Cyclometalated group 4 complexes supported by tridentate pyridine-2-phenolate-6-(σ-aryl) ligands: Catalysts for ethylene polymerization and comparisons with fluorinated analogues

Article abstract of DOI:10.1016/j.jorganchem.2007.05.040

An adaptable synthetic methodology for the tridentate dianionic pyridine-2-phenolate-6-aryl [O,N,C] ligand framework, comprising the aromatic σ-carbanion moiety as a chelating component, has been developed. A series of non-fluorinated group 4 bis(benzyl)

Full text of DOI:10.1016/j.jorganchem.2007.05.040

Journal of Organometallic Chemistry 692 (2007) 4750–4759
www.elsevier.com/locate/jorganchem
Cyclometalated group 4 complexes supported by tridentate
pyridine-2-phenolate-6-(r-aryl) ligands: Catalysts for
ethylene polymerization and comparisons with fluorinated analogues
*
Ka-Ho Tam, Jerry C.Y. Lo, Zhengqing Guo, Michael C.W. Chan
Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China
Received 15 April 2007; received in revised form 19 May 2007; accepted 19 May 2007
Available online 2 June 2007
Dedicated to Prof. Dr. Gerhard Erker for his inspiring research on the occasion of his 60th birthday.
Abstract
An adaptable synthetic methodology for the tridentate dianionic pyridine-2-phenolate-6-aryl [O,N,C] ligand framework, comprising
the aromatic r-carbanion moiety as a chelating component, has been developed. A series of non-fluorinated group 4 bis(benzyl) com-
plexes supported by [O,N,C] auxiliaries, with halogen and alkyl groups at the ‘R1’ position ortho to the metal-C(r-aryl) bond, have been
prepared by exploiting the cyclometalation of the ligand. All derivatives have been characterized by NMR spectroscopy, and the spectral
features concerning the metal-bound diastereotopic methylene groups have been highlighted. The capabilities of these complexes as cat-
alysts for olefin polymerization have been tested, and comparisons with the recently reported fluorine-containing Ti-[O,N,C] analogues
and related Hf-[N,N,C] derivatives are discussed. The titanium catalysts, in conjunction with MAO, displayed moderate to high activities
for ethylene polymerization (up to 200 g mmolꢀ1 hꢀ1).
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Benzyl complexes; Cyclometalation; Olefin polymerization; Post-metallocenes; r-Aryl ligand
1. Introduction
chelating unit by Hessen and coworkers [5], although only
low to moderate activities in propylene polymerization was
reported for Zr(IV) catalysts with tridentate dianionic
bis(r-aryl)amine ligands [6].
The development of new ‘post-metallocene’ complexes
as olefin polymerization catalysts, propelled by the pursuit
of novel materials and properties, and superior control
over reactivity, have proliferated [1]. The myriad of ancil-
lary ligand combinations that can support an active cata-
lytic species continues to expand, and in the impetus to
avoid the cyclopentadienyl group, C-based anionic ligands
have largely been overlooked. For group 4 complexes, the
limited studies have focused on simple allyl ligands [2] plus
tropidinyl [3] and heteroatom analogues [4], but in general
their inertness is insufficient and modest catalytic activities
are obtained. The r-aryl moiety has been employed as a
We previously presented the first direct observation of
weak intramolecular C–Hꢁ ꢁ ꢁF–C contacts in Group 4
post-metallocene catalysts bearing tridentate pyridine-2-
phenolate-6-(fluorinated r-aryl) ligands [7]. Moreover,
the structural parameters of the controversial [8] C–Hꢁ ꢁ ꢁ
F–C interaction was accurately determined for the first
time by a recent neutron diffraction study [9]. The observed
C–Hꢁ ꢁ ꢁF–C interactions are important with regards to
design implications in olefin polymerization catalysts. In
particular, they substantiate the DFT-derived ortho-
Fꢁ ꢁ ꢁH(b) ligand–polymer contacts proposed by Fujita
[10] to account for the remarkable living olefin polymeriza-
tion behavior at elevated temperatures displayed by Group
*
Corresponding author. Tel.: +852 2788 7805; fax: +852 2788 7406.
E-mail address: mcwchan@cityu.edu.hk (M.C.W. Chan).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.05.040

K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
4751
4 fluorinated phenoxyimine ‘FI’ catalysts [11]. Indeed,
unlike conventional agostic [12] and metalꢁ ꢁ ꢁcocatalyst
contacts [13,14], weak attractive non-covalent interactions
between a ‘non-innocent’ ligand and the polymer chain
may be considered as a new concept in polyolefin catalysis.
In this work, a new collection of Group 4 catalysts with
non-fluorinated substituents in the locality of the metal
center has been designed and synthesized from the facile
ortho-cyclometalation of pyridine-2-(20-phenol)-6-(aryl)
substrates. The principal aims of the present study is to
probe (a) the influence of the metal ion (Ti, Zr, Hf), and
(b) the impact of replacing the F or CF3 group [9] adjacent
to the metal–C(r-aryl) bond (termed the R1 position; see
Scheme 1) with substituents displaying different steric and
electronic characteristics, namely Br, Cl and methyl, upon
NMR spectroscopic properties and polymerization behav-
ior. The development of bromine-substituted ligands is
interesting because this potentially allows further derivati-
zation to novel ligands with a variety of aryl moieties at
R1 using Suzuki/Stille-type C–C coupling reactions. The
systematic study of all group 4 metals was deemed appro-
priate since researchers at Symyx and Dow have very
recently observed excellent propylene polymerization activ-
ities for related hafnium(IV) catalysts bearing tridentate
cyclometalated pyridylamido ligands [15].
chelating ligands have been one of the cornerstones of
advances in post-metallocene catalyst design [16]; (2) from
our recent work on a family of Zr(IV) catalysts bearing tri-
dentate pyridine-2,6-bis(aryloxide) [O,N,O] auxiliaries, we
concluded that strong binding by the central pyridyl moiety
is a critical factor in achieving exceptional catalytic efficien-
cies [17]; (3) aromatic r-carbanions are predominantly r-
donors with minimal p-donation (in contrast to strong p-
donors such as Cp), and can engender a catalytic center
with enhanced electrophilicity.
The geometry and rigidity of the [O,N,C] ligand are
important features, dictating that the R1 substituent ortho
to the metal–C(r-aryl) bond (Scheme 1) is in close proxim-
ity to the metal/catalytic site but is nevertheless ‘tied back’
to preclude interaction with the metal center. Furthermore,
facile modification of the R1 substituent has been demon-
strated through the development of a versatile synthetic
methodology for the ligand (see below). Lastly, as noted
by Hessen [6], it is a pre-requisite that the resultant
metal–C(r-aryl) bond is more inert compared with ali-
phatic counterparts [e.g. metal–C(polymer chain)].
2.2. Synthesis of Group 4 complexes bearing tridentate
pyridine-2-phenolate-6-(r-aryl) ligands
The 2-(20-phenol)-6-arylpyridine ligands were prepared
by significant modification of a literature synthesis for
2,6-bis(20-phenol)pyridine [18]. The 1-N,N-dimethylamino-
3-(substituted aryl)-3-oxo-1-propenes were prepared from
the reactions of N,N-dimethylformamide dimethyl acetal
with acetophenones bearing functional groups at the R1/
R2 or R1/R3 positions (Scheme 1). Treatment of the oxo-
propene substrates with 3,5-di-tert-butyl-2-methoxyace-
tophenone/potassium tert-butoxide followed by ammo-
2. Results and discussion
2.1. Design approach
We became attracted to the design and assembly of the
tridentate non-symmetric pyridine-2-aryloxide-6-(r-aryl)
[O,N,C] framework as a suitable ligand ensemble in olefin
polymerization catalysts: (1) aryloxide- and alkoxide-based
O
R3
R1
O
1)
+ KOtBu
R3
R1
O
R2
MeO
MeO
R2
OMe
CH NMe2
NMe2
2) NH4OAc
R3
R3
R1
R2
R2
N
N
E = Me
E = H
molten
pyHCl
M(CH2Ph)4
OE
O
R1
M
pentane/Et2O
R1
R2
R3
Ligand
(E = H)
Complex
M = Zr
M = Ti
M = Hf
H2LBr
H2LCl
H2LMe
1
2
3
4
5
6
7
8
9
H
Br
Cl
Br
H
Cl
CH3
CH3
H
Scheme 1.

4752
K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
nium acetate yielded the 2-(20-methoxyaryl)-6-arylpyri-
dines by cyclization, and subsequent demethylation using
molten pyridinium chloride afforded the desired ligands.
Hence, by exploiting the sequential nature of this route,
the use of different substituted acetophenones inherently
leads to the formation of non-symmetric ligands.
The proposed ligand design strategy is aided by the
accessibility of the synthetic procedure, and in particular,
the wide and facile availability of polysubstituted acetoph-
enone precursors. Hence, 2,5-dimethyl- and 2,5-dichloro-
acetophenone are commercially available, while 3,5-
dibromoacetophenone was prepared by the treatment of
1,3,5-tribromobenzene with n-butyllithium followed by
N,N-dimethylacetamide/HCl [19]. By considering the
cyclometalation process, the judicious incorporation of
substituents at selected positions on the acetophenone
can yield specific R1 groups that reside adjacent to the
metal center in the resultant complex (see below).
two methylene doublets for 10 (R1 = F) are highly symmet-
ric, it is intriguing to note that for 1 and 2 (R1 = Br, Cl
respectively), very slight broadening or ‘shortening’ of the
upfield doublet can apparently be detected (Fig. 2). Such
observations are customarily attributed to the steric conse-
quence of a neighboring substituent, although the fact that
the impact of the bulkier methyl group in 3 is seemingly
negligible appears to contradict this assumption. Neverthe-
less, without further evidence, we are reluctant to ascribe
this minimal broadening to any electronic effects caused
by the Br and Cl atoms.
It has been established that the distortion of M–CH2–Ph
groups, which becomes more prevalent at high-valent elec-
trophilic metal ions, can be indicated by 1H and 13C NMR
spectroscopy. The Mꢁ ꢁ ꢁPh interaction will reduce the M–
C–C angle and concomitantly increase the H–C–H angle,
2
1
resulting in decreased JH,H (<10 Hz) and enlarged JC,H
(>125 Hz) values [20]. The relevant NMR parameters for
complexes 1–9 are listed in Table 1. It is apparent that
the g2-coordination mode is observed for all titanium
and zirconium complexes, and the Mꢁ ꢁ ꢁPh interactions
Metalation of ligands H2LBr,Cl,Me containing acidic
ortho-aryl and phenol protons proceeded smoothly with
the M(CH2Ph)4 (M = Ti, Zr, Hf) precursors in diethyl
ether/pentane mixtures at ꢀ78 °C to give complexes 1–9
as dark red (Ti), yellow (Zr) and pale yellow (Hf) crystal-
line solids in moderate (40–60%) yields (Scheme 1). The
1H NMR spectra of ‘‘as-prepared’’ reaction mixtures after
removal of volatiles revealed that in each case the predom-
inant species is the desired complex. C–H activation is of
course favored over C–Cl and C–C activation respectively,
hence the choice of substituent at R3 ensures that cyclo-
metalation occurs at the designated aryl-H para to R2.
The complexes therefore incorporate a Br, Cl or Me substi-
tuent at the R1 position that is in close proximity to the
metal center but without contact, so that comparisons
may be drawn with the congeners bearing a CF3 or F group
at R1 [7,9].
1
for the former (2JH,H ca. 8.2 Hz and JC,H P 135 Hz) are
stronger. In addition, g2-benzyl groups may also be mani-
1
fested through a high-field H NMR shift for the ortho-Ph
resonances, although the use of this as a criterion is less
reliable because the resonances can also be influenced by
the ring currents of ancillary ligands [21]. Indeed, the
ortho-Ph resonances of all derivatives are observed at
around 6.5–6.8 ppm with no clear trends for different met-
2
als. The large JH,H values for the hafnium complexes sug-
gest that the extent of g2-coordination by the benzyl
groups is minimal.
2.4. Ethylene polymerization studies
The complexes herein have been evaluated as ethylene
polymerization catalysts in conjunction with MAO in
small-scale reactors (conditions: 20 mL toluene, 500 equiv
MAO, 1 atm of ethylene, 25 °C, 10 min reaction time).
The results (Table 2) show that all hafnium complexes
are inactive, which is in stark contrast to the excellent effi-
ciencies reported for the related Hf-[N,N,C] catalysts [15],
while the Ti/MAO systems display higher polymerization
2.3. Characterization by NMR spectroscopy
1
All complexes have been fully characterized by H and
13C NMR spectroscopy, including 135-DEPT and 2D
1H–1H, 13C–1H and NOE correlation experiments (see
Supporting information for selected spectra). As a repre-
sentative example to illustrate the assignment process, the
1H–1H COSY NMR spectrum of 1 is given in Fig. 1.
Because the resonances for H4,6 are easily identifiable from
related complexes, the weak 5-bond correlations detected
for H6 M H8 and H10 M H13 provide good indicators for
the assignment of all aryl hydrogens, and these are subse-
quently confirmed by NOE experiments.
activities (150–200 g of polymer mmolꢀ1
h
ꢀ1) than the
Zr/MAO counterparts. The NMR characterization data
indicate that the interaction between the metal and benzyl
groups, which reflects the electrophilicity of the metal cen-
ter, increases in the order Hf < Zr < Ti, and this is consis-
tent with the observed differences in activity between the
metals.
1
The H NMR spectra for the methylene region of the
titanium complexes 1–3, and the congeners bearing a F
(10) or CF3 (11) group respectively at R1, are displayed
in Fig. 2. For 3 (R1 = CH3), the diastereotopic methylene
hydrogens of the benzyl ligands are conventional and
appear as two doublets, in contrast to 11 (R1 = CF3) where
the upfield CH2 resonance appears as a multiplet due to
C–Hꢁ ꢁ ꢁF–C coupling with three F atoms [7]. While the
For the Ti catalysts, the variations in activity for the Br,
Cl or Me substituents at R1 (1–3 respectively), can be attrib-
uted to a combination of steric and electronic factors. Our
previous results have indicated that the coordination sphere
around the metal center and active site in these catalysts is
highly congested [9]. The presence of the bulkier CH3 sub-
stituent adjacent to the active site may therefore hinder

K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
4753
H9
H8
O
H10
H6
H13
Br
N
H4
H15
Ti
Br
H4
H15
H13 H6 H10
H9
H8& p
m
& o
*
Fig. 1. 1H–1H COSY NMR spectrum of 1 (400 MHz, C6D6 [*], 298 K). The weak 5-bond correlations for H6 M H8 and H10 M H13 (circled) aids the
assignment.
the approach and insertion of olefin substrates. In contrast,
the electron-withdrawing Cl or Br moiety is anticipated to
yield a more electrophilic as well as accessible catalytic site,
resulting in superior activities. Although bulky substituents
are often advocated for improving catalytic performance by
reducing termination processes, we conclude that for the R1
position of the Ti-[O,N,C] system, the methyl group is inef-
fective or even detrimental to catalytic efficiency and the
impact of R1 upon the metal electrophilicity is of greater
importance. For the Zr derivatives, possibly because of
the greater size of the metal center, the effects of steric hin-
drance exerted by R1 may be diminished.
[9, Table 2]. Apparently, the enhanced electrophilicity of
the Ti catalytic site due to the effects of multiple F atoms
becomes the dominant factor. In addition, the Tm values
suggest that the nature of the polyethylene materials
formed appear to be quite different from those by the fluo-
rinated congeners.
3. Conclusion
A new series of Ti, Zr, and Hf complexes supported by
cyclometalated [O,N,C] ligands, with substituents
appended at the R1 position ortho to the metal–C(r-aryl)
linkage, have been prepared as potential olefin polymeriza-
tion catalysts. All derivatives have been characterized by
NMR spectroscopy. The attention reserved for the R1
The observed activities in this work are of the same
magnitude but slightly lower than those for the fluorinated
Ti analogues 10 and 11 (R1 = F, CF3 respectively)

4754
K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
Table 2
Polymerization data
R2
R1
R3
Catalyst (lmol)
Yield (g)
Activitya
Tm (°C)
8
CH2Ph
CH2Ph
1 (6.5)
2 (6.4)
3 (6.3)
0.213
0.187
0.169
202
175
156
125
124
128
<
N
Ti
Ti
:
O
8
4 (6.5)
5 (6.2)
6 (6.3)
0.061
0
0.075
58
–
70
122
–
125
<
Zr
:
10: R1 = F
8
<
7 (6.4)
8 (6.5)
9 (6.5)
10 (6.4)
11 (6.3)
0
0
0
–
–
–
255
542
–
–
–
135
134
R2 = CF3, R3 = H
Hf
:
0.272
0.569
4.4
4.1
Conditions: 20 mL toluene, 500 equiv MAO, 1 atm p of ethylene, 25 °C,
1: R1 = R2 = Br
10 min reaction time.
R3 = H
a
Activity: g of polymer mmolꢀ1 hꢀ1
.
comparisons with fluorinated Ti analogues, and differences
in NMR spectroscopic and catalytic properties as a conse-
quence of the R1 group (Br and Cl cf. F; CH3 cf. CF3) have
been observed. It is evident that the fluorinated catalysts
display elevated activities. With regards to the impact of
the R1 substituent upon catalytic efficiency, the present
work indicates that the electrophilicity of the metal center
is more important than steric protection for the active site.
The inactivity of the Hf congeners is in stark contrast to
the exceptional activities reported for seemingly related
amido-type [N,N,C]-hafnium(IV) catalysts. The develop-
ment of the dibromo-substituted r-aryl fragment within
the [O,N,C] framework has been achieved, paving the
way for further derivatization towards different aryl groups
at the vital R1 position.
4.6
4.2
2: R1 = R3 = Cl
R2 = H
4.5
4.2
11: R1 = R2 = CF3
R3 = H
4.3
3.8
3: R1 = R3 = CH3
R2 = H
4. Experimental
4.1. General considerations
4.25
3.75
Fig. 2. 1H NMR spectra for diastereotopic CH2 region of Ti-[O,N,C]
complexes (400 MHz [600 MHz for 10], C6D6, 298 K; a 0.5 ppm range is
shown to facilitate comparison).
All reactions were performed under a nitrogen atmo-
sphere using standard Schlenk techniques or in a Braun
dry-box. All solvents were appropriately dried and distilled
1
then degassed prior to use. H and 13C NMR spectra were
Table 1
NMR parameters associated with M–benzyl coordination (C6D6)
recorded on a Bruker 500 DRX, 400 DRX or 300 FT-
NMR spectrometer (ppm) using Me4Si as internal stan-
dard. Peak assignments were based on combinations of
Complex
Ti
2JH,H (Hz)
1JC,H (Hz)
ortho-Ph (d)
8
<
1
2
3
8.2
8.2
8.3
136.1
137.1
134.7
6.63
6.63
6.60
1
DEPT-135, and 2-D H–1H, 13C–1H and NOE correlation
:
NMR experiments. Mass spectra (EI) were obtained on a
Finnigan MAT 95 mass spectrometer. Elemental analyses
were performed by Medac Ltd., UK. Melting points of
polymer samples were determined by differential scanning
calorimetry on a Perkin–Elmer DSC7. Methylaluminoxane
(MAO, 10 wt% solution in toluene) was purchased from
Aldrich and used as received. Ethylene (BOC, polymer
grade) was passed through Drierite and P2O5. 3,5-Dib-
romoacetophenone [19] and M(CH2Ph)4 (M = Ti, Zr, Hf)
[22] were prepared according to the literature procedure,
and the synthesis of H2LMe, 3 and 6 were given previously
[9].
8
4
5
6
9.4
9.3
9.8
134.5
135.1
132.7
6.80
6.49
6.71
<
Zr
:
8
<
a
7
8
9
130.3
131.2
129.3
6.76
b
10.4
10.8
Hf
:
6.70
a
A virtual singlet is observed.
Aryl-H resonances overlap.
b
substituent is justified because it is situated directly adja-
cent to the catalytic center and along the path of the incom-
ing olefin. In this study, it has been possible to make

K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
4755
4.2. Synthesis of 1-N,N-dimethylamino-3-(3,5-
dibromophenyl)-3-oxo-1-propene
34.6 mmol) under N2 at 220 °C for 10 h according to the
procedure described by Dietrich-Buchecker et al. [23] gave
H2LBr as a pale yellow solid which was recrystallized in n-
hexane. Yield: 0.68 g, 37%. 1H NMR (400 MHz, CDCl3): d
1.40 (s, 9H, tBu), 1.54 (s, 9H, tBu), 7.47 (d, J = 2.9 Hz, 1H,
H4), 7.53 (dd, J = 6.9, 3.8 Hz, 1H, H10), 7.68 (d,
J = 2.9 Hz, 1H, H6), 7.76 (t, J = 2.0 Hz, 1H, H15), 7.88–
7.91 (m, 2H, H8 and H9), 7.99 (d, J = 2.1 Hz, 2H, H13),
14.07 (s, 1H, OH). 13C NMR (126 MHz, C6D6): d 29.78
(CMe3), 31.76 (CMe3), 34.51 (CMe3), 35.51 (CMe3);
methine carbons: 118.61, 119.79, 121.32, 126.77, 128.95,
134.81, 138.73; 4° carbons: 118.09, 123.77, 137.89, 140.32,
141.92, 151.80, 156.57, 159.61. EI-MS (+ve, m/z): 517
[M+].
O
Br
NMe
2
Br
A
mixture of 3,5-dibromoacetophenone (8.7 g,
31.3 mmol) and N,N-dimethylformamide dimethyl acetal
(10 mL, 75 mmol) was refluxed for 18 h to give a red solu-
tion, after which dichloromethane (100 mL) was added.
The organic layer was washed with water and brine, dried
over sodium sulphate and the solvent was removed to give
a red oil. Purification was performed by silica gel flash chro-
matography using n-hexane:ethyl acetate (20:1) as eluent to
4.4. Synthesis of 1-N,N-dimethylamino-3-(2,5-
dichlorophenyl)-3-oxo-1-propene
1
give a red solid. Yield: 7.2 g, 69%. H NMR (300 MHz,
O
Cl
CDCl3): d 2.94 (br s, 3H, N–Me), 3.16 (br s, 3H, N–Me),
5.55 (d, J = 20.4 Hz, 1H, C@CH), 7.71 (s, 1H, H4), 7.80 (d,
J = 20.4 Hz, 1H, C@CH), 7.92 (s, 2H, H2).
4.3. Synthesis of H2LBr
NMe
2
Cl
The procedure described in Section 4.2 was followed
using 2,5-dichloroacetophenone (10 g, 52.9 mmol) and
9
8
7
10
11
N,N-dimethylformamide
dimethyl
acetal
(14 mL,
6
13
5
12
14
100 mmol) to give a red solid. Yield: 7.5 g, 58%. 1H
NMR (400 MHz, CDCl3): d 2.89 (br s, 3H, N–Me), 3.12
(br s, 3H, N–Me), 5.32 (d, J = 12.88 Hz, 1H, C@CH),
7.23–7.26 (m, 1H), 7.30–7.39 (m, 2H).
1
Br
N
2
4
15
13
OH
3
14
Br
4.5. Synthesis of H2LCl
A solution of 3,5-di-tert-butyl-2-methoxyacetophenone
(5.70 g, 22 mmol) and potassium tert-butoxide (5.00 g,
45 mmol) in THF (30 mL) was stirred for 2 h at room tem-
perature to give a yellow suspension. A solution of 1-N,
N-dimethylamino-3-(3,5-dibromophenyl)-3-oxo-1-propene
(7.22 g, 22 mmol) in THF (20 mL) was then added and the
mixture was stirred for 12 h at room temperature to give a
dark red solution. A solution of ammonium acetate (16 g,
208 mmol) in acetic acid (100 mL) was added to the mix-
ture. THF was removed by distillation over 2 h and the res-
idue was dried under vacuum. After extraction by
dichloromethane, purification was performed by silica gel
flash chromatography using n-hexane:ethyl acetate (20:1)
as eluent to give the 2-(20-methoxyaryl)-6-arylpyridine pre-
cursor (E = Me; Scheme 1) as a pale yellow solid. Yield:
9
8
7
10
11
Cl
6
13
5
12
14
1
N
2
4
15
17
OH
3
16
Cl
The procedure described in Section 4.3 was followed
using 1-N,N-dimethylamino-3-(2,5-dichlorophenyl)-3-oxo-
1-propene to give the 2-(20-methoxyaryl)-6-arylpyridine
precursor as a pale yellow solid. Yield: 6.0 g, 44%. 1H
t
NMR (400 MHz, CDCl3): d 1.35 (s, 9H, Bu), 1.45 (s,
1
t
3.8 g, 32%. H NMR (400 MHz, CDCl3): d 1.37 (s, 9H,
9H, Bu), 3.37 (s, 3H, OMe), 7.31 (dd, J = 8.6, 2.5 Hz,
t
tBu), 1.45 (s, 9H, Bu), 3.37 (s, 3H, OCH3), 7.43 (d,
1H, H15), 7.40–7.44 (s, 2H, H14 and H17), 7.56–7.59 (m,
2H, H4 and H10), 7.72 (d, J = 2.5 Hz, 1H, H6), 7.79–7.81
(m, 2H, H8 and H9).
J = 2.5 Hz, 1H), 7.59 (d, J = 2.5 Hz, 1H), 7.64 (dd,
J = 5.7, 3.0 Hz, 1H), 7.71 (s, 1H), 7.80–7.81 (m, 2H), 8.21
(d, J = 1.6 Hz, 2H).
Demethylation of the 20-methoxy precursor (1.87 g,
3.52 mmol) in molten pyridinium chloride (4.0 g,
Demethylation of the 20-methoxy precursor (7.0 g,
15.8 mmol) in molten pyridinium chloride (18 g, 155.8
mmol) under N2 at 220 °C for 10 h gave H2LCl as a pale

4756
K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
yellow solid which was recrystallized in n-hexane. Yield:
4.32 g, 64%. H NMR (400 MHz, CD2Cl2): d 1.37 (s, 9H,
The procedure described in Section 4.6 was followed
using H2LCl (0.260 g, 0.61 mmol) and Ti(CH2Ph)4
(0.250 g, 0.61 mmol) to give a dark red solid. Yield:
1
5-tBu), 1.48 (s, 9H, 3-tBu), 7.36 (dd, J = 10.7, 3.2 Hz, 1H,
H15), 7.42 (d, J = 3.0 Hz, 1H, H4), 7.46 (d, J = 10.6 Hz,
1H, H14), 7.48 (dd, J = 10.4, 1.5 Hz, 1H, H10), 7.59 (d,
J = 3.2 Hz, 1H, H17), 7.69 (d, J = 3.0 Hz, 1H, H6), 7.91
(t, J = 9.8 Hz, 1H, H9), 7.95 (dd, J = 10.4, 1.4 Hz, 1H,
H8), 13.99 (s, 1H, OH). EI-MS (+ve, m/z): 428 [M+].
1
0.21 g, 52%. H NMR (500 MHz, CD2Cl2): d 1.36 (s, 9H,
5-tBu), 1.84 (s, 9H, 3-tBu), 4.20 (d, J = 8.2 Hz, 2H, CH2),
4.47 (d, J = 8.2 Hz, 2H, CH2), 6.31 (t, J = 7.3 Hz, 2H, p-
Ph), 6.45 (t, J = 7.8 Hz, 4H, m-Ph), 6.63 (d, J = 7.3 Hz,
4H, o-Ph), 6.71 (t, J = 8.0 Hz, 1H, H9), 6.98 (d,
J = 8.3 Hz, 1H, H14), 7.10 (dd, J = 8.0, 0.6 Hz, 1H, H8),
7.15 (d, J = 8.2 Hz, 1H, H15), 7.37 (d, J = 2.3 Hz, 1H,
H6), 7.69 (dd, J = 8.0, 1.1 Hz, 1H, H10), 7.73 (d,
J = 2.4 Hz, 1H, H4). 13C NMR (126 MHz, CD2Cl2): d
31.11 (3-CMe3), 31.75 (5-CMe3), 34.71 (CMe3), 35.75
(CMe3), 97.41 (CH2), 121.77 (C8), 123.06 (C10), 124.10
(p-Ph), 124.86 (C6), 126.99 (C4), 127.62 (m-Ph), 130.84 (o-
Ph), 131.07 (C15), 132.39 (C14); 138.68 (C9); 4° carbons:
128.35, 128.49, 136.74, 136.90, 139.15, 141.91, 142.96,
156.95, 158.05, 161.74, 195.04. Anal. Calc. for
C39H39NOTiCl2 (656.55): C, 71.35; H, 5.99; N, 2.13.
Found: C, 71.60; H, 6.11; N, 2.22%.
4.6. Synthesis of titanium complex 1
9
8
7
10
11
6
5
13
16
1
12
Br
N
4
14
15
2
3
17
O
Ti
Br
4.8. Synthesis of zirconium complex 4
A solution of H2LBr (0.260 g, 0.50 mmol) in pentane
(20 mL) and diethyl ether (8 mL) was slowly added at
ꢀ78 °C to Ti(CH2Ph)4 (0.208 g, 0.50 mmol) in pentane
(15 ml) and diethyl ether (5 mL). The resultant dark red
solution was stirred for 1 h at ꢀ78 °C and for 12 h at room
temperature. Filtration and concentration of the mixture
9
8
7
10
11
6
5
13
16
1
12
Br
N
4
14
15
2
3
17
O
Zr
1
Br
gave a dark red solid at ꢀ78 °C. Yield: 0.17 g, 46%. H
NMR (500 MHz, C6D6): d 1.35 (s, 9H, 5-tBu), 1.82 (s,
9H, 3-tBu), 4.23 (d, J = 8.2 Hz, 2H, CH2), 4.55 (d,
J = 8.2 Hz, 2H, CH2), 6.30 (m, 3H, H8 and p-Ph), 6.41
(t, J = 7.7 Hz, 4H, m-Ph), 6.63 (m, 5H, H9 and o-Ph),
7.16 (s, 1H, H10), 7.32 (d, J = 1.4 Hz, 1H, H6), 7.40 (d,
J = 2.3 Hz, 1H, H13), 7.71 (d, J = 2.3 Hz, 1H, H15), 7.90
(d, J = 1.4 Hz, 1H, H4). 13C NMR (126 MHz, C6D6): d
31.04 (3-CMe3), 31.74 (5-CMe3), 34.68 (CMe3), 35.75
(CMe3), 98.19 (CH2), 116.23 (C8), 122.92 (C10), 124.04
(p-Ph), 124.39 (C13), 124.79 (C6), 127.22 (C15), 127.58 (m-
Ph), 130.84 (o-Ph), 135.62 (C4), 139.01 (C9); 4° carbons:
122.17, 127.27, 128.35, 132.54, 136.87, 137.01, 142.73,
145.93, 157.01, 161.48, 193.48. Anal. Calc. for C39H39NO-
TiBr2 (745.45): C, 62.84; H, 5.27; N, 1.88. Found: C, 62.74;
H, 5.43; N, 1.99%.
A solution of H2LBr (0.250 g, 0.48 mmol) in pentane
(20 mL) and diethyl ether (5 mL) was slowly added at
ꢀ78 °C to Zr(CH2Ph)4 (0.225 g, 0.49 mmol) in pentane
(15 ml) and diethyl ether (5 mL). The resultant yellow
solution was stirred for 1 h at ꢀ78 °C and for 12 h at room
temperature. Filtration and concentration of the mixture
gave a yellow solid at ꢀ78 °C. Yield: 0.18 g, 48%. 1H
NMR (500 MHz, C6D6): d 1.35 (s, 9H, 5-tBu), 1.70 (s,
9H, 3-tBu), 3.42 (d, J = 9.4 Hz, 2H, CH2), 3.56 (d,
J = 9.4 Hz, 2H, CH2), 6.26 (t, J = 7.3 Hz, 2H, p-Ph),
6.37 (t, J = 7.7 Hz, 4H, m-Ph), 6.49 (d, J = 7.7 Hz, 1H,
H8), 6.75 (t, J = 8.0 Hz, 1H, H9), 6.80 (d, J = 7.5 Hz,
4H, o-Ph), 7.16 (d, J = 4.4 Hz, 1H, H10), 7.32 (d,
J = 0.8 Hz, 1H, H6), 7.37 (d, J = 2.2 Hz, 1H, H13), 7.60
(d, J = 1.2 Hz, 1H, H4), 7.66 (d, J = 2.3 Hz, 1H, H15).
13C NMR (126 MHz, C6D6): d 30.81 (3-CMe3), 31.77 (5-
CMe3), 34.61 (CMe3), 35.68 (CMe3), 71.18 (CH2), 117.64
(C8), 123.64 (C10), 123.69 (p-Ph), 125.08 (C6), 125.20
(C13), 127.00 (C15), 129.05 (m-Ph), 129.51 (o-Ph), 134.02
(C4), 138.87 (C9); 4° carbons: 122.08, 126.63, 132.39,
136.22, 137.54, 142.30, 145.81, 154.99, 158.85, 161.42,
187.37. Anal. Calc. for C39H39NOZrBr2 (788.77): C,
59.39; H, 4.98; N, 1.77. Found: C, 59.63 H, 5.12; N,
1.95%.
4.7. Synthesis of titanium complex 2
9
8
7
10
11
Cl
13
6
5
1
12
14
15
N
4
2
3
17
O
16
Ti
Cl

K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
4757
4.9. Synthesis of zirconium complex 5
J = 8.0 Hz, 4H, o-Ph), 7.19 (d, J = 7.7 Hz, 1H, H10), 7.33
(d, J = 2.3 Hz, 1H, H13), 7.36 (d, J = 1.3 Hz, 1H, H6),
7.69 (d, J = 2.4 Hz, 1H, H15), 7.76 (d, J = 1.3 Hz, 1H,
H4). 13C NMR (126 MHz, C6D6): d 30.77 (3-CMe3),
31.79 (5-CMe3), 34.57 (CMe3), 35.64 (CMe3), 79.08
(CH2), 117.55 (C8), 123.61 (C10), 123.76 (p-Ph), 124.91
(C13), 125.65 (C6), 127.26 (C15), 128.47 (m-Ph), 129.85 (o-
Ph), 135.09 (C4), 139.22 (C9); 4° carbons: 122.48, 126.18,
133.24, 135.83, 138.05, 142.12, 146.82, 155.45, 158.83,
161.26, 195.99. Anal. Calc. for C39H39NOHfBr2 (876.04):
C, 53.47; H, 4.49; N, 1.60. Found: C, 53.85; H, 4.43; N,
1.71%.
9
8
7
10
11
Cl
13
6
5
1
12
14
15
N
4
2
3
17
O
16
Zr
Cl
The procedure described in Section 4.8 was followed
using H2LCl (0.220 g, 0.51 mmol) and Zr(CH2Ph)4
(0.235 g, 0.52 mmol) to give a yellow solid. Yield: 0.17 g,
4.11. Synthesis of hafnium complex 8
1
48%. H NMR (500 MHz, CD2Cl2): d 1.37 (s, 9H, 5-tBu),
9
1.66 (s, 9H, 3-tBu), 2.99 (d, J = 9.3 Hz, 2H, CH2), 3.07
(d, J = 9.3 Hz, 2H, CH2), 6.37 (t, J = 7.2 Hz, 2H, p-Ph),
6.41 (t, J = 7.4 Hz, 4H, m-Ph), 6.49 (d, J = 7.5 Hz, 4H,
o-Ph), 7.10 (d, J = 8.3 Hz, 1H, H14), 7.13 (d, J = 8.2 Hz,
1H, H15), 7.39 (d, J = 2.4 Hz, 1H, H6), 7.54 (d,
J = 9.0 Hz, 1H, H8), 7.56 (d, J = 2.4 Hz, 1H, H4), 7.66 (t,
J = 8.0 Hz, 1H, H9), 7.80 (dd, J = 8.0, 1.2 Hz, 1H, H10).
13C NMR (126 MHz, CD2Cl2): d 30.04 (3-CMe3), 30.92
(5-CMe3), 34.03 (CMe3), 34.87 (CMe3), 68.76 (CH2),
122.63 (C10), 122.75 (p-Ph), 123.49 (C8), 124.96 (C6),
126.16 (C4), 128.18 (m-Ph), 128.40 (o-Ph), 128.61 (C15),
131.32 (C14); 137.99 (C9); 4° carbons: 126.11, 127.74,
128.14, 128.22, 128.56, 135.03, 136.37, 142.16, 159.10,
160.51, 187.25. Anal. Calc. for C39H39NOZrCl2 (699.87):
C, 66.93; H, 5.62; N, 2.00. Found: C, 67.17; H, 5.42; N,
2.24%.
8
7
10
11
Cl
13
6
5
1
12
14
15
N
4
2
3
17
O
16
Hf
Cl
The procedure described in Section 4.10 was followed
using H2LCl (0.220 g, 0.51 mmol) and Hf(CH2Ph)4
(0.280 g, 0.52 mmol) to give a pale yellow solid. Yield:
1
0.17 g, 42%. H NMR (500 MHz, CD2Cl2): d 1.39 (s, 9H,
5-tBu), 1.69 (s, 9H, 3-tBu), 2.69 (d, J = 10.4 Hz, 2H,
CH2), 2.79 (d, J = 10.4 Hz, 2H, CH2), 6.39–6.45 (m, 10H,
p-, m- and o-Ph), 7.17 (d, J = 8.2 Hz, 1H, H14), 7.29 (d,
J = 2.4 Hz, 1H, H6), 7.31 (d, J = 8.3 Hz, 1H, H15), 7.56
(dd, J = 8.0, 1.0 Hz, 1H, H8), 7.58 (d, J = 2.4 Hz, 1H,
H4), 7.64 (t, J = 8.0 Hz, 1H, H9), 7.82 (dd, J = 8.0,
1.2 Hz, 1H, H10). 13C NMR (126 MHz, CD2Cl2): d 30.00
(3-CMe3), 30.94 (5-CMe3), 33.99 (CMe3), 34.83 (CMe3),
76.86 (CH2), 122.54 (C10), 122.84 (p-Ph), 123.53 (C8),
124.73 (C6), 126.40 (C4), 127.60 (m-Ph), 128.69 (o-Ph),
129.56 (C15), 134.67 (C14); 138.43 (C9); 4° carbons:
125.59, 129.22, 131.78, 136.83, 139.40, 141.91, 142.22,
154.28, 159.02, 160.52, 195.66. Anal. Calc. for
C39H39NOHfCl2 (787.14): C, 59.51; H, 4.99; N, 1.78.
Found: C, 59.56; H, 4.93; N, 1.85%.
4.10. Synthesis of hafnium complex 7
9
8
7
10
11
6
5
13
16
1
12
Br
N
4
14
15
2
3
17
O
Hf
Br
A solution of H2LBr (0.210 g, 0.41 mmol) in pentane
(20 mL) and diethyl ether (5 mL) was slowly added at
ꢀ78 °C to Hf(CH2Ph)4 (0.230 g, 0.42 mmol) in pentane
(15 ml) and diethyl ether (5 mL). The resultant pale yellow
solution was stirred for 1 h at ꢀ78 °C and for 12 h at room
temperature. Filtration and concentration of the mixture
gave a pale yellow solid at ꢀ78 °C. Yield: 0.14 g, 39%.
1H NMR (500 MHz, C6D6): d 1.35 (s, 9H, 5-tBu), 1.74 (s,
9H, 3-tBu), 3.21 (virtual s, 4H, CH2), 6.31 (t, J = 7.3 Hz,
2H, p-Ph), 6.39 (t, J = 7.5 Hz, 4H, m-Ph), 6.43 (d,
J = 7.4 Hz, 1H, H8), 6.70 (t, J = 8.0 Hz, 1H, H9), 6.76 (d,
4.12. Synthesis of hafnium complex 9
9
8
7
10
11
18
6
5
13
16
1
12
14
15
N
4
2
3
17
O
Hf
19

4758
K.-H. Tam et al. / Journal of Organometallic Chemistry 692 (2007) 4750–4759
(b) S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000)
The procedure described in Section 4.10 was followed
using H2LMe (0.214 g, 0.55 mmol) and Hf(CH2Ph)4
(0.300 g, 0.55 mmol) to give a pale yellow solid. Yield:
1169;
(c) V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283.
[2] (a) G.J. Pindado, M. Thornton-Pett, M. Bouwkamp, A. Meetsma,
B. Hessen, M. Bochmann, Angew. Chem. Int. Ed. Engl. 36 (1997)
2358;
(b) B. Ray, T.G. Neyroud, M. Kapon, Y. Eichen, M.S. Eisen,
Organometallics 20 (2001) 3044.
[3] S.J. Skoog, C. Mateo, G.G. Lavoie, F.J. Hollander, R.G. Bergman,
Organometallics 19 (2000) 1406.
1
0.20 g, 49%. H NMR (500 MHz, C6D6): d 1.36 (s, 9H,
5-tBu), 1.81 (s, 9H, 3-tBu), 2.15 (s, 3H, Me18), 2.980(d,
J = 10.8 Hz, 2H, CH2), 3.05 (s, 3H, Me19), 3.09 (d,
J = 10.8 Hz, 2H, CH2), 6.35 (t, J = 7.4 Hz, 2H, p-Ph),
6.47 (t, J = 7.7 Hz, 4H, m-Ph), 6.70 (d, J = 7.6 Hz, 4H,
o-Ph), 6.75 (dd, J = 7.9, 1.0 Hz, 1H, H10), 6.83 (t,
J = 7.9 Hz, 1H, H9), 6.97 (d, J = 7.6 Hz, 1H, H14), 7.16
(m, 2H, H15 and H8), 7.35 (d, J = 2.4 Hz, 1H, H6), 7.71
(d, J = 2.4 Hz, 1H, H4). 13C NMR (126 MHz, C6D6): d
22.63 (Me18), 25.07 (Me19), 30.91 (3-CMe3), 31.84 (5-
CMe3), 34.58 (CMe3), 35.67 (CMe3), 77.78 (CH2), 121.65
(C8), 122.04 (C10), 123.24 (p-Ph), 125.08 (C6), 126.72
(C4), 128.13 (m-Ph), 129.91 (o-Ph), 130.70 (C15), 132.73
(C14); 138.41 (C9); 4° carbons: 126.59, 130.66, 136.01,
137.90, 141.68, 142.11, 145.59, 156.27, 159.43, 165.65,
203.01. Anal. Calc. for C45H41NOHf (746.32): C, 65.99;
H, 6.08; N, 1.88. Found: C, 65.74; H, 5.95; N, 2.04%.
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(c) J. Saito, Y. Suzuki, H. Makio, H. Tanaka, M. Onda, T. Fujita,
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Organometallics 12 (1993) 1491;
4.13. Polymerization procedure
Schlenk-line ethylene polymerization runs were carried
out under atmospheric pressure in toluene in a 100 mL glass
reactor containing a magnetic stir bar. The stirred solution
containing the catalyst was thermostated to the required
temperature and purged with ethylene for 15 minutes. Poly-
merization was initiated by adding a toluene solution of
methylaluminoxane(MAO), andthe reactor was maintained
under 1 atmosphere of ethylene for the duration of the poly-
merization. After the prescribed time, HCl-acidified metha-
nol (40 mL) was added to terminate the polymerization,
and the ethylene gas feed was stopped. The resultant solid
polymer was collected by filtration, washed with acidified
methanol and dried under vacuum at 80 °C for 12 h.
(b) X. Yang, C.L. Stern, T.J. Marks, J. Am. Chem. Soc. 116 (1994)
10015;
(c) E.Y.X. Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391.
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(c) J. Karl, G. Erker, R. Fro¨hlich, J. Am. Chem. Soc. 119 (1997)
11165;
Acknowledgements
The work described in this paper was supported by City
University of Hong Kong (7001930) and the Research
Grants Council of Hong Kong (CityU 100406 and CityU
2/06C).
(d) J. Karl, M. Dahlmann, G. Erker, K. Bergander, J. Am. Chem.
Soc. 120 (1998) 5643;
(e) Y. Sun, R.E.V.H. Spence, W.E. Piers, M. Parvez, G.P.A. Yap, J.
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(2000) 7986.
Appendix A. Supplementary material
[15] T.R. Boussie, G.M. Diamond, C. Goh, K.A. Hall, A.M. LaPointe,
M.K. Leclerc, V. Murphy, J.A.W. Shoemaker, H. Turner, R.K.
Rosen, J.C. Stevens, F. Alfano, V. Busico, R. Cipullo, G. Talarico,
Angew. Chem. Int. Ed. 45 (2006) 3278.
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1493;
(b) H. Kawaguchi, T. Matsuo, J. Organomet. Chem. 689 (2004) 4228.
[17] (a) M.C.W. Chan, K.H. Tam, Y.L. Pui, N. Zhu, J. Chem. Soc.
Dalton Trans. (2002) 3085;
As a representative example of the assignment process for
each complex, the 1H, 1H–1H COSY, NOESY and 13C–1H
COSY NMR spectra of Ti complex 3 are presented in Figs.
S1–S5. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.jorganchem.
2007.05.040.
(b) M.C.W. Chan, K.H. Tam, N. Zhu, P. Chiu, S. Matsui,
Organometallics 25 (2006) 785.
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