Synthesis and spectroscopic characterization of group 4 post-metallocenes bearing (σ-aryl)-2-phenolate-6-pyridyl and -isoquinolinyl auxiliaries

Article abstract of DOI:10.1039/c5dt02497h

A new series of group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N] ligands have been prepared, and all derivatives have been characterized by multinuclear NMR spectroscopy. In the ¹H NMR spectrum of the Ti derivative where [N] = (ortho-F)-substituted isoquinolinyl, one of the two CH₂ resonances is observed as a doublet of doublets (collapsing to a normal d upon ¹⁹F-decoupling), whereas the [¹H,¹⁹F]-HMQC correlation spectrum reveals a strong crosspeak for this dd resonance only, thus indicating the presence of intramolecular C-H·F-C interactions. [¹H,¹⁹F]-HMBC experiments have been performed which reveal a significant scalar component for this coupling and confirm that the interactions are genuine. The contrasting NMR spectral patterns for the (ortho-F)-pyridyl Hf analogue, which exhibits two sets of non-identical doublet of doublets for the methylene resonances, have been rationalized. The activities of the isoquinolinyl-based Ti-[O,C,N] catalysts for ethylene polymerization are superior to those of pyridyl-based congeners.

Full text of DOI:10.1039/c5dt02497h

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Synthesis and spectroscopic characterization of
group 4 post-metallocenes bearing (σ-aryl)-
Cite this: DOI: 10.1039/c5dt02497h
2
-phenolate-6-pyridyl and -isoquinolinyl auxiliaries†‡
Jerry C. Y. Lo, Loi-Chi So and Michael C. W. Chan*
A new series of group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N]
ligands have been prepared, and all derivatives have been characterized by multinuclear NMR spectro-
1
scopy. In the H NMR spectrum of the Ti derivative where [N] = (ortho-F)-substituted isoquinolinyl, one of
19
the two CH
2
resonances is observed as a doublet of doublets (collapsing to a normal d upon F-decoupling),
1
19
whereas the [ H, F]-HMQC correlation spectrum reveals a strong crosspeak for this dd resonance only,
1
19
thus indicating the presence of intramolecular C–H⋯F–C interactions. [ H, F]-HMBC experiments have
been performed which reveal a significant scalar component for this coupling and confirm that the inter-
actions are genuine. The contrasting NMR spectral patterns for the (ortho-F)-pyridyl Hf analogue, which
exhibits two sets of non-identical doublet of doublets for the methylene resonances, have been rational-
ized. The activities of the isoquinolinyl-based Ti-[O,C,N] catalysts for ethylene polymerization are superior
to those of pyridyl-based congeners.
Received 1st July 2015,
Accepted 31st July 2015
DOI: 10.1039/c5dt02497h
www.rsc.org/dalton
results carry significant implications for post-metallocene cata-
lyst design, since they corroborate the practical feasibility of
Introduction
The ongoing search for new ‘post-metallocene’ olefin polymer- the ortho-F⋯H(β) ligand–(polymer chain) contacts proposed6
ization catalysts, exhibiting ever superior activity, selectivity for living group 4 fluorine-rich bis(phenoxyimine) catalysts,
and control, has culminated in the development of novel as well as in the context of ‘weak attractive ligand–polymer
1
materials with unprecedented properties. Sterically demand- interactions’ (WALPI), a novel strategy offering the ability to
ing substituents neighboring the active site can confer vital manipulate the reactivity of the polymer chain during cata-
2
7
protection from chain transfer and termination processes.
lysis. Importantly, reports concerning late transition metal cata-
Electron-withdrawing functional groups have been introduced lyst systems have recently appeared that signal the potential
to augment the electrophilicity of the catalytic center in antici- and generality of the WALPI concept for influencing polymeriz-
3
8,9
pation of improved efficiencies, and to diminish undesirable ation reactions.
intermolecular interactions (such as ion-pairing) for fluorine-
rich moieties.
High efficiencies have been achieved for Ti-[O,N,C] cata-
lysts, but one drawback is that they frequently produce poly-
4
We have developed a new family of group 4 pyridine-2- olefin materials with high M /M , indicative of multisite
w
n
5
,10
phenolate-6-(σ-aryl) [O,N,C] post-metallocene complexes with behavior.
With the aid of DFT calculations, investigations
interesting spectroscopic and catalytic characteristics. In par- into the catalytic impact of both σ-aryl and phenolate substitu-
ticular, we have described the observation of weak and elusive ents have revealed several kinetically competitive polymeriz-
C–H⋯F–C interactions in bis(benzyl) derivatives bearing ation pathways as well as active sites, including an “ethylene-
fluorinated substituents using multinuclear NMR spectroscopy assimilated” (comprising ethylene insertion into the Ti–C(σ-
5
11
and, for the first time, a neutron diffraction study. These aryl) bond) species, in addition to conventional chain propa-
1
2
gation. The analogous olefin insertion into the Hf–C(σ-aryl)
bond of pyridylamido Hf-[N,N,C] catalysts, and the conse-
quences of this upon polymerization behavior, have been
Department of Biology and Chemistry, City University of Hong Kong, Tat Chee
Avenue, Kowloon, Hong Kong, China. E-mail: mcwchan@cityu.edu.hk
In memory of Professor Ken Wade, a teacher and colossus amongst us.
1
3
described.
†
The (σ-aryl)-2-phenolate-6-pyridyl [O,C,N] framework (which
was anticipated to be structurally analogous to the [O,N,C]
system) was thus devised to circumvent the problems arising
from the said olefin assimilation, since formation of the
‡
Electronic supplementary information (ESI) available: Experimental details and
characterization data for 2-phenol-6-pyridylbenzene ligands, additional multi-
nuclear NMR spectra, and table of ethylene polymerization results. See DOI:
10.1039/c5dt02497h
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resultant 8-membered metallacycle is disfavored. However,
evaluation of Ti-[O,C,N] catalysts for olefin polymerization
revealed activities that are significantly lower than their
1
4
[
O,N,C] counterparts. The principal aim of this study is to
enhance the olefin polymerization efficiency of [O,C,N] cata-
lysts by the following approaches. (1) Incorporation of
electron-donating σ-aryl substituents. Strong binding by the
central chelating group in a group 4 [O,L,O] catalyst has been
predicted to afford lower barriers for olefin insertion and
1
5
hence increased activities, and our work on Zr-[O,N,O] cata-
1
6
lysts corroborate this. Since π-donation from the σ-aryl
1
7,18
moiety is minimal,
and considerably weaker than pyridyl,
we reasoned that the incorporation of an electron-donating
group at the σ-aryl ring may increase its binding capability,
possibly leading to increased efficiencies. (2) Steric encum-
brance at the N(pyridyl) moiety. The introduction of a fused
benzo group as a σ-aryl substituent in Ti-[O,N,C] catalysts
afforded superior polymerization activities for the resultant
1
0
σ-naphthyl catalysts, and this has been rationalized both Scheme 2 Synthesis of complexes 1–8.
thermodynamically (by alleviating steric repulsion) and in
kinetic terms (the activation barrier to the ethylene-assimilated
species is particularly low for σ-naphthyl, and this pathway
proceeds faster than conventional propagation). Hence, an was synthesized by refluxing in a HCl/THF mixture. H
1
2
6
2
L was
equivalent strategy of incorporating a fused benzo unit at the similarly prepared using I-5 and then I-7.
pyridyl ring to yield [O,C,N(isoquinolinyl)] derivatives was
adopted. Finally, derivatives bearing Cl and F atoms ortho to ligands with M(CH
The cyclometalation reaction of the respective [O,C,N]
Ph) (M = Ti, Zr or Hf) was performed in
2
4
the M–N(pyridyl) bond have been prepared to evaluate the diethyl ether/n-pentane at −78 °C, then warmed to 25 °C and
influence of halogen substituents close to the metal center stirred to afford the desired product in moderate yields of
upon spectroscopic and catalytic properties.
36–60% (Scheme 2). However, these reaction conditions were
not applicable for the synthesis of the Zr congeners of 2, 7 and
8
. A variety of different solvents were employed in subsequent
1
attempts to prepare these Zr derivatives, but H NMR charac-
terization of the resultant reaction mixture gave broad or
minimal resonances.
Results and discussion
Synthesis
5
6
The synthesis of H2L and H2L ligands is described below
Scheme 1; for synthetic details of 2-phenolate-6-pyridyl-
benzene ligands, see the ESI‡). Protection of the hydroxyl group
Multinuclear NMR characterization and scalar coupling across
(
C–H⋯F–C interactions
1
13
in I-1 and attachment of the [1,3,2]dioxaborolane group gave I-3. All complexes have been characterized by H and C NMR
5
1
1
Suzuki-coupling of I-3 and I-4 yielded I-6, and the H
2
L ligand spectroscopy, including 135-DEPT, and 2D [ H, H]-COSY,
5,6
Scheme 1 Synthesis of H
2
L
.
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1
1
3
1
19
1
[
[
C, H]-HSQC and ROESY experiments, plus F NMR and the benzyl groups. A crosspeak in the H ROESY spectra of 5
19
H, F]-HMQC experiments for 3 and 8. As an illustrative and 6 between OMe and the pyridyl hydrogen adjacent to the
1
17
example, the H NMR spectrum of 8 has been fully assigned O atom (H ) confirms their close proximity, and the signifi-
1
7
(Fig. S1‡).
cantly downfield-shifted resonance for H
the benzyl 8.17 ppm respectively in C D , compared with e.g. 6.75 ppm in
(at 8.25 and
1
9,20
Based on the accepted spectroscopic criteria,
6
6
1
ligands in the Hf complex 3 are normal (η ), but all Ti and Zr 1) is attributed to hydrogen bonding with the OMe moiety.
derivatives exhibit η -benzyl groups. We have previously recog-
nized a good correlation between the H NMR spectroscopic metry and the methylene hydrogens are diastereotopic, appear-
features of the benzyl moieties in [O,C,N] and [O,N,C] deriva- ing as a doublet of doublets in the AB pattern for 1 and 4–7.
tives and their crystallographically determined conformation: For complexes 2, 3 and 8, investigations regarding possible
2
The benzyl groups in all the derivatives are related by sym-
1
(
1) for ‘anti,anti’ conformations, in which both benzyl units intramolecular coupling involving the F atom at X have been
1
protrude towards the central ring system, the p-Ph appears at undertaken. In the H NMR spectrum (C
6 6
D ) of 8, while the
<
6.55 ppm (in C ) and the chemical shifts for o-, m-, p-Ph downfield doublet for the diastereotopic methylene protons at
6 6
D
b
appear in an o > m > p sequence; (2) for ‘syn,anti’ benzyl 4.07 ppm for H is normal (thus implying no Ti⋯F inter-
ligands, the p-Ph is observed at >6.60 ppm and a sequence of action), the upfield resonance at 3.36 ppm for H appears as
m > o > p is evident.
a
5
b,12,14
2
1h
Accordingly, all complexes in this an overlapping doublet of doublets ( JH,H = 8.8 Hz, “ JH,F” =
work are proposed to exhibit the ‘anti,anti’ conformation for 3.6 Hz; Fig. 1), which collapses to a normal doublet upon
1
1
19
Fig. 1 H NMR spectrum (400 MHz, C
6 6
D
19
*, 298 K) for complex 8 (a) with the expanded methylene region, and 1D [ H, F]-HMBC NMR spectra
1
showing signals arising from (b) both H– F scalar (J) and cross correlation (CR) interactions; (c) exclusively from scalar coupling (J) and (d) exclu-
sively from dipolar cross correlation (CR).
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1
9
19
F-decoupling (Fig. S2‡). In addition, a doublet at 84.08 ppm
F nucleus, while strong crosspeaks are evident for both dd
1
3
1
1
19
1
19
(
JC,F = 7.0 Hz) for the methylene carbon in the C{ H} NMR resonances in the [ H, F]-HMQC spectrum. The [ H, F]-
1
19
19
spectrum, plus a strong crosspeak in the [ H, F]-HMQC spec- HMBC (J) spectrum for 3 also confirms that the F-coupling
trum (Fig. S2‡), are observed. Although the H– F coupling evident for both dd peaks is scalar in nature (Fig. S3‡). Com-
observed for 8 is classified as “ JH,F” ( J refers to n-bond pared with 2, this additional F-coupling for 3 may conceiva-
1
19
1
h
nh
19
J-coupling occurring through a hydrogen bond), clarification is bly occur by invoking C−H⋯F−C interactions (but assuming,
1
19
1h
3h
necessary because apparent H– F scalar coupling (J, with albeit unlikely, that
JH,F and
JH,F values are comparable),
3
chemical connectivity) through non-covalent contacts can or through a Hf⋯F interaction, to afford comparable JH,F
contain interference from cross-correlation (CR) interactions, values for all CH
which occur through space without bonding. Crucially, the respectively).
2
protons (Fig. 2, scheme A and B
potential applicability of the C–H⋯F–C contact in olefin
polymerization catalysis is only viable if the observed coupling valent spectroscopic observations for the CH
At this juncture, it is pertinent to consider the directly equi-
hydrogens of the
rather than F; single dq plus normal d reso-
2
CF
3
contains a J component and the non-covalent interaction is
2
(X = CF
3
7
1
19
CF
3
therefore genuine. Hence, a series of highly sensitive [ H, F]- nances) and 3
(two dq peaks) congeners, which correspond
1
9
CF
3
HMBC experiments have been performed to separate the con- to coupling with three F nuclei. In the case of 3 , evidence
tributions from J coupling and CR interference. Saliently, the in support of mechanism B was provided by the X-ray crystal
1
19
19
14
3c,22
[
H, F]-HMBC (J) spectrum (Fig. 1c) shows that the F-coup- structure, which revealed a close Hf⋯F interaction.
In
a
ling for the upfield H resonance contains a significant scalar this previous study, comparisons with [O,N,C] relatives also
component, thereby confirming that the C–H⋯F–C interaction indicate that the X substituent in [O,C,N] complexes is posi-
in 8 occurs with chemical connectivity. In accordance with tioned in closer proximity to the methylene groups and metal
b
CF
3
CF
3
this, the resonance for the other CH
2
hydrogen (H –C–H⋯F– center. Hence, by analogy to the 2
and 3
F-coupling observed for 2 and 3 are assigned to schemes A
JH,F). By extension, the doublet C{ H} and B respectively (although some contribution from A for 3
NMR signal for the methylene carbon at 84.08 ppm can be cannot be discounted).
derivatives, the
1
9
19
C) appears as a ‘normal’ doublet apparently without F-coup-
1
h
3h
21
13
1
ling (i.e. JH,F
≫
2
h
ascribed to
J
C,F (= 7.0 Hz). Altogether, these findings signify
Although long-range C–H⋯F–C coupling in fluorine-
the occurrence of scalar coupling across C–H⋯F–C inter- containing organic molecules has been studied for several
1
9
23
1
19
actions with a single F nucleus.
decades,
reports detailing intramolecular H– F (and
1
19
19
13
19
As expected, comparable [ H, F]-HMBC (J) results and F-
C– F) coupling in fluorinated organometallic complexes are
1
h
2h
14
8d,24
coupling ( JH,F = 3.5 Hz, JC,F = 6.3 Hz) are observed for 2.
sparse in the literature.
However, for the Hf congener 3, the H NMR peaks for the approximate relationship of JC,F ≈ n JH,F (n = 1.4 − 2.7) is con-
CH hydrogens are patently different; namely, they appear as sistently observed for the unusual coupling in these literature
two sets of non-identical doublet of doublets (Fig. 2; collapsing examples as well as the [O,C,N] (X = CF , F; n = 1.8 (for 2), 1.4
It is worthy of remark that an
1
2
3
1
9
to two normal AB doublets upon F-decoupling), indicating and 2.3 (for 3), and 1.9 (for 8) respectively) and [O,N,C] (X =
3
non-equivalent coupling between the methylene protons and a CF ) complexes in our work, and that this relationship is con-
1
1h
3h
Fig. 2 H NMR spectra (400 MHz, C
6
D
6
3
, 298 K) for diastereotopic methylene hydrogen atoms in 2 and 3, with schemes A (
J
H,F
≫
JH,F; M = Ti,
1
19
nh
applicable to complexes 2 and 8) and B ( JH,F via M⋯F; M = Hf, applicable to complex 3) to rationalize H– F coupling ( J refers to n-bond J-coup-
ling occurring through a hydrogen bond).
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2
h
2
served for a wide range of both
J
C,F (for C–H⋯F–C) and JC,F
(
for H–C–M⋯F–C) values.
It is intriguing to note that for 5 and 7 (X = Cl), slight
broadening or ‘shortening’ of the downfield methylene reso-
nance is apparent. Such findings are conventionally ascribed
to the steric effects of a neighboring substituent, although the
observation that the impact of a methyl group is negligible
appears to challenge this supposition (see Fig. S4 and S5 for
Fig. 3 Steric effects in Ti-[O,C,N] catalysts. For isoquinolinyl species 7
details‡). Nevertheless, it may be premature to attribute this and 8 (X = Cl, F), the metal geometry would be altered and the active
site would become more accessible.
minimal broadening to the electronic influence of the Cl atom.
Ethylene polymerization studies
erately active. These results also tentatively imply that the low
activities evident for [O,C,N] catalysts may originate from the
significantly lower susceptibility of the M–N(py) bond to
undergo olefin insertion, thus transforming into a more open
The complexes in this study were evaluated as catalysts for the
polymerization of ethylene using MAO [Table S1;‡ conditions:
5
2
00 equiv. of MAO, 20 ml of toluene, 1 atm ethylene feed,
0 °C, 10 min reaction time; activity in g(polymer) (mmol
−
1
−1
and efficient “olefin-assimilated” catalytic species (as is appar-
catalyst)
h ]. The ratio and nature of the cocatalyst exerts a
1
2
ent for the [O,N,C] system ).
profound influence upon catalytic behavior and performance
(
including activity), and such effects are also dependent on the
4
a,25
catalyst system.
Conclusions
The Hf derivative 3 is not active, and the low efficiencies of
−
1
−1
1
5
and 6 (7 and 4 g mmol
h
respectively), as well as 2, 4 and New F- and Cl-substituted [O,C,N] bis(benzyl) post-metallocene
h ), correspond to those previously reported complexes have been synthesized. Interestingly, the more
(≤1 g mmol−
1
−1
−
1
−1 14
for [O,C,N] catalysts (activities <10 g mmol
h ). The activi- upfield of the two methylene resonances in 8 appears as a
1
h
ties for 4 and 5 are similar to 1, suggesting that the incorpor- doublet of doublets (
J
H,F = 3.6 Hz). Considered together with
2
h
1
13
ated substituents (Me and OMe) may not impact significantly a doublet peak ( JC,F = 7.0 Hz) in the H-decoupled C NMR
upon the electron-donating capability of the σ-aryl moiety, or spectrum for the methylene carbon, and a strong crosspeak in
1
19
that this attribute does not influence catalytic activity. Interest- the [ H, F]-HMQC spectrum for the dd resonance only, these
1
19
13
19
ingly, 7 and 8 display moderate activities of 22 and 60 g features are consistent with H– F (and C– F) coupling
mmol−
4
1
h
−1
respectively, and M
n w n
and M /M values of up to through intramolecular C–H⋯F–C interactions. The spectro-
5
.0 × 10 and ca. 4 respectively were determined for the resul- scopic observation of such weak and elusive interactions
tant polymers. Complex 8 was also evaluated for ethylene remains sparse in the literature. Importantly, [ H, F]-HMBC
polymerization using Bu
conditions: 0.6 µmol of catalyst, Bu
2
6
1
19
i
3
Al/[Ph
3
C][B(C
6
F
5
)
4
] as a cocatalyst experiments have been performed that can distinguish
C][B(C ]/cata- between scalar (J) coupling and cross correlation inter-
i
[
3
Al/[Ph
3
6 5 4
F )
lyst (50/2/1 equiv. respectively), 10 mL of toluene, 7 atm ethyl- ference, revealing a significant scalar component for the
ene feed, 20 min reaction time]. Good efficiencies are observed dd resonance, and thereby confirming that the C–H⋯F–C
−
1
−1
−1
−1
1h
2h
at 50 °C [200 g mmol
h
(mol L of ethylene) ] and 75 °C interaction is genuine and the
J
H,F and (by extension)
J
C,F
260 g mmol−
/M = 2.8].
Although the activities for 7 and 8 are not exceptional and
1
h
−1
(mol L of ethylene)−1; Mn = 2.2 × 10 , notations are appropriate. The appearance of two non-identi-
−1
5
[
M
w
n
cal doublet of doublets for the methylene hydrogens in the
H NMR spectrum of the Hf derivative 3 has been rational-
1
lower than those typically observed for [O,N,C] relatives (e.g. ized, with reference to the structurally characterized CF ana-
3
3
for the [O,N,C] analogue of 1 under comparable conditions logue, by attributing the coupling to JH,F mediated through a
−
1
−1 18
using MAO, activity = 175 g mmol
h
), this is the first Hf⋯F–C interaction.
Steric and electronic factors have been invoked to influence
time that [O,C,N] catalysts with moderately high efficiencies
have been developed. The introduction of isoquinoline into and elevate the catalytic efficiencies of [O,C,N] complexes for
the [O,C,N] system evidently enhances catalytic activity. Like ethylene polymerization. Complexes 7 and especially 8 dis-
1
0
the ‘py-adjacent’ σ-aryl substituent in [O,N,C] catalysts, the played moderately high catalytic activities, which are the
additional fused benzo group in 7 and 8 causes steric repul- highest recorded for the [O,C,N] system. Generally, the employ-
sion between the isoquinolinyl and σ-aryl moieties, which ment of isoquinoline as the N-chelating moiety has resulted in
would result in their twisting and hence straining of especially improved catalytic performance. These results tentatively
the Ti–N(isoquinolinyl) bond, leading finally to a slight suggest that the habitually poor efficiencies of [O,C,N] catalysts
change in metal geometry as well as enhanced accessibility for may be due to their aversion to undergo olefin assimilation or
substrates at the active site (Fig. 3). Reports of related post- comparable reactions to generate a more accessible active site,
metallocene complexes such as Zr-bis(substituted 8-quinolino- in contrast to the [O,N,C] derivatives. This study can pave way
2
0
27
lato)
and Zr-bis(amidoquinolinyl)
have appeared, with towards the development of more efficient chelating σ-aryl
ethylene polymerization efficiencies ranging from low to mod- olefin polymerization catalysts.
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9
4
(
7
C
t, J = 7.8 Hz, 1H, H ), 7.70 (d, J = 2.30 Hz, 1H, H ), 7.94 (d, J =
Experimental section
General considerations
8
6
13
.9 Hz, 1H, H ), 8.04 (d, J = 2.1 Hz, 1H, H ). C NMR (100 MHz,
): δ 31.38 (3-CMe ), 31.99 (5-CMe ), 34.923 (CMe ), 36.00
), 83.45 ( JCH = 132.4 Hz, CH ), 117.40 (C ), 120.88 (C ),
D
6 6
3
3
3
1
17
15
All reactions were performed under a nitrogen atmosphere (CMe
using standard Schlenk techniques or in a Braun dry-box. All 122.26 (C ), 122.98 (C ), 123.08 (p-Ph), 123.41 (C ), 127.36 (C ),
3
2
1
0
6
4
9
8
16
solvents were appropriately dried and distilled and then 127.90 (o-Ph), 128.36 (C ), 129.38 (m-Ph), 141.83 (C ); 4°
degassed prior to use. Methylaluminoxane (MAO, 10 wt% solu- carbons: 135.12, 136.02, 139.53, 139.84, 143.05, 149.80, 164.42,
tion in toluene; purchased from Aldrich) was pretreated by 197.48. Anal. calcd for C H NOTiCl (622.10): C, 75.30; H, 6.48;
3
9
40
removing all volatiles under vacuum for 12 hours to minimize N, 2.25. Found: C, 75.10; H, 6.65; N, 2.18.
residual amounts of “free” trimethylaluminium, after which
Complex 3.
dried toluene was added to give a 10 wt% solution that was
1
13
freshly prepared before use. H, C (referenced to residual
1
9
solvent peaks) and F (external trifluoroacetic acid reference)
NMR spectra were recorded at 298 K on a Bruker Avance 400
(
or 300) FT-NMR spectrometer (ppm). Peak assignments were
1
1
13
1
based on combinations of DEPT-135, and 2-D H– H, C– H
and NOE correlation NMR experiments. Elemental analyses
were performed on a Vario EL elemental analyzer (Elementar
Analysensysteme GmbH). For polymer analysis, gel permeation
chromatographs were obtained on a PL-GPC 220 instrument
versus polyethylene standards at 160 °C in 1,2,4-trichloro-
benzene. The melting point of the polymer was determined
using a PerkinElmer STA6000 simultaneous thermal analyzer,
running under a nitrogen atmosphere with the increasing
2
2
A solution of H L (0.191 g, 0.51 mmol) in pentane (20 mL)
and diethyl ether (2 mL) was added dropwise at −78 °C to
Hf(CH Ph) (0.289 g, 0.53 mmol) in pentane (10 mL) and
diethyl ether (2 mL). The reaction mixture was stirred for
hour at −78 °C and for 16 hours at room temperature. After
filtration and concentration, the solution was cooled to −78 °C
for 24 hours to give an orange solid, which was collected by fil-
tration. Yield: 0.225 g, 60%. H NMR (400 MHz, C
s, 9H, 5- Bu), 1.85 (s, 9H, 3- Bu), 2.51 (dd, J
2
4
−
1
temperature rate of 10 °C min from 100 to 170 °C. Synthetic
procedures for the 2-phenol-6-pyridylbenzene ligands are given
in the ESI.‡ The synthesis of I-1 and complex 2, and details
1
1
19
concerning [ H, F]-HMBC experiments (adapted from
1
6
D
6
): δ 1.45
1
31
28
[
H, P]-HMBC experiments described by Rüterjans ), have
t
t
(
3
= 11.2 Hz, JH,F
=
H,H
1
4
been reported previously.
.6 Hz, 2H, CH
CH ), 5.83–5.86 (m, 1H, H ), 6.39–6.43 (m, 2H, p-Ph),
.53–6.60 (m, 8H, m-Ph and o-Ph), 6.66–6.69 (m, 2H, H and
2
), 2.73 (dd, JH,H = 11.2 Hz, JH,F = 2.2 Hz, 2H,
1
5
2
Synthesis
16
6
1
7
9
10
Complex 1.
H ), 7.01–7.07 (m, 2H, H and H ), 7.68 (d, J = 2.4 Hz, 1H,
H ), 8.06 (d, J = 2.0 Hz, 1H, H ), 8.14 ppm (d, J = 7.2 Hz, 1H,
H ). C NMR (101 MHz, C D ): δ 31.00 (3-CMe ), 32.06
4
6
8
13
6
6
3
(
5-CMe
3
), 34.81 (CMe
3
), 35.89 (CMe
3
), 73.01 (d, JC,F = 5.0 Hz,
1
15
JC,H = 125.3 Hz, CH ), 105.63 (d, JC,F = 105.6 Hz, C ), 116.00
2
1
7
10
6
(
1
(
1
d, JC,F = 3.0 Hz, C ), 122.48 (C ), 122.73 (p-Ph), 123.24 (C ),
23.55 (C ), 127.76 (C ), 128.23 (o-Ph), 128.78 (C ), 128.97
m-Ph), 145.24 (d, JC,F = 10.0 Hz, C ); 4° carbons: 133.50,
37.50, 137.79, 141.49, 142.27, 146.42, 155.61, 162.77, 163.47
4
9
8
1
6
1
4
19
(
d, JC,F = 146.9 Hz, C ), 198.11. F NMR (376 MHz, C
6 6
D ):
δ −70.2. Anal. calcd for C H NOHfF (736.23): C, 63.62;
L (0.29 g, 0.73 mmol) in pentane (30 mL) H, 5.48; N, 1.90. Found: C, 63.41; H, 5.84; N, 1.79.
3
9
40
1
A solution of H
2
and diethyl ether (2 mL) was slowly added at −78 °C to
Ti(CH Ph) (0.30 g, 0.73 mmol) in pentane (20 ml) and diethyl
Complex 4.
2
4
ether (4 mL). The resultant red solution was stirred for 1 hour
at −78 °C and for 12 hours at room temperature. Filtration and
concentration of the mixture gave a dark red crystalline solid
at −78 °C, which was collected by filtration. Yield: 0.17 g, 38%.
1
t
H NMR (400 MHz, C D ): δ 1.45 (s, 9H, 5- Bu), 1.98 (s, 9H,
- Bu), 3.38 (d, J = 8.8 Hz, 2H, CH
6
6
t
3
2
), 4.10 (d, J = 8.8 Hz, 2H,
CH
2
), 6.38 (t, J = 7.1 Hz, 2H, p-Ph), 6.46 (dd, J = 7.8, 0.8 Hz, 1H,
1
5
H ), 6.50 (t, J = 7.6 Hz, 4H, m-Ph), 6.55 (d, J = 7.1 Hz, 4H, o-
Ph), 6.63 (t, J = 7.9 Hz, 1H, H ), 6.74–6.77 (m, 2H, H
1
6
10,17
), 7.89
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Paper
3
A solution of H
2
L
(0.284 g, 0.696 mmol) in pentane
Complex 6.
(
−
(
15 mL) and diethyl ether (7 mL) was added dropwise at
78 °C to Ti(CH Ph) (0.287 g, 0.696 mmol) in pentane
15 mL) and diethyl ether (3 mL). The resultant red solution
2
4
was stirred for 1 hour at −78 °C and for 12 hours at room
temperature. Filtration and concentration of the reaction
mixture gave a dark red crystalline solid. Yield: 0.20 g, 45%.
1
t
H NMR (400 MHz, CD Cl ): 1.44 (s, 9H, 5- Bu), 1.78 (s, 9H,
2
2
t
3
- Bu), 2.22 (s, 3H, Me), 3.13 (d, J = 8.8 Hz, 2H, CH
), 6.29 (d, J = 7.6 Hz, 4H, o-Ph), 6.35 (t, J =
.0 Hz, 2H, p-Ph), 6.44 (t, J = 7.4 Hz, 4H, m-Ph), 6.89 (s, 1H,
2
), 3.62 (d,
J = 8.8 Hz, 2H, CH
7
2
1
0
4
15
8
H ), 7.42–7.44 (m, 2H, H and H ), 7.46 (s, 1H, H ), 7.56 (d,
J = 8.0 Hz, 1H, H ), 7.68 (s, 1H, H ), 7.84 (t, J = 8.0 Hz, 1H, (9 mL) and diethyl ether (20 mL) was added dropwise at
2 4
A solution of Zr(CH Ph) (0.232 g, 0.509 mmol) in pentane
1
7
6
1
6
13
4
H ). C NMR (101 MHz, CD Cl ): 21.72 (Me), 31.15 (3- −78 °C to H L (0.205 g, 0.484 mmol) in pentane (20 mL). The
2
2
2
CMe
3
), 31.87 (5-CMe
3
), 34.95 (CMe
3
), 35.83 (CMe
3
), 82.93 resultant mixture was stirred for 1 hour at −78 °C and for
1
17
10
6
(
J
CH = 130.8 Hz, CH
2
), 117.88 (C ), 121.44 (C ), 122.06 (C ), 12 hours at room temperature. After concentration, the
4
15
1
1
1
1
22.41 (p-Ph), 123.20, 124.01, (C and C ), 127.69 (m-Ph), mixture was cooled to −25 °C for 1 hour. Filtration of the solu-
8 16
1
28.43 (C ), 128.67 (o-Ph), 142.96 (C ); 4° carbons: 125.58, tion gave an orange solid. Yield: 0.12 g, 36%. H NMR
t
t
28.50, 129.31, 129.56, 134.60, 135.55, 136.83, 139.43, (400 MHz, C D ): δ 1.50 (s, 9H, 5- Bu), 1.91 (s, 9H, 3- Bu), 2.80
39.77, 140.32, 142.91. Anal. calcd for C H NOClTi (d, J = 9.6 Hz, 2H, CH ), 3.11 (d, J = 9.6 Hz, 2H, CH ), 3.22 (s,
6
6
4
0
42
2
2
1
5
(
636.11): C, 75.53; H, 6.66; N, 2.20. Found: C, 75.47; H, 6.36; 3H, OMe), 6.19 (d, J = 7.6 Hz, 1H, H ), 6.33 (t, J = 7.2 Hz, 2H,
9
N, 2.27.
p-Ph), 6.40 (d, J = 8.8 Hz, 1H, H ), 6.49 (t, J = 7.4 Hz, 4H, m-Ph),
1
6
Complex 5.
6.58 (d, J = 7.6 Hz, 4H, o-Ph), 6.70 (t, J = 8.0 Hz, 1H, H ), 7.65
4
8
(
2
d, J = 2.0 Hz, 1H, H ), 7.97 (d, J = 8.8 Hz, 1H, H ), 8.02 (d, J =
6
17
13
.0 Hz, 1H, H ), 8.17 (d, J = 8.4 Hz, 1H, H ). C NMR
(
(
101 MHz, C D ): δ 31.77 (3-CMe ), 32.70 (5-CMe ), 35.41
6 6 3 3
CMe ), 36.46 (CMe ), 55.35 (OMe), 66.06 ( JCH = 130.3 Hz,
3 3
1
9
15
4
CH ), 111.44 (C ), 120.83 (C ), 122.90 (C ), 122.97 (p-Ph),
2
6
17
8
1
1
1
23.63 (C ), 124.06 (C ), 128.31 (o-Ph), 129.36 (m-Ph), 130.70 (C ),
42.24 (C ); 4° carbons: 129.90, 134.77, 136.91, 137.51,
39.03, 142.65, 148.31, 154.98, 157.68, 164.30, 197.44. Anal.
1
6
calcd for C H NO ClZr (695.45): C, 69.08; H, 6.09; N, 2.01.
4
0
42
2
Found: C, 68.76; H, 6.46; N, 2.20.
Complex 7.
Ti(CH
added dropwise at −78 °C to H
diethyl ether (5 mL). The resultant mixture was stirred for
hour at −78 °C and for 12 hours at room temperature. After
2 4
Ph) (0.200 g, 0.485 mmol) in pentane (35 mL) was
4
2
L (0.196 g, 0.462 mmol) in
1
concentration, the mixture was cooled to −25 °C for 2 hours.
Filtration of the solution gave a red solid. Yield: 0.15 g, 50%.
1
t
H NMR (400 MHz, C
6
D
6
): δ 1.48 (s, 9H, 5- Bu), 1.99 (s, 9H,
- Bu), 3.12 (s, 3H, OMe), 3.39 (d, J = 8.8 Hz, 2H, CH ), 4.10 (d,
J = 8.8 Hz, 2H, CH ), 6.24 (d, J = 8.8 Hz, 1H, H ), 6.40 (t, J =
t
3
2
1
5
2
9
7
7
.2 Hz, 2H, p-Ph), 6.49 (dd, J = 8.0, 0.8 Hz, 1H, H ), 6.55 (t, J =
.6 Hz, 4H, m-Ph), 6.60 (d, J = 7.2 Hz, 4H, o-Ph), 6.84 (t, J = 8.0
5
A solution of H
2
L (0.20 g, 0.45 mmol) in pentane (12 mL)
1
6
4
Hz, 1H, H ), 7.66 (d, J = 2.4 Hz, 1H, H ), 7.85 (d, J = 8.8 Hz, and diethyl ether (3 mL) was added dropwise at −78 °C to
1
1
CMe ), 35.47 (CMe ), 36.51 (CMe ), 55.49 (OMe), 84.07 ( J
1
8
6
H, H ), 7.94 (d, J = 2.0 Hz, 1H, H ), 8.25 (dd, J = 8.4, 0.8 Hz, Ti(CH
2
Ph)
4
(0.195 g, 0.473 mmol) in pentane (3 mL). The
1
7
13
H, H ). C NMR (101 MHz, C D ): δ 31.97 (3-CMe ), 32.62 (5- resultant mixture was stirred for 1 hour at −78 °C and for
6 6 3
1
=
12 hours at room temperature. After filtration and
3
3
3
CH
1
5
6
4
31.8 Hz, CH
2
), 112.12 (C ), 122.62 (C ), 122.91 (C ), 123.08 concentration, the mixture was cooled to −25 °C for 12 hours.
9
17
(C ), 123.47 (p-Ph and C ), 128.86 (m-Ph), 129.90 (o-Ph), Filtration of the solution gave a red solid. Yield: 0.12 g, 40%.
8
16
1
t
1
1
29.95 (C ), 142.54 (C ); 4° carbons: 127.77, 132.92, 136.15,
36.29, 140.82, 143.48, 149.89, 155.84, 157.57, 164.27, 200.39. 3- Bu), 3.49 (d, J = 8.9 Hz, 2H, CH
ClTi (652.13): C, 73.67; H, 6.49; N, CH ), 6.25 (t, J = 7.2 Hz, 2H, p-Ph), 6.33 (t, J = 7.3 Hz, 4H,
H NMR (400 MHz, C D ): δ 1.45 (s, 9H, 5- Bu), 1.99 (s, 9H,
6 6
t
2
), 4.09 (d, J = 8.9 Hz, 2H,
Anal. calcd for C40
2
H
42NO
2
2
9
.15. Found: C, 73.37; H, 6.61; N, 2.09.
m-Ph), 6.54 (d, J = 7.2 Hz, 4H, o-Ph), 6.88 (t, J = 7.7 Hz, 1H, H ),
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1
9
10
15
17
6
7
7
8
.89–6.93 (m, 1H, H ), 6.99–7.03 (m, 3H, H , H and H ), under 1 atmosphere of ethylene for the duration of the
1
8
4
.11 (td, J = 7.6, 1.0 Hz, 1H, H ), 7.71 (d, J = 2.3 Hz, 1H, H ), polymerization. After the prescribed time, HCl-acidified
.96 (d, J = 7.9 Hz, 1H, H ), 8.02 (d, J = 2.1 Hz, 1H, H ), methanol (40 mL) was added to terminate the polymerization,
.08 (d, J = 8.6 Hz, 1H, H ). C NMR (101 MHz, C D ): δ 31.93 and the ethylene gas feed was stopped. Ethylene polymeriz-
6 6
3-CMe ), 32.53 (5-CMe3), 35.46 (CMe3), 36.55 (CMe3), ation tests using Bu Al/[Ph C][B(C F ) ] as a cocatalyst at 7
3 3 3 6 5 4
8
6
2
0
13
i
(
1
6
8
1
1
1
1
4.52 ( JCH = 130.4 Hz, CH
2
), 120.59, 122.83 (C ), 123.36 (p-Ph), atm ethylene pressure were similarly carried out using a Teflon
4
24.01 (C ), 126.54, 127.55, 127.69, 128.30 (m-Ph), 128.38, liner in a 100 mL Parr stainless steel high-pressure reactor
28.90, 129.40 (o-Ph), 130.23 (C ), 133.41; 4° carbons: 124.86, equipped with a paddle-like stirrer. The resultant solid
35.38, 136.70, 140.68, 141.08, 141.25, 141.58, 142.27, 143.67, polymer was collected by filtration, washed with methanol
58.40, 168.64, 199.34. Anal. calcd for C43H42NOClTi (672.16): (20 mL) and concentrated HCl (2 mL), and dried under
2
0
C, 76.84; H, 6.30; N, 2.08. Found: C, 76.62; H, 6.02; N, 2.11.
Complex 8.
vacuum at 80 °C for 12 hours. Errors for the activity values are
estimated to be ±10%, based on previous polymerization tests
using the same experimental procedure and reactor.
Acknowledgements
The work described in this paper was fully supported by a
grant from the Research Grants Council of the Hong Kong
Special Administrative Region, China (CityU 100409). We are
grateful to Dr Cham-Chuen Liu for technical assistance, and to
1
19
Dr Kong-Hung Sze (HKU) for assistance with [ H, F]-HMBC
experiments.
6
A solution of H
2
L
(0.202 g, 0.472 mmol) in pentane
(17 mL) and diethyl ether (3 mL) was added dropwise at
−
78 °C to Ti(CH Ph) (0.205 g, 0.497 mmol) in pentane
2
4
Notes and references
(3 mL). The resultant mixture was stirred for 1 hour at −78 °C
and for 12 hours at room temperature. Filtration of the solu-
1 (a) L. Resconi, J. C. Chadwick and L. Cavallo, in Comprehen-
sive Organometallic Chemistry III, ed. R. H. Crabtree,
D. M. P. Mingos and M. Bochmann, Elsevier, Oxford, 2007,
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prehensive Organometallic Chemistry III, ed. R. H. Crabtree,
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N. Meijboom, C. Ganter and A. G. Orpen, J. Am. Chem. Soc.,
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1
tion gave a red solid. Yield: 0.11 g, 36%. H NMR (400 MHz,
t
t
6 6
C D ): δ 1.44 (s, 9H, 5- Bu), 1.98 (s, 9H, 3- Bu), 3.36 (dd,
1
h
J
H,H = 8.8 Hz,
2
JH,F = 3.6 Hz, 2H, CH ), 4.07 (d, JH,H = 8.8 Hz,
2
4
6
H
H, CH ), 6.28 (t, J = 7.4 Hz, 2H, p-Ph), 6.37 (t, J = 7.6 Hz,
2
1
5
H, m-Ph), 6.51 (s, 1H, H ), 6.54 (d, J = 7.2 Hz, 4H, o-Ph),
9
19
10
.87–6.92 (m, 2H, H and H ), 7.10–7.13 (m, 3H, H ,
1
7
18
4
and H ), 7.71 (d, J = 2.4 Hz, 1H, H ), 7.96 (d, J =
8
6
7
8
3
.6 Hz, 1H, H ), 8.02 (d, J = 2.0 Hz, 1H, H ), 8.16 (d, J =
.8 Hz, 1H, H ). C NMR (101 MHz, C
2
0
13
6
D
6
): δ 31.86 (3-CMe
3
),
2.52 (5-CMe3), 35.47 (CMe3), 36.55(CMe3), 84.08 (d,
2
h
1
2
J
C,F = 7.0 Hz,
2 C,F
JCH = 129.3 Hz, CH ), 102.03 (d, J =
1
5
6
4
2
8.2 Hz, C ), 122.99 (C ), 123.40 (p-Ph), 124.01 (C ), 127.28
(
d, JC,F = 6.0 Hz), 127.46, 127.55, 127.85, 128.37 (m-Ph),
28.52 (C ), 129.62 (o-Ph), 129.97 (C ), 133.34; 4° carbons:
8
20
1
1
1
24.08, 135.80, 136.84, 140.00, 141.60, 142.29, 143.78, 158.20,
1
14
19
59.07 (d, JC,F = 244.5 Hz, C ), 166.05, 198.16. F NMR
): δ −79.70. Anal. calcd for C43 42NOFTi
655.71): C, 78.77; H, 6.46; N, 2.14. Found: C, 78.49; H, 6.36;
(376 MHz, C
6
D
6
H
(
N, 2.07.
3 Examples: (a) T. Tsukahara, D. C. Swenson and
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Polymerization procedures
(
b) P. E. O’Connor, D. J. Morrison, S. Steeves, K. Burrage
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cocatalyst 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 thermo-
stated to the required temperature and purged with ethylene
for 15 minutes. Polymerization was initiated by adding a
toluene solution of MAO, and the reactor was maintained
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5
1
3
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(a) S. C. F. Kui, N. Zhu and M. C. W. Chan, Angew. Chem., 21 Upon closer inspection, the downfield ‘normal’ H NMR
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doublet for the other methylene proton (H –C–H⋯F–C) in
1
9
8 does engage in F-coupling, as evidenced by the weaker
1
19
but discernible crosspeak in the [ H, F]-HMQC spectrum,
1
19
6
as well as the scalar coupling in the [ H, F]-HMBC (J)
spectrum. The substantially smaller magnitude of this
1
19
3h
H- F coupling ( JHF) is entirely consistent with the postu-
1
h
lated H–C–H⋯F–C coupling mechanism (since
J
HF
≫
3
h
J
HF).
7
8
(a) C.-C. Liu and M. C. W. Chan, Acc. Chem. Res., 2015, 48, 22 (a) H. Plenio, Chem. Rev., 1997, 97, 3363; (b) M. Dahlmann,
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3
773; (b) M. P. Weberski Jr., C. Chen, M. Delferro and
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2
9
A. Iwashita, M. C. W. Chan, H. Makio and T. Fujita, Catal. 24 (a) H. C. Clark and L. E. Manzer, J. Chem. Soc., Chem.
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1 The term “olefin-assimilated” has been proposed to un-
2 3
ambiguously describe the modified [M–C H R–aryl] species
arising from olefin insertion into the M–C(sp ) bond of a
chelating σ-aryl ligand.
2 J. C. Y. Lo, M. C. W. Chan, P.-K. Lo, K.-C. Lau, T. Ochiai
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(
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