Coordination and reactivity study of titanium phenoxo complexes containing a bulky bidentate imino-N-heterocyclic carbene ligand

Article abstract of DOI:10.1016/j.jorganchem.2012.05.018

The synthesis and structural characterisation of early transition metal complexes containing the aryl-substituted acyclic imino-N-heterocyclic carbene ligand are reported. X-ray crystallographic studies of titanium phenoxo complexes confirmed that the NHC ligand coordinates through the carbenoid carbon and the imine nitrogen atoms to form an octahedral complex. NMR spectroscopic analyses revealed restricted rotation about the aryl bonds. Attempts to prepare the corresponding titanium imido complex repeatedly led to decomposition products, presumably due to the enhanced reactivity of the imine group resulting in its cleavage from the C^Imine ligand scaffold. The catalytic activities of the phenoxo complexes towards ethylene polymerisation were assessed.

Full text of DOI:10.1016/j.jorganchem.2012.05.018

Journal of Organometallic Chemistry 715 (2012) 26e32
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Coordination and reactivity study of titanium phenoxo complexes containing
a bulky bidentate imino-N-heterocyclic carbene ligand
*
Timothy G. Larocque, Gino G. Lavoie
Department of Chemistry, York University, 4700 Keele Street, Toronto, Canada M3J 1P3
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and structural characterisation of early transition metal complexes containing the aryl-
substituted acyclic imino-N-heterocyclic carbene ligand are reported. X-ray crystallographic studies of
titanium phenoxo complexes confirmed that the NHC ligand coordinates through the carbenoid carbon
and the imine nitrogen atoms to form an octahedral complex. NMR spectroscopic analyses revealed
restricted rotation about the aryl bonds. Attempts to prepare the corresponding titanium imido complex
repeatedly led to decomposition products, presumably due to the enhanced reactivity of the imine group
resulting in its cleavage from the C^Imine ligand scaffold. The catalytic activities of the phenoxo
complexes towards ethylene polymerisation were assessed.
Received 29 March 2012
Received in revised form
17 May 2012
Accepted 18 May 2012
Keywords:
Bidentate imino-N-heterocyclic carbene
Titanium phenoxide complexes
Ethylene polymerisation
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Results and discussion
N-Heterocyclic carbene (NHC) ligands have played a dominant
role in transition metal chemistry since the first isolation by
2.1. Synthesis of TiCl2(2,6-OC6H3eMe2)2(C^Imine) (1)
Arduengo in 1991 [1]. The strong
s
-donating and weak
p
-accepting
In an attempt to improve the catalytic activity of Ti(C^Imine)-
type complexes towards olefin polymerisation and oligomerisa-
tion, we decided to replace two chloride atoms with other ancillary
ligands. In view of the success of catalysts bearing aryloxo and imido
capabilities of NHCs have contributed to the widespread applica-
tion of NHCs as ancillary ligands [2e5]. Despite the overwhelming
interest of NHC coordination and their use as ancillary ligands for
catalysis, little has been done in developing NHC-based catalysts for
ancillary ligands for a-olefin polymerisation [13e23], we chose to
the polymerisation of ethylene and
a
-olefins [6e8].
prepare titanium complexes of 1-(1-(2,6-dimethylphenylimino)-
2,2-dimethylpropyl)-3-(2,4,6-trimethylphenyl)imidazol-2-ylidene
carbene (C^Imine) containing aryloxo or imido groups as ancillary
ligands in an attempt to develop structureeproperty relationships
for ethylene polymerisation.
Recently, we have reported NHC analogues of bulky
a
-diimines
(A) and 2,6-diiminopyridines (B) in an attempt to generate ther-
mally stable catalytic systems (Fig. 1) [9e11]. Our initial work with
early transition metals focussed on the synthesis of group 4 and 6
metal halide complexes coordinated by C^Imine, the first free car-
bene of this class ever reported (Scheme 1) [12]. The catalytic
activities of these new complexes towards ethylene polymerisation
were assessed. TiCl4(C^Imine) showed promising activities and
thereby warranted further tailoring of the steric and electronic
parameters of the complex through ligand variations [12]. We
herein report the synthesis and isolation of the corresponding
titanium aryloxo complexes and the attempted synthesis of tita-
nium imido complexes.
Attempts to treat TiCl4(C^Imine) with 2 equiv of Na(2,6-
OC6H3eMe2) under
a
variety of reaction conditions led to
result, the TiCl2(2,6-
a
mixture of reaction products. As
a
OC6H3eMe2)2(THF)2 metal precursor [24] was prepared and
treated with 1 equiv of C^Imine in toluene to give compound 1 as
an orange powder in good yield (82%). The solution 1H NMR
spectrum is consistent with the desired product. The presence of
two ortho methyl resonances for the 2,6-dimethylphenoxide
ligands at
d 2.58 and 2.41 is a strong indication of the cis arrange-
ment of these ligands. A decrease in the C]N stretching frequency
from 1662 cmꢀ1 for the free ligand to 1609 cmꢀ1 for 1 suggests
coordination of the ligand to the metal centre in a bidentate mode
through both the carbenoid carbon and the imine nitrogen atoms. A
comparable decrease in stretching frequency was also observed in
* Corresponding author. Tel.: þ1 417 736 2100x77728; fax: þ1 416 736 5936.
E-mail address: glavoie@yorku.ca (G.G. Lavoie).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.05.018

T.G. Larocque, G.G. Lavoie / Journal of Organometallic Chemistry 715 (2012) 26e32
27
89.26ꢁ, respectively. The phenoxide ring cis to the carbene is almost
perfectly aligned with the mesityl ring, with an N2eC1eTi1eO1
torsion angle of 0.7(3)ꢁ. These two rings are also approximately
coplanar, as evidenced by the small angle (3.4ꢁ) between the mean
planes formed by each ring. In contrast, the phenoxide ring trans to
the carbene is neither well aligned nor coplanar with the xylyl ring
of C^Imine, with a C6eN3eTi1eO2 torsion angle of 25.1(2)ꢁ and an
angle between the planes formed by each ring of 15.9ꢁ.
Interestingly, previous attempts to grow crystals of 1 from slow
liquid diffusion of pentane into a saturated THF solution at ꢀ35 ꢁC
resulted in the decomposition product 2, with two coordinated
mesitylimidazole fragments bound to titanium cis to each other
(Fig. 3). Nucleophilic attack of adventitious water on the iminic
carbon of the bidentate ligand, which has become a better elec-
trophile through replacement of two chlorides in TiCl4(C^Imine)
with the more electronegative phenoxide ligands, likely accounts
for its decomposition to mesitylimidazole and N-(2,6-
dimethylphenyl)pivaloylamide. Interestingly, such cleavage of the
N1eC4 bond has not been reported for more electron-rich late
transition metal analogues [9]. Compound 2 was independently
synthesized by reacting 2 equiv of 1-(2,4,6-trimethylphenyl)imid-
azole with TiCl2(2,6-OC6H3-Me2)2(THF)2.
Fig. 1. Precursors to bulky (arylimino)alkylimidazol-2-ylidene carbenes.
TiCl4(C^Imine) and other related early transition metal complexes
[12].
In order to confirm the proposed structure of 1, we attempted to
isolate single crystals suitable for X-ray crystallographic studies.
Crystals of the desired product were successfully grown at ꢀ35 ꢁC
under nitrogen by slow liquid diffusion of pentane into a saturated
CH2Cl2 solution. Analysis of the X-ray diffraction data confirmed the
coordination of the ligand through the carbenoid carbon of the
carbene and the imine nitrogen, with a C1eTi1eN3 bite angle of
68.77(10)ꢁ, slightly smaller than that observed in TiCl4(C^Imine)
[12] (Fig. 2). The structure shows both chloride atoms trans to each
other. As expected, the titanium centre of 1 exhibits a pseudo-
octahedral coordination geometry, commonly observed in
TiCl2(OAr)2L2 complexes [25,26]. Angles about the metal centre
range from 76.25(8)ꢁ to 100.80(10)ꢁ (Table 1).
2.2. Synthesis of TiCl2(2,6-OC6H4O)(C^Imine) (3)
Considering that the cis arrangement of chloride ligands is
critical in the formation of active olefin polymerisation catalysts,
we decided to prepare the catecholate titanium complex, with the
expectation that the desired cis-chloride isomer would be
produced. Similar to our observations with compound 1, attempts
to treat TiCl4(C^Imine) with 1 equiv of Li2(2,6-OC6H4O) under
a variety of reaction conditions led to a mixture of reaction prod-
ucts. The TiCl2(2,6-OC6H4O)(THF)2 metal precursor was thus
prepared [30] and treated with 1 equiv of C^Imine in toluene to give
compound 3 in good yield (84%) as a dark red powder (Scheme 2).
Compound 3, like compound 1, has a lower C]N stretching
Upon coordination of C^Imine to titanium in 1, the C]N bond
ꢀ
length increases slightly from 1.266(3) to 1.270(4) A, consistent
with the observed decrease in the corresponding IR stretching
frequency. The strong s-donating ability of the carbene gives rise to
the trans influence and is illustrated by the longer TieO2 bond
ꢀ
trans to the carbene (1.821(2) A), compared to that for TieO1 cis to
ꢀ
the carbene (1.795(2) A). The Ti1eC1 and Ti1eN3 bond distances
ꢀ
were determined to be 2.226(3) and 2.379(2) A, respectively. Both
values are slightly greater than those observed in the tetrachloride
complex TiCl4(C^Imine) [12], possibly due to the larger sterics of
the phenoxide ligands or to its stronger trans influence compared
to that of chlorides [27]. Interestingly, both the Ti1eO1eC26 and
the Ti1eO2eC34 bond angles are equivalent at 179.1(2)ꢁ.
frequency (nC
¼
1610 cmꢀ1) than that of the free carbene, sug-
N
gesting that the ligand is also coordinating through the imine
nitrogen.
Crystals of 3 suitable for single crystal X-ray diffraction were
successfully grown at ꢀ35 ꢁC under nitrogen by slow liquid diffu-
sion of pentane into a saturated CH2Cl2 solution. X-ray crystallo-
graphic analysis confirmed the coordination of the ligand through
both the central imidazol-2-ylidene carbon and the imine nitrogen,
with a slightly larger C1eTi1eN3 bite angle (70.20(10)ꢁ) than that
observed in 1, a result of replacing two 2,6-dimethylphenoxide
ligands with the smaller bidentate 2,6-catecholate (Fig. 4). This
allows for the C^Imine ligand to be closer to the metal centre,
resulting in shorter Ti1eC1 and Ti1eN3 bonds compared to those
observed in 1. As expected, the titanium centre adopts a pseudo-
octahedral coordination geometry with bond angles about the
metal centre ranging from 70.20(10) to 99.83(10)ꢁ (Table 1).
As observed for compound 1, coordination of C^Imine results in
As expected, we see significant multiple bond character
ꢀ
between the metal and the oxygen with the Ti1eO1 (1.795(2) A)
ꢀ
and Ti1eO2 (1.821(2) A) lengths closer to the expected bond
ꢀ
distance of a Ti]O double bond (1.74 A) than of a TieO single bond
ꢀ
(1.99 A) [28,29]. The steric constraint imposed by the formation for
the metallacycle leads to a yaw distortion of 10.0ꢁ, slightly higher
than that observed in TiCl4(C^Imine) (9.1ꢁ) [12] but considerably
smaller than in square planar nickel complexes of C^Imine
(14.5e15.7ꢁ) [9], further illustrating the effect of having a six-
coordinate metal centre and sterically-demanding phenoxide
ligands.
The xylyl and mesityl rings of C^Imine are almost orthogonal to
the best plane formed by the imidazol-2-ylidene ring, at 82.40ꢁ and
ꢀ
an increase in the C]N bond length from 1.266(3) to 1.288(4) A,
which is in agreement with the related decrease in the C]N bond
IR stretching frequency. The formation of the metallacycle leads to
a yaw distortion of 9.0ꢁ. To our surprise, we do not see elongation of
Ar
Ar
N
N
MCln(THF)y
MCln(THF)x
toluene
Mes
Mes
N
the Ti1eCl2 bond from the trans influence of the strong s-donating
tBu
tBu
N
N
N
carbene. The Ti1eCl1 and the Ti1eCl2 bond lengths were deter-
ꢀ
mined to be 2.3427(9) and 2.3064(10) A, respectively and the
C^Imine
longer Ti1eCl1 bond length could be a result of steric crowding of
the catecholate ligand. The 2,6-dimethylphenyl and 2,4,6-
trimethylphenyl rings are twisted 88.87ꢁ and 80.97ꢁ off the imi-
dazol-2-ylidene ring, respectively. The catecholate and mesityl
rings are approximately coplanar with C14 lying over O2, with an
M = Ti; n = 3,4
M = Zr, Hf; n = 4
M = Cr; n = 2,3
Scheme 1. Synthesis of group 4 and 6 metal halide complexes of C^Imine.

28
T.G. Larocque, G.G. Lavoie / Journal of Organometallic Chemistry 715 (2012) 26e32
C24
C3
C2
C20
N2
C23
N3
C15
C19
C16
C18
N1
C25
C4
C5
C17
C14
C22
C1
Cl1
C21
C33
Ti1
C6
C13
C11
C31
C30
C12
C29
O1
C7
C40
C35
C26
Cl2
C27
C10
C9
C28
O2
C8
C32
C34
C41
C36
C39
C37
C38
Fig. 2. ORTEP drawing (50% probability) of 1. H atoms and a CH2Cl2 solvent molecule are omitted for clarity.
angle between the best planes formed by each ring of 7.94ꢁ and
a C14eO2 distance of 3.388 A. Lastly, the ipso carbon (C6) of the
and meta protons of the xylyl ring, while those at
the inequivalent meta protons of the mesityl ring. The resonance at
2.47 corresponds to the broad ortho methyl protons of the xylyl
ring and to one of the two ortho methyl groups of the mesityl ring,
with the second set of inequivalent ortho methyl protons reso-
d 5.88 and 5.40 are
ꢀ
xylyl ring is in closer proximity to both Cl2 and C25, at 3.169 and
d
ꢀ
2.840 A, respectively.
The solution 1H NMR spectrum for compound 3 at room
temperature was surprisingly more complicated than that of
nating at d 1.58. The magnetic inequivalence of the protons for both
compound 1. Broad resonances in the aromatic region at
and 5.40 and in the benzylic region at 2.47 and 1.58, each
respectively integrating to 3, 1, 1, 9 and 3 protons were observed.
d
6.41, 5.88
the mesityl and xylyl rings, and the presence of broad resonances
suggest restricted rotation for both aryl rings.
d
This was further supported by variable-temperature NMR
The broad resonance at
d 6.41 corresponds to the overlapping para
experiments (Fig. 5). A 1H NMR spectrum of 3 in CDCl3 was acquired
Table 1
Selected bond lengths and angles for compounds TiCl4(C^Imine), 1 and 3.
TiCl4(C^Imine) [12]
1
3
C19
C20
ꢀ
Bond lengths (A)
C18
TieC1
TieN3
TieCl1
TieCl2
TieCl3
TieCl4
TieO1
TieO2
N1eC1
N2eC1
N1eC4
N3eC4
C2eC3
2.167(5)
2.358(4)
2.2370(16)
2.2930(18)
2.2775(18)
2.2808(16)
e
2.226(3)
2.379(2)
2.3844(9)
2.3245(9)
e
2.186(3)
2.336(3)
2.3427(9)
2.3064(10)
e
C21
C17
C24
C16
C22
N4
C13
e
e
1.795(2)
1.821(2)
1.375(4)
1.344(4)
1.431(4)
1.270(4)
1.329(4)
1.892(2)
1.854(2)
1.376(4)
1.338(4)
1.441(4)
1.288(4)
1.326(5)
C15
C14
C31
e
C12
1.373(6)
1.344(6)
1.448(6)
1.288(6)
1.329(8)
C27
N3
C9
C8
C7
Cl1
O2
C26
C25
C1
O1
C4
N2
C28
Ti1
N1
Bond angles (ꢁ)
C1eTieN3
N1eC4eN3
N1eC1eN2
C1eTieCl1
CleTieCl2
C1eTieCl3
Cl1eTieCl3
C1eTieCl4
Cl2eTieCl3
C1eTieO1
C1eTieO2
O1eTieO2
Cl1eTieO1
Cl1eTieO2
C2
C29
C3
Cl2
C30
70.42(16)
112.3(4)
104.7(4)
97.18(14)
83.34(15)
82.16(15)
83.32(15)
158.65(15)
165.21(7)
e
68.77(10)
113.3(3)
104.8(2)
76.25(8)
83.47(8)
e
70.20(10)
112.9(3)
105.0(3)
82.07(8)
157.71(8)
e
C6
C5
C39
C32
C33
C10
C40
C34
C38
C37
e
e
C35
e
e
e
e
C36
97.73(10)
160.54(10)
100.80(10)
97.17(7)
95.49(7)
88.97(10)
99.83(10)
81.26(9)
169.24(8)
94.34(7)
e
e
e
e
Fig. 3. ORTEP drawing (50% probability) of 2. H atoms are omitted for clarity.

T.G. Larocque, G.G. Lavoie / Journal of Organometallic Chemistry 715 (2012) 26e32
29
Mes = 2,4,6-trimethylphenyl
DMP = 2,6-dimethylphenyl
O
Ti
Cl
Ti
Cl
O
DMP
tBu
DMP
tBu
DMP
N
N
O
N
O
Cl
N
TiCl2(O-DMP)2(THF)2
toluene
TiCl2(1,2-OC6H4O)(THF)2
toluene
Cl
N
Mes
Mes
Mes
tBu
N
N
N
N
1
3
C^Imine
Scheme 2. Synthesis of titanium complexes 1 and 3 from free carbene, C^Imine.
at 21 ꢁC. The temperature was gradually increased and spectra were
Reaction of 2 equiv of tert-butylamine with TiCl4(C^Imine) under
a variety of reaction conditions led to a mixture of reaction products
despite the various reaction conditions and solvents (THF,
dichloromethane, chloroform) investigated. Attempts to separate
the components of the reaction mixture were unsuccessful. In all
cases, the resulting spectra contained a number of unidentified
species. All spectra interestingly showed the same two character-
recorded at 5 ꢁC intervals up to a final temperature of 50 ꢁC. Both
meta proton resonances of the mesityl ring at
d
5.88 and 5.40
coalesced at
d
5.63 at approximately 40 ꢁC, with estimated values
for the rate constant and the free energy of activation (
D
Gz) of
320 sꢀ1 and 59 kJ molꢀ1, respectively. The NMR spectrum recorded
at 50 ꢁC showed further line sharpening of this resonance and of
that assigned to the meta aromatic protons of the xylyl (
d
6.41).
istic resonances of equal intensity at d 8.6 and 8.3 also observed for
Interestingly, in addition to becoming sharper, the relative inte-
the decomposition product 2.
gration of the resonance at
d
2.47 decreased from the original 9
As a result, we decided to adopt the same strategy used in the
preparation of 1 and 3 and to attempt simple ligand displacement
reactions with titanium imido precursors containing a labile ligand.
Thus, TiCl2(tert-butylimido)(NHMe2)2, TiCl2(tert-butylimido)(py)3,
TiCl2(tert-butylimido)(TMEDA) and TiCl2(tert-butylphenylimi-
do)(TMEDA) were prepared [31,32] and each one was treated with
1 equiv of C^Imine in several solvents (THF, toluene, diethyl ether
and chloroform) and at various reaction conditions. In all cases,
a complex mixture of unidentified compounds was generated and
attempts to isolate the components were unsuccessful. The 1H NMR
spectra displayed the same distinctive downfield resonances
reported above. We believe that upon coordination to the electro-
positive titanium centre, the C]N bond becomes more electro-
philic and more susceptible to nucleophilic attack, thus resulting in
decomposition. This decomposition pathway might be mitigated in
compounds 1 and 3 thanks to the bulkier hexacoordinate metal
centres and to the greater electron-donating capabilities of two
phenoxide ligands, compared to one single imido ligand.
protons at room temperature to 6 protons at 50 ꢁC, which were
assigned to the methyl protons of the xylyl ring. The elevated
temperature also resulted in broadening of the ortho methyl
resonance from the mesityl ring at
of coalescence with the other resonance for the magnetically-
inequivalent methyl protons at 2.47 (Fig. 5).
d 1.58, indicating the beginning
d
The restricted rotation likely results from the sterics about the
hexacoordinate metal centre introduced by both the ortho-
substituted aryl rings, the large tert-butyl group and by the rigid
bidentate catecholate ligand. While distances of the ipso carbon (C6
and C14) of both aryl rings to nearby atoms (vide supra) may
suggest a greater energy barrier for rotation of the xylyl ring
compared to that of the mesityl ring, our variable-temperature
experiments clearly indicate otherwise. This is reasonable consid-
ering that the dianionic catecholate ligand produces a stiff chelate
with the metal centre and that the neutral iminic nitrogen atom
(N3) forms a weaker and more labile dative bond with the metal
centre. Upon restoring the temperature of the solution back to
25 ꢁC, the original spectrum was restored, further supporting
restricted rotation of both the xylyl and mesityl rings, and indi-
cating no thermal decomposition.
2.4. Ethylene polymerisation catalysis
The catalytic activities of compounds 1 and 3 towards ethylene
polymerisation in toluene were studied at atmospheric pressure
and room temperature in the presence of 1000 equiv methyl-
aluminoxane (MAO) as cocatalyst. In both cases, only trace
amounts of polyethylene (PE) were recovered and no soluble
waxes or low molecular weight oligomers were generated. In
contrast, the parent TiCl4(C^Imine) complex showed productiv-
ities of 40 kg PE mol Mꢀ1 hꢀ1 [12]. Coordination of the iminic
nitrogen (N3) to the more Lewis acidic metal centre enhances the
electrophilicity of the iminic carbon (C4) in compounds 1 and 3,
making it more susceptible to nucleophilic attack and to decom-
position into complexes such as compound 2, which was itself
also found to be inactive in ethylene polymerisation under
comparable conditions.
2.3. Attempted synthesis of TiCl2(]NeR)(C^Imine)
In an attempt to further expand the library of potential catalysts,
we decided to prepare the titanium imido dichloride complex.
C3
C24
C2
C22
C19
C18
C16
N2
C23
N1
C17
C14
C20
C5
C4
N3
C25
C21
C1
C15
C27
C28
C13
O1
C29
C30
C26
C11
C31
Ti1
C6
C12
3. Conclusions
O2
Cl1
C10
C7
New titanium complexes containing a bidentate imino-N-
heterocyclic carbene were prepared as potential catalysts for olefin
polymerisation. The metal electronics and sterics about the metal
centre were tuned through coordination of either two phenoxide
ligands (1) or one catecholate ligand (3). NMR experiments
C9
Cl2
C8
Fig. 4. ORTEP drawing (50% probability) of 3. H atoms and a pentane solvent molecule
were omitted for clarity.

30
T.G. Larocque, G.G. Lavoie / Journal of Organometallic Chemistry 715 (2012) 26e32
1
Fig. 5. Selected regions of the H NMR spectra (CDCl3, 300 MHz) of 3 at temperatures ranging from 21 to 50 ꢁC.
revealed restricted rotation of both aryl rings that are part of the
imino-carbene ligand scaffold. The solid-state structure of both
complexes was confirmed by X-ray diffraction studies. Attempts to
make a related titanium imido complex failed, presumably due to
the sensitivity of the imine group towards nucleophilic attack, as
evidenced by the formation of the bis(imidazole) decomposition
product 2. The catalytic activities of the phenoxide complexes
towards ethylene polymerisation were assessed and found to be
significantly lower than that previously reported for the tetra-
chloride complex.
OC6H3eMe2)2(THF)2 and TiCl2(1,2-OC6H4O)(THF)2 were prepared
analogous to the literature procedure. The product was further
purified by dissolving it in THF with subsequent precipitation from
pentane to yield the THF adduct [24,30]. Deuterated NMR solvents
were purchased from Cambridge Isotope Laboratories. MAO was
graciously donated by Albemarle Corp.
4.2. Synthesis of complexes 1e3
4.2.1. Synthesis of TiCl2(2,6-OC6H3eMe2)2(C^Imine) (1)
4. Experimental
A solution of C^Imine (107 mg, 0.287 mmol) dissolved in
toluene (5 mL) was added to a toluene solution of TiCl2(2,6-
OC6H3eMe2)2(THF)2 (145 mg, 0.287 mmol) and the dark red solu-
tion was stirred at room temperature for 4 h. Volatiles were
removed under reduced pressure and the product was washed with
pentane (15 mL) to yield a bright orange-red powder. A spectro-
scopically pure product was acquired by recrystallisation from
CH2Cl2 and pentane (172 mg, 82%). Crystals suitable for X-ray
diffraction study were grown at ꢀ35 ꢁC under nitrogen by slow
liquid diffusion of pentane into a saturated CH2Cl2 solution. 1H NMR
4.1. General methods
All manipulations were performed under a dinitrogen atmo-
sphere in a drybox or using standard Schlenk techniques. Solvents
used in the preparation of air and/or moisture sensitive compounds
were dried using an MBraun Solvent Purification System fitted with
alumina columns and stored over molecular sieves under a positive
pressure of dinitrogen. Deuterated solvents were degassed using
three freezeepumpethaw cycles. C6D6 and CDCl3 were vacuum
distilled from sodium and CaH2, respectively, and stored under
dinitrogen. NMR spectra were recorded on a Bruker DRX 600 (1H at
600 MHz, 13C at 150.9 MHz), Bruker AV 400 (1H at 400 MHz, 13C at
100 MHz) or Bruker AV 300 (1H at 300 MHz, 13C at 75.5 MHz)
spectrometer and are at room temperature unless otherwise stated.
The spectra were referenced internally relative to the residual
protio-solvent (1H) and solvent (13C) resonances and chemical
(400 MHz, C6D6):
d
6.93 (d, J ¼ 2.0, 1H, NCHCN(mesityl)), 6.77e6.49
(m, 9H, p-CH(2,6-xylyl) þ p-CH(phenoxide) þ p-CH(phenoxide) þ m-
CH(2,6-xylyl) þ m-CH(phenoxide) þ m-CH(phenoxide)), 6.47 (s, 2H, m-
CH(mesityl)), 5.94 (d, J ¼ 2.0, 1H, NCCHN(mesityl)), 2.58 (s, 6H, o-
CH3(phenoxide)), 2.55 (s, 6H, o-CH3(2,6-xylyl)), 2.43 (s, 6H, o-CH3(mesityl)),
2.41 (s, 6H, o-CH3(phenoxide)), 1.84 (s, 3H, p-CH3(mesityl)), 0.88 (s, 9H,
(CH3)3C); 13C{1H} NMR (100 MHz, C6D6):
d 201.2 (NCN), 167.9 (Cip-
so(phenoxide)), 165.7 (Cipso(phenoxide)), 162.9 (C]N), 146.0 (Cipso(2,6-
xylyl)), 139.8 (p-C(mesityl)), 135.6 (o-C(mesityl)), 131.6 (o-C(2,6-xylyl)),
131.2 (o-C(phenoxide)), 130.5 (o-C(phenoxide)), 129.7 (m-CH(mesityl)),
129.1 (Cipso(mesityl)), 129.0 (m-CH(2,6-xylyl)), 128.7 (m-CH(phenoxide)),
128.6 (m-CH(phenoxide)), 126.0 (p-CH(2,6-xylyl)), 122.1 (p-CH(phenoxide)),
121.7 (NCCN(mesityl)), 121.3 (p-CH(phenoxide)), 119.6 (NCCN(mesityl)),
40.7 ((CH3)3C), 30.2 ((CH3)3C), 22.0 (o-CH3(2,6-xylyl)), 21.3 (p-
CH3(mesityl)), 20.5 (o-CH3(phenoxide)), 19.8 (o-CH3(mesityl)), 19.2 (o-
shifts were reported with respect to
d
¼ 0 for tetramethylsilane.
Elemental compositions and exact masses were determined by
either ANALEST Laboratory of the University of Toronto or by
Guelph Chemical Laboratories Inc. located in Guelph, Ontario.
All metal precursors were purchased from either BDH or
SigmaeAldrich. N-(2,6-Dimethylphenyl)acetamide was purchased
from SigmaeAldrich or Alfa Aesar and used without further puri-
fication. 1-(1-(2,6-Dimethylphenylimino)-2,2-dimethylpropyl)-3-
CH3(phenoxide)). FTIR (cast film) nC
C41H49Cl2N3O2Ti (%): C, 67.03; H, 6.72; N, 5.72. Found (%): C, 66.84;
H, 7.01; N, 5.69.
¼
1616 cmꢀ1. Anal. Calcd for
N
(2,4,6-trimethylphenyl)imidazol-2-ylidene
prepared using the published procedure [12]. TiCl2(2,6-
(C^Imine)
was

T.G. Larocque, G.G. Lavoie / Journal of Organometallic Chemistry 715 (2012) 26e32
31
4.2.2. Synthesis of TiCl2(2,6-OC6H3eMe2)2(1-(2,4,6-
trimethylphenyl)imidazole)2 (2)
(o-CH3(mesityl)). Not all 13C assignments could be made due to poorly
defined correlations from the broad resonances. FTIR (cast film)
A
solution of 1-(2,4,6-trimethylphenyl)imidazole (144 mg,
nC ]
N 1610 cmꢀ1. Anal. Calcd for C31H35Cl2N3O2Ti (%): C, 62.01; H,
0.776 mmol) dissolved in toluene (5 mL) was added to a toluene
solution of TiCl2(2,6-OC6H3eMe2)2(THF)2 (196 mg, 0.388 mmol) and
the dark red solution was stirred at room temperature for 3 h.
Volatiles were removed under reduced pressure and the product
was purified by multiple recrystallisations from CH2Cl2 and pentane
5.88; N, 7.00. Found (%): C, 61.78; H, 6.12; N, 6.47.
4.3. General procedure for ethylene polymerisation
Ethylene polymerisation was performed at atmospheric pres-
sure and room temperature in a 200-mL Schlenk flask containing
a magnetic stir bar. The flask was conditioned in an oven at 160 ꢁC
for at least 12 h prior to use. The hot flask was brought to room
temperature under dynamic vacuum, and back-filled with ethylene.
This cycle was repeated a total of three times. Under an atmosphere
of ethylene, the flask was charged with 20 mL of dry toluene and
1000 equiv of methylaluminoxane (MAO). The solution was stirred
for 15 min before a solution of the catalyst in toluene was intro-
duced into the flask via a syringe. The reaction mixture was
vigorously stirred for 10 min after the addition of the catalyst, and
subsequently quenched with a 50:50 mixture of concentrated
hydrochloric acid and methanol. The resulting mixture was filtered
and any solid collected was washed with distilled water. Solids
collected were dried under vacuum at approximately 60 ꢁC for
several hours.
(201 mg, 70%). 1H NMR (400 MHz, CDCl3):
d 8.18 (s, 2H, NCHN(mesi-
tyl)), 7.74 (s, 2H, NCCHN(mesityl)), 6.94 (s, 4H, m-CH(mesityl)), 6.87
(d, J ¼ 7.4, 4H, m-CH(phenoxide)), 6.77 (s, 2H, NCHCN(mesityl)), 6.70 (t,
J ¼ 7.4, 2H, p-CH(phenoxide)), 2.33 (s, 18H, o-CH3(phenoxide), p-CH3(me-
sityl)), 1.95 (s, 12H, o-CH3(mesityl)); 13C{1H} NMR (100 MHz, CDCl3):
d
166.4 (Cipso(phenoxide)), 141.2 (NCHN), 139.6 (p-C(mesityl)), 134.8
(o-C(mesityl)), 132.4 (Cipso(mesityl)), 130.8 (NCCN), 129.4 (o-C(phenoxide)),
129.2 (m-CH(mesityl)), 127.9 (m-CH(phenoxide)), 121.7 (p-CH(phenoxide)),
118.8 (NCCN), 21.0 (p-CH3(mesityl)), 17.5 (o-CH3(phenoxide)), 17.3
(o-CH3(mesityl)). Anal. Calcd for C40H46Cl2N2O2Ti (%): C, 65.49; H,
6.32; N, 7.64. Found (%): C, 65.72; H, 6.13; N, 7.77.
4.2.3. Synthesis of TiCl2(1,2-OC6H4O)(C^Imine) (3)
A solution of C^Imine (150 mg, 0.401 mmol) dissolved in toluene
(2 mL) was added to a toluene solution (5 mL) of TiCl2(1,2-
OC6H4O)(THF)2 (149 mg, 0.401 mmol). The dark red solution was
allowed to stir for 4 h. The volume was reduced under reduced
pressure and the product was precipitated with pentane. The
supernatant was removed and the product was dried in vacuo to
yield a dark red powder. An analytically pure product was isolated
by recrystallisation from CH2Cl2 and pentane (202 mg, 84%). Crys-
tals suitable for X-ray diffraction study were grown at ꢀ35 ꢁC under
nitrogen by slow liquid diffusion of pentane into a saturated CH2Cl2
4.4. X-ray crystallographic studies
X-ray crystallographic data for compounds 1 and 2 were
collected at the University of Toronto on a Bruker-Nonius Kappa-
CCD diffractometer using monochromated Mo
Ka
radiation
¼ 0.71073 A) at 150 K and were measured using a combination of
scans and scans with offsets, to fill the Ewald sphere. Intensity
ꢀ
(
4
l
u
k
solution. 1H NMR (400 MHz, CDCl3):
d
7.93 (d, J ¼ 2.0, 1H,
data were processed using the Denzo-SMN package [33]. Absorp-
tion corrections were carried out using SORTAV [34]. X-ray crys-
tallographic data for compound 3 was collected at McMaster
NCHCN(mesityl)), 7.07 (d, J ¼ 2.0, 1H, NCCHN(mesityl)), 7.03e6.99 (m,
4H, CH(aryl)), 6.41 (br s, 3H, m-CH(2,6-xylyl), p-CH(2,6-xylyl)), 5.88 (br s,
1H, m-CH(mesityl)), 5.40 (br s, 1H, m-CH(mesityl)), 2.47 (br s, 9H,
o-CH3(aryl)), 2.24 (s, 3H, p-CH3(mesityl)), 1.58 (br s, 3H, o-CH3(aryl)), 1.43
University on
chromated Mo K
measured using
a Bruker APEX2 diffractometer using mono-
ꢀ
a
radiation (
l
¼ 0.71073 A) at 100 K and were
(s, 9H, (CH3)3C); 13C{1H} NMR (100 MHz, CDCl3):
d 197.2 (NCN),
4
and scans. Unit cell parameters were deter-
u
166.9 (C]N), 158.7 (C(aryl)), 145.2 (C(aryl)), 139.4 (p-C(mesityl)), 134.8
(C(aryl)), 133.9 (C(aryl)), 129.3 (m-CH(mesityl)), 129.0 (C(aryl)), 128.3 (m-
CH(2,6-xylyl)), 126.7 (p-CH(2,6-xylyl)), 123.8 (NCCN(mesityl)), 119.9
(NCCN(mesityl)), 111.2 (o-C(mesityl)), 40.7 ((CH3)3C), 30.4 ((CH3)3C),
21.0 (p-CH3(mesityl)), 20.0 (o-CH3(mesityl)), 19.0 (o-CH3(2,6-xylyl)), 16.6
mined using at least 50 frames from three different orientations.
Data were processed using SAINT, and corrected for absorption
with accurate face-indexing as well as redundant data (SADABS),
and solved using direct methods and the SHELX program suite. The
structures were solved and refined using SHELXTL V6.1 [35] for full-
Table 2
Crystal data and structure refinement details for compounds 1, 2 and 3.
1
2
3
Empirical formula
Formula weight/g molꢀ1
Crystal size/mm
C41.5H50Cl3N3O2Ti
777.10
C40H46Cl2N4O2Ti
733.61
0.26 ꢂ 0.20 ꢂ 0.14
2.55e27.50
ꢃ11; ꢃ17; ꢀ20,21
Triclinic
C38.5H52.5Cl2N3O2Ti
708.14
0.25 ꢂ 0.22 ꢂ 0.20
2.64e27.50
ꢀ23,22; ꢀ12,13; ꢀ26,27
Monoclinic
P21/n
18.2261(5)
10.6412(3)
21.3160(6)
90
0.31 ꢂ 0.27 ꢂ 0.23
1.73e26.36
ꢀ17,16; ꢀ20,19; ꢀ22,16
Monoclinic
P21/c
13.7876(18)
16.111(2)
18.264(2)
90
q
Range/deg
h; k; l Range
Crystal system
Space group
P-1
ꢀ
a/A
8.8050(2)
13.5093(4)
16.7090(4)
98.6120(12)
104.3730(16)
91.6390(16)
2
ꢀ
b/A
ꢀ
c/A
ꢁ
ꢁ
ꢁ
/
a
/
b
/
110.3690(10)
90
4
109.588(2)
90
4
g
Z
Dcalcd/Mg mꢀ3
1.332
1.283
1.231
F(000)
1636
772
1506
No. of reflns collected/unique
No. data/restrnts/params
21,314/8744
8744/0/482
0.0612, 0.1498
0.1234, 0.1850
1.040
22,446/8648
8648/0/452
0.0589, 0.1453
0.1199, 0.1811
1.035
42,162/7768
7768/7/421
0.0561, 0.1464
0.0882, 0.1711
1.045
Final R indices [F2 < 2 (F2)]: R1, wR2
s
R indices (all data): R1, wR2
Goodness-of-fit on F2

32
T.G. Larocque, G.G. Lavoie / Journal of Organometallic Chemistry 715 (2012) 26e32
matrix least-squares refinement was based on F2. All H atoms were
included in calculated positions and allowed to refine in riding-
motion approximation with Uiso-tied to the carrier atom. Details
of the X-ray crystal data and structure refinement details are listed
in Table 2. Other crystallographic data (tables of atomic coordinates
with isotropic and anisotropic displacement parameters, bond
lengths and angles) are provided as Supplementary material.
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Acknowledgements
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GGL gratefully acknowledges financial support from the Ontario
Ministry of Research and Innovation for an Early Researcher Award,
the Natural Sciences and Engineering Research Council of Canada
for a Discovery Grant and a Research and Tools Instrumentation
Grant, the Canadian Foundation for Innovation and the Ontario
Research Fund for infrastructure funding, and York University for
start-up funds. GGL and TGL also wish to thank Dr. Alan J. Lough of
the University of Toronto (Toronto, Ontario), and Dr. James F. Britten
and Dr. Hilary A. Jenkins both of McMaster University (Hamilton,
Ontario) for X-ray data acquisition and their gracious assistance in
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CCDC 856682 (for 1), CCDC 856683 (for 2), and CCDC 856684
(for 3) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.cccdc.cam.ac.uk/
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Supplementary data associated with this article can be found, in
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