Effect of terminal aryloxo ligands in ethylene polymerization using titanatranes of the type, [Ti(OAr){(O-2,4-R2C6H 2)-6-CH2}3N]: Synthesis and structural analysis of the heterobimetallic complexes of

Article abstract of DOI:10.1021/om3008635

Effects of aryloxo terminal ligands and AlMe₃ in ethylene polymerization using a series of Ti(OAr)[{(O-2,4-R₂C ₆H₂)-6-CH₂}₃N] [R = Me (1), ^tBu (2); Ar = 2,6-Me₂C₆

Full text of DOI:10.1021/om3008635

Article
pubs.acs.org/Organometallics
Effect of Terminal Aryloxo Ligands in Ethylene Polymerization Using
Titanatranes of the Type, [Ti(OAr){(O-2,4‑R2C6H2)‑6-CH2}3N]: Synthesis
and Structural Analysis of the Heterobimetallic Complexes of
Titanatranes with AlMe3
Yuki Takii,† Prabhuodeyara M. Gurubasavaraj,‡ Shohei Katao,‡ and Kotohiro Nomura*,†,‡
†Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan
‡Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara
630-0101, Japan
S
* Supporting Information
ABSTRACT: Effects of aryloxo terminal ligands and AlMe3 in
ethylene polymerization using a series of Ti(OAr)[{(O-2,4-
t
R2C6H2)-6-CH2}3N] [R = Me (1), Bu (2); Ar = 2,6-Me2C6H3
(a), 2,6-iPr2C6H3 (b), 2,6-Ph2C6H3 (c), 2,6-F2C6H3 (d), C6F5 (e)]
(1a−1e, 2d,2e) in the presence of methylaluminoxane (MAO)
have been explored. Reactions of 1b,1d,1e, which showed an
increase in the activity upon addition of a small amount of AlMe3,
with 1.0 equiv of AlMe3 afforded heterobimetallic Ti−Al
complexes, TiMe(O-2,6-iPr2C6H3)[(O-2,4-Me2C6H2-6-CH2)(μ2-
O-2,4-Me2C6H2-6-CH2)(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)N]
(3b) and [TiMe{(O-2,4-Me2C6H2-6-CH2)2(μ2-O-2,4-Me2C6H2-
6-CH2)N}][Me2Al(μ2-OAr)] [Ar = 2,6-F2C6H3 (3d), C6F5 (3e)],
in moderate yields, and their structures were determined by X-ray
crystallography. In contrast, the similar reaction of 1a (which
showed a decrease in the activity upon addition of AlMe3) yielded [Al(μ2-O-2,6-C6H3)Me2]2 and TiMe[{(O-2,4-Me2C6H2)-6-
CH2}3N] as isolated forms: [Al(μ2-OC6F5)Me2]2 was isolated from the mixture in the reactions of 1c,2d,2e. The isolated
heterobimetallic complexes (3b,3d,3e) exhibited high catalytic activities for ethylene polymerization in the presence of MAO,
suggesting that these bimetallic species play a role in this catalysis.
atrane ligands,13,14 including main group metals to transition-
INTRODUCTION
■
metal complexes. Titanatranes among group 4 metals have
The design of efficient molecular catalysts for precise olefin
been utilized in organic synthesis,14a−f and syndiospecific
polymerization has been one of the most attractive research
styrene polymerization.14g−k We have focused on titanatranes
fields since the discovery of Ziegler−Natta catalysts.1−7 In the
that feature two or three aryloxo arms as the catalyst precursors
typical polymerization process, transition-metal complexes are
for olefin polymerization.15,16 We first demonstrated that
activated by different types of cocatalysts to form cationic
t
Ti(OiPr)[(O-2,4-R2C6H2-6-CH2)3N] (R = Me, Bu) were
species, which are proposed to be an active species in this
catalysis.2d,8,9 Al reagents, such as Al alkyl methylaluminoxane
effective as catalyst precursors for ethylene polymerization in
(MAO), play an important role as cocatalysts,10 and these Al
the presence of MAO, and the activities remarkably increased at
higher temperature even at 100−120 °C.15a The activity also
complexes are also involved in the catalysis by forming
increased upon addition of a small amount of AlMe3.15a
heterobimetallic complexes or counteranions with titanium
complexes.8,11,12 These bimetallic complexes exhibit high
catalytic activity to produce polymers with different micro-
structures. The activation of metal complexes is usually
associated with a decrease in complex stability due to the
electronic deficiency of the metal center,8,9 but this would be
improved/tuned by ligand modifications with several donor
atoms.
Atrane ligands contain a neutral nitrogen atom that facilitates
coordination in a chelate fashion when necessary by providing
the metal with additional electronic density. There have been
many reports for the synthesis of complexes containing the
Recently, we isolated heterobimetallic Ti−Al complexes of the
type, [TiMe{(μ2-O-2,4-R2C6H2-6-CH2)(O-2,4-R2C6H2-6-
CH2)2N}][R′2Al(μ2-OiPr)], and demonstrated that these are
effective as catalyst precursors for ethylene polymerization.
Recently, we isolated heterobimetallic Ti−Al complexes
containing a tris(aryloxo)amine ligand of the type, [TiMe{(μ2-
O-2,4-R2C6H2-6-CH2)(O-2,4-R2C6H2-6-CH2)2N}][Me2Al(μ2-
OiPr)], which exhibited moderate catalytic activities for
Received: September 6, 2012
© XXXX American Chemical Society
A
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Scheme 1
Scheme 2
ethylene polymerization in toluene in the presence of MAO at
80−120 °C.15e In particular, [TiMe{(μ2-O-2,4-tBu2C6H2-6-
CH2)(O-2,4-tBu2C6H2-6-CH2)2N}][Me2Al(μ2-OiPr)] itself
polymerizes ethylene without cocatalysts to afford a high-
molecular-weight polymer with a uniform distribution.15e We
also reported that the isolated Ti−Al heterobimetallic complex,
[TiMe{(O-2,4-Me2C6H2-6-CH2)2(μ2-OCH2CH2)N}][Me2Al-
(μ2-OtBu)], showed moderate catalytic activity for ethylene
polymerization without cocatalysts at 120 °C, affording a high-
molecular-weight polymer with a uniform distribution.15b
These results clearly suggest a hypothesis that the cationic
species generated by cleavage of the Ti−O bonds play an
important role as the active species in this catalysis (Scheme 1).
Later, we reported that the activity in ethylene polymer-
i z a t i o n u s i n g [ T i ( O A r ) { ( O - 2 , 4 - M e 2 C 6 H 2 - 6 -
CH2)2(OCH2CH2)N}]n (n = 1, 2) was strongly affected by
the terminal aryloxo substituents especially in the ortho
position. The facts thus suggested that the type of aryloxo
ligand presumably affects the equilibrium process in generation
of the catalytically active species shown in Scheme 1. In this
paper, we describe the preparation and characterization of a
series of titanatranes bearing substituted aryloxo ligands of the
type, Ti(OAr)[{(O-2,4-Me2C6H2)-6-CH2}3N] [Ar = 2,6-
Me2C6H3 (1a), 2,6-Ph2C6H3 (1c), 2,6-F2C6H3 (1d), C6F5
(1e)], and their use as the catalyst precursors for ethylene
polymerization in the presence of MAO. We also explored the
effect of AlMe3 on the catalytic activity and isolated several
heterobimetallic Ti−Al complexes that may provide insight into
the nature of the catalytic species that may be involved in the
ethylene polymerization process.17
RESULTS AND DISCUSSION
■
Synthesis of Ti(OAr)[{(O-2,4-R2C6H2)-6-CH2}3N] [R = Me
t
(1a−1e), Bu (2d,2e); Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3
(b), 2,6-Ph2C6H3 (c), 2,6-F2C6H3 (d), C6F5 (e)]. A series of
titanatranes bearing substituted aryloxo ligands of the type,
Ti(OAr)[{(O-2,4-Me2C6H2)-6-CH2}3N] [Ar = 2,6-Me2C6H3
(1a), 2,6-Ph2C6H3 (1c), 2,6-F2C6H3 (1d), C6F5 (1e)], were
prepared according to a modified procedure for the synthesis of
the 2,6-iPr2C6H3 analogue (1b, Scheme 2).18 In situ formation
of Ti(OAr)(OiPr)3 by treatment of Ti(OiPr)4 with 1 equiv of
ArOH and subsequent reaction with tris(2-hydroxy-3,5-
dimethylbenzyl)amine in toluene at 25 °C afforded 1a,1c−1e
in 62.1−93.4% yields as yellow-orange microcrystals. The
resultant complexes were identified by 1H and 13C NMR
spectra and elemental analysis, and complexes 1d,1e were also
identified by 19F NMR spectra. According to our previous
report as well as that in the 2,6-diisopropyl phenoxy analogue
(1b),18 the resultant complexes should have monomeric
1
structures, and no significant changes in the H NMR spectra
were observed by varying the measurement temperature.
The similar reaction of Ti(OiPr)4 with 2,6-F2C6H3OH or
C6F5OH and subsequent reaction with tris(2-hydroxy-3,5-di-
tert-butylbenzyl)amine in toluene afforded the other aryloxo
modified titanatranes, Ti(OAr)[{(O-2,4-tBu2C6H2)-6-CH2}3N]
[Ar = 2,6-F2C6H3 (2d), C6F5 (2e)]. Complexes 2d,2e were also
1
identified by H, 13C, and 19F NMR spectra and elemental
analysis. However, the reactions with 2,6-Me2C6H3OH,
2,6-iPr2C6H3OH, and 2,6-Ph2C6H3OH in place of 2,6-
F2C6H3OH afforded Ti(OiPr)[{(O-2,4-tBu2C6H2)-6-CH2}3N]
(2f) (Scheme 2). Since the reaction products of Ti(OiPr)3(O-
2,6-iPr2C6H3)18 with [{(HO-2,4-tBu2C6H2)-6-CH2}3N] af-
forded the isopropoxy analogue (2f),19 it thus seems likely
B
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t
Table 1. Ethylene Polymerization by Ti(OAr)[{(O-2,4-R2C6H2)-6-CH2}3N] [R = Me (1), Bu (2); Ar = 2,6-Me2C6H3 (a),
a
2,6-iPr2C6H3 (b), 2,6-Ph2C6H3 (c), 2,6-F2C6H3 (d), C6F5 (e)] (1a−1e, 2d,2e)−MAO (MAO/AlMe3) Catalyst Systems
b
b
c
d
d
run
Ar (complex)
d-MAO/mmol (Al/Ti)
AlMe3/μmol (Al/Ti)
temp/°C
yield/mg
activity
Mw × 10−5
Mw/Mn
1
2
3
4
5
2,6-Me2C6H3 (1a)
2,6-Me2C6H3 (1a)
2,6-iPr2C6H3 (1b)
2,6-iPr2C6H3 (1b)
2,6-iPr2C6H3 (1b)
2,6-iPr2C6H3 (1b)
2,6-iPr2C6H3 (1b)
2,6-iPr2C6H3 (1b)
2,6-Ph2C6H3 (1c)
2,6-Ph2C6H3 (1c)
2,6-Ph2C6H3 (1c)
2,6-F2C6H3 (1d)
2,6-F2C6H3 (1d)
C6F5 (1e)
3.0 (30 000)
3.0 (30 000)
3.0 (30 000)
3.0 (30 000)
4.0 (40 000)
4.0 (40 000)
4.0 (40 000)
4.0 (40 000)
3.0 (30 000)
3.0 (30 000)
4.0 (40 000)
3.0 (30 000)
3.0 (30 000)
2.0 (20 000)
2.0 (20 000)
3.0 (30 000)
3.0 (30 000)
2.0 (20 000)
2.0 (20 000)
3.0 (30 000)
3.0 (30 000)
2.0 (20 000)
2.0 (20 000)
3.0 (30 000)
3.0 (30 000)
100
100
100
100
100
120
100
120
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
97.8
88.5
978
885
7.88
6.86
8.14
9.02
7.46
3.09
2.66
2.51
2.07
2.58
1.0 (10)
1.0 (10)
103.7
150.2
78.7
1040
1500
787
e
6
97.1
971
7
1.0 (10)
1.0 (10)
134.9
474.0
242.9
159.2
231.4
74.6
1350
4740
2430
1590
2310
746
8.01
1.91
8.94
6.05
7.14
7.70
8.16
9.10
9.42
7.60
8.40
9.05
7.07
7.59
6.28
7.94
6.38
6.62
5.70
2.35
2.1
e
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
3.11
2.32
2.14
2.80
2.22
2.82
2.74
2.46
2.21
2.72
2.11
2.56
2.35
2.40
2.18
2.46
2.37
1.0 (10)
1.0 (10)
1.0 (10)
1.0 (10)
1.0 (10)
1.0 (10)
1.0 (10)
1.0 (10)
104.3
97.3
1040
973
C6F5 (1e)
143.3
109.3
153.2
93.9
1430
1090
1530
939
C6F5 (1e)
C6F5 (1e)
2,6-F2C6H3 (2d)
2,6-F2C6H3 (2d)
2,6-F2C6H3 (2d)
2,6-F2C6H3 (2d)
C6F5 (2e)
89.1
891
92.6
926
75.1
751
113.5
81.9
1140
819
C6F5 (2e)
C6F5 (2e)
108.6
73.0
1090
730
C6F5 (2e)
a
Conditions: catalyst, 0.1 μmol; n-octane, 30 mL; ethylene, 8 atm; 100 °C; 60 min; d-MAO (prepared by removing AlMe3 and toluene from
b
c
d
e
commercially available MAO). Al/Ti molar ratio. Activity in kg-PE/mol-Ti·h. GPC data in o-dichlorobenzene vs polystyrene standards. Cited
from ref 15a.
that the ligand exchange between aryloxide and isopropoxide
occurred in the reaction mixture probably due to a steric
effect.20 The reaction of 2f with 1 equiv of 2,6-Me2C6H3OH in
C6D6 at 25 °C did not take place even after 24 h.
distributions. As reported previouly,15a the activities by 1b,1f
in toluene instead of n-octane showed low activity, and we
assumed that this would be due to coordination of toluene to
the proposed catalytically active species.22
Ethylene Polymerization by Ti(OAr)[{(O-2,4-R2C6H2)-6-
Observed activities in the ethylene polymerizations by
Ti(OAr)[{(O-2,4-Me2C6H2)-6-CH2}3N] [Ar = 2,6-Me2C6H3
(1a), 2,6-Ph2C6H3 (1c), 2,6-F2C6H3 (1d), C6F5 (1e)]−MAO
catalyst systems (under optimized Al/Ti molar ratios)
increased in the order: Ar = 2,6-F2C6H3 (1d, 746 kg-PE/mol-
Ti·h, run 12) < 2,6-Me2C6H3 (1a, 978, run 1) < 2,6-iPr2C6H3
(1b, 1037, run 3) < C6F5 (1e, 1093, run 16) < 2,6-Ph2C6H3
(1c, 2429, run 9). The results thus suggest that the activity was
influenced by the terminal aryloxide ligand employed. It should
be noted that the catalytic activities displayed by 1b,1d,1e−
MAO catalyst systems increased upon addition of a small
amount of AlMe3 (runs 4, 7, 8, 13, 15, 17), whereas those for
1a,1c−MAO catalyst systems decreased (runs 2 and 10). We
believe that these are in unique contrast in these catalysts,
because the observed effect is highly influenced by the terminal
aryloxide ligand employed. In all cases, the resultant polymers
(prepared at 100 °C) possessed relatively high molecular
weights with unimodal molecular weight distributions (Mw =
(6.05−9.42) × 105, Mw/Mn = 2.07−3.11), and significant
decreases/increases in the Mw values were not observed under
these conditions. These results also suggest that these ethylene
polymerizations proceeded with uniform catalytically active
species irrespective of the kind of terminal aryloxide ligand
(OAr) employed.
t
CH2}3N] (R = Me, Bu) in the Presence of Al Cocatalysts.
Ethylene polymerizations by Ti(OAr)[{(O-2,4-R2C6H2)-6-
CH2}3N] [R = Me, Ar = 2,6-Me2C6H3 (1a), 2,6-Ph2C6H3
t
(1c), 2,6-F2C6H3 (1d), C6F5 (1e); R = Bu (2d,2e)] were
conducted in n-octane (ethylene, 8 atm; 100 °C; 60 min) in the
presence of methylaluminoxane (MAO). MAO white solid (d-
MAO), prepared by removing AlMe3 and toluene from the
commercially available samples (PMAO-S, 6.8 wt % in toluene,
Tosoh Finechem Co.), was chosen, because it was generally
effective in the preparation of high-molecular-weight ethylene/
α-olefin copolymers with unimodal molecular weight distribu-
tions exemplified by using catalysts based on Cp*TiCl2(O-
2,6-iPr2C6H3) and [Me2Si(C5Me4)(NtBu)]TiCl2.21 This is also
because, as reported previously,15 we also conducted these
ethylene polymerizations in the copresence of a small amount
of AlMe3 (10 equiv to Ti). The results are summarized in Table
1.
As reported previously in ethylene polymerization using the
Ti(OiPr)[{(O-2,4-Me2C6H2)-6-CH2}3N] (1f)−MAO catalyst
system,15e the catalytic activity by the 1b−MAO catalyst system
increased at high temperature (100 → 120 °C, runs 5 and 6)
and the activities increased upon addition of AlMe3 in a small
amount (10 equiv to Ti, runs 5−8). The resultant polymers
prepared by the 1b−MAO catalyst system possessed relatively
high molecular weights with unimodal molecular weight
The catalytic activities by Ti(OAr)[{(O-2,4-tBu2C6H2)-6-
CH2}3N] [Ar = 2,6-F2C6H3 (2d), C6F5 (2e)] were somewhat
C
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Scheme 3
Figure 1. ORTEP drawings for TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-6-CH2)(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)N]
(3b, left) and [TiMe{(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)2}N][Me2Al(μ2-OAr)] [Ar = 2,6-F2C6H3 (3d, middle), C6F5 (3e, right)].
Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity.23
higher than those by the methyl analogues (1d,1e) under the
same conditions [activity: 939 kg-PE/mol-Ti·h (by 2d, run 18)
vs 746 kg-PE/mol-Ti·h (by 1d, run 12); 1135 kg-PE/mol-Ti·h
(by 2e, run 22) vs 1093 kg-PE/mol-Ti·h (by 1e, run 16)]. In
contrast to the above results by 1d,1e (runs 13, 15, 17), the
activities by 2d,2e decreased upon addition of AlMe3 (runs 19,
21, 23, 25). The observed difference may be explained as due to
activities for ethylene polymerization in toluene in the presence
of MAO, and the observed activities were relatively close to
those observed by the tris(aryoloxo)amine analogues (1f, 2f) in
the presence of MAO upon addition of AlMe3.15e Moreover,
the tert-butyl analogue itself polymerizes ethylene, affording a
high-molecular-weight polymer with a uniform distribution.15e
Therefore, we explored reactions of Ti(OAr)[{(O-2,4-
t
t
R2C6H2)-6-CH2}3N] [R = Me (1a−1e), Bu (2d,2e); Ar =
a steric bulk of the Bu substituent compared to Me on the
2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b), 2,6-Ph2C6H3 (c), 2,6-
F2C6H3 (d), C6F5 (e)] with AlMe3 to clarify reasons for the
observed results in Table 1.
chelate phenoxy ligand in titanatranes. The resultant polymers
possessed relatively high molecular weights with unimodal
distributions (Mw = (5.70−9.05) × 105, Mw/Mn = 2.11−2.72),
and significant decreases/increases in the molecular weights
were not observed under these conditions. These results also
suggest that these ethylene polymerizations proceeded with
uniform catalytically active species.
The reactions of 1b,1d,1e, which showed an increase in the
activity upon addition of a small amount of AlMe3, with 1.0
equiv of AlMe3 afforded the corresponding heterobimetallic
Ti−Al complexes (3b,3d,3e) in moderate yields (50.6−76.1%;
Scheme 3). The resultant complexes were identified by 1H and
13C (and 19F) NMR spectra and elemental analyses, and their
structures were determined by X-ray crystallography (Figure 1),
as described below.23 These complexes are soluble in toluene,
THF, hexane, and chloroform and were very stable as
microcrystals that can be stored for long periods in the drybox
without partial decomposition (at room temperature or in the
freezer at −30 °C).
Reaction of Ti(OAr)[{(O-2,4-R2C6H2)-6-CH2}3N] with
AlMe3, and Structural Analysis of the Heterobimetallic
Ti−Al Complexes. We previously reported that heterobime-
tallic Ti−Al complexes containing a tris(aryloxo)amine ligand
of the type, [TiMe{(μ2-O-2,4-R2C6H2-6-CH2)(O-2,4-R2C6H2-
t
6-CH2)2N}][Me2Al(μ2-OiPr)] (R = Me, Bu), prepared by
reacting Ti(OiPr)[(O-2,4-R2C6H2-6-CH2)3N] (1f, 2f) with 1.0
equiv of AlMe3 in toluene, exhibited moderate catalytic
D
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Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for TiMe[(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-
CH2)2N][Me2Al(μ2-OAr)] [Ar = 2,6-F2C6H3 (3d), C6F5 (3e)] and TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-6-CH2)(Me2Al-
a
μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)N] (3b)
3b
3d
3e
selected bond distances (Å)
Ti(1)−O(1)
Ti(1)−O(2)
Ti(1)−O(3)
Ti(1)−O(4)
Ti(1)−N(1)
Ti(1)−C(1)
Al(1)−O(1)
Al(1)−O(2)
Al(1)−C(2)
Al(1)−C(3)
2.115(3)
2.102(3)
1.810(3)
1.806(2)
2.334(4)
2.082(5)
1.829(3)
1.872(3)
1.947(6)
1.950(5)
2.1766(12)
2.2136(16)
2.0532(17)
1.8049(16)
1.8262(17)
2.4270(14)
2.0656(13)
1.8090(11)
1.8238(11)
2.4263(12)
2.0881(15)
1.8411(13)
1.8355(13)
1.953(2)
2.0984(17) Ti(1)−C(7)
1.8534(17)
1.8368(17)
1.9526(19) Al(1)−C(8)
1.953(3) Al(1)−C(9)
1.955(2)
selected bond angles (deg)
O(1)−Ti(1)−O(2)
O(1)−Ti(1)−O(3)
O(1)−Ti(1)−O(4)
O(1)−Ti(1)−N(1)
O(2)−Ti(1)−O(3)
O(2)−Ti(1)−O(4)
O(2)−Ti(1)−N(1)
O(3)−Ti(1)−O(4)
O(3)−Ti(1)−N(1)
O(1)−Ti(1)−C(1)
O(2)−Ti(1)−C(1)
O(3)−Ti(1)−C(1)
N(1)−Ti(1)−C(1)
Ti(1)−O(1)−Al(1)
Ti(1)−O(2)−Al(1)
O(1)−Al(1)−O(2)
C(2)−Al(1)−C(3)
71.06(12)
167.30(15)
90.64(13)
83.19(13)
96.33(14)
157.71(13)
80.65(14)
101.29(15)
84.71(15)
87.96(16)
92.32(19)
99.85(19)
170.11(19)
101.23(13)
100.26(14)
82.92(15)
117.5(2)
69.03(4)
164.17(5)
85.93(5)
92.14(5)
95.89(5)
150.85(5)
82.36(5)
107.16(6)
80.71(5)
93.95(6)
92.38(6)
91.38(6)
169.96(5)
100.74(5)
105.17(5)
81.73(6)
116.79(10)
68.56(6)
164.96(8)
84.21(7)
91.80(6)
97.26(7)
148.71(7)
81.68(6)
107.85(8)
80.83(6)
93.26(7) O(1)−Ti(1)−C(7)
93.21(8) O(2)−Ti(1)−C(7)
92.50(8) O(3)−Ti(1)−C(7)
170.96(8) N(1)−Ti(1)−C(7)
100.30(7)
107.07(8)
81.42(8)
118.40(11) C(8)−Al(1)−C(9)
The details are shown in the Supporting Information.23
a
Microcrystals of 3b,3d,3e suitable for their crystallographic
corresponding to Ti−O(3) and Ti−O(4) distances]: these
distances are also longer than those in Al−O bond distances
[1.829(3)−1.872(3) Å, corresponding to Al−O(1) and Al−
O(2) distances]. These are a similar observation to that in the
[TiMe{(μ2-O-2,4-R2C6H2-6-CH2)(O-2,4-R2C6H2-6-
CH2)2N}][Me2Al(μ2-OiPr)], reported previously.15e The re-
sults in 3d,3e thus clearly indicate that the resultant complexes
possess Ti−Me bonds by replacement of the OAr group with
AlMe3, and the structure of 3b would be formed by
rearrangement as a stable form after the alkylation (replace-
ment).
These complexes also fold a distorted tetrahedral geometry
around Al, and the C(2)−Al(1)−C(3) bond angles in these
complexes [C(8)−Al−C(9) in 3e] were 116.79(10)−
118.40(11)°, although the O(1)−Al(1)−O(2) bond angles
were small [81.42(8)° and 82.92(15)°]. As described above,
Al−O bond distances [1.829(3)−1.872(3) Å] are shorter than
the Ti−O (in μ2-O) bond distances [2.0532(17)−2.2136(16)
Å].
analyses were grown from a hot toluene solution upon cooling,
and their structures are shown in Figure 1. The selected bond
distances and angles are summarized in Table 2.23 These
complexes fold a distorted octahedral geometry around
titanium consisting of a C−Ti−N axis [170.11(19)° for 3b;
169.96(5)° for 3d; 170.96(8)° for 3e] and a distorted plane of
one terminal aryloxo ligand and three aryloxo chelate ligands
[total bond angles of the O(1)−Ti(1)−O(2), O(2)−Ti(1)−
O(3), O(3)−Ti(1)−O(4), and O(1)−Ti(1)−O(4) for 3d,3e
were 358.01° and 357.88°, respectively; the total bond angle for
3b was 359.32°]. The coordination sphere of titanium consists
of one methyl and four oxygen atoms, including three oxygens
from the atrane ligand, and the titanium atoms in 3b,3d,3e are
ligated via a transannular interaction stemming from the
bridgehead amino nitrogen. The average O−Ti−N bond angles
for 3b, 3d, and 3e are 85.52, 84.80, and 84.62°, respectively,
suggesting a displacement of the titanium atom toward the axial
oxygen, similar to the observation made in the case of the other
heterobimetallic Ti−Al complexes.15b,e
Moreover, Ti−O(1) and Ti−O(2) bond distances in
3b,3d,3e [2.0532(17)−2.2136(16) Å] are relatively longer
than those in [TiMe{(μ2-O-2,4-R2C6H2-6-CH2)(O-2,4-
R2C6H2-6-CH2)2N}][Me2Al(μ2-OiPr)] [2.071(13), 2.072(11)
Note that Al atoms in 3d,3e are ligated through oxygen
atoms in the terminal aryloxo ligand and the atrane ligand,
whereas Al atoms in 3b are ligated through two oxygen atoms
in the atrane ligand. Therefore, Ti−O (in μ2-O) bond distances
in 3b,3d,3e [2.0532(17)−2.2136(16) Å, corresponding to Ti−
O(1) and Ti−O(2) distances] are longer than the other Ti−O
distances in the aryloxo ligands [1.8049(16)−1.8262(17) Å,
t
Å in R = Me; 2.0673(19), 2.095(2) Å in R = Bu], reported
previously.15e These are probably due to a steric bulk of the
aryloxo fragment. It is assumed that longer (rather weak) Ti−O
bond distances would be probably more suited in terms of
E
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Scheme 4
Scheme 5
Scheme 6
generation of the assumed catalytically active species from
[TiMe{(μ2-O-2,4-tBu2C6H2-6-CH2)(O-2,4-R2C6H2-6-
CH2)2N}][Me2Al(μ2-OiPr)],15e generated by dissociation of
two Ti−O bonds bridged to the Al atom.
Moreover, [Al(μ2-OC6F5)Me2]2 (6) was an only isolated
product from the reaction mixture of Ti(OC6F5)[{(O-
2,4-tBu2C6H2)-6-CH2}3N] (2e) with AlMe3, and 6 was
identified by NMR spectra and X-ray crystallographic analysis
(Scheme 5).24 The isolated compound (white microcrystals) in
the reaction of 2d with AlMe3 conducted under the same
conditions showed similar resonances assumed as [Al(μ2-O-2,6-
In contrast to the results in the reactions of 1b,1d,1e, isolated
compounds (crystals) from a reaction mixture of Ti(O-2,6-
Me2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N] (1a) with AlMe3
were [Al(μ2-O-2,6-Me2C6H3)Me2]2 (5, 38.2%) and TiMe-
[{(O-2,4-Me2C6H2)-6-CH2}3N] (4) identified by X-ray
crystallographic analysis (Scheme 4).24 Formation of 4 could
only be confirmed by isolation after careful repetitive
recrystallization (shown in the Experimental Section). The
result may suggest that, once formed, the heterobimetallic Ti−
Al complex was converted to the methyl species (4) and
aluminum phenoxide (5) by dissociation, although the reaction
in 1b afforded thermally stable 3b in relatively high yield
(76.1%). The attempted reaction of the diphenyl analogue (1c)
with AlMe3 in toluene afforded complex mixtures, and no
complexes could be isolated cleanly from the reaction mixture.
These results by 1a,1c were thus in unique contrast to those by
1b,1d,1e, affording the heterobimetallic Ti−Al complexes
(3b,3d,3e), but the results also corresponded well to the
experimental facts in the above ethylene polymerization,
especially the effect of AlMe3 toward the activity.
1
F2C6H3)Me2]2 on the basis of the H and 19F NMR spectra.
Because these reactions did not afford the heterobimetallic Ti−
Al complexes, the results were also compatible with the
experimental results that the activities in ethylene polymer-
ization decreased upon the addition of AlMe3. Taking into
account these experimental results, it is thus highly suggested
that formation of the heterobimetallic Ti−Al complexes plays
an important role toward the catalytic activities in the presence
of AlMe3.
As an another approach for modification of Al in [TiMe{(μ2-
O-2,4-tBu2C6H2-6-CH2)(O-2,4-tBu2C6H2-6-CH2)2N}][Me2Al-
(μ2-OiPr)], which showed catalytic activity for ethylene
polymerization without additional cocatalysts, we conducted a
reaction of Ti(OiPr)[{(O-2,4-tBu2C6H2)-6-CH2}3N] (2f) with
1 equiv of Me2AlCl. The isolated crystalline material from this
reaction was identified as TiCl[{(O-2,4-tBu2C6H2)-6-CH2}3N]
on the basis of NMR measurements and elemental analysis
(Scheme 6).25 Moreover, the reaction of 2f with [Al(μ2-
F
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Table 3. Ethylene Polymerization by TiMe[(O-2,4-Me2C6H2-6-CH2)2(μ2-O-2,4-Me2C6H2-6-CH2)N][Me2Al(μ2-OAr)] [Ar = 2,6-
F2C6H3 (3d), C6F5 (3e)]−MAO and TiMe(O-2,6-iPr2C6H3)[(O-2,4-Me2C6H2-6-CH2)(μ2-O-2,4-Me2C6H2-6-CH2)(Me2Al-μ2-O-
a
2,4-Me2C6H2-6-CH2)N] (3b)−MAO Catalyst Systems
b
c
d
d
run
complex (μmol)
temp/°C
d-MAO/mmol (Al/Ti)
AlMe3 /μmol
yield/mg
activity
Mw × 10−5
Mw/Mn
26
27
28
29
30
31
32
33
4
3b (1.0)
3b (1.0)
3b (1.0)
3b (0.1)
3b (0.1)
3b (0.1)
3b (0.1)
3b (0.1)
1b (0.1)
1b (0.1)
3d (1.0)
3d (1.0)
3d (1.0)
3d (0.1)
3d (0.1)
3d (0.1)
3d (0.1)
3d (0.1)
1d (0.1)
3e (1.0)
3e (1.0)
3e (1.0)
3e (0.1)
3e (0.1)
3e (0.1)
3e (0.1)
3e (0.1)
1e (0.1)
1e (0.1)
80
100
120
80
trace
trace
trace
140.0
158.7
85.0
trace
trace
trace
1400
1590
850
3.0 (30 000)
3.0 (30 000)
3.0 (30 000)
2.0 (20 000)
4.0 (40 000)
3.0 (30 000)
4.0 (40 000)
11.4
8.76
5.50
9.15
7.65
9.02
8.01
2.02
2.06
2.13
2.28
2.11
2.07
2.35
100
120
100
100
100
100
80
125.3
142.2
150.2
134.9
trace
trace
trace
95.6
1250
1420
1500
1350
trace
trace
trace
956
1.0
1.0
7
34
35
36
37
38
39
40
41
13
42
43
44
45
46
47
48
49
15
17
100
120
80
3.0 (30 000)
3.0 (30 000)
3.0 (30 000)
2.0 (20 000)
4.0 (40 000)
4.0 (40 000)
11.0
7.96
4.07
8.95
7.17
8.16
2.17
2.20
2.15
2.14
2.19
2.22
100
120
100
100
100
80
143.8
76.0
1440
760
126.6
122.2
104.3
trace
trace
trace
123.0
170.6
56.0
1270
1220
1040
trace
trace
trace
1230
1710
560
1.0
100
120
80
3.0 (30 000)
3.0 (30 000)
3.0 (30 000)
2.0 (20 000)
4.0 (40 000)
3.0 (30 000)
4.0 (40 000)
insoluble
7.99
insoluble
100
120
100
100
100
100
2.38
2.31
2.27
2.08
2.74
2.21
3.51
138.8
101.7
143.3
153.2
1390
1020
1430
1530
8.55
7.18
1.0
1.0
9.42
8.40
a
b
c
d
Conditions: n-octane, 30 mL; ethylene, 8 atm; 60 min; d-MAO. Al/Ti molar ratio. Activity in kg-PE/mol-Ti·h. GPC data in o-dichlorobenzene
vs polystyrene standards.
OC6F5)Me2]2 (6) in CDCl3 afforded a simple mixture of 2f and
Ti(OC6F5)[{(O-2,4-tBu2C6H2)-6-CH2}3N] (2) after the ligand
exchange (Scheme 6).26 These results thus suggest that a
careful design of both titanatranes and Al reagents should be
required for the efficient synthesis of Ti−Al heterobimetallic
complexes.
temperature (runs 29−31). These results thus suggest that, as
assumed in the previous report in [TiMe{(μ2-O-2,4-R2C6H2-6-
CH2)(O-2,4-R2C6H2-6-CH2)2N}][R′2Al(μ2-OiPr)],15e the bi-
metallic complexes, first formed in the reaction mixture
containing the precursors of 1b in the presence of MAO and
a small amount of AlMe3, play a role in this catalysis. We
assume that a decrease in the activity by 3b at 120 °C would be
probably due to a stability of the catalytically active species
under these conditions.
The activities by the 2,6-F2C6H3 analogue (3d) were higher
than that by 1d under the similar conditions: moderate activity
was observed at 80 °C, and the activity decreased at 120 °C, as
observed in the polymerization by 3b. Moreover, the activities
by the C6F5 analogue (3e) were higher than that by 1e under
similar conditions, although the activity by 3e was highly
affected by MAO concentration conditions employed (runs 46,
48, 49). The resultant polymers possessed high molecular
weights with unimodal molecular weight distributions, and
significant differences in Mw values were observed between the
resultant polymers prepared by 1d,1e and 3d,3e. These results
also suggest that, as proposed previously,15b,e the bimetallic
complexes, first formed in the reaction mixture containing the
precursors of 1d,1e in the presence of MAO and a small
amount of AlMe3, play a role in these catalyses.
Ethylene Polymerization by TiMe(O-2,6-iPr2C6H3)[(μ2-
O-2,4-Me2C6H2-6-CH2)(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)-
(O-2,4-Me2C6H2-6-CH2) N] (3b) and TiMe[(μ2-O-2,4-
Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)2N][Me2Al(μ2-
OAr)] [Ar = 2,6-F2C6H3 (3d), C6F5 (3e)] in the Presence of
MAO. Ethylene polymerization by the isolated heterobimetallic
Ti−Al complexes, TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-
6-CH2)(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-
CH2)N] (3b) and [TiMe{(O-2,4-Me2C6H2-6-CH2)2(μ2-O-2,4-
Me2C6H2-6-CH2)}N][Me2Al(μ2-OAr)] [Ar = 2,6-F2C6H3
(3d), C6F5 (3e)], was conducted in n-octane for 1 h in the
presence of MAO. The results are summarized in Table 3.
The catalytic activities by 3b at 100 °C were slightly higher
than those by 1b in the presence of MAO/AlMe3 under the
similar conditions (runs 4, 7 vs runs 30, 33). The relatively high
catalytic activity was observed even at 80 °C (run 29). The
resultant polymers prepared by 1b and 3b (at 100 °C)
possessed high molecular weights with unimodal molecular
weight distributions, and no significant differences in the Mw
values were observed. The Mw values decreased at high
As described above, Ti−O(1) and Ti−O(2) bond distances
in 3b,3d,3e [2.0533(19)−2.2137(17) Å] are relatively longer
G
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Scheme 7
than those in [TiMe{(μ2-O-2,4-R2C6H2-6-CH2)(O-2,4-
R2C6H2-6-CH2)2N}][Me2Al(μ2-OiPr)] [2.071(13), 2.072(11)
Å in R = Me; 2.0673(19), 2.095(2) Å in R = Bu], reported
the activity upon addition of a small amount of AlMe3, with 1.0
equiv of AlMe3 afforded the corresponding heterobimetallic
Ti−Al complexes, TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-
6-CH2)(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-
CH2)N] (3b) and TiMe[(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-
Me2C6H2-6-CH2)2N][Me2Al(μ2-OAr)] [Ar = 2,6-F2C6H3 (3d),
C6F5 (3e)], in moderate yields. In contrast, TiMe[{(O-2,4-
Me2C6H2)-6-CH2}3N] (4) and [Al(μ2-O-2,6-Me2C6H3)Me2]2
(5) were isolated from the reaction mixture of 1a (showed a
decrease in the activity upon addition of AlMe3) with AlMe3
conducted under the same conditions: the reactions of 1c,
2d,2e afforded complex mixtures except an isolation of [Al(μ2-
OC6F5)Me2]2. The isolated heterobimetallic complexes
(3b,3d,3e) exhibited high catalytic activities for ethylene
polymerization in the presence of MAO, suggesting that the
present bimetallic species play a role in this catalysis (Scheme
7). However, unfortunately, these heterobimetallic complexes
(3b,3d,3e) showed negligible catalytic activities for ethylene
polymerization in the absence of MAO, because these
complexes decomposed gradually in n-octane at 100 °C.
These observations thus clearly suggest that MAO would play a
role for stabilization of the catalytically active species in this
catalysis.
t
previously.15e We expected that longer (rather weak) Ti−O
bond distances would be more suited in terms of generation of
the assumed catalytically active species,15e generated by
dissociation of two Ti−O bonds bridged to the Al atom.
However, these complexes (3b,3d,3e) showed negligible
catalytic activities (trace amount of polymers) in the absence
of MAO at 100 °C (Table 3): the activities were negligible at
80 and 120 °C. To understand why 3d,3e showed negligible
activities, we examined their thermal stabilities in n-octane at
100 °C (under polymerization conditions). Although pre-
viously isolated Ti−Al [TiMe{(μ2-O-2,4-R2C6H2-6-CH2)(O-
2,4-R2C6H2-6-CH2)2N}][Me2Al(μ2-OiPr)] (R = Me, tBu) were
thermally stable in toluene-d8 at various temperatures,15e we
observed that 3d,3e decomposed gradually at 100 °C in n-
octane even after 30 min (monitored by both 1H and 19F NMR
spectra).27 These results clearly indicate that MAO helps
stabilize the catalytically active species derived from 3d,3e
during the ethylene polymerization process.
CONCLUDING REMARKS
■
Taking into account these results, it becomes clear that we
have to consider steric bulk of both bridged ligands (ligand
substituent in the atrane ligand and/or terminal ligand) for
designing efficient catalysts for the desired purpose (to exhibit
activity without cocatalyst). We highly believe that these facts
should be potentially important for designing more efficient
catalysts in precise olefin polymerization, especially catalysts
A series of titanatranes containing a tris(phenoxy)amine ligand
of the type, Ti(OAr)[{(O-2,4-R2C6H2)-6-CH2}3N] [R = Me
t
(1), Bu (2); Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b), 2,6-
Ph2C6H3 (c), 2,6-F2C6H3 (d), C6F5 (e)] (1a−1e, 2d,2e), have
been employed as the catalyst precursors for ethylene
polymerization in the presence of methylaluminoxane
(MAO). Reactions of 1b,1d,1e, which showed increases in
H
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140.6 (aromatic carbon resonances). Anal. Calcd for C45H43NO4Ti: C,
76.16; H, 6.11; N, 1.97. Found: C, 75.83; H, 6.03; N, 2.19.
without the presence of excess Al cocatalysts, and we are now
preparing various titanatranes: these results will be introduced
in the future as our subsequent contribution.
Synthesis of Ti(O-2,6-F2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N]
(1d). The procedure for the synthesis of 1d was conducted by the
similar procedure for 1a, except that 2,6-F2C6H3OH was used in place
1
EXPERIMENTAL SECTION
of 2,6-Me2C6H3OH. Yield: 0.897 g (75.6%). H NMR (CDCl3): δ
■
2.13 (s, 9H, Ar-CH3), 2.26 (s, 9H, Ar-CH3), 2.44 and 3.89 (br.s, 6H,
NCH2), 6.34 (m, 1H, terminal Ar-H), 6.42 (br.s, 3H, Ar-H), 6.77 (m,
2H, terminal Ar-H), 7.00 (br.s, 3H, Ar-H). 13C NMR (CDCl3): δ 15.7
(Ar-CH3), 20.7 (Ar-CH3), 58.8 (NCH2), 123.3, 124.4, 127.3, 130.5,
131.0, 160.1 (aromatic carbon resonances). 19F NMR (CDCl3): δ
−130.5 (br. s). Anal. Calcd for C33H33F2NO4Ti·CH2Cl2: C, 60.19; H,
5.20; N, 2.06. Found: C, 59.83; H, 4.84; N, 2.03.
General Procedures. All experimental procedures were carried
out under an atmosphere of dry nitrogen using standard Schlenk
techniques or using a Vacuum Atmospheres drybox unless otherwise
specified. All chemicals used were of reagent grade and were purified
by standard purification procedures. Toluene (anhydrous grade, Kanto
Kagaku Co., Ltd.) for polymerization was stored in a bottle in the
drybox in the presence of molecular sieves (a mixture of 3A 1/16, 4A
1/8, and 13X 1/16). Polymerization grade ethylene (purity > 99.9%,
Sumitomo Seika Co. Ltd.) was used as received. Toluene and AlMe3
from commercially available methylaluminoxane [PMAO-S, 9.5 wt %
(Al) toluene solution, Tosoh Finechem Co.] were removed under
reduced pressure (at ca. 50 °C for removing toluene and AlMe3 and
then heated at >100 °C for 1 h for completion) in the drybox to give
white solids. Tris(2-hydroxy-3,5-dimethylbenzyl)amine and tris(2-
hydroxy-3,5-di-tert-butylbenzyl)amine were prepared according to a
published procedure.28 Ti(O-2,6-iPr2C6H3)[{(O-2,4-Me2C6H2)-6-
CH2}3N] (1b) was prepared according to a published method.18
Molecular weights and molecular weight distributions for poly-
ethylene were measured by gel permeation chromatography (Tosoh
HLC-8121GPC/HT) with a polystyrene gel column (TSK gel
GMHHR-H HT × 2, 30 cm ×m7.8 mmφ, ranging from <102 to
<2.8 × 108 MW) at 140 °C using o-dichlorobenzene containing 0.05
w/v % 2,6-di-tert-butyl-p-cresol as eluent. The molecular weight was
calculated by a standard procedure based on the calibration with
standard polystyrene samples.
Synthesis of Ti(OC6F5)[{(O-2,4-Me2C6H2)-6-CH2}3N] (1e). The
procedure for the synthesis of 1e was conducted by the similar
procedure for 1a, except that C6F5OH was used in place of 2,6-
Me2C6H3OH. Yield: 1.210 g (93.4%). 1H NMR (C6D6): δ 2.12 (s, 9H,
Ar-CH3), 2.20 (s, 9H, Ar-CH3), 2.42 amd 3.82 (br.s, 6H, NCH2), 6.41
(br.s, 3H, Ar-H), 6.68 (br.s, 3H, Ar-H). 13C NMR (CDCl3): δ 15.7
(Ar-CH3), 20.7 (Ar-CH3), 58.8 (NCH2), 123.2, 124.2, 127.4, 131.0,
131.2, 160.1 (aromatic carbon resonances). 19F NMR (C6D6): δ
−171.7 (br. t, para-F), −166.8 (br. d, meta-F), −160.7 (br. d, ortho-F).
Anal. Calcd for C33H30F5NO4Ti: C, 61.22; H, 4.67; N, 2.16. Found: C,
60.97; H, 4.67; N, 2.16.
Synthesis of Ti(O-2,6-F2C6H3)[{(O-2,4-tBu2C6H2)-6-CH2}3N]
(2d). The procedure for the synthesis of 2d was conducted by the
similar procedure for 1a, except that 2,6-F2C6H3OH and tris(2-
hydroxy-3,5-di-tert-butylbenzyl)amine were used in place of 2,6-
Me2C6H3OH and tris(2-hydroxy-3,5-dimethylbenzyl)amine. Yield:
1
1.131 g (66.8%). H NMR (C6D6): δ 1.33 (s, 27H, C(CH3)3), 1.59
(s, 27H, C(CH3)3), 2.68 (br.d, 3H, NCH2), 4.13 (br.d, 3H, NCH2),
6.40 (m, 1H, terminal Ar-H), 6.76 (m, 2H, terminal Ar-H), 6.80 (br.d,
3H, Ar-H), 7.43 (br.d, 3H, Ar-H). 13C NMR (CDCl3): δ 29.7
((CH3)3C), 31.8 ((CH3)3C), 34.6 ((CH3)3C), 35.0 ((CH3)3C), 59.1
(NCH2), 111.3, 118.1, 123.5, 124.0, 135.8, 143.5, 160.9 (aromatic
carbon resonances). 19F NMR (C6D6): δ −127.5 (br. s). Anal. Calcd
for C51H69F2NO4Ti·n-hexane: C, 73.45; H, 8.97; N, 1.50. Found: C,
72.83; H, 8.95; N, 1.68.
Elemental analyses were performed by using an EAI CE-440 CHN/
1
O/S elemental analyzer (Exeter Analytical, Inc.). All H, 13C, and 19F
NMR spectra were recorded on a Bruker AV500 spectrometer (500.13
1
MHz for H, 125.77 MHz for 13C). All spectra were obtained in the
solvent indicated at 25 °C unless otherwise noted. Chemical shifts are
given in parts per million and are referenced to SiMe4 (δ 0.00 ppm,
1H, 13C), CFCl3 (δ 0.00, 19F). Coupling constants are given in hertz.
Synthesis of Ti(OC6F5)[{(O-2,4-tBu2C6H2)-6-CH2}3N] (2e). The
procedure for the synthesis of 2e was conducted by the similar
procedure for 2d, except that C6F5OH was used in place of 2,6-
F2C6H3OH. Yield: 1.357 g (75.4%). 1H NMR (C6D6): δ 1.32 (s, 27H,
C(CH3)3), 1.52 (s, 27H, C(CH3)3), 2.64 (br.d, 3H, NCH2), 4.05
(br.d, 3H, NCH2), 6.78 (br.d, 3H, Ar-H), 7.41 (br.d, 3H, Ar-H). 13C
NMR (C6D6): δ 29.8 ((CH3)3C), 31.8 ((CH3)3C), 34.6 ((CH3)3C),
35.2 ((CH3)3C), 60.0 (NCH2), 123.9, 124.3, 136.1, 144.2, 161.4
(aromatic carbon resonances). 19F NMR (C6D6): δ −171.9 (br. t,
para-F), −167.1 (br. d, meta-F), −158.1 (br. d, ortho-F). Anal. Calcd
for C51H66F5NO4Ti·n-hexane: C, 69.43; H, 8.18; N, 1.42. Found: C,
69.40; H, 7.95; N, 1.56.
Synthesis of Ti(O-2,6-Me2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N]
(1a). Into a toluene solution (10 mL) containing 2,6-Me2C6H3OH
(0.244 g, 2.00 mmol) was added dropwise into a toluene solution (10
mL) containing Ti(OiPr)4 (0.568 g, 2.00 mmol) at room temperature.
After 1 h, a toluene solution (10 mL) containing tris(2-hydroxy-3,5-
dimethylbenzyl)amine (0.839 g, 2.00 mmol) was then added dropwise
into the above reaction mixture (containing titanium and phenol). The
reaction mixture was stirred at room temperature overnight, and then
the volatiles were evaporated under vacuum, leaving yellow solids. The
resultant solids were added to 20 mL of toluene, and the yellow
solution was filtered through a Celite pad. The filtrate was placed in
vacuo to give a yellow solid. The complex 1a was isolated as orange-
yellow crystals from the chilled CH2Cl2/n-hexane solution (−30 °C).
Yield: 0.723 g (62.1%). 1H NMR (C6D6): δ 2.15 (s, 9H, Ar-CH3), 2.19
(s, 9H, Ar-CH3), 2.47 (br.d, 2H, N-CH2), 2.80 (s, 6H, terminal Ar-
CH3), 3.94 (br.d, 2H, N-CH2), 6.45 (br.s, 3H, Ar-H), 6.73 (br.s, 3H,
Ar-H), 6.94 (t, 1H, J = 7.4 Hz, terminal Ar-H), 7.14 (d, 2H, J = 7.4 Hz,
terminal Ar-H). 13C NMR (CDCl3): δ 16.1 (Ar-CH3), 18.0 (terminal
Ar-CH3), 20.7 (Ar-CH3), 58.7 (N-CH2), 120.7, 123.4, 124.4, 127.2,
127.4, 127.7, 130.1, 131.0, 159.3, 165.5 (aromatic carbon resonances).
Anal. Calcd for C35H39NO4Ti: C, 71.79 (69.74 + Ti − C); H, 6.71; N,
2.39. Found: C, 69.82; H, 6.71; N, 2.50.
Synthesis of Ti(O-2,6-Ph2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N]
(1c). The procedure for the synthesis of 1c was conducted by the
similar procedure for 1a, except that 2,6-Ph2C6H3OH was used in
place of 2,6-Me2C6H3OH. Yield: 0.888 g (62.6%). 1H NMR (CDCl3):
δ 1.76 (s, 9H, Ar-CH3), 2.21 (s, 9H, Ar-CH3), 2.87 and 3.87 (br.s, 6H,
NCH2), 6.64 (br.s, 3H, Ar-H), 6.78 (br.s, 3H, aryl-H), 7.00 (t, 2H, J =
7.4 Hz, Ar-H), 7.04 (t, 1H, J = 7.6 Hz, Ar-H), 7.14 (t, 4H, J = 7.6 Hz,
Ar-H), 7.28 (d, 2H, J = 7.5 Hz, Ar-H), 7.80 (d, 4H, J = 7.2 Hz, Ar-H).
13C NMR (CDCl3): δ 15.9 (Ar-CH3), 20.7 (Ar-CH3), 58.6 (NCH2),
Synthesis of TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-6-CH2)-
(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)N] (3b).
Into a toluene solution (10 mL) containing Ti(O-2,6-iPr2C6H3)[{(O-
2,4-Me2C6H2)-6-CH2}3N] (0.642 g, 1.0 mmol) was added slowly
AlMe3 (1.0 mL, of 1.0 M n-hexane solution) at room temperature. The
reaction mixture was then stirred at room temperature for 2 h. The
volatiles were evaporated under vacuum, and to the resultant orange
solid was added 15 mL of toluene. The orange solution was then
filtered through a Celite pad. The filtrate was removed under vacuum
to obtain orange solids. The complex was isolated as orange
microcrystals from the hot toluene solution. Yield: 0.543 g (76.1%).
1H NMR (CDCl3, 25 °C): δ −1.35 (s, 3H, Al-CH3), −0.41 (s, 3H, Al-
CH3) 1.02 (br.s, 12H, CH(CH3)2), 1.43 (s, 3H, Ti−CH3) 1.98 (s, 3H,
Ar-CH3), 2.01 (s, 3H, Ar-CH3), 2.16 (s, 3H, Ar-CH3), 2.22 (s, 3H, Ar-
CH3), 2.37 (s, 3H, Ar-CH3), 2.45 (s, 3H, Ar-CH3), 2.81 (d, J = 13 Hz,
1H, N-CH), 3.20 (d, J = 13 Hz, 1H, N-CH), 3.31 (d, J = 13 Hz, 1H,
N-CH), 3.74 (br.s, 2H, CH(CH3)2), 3.91 (d, J = 13 Hz, 1H, N-CH),
4.18 (d, J = 13 Hz, 1H, N-CH), 4.30 (d, J = 13 Hz, 1H, N-CH), 6.22
(s, 1H, Ar-H), 6.50 (s, 1H, Ar-H), 6.55 (s, 1H, Ar-H), 6.62 (s, 1H, Ar-
H), 6.66 (s, 1H, Ar-H), 6.88 (s, 1H, Ar-H), 6.90 (t, J = 7 Hz, 1H,
120.8, 123.2, 124.3, 126.5, 127.0, 127.9, 129.8, 130.0, 130.8, 133.3,
I
dx.doi.org/10.1021/om3008635 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Crystal Data and Structure Refinement Parameters for Complexes, TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-6-
CH2)(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)N] (3b), [TiMe{(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-
6-CH2)2}N][Me2Al(μ2-O-2,6-F2C6H3)] (3d), and [TiMe{(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)2N}][Me2Al(μ2-
a
OC6F5)] (3e)
b
3b
3d
3e
empirical formula
C91H112Al2N2O8Ti2
1511.66
C36H42AlF2NO4Ti
665.61
C37H41AlCl2F5NO4Ti
804.51
fw
cryst color, habit
orange, needle
0.05 × 0.02 × 0.01
triclinic
orange, block
0.190 × 0.120 × 0.09
triclinic
orange, block
0.180 × 0.170 × 0.100
triclinic
cryst size (mm)
cryst syst
space group
P1 (No. 2)
̅
P1 (No. 2)
̅
P1 (No. 2)
̅
a (Å)
9.5175(7)
12.2092(10)
18.6971(17)
104.352(3)
97.765(2)
93.793(2)
2074.3(3)
1
10.0973(3)
11.9776(3)
15.2802(3)
68.0736(7)
78.2313(7)
83.2675(7)
1676.73(6)
2
11.6357(3)
11.9512(3)
15.3879(3)
109.5937(7)
99.5987(7)
106.3486(7)
1851.96(7)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
Dcalcd
μ (Mo Kα) cm−1
1.210
1.318
1.443
2.697
3.318
4.645
F000
806.00
700.00
832.00
2θ max (deg)
48.8
54.9
54.9
no. of deflns collected/unique
observed reflns [I > 2σ(I)]
GOF
15 548/6790 (Rint = 0.0104)
6790
16 760/7639 (Rint = 0.0194)
7639
18 599/8454 (Rint = 0.0173)
8454
1.032
1.058
1.092
R1, wR2 [I > 2σ(I)]
0.0742, 0.1812
0.0397, 0.1145
0.58/−0.30
0.0483, 0.1396
0.73/−0.61
largest diff peak/hole [e Å−3
]
0.36/−0.43
Detailed results are shown in the Supporting Information.23 The crystal contained CH2Cl2 in the formula (with certain ratio).
a
b
terminal Ar-H), 7.00 (br.d, 3H, Ar-H). 13C NMR (CDCl3, 25 °C): δ
14.3 (Al-CH3), 15.6 (Al-CH3), 17.1 (Ar-CH3), 18.7 (Ar-CH3), 20.4
(Ar-CH3), 20.5 (Ar-CH3), 20.7 (Ar-CH3), 26.0 ((CH3)2CH), 22.8
((CH3)2CH), 31.7 ((CH3)2CH), 60.2 (N-CH2), 64.0 (N-CH2), 64.5
(N-CH2), 65.61 (Ti-CH3), 122.4, 122.7, 123.4, 123.8, 125.7, 126.6,
128.2, 128.6, 129.1, 130.3, 130.7, 130.9, 131.2, 131.4, 132.1, 151.6,
158.2, 161.2 (aromatic carbon resonances). Anal. Calcd for
C42H56AlNO4Ti: C, 70.68; H, 7.91; N, 1.96. Found: C, 70.22; H,
8.36; N, 1.96.
3H, Al-CH3), 1.93 (s, 3H, Ar-CH3), 1.98 (s, 3H, Ar-CH3), 2.00 (s, 3H,
Ar-CH3), 2.15 (s, 6H, Ar-CH3), 2.19 (s, 3H, Ar-CH3), 2.43 (s, 3H, Ti-
CH3), 2.72 (d, J = 13 Hz, 1H, N-CH), 2.93 (d, J = 13 Hz, 1H, N-CH),
3.09 (d, J = 13 Hz, 1H, N-CH), 3.66 (d, J = 13 Hz, 1H, N-CH), 4.05
(d, J = 13 Hz, 1H, N-CH), 4.27 (d, J = 13 Hz, 1H, N-CH), 6.13 (s,
1H, Ar-H), 6.46 (s, 1H, Ar-H), 6.49 (s, 1H, Ar-H), 6.62 (s, 1H, Ar-H),
6.71 (s, 1H, Ar-H), 6.75 (s, 1H, Ar-H). 13C NMR (CDCl3): δ 15.77
(Al-CH3), 15.80 (Al-CH3), 17.07 (Ar-CH3), 20.36 (Ar-CH3), 20.66
(Ar-CH3), 20.69 (Ar-CH3), 60.64 (N-CH), 61.98 (N-CH), 62.96 (N-
CH), 67.56 (Ti-CH3), 124.09, 124.54, 124.61, 125.80, 126.72, 126.80,
127.18, 127.65, 129.53, 130.14, 130.30, 130.38, 130,79, 131.56, 132.32,
150.03, 158.09, 159.38 (aromatic carbon resonances). 19F-NMR
(CDCl3): δ −151.40 (br. d, ortho-F), −164.29 (br. t, meta-F),
−164.70 (br. t, para-F). Anal. Calcd for C36H39AlF5NO4Ti·CH2Cl2: C,
55.24; H, 5.14; N, 1.74. Found: C, 55.22; H, 5.05; N, 1.89.
Synthesis of [TiMe{(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-
Me2C6H2-6-CH2)2}N][Me2Al(μ2-O-2,6-F2C6H3)] (3d). The procedure
for the synthesis of 3d was conducted by the similar procedure for 3b,
except that Ti(O-2,6-F2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N] was
used in place of Ti(O-2,6-iPr2C6H3){(O-2,4-Me2C6H2-6-CH2)3N}.
1
Yield: 0.377 g (50.6%). H NMR (CDCl3): δ −0.82 (s, 3H, Al-CH3),
−0.56 (s, 3H, Al-CH3), 1.94 (s, 3H, Ar-CH3), 1.98 (s, 3H, Ar-CH3),
2.01 (s, 3H, Ar-CH3), 2.14 (s, 6H, Ar-CH3), 2.16 (s, 3H, Ar-CH3),
2.44 (s, 3H, Ti-CH3), 2.71 (d, J = 13 Hz, 1H, N-CH), 2.92 (d, J = 13
Hz, 1H, N-CH), 3.03 (d, J = 13 Hz, 1H, N-CH), 3.66 (d, J = 13 Hz,
1H, N-CH), 4.10 (d, J = 13 Hz, 1H, N-CH), 4.41 (d, J = 13 Hz, 1H,
N-CH), 6.14 (s, 1H, Ar-H), 6.44 (s, 1H, Ar-H), 6.48 (s, 1H, Ar-H),
6.60 (s, 1H, Ar-H), 6.69 (s, 2H, Ar-H), 6.79 (br.d, 2H, terminal Ar-H),
6.99 (m, 1H, terminal Ar-H). 13C NMR (CDCl3): δ 15.85 (Al-CH3),
15.92 (Al-CH3), 17.14 (Ar-CH3), 20.38 (Ar-CH3), 20.70 (Ar-CH3),
60.61 (N-CH), 62.04 (N-CH), 62.94 (N-CH), 67.28 (Ti-CH3),
111.98, 112.40, 122.00, 124.24, 126.72, 127.56, 129.59, 130.13, 130.41,
131.39, 131.96, 150.30, 158.49, 159.26 (aromatic carbon resonances).
19F NMR (CDCl3): δ −122.17 (br. s). Anal. Calcd for
Reaction of Ti(O-2,6-Me2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N]
(1a) with AlMe3. Into a cold toluene solution (20 mL) containing
1a (0.293 g, 0.50 mmol) chilled at −30 °C was added slowly a cold
toluene solution containing AlMe3 (1.05 M n-hexane solution, 0.50
mmol). The reaction mixture was then warmed to room temperature
with stirring, which was continued for 1 h. The volatiles were
evaporated under vacuum, and to the resultant orange-brown oil was
added 15 mL of toluene. The solution was then filtered through a
Celite pad. The filtrate was removed under vacuum to obtain an
orange sticky solid; the solid was then dissolved in n-hexane and
placed in the freezer chilled at −30 °C (for ca. 1 month). A mixture of
white and orange microcrystals were obtained, and the mixture was
dissolved with cold toluene for separation (extracted with cold
toluene). The white microcrystals were then isolated after removing
toluene and recrystallized from a minimum amount of n-hexane (at
−30 °C). The white microcrystals were identified as [Al(μ2-O-2,6-
Me2C6H3)Me2]2 (5) determined by X-ray crystallography.24 Yield:
0.068 g (38.2%). 1H NMR (C6D6, 25 °C): δ −0.41 (s, 12H, Al-CH3),
2.40 (s, 12H, Ar-CH3), 6.80 (t, 2H, Ar-H), 6.86 (d, 4H, Ar-H). The
orange brown solid, which was insoluble with cold toluene in the
mixture of crystals, was dissolved in a minimum amount of CH2Cl2
C36H42AlF2NO4Ti: C, 64.96; H, 6.36; N, 2.10. Found: C, 63.93; H,
6.57; N, 2.09.
[TiMe{(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2)2N}]-
[Me2Al(μ2-O-C6F5)] (3e). The procedure for the synthesis of 3e was
conducted by the similar procedure for 3b, except that Ti(OC6F5)-
[{(O-2,4-Me2C6H2)-6-CH2}3N] was used in place of Ti(O-
2,6-iPr2C6H3)[{(O-2,4-Me2C6H2)-6-CH2}3N]. Yield: 0.534 g
(74.2%). 1H NMR (CDCl3): δ −0.81 (s, 3H, Al-CH3), −0.56 (s,
J
dx.doi.org/10.1021/om3008635 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and layered with n-hexane. Careful repetitive recrystallization from the
chilled CH2Cl2/n-hexane eventually afforded pure orange micro-
crystals of TiMe[{(O-2,4-Me2C6H2)-6-CH2}3N] (4) only determined
by X-ray crystallography.
polymer was collected on a filter paper by filtration and was adequately
washed with MeOH and then dried under vacuum.
ASSOCIATED CONTENT
■
Reaction of Ti(OC6F5)[{(O-2,4-tBu2C6H2)-6-CH2}3N] (2e) with
AlMe3. Into a cold toluene solution (20 mL) containing 2e (0.423 g,
0.50 mmol) chilled at −30 °C was added slowly a cold toluene
solution containing AlMe3 (1.05 M n-hexane solution, 0.50 mmol).
The reaction mixture was then warmed to room temperature with
stirring, which was continued for 2 h. The volatiles were evaporated
under vacuum, and to the resultant yellow oil was added 15 mL of
toluene. The solution was then filtered through Celite pad. The filtrate
was removed under vacuum; the oil was then dissolved in n-hexane
and placed in the freezer chilled at −30 °C. White microcrystals
determined as [Al(μ2-OC6F5)Me2]2 (6) by X-ray crystallographic
analysis24 were collected from the chilled solution (after ca. 2 weeks).
Yield: 0.051 g (42.2%). 1H NMR (C6D6, 25 °C): δ −0.56 (s, 12H, Al-
CH3). 19F NMR (C6D6, 25 °C): δ −154.4 (br. d, ortho-F), −161.0 (br.
t, meta-F), −162.5 (br., t, para-F).
S
* Supporting Information
1H NMR spectra for monitoring the reaction of Ti(OiPr)3(O-
2,6-iPr2C6H3) with [{(HO-2,4-tBu2C6H2)-6-CH2}3N]; H and
1
19F NMR spectra for the reaction mixture of Ti(OiPr)[{(O-
2,4-tBu2C6H2)-6-CH2}3N] (2f) with [Al(μ2-OC6F5)Me2]2 (6)
in CDCl3; 1H and 19F NMR spectra after heating of
[TiMe{(μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-
CH2)2N}][Me2Al(μ2-OAr)] [Ar = 2,6-F2C6H3 (3d), C6F5
(3e)] in n-octane at 100 °C; and a table summarizing crystal
data and structure refinement parameters, including structure
reports and CIF files, for TiMe[{(O-2,4-Me2C6H2)-6-CH2}3N]
(4), [Al(μ2-O-2,6-Me2C6H3)Me2]2 (5), and [Al(μ2-OC6F5)-
Me2]2 (6) and structure reports, including CIF files, for
TiMe(O-2,6-iPr2C6H3)[(μ2-O-2,4-Me2C6H2-6-CH2)(Me2Al-
μ2-O-2,4-Me2C6H2-6-CH2)(O-2,4-Me2C6H2-6-CH2) N] (3b)
and 3d,3e. This material is available free of charge via the
Internet at http://pubs.acs.org.
Reaction of Ti(O-2,6-F2C6H3){(O-2,4-tBu2C6H2-6-CH2)3N} (2d)
with AlMe3 was conducted according to the analogous procedure for
2f. White microcrystals assumed as [Al(μ2-O-2,6-F2C6H3)Me2]2 by
NMR spectra were collected from the chilled solution. Yield: 0.045 g
(48.0%). 1H NMR (C6D6, 25 °C): δ −0.16 (s, 12H, Al-CH3), 6.16 (t,
2H, Ar-H), 6.37 (d, 4H, Ar-H). 19F NMR (C6D6, 25 °C): δ −126.0
(br. s).
AUTHOR INFORMATION
Corresponding Author
*Tel/Fax: +81-42-677-2547. E-mail: ktnomura@tmu.ac.jp.
■
Reaction of Ti(OiPr)[{(O-2,4-tBu2C6H2)-6-CH2}3N] (2f) with
Me2AlCl. A cold toluene solution (10 mL) containing Me2AlCl
(1.08 M in n-hexane, 0.50 mmol) chilled at −20 °C was added
dropwise into a cold toluene solution (10 mL, chilled at −20 °C)
containing Ti(OiPr)[(O-2,6-tBu2-C6H3)3N] (2f, 0.388 g, 0.50 mmol)
at room temperature. The reaction mixture was then stirred at room
temperature for 2 h. The volatiles were evaporated in vacuo, and to the
resultant orange solid was added 15 mL of toluene. The orange
solution was then filtered through a Celite pad. The filtrate was
removed under vacuum to obtain orange solids. The complex was
isolated as orange microcrystals from CH2Cl2/n-hexane solution.
Yield: 0.208 g (63.8%). 1H NMR (C6D6): δ 1.32 (s, 27H, CH(CH3)3),
1.66 (s, 27H, CH(CH3)3), 2.55 (d, J = 13.8 Hz, 3H, N-CH), 3.95 (d, J
= 13.8 Hz, 3H, N-CH), 6.76 (d, J = 2.35 Hz, 3H, Ar-H), 7.43 (d, J =
2.35 Hz, 3H, Ar-H). The spectral data were highly analogous to those
reported previously.25 Anal. Calcd for C45H66ClNO3Ti·n-hexane: C,
73.05; H, 9.62; N, 1.67. Found: C, 73.61; H, 9.56; N, 1.73. The
microcrystals were then dissolved in benzene and placed in vacuum to
give another solid containing benzene. Anal. Calcd for
C45H66ClNO3Ti·1.5C6H6: C, 74.59; H, 8.69; N, 1.61. Found: C,
74.62; H, 8.66; N, 1.63.
Crystallographic Analysis. All measurements were made on a
Rigaku RAXIS-RAPID imaging plate diffractometer with graphite-
monochromated Mo Kα radiation. All structures were solved by direct
methods29 and expanded using Fourier techniques, and the non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included, but not refined. All calculations were performed using the
CrystalStructure30 crystallographic software package except for
refinement, which was performed using SHELXL-97.31 Table 4
summarizes selected crystal collection parameters, and the detailed
structure reports, including their CIF files, are shown in the
Supporting Information.23
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The present research is partly supported by a Grant-in-Aid for
Scientific Research (B) from the Japan Society for the
Promotion of Science (JSPS, Nos. 21350054, 24350049), and
P.M.G. is grateful to the Japan Society for the Promotion of
Science (JSPS) for a postdoctoral fellowship (No. P08039). We
express their thanks to Tosoh Finechem Co. for donating MAO
(PMAO-S).
REFERENCES
■
(1) Selected reviews/accounts in the 1990s; see: (a) Britovsek, G. J.
P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428.
(b) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.
(c) Suhm, J.; Heinemann, J.; Worner, C.; Muller, P.; Stricker, F.;
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1
(26) H and 19F NMR spectra for the mixture in the reaction of
Ti(OiPr)[{(O-2,4-tBu2C6H2)-6-CH2}3N] (2f) with [Al(μ2-OC6F5)
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1
(27) H and 19F NMR spectra after heating of [TiMe{(μ2-O-2,4-
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= 2,6-F2C6H3 (3d), C6F5 (3e)] in n-octane at 100 °C for 30 min are
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dx.doi.org/10.1021/om3008635 | Organometallics XXXX, XXX, XXX−XXX