Imido titanium compounds bearing the 6-dimethylamino-1,4,6-trimethyl-1,4- diazacycloheptane ligand: Synthesis, structures, solution dynamics and ethylene polymerisation capability

Article abstract of DOI:10.1039/b802027b

Reaction of Me₄DACH (6-dimethylamino-1,4,6-trimethyl-1,4- diazacycloheptane) with Ti(N^tBu)Cl₂(py)₃ or Ti(N^tBu)Cl₂(NHMe₂)₂ gave Ti(N ^tBu)(Me₄DACH)Cl₂ (1) which in CD ₂Cl₂ solution exists as a mixture of trans and cis isomers (defined with respect to the imido ligand and the exocyclic NMe₂ donor of Me₄DACH). Aryl imido analogues of 1 were prepared from Ti(NAr)Cl₂(NHMe₂)₂ and Me₄DACH forming Ti(NAr)(Me₄DACH)Cl₂ (Ar = 2,6-C₆H ₃Me₂ (2), 2,6-C₆H₃ ⁱPr₂ (3), 2-C₆H₄^tBu (4), 2-C₆H₄CF₃ (5)) which also exist as isomers in solution. The activation parameters for the interconversion of trans- and cis-3 were measured by VT NMR spectroscopy. The solid state structures of trans-1, 3 and 4 and cis-2 have been determined. In the presence of MAO or dried MAO the compounds 1-5 act as moderatley productive ethylene polymerisation catalysts, with a modest productivity gain found on moving from the 1/MAO to 1/dried MAO catalyst system. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b802027b

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www.rsc.org/dalton | Dalton Transactions
Imido titanium compounds bearing the 6-dimethylamino-1,4,6-trimethyl-1,4-
diazacycloheptane ligand: synthesis, structures, solution dynamics and
ethylene polymerisation capability†
Gregory J. Hayday, Chao Wang, Nicholas H. Rees and Philip Mountford*
Received 5th February 2008, Accepted 11th March 2008
First published as an Advance Article on the web 9th April 2008
DOI: 10.1039/b802027b
Reaction of Me4DACH (6-dimethylamino-1,4,6-trimethyl-1,4-diazacycloheptane) with
Ti(NtBu)Cl2(py)3 or Ti(NtBu)Cl2(NHMe2)2 gave Ti(NtBu)(Me4DACH)Cl2 (1) which in CD2Cl2
solution exists as a mixture of trans and cis isomers (defined with respect to the imido ligand and the
exocyclic NMe2 donor of Me4DACH). Aryl imido analogues of 1 were prepared from
Ti(NAr)Cl2(NHMe2)2 and Me4DACH forming Ti(NAr)(Me4DACH)Cl2 (Ar = 2,6-C6H3Me2 (2),
i
t
2,6-C6H3 Pr2 (3), 2-C6H4 Bu (4), 2-C6H4CF3 (5)) which also exist as isomers in solution. The activation
parameters for the interconversion of trans- and cis-3 were measured by VT NMR spectroscopy. The
solid state structures of trans-1, 3 and 4 and cis-2 have been determined. In the presence of MAO or
dried MAO the compounds 1–5 act as moderatley productive ethylene polymerisation catalysts, with a
modest productivity gain found on moving from the 1/MAO to 1/dried MAO catalyst system.
Introduction
Homogeneous olefin polymerisation catalysts have been a continu-
ing focus of academic and industrial interest, and a diverse number
of systems have been investigated with the purpose of optimizing
catalyst performance and polymer properties.1–23 Of particular
relevance to our present contribution is the ability of certain
transition metal imido compounds (general class M(NR)(L)X2)
to act as Ziegler-type olefin polymerisation catalysts. The first
systems of this type were derived from bis(imido)chromium
t
dichloride and dialkyl compounds Cr(NR)2X2 (R = Bu or 2,6-
C6H3 Pr2; X = Cl, Me or CH2Ph),24,25 and a number of other Group
i
4, 5 and 6 systems have since been reported.23
As part of our broad research program in titanium imido
chemistry26–28 we have targeted compounds of the type Ti(NR)(fac-
Fig.
1
Top: Previously-reported compounds of the type
N3)Cl2 (Fig. 1; fac-N3 = triazacyclohexane (TACH),29,30 triaza-
cyclononane (TACN)30–35 or tris(3,5-dimethylpyrazolyl)methane
(TPM)36,37) as potential olefin polymerisation precatalysts, along
with other Group 4 and 5 imido systems.38,39 To gain an
understanding of the underlying organometallic chemstry of
these systems we described the synthesis, properties and DFT
bonding analysis of well-defined macrocycle-supported imido
titanium monoalkyl cations [Ti(NtBu)(TACN)R]+ (R = Me or
CH2SiMe3), along with stoichiometric C–H bond and solvent
activation reactions, insertion reactions and addition products
with AlMe3.40–42
Ti(NR)(fac-N3)Cl2 (fac-N3 = TACN, TACH or TPM; R = alkyl
or aryl). Bottom: The Me4DACH ligand and its neutral and cationic
Group 3 compounds (anions omitted).
of both the particular fac-N3 ligand and the imido N-substituent,
R. The triazacyclononane systems Ti(NR)(TACN)Cl2 showed
ambient temperature productivities as high as ca. 600 kg mol−1 h−1
t
bar−1 for bulky alkyl imido groups (R = Bu),30,31,35 whereas for
the tris(pyrazolyl)methane systems Ti(NR)(TPM)Cl2 the highest
ambient temperature productivities (ca. 1200 kg mol−1 h−1 bar−1)
were found only for bulky aryl imido homologues (R = 2-
The properties and ethylene polymerisation productivities of the
Ti(NR)(fac-N3)Cl2 systems are highly dependent on the identity
i
t
C6H4Rꢀ or 2,6-C6H3Rꢀ2; e.g., Rꢀ = Pr, CF3, Bu).37 Under high
temperature (100 ◦C), industrially relevant conditions the TACN
and TPM catalyst families showed productivites in excess of 1–
2 × 105 kg mol−1 h−1 bar−1 with narrow polydispersities and
desirable molecular weights. In contrast, the triazacyclohexane
catalyst systems Ti(NR)(TACH)Cl2 gave very low productivities
and broad molecular weight distributions, regardless of the imido
R-substituent.30
Chemistry Research Laboratory, University of Oxford, Mansfield Road,
Oxford, UK OX1 3TA. E-mail: philip.mountford@chem.ox.ac.uk
1
† Electronic supplementary information (ESI) available: H NMR spec-
trum of 3 at 243 K; plots of molecular weight distributions determined
by GPC for the polyethylenes produced by 1, 3, 4 and 5. CCDC reference
numbers 676927–676930. For ESI or crystallographic data in CIF or other
electronic format see DOI: 10.1039/b802027b
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48
Despite the success of the TACN and TPM Ti(NR)(fac-
N3)Cl2 systems, there remains considerable scope for development
and improvement. Through combinatorial-type synthesis and
screening30,31,37 the dependence of polymerisation productivity
on the imido R-substituent is fairly well understood (over 80
different R-groups have been evaluated for TACN and TPM).
The dependence of the productivity on the fac-N3 donor lig-
ands is, however, much less well explored. In this context our
attention was drawn to recent reports of the 6-dimethylamino-
1,4,6-trimethyl-1,4-diazacycloheptane ligand (Me4DACH, Fig. 1)
and its homologues.43–46 The synthesis of Me4DACH is relatively
facile43 and potentially more versatile compared to that of TACN
and TPM. Surprisingly, its coordination chemistry is virtually
unexplored (no reports for metals outside of Group 3, Groups
8–10) and so there is much to learn in general terms regarding its
structural chemistry and the solution dynamics of its compounds.
Moreover, Hessen and coworkers have very recently reported
neutral and cationic Group 3 complexes of Me4DACH (Fig. 1)
whose ethylene polymerisation capability45,46 compares well with
the known TPM and TACN analogues.47 In this contribution
we therefore describe the synthesis, structures and ethylene
polymerisation capabilities of new imido titanium complexes of
Me4DACH.
yield from either Ti(NtBu)Cl2(py)3 or Ti(NtBu)Cl2(NHMe2)2
by Lewis base exchange, the chelating nature of Me4DACH
presumably contributing to the thermodynamic driving force in
these reactions. The reaction with Ti(NtBu)Cl2(py)3 proceeded
1
smoothly to completion at room temperature (as judged by H
monitoring) whereas with Ti(NtBu)Cl2(NHMe2)2 best results were
obtained by heating at 60 ◦C. Samples of 1 were identical (in
particular the ratio of the two isomers, vide infra), regardless of
their method of preparation.
For the preparation of the aryl imido analogues Ti(NAr)-
i
(Me4DACH)Cl2 (Ar = 2,6-C6H3Me2 (2), 2,6-C6H3 Pr2 (3), 2-
t
C6H4 Bu (4), 2-C6H4CF3 (5)) we used only the route starting
from Ti(NAr)Cl2(NHMe2)2 (Scheme 1). This is because the
corresponding tris(pyridine) synthons Ti(NAr)Cl2(py)3 are less
conveniently prepared and susceptible to pyridine loss leading
to the formation of poorly soluble dimers.48–50 The new com-
pounds 2–5 were obtained in 70–85% isolated yield after heating
Ti(NAr)Cl2(NHMe2)2 with Me4DACH (1 equiv.) in benzene for
16 h.
All five compounds Ti(NR)(Me4DACH)Cl2 (1–5) exist as
mixtures of isomers in solution. These are designated trans and
cis (as defined in Scheme 1) with regard to the relative positions of
the imido ligand and the NMe2 donor of Me4DACH. The isomers
are in dynamic equilibrium with each other as determined by
variable temperature NMR spectroscopy. The ratio of trans to cis
isomers depends mostly on the imido N-substituent as summarised
in Table 1 although there is no apparent pattern. Variable
temperature experiments showed that the trans/cis equilibium
contants were virtually temperature-independent. Examples of
both trans- and cis-Ti(NR)(Me4DACH)Cl2 have been structurally
characterised (vide infra). Upon dissolving a single crystal of either
the pure trans or cis isomer an equilibrium mixture is again formed,
suggesting that the isomer obtained in the solid state results from
differences in solubility or crystal packing forces and confirming
the dynamic nature of the trans/cis equilibria.
Results and discussion
Synthesis, solid state structures and solution dynamics of
Ti(NR)(Me4DACH)Cl2
The choice of imido N-substituent (R) was based on those
found to be successful previously in the TACN (R = tBu
t
i
or 2-C6H4 Bu) or TPM (R = 2,6-C6H3Me2, 2,6-C6H3 Pr2, 2-
t
C6H4 Bu, 2-C6H4CF3) catalyst families.30,31,37 The syntheses of
the new Me4DACH compounds are summarised in Scheme 1.
Ti(NtBu)(Me4ACH)Cl2 (1) was prepared in 60–70% isolated
Scheme 1 Synthetic routes to Ti(NR)(Me4DACH)Cl2 (1–5).
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Table 1 Amounts of trans and cis isomers for Ti(NR)(Me4DACH)Cl2
t
i
t
(R = Bu (1), 2,6-C6H3Me2 (2), 2,6-C6H3 Pr2 (3), 2-C6H4 Bu (4), 2-C6H4CF3
(5)) in CD2Cl2 solution at 293 K
Compound
% trans isomer
% cis isomer
1
2
3
4
5
43
21
18
28
53
57
79
82
72
47
The NMR spectrum of Ti(NtBu)(Me4DACH)Cl2 (1) is shown
in Fig. 2 by way of example, with the methyl group resonances for
each isomer labelled (full assignments for 1 and all the compounds
were achieved through 1- and 2-dimensional correlation and NOE
experiments—see Experimental section). The trans isomer (1-
trans) has molecular Cs symmetry (confirmed by X-ray crystal-
lography, vide infra) and so gives rise to only one resonance for the
Me4DACH ligand NMe2 substituent (2.18 ppm, integral 6H) and
another (2.97 ppm, 6 H) for the ring 1- and 4-position NMe groups.
In contrast, 1-cis possesses no molecular symmetry elements and
so four resonances (2.27 & 2.67 and 3.13 & 3.20 ppm, respectively,
each integral 3H) are seen for these groups. In both 1-trans and
1-cis the tert-butyl and Me4DACH ring 6-Me groups appear as
singlets between 0.7 and 1.1 ppm.
Fig. 3 Simulated (left) and observed (right) 1H NMR spectra of
Ti(N-2,6-C6H3 Pr2)(Me4DACH)Cl2 (3), corresponding to the resonances
i
of CHMe2 in the cis-isomer (upfield) and trans-isomer (downfield) over
the stated range of temperatures.
strongly dissociative process (e.g. Me4DACH ligand dissociation)
and is more suggestive of an “in-place” rotation mechanism
proposed previously for intramolecular exchange processes in
various triazacyclohexane-imido and related titanium compounds
Ti(NR)(TACH)Cl2 (R = alkyl, aryl or NPh2).29,35,53 Note also that
the dynamic processes for Ti(NR)(Me4DACH)Cl2 do not involve
exchange of (added) free and coordinated Me4DACH ligand, and
nor is there exchange of the “up” and “down” (with respect to the
metal center) Me4DACH ring methylene hydrogens. Although all
of these observations militate against a fully dissociative exchange
mechanism, a partial dissociation cannot be excluded (e.g. j3 →
j2 coordination to form a 5-coordinate intermediate).
Fig.
2
The 1H NMR spectrum of Ti(NtBu)Cl2(Me4DACH) (1)
Diffraction-quality crystals of trans-Ti(NR)(Me4DACH)Cl2
(499.9 MHz, CD2Cl2, 293 K). Methyl group peaks for 1-trans and 1-cis are
labelled ꢀ and * respectively.
t
i
t
(R = Bu (1-trans), 2,6-C6H3 Pr2 (3-trans) and 2-C6H4 Bu (4-
trans)) were grown from CH2Cl2 or CH2Cl2–pentane solutions.
Their molecular structures are shown in Fig. 4. Cooling a
CH2Cl2 solution of 2 gave single crystals of cis-Ti(N-2,6-
C6H3Me2)(Me4DACH)Cl2 (2-cis) the structure of which is shown
in Fig. 5. Selected distances and angles for all four structures are
given in Table 2.
Molecules of 1-trans and 3-trans lie across crystallographic
mirror planes, whereas 4-trans has local molecular Cs symmetry at
Ti(1) (broken only by the aryl tert-butyl substituent). Each has an
approximately octahedral titanium center with cis chloride ligands
and the NMe2 group of Me4DACH lying approximately trans
to the imido ligand. All three structures are consistent with the
trans-Ti(NR)(Me4DACH)Cl2 geometries proposed in Scheme 1
for these isomers, assuming free rotation about the Cipso–Nimide
bond of 4-trans in solution. The general structural trends within
this series of trans-Ti(NR)(Me4DACH)Cl2 molecules are analo-
gous to those reported previously for structurally characterised
As is evident from Fig. 2,1-trans and 1-cis are in very slow
exchange (if at all) on the NMR timescale at room temperature.
The spectra of 2, 3 and 5 are broad at room temperature,
i
however, and Ti(N-2,6-C6H3 Pr2)(Me4DACH)Cl2 (3) was chosen
for further studies of the exchange process between 3-trans and
1
3-cis. The H NMR spectrum (see ESI†) of 3 at 243 K shows
distinct resonances for the trans and cis isomers. Upon warming,
these resonances broaden and at 315 K a broad, time-averaged
spectrum is obtained. Eight chemical exchange rate constants
1
for the interconversion of 3-trans and 3-cis were obtained by H
NMR line shape analysis51,52 in CD2Cl2 solution between 263 K
and 315 K using the isopropyl methine proton resonances of
the imido ligands. Fig. 3 shows the observed and simulated sub-
spectra. Fitting the rate contants to the Eyring equation51 yielded
the activation parameters DH‡ = 62.0(5.7) kJ mol−1 and DS‡ =
−5(19) J mol−1 K−1. The small value of DS‡ is inconsistent with a
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t
i
t
Fig. 4 Displacement ellipsoid plot (20% probability) of trans-Ti(NR)(Me4DACH)Cl2 (R = Bu (1-trans), 2,6-C6H3 Pr2 (3-trans) or 2-C6H4 Bu (4-trans)).
H atoms and CH2Cl2 of crystallisation omitted for clarity. Atoms carrying the suffix ‘A’ are related to their counterparts by the symmetry operator x,
−y + 1/2, z.
t
Ti(NR)(TACN)Cl2 and Ti(NR)(TACH)Cl2 complexes (R = Bu
trans aryl imides 3-trans and 4-trans whereas the Ti–Cl bonds are
somewhat shorter in the latter. The Ti–NMe (intracyclic) distances
(Ti(1)–N(2) and Ti(1)–N(3)) are very different in 2-cis due the
trans influence of the imido ligand, whereas the Ti–NMe2 distance
(Ti(1)–N(1)) is now the shortest contact between titanium and
Me4DACH. It is interesting to note that the Ti(1)–N(2) (trans to
or various aryl groups).29,32,35,54 For example, the Ti Nimide distance
=
t
is shortest for R = Bu whereas the Ti–Cl distances are the
longest, due to the better donor ability of tert-butyl imido ligands
compared to aryl imides.49,53,55 All three compounds clearly show
the strong trans influences of the imido ligands with the Ti–NMe2
distances being substantially longer than the Ti–NMe distances. In
general, the distances and angles associated with 1-trans–4-trans
are much more comparable to those of the previously reported
TACN homologues than the TACH ones.
˚
˚
=
Ti Nimide) distance in 2-cis is only 2.413(2) A (ca. 0.11 A longer
than the average of the other Ti–NDACH contacts) whereas in the
˚
trans isomers Ti(1)–N(1) ranges from 2.483(2) to 2.491(2) A (ca.
˚
0.19 to 0.22 A longer than the other Ti–NDACH contacts). In 2-cis
Molecules of cis-Ti(N-2,6-C6H3Me2)(Me4DACH)Cl2 (2-cis,
Fig. 5) do not possess Cs symmetry in the solid state and the
structure of 2-cis is fully consistent with those proposed in general
for the cis-Ti(NR)(Me4DACH)Cl2 isomers in solution (Scheme 1).
an intracyclic NMe is trans to the imido ligand whereas in the
=
trans isomers the exocyclic NMe2 group is trans to Ti NR. This
latter orientation of the Me4DACH ligand therefore appears to
allow more flexibility. The shorter Ti(1)–N(1) bond appears to
be responsible for Ti(1)–Cl(1) (trans to N(1)) being somewhat
=
The Ti Nimide distance in 2-cis is comparable to those in the
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in comparison with the previous TACN and TPM systems.
According to GPC analysis (Table 3 and Fig. S2 of the ESI†)
the PEs produced had one principal lower molecular weight
component (ca. 80–90 wt%) with a Mw/Mn value of ca 2–
4. Broad and featureless higher molecular weight components
were also evident from the GPC analyses but formed only
a small proportion of the bulky polymer. 1H NMR analysis
(100 ◦C, 1,2-C6D4Cl2) of the soluble portion of the PEs from
Ti(NtBu)(Me4DACH)Cl2 (1) showed only saturated end groups,
consistent with chain transfer to AlMe3 (or another aluminium
species in solution).18,56 Examination of the ethylene uptake traces
for the polymerisations (mass flow of ethylene into the reactor)
showed that only precatalyst 1 gave a sustained uptake over
the course of the experiments, the other systems halting uptake
within a few minutes. This compares with the behaviour of the
corresponding triazacyclonone-supported catalysts for which the
tert-butyl imido homologue was the most long-lived.
As-supplied commercial MAO typically contains between 20–
30 wt% “free” AlMe3. It has been shown by others57–61 (and our-
selves for imido titanium catalysts30,35,40,42) that AlMe3 can bind to
the electron-deficient active species in Ziegler-type polymerisation
systems, thus inhibiting or even halting catalyst activity.18 Indeed,
the formation of saturated PEs in these systems is indirect evidence
of the role of heterobimetallic Ti–Al species.56 It has also been
shown that free aluminium alkyls can abstract certain neutral fac-
N3 ligands leading to catalyst decomposition.62 However, NMR
tube scale reactions between added AlMe3 to solutions of 1–5 gave
no evidence for abstraction of the Me4DACH ring. Nonetheless,
we thus decided to re-evaluate the series 1–5 using MAO that had
been dried in vacuo for 16 h to removed residual AlMe3 (confirmed
by 1H NMR, d-MAO).
Fig. 5 Displacement ellipsoid plot (20% probability) of cis-Ti(N-2,6-
C6H3Me2)(Me4DACH)Cl2 (2-cis). H atoms and CH2Cl2 of crystallisation
omitted.
longer than Ti(1)–Cl(2). As for the trans-Ti(NR)(Me4DACH)Cl2
isomers, the distances and angles associated with 2-cis are
comparable to those of the previously reported TACN homo-
logues.
Ethylene polymerisation studies
As mentioned, TACN and TPM-supported imido titanium com-
plexes Ti(NR)(fac-N)3Cl2 are very active ethylene polymerisation
catalysts when used in conjunction with MAO co-catalyst (pro-
ductivities in the range 600–1200 kg mol−1 h−1 bar−1 at ambient
temperature).30,31,37 The new compounds Ti(NR)(Me4DACH)Cl2
(1–5) were evaluated under the same ambient temperature condi-
tions as used in these previous studies. The polymerisation results
are summarised in Table 3. Plots of molecular weight distributions
determined by GPC for the polyethylenes produced by 1–5 are
given in the ESI.†
The productivity of 1 using d-MAO was somewhat improved
compared to as-supplied MAO, but the value obtained (85 kg
mol−1 h−1 bar−1) remained an order of magnitude lower than the
Ti(NtBu)(TACN)Cl2 analogue for example. The molar masses of
both the high and low molelcular weight components of the PEs
produced with 1/d-MAO were higher than those obtained with
as-supplied MAO, consistent with reduced frequency of chain
transfer to aluminium. The same trend was seen with the PEs
The productivity figures for 1–5 with as-supplied (Albermarle)
MAO are uniformly poor (5–22 kg mol−1 h−1 bar−1), especially
◦
t
i
˚
Table 2 Selected bond lengths (A) and angles ( ) for Ti(NR)(Me4DACH)Cl2 (R = Bu (1-trans), 2,6-C6H3Me2 (2-cis), 2,6-C6H3 Pr2 (3-trans) and
t
2-C6H4 Bu (4-trans))
Parameter
1-trans
1.702(3)
2-cis
1.7253(19)
2.2876(19)
2.4132(19)
2.3210(19)
2.3956(7)
2.3876(7)
1.385(3)
3-trans
1.728(2)
2.492(2)
2.307(2)
2.307(2)
2.3715(5)
2.3715(5)
1.394(3)
4-trans
1.726(4)
2.483(4)
2.253(4)
Ti(1)–Nimido
Ti(1)–NMe2
Ti(1)–NMe
2.491(3)
2.274(2)
2.274(2)
2.3895(7)
2.3895(7)
1.444(5)
169.18(12)
96.07(11)
96.07(11)
99.19(7)
99.19(7)
97.98(4)
171.7(3)
Ti(1)–NMe
2.302(4)
Ti(1)–Cl(1)
2.3577(14)
2.3683(14)
1.401(7)
169.93(17)
95.91(17)
102.62(18)
99.14(14)
94.63(14)
97.29(6)
Ti(1)–Cl(2/1Aa)
N
N
N
N
N
imido–C
imido–Ti(1)–NMe2
imido–Ti(1)–NMe
imido–Ti(1)–NMe
imido–Ti(1)–Cl(1)
96.68(8)
170.32(9)
171.78(8)
104.56(8)
97.77(7)
98.93(6)
94.10(3)
97.53(7)
97.53(7)
97.56(5)
97.56(5)
100.02(3)
172.9(2)
Nimido–Ti(1)–Cl(2/1Aa)
Cl(1)–Ti(1)–Cl(2/1Aa)
Ti(1)–Nimido–C
169.58(16)
155.9(4)
a Related to its counterpart by the operator x, −y + 1/2, z.
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Table 3 Ethylene polymerisation data for Me4DACH-supported titanium imido catalysts using MAO or d-MAO as co-catalysta
Co-
Yield of
PE/g
Productivity/kg
mol−1 h−1 bar−1
Low molecular wt. fraction
High molecular wt. fraction
Entry
Precatalyst
catalyst
Mw
Mw/Mn
wt% b
Mw
Mw/Mn
wt% b
1
2
Ti(NtBu)(Me4DACH)Cl2 (1)
Ti(N-2,6-C6H3Me2)
MAO
MAO
0.31
0.08
22
5
3 965
3.0
90
329 500
2.2
10
c
c
c
c
c
c
(Me4DACH)Cl2 (2)
i
3
4
5
Ti(N-2,6-C6H3 Pr2)
MAO
MAO
MAO
0.16
0.07
0.07
10
5
11 050
23 900
14 450
2.1
4.1
3.8
81
828 000
3.2
19
(Me4DACH)Cl2 (3)
t
d
d
d
d
Ti(N-2-C6H4 Bu)
(Me4DACH)Cl2 (4)
Ti(N-2-C6H4CF3)
5
89
569 500
2.0
11
(Me4DACH)Cl2 (5)
Ti(NtBu)(Me4DACH)Cl2 (1)
Ti(N-2,6-C6H3Me2)
(Me4DACH)Cl2 (2)
6
7
d-MAO
d-MAO
1.28
0.04
85
3
21 300
5.1
91
1 020 000
1.6
9
c
c
c
c
c
c
i
8
9
Ti(N-2,6-C6H3 Pr2)
d-MAO
d-MAO
d-MAO
0.18
0.09
0.20
12
6
20 200
37 800
31 550
2.5
2.7
3.7
90
84
66
1 340 000
839 500
843 500
2.2
1.7
1.9
10
16
34
(Me4DACH)Cl2 (3)
t
Ti(N-2-C6H4 Bu)
(Me4DACH)Cl2 (4)
Ti(N-2-C6H4CF3)
(Me4DACH)Cl2 (5)
10
13
a Conditions: 6 bar C2H4 on demand, Al : Ti = 1500 with 5 lmol precatalyst loading, 250 mL toluene, 30 min, 22–24 ◦C; MAO refers to toluene solutions
of MAO as supplied; d-MAO refers to dried, solid MAO free of AlMe3; all values are from duplicate experiments/analyses. b For bimodal polymer
samples “wt%” refers to proportions of the two fractions. c Insufficient PE for GPC analysis. d No clear high molecular weight fraction.
formed with 3–5/d-MAO. Unfortunately no productivity gain
was seen for any of the aryl imido compounds on switching to
d-MAO. The origins of the low productivity using as-supplied
MAO can only partly (if at all in most cases) be attributed to
the presence of free AlMe3. It remains more likely that homo-
dimerisation or complexation/ligand abstraction side-reactions
involving other aluminium sites of MAO are responsible for the
low productivities.
We made numerous attempts to prepare well-defined dialkyl
derivatives of 1–5 so as to be able to use stoichiometric activators
and to move away from MAO as a co-catalyst. Unfortunately these
led to ill-defined mixtures.
complexation/ligand abstraction side-reactions involving other
aluminium sites of MAO are responsible for the low productivities.
Experimental section
General methods and instrumentation
All manipulations were carried out using standard Schlenk line or
dry-box techniques under an atmosphere of argon or of dinitrogen.
˚
Protio- and deutero-solvents were pre-dried over activated 4 A
molecular sieves and were refluxed over the appropriate drying
agent, distilled and stored under dinitrogen in Teflon valve
ampoules. NMR samples were prepared under dinitrogen in
5 mm Wilmad 507-PP tubes fitted with J. Young Teflon valves.
1
1H, 13C{ H} and 19F NMR spectra were recorded on Varian
Conclusions
Mercury-VX 300 and Varian Unity Plus 500 spectrometers.
1H and 13C assignments were confirmed when necessary with
the use of DEPT-135, DEPT-90, and two dimensional 1H–
1H and 13C–1H NMR experiments. 1H and 13C spectra were
referenced internally to residual protio-solvent (1H) or solvent
(13C) resonances, and are reported relative to tetramethylsilane
(d = 0 ppm). 19F spectra were referenced externally to CFCl3.
Chemical shifts are quoted in d (ppm) and coupling constants in
Hertz. Infrared spectra were recorded on a Perkin Elmer 1710
FTIR spectrometer as a Nujol mull between NaCl plates. Infrared
data are quoted in wavenumbers (cm−1). Mass spectra were
recorded by the mass spectrometry service of Oxford University’s
Department of Chemistry. Elemental analyses were carried out
by the Elemental Analysis Service at the London Metropolitan
University. GPC analyses were carried out by Rapra Technology
Ltd. in 1,2,4-trichlorobenzene solvent at 160 ◦C relative to
polystyrene calibrants and using the appropriate Mark Houwink
We have reported the synthesis, solid state structures and solution
dynamics of a series of imido titanium complexes of the virtually
unexplored Me4DACH ligand. The synthetic yields were high and
the X-ray crystal structures indicated that from a structural point
of view Me4DACH resembles the very widely studied TACN lig-
and. However, the presence of the exocyclic NMe2 donor appears
to impart some greater conformational flexibility on Me4DACH
compared to TACN. The interconversion between trans- and cis-
Ti(NR)(Me4DACH)Cl2 has been assessed by variable temperature
NMR and found to be facile for certain aryl imido groups
with a low entropy of activation. In contrast to the TACN
and TPM analogues, the complexes Ti(NR)(Me4DACH)Cl2 form
predominantly single-site type Ziegler catalysts of comparatively
poor productivity. The origins of the low productivity using as-
supplied MAO can only partly be attributed to the presence of
free AlMe3. It remains more likely that homo-dimerisation or
3306 | Dalton Trans., 2008, 3301–3310
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parameters for polyethylene. The Me4DACH ligand coordinates to
the titanium imido dichloride moiety present in compounds 1–5 in
two configurations; a trans configuration and a cis configuration.
Isomer ratio: (1-trans : 1-cis) (43 : 57). IR (NaCl plates, Nu-
jol, cm−1): 1699 (w), 1684 (w), 1653 (m), 1559 (m), 1540 (m), 1350
(m), 1243 (s), 1209 (w), 1033 (s), 945 (w), 826 (s). FI-HRMS: m/z
found (calcd for C14H32Cl2N4Ti [M]+), 374.1501 (374.1483). Anal.
Found (calcd for C14H32Cl2N4Ti): C, 44.9 (44.8); H, 8.7 (8.6); N,
14.8 (14.9)%.
Starting materials
Data for 1-trans. 1H NMR (CD2Cl2, 499.9 MHz, 293 K): 3.98
(2 H, m, Ha(down)), 3.29 (2 H, d, 2J = 14.0 Hz, Hb(down)), 2.97 (6 H, s,
NMe), 2.94 (2 H, m, Ha(up)), 2.46 (2 H, d, 2J = 14.0 Hz, Hb(up)), 2.18
The compounds 6-dimethylamino-1,4,6-trimethyl-1,4-diazacyclo-
t
heptane (Me4DACH),43 Ti(NR)(NMe2)2Cl2 (R = Bu or aryl)48,63
and Ti(NtBu)Cl2(py)3,49,64 were prepared according to the lit-
erature methods. MAO (10% w/w in toluene) was obtained
from Albermarle. Dried MAO (d-MAO) was prepared from an
as-supplied toluene solution dried under dynamic vacuum for
16 h. Analysis by 1H NMR (C6D6) showed free negligible AlMe3
content. Other reagents were purchased and used without further
purification.
1
(6 H, s, NMe2), 1.08 (9 H, s, tBu), 0.75 (3 H, s, CMe) ppm. 13C-{ H}
NMR (CD2Cl2, 75.4 MHz, 293 K): 69.7 (Cb), 69.5 (NCMe3), 63.4
(Ca), 60.1 (CMe), 53.8 (NMe), 42.2 (NMe2), 30.8 (NCMe3), 10.8
(CMe) ppm.
1
Data for 1-cis. H NMR (CD2Cl2, 499.9 MHz, 293 K): 3.75
2
(1 H, d, overlapping s and m, J = 14.3 Hz, Hh(down)), 3.72 (1 H,
m, overlapping s and m, Hf(down)), 3.38 (1 H, m, He(down)), 3.20 (3 H,
s, NMeb), 3.13 (3 H, s, NMed), 2.95 (1 H, d, overlapping s and
d, 2J = 14.8 Hz, Hg(down)), 2.67 (3 H, s, NMec), 2.61 (1 H, d, 2J =
14.3 Hz, Hh(up)), 2.55 (1 H, m, Hf(up)), 2.29 (1 H, m, He(up)), 2.27 (3 H,
s, NMea), 2.25 (1 H, d, 2J = 14.8 Hz, Hg(up)), 1.07 (9 H, s, tBu), 0.89
Labelling scheme
Compounds 1–5 exist as cis and trans isomers (as defined in
1
1
Scheme 1), each giving rise to a distinct set of H and 13C-{ H}
NMR resonances. Fig. 6 gives the labelling system used for clarity
to assign the 1H and 13C-{ H} NMR spectra for 1–5.
1
(3 H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2, 75.4 MHz, 293 K):
1
70.8 (Ch), 69.7 (NCMe3), 68.8 (Cg), 63.1 (Cf), 62.1 (CMe), 59.4
(Ce), 55.4 (NMeb), 49.7 (NMea), 48.4 (NMed), 45.8 (NMec), 30.9
(NCMe3), 11.5 (CMe) ppm.
Ti(N-2,6-C6H3Me2)(Me4DACH)Cl2 (2)
A
solution of Ti(N-2,6-C6H3Me2)Cl2(NHMe2)2 (0.23 g,
0.70 mmol) in benzene (15 mL) was combined with Me4DACH
(0.13 g, 0.70 mmol) and the mixture heated at 60 ◦C for 16 h. Soon
after ligand addition, a yellow solid began to precipitate from
the initially red-brown solution. The solvent volume was reduced
to ca. 5 mL and pentane (15 mL) was added, the solids filtered
off and washed with pentane (3 × 15 mL). The resulting yellow
powder was dried under reduced pressure. Yield: 0.23 g (79%).
Diffraction-quality crystals of 2 were grown from a sub-saturated
CH2Cl2 solution at room temperature.
Isomer ratio: (2-trans : 2-cis) (21 : 79). IR (NaCl plates, Nu-
jol, cm−1): 1402 (m), 1283 (s), 959 (m), 927 (w), 687 (w), 665
(m). EI-HRMS: m/z found (calcd for C18H32Cl2N4Ti [M]+),
422.1487 (422.1483). Anal. Found (calcd for C18H32Cl2N4Ti): C,
50.9 (51.1); H, 7.6 (7.6); N, 13.1 (13.2)%.
Fig. 6 System for assigning chemical environments in the cis- and
trans-configurations of the Me4DACH supported compounds (1–5),
viewed projected onto the Ti(NR)Cl2 plane.
Ti(NtBu)(Me4DACH)Cl2 (1)
(a) From Ti(NtBu)Cl2(NHMe2)2. To a stirred solution of
Ti(NtBu)Cl2(NHMe2)2 (0.14 g, 0.50 mmol) in benzene (15 mL)
was added Me4DACH (0.09 g, 0.50 mmol) and the mixture heated
at 60 ◦C for 16 h. The initially red-orange solution changed to
an opaque suspension shortly after ligand addition. The solvent
volume was reduced to ca. 5 mL and pentane (10 mL) was added,
the solids filtered off and washed with pentane (3 × 10 mL). The
resulting tan-cream powder was dried in vacuo. Yield: 0.14 g (73%).
Data for 2-trans.1H NMR (CD2Cl2, 499.9 MHz, 243 K): 6.73
(2 H, d, 3J = 7.4 Hz, m-2,6-C6H3Me2), 6.49 (1 H, t, 3J = 7.4 Hz, p-
2,6- C6H3Me2), 3.79 (2 H, m, Ha(down)), 3.32 (2 H, d, 2J = 14.0 Hz,
Hb(down)), 3.08 (6 H, s, NMe), 2.89 (2 H, m, Ha(up)), 2.69 (6 H, s,
overlapping 2 × s, C6H3Me2), 2.51 (2 H, d, 2J = 14.0 Hz, Hb(up)),
1
2.26 (6 H, s, NMe2), 0.78 (3 H, s, CMe) ppm. 13C-{ H} NMR
(CD2Cl2, 125.7 MHz, 243 K): 157.5 (i-2,6-C6H3Me2), 134.1 (o-2,6-
C6H3Me2), 127.6 (m-2,6-C6H3Me2), 120.7 (p-2,6-C6H3Me2), 70.2
(Cb), 62.8 (overlapping 2 × s, Ca), 59.1 (CMe), 54.2 (NMe), 42.2
(NMe2), 10.8 (CMe) ppm.
(b) From Ti(NtBu)Cl2(py)3. A red solution of Ti(NtBu)Cl2(py)3
(0.50 g, 1.17 mmol) in benzene (15 mL) was combined with
Me4DACH (0.22 g, 1.17 mmol) and stirred at ambient temperature
for 16 h. Soon after ligand addition an opaque suspension formed.
The solvent volume was reduced to ca. 5 mL and pentane (10 mL)
was added, the solids filtered off and washed with pentane (3 ×
10 mL). The resulting tan-cream powder was dried under reduced
pressure. Yield: 0.27 g (62%). Diffraction-quality crystals of 1 were
grown from a sub-saturated CH2Cl2 solution at room temperature.
1
Data for 2-cis. H NMR (CD2Cl2, 499.9 MHz, 243 K): 6.73
(2 H, d, 3J = 7.4 Hz, m-2,6- C6H3Me2), 6.48 (1 H, t, 3J = 7.4 Hz,
p-2,6- C6H3Me2), 3.85 (1 H, m, Hf(down)), 3.57 (1 H, d, 2J = 14.9 Hz,
Hh(down)), 3.35 (1 H, m, He(down)), 3.17 (3 H, s, NMeb), 3.13 (1 H, d,
2J = 14.8 Hz, Hg(down)), 2.99 (3 H, s, NMed), 2.78 (3 H, s, NMec),
2
2.69 (6 H, s, overlapping 2 × s, C6H3Me2), 2.66 (1 H, d, J =
14.9 Hz, Hh(up)), 2.60 (1 H, m, Hf(up)), 2.44 (1 H, m, He(up)), 2.41
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(3 H, s, NMea), 2.29 (1 H, d, 2J = 14.8 Hz, Hg(up)), 0.88 (3H, s, CMe)
to ca. 5 mL and pentane (15 mL) was added, the solids filtered
off and washed with pentane (3 × 10 mL). The volatiles were
removed under reduced pressure, affording a light brown powder.
Yield: 0.23 g (70%). Diffraction-quality crystals of 4 were grown
from a sub-saturated CH2Cl2 solution at room temperature.
Isomer ratio: (4-trans : 4-cis) (28 : 72). IR (NaCl plates, Nu-
jol, cm−1): 1583 (w), 1426 (s), 1399 (w), 1332 (w), 1289 (s), 1235
(w), 1140 (s), 956 (m), 938 (m), 882 (w), 863 (w), 837 (m), 823 (m),
757 (m). EI-HRMS: m/z found (calcd for C20H36Cl2N4Ti [M]+),
450.1798 (450.1796). Anal. Found (calcd for C20H36Cl2N4Ti): C,
53.2 (53.2); H, 7.9 (8.0); N, 12.4 (12.4)%.
1
ppm. 13C-{ H} NMR (CD2Cl2, 125.7 MHz, 243 K): 157.5 (i-2,6-
C6H3Me2), 134.1 (o-2,6-C6H3Me2), 127.6 (m-2,6-C6H3Me2), 120.7
(p-2,6-C6H3Me2), 70.1 (Ch), 69.2 (Cg), 63.5 (Cf), 62.8 (overlapping
2 × s, CMe), 59.8 (Ce), 54.8 (NMeb), 51.1 (NMea), 45.9 (NMed),
45.3 (NMec), 19.6 (C6H3Me2) 11.5 (CMe) ppm.
i
Ti(N-2,6-C6H3 Pr2)(Me4DACH)Cl2 (3)
Me4DACH (0.18 g, 0.96 mmol) was added to a stirred solution of
i
Ti(N-2,6-C6H3 Pr2)Cl2(NHMe2)2 (0.37 g, 0.96 mmol) in benzene
◦
(15 mL) and the mixture heated at 60 C for 16 h. The initially
Data for 4-trans. 1H NMR (CD2Cl2, 499.9 MHz, 243 K): 7.79
(1 H, dd, 3J = 6.9 Hz, 4J = 1.2 Hz, 6-C6H4 Bu), 7.06 (1 H, dd, 3J =
t
red-brown solution lightened to a green-brown suspension shortly
after ligand addition. The solvent volume was reduced to ca. 5 mL
and pentane (15 mL) was added, the solids filtered off and washed
with pentane (3 × 15 mL). The resulting mustard powder was dried
under reduced pressure. Yield: 0.36 g (78%). Diffraction-quality
dark orange crystals of 3 were grown from a pentane–CH2Cl2
solution.
4
t
3
6.3 Hz, J = 1.2 Hz, 3-C6H4 Bu), 7.00 (1 H, app. t, J = 7.6 Hz,
5-C6H4 Bu), 6.69 (1 H, app. t, 3J = 8.1 Hz, 4-C6H4 Bu), 3.89 (2 H,
t
t
2
m, Ha(down)), 3.34 (2 H, d, J = 14.3 Hz, Hb(down)), 3.02 (6 H, s,
2
NMe), 2.88 (2 H, m, Ha(up)), 2.55 (2 H, d, J = 14.3 Hz, Hb(up)),
t
2.30 (6 H, s, NMe2), 1.48 (9 H, s, overlapping 2 × s, Bu), 0.78
(3 H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2, 75.4 MHz, 293 K):
1
t
t
t
Isomer ratio: (3-trans : 3-cis) (18 : 82). IR (NaCl plates, Nu-
jol, cm−1): 1423 (m), 1328 (m), 1269 (w), 1101 (m), 1035 (w),
1028 (w), 995 (s), 964 (s), 939 (m), 889 (s), 828 (w), 749 (m),
713 (s). EI-HRMS: m/z found (calcd for C22H40Cl2N4Ti [M]+),
478.2093 (478.2109). Anal. Found (calcd for C22H40Cl2N4Ti): C,
55.0 (55.1); H, 8.5 (8.4); N, 11.6 (11.7)%.
159.4 (1-C6H4 Bu), 140.2 (2-C6H4 Bu), 133.3 (6-C6H4 Bu), 126.3
t
t
t
(5-C6H4 Bu), 125.7 (3-C6H4 Bu), 121.5 (4-C6H4 Bu), 70.5 (Cb), 62.3
(Ca), 60.6 (CMe), 53.4 (NMe), 43.2 (NMe2), 35.8 (CMe3), 31.5
(CMe3), 11.3 (CMe) ppm.
1
Data for 4-cis. H NMR (CD2Cl2, 499.9 MHz, 243 K): 7.68
3
4
t
(1 H, dd, J = 6.6 Hz, J = 1.4 Hz, 6-C6H4 Bu), 7.07 (1 H, dd,
Data for 3-trans. 1H NMR (CD2Cl2, 499.9 MHz, 243 K): 6.85
3J = 6.6 Hz, 4J = 1.2 Hz, 3-C6H4 Bu), 7.00 (1 H, app. t, 3J = 7.6 Hz,
t
(2 H, d, 3J = 7.1 Hz, m-2,6-C6H3 Pr2), 6.67 (1 H, t, 3J = 7.1 Hz,
5-C6H4 Bu), 6.69 (1 H, app. t, 3J = 8.1 Hz, 4-C6H4 Bu), 3.69 (1 H, d,
2J = 14.7 Hz, Hh(down)), 3.66 (1 H, m, Hf(down)), 3.40 (1 H, m, He(down)),
3.17 (3 H, s, NMeb), 3.09 (1 H, d, 2J = 14.9 Hz, Hg(down)), 2.95 (3 H,
s, NMed), 2.72 (3 H, s, NMec), 2.65 (1 H, d, 2J = 14.7 Hz, Hh(up)),
2.59 (1 H, m, Hf(up)), 2.44 (3 H, s, NMea), 2.41 (1 H, m, He(up)),
2.36 (1 H, d, 2J = 14.9 Hz, Hg(up)), 1.48 (9 H, s, overlapping 2 × s,
i
t
t
p-2,6-C6H3 Pr2), 4.61 (2 H, sept., 3J = 6.9 Hz, CHMe2), 3.75 (2 H,
i
2
m, Ha(down)), 3.37 (2 H, d, J = 14.7 Hz, Hb(down)), 3.07 (6 H, s,
2
NMe), 2.88 (2 H, m, Ha(up)), 2.49 (2 H, d, J = 14.7 Hz, Hb(up)),
2.32 (6 H, s, NMe2), 1.19 (12 H, d, 3J = 6.9 Hz, overlapping 2 ×
1
d, CHMe2), 0.81 (3 H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2,
i
1
75.4 MHz, 293 K): 155.1 (overlapping 2 × s, i-2,6-C6H3 Pr2), 145.8
tBu), 0.87 (3 H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2, 75.4 MHz,
i
i
i
t
t
t
(o-2,6-C6H3 Pr2), 123.7 (m-2,6-C6H3 Pr2), 122.3 (p-2,6-C6H3 Pr2),
70.7 (Cb), 62.2 (Ca), 60.0 (overlapping 2 × s, CMe), 53.7 (NMe),
42.8 (NMe2), 26.4 (CHMe2), 25.1 (CHMe2), 10.6 (CMe) ppm.
293 K): 159.0 (1-C6H4 Bu), 141.0 (2-C6H4 Bu), 132.6 (6-C6H4 Bu),
t
t
t
126.2 (5-C6H4 Bu), 125.7 (3-C6H4 Bu), 121.5 (4-C6H4 Bu), 71.2
(Ch), 68.8 (Cg), 64.1 (Cf), 63.1 (CMe), 59.8 (Ce), 54.3 (NMeb), 51.7
(NMea), 46.3 (NMec), 45.9 (NMed), 35.9 (CMe3), 31.5 (CMe3),
11.8 (CMe) ppm.
1
Data for 3-cis. H NMR (CD2Cl2, 499.9 MHz, 243 K): 6.85
(2 H, d, 3J = 7.7 Hz, m-2,6-C6H3 Pr2), 6.66 (1 H, t, 3J = 7.7 Hz,
i
p-2,6-C6H3 Pr2), 4.49 (2 H, app. sept.,3J = 6.8 Hz, CHMe2), 3.94
i
(1 H, m, Hf(down)), 3.57 (1 H, d, 2J = 14.5 Hz, Hh(down)), 3.42 (1 H, m,
He(down)), 3.16 (1 H, d,2J = 14.6 Hz, Hg(down)), 3.13 (3 H, s, NMeb),
Ti(N-2-C6H4CF3)(Me4DACH)Cl2 (5)
2
2.96 (3 H, s, NMed), 2.80 (3 H, s, NMec), 2.65 (1 H, d, J =
To a stirred solution of Ti(N-2-C6H4CF3)Cl2(NHMe2)2 (0.18 g,
0.49 mmol) in benzene (15 mL) was added Me4DACH (0.09 g,
0.49 mmol) and the mixture heated at 60 ◦C for 16 h. The initially
red-brown solution changed to an orange suspension shortly after
ligand addition. The solvent volume was reduced to ca. 5 mL and
pentane (15 mL) was added, the solids filtered off and washed
with pentane (3 × 10 mL). The resulting bright orange powder
was dried in vacuo. Yield: 0.19 g (85%).
14.5 Hz, Hh(up)), 2.61 (1 H, m, Hf(up)), 2.47 (3 H, s, NMea), 2.46
2
(1 H, m, He(up)), 2.29 (1 H, d, J = 14.6 Hz, Hg(up)), 1.23 (6 H,
3
3
d, J = 6.8 Hz, CHMe2), 1.17 (6 H, d, J = 6.8 Hz, overlapping
2 × d, CHMe2), 0.90 (3H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2,
1
i
75.4 MHz, 293 K): 155.1 (overlapping 2 × s, i-2,6-C6H3 Pr2), 145.7
i
i
i
(o-2,6-C6H3 Pr2), 123.6 (m-2,6-C6H3 Pr2), 122.0 (p-2,6-C6H3 Pr2),
70.3 (Ch), 69.4 (Cg), 63.6 (Cf), 62.8 (CMe), 60.0 (overlapping 2 × s,
Ce), 53.9 (NMeb), 51.3 (NMea), 45.3 (NMec), 45.1 (NMed), 26.8
(CHMe2), 25.6 (CHMe2), 24.6 (CHMe2), 11.2 (CMe) ppm.
Isomer ratio: (5-trans : 5-cis) (53 : 47). IR (NaCl plates, Nu-
jol, cm−1): 1589 (w), 1551 (w), 1444 (s, sh), 1336 (s), 1280 (w), 1233
(w), 1167 (w), 1122 (s), 1027 (s), 961 (m), 935 (w), 828 (w), 775 (s),
710 (w). EI-HRMS: m/z found (calcd for C17H27Cl2F3N4Ti [M]+),
462.1057 (462.1044). Anal. Found (calcd for C17H27Cl2F3N4Ti): C,
44.0 (44.1); H, 5.8 (5.9); N, 12.0 (12.1)%.
t
Ti(N-2-C6H4 Bu)(Me4DACH)Cl2 (4)
t
Ti(N-2-C6H4 Bu)Cl2(NHMe2)2 (0.26 g, 0.73 mmol) was dissolved
in benzene (15 mL) and combined with Me4DACH (0.14 g,
0.73 mmol). The mixture was heated at 60 ◦C and stirred for 16 h.
The initially dark orange solution changed to a brown suspension
shortly after ligand addition. The solvent volume was reduced
Data for 5-trans. 1H NMR (CD2Cl2, 499.9 MHz, 293 K): 7.94
3
3
(1 H, d, J = 8.0 Hz, 6-C6H4CF3), 7.32 (1 H, d, J = 7.9 Hz,
3
3-C6H4CF3), 7.29 (1 H, app. t, J = 7.6 Hz, 5-C6H4CF3), 6.79
(1 H, app. t, 3J = 7.6 Hz, 4-C6H4CF3), 3.89 (2 H, m, Ha(down)), 3.39
3308 | Dalton Trans., 2008, 3301–3310
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2
(2 H, d, J = 13.8 Hz, Hb(down)), 3.00 (6 H, s, overlapping 2 × s,
(b) d-MAO as co-catalyst. d-MAO (0.44 g, 7.50 mmol,
1500 equiv.) was dissolved in toluene (200 mL) and sonicated
for 30 min to form a co-catalyst solution (200 mL). Co-catalyst
(MAO or d-MAO) solution (200 mL) was transferred to the glass
reactor (1000 mL) and stirred for 5 min at 1000 rpm. The pre-
catalyst (1–5, 5 lmol) was dissolved in toluene (50 mL) and added
to the co-catalyst solution. The combined mixture was stirred at
1000 rpm for a further 10 min to activate the pre-catalyst. The
reactor was then degassed under dynamic vacuum prior to the
addition of ethylene at a 6 bar dynamic pressure. On ethylene
application, the stirring rate was increased to 1500 rpm. After
30 min the ethylene supply was isolated and the pressure released.
The mixture was quenched by the dropwise addition of MeOH
(10 mL). Distilled water (50 mL) was added, followed by 10%
HCl in MeOH (∼30 mL, until pH = 1). Subsequently the reaction
mixture was stirred for 15 min, filtered and washed with distilled
water (1000 mL). The polyethylene product was then dried at
approximately 85 ◦C (∼ 3 d) to constant weight.
NMe), 2.88 (2 H, m, Ha(up)), 2.56 (2 H, d, 2J = 13.8 Hz, Hb(up)), 2.40
(6 H, s, NMe2), 0.84 (3 H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2,
1
75.4 MHz, 293 K): 155.8 (1-C6H4CF3), 132.3 (5-C6H4CF3), 132.0
(6-C6H4CF3), 125.4 (q, 3J = 5.4, 3-C6H4CF3), 120.5 (4-C6H4CF3),
70.6 (Cb), 62.6 (Ca), 60.9 (CMe), 53.7 (NMe), 43.3 (NMe2), 11.1
(CMe) ppm. 19F NMR (CD2Cl2, 282.4 MHz, 293K): −59.6 ppm.
Data for 5-cis. 1H NMR (CD2Cl2, 499.9 MHz, 293 K): 7.94 (1 H,
d, 3J = 8.0 Hz, 6-C6H4CF3), 7.32 (1 H, d, 3J = 7.9 Hz, 3-C6H4CF3),
7.29 (1 H, app. t, 3J = 7.6 Hz, 5-C6H4CF3), 6.79 (1 H, app. t, 3J =
2
7.6 Hz, 4-C6H4CF3), 3.79 (1 H, m, Hf(down)), 3.68 (1 H, d, J =
14.4 Hz, Hh(down)), 3.52 (1 H, m, He(down)), 3.18 (1 H, d, 2J = 14.7 Hz,
Hg(down)), 3.17 (3 H, s, NMeb), 3.00 (3 H, s, overlapping 2 × s,
2
NMed), 2.74 (3 H, s, NMec), 2.68 (1 H, d, J = 14.4 Hz, Hh(up)),
2.63–2.44 (1 H, m, overlapping 2 × m, Hf(up)), 2.63–2.44 (1 H, m,
overlapping 2 × m, He(up)), 2.54 (3 H, s, NMea), 2.40 (1 H, d, 2J =
14.7 Hz, Hg(up)), 0.91 (3 H, s, CMe) ppm. 13C-{ H} NMR (CD2Cl2,
1
75.4 MHz, 293 K): 156.1 (1-C6H4CF3), 132.3 (5-C6H4CF3), 132.0
(6-C6H4CF3), 125.4 (q, 3J = 5.4, 3-C6H4CF3), 120.5 (4-C6H4CF3),
71.1 (Ch), 69.4 (Cg), 63.9 (Cf), 63.1 (CMe), 60.3 (Ce), 53.9 (NMeb),
51.4 (NMea), 46.6 (NMec), 46.1 (NMed), 11.6 (CMe) ppm. 19F
NMR (CD2Cl2, 282.4 MHz, 293K): −59.8 ppm.
Crystal structure determinations of Ti(NR)(Me4DACH)Cl2·
t
xCH2Cl2 (R = Bu (1-trans), 2,6-C6H3Me2 (2-cis·2CH2Cl2),
In each isomer the CF3 and 2-C6H4CF3 13C resonances were not
observed.
i
t
2,6-C6H3 Pr2 (3-trans·CH2Cl2), and 2-C6H4 Bu (4-trans))
Crystal data collection and processing parameters are given in
Table 4. Crystals were mounted on glass fibers using perfluo-
ropolyether oil and cooled rapidly in a stream of cold N2 using
an Oxford Cryosystems Cryostream unit. Diffraction data were
measured using an Enraf-Nonius KappaCCD diffractometer. As
appropriate, absorption and decay corrections were applied to
the data and equivalent reflections merged.65 The structures were
solved by direct methods (SIR9266) and further refinements and
all other crystallographic calculations were performed using the
CRYSTALS program suite.67
Procedure for ethylene polymerisation using MAO and dried MAO
(d-MAO)
The ethylene polymerisation procedure used either as-supplied
MAO (Albermarle) or d-MAO (dried under vacuum for 16 h) as
co-catalyst in 1500 equiv. excess to the pre-catalyst.
(a) MAO as co-catalyst. Toluene (195 mL) was added to MAO
(10% w/w in toluene, 5 mL, 7.5 mmol, 1500 equiv.) to form a co-
catalyst solution (200 mL).
t
Table 4 X-Ray data collection and processing parameters for Ti(NR)(Me4DACH)Cl2·xCH2Cl2 (R = Bu (1-trans), 2,6-C6H3Me2 (2-cis·2CH2Cl2),
i
t
2,6-C6H3 Pr2 (3-trans·CH2Cl2) and 2-C6H4 Bu (4-trans)
Parameter
1-trans
2-cis·2CH2Cl2
3-trans·CH2Cl2
4-transa
Empirical formula
C14H32Cl2N4Ti
375.24
150
0.71073
Pcmn
7.6347(3)
11.2775(6)
22.2136(9)
90
C18H32Cl2N4Ti·2CH2Cl2
C22H40Cl2N4Ti·CH2Cl2
C20H36Cl2N4Ti
451.34
150
0.71073
Pna21
23.3237(9)
12.9435(4)
7.7526(3)
90
M
593.15
564.32
150
T/K
150
0.71073
P 21/c
12.1817(2)
15.2253(2)
15.2192(3)
90
106.8996(6)
90
2700.81(8)
11656
6117
0.027
4
˚
k/A
0.71073
Pcmn
9.3464(2)
13.9957(3)
21.1047(5)
90
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90
90
90
90
90
90
3
˚
V/A
1912.6(15)
6496
2259
0.109
4
1.303
0.727
2760.69(11)
11674
3261
0.037
4
1.367
0.716
2340.43(15)
5186
Reflections measured
Unique reflections
Rint
4998
0.00b
Z
4
d(calcd)/Mg m−1
l/mm−1
1.459
0.927
1.281
0.606
R indicesc
R1 = 0.0580
R1 = 0.0330
R1 = 0.0291
R1 = 0.0495
[I>3r(I)]
Rw = 0.0602
Rw = 0.0383
Rw = 0.0347
Rw = 0.0478
ꢀ
ꢀ
ꢀ
√
a Flack parameter for 4-trans was 0.56(5) indicating intimate twinning. b Friedel pairs not merged. c R1 = ꢁFo| − |Fcꢁ/ |Fo|; Rw =
{
w (|Fo| −
ꢀ
|Fc|)2/ w|Fo|2}.
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 3301–3310 | 3309
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35 P. D. Bolton, N. Adams, E. Clot, A. R. Cowley, P. J. Wilson, M.
Schro¨der and P. Mountford, Organometallics, 2006, 25, 5549.
36 S. C. Lawrence, M. E. G. Skinner, J. C. Green and P. Mountford, Chem.
Commun., 2001, 705.
37 H. R. Bigmore, S. R. Dubberley, M. Kranenburg, S. C. Lawrence, A. J.
Sealey, J. D. Selby, M. Zuideveld, A. R. Cowley and P. Mountford,
Chem. Commun., 2006, 436.
Acknowledgements
We thank the EPSRC, Oxford University and the Clarendon Fund
for support (CW).
38 H. R. Bigmore, M. Zuideveld, R. M. Kowalczyk, A. R. Cowley, M.
Kranenbrug, E. J. L. McInnes and P. Mountford, Inorg. Chem., 2006,
45, 6411.
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3310 | Dalton Trans., 2008, 3301–3310
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