Synthesis of Ti(iv) complexes of donor-functionalised phenoxy-imine tridentates and their evaluation in ethylene oligomerisation and polymerisation

Article abstract of DOI:10.1039/c3dt32465f

A number of analogues of the Mitsui Chemicals ethylene trimerisation system (IV) have been explored, in which one of the donor atoms have been modified. Thus, a series of mono-anionic tridentate phenoxy-imine (3-(t-butyl)-2-(OH)- C₆H₄CN(C(CH₃)₂CH₂OMe) 1, 3-(adamantyl)-2-(OH)-C₆H₄CN(2′-(2′′- (SMe)C₆H₄)-C₆H₄) 2, 3-(t-butyl)-2-(OSiMe₃)-C₆H₄CN(C(CH ₃)₂CH₂OMe) 3) or phenoxy-amine (3,5-di(t-butyl)-2-(OH)-C₆H₄CH₂-N(2′- (2′′-(OMe)C₆H₄)-C₆H₄) 4) ligands have been prepared and reacted with TiCl₄ or TiCl ₄(thf)₂ to give the mono-ligand complexes 5-7. The solid state structures of compounds 4-6 have been determined. Complexes 5-7 have been tested for their potential as ethylene oligomerisation/polymerisation systems in conjunction with MAO activator and benchmarked against the Mitsui phenoxy-imine trimerisation system IV. While the phenoxy-amine complex 6 shows a propensity for polymer formation, the phenoxy-imine complexes 5 and 7 show somewhat increased formation of short chain LAOs. Complex 5 is selective for 1-butene in the oligomeric fraction, while 7 displays liquid phase selectivity to 1-hexene. As such 7, which is a sulfur substituted analogue of the Mitsui system IV, displays similar characteristics to the parent catalyst. However, its utility is limited by the lower activity and predominant formation of polyethylene.

Full text of DOI:10.1039/c3dt32465f

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Synthesis of Ti(IV) complexes of donor-functionalised
phenoxy-imine tridentates and their evaluation in
ethylene oligomerisation and polymerisation†
Cite this: DOI: 10.1039/c3dt32465f
James A. Suttil,a Miranda F. Shaw,a David S. McGuinness,*a Michael G. Gardinera and
Stephen J. Evansb
A number of analogues of the Mitsui Chemicals ethylene trimerisation system (IV) have been explored, in
which one of the donor atoms have been modified. Thus, a series of mono-anionic tridentate phenoxy-
imine (3-(t-butyl)-2-(OH)-C6H4CvN(C(CH3)2CH2OMe) 1, 3-(adamantyl)-2-(OH)-C6H4CvN(2’-(2’’-(SMe)-
C6H4)-C6H4) 2, 3-(t-butyl)-2-(OSiMe3)-C6H4CvN(C(CH3)2CH2OMe) 3) or phenoxy-amine (3,5-di(t-butyl)-
2-(OH)-C6H4CH2-N(2’-(2’’-(OMe)C6H4)-C6H4) 4) ligands have been prepared and reacted with TiCl4 or
TiCl4(thf)2 to give the mono-ligand complexes 5–7. The solid state structures of compounds 4–6 have
been determined. Complexes 5–7 have been tested for their potential as ethylene oligomerisation/poly-
merisation systems in conjunction with MAO activator and benchmarked against the Mitsui phenoxy-
imine trimerisation system IV. While the phenoxy-amine complex 6 shows a propensity for polymer for-
mation, the phenoxy-imine complexes 5 and 7 show somewhat increased formation of short chain LAOs.
Complex 5 is selective for 1-butene in the oligomeric fraction, while 7 displays liquid phase selectivity to
1-hexene. As such 7, which is a sulfur substituted analogue of the Mitsui system IV, displays similar
characteristics to the parent catalyst. However, its utility is limited by the lower activity and predominant
formation of polyethylene.
Received 17th October 2012,
Accepted 29th January 2013
DOI: 10.1039/c3dt32465f
www.rsc.org/dalton
examples of systems based on titanium have appeared in the
literature.1,4,5,9–14
Introduction
The conversion of olefins into higher olefin feedstocks and
Phenoxy-imine ligands are a particularly attractive ligand
polyolefins by transition metal catalysts is a field of research system due to the high degree of functionalisation that can be
that receives continual attention from groups in both acade- incorporated through simple synthetic methods. As such, it is
mia and industry. In more recent years, there has been a par- unsurprising that they have been employed as ligands in ethyl-
ticular focus on the selective conversion of ethylene into ene polymerisation systems for a wide range of metals. A par-
polymer grade linear alpha olefins (LAOs) such as 1-butene, ticularly efficient example of such catalysts are the bis-ligated
1-hexene and 1-octene.1–8 Such processes avoid the formation phenoxy-imine complexes of titanium and zirconium (termed
of the high molecular weight fractions of LAOs, which are typi- FI catalysts, I).15–22 Such systems are highly active and well
cally formed during full-range processes that yield Schulz– known for their controlled olefin polymerisation/co-polymeris-
Flory or Poisson distributions of products, and are of lower ation. This initial discovery by Coates21 and Fujita18 indepen-
value than their short chain counterparts. While chromium is dently has led to a wide range of studies on the bis-ligated
the transition metal present in the majority of catalysts systems.
reported for the selective trimerisation of ethylene, several
However, examples of mono-ligated group IV complexes are
less well known. Work by Lapido and co-workers and Lancas-
ter and co-workers has demonstrated the generation of mono-
ligated bidentate complexes (II) of Ti and Zr and shown their
efficiency towards ethylene polymerisation.23–25 More recently,
examples of mono-ligated tridentate phenoxy-imine systems
(III) have been explored in the literature.26–37 Such compounds
are reported to be efficient catalysts for ethylene polymeris-
ation and show good incorporation for a wide variety of olefins
during ethylene/olefin co-polymerisation.28–37
aSchool of Chemistry, University of Tasmania, Private Bag 75, Hobart, 7001,
Australia. E-mail: david.mcguinness@utas.edu.au; Fax: +61 (0) 362262858;
Tel: +61 (0) 362262783
bSasol Technology Ltd, PO Box 1183, Sasolburg, 1947, South Africa.
E-mail: Stephen.evans@sasol.com
†Electronic supplementary information (ESI) available: Details of X-ray structure
of S1. CCDC 902939–902942. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3dt32465f
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However, until recently selective oligomerisation systems
based on the phenoxy-imine ligand motif were unknown. In
2009, researchers from Mitsui Chemicals first disclosed in the
patent literature a highly active trimerisation system based on
this motif (IV).38 The most active of these compounds have
been reported to yield activities in excess of 6800 kg (mol Ti)−1
h−1 bar−1 and 1-hexene selectivity greater than 93%.9 While
complex IV represents the optimised system, a large range of
modifications to the ligand structure are detailed in the patent
covering this work.38
Scheme 1 Synthesis of ligand 4.
The studies by Fujita and co-workers have thoroughly inves-
tigated the ligands effect on 1-hexene selectivity and catalyst
activity by varying the sterics of 4- and 6-position of the phen-
oxide ring, the nature of the carbon bridge between the imine
nitrogen and the pendant donor, the nature of the ether sub-
stituent and atom choice for the pendant donor for atoms
with a hard Lewis basic nature.9,38 However, in both the aca-
demic and patent literature there are no studies exploring ana-
logous complexes containing amines in place of imines or
including soft Lewis bases as donors. Herein we report the
preparation and characterisation of such a series of analogues
of the Mitsui trimerisation system and their catalytic behaviour
in conjunction with methylaluminoxane (MAO).
Fig. 1 Molecular structure of 4. Thermal ellipsoids are shown at the 50% prob-
ability level. All methyl, methylene and aromatic-ring hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°): O1–H1 0.90(2),
H1⋯O2, N1 2.41, 2.03, O1–H1⋯O2, N1 123.9, 147.8.
Results and discussion
Synthesis and structures
require extensive purification.32,39–41 Preparation of ligand 4
was readily achieved by the reaction of 3,5-di-tert-butyl-2-hydro-
The salicylaldimine ligands 1 and 2 were prepared through the xybenzyl bromide with 2-(2′-methoxyphenyl)-N-methylaniline
condensation reaction of the appropriate salicylaldehyde with in the presence of triethylamine (Scheme 1) by an analogous
the desired amine. Ligand 1 was further derivatised to give the literature procedure.42 In all cases the ligand systems have
1
trimethylsilyl ether 3; these ethers have been shown to be been characterised by H and 13C NMR and mass spectra. In
more selective in generating 1 : 1 complexes when reacted with addition, crystals of ligand 4 were grown from a saturated solu-
TiCl4(thf)2.24,25 Ligands of the type 4 would typically be pre- tion in petroleum spirits and the structure determined by
pared by the reduction of the appropriate salicylaldimine, X-ray crystallography (Fig. 1). The solid state structure clearly
however this methodology was found to be low yielding and shows the intramolecular H-bond interactions between the
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Scheme 2 Synthesis of complex 5.
Scheme 3 Synthesis of complex 6.
Scheme 4 Synthesis of complex 7.
complex a bis-ligated system was isolated (S1†), the crystal
structure of which is shown in the ESI.†
Fig. 2 Molecular structure of 5. Thermal ellipsoids are shown at the 50% prob-
ability level (one of two, similar molecules shown). A disordered lattice DCM
molecule is omitted for clarity, as are all methyl, methylene and aromatic-ring
hydrogen atoms. Selected bond lengths (Å) and angles (°): Ti–Ophenoxide,ether
1.783(3)–1.785(3), 2.122(4)–2.124(3), Ti–N 2.160(4)–2.167(4), Ti–Cl 2.2892(16)–
2.3363(15), O–Ti–Nphenoxide,ether 84.29(16)–84.71(16), 74.13(15)–74.25(14), O–
Ti–O 158.48(16)–158.81(16), X–Ti–Ycis(acyclic),trans(acyclic) 84.68(10)–104.69(12),
169.41(6)–172.73(6), Cphenoxide–O–Ti 143.5(3)–143.8(3).
Work by researchers at Mitsui Chemicals has shown that
the reaction between TiCl4 and salicylaldimine ligands with
extended carbon chains (greater than four) between the imine
moiety and a donor moiety can react cleanly and efficiently to
yield mono-anionic tridentate titanium complexes.9,38 The
reaction of ligands 2 and 4 with TiCl4 has been undertaken in
toluene to yield the complexes 6 and 7 as dark red solids in
1
phenolic hydrogen and both the amine and methoxy good yields (Schemes 3 and 4). The H NMR of complex 6 in
functionalities.
CD2Cl2 is somewhat complicated. The –N(CH3)H– resonance
The dehalosilylation reaction of trimethylsilyl ether 3 with occurs as a broad singlet at δ 8.05; this proton in turn couples
TiCl4(thf)2 proceeded cleanly to yield complex 5 in good yield to both the amine methyl group yielding a doublet at δ 3.75
(Scheme 2). All the titanium complexes discussed herein have (3J = 5.1 Hz) and to the methylene protons. Furthermore, the
been characterised with 1H and 13C NMR spectroscopy and methylene protons, along with the NH proton, are diastereoto-
elemental analysis. Crystals suitable for X-ray diffraction were pic presenting as an ABX spin system with pseudodoublets at
grown by evaporation of a concentrated dichloromethane solu- δ 4.28 and δ 5.70 (2JA,B ≈ 12.8 Hz and 3JA,X/B,X ≈ 2.1 and 9.9 Hz),
tion of 5 (Fig. 2). The complex displays a distorted octahedral the assignment of the methylene protons was further con-
geometry with a meridional arrangement of the tridentate firmed using COSY spectroscopy. Crystals suitable for X-ray
ligand. This arrangement is well known for mono-ligated sali- diffraction were prepared by evaporation of a saturated dichloro-
cylaldimine complexes of titanium bearing one to two carbon methane solution of complex 6 (Fig. 3). The solid state struc-
linkers between the imine nitrogen and the donor ture shows the ligands arranged in a slightly distorted trigonal
moiety.26,27,31,33–37 Comparison of the key bond lengths with a bipyramidal geometry around the titanium centre. The distor-
previously reported analogous system derived from (1R,2S)- tion around the titanium centre is apparent in the Cl3–Ti–Cl4
(−)-1-aminoindanol26 shows good agreement between the Ti– bond angle (175.25(3)°), O1–Ti1–Cl2 bond angle (116.60(7)°)
Ophenoxide (1.784(3)–1.785(3)/1.7924(16) Å) and Ti–N bond and O1–Ti1–Cl4 bond angle (94.75(7)°). Additionally, the Ti–
lengths (2.160(4)–2.1674(4)/2.1570(19) Å) while the Ti–Odonor Clax bond lengths (2.3114(8)–2.3716(8) Å) are somewhat length-
(2.122(4)–2.124(3)/2.0514(17) Å) is somewhat lengthened in our ened compared to the Ti–Cleq bond lengths (2.2554(8)–2.2695(8)
complex; a result which may be attributed to the reduced Å); the longest of which is the Ti–Cl3 bond (2.3716(8) Å).
Lewis basic nature of the methoxy- versus hydroxyl-functional- This lengthing can be attributed to the H1⋯Cl3 interaction
ity. Attempts to prepare an analogous complex where the (2.63 Å) reducing the hard Lewis basicity of the chloro ligand
6-position of the phenoxide ring is unsubstituted were also and thus reducing its capacity to donate to the titanium metal
undertaken, however instead of the desired mono-ligated centre. The ammonium proton also feels a hydrogen bonding
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ligand where it occurs at δ 13.11, which integrates for one
proton and has been assigned to the hydroxy proton of the
ligand system, however the imine proton does not show the
characteristic splitting that has been reported for analogous
complexes of Ti wherein the proton is associated with the
nitrogen centre.48 This, and the considerable broadening of
the NMR signals, is highly suggestive that the ligand is associ-
ated with the titanium centre but that deprotonation has not
occurred, a fact that is consistent with the elemental analysis.
However, without a solid state structure it is hard to speculate
on the exact geometry and as such the connectivity shown in
Scheme 4 is tentative.
Ethylene oligomerisation and polymerisation
The titanium complexes 5–7 have been screened for ethylene
oligomerisation/polymerisation activity in combination with
methylaluminoxane (MAO). While complexes 6 and 7 have
been prepared as what are essentially the hydrochloric acid
adducts of the desired mono-anionic tridentate systems, analo-
gous systems have been shown in the literature to readily liber-
ate the acid under basic conditions.41,48,50 Furthermore, the
inventors of the highly active Mitsui system demonstrate in
their patent literature that the reaction mixture of the ligand
and TiCl4 can be employed as an olefin oligomerisation cata-
lyst without purification.38 As such it is easy to conceive a
similar process upon introduction of the alkylaluminium co-
catalysts to our isolated complexes, to yield the desired mono-
anionic tridentate systems.
Fig. 3 Molecular structure of 6. Thermal ellipsoids are shown at the 50% prob-
ability level (lattice solvent DCM and toluene are omitted). All methyl, methylene
and aromatic-ring hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°): Ti–O 1.7573(18), Ti–Cl 2.2554(8)–2.3716(8), N1–H1
0.77(4), H1⋯O2, Cl3 2.50, 2.63, O–Ti–Cleq/ax,eq/eq 89.91(7)–94.75(7), 116.60(7)–
120.98(7), Cl–Ti–Cleq/ax,eq/eq,ax/ax 87.24(3)–89.88(3), 122.24(3), 175.25(3), Ti1–
O1–C1 167.23(17), N1–H1⋯O2,Cl3 116.9, 147.0.
The results of the catalytic testing are shown in Table 1.
Complex IV has been included as a benchmark for our novel
interaction with the methoxy substituent (2.50 Å). Trigonal systems. Under optimised conditions this complex has been
bipyramidal geometries for titanium are, to the authors’ reported to yield 1-hexene selectivities in excess of 93% and
knowledge, relatively rare with complexes typically preferring activities greater than 6800 kg (mol Ti)−1
h
−1 bar−1.9 Under our
to assume either a piano stool type ligand arrangement or an non-optimised conditions complex IV yielded a significantly
octahedral geometry via coordination of pendant donors or lower activity, albeit still highly active, than that reported in
chloro-bridging forming oligomeric species. However examples the literature (Table 1, entry 1).9 The selectivity of the catalyst
for Ti(II) and Ti(III),43 cyclopentadienyl stabilised Ti(IV) and in our hands compares favourably with the previously reported
Zr(IV)44,45 and Ti(IV) alkoxy46 and amido47 ligand systems have values including high selectivity towards 1-hexene and low
previously appeared in the literature. Overall, a titanate polymer formation. The majority of the C8+ fraction consisted
complex has been generated which is charge stabilised intra- of three C10 isomers which is consistent with previous reports
molecularly by the ligands cationic ammonium moiety. As wherein 1-hexene and ethylene are cotrimerised to form
such, it is apparent that the amine functionality of 4 acts as a branched oligomers.9 However, unlike the original reports by
base capturing the proton generated during synthesis; analo- the researchers at Mitsui Chemicals we noted small portions
gous reactions have previously been noted for group IV of 1-butene (0.5%), 1-octene (0.3%) and C12H24 (0.1%) and
metals.48–50 Previous work has shown that analogous com- C14H28 (0.1%) branched isomers amongst the liquid fraction.
pounds readily liberate hydrochloric acid in the presence of tri- The C14 fraction is readily explained by the co-trimerisation of
ethylamine, however attempts employing complex 6 yielded two molecules of 1-hexene with one molecule of ethylene. To
complex mixtures of 6, 6-HCl and triethylamine hydrochloride. the contrary, the C12 isomers may result from co-trimerisation
Attempts to prepare HCl free 6 by deprotonation of the ligand of 1-octene with two ethylene molecules or the dimerisation of
with n-butyllithium or NaN(SiMe3)2 and subsequent reaction two 1-hexene molecules; given the relatively low abundance of
with TiCl4 yielded only an intractable mixture with no isolable 1-octene in the catalysis mixture, formation through the dimer-
species.51 Similarly, preparation of the trimethylsilyl ether isation route seems the most likely. In order to confirm that
derivative of 4, upon introduction to TiCl4, yielded the same the C12 isomers were the result of dimerisation of 1-hexene, a
result.
catalytic run was performed wherein upon activation of the cat-
The 1H NMR of complex 7 in CD2Cl2 shows a broadened alyst a portion of 1-hexene was added but no ethylene was
singlet at δ 8.73, shifted significantly upfield from the free introduced to the system. Upon quenching and analysis of the
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Table 1 Ethylene oligomerisation/polymerisation with 5–7 and MAOa
Entry
Catalyst
MAO equiv.
Activityb
% 1-Butene
% 1-Hexene
% 1-C8+
% Polyethylene
1
2
3
4
5
6
7
8
IV
5
6
7
7
7
7
7
300
300
300
300
400
1000
200
100
236
0.6
14
24
29
28
7
0.5
7.4
1.1
0.5
0.3
0.3
Trace
0.9
87.5
0.7
1.6
11.3
9.7
3.5
9.0
—
3.0
91.9
96.3
86.9
89.7
95.9
75.2
97.5
1.0
1.3
0.3
0.3
—
24.8
0.3
13
1.3
a Conditions: 20 μmol catalyst loading, toluene (50 mL), 5 bar ethylene, 30 °C, 30 min. b kg product {(mol metal) h bar}−1
.
liquid oligomers a series of dimers, trimers and tetramers colour which dissipated in contact with air and during the
were detected, of which the dimers were the most prevalent. polymer washing. This colour is indicative of catalyst reduction
However, significant isomerisation of the residual 1-hexene to a titanium(III) species54 – a process which has been reported
into two new isomers was also noted; such isomerisation is for some titanium compounds in combination with alkyl-
not evident in the presence of ethylene and as such it is hard aluminiums.55,56 Tang and co-workers have previously reported
to draw firm conclusions on the exact mode by which the C12 that mono-anionic tridentate systems with the phenoxy-imine
isomers are formed.
motif of the form [−ONO] can readily stabilise the Ti(IV) metal
In all cases the novel precatalysts show reduced activities centre in conjunction with modified MAO. In the same study
and selectivities in comparison to the parent system for ethyl- analogous compounds of the form [−ONS] were shown to
ene trimerisation. Complex 5 showed the lowest activity of all readily undergo reduction in the presence of the same activa-
the complexes that were screened (Table 1, entry 2) and while tor yielding ethylene polymerisation catalysts.33 It is possible
a considerable amount of polymer was formed the liquid to suggest that a similar reduction is occurring in our system
phase showed interesting selectivity towards 1-butene (7.4% wherein the majority of the 1-hexene is formed in the initial
overall). Similar mono-ligated bidentate phenoxy-imine com- period of catalysis and as time progresses the catalyst reduces
pounds have been shown to dimerise ethylene in combination to form a titanium(III) polymerisation species. Alternatively,
with some alkylaluminiums.52 Previous reports have suggested upon activation it is also possible to envisage that a catalytic
that short alkyl-chains (less than four carbons) between the mixture forms wherein some of the complex remains as the
imine functionality and the donor moiety, as is the case in this titanium(IV) trimerisation species while the majority is reduced
complex, can lead to a selectivity shift from ethylene oligomeri- to the titanium(III) polymerisation species. Following this
sation to polymerisation.38 In a related study of such short notion, increasing the concentration of MAO employed in cata-
chain complexes it was found that having a hard Lewis basic lysis from 300 to 400 and 1000 equivalents (cf. Table 1, entries
donor such as an ether considerably impeded the activity of 4–6) gave comparable activities but showed
a marked
catalyst when compared to softer Lewis basic donors and as reduction in 1-hexene selectivity, suggesting a reduction in the
such may be the reason for the low activity.33 Complex 6, while concentration of the ethylene trimerisation catalyst. In an
being moderately active for ethylene polymerisation, showed effort to reduce the rate of reduction of the metal centre and to
unremarkable selectivity in the liquid phase (Table 1, entry 3) increase the selectivity of the catalyst to 1-hexene, a number of
yielding a series of even-numbered linear alpha olefins from runs employing low MAO loadings were employed (Table 1,
C4–C28. From the catalytic data it appears that the conjugation entries 7 and 8). Reducing the MAO loading to 200 equivalents
between the phenoxide anion and the imine moiety, present did indeed increase the 1-hexene selectivity, although was
in IV, plays an important role in stabilising the catalyst accompanied by a reduced activity. A further reduction in MAO
towards ethylene trimerisation, although structural changes loading down to 100 equivalents unfortunately led to a com-
brought about by introduction of the amine may also play a plete loss of selectivity forming only a series of LAOs and
role.
polymer; such a change in selectivity is highly suggestive that
Complex 7, which is the most structurally similar to the insufficient activator is present to generate the targeted cataly-
Mitsui system IV, under the initial conditions gave the greatest tic species, and perhaps a different active species is forming.
selectivity towards 1-hexene (11%) of the novel systems To definitively ascertain whether the reduction of the titanium
explored herein (Table 1, entry 4), with the remaining product centre is occurring during the early stages of the reaction, or
predominately consisting of polymer. It was noted that premix- as a gradual process throughout the catalysis, a short run was
ing of the precatalyst with MAO changed the solution colour performed wherein the catalyst was activated with MAO before
from a bright orange to a pale yellow which is consistent with being exposed to ethylene for 30 seconds and then being
an alkylated titanium(IV) species,33,53 however upon com- quenched with hydrochloric acid. Analysis of products showed
pletion of the catalytic run the polymer obtained a deep purple a mixture of polyethylene (99%) and 1-hexene, which is highly
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supportive of a mechanism wherein the majority of the catalyst (3.00 g, 17.9 mmol), palladium(II) chloride (0.32 g,
is reduced to the titanium(III) species in the initial period of 1.79 mmol), triphenylphosphine (0.94 g, 3.58 mmol) and pot-
catalysis.
assium carbonate (3.69 g, 26.7 mmol) were suspended in
The formation of both short chain oligomers and polymer 45 mL of toluene and heated to 100 °C overnight. The resulting
indicates a number of active species to be present, possibly brown solution was cooled to room temperature and diluted
operating via different mechanisms. On a number of other with 45 mL of deionised water. The organic phase was separ-
occasions we have observed such behaviour with Ti cata- ated and the aqueous phase was extracted with 3 × 45 mL of
lysts.52,57 This frequently takes the form of oligomers formed toluene. The organic phases were combined, dried with
via a metallacycle mechanism, and polymer most likely result- sodium sulphate and the volatiles were removed under
ing from a Cossee mode of chain growth. This may, in these reduced pressure. The remaining brown residue was purified
other cases, be likewise due to oxidation state changes of tita- by column chromatography (1 : 4 ethyl acetate : petroleum
nium, as has been suggested above, although further work is spirits) to yield the title compound as a white solid in 40%
necessary to confirm this.
yield (1.54 g, 7.14 mmol). 1H NMR (CD2Cl2, 299.89 MHz): δ
6.75–7.41 (m, 8H, aryl-H), 3.58 (br s, 2H, NH2), 2.38 (s, 3H,
SCH3). 13C NMR (CD2Cl2, 75.41 MHz): δ 126.2, 137.6, 139.0,
144.6 (aryl-Cipso), 115.7, 116.3, 125.0, 125.2, 128.7, 129.9, 130.7,
130.8 (aryl-C), 15.4 (SCH3). MS (electron ionisation): m/z 215
Conclusions
Herein we have prepared a number of analogues to the Mitsui [M]+.
(Ti phenoxy-imine) ethylene trimerisation system.9 This cata-
Preparation of 2-(2′-methoxyphenyl)-N-methylaniline. 2-
lyst is clearly sensitive to changes in the bridging group Bromo-N-methylaniline (1.29 g, 6.91 mmol), 2-methoxyphenyl-
linking the third donor atom, the identity of this donor, and boronic acid (1.00 g, 6.58 mmol), palladium(II) chloride
also changes to the imine donor (reduction to an amine). Of (0.12 g, 0.658 mmol), triphenylphosphine (0.35 g, 1.32 mmol)
the modifications evaluated, the best result with respect to and potassium carbonate (1.36 g, 9.87 mmol) were combined
ethylene trimerisation was obtained when a thioether was and degassed with five vacuum/argon refill cycles. 15 mL of
introduced in place of the ether (complex 7). In this case sub- toluene was added and the suspension was heated to 100 °C
stantial selectivity towards 1-hexene was displayed in the oligo- overnight. The resulting dark brown suspension was cooled
meric products, however the formation of polyethylene still and washed with 30 mL of brine solution. The brine solution
dominates. This may be due to reduction of the catalyst to was back extracted with 2 × 20 mL of toluene and the organic
Ti(III), whereas 1-hexene is expected to result from a Ti(II)/Ti(IV) phases were combined, dried on sodium sulphate, filtered and
cycle. Further work is required to confirm this however. This concentrated to give a brown residue. The residue was purified
work again illustrates the tendency of Ti precatalysts to form by column chromatography (1 : 4 ethyl acetate : petroleum
multiple active sites following activation with MAO, and hence spirits) to give a white solid, which upon washing with 2 ×
to display multi-mechanism behaviour. The challenge in 5 mL petroleum spirits, was identified as the title compound
obtaining selective oligomerisation with these systems there- in 41% yield (0.57 g, 2.69 mmol). 1H NMR (CDCl3,
fore seems to lie in control of this behaviour.
299.89 MHz): δ 7.23–7.56 (m, 3H, aryl-H), 6.96–7.10 (m, 3H,
aryl-H), 6.73–6.82 (m, 2H, aryl-H), 3.81 (s, 1H, NH), 3.78 (s, 3H,
OCH3), 2.80 (s, 3H, NCH3). 13C NMR (CDCl3, 75.41 MHz): δ
146.8, 157.0 (aryl-Cipso), 110.3, 111.5, 117.0, 121.3, 128.7, 128.8,
129.1. 130.7, 131.6, 132.1 (aryl-C), 55.9 (OCH3), 31.2 (NCH3).
MS (electrospray ionisation): m/z 214.1 [M + H]+.
Experimental
General
All manipulations were performed under an atmosphere of
Preparation ligand 1. 3-tert-Butylsalicylaldehyde (1.54 g,
UHP argon (BOC gases) using standard Schlenk techniques or 8.66 mmol), 2-methyl-3-methoxypropyl-2-amine (0.89 g,
in an MBraun glovebox unless otherwise stated. Solvents, 8.66 mmol) and 3 Å molecular sieves were combined with
excluding dichloromethane, were purified by passage through 20 mL of diethyl ether and the bright yellow mixture was
an Innovative Technologies purification system and, where stirred overnight. The sieves were removed via filtration and
appropriate, stored over a sodium mirror. Anhydrous dichloro- were washed with a further 3 × 20 mL portions of diethyl
methane was purchased from Sigma-Aldrich and stored over ether. The organic fractions were combined and the volatiles
3 Å molecular sieves. CP grade ethylene (BOC gases) was puri- were removed in vacuo to give a yellow liquid which was puri-
fied by passage through a column of activated 3 Å molecular fied by flash distillation at 130 °C under full pump vacuum
sieves and alumina. NMR spectra were recorded on a Varian yielding the title compound as a yellow liquid in 52% yield
Mercury Plus NMR spectrometer operating at 300 MHz (1H) or (1.19 g, 4.53 mmol). 1H NMR (CD2Cl2, 299.89 MHz): δ 14.63 (s,
75 MHz (13C) at room temperature. MAO was supplied by Albe- 1H, OH), 8.40 (s, 1H, NvCH), 7.30 (dd, J = 1.50, 6.00 Hz, 1H,
marle as a 10% solution in toluene. Complex IV was prepared aryl-H), 7.14 (dd, J = 1.50, 6.00 Hz, 1H, aryl-H), 6.79 (t, J = 7.50
according to the literature method.9
Hz, 1H, aryl-H), 3.38 (s, 2H, CH2–O–CH3), 3.35 (s, 2H, CH2–O–
Preparation of 2-(2′-(methylthio)phenyl)aniline. 2-Bromo- CH3), 1.42 (s, 9H, C(CH3)3), 1.31 (s, 6H, C(CH3)2). 13C NMR
aniline (3.23 g, 18.7 mmol), 2-(methylthio)phenylboronic acid (CD2Cl2, 75.41 MHz): δ 162.9 (NvCH), 119.2, 137.7, 161.3
Dalton Trans.
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(aryl-Cipso), 117.8, 129.5, 130.3 (aryl-C), 81.1 (CH2–O–CH3), 60.2 3 × 60 mL portions of deionised water. The organic phase was
(C(CH3)2), 59.6 (CH2–O–CH3), 35.1 (C(CH3)3), 29.5 (C(CH3)3), then dried on sodium sulphate, filtered and the volatiles
24.6 (C(CH3)2). MS (electrospray ionisation): m/z 264.4 [M]+.
removed in vacuo to give a yellow residue which was recrystal-
Preparation of ligand 2. 2-(2′-(Methylthio)phenyl)aniline lised from 10 mL petroleum spirits at −20 °C to give com-
(1.03 g, 4.76 mmol) and 2-hydroxy-5-methyl-3-(1-adamantyl)- pound 4 as white needles in 18% yield (0.21 g, 0.484 mmol).
benzaldehyde (1.29 g, 4.75 mmol) were combined and heated Subsequent concentration and recooling of the supernatant
to 120 °C overnight with stirring to give an orange solid. gave a second crop of 4 (0.14 g, 0.334 mmol, yield: 12%, total
Unreacted starting material was sublimed by heating the reac- yield: 40%). 1H NMR (CD2Cl2, 299.89 MHz): δ 9.37 (s, 1H, OH),
tion mixture to 240 °C under vacuum. The remaining solid 6.87–7.42 (m, 10H, aryl-H), 4.06 (s, 2H, CH2), 3.79 (s, 3H,
was extracted with 20 mL of dichloromethane, filtered and OCH3), 2.33 (s, 3H, NCH3), 1.31 (s, 9H, C(CH3)3), 1.25 (s, 9H,
dried under reduced pressure to give the title compound as an C(CH3)3). 13C NMR (CD2Cl2, 75.41 MHz): δ 121.2, 129.6, 135.5,
orange solid in 99% yield (2.20 g, 4.70 mmol). 1H NMR 136.1, 140.8, 151.8, 154.2, 156.8 (aryl-Cipso), 111.3, 120.8, 120.9,
(CD2Cl2, 299.89 MHz): δ 13.11 (s, 1H, OH), 8.53 (s, 1H, 123.2, 124.3, 125.2, 128.9, 129.3, 131.4, 132.3 (aryl-C), 61.0
NvCH), 6.74–7.51 (m, 10H, aryl-H), 2.37 (s, 3H, SCH3), 2.25 (s, (CH2), 55.6 (OCH3), 42.2 (NCH3), 34.4, 35.1 (C(CH3)3), 29.6,
3H, aryl-CH3), 2.04 (s, 9H, adamantyl-4,6,10-CH2 and adaman- 31.8 (C(CH3)3). MS (electrospray ionisation): m/z 432.2
tyl-CH), 1.77 (s, 6H, adamantyl-2,8,9-CH2). 13C NMR (CD2Cl2, [M + H]+.
75.41 MHz): δ 163.4 (NvCH), 127.3, 130.7, 136.0, 137.8, 138.4,
Preparation of complex 5. Compound 3 (0.30 g, 0.91 mmol)
138.6, 147.1, 158.8 (aryl-Cipso), 118.6, 124.9, 125.2, 126.8, 128.5, was taken up in 15 mL of dichloromethane and was added
129.5, 130.4, 130.5, 131.1, 131.7 (aryl-C), 29.6, 37.5, 40.5 (ada- dropwise to TiCl4(thf)2 (0.30 g, 0.91 mmol) in 15 mL of
mantyl-C), 37.2 (quaternary adamantyl-C), 20.7 (Ar-CH3), 15.8 dichloromethane at −95 °C with vigorous stirring. Upon com-
(SCH3). MS (electron ionisation): m/z 467 [M]+.
plete addition the acetone/liquid nitrogen slurry was removed
Preparation of ligand 3. 1 (0.62 g, 2.37 mmol) was dissolved and the reaction mixture was allowed to return to room temp-
in 10 mL of petroleum spirits with stirring. The bright yellow erature. The orange solution was stirred overnight. The vola-
solution was cooled to −78 °C and n-butyllithium (1.48 mL, tiles were removed in vacuo and the resulting orange solid was
2.37 mmol, 1.6 M in hexanes) was added dropwise. Upon com- washed with 2 × 10 mL of petroleum spirits before being dried
plete addition the resulting white suspension was allowed to under reduced pressure to give 5 as an orange powder in 74%
warm to room temperature and stirred for 4 hours. The super- yield (0.28 g, 0.67 mmol). Large orange needles suitable for
natant was then removed via cannula filtration and the remain- X-ray diffraction were grown by evaporation of a dichloro-
1
ing white solid was washed with a further 10 mL portion of methane solution of 5. H NMR (CD2Cl2, 299.89 MHz): δ 8.33
petroleum spirits before being dried in vacuo. The solid was (s, 1H, NvCH), 7.66 (dd, J = 1.50, 6.60 Hz, 1H, aryl-H), 7.47
then dissolved in 10 mL of tetrahydrofuran and 2.5 mL of tri- (dd, J = 1.50, 6.60 Hz, 1H, aryl-H), 7.19 (t, J = 7.80 Hz, 1H,
methylsilyl chloride added. The solution was then heated to aryl-H), 4.41 (s, 3H, CH2–O–CH3), 4.27 (s, 2H, CH2–O–CH3),
60 °C overnight. Upon cooling the volatiles were removed 1.53 (s, 6H, C(CH3)2), 1.51 (s, 9H, C(CH3)3). 13C NMR (CD2Cl2,
under reduced pressure and the remaining residue was 75.41 MHz): δ 162.5 (NvCH), 127.4, 137.3, 160.7 (aryl-Cipso),
extracted with 20 mL of petroleum spirits. Concentration of 125.2, 133.6, 134.6 (aryl-C), 86.2 (CH2–O–CH3), 68.8 (CH2–O–
the extract gave the title compound as a yellow liquid in 38% CH3), 66.1 (C(CH3)2), 35.5 (C(CH3)3), 29.8 (C(CH3)3), 27.2 (C
yield (0.30 g, 0.91 mmol). 1H NMR (CD2Cl2, 299.89 MHz): δ (CH3)2). Anal. Calcd for C16H24NO2TiCl3: C 46.13, N 3.36,
8.51 (s, 1H, NvCH), 7.75 (dd, J = 1.80, 6.00 Hz, 1H, aryl-H), H 5.81. Found: C 46.39, N 3.31, H 5.68.
7.37 (dd, J = 1.80, 6.00 Hz, 1H, aryl-H), 6.91 (t, J = 7.50 Hz, 1H,
Preparation of complex 6. Titanium(IV) tetrachloride (0.15 g,
aryl-H), 3.36 (s, 3H, CH2–O–CH3), 3.32 (s, 3H, CH2–O–CH3), 0.81 mmol) in 10 mL of toluene was cooled to −95 °C with vig-
1.40 (s, 9H, C(CH3)3), 1.26 (s, 6H, C(CH3)2), 0.33 (s, 9H, orous stirring. To the resulting bright orange solution was
Si(CH3)3). 13C NMR (CD2Cl2, 75.41 MHz): δ 129.5, 141.4, 154.8 added dropwise a solution of 4 (0.32 g, 0.73 mmol) in 5 mL of
(aryl-Cipso), 154.4 (NvCH), 121.5, 126.5, 129.7 (aryl-C), 81.7 toluene. Upon complete addition the resulting dark red sol-
(CH2–O–CH3), 61.2 (C(CH3)2), 59.4 (CH2–O–CH3), 35.1 ution was allowed to return to room temperature and stirred
(C(CH3)3), 30.8 (C(CH3)3), 24.7 (C(CH3)2), 2.06 (Si(CH3)3). MS overnight. The volatiles were removed in vacuo and the result-
(electron ionisation): m/z 335 [M]+.
ing dark red powder was dried for one hour. The powder was
Preparation of ligand 4. 3,5-Di-tert-butyl-2-hydroxybenzyl washed with 3 × 5 mL of petroleum spirits and dried to give
bromide (0.62 g, 2.69 mmol) and 2-(2′-methoxyphenyl)-N- the title compound in 80% yield (0.36 g, 0.58 mmol). Crystals
methylaniline (0.57 g, 2.69 mmol) were combined and suitable for X-ray crystallography were grown by evaporation of
degassed using five vacuum/argon refill cycles. The solids were
a
dichloromethane solution of 6. 1H NMR (CD2Cl2,
dissolved in 70 mL of tetrahydrofuran and triethylamine 299.89 MHz): δ 8.05 (bs, 1H, N+–H–O−), 7.79 (m, 2H, aryl-H),
(0.42 mL, 2.96 mmol) was added dropwise to give a white sus- 7.62 (m, 1H, aryl-H), 7.37–7.44 (m, 3H, aryl-H), 6.99 (d, J =
pension which was stirred for two hours at room temperature. 8.1 Hz, 1H, aryl-H), 6.78 (t, J = 7.5 Hz, 1H, aryl-H), 5.97 (m, 2H,
The suspension was filtered and the filtrate was concentrated aryl-H), 5.70 (dd, J = 2.1, 12.8 Hz, 1H, CH2), 4.28 (dd, J = 9.9,
under reduced pressure to yield a yellow liquid. The liquid was 12.8 Hz, 1H, CH2), 3.79 (s, 3H, OCH3), 3.75 (d, J = 5.1 Hz, 3H,
redissolved in 50 mL of dichloromethane and washed with NCH3), 1.43 (s, 9H, C(CH3)3), 1.04 (s, 9H, C(CH3)3). 13C NMR
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(CD2Cl2, 75.41 MHz): δ 170.1 (O aryl-Cipso), 121.2, 122.0, 134.9, for 5 which could be modelled as a two site complementary
138.0, 140.8, 147.3, 155.4 (aryl-Cipso), 112.4, 120.4, 122.4, 127.4, occupancy of DCM with common chloride. Disordered toluene
127.8, 130.7, 130.8, 131.4, 131.9, 133.1 (aryl-C), 62.3 (CH2), lattice solvent was apparent for 6, residing on 4bar symmetry
56.0 (OCH3), 47.4 (NCH3), 34.9, 36.1 (C(CH3)3), 31.2, 31.4 sites, and was similarly modelled. Details of the disorder mod-
(C(CH3)3). Anal. Calcd for C29H37NO2TiCl4: C 56.06, N 2.25, H elling are provided in the cif files. Ammonium, imminium and
6.01. Found: C 55.22, N 1.75, H 5.39.
phenolic protons were located and positionally refined in the
Preparation of complex 7. To titanium(IV) tetrachloride cases of 4 and 6. All other hydrogen atoms were placed in cal-
(0.6 mL, 0.49 mmol) in 10 mL of toluene at −95 °C was added culated positions and refined using a riding model with fixed
dropwise compound 2 (0.26 g, 0.44 mmol) in 6 mL of toluene. C–H distances of 0.95 Å (sp2CH), 0.99 Å (CH2), 0.98 Å (CH3).
The dark red solution was allowed to return to room tempera- The thermal parameters of all hydrogen atoms were estimated
ture and stirred overnight. The volatiles were removed in vacuo as Uiso(H) = 1.2Ueq(C) except for CH3 where Uiso(H) = 1.5Ueq(C).
and the resulting dark red honeycomb was crushed into a A summary of crystallographic data given below.
powder which was washed with 3 × 10 mL of petroleum spirits.
Crystal data for 4. C29H37NO2, M = 431.60, monoclinic, a =
The solid was then dissolved in dichloromethane, filtered and 26.9936(15), b = 10.4290(19), c = 18.5420(17) Å, β = 107.509(4)°,
dried in vacuo. The dark red solid was then dissolved in diethyl U = 4978.0(11) Å3, T = 100 K, space group C2/c (no. 15), Z = 8,
ether and a red powder was precipitated via layering with pet- 41 288 reflections measured, 6157 unique (Rint = 0.0323), 5469
roleum spirits. Isolation of the solid via filtration gave the title > 4σ(F), R = 0.0486 (observed), Rw = 0.1321 (all data). Crystal
compound in 70% yield (0.20 g, 0.31 mmol). 1H NMR (CD2Cl2, data for 5: C16H24Cl3NO2Ti·1/2(CH2Cl2), M = 459.07, triclinic, a
299.89 MHz): δ 8.73 (bs, 1H, H–O), 8.03 (s, 1H, NvCH), = 8.1970(18), b = 16.344(3), c = 16.526(2) Å, α = 90.003(2), β =
7.04–7.52 (m, 10H, aryl-H), 2.62 (s, 3H, SCH3), 2.31 (s, 3H, aryl- 103.428(5) γ = 103.650(7)°, U = 2089.1(7) Å3, T = 100 K, space
ˉ
CH3), 2.12–2.17 (m, 9H, adamantly-CH), 1.85 (m, 6H, ada- group P1 (no. 2), Z = 4, 28 454 reflections measured, 7664
mantly-CH). 13C NMR (CD2Cl2, 75.41 MHz): δ 193.6 (NvCH), unique (Rint = 0.0250), 7257 > 4σ(F), R = 0.0796 (observed), Rw
=
123.9, 124.6, 124.7, 127.3, 128.8, 129.0, 129.1, 130.3, 131.1, 0.2232 (all data). Crystal data for 6: C29H37Cl4NO2Ti·5/4
132.7, 132.9, 134.4, 136.9, 139.9, 140.1 (aryl-C), 28.5, 36.2, 39.6, (C7H8)·CH2Cl2, M = 821.39, tetragonal, a = 22.585(2), c =
3
ˉ
39.8 (adamantly-C), 19.8 (Ar-CH3), 14.6 (SCH3). Anal. Calcd for 16.1750(18) Å, U = 8250.7(14) Å , T = 100 K, space group I4 (no.
C31H33NOSTiCl4: C 56.64, N 2.13, S 4.88, H 5.06. Found: 82), Z = 8, 68 917 reflections measured, 10 587 unique (Rint
=
C 56.62, N 2.07, S 5.19, H 4.88.
0.0568), 9354 > 4σ(F), R = 0.0433 (observed), Rw = 0.1127 (all
data). Crystal data for S1:† C24H34Cl4N2O4Ti, M = 604.23, tricli-
nic, a = 8.3590(9), b = 9.5330(5), c = 10.1630(5) Å, α = 86.070(5),
Ethylene polymerisation/oligomerisation
A 0.3 L stainless steel Parr 5500 Compact Mini Reactor was pre- β = 67.242(6), γ = 67.192(6)°, U = 685.24(9) Å3, T = 100 K, space
ˉ
heated to 120 °C and flushed with four vacuum/argon cycles group P1 (no. 2), Z = 1, 7522 reflections measured, 1945
and two ethylene purges. The reactor was cooled to the appro- unique (Rint = 0.0204), 1869 > 4σ(F), R = 0.0281 (observed), Rw
priate temperature and charged with toluene (total solvent 0.0677 (all data).
volume of 50 mL). The catalyst (20 μmol) in 10 mL of toluene
=
was then activated, in a Schlenk to observe any colour
changes, with 300 equivalents of MAO before injection into
Acknowledgements
the reactor. During the reaction, the pressure was kept con-
stant with a replenishing flow of ethylene. After 30 minutes
run time the replenishment of ethylene was ceased and the
reactor cooled to <10 °C before purging of excess ethylene to
atmospheric pressure and injection of a weighed amount of
nonane standard. Residual MAO was quenched with ∼10%
HCl solution and samples of the reaction mixture were taken
for analysis and quantification of soluble analytes via GC and
where appropriate GC-MS. Any polymer formed was removed
via filtration and washed with 10% HCl and methanol before
drying at ∼60 °C for 3 days.
The Australian Research Council is thanked for financial
support through grant FT100100609 to DSM and an Australian
Postgraduate Award to JAS. We thank Sasol Technology Ltd for
funding and permission to publish this work. Albemarle Asia
Pacific is thanked for donating the MAO solution. Noel Davies
and Thomas Rodemann of the UTas Central Science Labora-
tory are thanked for MS and elemental analysis measurements
respectively. Data for the structures of complexes 4–6 were
obtained on the MX1/MX2 beamlines at the Australian Syn-
chrotron, Victoria, Australia.
X-ray crystallography
Data for 4–6 and S1† were collected at −173 °C on crystals
mounted on a Hampton Scientific cryoloop at the MX1 beam-
line of the Australian Synchrotron.58 The structures were
solved by direct methods with SHELXS-97, refined using full-
matrix least-squares routines against F2 with SHELXL-97,59
and visualised using X-SEED.60 All non-hydrogen atoms were
refined anisotropically. Disordered lattice solvent was apparent
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