 129.44 (Ar),
130.64 (Cp), 131.58 (Ar), 132.99 (Ar), 133.35 (Ar). IR (KBr) (cm-1): 2962, 1543, 1441,
17

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1261, 1022, 800. Elemental Analysis (%). Expected: C 64.50, H 6.86. Found: C 64.35, H
#
1
6.74. meso-Ind2ZrCl2 H NMR (400 MHz, CDCl3): δ 2.13 (s, 6H, Cp-Me), 2.18 (s, 6H, Ar-
Me), 2.19 (s, 6H, Ar-Me), 2.23 (s, 6H, Ar-Me), 2.51 (s, 6H, Cp-Me), 2.52 (s, 6H, Ar-Me),
5.83 (s, 2H, Cp-H). 1H NMR (400 MHz, C6D6): δ 2.00 (s, 6H, Cp-Me), 2.02 (s, 6H, Ar-Me),
2.05 (s, 6H, Ar-Me), 2.06 (s, 6H, Ar-Me), 2.54 (s, 6H, Cp-Me), 2.55 (s, 6H, Ar-Me), 5.60 (s,
2H, Cp-H). 1H NMR (500 MHz, C7D8): δ 1.98 (s, 6H, Cp-Me), 2.02 (s, 6H, Ar-Me), 2.04 (s,
6H, Ar-Me), 2.05 (s, 6H, Ar-Me), 2.49 (s, 6H, Cp-Me), 2.50 (s, 6H, Ar-Me), 5.57 (s, 2H, Cp-
13
H). C {1H} NMR (400 MHz, CDCl3): δ 15.04 (Cp-Me), 15.95 (Ar-Me), 16.51 (Ar-Me),
16.53 (Ar-Me), 16.70 (Cp-Me), 17.10 (Ar-Me), 96.63 (Cp-H), 120.81 (Cp), 126.67 (Ar),
126.81 (Ar), 126.94 (Ar), 129.59 (Cp), 130.41 (Ar), 133.10 (Ar), 133.51 (Ar). IR (KBr)
(cm-1): 2920, 1542, 1441, 1382, 1261, 1064, 1024, 792. Elemental Analysis (%). Expected: C
64.50, H 6.86. Found: C 64.37, H 6.81.
Ind#2HfCl2
Two equivalents of Ind#Li (2 g, 9.71 mmol) were added to one equivalent of HfCl4 (1.55 g,
4.86 mmol) in a Schlenk tube inside a glove box, and were stirred in 70 mL benzene under
nitrogen for 72 h. The mixture was allowed to settle, and the solution decanted. The solid was
extracted with further benzene (1 x 50 mL) and the filtrates combined and reduced in vacuo.
The mixture was recrystallised from hot hexane affording an orange crystalline solid in 34 %
yield (1.06 g, 1.64 mmol). This solid comprised an equal mixture of both the rac- and meso-
isomeric forms which proved inseparable by fractional crystallisation from common
laboratory solvents. Crystals of each isomer suitable for X-ray diffraction were picked by eye
#
1
under a microscope. rac-Ind2HfCl2 H NMR (400 MHz, C6D6): δ 1.63 (s, 6H, Cp-Me), 2.10
(s, 6H, Ar-Me), 2.17 (s, 6H, Ar-Me), 2.41 (s, 6H, Ar-Me), 2.51 (s, 6H, Cp-Me), 2.56 (s, 6H,
Ar-Me), 5.99 (s, 2H, Cp-H). 13C {1H} NMR (400 MHz, C6D6): δ 14.06 (Cp-Me), 14.93 (Cp-
Me), 16.39 (Ar-Me), 16.57 (Ar-Me), 17. 64 (Ar-Me), 17.64 (Ar-Me), 91.89 (Cp-H), 116.29
(Cp), 123.37 (Ar), 124.83 (Ar), 127.94 (Ar), 129.27 (Cp), 130.18 (Ar), 130.79 (Ar), 132.36
(Ar). IR (KBr) (cm-1): 2923, 1543, 1442, 1382, 1261, 1027, 792. Elemental Analysis (%).
#
1
Expected: C 55.54, H 5.91. Found: C 55.63, H 6.01. meso-Ind2HfCl2 H NMR (400 MHz,
C6D6): δ 2.00 (s, 6H, Cp-Me), 2.08 (s, 12H, Ar-Me), 2.11 (s, 6H, Ar-Me), 2.53 (s, 6H, Cp-
13
Me), 2.59 (s, 6H, Ar-Me), 5.48 (s, 2H, Cp-H). C {1H} NMR (400 MHz, C6D6): δ 14.93
(Ar-Me), 15.86 (Ar-Me), 16.33 (Ar-Me), 16.57 (Ar-Me), 16.60 (Cp-Me), 17.29 (Cp-Me),
94.27 (Cp-H), 118.10 (Cp), 126.27 (Ar), 126.34 (Ar), 126.56 (Ar), 128.40 (Cp), 130.60
18

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(Ar), 132.64 (Ar), 132.94 (Ar). IR (KBr) (cm-1): 2923, 1543, 1442, 1382, 1261, 1027, 792.
Elemental Analysis (%). Expected: C 55.54, H 5.91. Found: C 55.65, H 6.00.
rac-Ind#2Zr(CH2Ph)2
One equivalent of rac-Ind#2ZrCl2 (100 mg, 179 μmol) was stirred with two equivalents
K(CH2Ph) (51 mg, 394 μmol) in 10 mL benzene for 18 hours. The reaction mixture was dried
in vacuo and the residues extracted with hexane. The product was obtained as a yellow
powder in 59% yield. Crystals suitable for X-ray analysis were grown from a saturated
1
toluene solution cooled to −35 °C. H NMR (400 MHz, C6D6): δ 1.01 (d, J = 11.1 Hz, 2H,
PhCH2), 1.19 (d, J = 11.1 Hz, 2H, PhCH2), 1.80 (s, 6H, Cp-Me), 2.02 (s, 6H, Ar-Me), 2.08
(s, 6H, Ar-Me), 2.10 (s, 6H, Ar-Me), 2.17 (s, 6H, Cp-Me), 2.39 (s, 6H, Ar-Me), 4.90 (s, 2H,
Cp-H), 6.91 (d, J = 7.6 Hz, 4H, o-Ph), 6.94 (t, J = 7.4 Hz, 2H, p-Ph), 7.21 (d, J = 7.6 Hz, 4H,
m-Ph). 1H NMR (500 MHz, C7D8): δ 0.94 (d, J = 11.1 Hz, 2H, PhCH2), 1.10 (d, J = 11.1 Hz,
2H, PhCH2), 1.78 (s, 6H, Cp-Me), 1.98 (s, 6H, Ar-Me), 2.08 (s, 6H, Ar-Me), 2.09 (s, 6H, Ar-
Me), 2.16 (s, 6H, Cp-Me), 2.38 (s, 6H, Ar-Me), 4.83 (s, 2H, Cp-H), 6.83 (d, J = 7.6 Hz, 4H,
13
o-Ph), 6.86 (t, J = 7.6 Hz, 2H, p-Ph), 7.14 (d, J = 7.5 Hz, 4H, m-Ph). C {1H} NMR (400
MHz, C6D6): δ 13.58 (Ar-Me), 15.02 (Ar-Me), 16.37 (Ar-Me), 16.52 (Ar-Me), 16.61 (Ar-
Me), 17.66 (Ar-Me), 66.75 (CH2Ph), 100.77 (Cp-H), 114.04 (Cp), 121.59 (p-Ph), 125.12
(Ar), 126.71(Ar), 127.76 (o-Ph), 127.99 (m-Ph), 128.17 (Ar), 128.62 (Ar), 128.76 (Cp),
130.70 (Ar), 132.93 (Ar), 152.84(i-Ph). IR (KBr) (cm-1): 2963, 1543, 1261, 1094 1022, 802.
Crystallographic Details
Single crystals of rac-Ind2#ZrCl2 were grown from a hexane solution, C30H38ZrCl2, Mr
= 560.76, monoclinic, P21/c, a = 17.2538(13) Å, b = 9.0136(5) Å, c = 18.3402(16) Å,
β =114.553(10)°, V = 2594.3(4) Å3, Z = 4, T = 100 K, block, orange, 5499 independent
reflections, R1 = 0.046 wR2 = 0.116 [I >2σ(I)]. CCDC 1040220.
Single crystals of meso-Ind2#ZrCl2 were grown from a hexane solution, C30H38ZrCl2, Mr
= 560.76, monoclinic, P21/n, a = 12.55987(11) Å, b = 14.56043(10) Å, c =
14.41692(11) Å, β =98.3967(8)°, V = 2608.26(3) Å3, Z = 4, T = 100 K, block, orange,
9280 independent reflections, R1 = 0.061 wR2 = 0.196 [I >2σ(I)]. CCDC 1040221.
Single crystals of rac-Ind2#HfCl2 were grown from a hexane solution, C30H38HfCl2, Mr
= 648.03, monoclinic, P21/c, a = 17.3610(2) Å, b = 9.08256(7) Å, c = 18.4055(2) Å,
β =114.8387(16)°, V = 2633.74(4) Å3, Z = 4, T = 150 K, block, yellow, 5492
independent reflections, R1 = 0.017 wR2 = 0.042 [I >2σ(I)]. CCDC 1040223.
19

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Single crystals of meso-Ind2#HfCl2 were grown from a hexane solution, C30H38HfCl2,
Mr = 648.03, monoclinic, P21/n, a = 12.5691(1) Å, b = 14.6272(1) Å, c =
14.3927(2) Å, β =98.6310(9)°, V = 2616.14(5) Å3, Z = 4, T = 150 K, block, yellow,
5435 independent reflections, R1 = 0.027 wR2 = 0.076 [I >2σ(I)]. CCDC 1040224.
Single crystals of rac-Ind2#Zr(CH2Ph)2 were grown from a hexane solution, C44H50Zr,
Mr = 670.10, monoclinic, P21/n, a = 13.3970(1) Å, b = 18.3318(1) Å, c =
14.3130(1) Å, β =93.7834(7)°, V = 3507.48(4) Å3, Z = 4, T = 150 K, block, yellow,
7269 independent reflections, R1 = 0.026 wR2 = 0.071 [I >2σ(I)]. CCDC 1040222.
DFT Calculation Details
All DFT calculations were performed with the ORCA program package.40 The
geometry optimisations of the complexes and single-point calculations on the
optimized geometries were carried out at the BP8628,29 and B3LYP25–27 levels of DFT.
The def2-TZVP(-f) basis set in the scalar relativistic recontraction reported by Neese
et al. (segmented all-electron relativistic basis sets, SARC) was applied.41,42 For all
elements up to bromine, the SARC basis sets are simply scalar relativistic
recontractions of the basis sets developed by the Karlsruhe group,43,44 while for
heavier elements, the primitives and contraction patterns were designed in references
39 and 40. The Coulomb fitting basis set of Weigend45 was used in uncontracted form
in all calculations. The RI46–48 approximation was used to accelerate the calculations.
Orbitals were generated with the program Chimera.49
Polymerisation Details
Each of the catalysts was dissolved in hexane to form a stock solution with a
concentration of 0.2 mg/ml. 1 ml stock solution was added to a dry 150 ml ampoule
along with the required ratio of aluminium activator (MAO) and 49 ml dry, degassed
hexane and sealed with a Rotaflo tap. The ampoule was degassed on a Schlenk line,
heated to the required temperature in an oil bath, and exposed to ethylene gas at a
pressure of 2 bar for 30 minutes. On completion, the ethylene was removed under
vacuum and the polymer filtered on a sintered glass frit, dried in the vacuum oven
overnight at room temperature and weighed. Each polymerisation was carried out in
duplicate.
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Acknowledgements
We would like to thank Diamond Light Source for an award of beamtime on
BeamLine I19 and Chemical Crystallography (University of Oxford) for use of their
instruments. T.A.Q.A. and Z.R.T. would like to thank SCG Chemicals for financial
support. J.-C.B. would like to thank the University of Oxford and SCG Chemicals for
funding.
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*Highlights (for review)
ACCEPTED MANUSCRIPT



New hexamethylindenyl zirconocene derivatives have been prepared.
rac-Ind2#ZrCl2 is a catalyst for ethylene polymerisation.
Peak catalytic activity of 1059 kgPE/molZr/h/bar was observed at 60 °C .

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Electronic Supporting Information
Synthesis, Characterisation, and Polymerisation Studies of Indenyl Zirconocenes and
Hafnocenes
Thomas A. Q. Arnold, Jean-Charles Buffet, Zoë Turner and Dermot O’Hare*
Table of Contents
1. Density Functional Theory studies
2. 1H NMR Spectroscopy
3. Depiction of Structural Parameters
p2
p5
p6
1

ACCEPTED MANUSCRIPT
1. Density Functional Theory studies
Fig. S1: Illustration of the DFT-computed HOMO (left) and LUMO (right) calculated for meso-1 at the B3LYP
level.
Fig. S2: Illustration of the DFT-computed HOMO (left) and LUMO (right) calculated for meso-1 at the BP86
level.
2