High temperature ethylene polymerization catalyzed by titanium(iv) complexes with tetradentate aminophenolate ligands in cis-O, N, N chelating mode

Article abstract of DOI:10.1039/c4dt01122h

A series of titanium trichloride complexes 1a-4a, 7a-10a ligated with claw-type tetradentate aminophenolate ligands were synthesized from the direct reaction of TiCl₄(THF)₂ with 1 equiv. of the corresponding aminophenol in the presence of triethylamine. For comparison purposes, titanium isopropoxide complexes 5e-8e were also synthesized via the reaction of Ti(OⁱPr)₄ and 1 equiv. of the proligand. Similar reactions of ZrCl₄(THF)₂ with the corresponding aminophenol ligands in the presence of triethylamine only allowed the isolation of zirconium complex 8b. The X-ray diffraction studies reveal that titanium trichloride complexes 2a, 9a and titanium triisopropoxide complex 5e all possess a distorted octahedral geometry with the tetradentate aminophenolate ligand in cis-O, N, N chelating mode, where the methoxy group of the aryl unit does not coordinate with the metal center in the solid state. Upon activation with MMAO, these titanium and zirconium(iv) complexes exhibited moderate to high catalytic activities for ethylene polymerization at 30-120 °C, producing high-molecular-weight polyethylenes with broad distributions (M _w/M_n = 10.2-34.8). The activities of titanium trichloride complexes are significantly higher than those of titanium isopropoxide and zirconium trichloride complexes at high temperatures. The highest activity of 15 456 kg (mol-Ti h)^-1 could be achieved by titanium trichloride complex 8a with bromo groups on both ortho- and para-positions of the phenolate ring of the ligand at 120 °C. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt01122h

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High temperature ethylene polymerization
catalyzed by titanium(IV) complexes with
tetradentate aminophenolate ligands in
cis-O, N, N chelating mode†
Cite this: Dalton Trans., 2014, 43,
12663
Ruiguo Zhao, Taotao Liu, Liying Wang and Haiyan Ma*
A series of titanium trichloride complexes 1a–4a, 7a–10a ligated with claw-type tetradentate amino-
phenolate ligands were synthesized from the direct reaction of TiCl4(THF)2 with 1 equiv. of the corres-
ponding aminophenol in the presence of triethylamine. For comparison purposes, titanium isopropoxide
complexes 5e–8e were also synthesized via the reaction of Ti(OiPr)4 and 1 equiv. of the proligand. Similar
reactions of ZrCl4(THF)2 with the corresponding aminophenol ligands in the presence of triethylamine
only allowed the isolation of zirconium complex 8b. The X-ray diffraction studies reveal that titanium tri-
chloride complexes 2a, 9a and titanium triisopropoxide complex 5e all possess a distorted octahedral
geometry with the tetradentate aminophenolate ligand in cis-O, N, N chelating mode, where the
methoxy group of the aryl unit does not coordinate with the metal center in the solid state. Upon acti-
vation with MMAO, these titanium and zirconium(IV) complexes exhibited moderate to high catalytic
activities for ethylene polymerization at 30–120 °C, producing high-molecular-weight polyethylenes with
broad distributions (Mw/Mn = 10.2–34.8). The activities of titanium trichloride complexes are significantly
higher than those of titanium isopropoxide and zirconium trichloride complexes at high temperatures.
The highest activity of 15 456 kg (mol-Ti h)−1 could be achieved by titanium trichloride complex 8a with
bromo groups on both ortho- and para-positions of the phenolate ring of the ligand at 120 °C.
Received 16th April 2014,
Accepted 28th May 2014
DOI: 10.1039/c4dt01122h
www.rsc.org/dalton
able attention and became another hotspot in the field of
olefin polymerization. For group 4 non-metallocene catalysts
Introduction
Since the discovery of metallocene–MAO catalytic systems for in particular,47–62 upon activation with a suitable cocatalyst,
olefin polymerization, great achievements have been made in their performance in catalytic olefin polymerization can meet
the fields of syntheses and catalytic applications of well- and even exceed those of metallocene catalysts in many
defined metallocene complexes.1–16 But when people found aspects. For example, the phenoxy-imine and pyrrolide-imine
that non-metallocene complexes of a variety of metals, includ- group 4 complexes developed by Fujita and co-workers, namely
ing early,17–24 middle25–30 and late transition metals31–42 as FI and PI catalysts,63–78 when activated with MAO (methylalumi-
well as rare earth metals,43–46 could also act as efficient cata- noxane) or MMAO (modified-methylaluminoxane), exhibited
lysts for olefin polymerization and moreover they were readily unprecedented activities for olefin polymerization. Furthermore,
accessible in comparison to metallocene complexes, the study they can be used to precisely control polymer microstructures,
on developing non-metallocene catalysts attracted consider- achieve living polymerization of ethylene and propylene, gene-
rate highly isotactic and syndiotactic polypropylenes, and will-
fully produce polyolefins of low molecular weight to millions of
ultra-high molecular weight. Besides all the attractive properties
displayed by non-metallocene catalysts, one noticeable draw-
back is that non-metallocene complexes are generally less stable
Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of
Organometallic Chemistry, East China University of Science and Technology,
Shanghai 200237, P. R. China. E-mail: haiyanma@ecust.edu.cn;
Fax: +86 21 64253519
at high reaction temperatures which are however required by
industrial polymerization processes.12 This drawback to a great
extent limits potential industrial applications of the vast
majority of non-metallocene complexes.
So far, some thermally stable non-metallocene complexes
for olefin polymerization have been obtained through the utili-
†Electronic supplementary information (ESI) available: Figures, tables, and CIF
files, giving NMR spectra of complexes 1c, 1a–4a, 6a–10a, 8b and 5e–8e, 1H NMR
spectrum of typical polymer obtained by 8a–MMAO (entry 17), variable-tempera-
ture 1H NMR spectra of 2a and 5e in toluene-d8, X-ray crystallographic data for
complexes 2a, 9a, 8b and 5e. CCDC 968903 (2a), 968904 (9a), 991086 (5e) and
968905 (8b). For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c4dt01122h
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zation of ligands with multiple donor groups. For instance, ence of multiple donor groups within the ligand framework
Janiak and co-workers79 reported that β-diketonato zirconium may play an essential role in stabilizing the active center, thus
complexes bearing two different substituents on the α-position leading to great enhancement of thermal stability and catalytic
showed high catalytic activities for ethylene polymerization at activity at high temperature. Inspired by these results, we are
70 °C, which could meet and even exceed that of Cp2ZrCl2 interested to obtain titanium and zirconium complexes sup-
under the same conditions. Fujita’s group80 reported that, ported with uninegative multidentate aminophenolate ligands.
upon activation with MAO, a FI-type catalyst, [3-tBu-2-(O)- In this work, a straightforward and efficient synthetic strategy
C6H3CHvNPh]2TiCl2, was highly active in catalyzing ethylene to prepare titanium, zirconium trichloride complexes and tita-
polymerization (47 800 kg PE (mol-Ti h)−1) at 75 °C with nium isopropoxide complexes, ligated with tetradentate
n-heptane as the solvent. Sun and coworkers81 reported a ONNO−-type aminophenolate ligands, was reported. The ethyl-
series of bis(6-benzimidazolylpyridine-2-carboxylimidate) tita- ene polymerization reactions of the synthesized titanium and
nium complexes bearing different substituents on the N-imino zirconium complexes with various substituents on the phenol-
moiety which were capable of catalyzing the living polymeri- ate ring and the pendant group were studied. In the presence
zation of ethylene and exhibited high catalytic activities at of MMAO, titanium trichloride complexes showed moderate to
80 °C in the presence of MAO (5040–9720 kg PE (mol-Ti h)−1). high activities in catalyzing ethylene polymerization even at
There are only a few examples of group 4 non-metallocene cat- high temperatures of 100–160 °C.
alysts that are thermal stable and active at temperatures close
to or higher than 100 °C. In 2009, Chan and co-workers82
reported some titanium complexes supported by pyridine-
2-phenolate-6-(σ-aryl) ancillary ligands which displayed excel-
Results and discussion
Synthesis and characterization of titanium and zirconium
lent ethylene polymerization activities up to 22 000 kg PE (mol-
Ti h)−1 at 100 °C with borate as cocatalyst. Tang’s group83 deve-
complexes
loped a series of tridentate titanium complexes [O−N(H)X]TiCl3
The claw-type aminophenol proligands L1–7H and L9–11H were
(X = S or P), which exhibited good thermal stability and high synthesized according to the reported method as illustrated in
activities toward ethylene polymerization at 110 °C, and the Scheme 1:85,86 the condensation reaction of N,N-dimethyl-1,2-
highest activity of 5400 kg PE (mol-Ti h atm)−1 was achieved.
ethanediamine with the benzaldehyde derivative in refluxing
Very recently, our group84 reported a series of novel eight-co- ethanol yielded the corresponding Schiff-base compounds,
ordinate zirconium dichloride complexes bearing two pyridyli- which were sequentially reduced to amines with excess NaBH4;
mino phenolate ligands which possessed excellent thermal
without further purification, the resultant secondary amines
stability and long lifetime. Upon activation with MMAO, these were subjected to Mannich reactions with substituted phenols
complexes displayed high activities up to 1040 kg PE (mol- to afford the target proligands. Analytically pure aminophenol
Zr h)−1 at 140 °C in o-xylene toward ethylene polymerization,
proligands were obtained through column chromatography as
and a lifetime of nearly 5 h at 140 °C could be obtained colorless to light yellow oily substances or white powders in
together with a satisfactory activity of 420 kg PE (mol-Zr h)−1
From the above exciting reports, it is deduced that the exist-
.
moderate yields. A similar route was adopted to synthesize the
proligand L8H, but no target product could be isolated. Alter-
Scheme 1 Synthesis and structures of the proligands L1–11H.
12664 | Dalton Trans., 2014, 43, 12663–12677
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Scheme 2 Synthesis of titanium and zirconium complexes.
natively, the resultant secondary amine was reacted with vide post), probably formed by a partially hydrolysis reaction of
6-bromomethyl-2,4-dibromophenol to give readily the desired 8a with a trace amount of water contained in the solvent.92
product in high yield (Scheme 1).87–89
Because of the unsuccessful preparation or purification of
The first attempt to synthesize the target titanium trichlo- titanium trichloride complexes 5a, 6a, titanium isopropoxide
ride complex 1a was performed by reacting the neutral pro- complexes 5e–8e bearing halogen substituted aminophenolate
ligand L1H with TiCl4 in 1 : 1 molar ratio in toluene.90 After a ligands were synthesized via the reaction of the neutral pro-
normal work-up procedure, a pale orange powder and a red ligands L5–8
H with 1
equiv. of Ti(OiPr)4 in toluene
powder were isolated sequentially. The former is likely a tita- (Scheme 3).93 In comparison with the corresponding trichlo-
nium hydrochloride adduct (L1H)TiCl4·HCl (1c), as character- ride complexes, all the titanium isopropoxide complexes could
ized by the existence of two “active hydrogens” at 10.75 and be easily purified and isolated in moderate yields as colorless
10.22 ppm in its 1H NMR spectrum (see ESI†).81,84 The latter is crystals, since they are fairly soluble in hexane.
the target titanium complex 1a but contaminated with a small
The strategy of adding excess triethylamine to trap hydro-
amount of 1c, which however could not be further purified via gen chloride was further used in the synthesis of the corres-
repetitive recrystallization procedures. In view of the formation ponding zirconium trichloride complexes. Proligands L1H,
of 1c, the reaction of TiCl4(THF)2 with 1 equiv. of the neutral L2H and L7–10H were treated with 1 equiv. of ZrCl4(THF)2 in
proligand L1H in the presence of excess triethylamine was the presence of excess triethylamine in THF. However, from
carried out, which finally enabled the isolation of analytically the reaction mixtures, only complex 8b was successfully iso-
pure 1a, shown in Scheme 2.91
lated via recrystallization with a mixture of toluene and THF.
The other reactions generated unidentifiable substances
Similar reactions of the neutral proligands L2–4H, L7–10
H
with 1 equiv. of TiCl4(THF)2 in the presence of excess triethyl- and no target zirconium complex could be detected
amine in THF readily afforded the target titanium trichloride spectroscopically.
complexes 2a–4a, 7a–10a as red to deep red crystalline solids
The stoichiometric structures of all the synthesized tita-
in moderate to high yields (Scheme 2). The corresponding tita- nium and zirconium complexes were confirmed on the basis
nium trichloride complexes ligated with ligands L5 and L11 of 1H and 13C NMR spectroscopy as well as elemental analysis.
could not be obtained via a similar approach, while the reac- The 1H NMR spectrum of 1a in CDCl3 shows the disappear-
tion of proligand L6H with TiCl4(THF)2 in the presence of tri- ance of the phenoxy proton signal of L1H at δ 10.67 ppm. The
ethylamine did enable the isolation of
a red powder
characterized as complex 6a mainly, which however could not
be purified via recrystallization probably due to the close solu-
bility of the target complex and impurities in toluene. Possibly,
due to the substitution of halogen atoms in the ligand frame-
work, complexes 7a and 8a are slightly soluble in toluene or
THF, which is in contrast to the satisfactory solubility of com-
plexes 1a–4a, 9a and 10a in toluene. Furthermore, a shiny red
crystal was accidentally gained from a saturated solution of
complex 8a in toluene. X-ray diffraction analysis revealed that
it is a binuclear, oxygen-bridged titanium complex (8d,
Scheme 3 Synthesis of titanium isopropoxide complexes 5e–8e.
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resonances of the methyl protons of the dimethylamido group isomers of complex 2a was further studied by variable temp-
1
N(CH3)2 appear as two sharp singlets and four doublets are erature H NMR spectroscopy in the temperature range of 20
observed for the two bridging methylene units of Ar–CH2–N to 100 °C in toluene-d8 (see ESI†). It can be noted that with the
moieties as compared to the singlet in the free ligand. Further- increase of temperature, the proportion of the trans-isomer
more, four multiplets accounting for the ethylene protons increases slightly, but with all signals still in a relatively sharp
(NCH2CH2NMe2) are displayed. All these features indicate the state, implying that some isomerization processes do occur,
coordination of both amino units of the ligand to the titanium but the structures of the isomers are not as fluxional as we
center. In contrast to these obvious differences displayed in anticipated.
the spectra of complex 1a and free ligand L1H, it is found that
Different patterns are displayed in the 1H NMR spectra of
the sharp resonance assignable to Ar–OCH3 in complex 1 titanium isopropoxide complexes 5e–8e. At ambient tempera-
hardly changes when compared to that of the free ligand. ture, except for complex 7e, the aliphatic protons of the corres-
Similar phenomena are also witnessed in the proton NMR ponding ligand in complexes 5e, 6e and 8e all resonate as
spectra of the rest of the titanium and zirconium complexes. broad signals, whereas in the low field region some small
Therefore, it is suggested that the methoxy group of the tetra- peaks could be observed in addition to the well-coupled, domi-
dentate aminophenolate ligand in these complexes does not nant resonances. Therefore, the existence of isomers is
take part in a coordination with the metal center, as they suggested for these titanium isopropoxide complexes and the
behave in the solid state (vide post).
cis-isomer should be the major one according to the X-ray
Noticeably, careful analysis of the 1H NMR spectra of the molecular structure of 5e. The variable temperature 1H NMR
trichloride complexes indicates that in addition to the main spectra of complex 5e further indicate that a similar coordi-
set of signal peaks attributable to the aminophenolate ligand, nation mode of the ligand wrapping around the metal center
there exists a series of small peaks in the vicinity of the former as that of the titanium trichloride complexes could be
signals, which are also consistent with the stoichiometric observed below 0 °C (see ESI†). Four well-coupled doublets
1
structure of the ligand. For example, in the H NMR spectrum attributable to the two Ar–CH2–N units and four multiplets
of complex 1a, the proton resonance of tert-butyl group is accounting for the ethylene protons (NCH2CH2NMe2) as well
observed at δ 1.55 ppm as one sharp singlet; in addition, one as two sharp N(CH3)2 signals are displayed, indicative of the
small singlet at 1.56 ppm can also be observed. Similarly, the coordination of two nitrogen donors to the metal center. The
methyl protons of the dimethylamido group (N(CH3)2) resonate participation of the aromatic methoxy group to coordinating
at δ 3.12, 2.63 ppm as two big sharp singlets and at δ 3.44, with the metal center is not observed. As the temperature
3.18 ppm as two small singlets, respectively. The ratio of all increases, the signals of all the aliphatic protons of 5e become
minor signals is in correspondence to that of ligand L1. All broad and coalesce gradually and finally become sharp again
these indicate that complex 1a has two isomers in solution. A at about 80 °C. Two singlets accounting for the Ar–CH2–N
similar event also occurs for titanium complexes 2a–4a and units and one singlet for the N(CH3)2 unit imply either the dis-
7a–10a as well as zirconium complex 8b. Hexa-coordinated sociation of the nitrogen donors from the metal center or a
titanium complexes supported by a tridentate ligand adopting fast coordination–dissociation equilibrium. All these features
cis- or trans-configurations have been reported previously.83,94 suggest that complexes 5e–8e are more fluxional in solution
According to this, there are two conceivable configurational than their trichloride analogues.
isomers for octahedral complexes featuring a prochiral triden-
tate aminophenolate ligand, of which both of the chiral-at-
metal cis- and trans-isomers exist as two stereoisomers,
X-ray molecular structures of titanium complexes 2a, 9a, 8d
and 5e
respectively (Fig. 1). On the basis of X-ray diffraction studies of Single crystals of complexes 2a, 9a, 8d and 5e suitable for X-ray
complexes 2a, 9a and 8d, where in each case the tetradentate diffraction studies were obtained from saturated toluene solu-
aminophenolate ligand is coordinated to the metal center in a tions at −20 °C. The molecular structures of complexes 2a, 9a,
cis-O, N, N chelating mode in the solid state, it is believed that 8d and 5e are given in Fig. 2–5.
the cis-isomer should be dominant in solution for this series
In the solid state, complex 2a possesses a distorted octa-
of complexes. Moreover, the possibility of isomerization of two hedral geometry, where the titanium center is coordinated by
the aminophenolate ligand in a cis-chelating mode through
two nitrogen atoms of the diamino moieties and the phenolate
oxygen atom of the ligand. The distance from O2 to Ti atom is
5.127 Å, much larger than the sum of atomic radii of titanium
and oxygen (r(Ti) = 2.110 Å, r(O) = 1.520 Å),95 demonstrating that
the aryl ether oxygen atom is not involved in coordination with
the metal center. The Ti–O1 bond length is 1.791(5) Å; the Ti–N
bond lengths are 2.343(6) and 2.300(7) Å; and the Ti–Cl bond
lengths are 2.340(2), 2.296(3) and 2.276(3) Å. All these bond
distances are in agreement with those observed for related
N- and O-functionalized titanium dichloride complexes.17,82
Fig. 1 Possible octahedral configuration isomers of titanium and zirco-
nium complexes with the tridentate prochiral aminophenolate ligand.
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Fig. 2 Molecular structure of complex 2a with thermal ellipsoids drawn
at the 30% level, hydrogen atoms and uncoordinated solvent are
omitted for clarity. The selected bond lengths (Å) and angles (°): Ti–O1
1.791(5), Ti–N1 2.343(6), Ti–N2 2.300(7), Ti–Cl3 2.276(3), Ti–Cl1
2.340(2), Ti–Cl2 2.296(3), N2–Ti–N1 77.9(2), Cl2–Ti–N1 90.23(17),
Cl3–Ti–Cl2 102.90(11), O1–Ti–N2 91.8(2), Cl3–Ti–N2 89.34(19), O1–Ti–
N1 81.1(2), O1–Ti–Cl1 171.81(19).
Fig. 4 Molecular structure of complex 5e with thermal ellipsoids drawn
at the 30% level, hydrogen atoms and uncoordinated solvent are
omitted for clarity. The selected bond lengths (Å) and angles (°): Ti1–O1
1.949(3), Ti1–O3 1.836(3), Ti1–O4 1.787(3), Ti1–O5 1.808(3), Ti1–N2
2.387(4), Ti1–N1 2.390(3), O4–Ti1–O5 104.58(15), O3–Ti1–O1
160.37(13), O4–Ti1–N2 90.30(14), O1–Ti1–N2 81.73(13), O5–Ti1–N1
88.82(13), O1–Ti1–N1 79.06(11), N2–Ti1–N1 76.07(12).
Fig. 3 Molecular structure of complex 9a with thermal ellipsoids drawn
at the 30% level, hydrogen atoms are omitted for clarity. The selected
bond lengths (Å) and angles (°): Ti1–O1 1.783(3), Ti1–N2 2.310(4),
Ti1–Cl3 2.2721(18), Ti1–N1 2.326(4), Ti1–Cl2 2.282(2), Ti1–Cl1
2.3493(19), Cl3–Ti1–Cl2 103.08(7), Cl3–Ti1–N2 90.10(13), O1–Ti1–N2
91.95(16), O1–Ti1–N1 81.77(14), Cl2–Ti1–N1 89.72(10), O1–Ti1–Cl1
172.81(11), N2–Ti1–N1 77.49(15).
Fig. 5 Molecular structure of complex 8d with thermal ellipsoids drawn
at the 30% level, hydrogen atoms and uncoordinated solvent are
omitted for clarity. The selected bond lengths (Å) and angles (°): Ti1–O1
1.831(5), Ti2–O1 1.801(5), Ti2–O1–Ti1 177.4(3), O1–Ti1–N2 170.2(2),
O1–Ti2–N4 167.9(2).
Complexes 9a and 5e show similar molecular structures to
that of 2a. The geometry around titanium is a distorted octa-
hedron and the ligand coordinates in cis-fashion. Much larger
distances from methoxy oxygen to Ti atom (9a: 5.221 and 5e:
6.006 Å) than the sum of atomic radii of titanium and oxygen
indicate that the aryl ether oxygen is not coordinated too.
Although the pendant aryl ether group is located far away from
The sum of specific angles around the Ti center (N1–Ti1–Cl2,
Cl3–Ti1–Cl2, N2–Ti1–Cl3 and N2–Ti1–N1) is 360.37°, very close
to the ideal 360°, proving that Ti, N1, N2, Cl2, Cl3 are nearly
perfectly coplanar. On the basis of this lead, O1, Ti1, Cl1 (O1–
Ti1–Cl1 = 171.18(19)°) occupy the axial position of the octa-
hedron with O1 and Cl1 located on the upper or lower side of
the above plane, respectively. Furthermore, the N1–Ti1–N2,
O1–Ti1–N1, and O1–Ti1–N2 bond angles are 77.9(2)°, 81.2(2)°
and 91.8(2)°, close to 90°, indicating that the three co-
ordinated heteroatoms O1, N1 and N2 are located in a cis-
fashion and therefore three chloride ligands are also located
in a cis-position to each other, which is beneficial to the
polymerization of olefins.17
t
the metal center, when Bu and Me groups are introduced to
the pedant group in 9a, the steric influence of the bulky aryl
ether ring on bond lengths still exists. The bond length of
Ti1–N1 is slightly shorter than that in 2a (2.326(4) versus
2.343(6) Å), while the bond length of Ti1–N2 is slightly longer
(2.310(4) versus 2.300(7) Å). As for complex 5e, due to the
replacement of chloride ligands by isopropoxide groups, the
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bond angles of O1–Ti–N1, O1–Ti–N2 and N1–Ti–N2 are slightly ethylene polymerization even at high temperatures. The ligand
larger and the Ti–O1, Ti–N1, and Ti–N2 bond lengths are structure, reaction temperature and the molar ratio of Al/Ti
slightly longer than those observed in complexes 2a and 9a, influence both the activities of the complexes and the mole-
respectively.
Complex 8d is the hydrolysis product of complex 8a, and
cular weights of the resultant polyethylenes.
Upon treatment of 1000 equiv. of MMAO as cocatalyst at
possesses an oxygen-bridged binuclear structure. Each tita- 1 MPa of ethylene pressure, titanium trichloride complexes
nium center has a distorted octahedral geometry with the 1a–4a and 7a–10a show moderate to high activities at high
tetradentate aminophenolate ligand in tridentate, cis-O, N, N temperatures of 100 °C and 120 °C, affording linear polyethy-
chelating mode, which is similar to those of 2a, 9a and 5e. The lenes of high molecular weights (Table 1). The data in Table 1
Ti1–O1–Ti2 bond angle is 177.4(3)°, almost equal to 180°, demonstrate that the steric and electronic effects of the substi-
showing that the two titanium atoms linked by the bridging tuents on the ortho- and para-positions of the phenolate ring
oxygen atom are nearly linear. The Ti1–O1 bond length is of the ligand exert significant influence on the catalytic activi-
1.831(5) Å, slightly longer than Ti2–O1 (1.801(5) Å), and the ties of these complexes. Complexes 7a and 8a with halogen
N2–Ti1–O3 bond angle is 170.2(2)°, slightly larger than groups on the ortho- and para-positions of the phenolate ring
N4–Ti2–O3 (167.9(2)°), indicating that 8d has a asymmetric show much higher activities than complexes 1a–4a with alkyl
C1-configuration.
or aralkyl substituents for ethylene polymerization at 120 °C
(entries 13, 16 versus entries 2, 5, 8, 10), suggesting that the
electronic effect of the substituents may have played a signifi-
cant role in ethylene polymerization. For example, the catalytic
activity of complex 8a with bromo groups substituted on the
ortho- and para-positions reaches 2082 kg (mol-Ti h)−1 at
120 °C, whereas complex 2a with o-tBu and p-tBu provides an
activity of 852 kg (mol-Ti h)−1 under the same conditions. At
the same time, for complexes 7a and 8a with halogen substi-
tution, an obvious increase of the catalytic activity is observed
when chloro groups are replaced by bromo groups, which
might be attributable to the increase of the steric bulkiness of
Ethylene polymerization
Ethylene polymerizations using the synthesized titanium and
zirconium complexes as precatalysts under different con-
ditions were examined and the results are summarized in
Tables 1–3. When activated with MMAO, titanium isopropox-
ide complexes 5e–8e and zirconium complex 8b exhibit moder-
ate catalytic activities for ethylene polymerization. More
efficient than the titanium isopropoxide and zirconium tri-
chloride analogues, in conjunction with MMAO, titanium tri-
chloride complexes 1a–4a, 7a–10a show good activities for
Table 1 Ethylene polymerization catalyzed by complexes 1a–4a, 7a–10a and 8ba
Entry
Cat.
Al/M
Temp. (°C)
PE (mg)
Activity (kg (mol-M h)−1
)
Mηb (104 g mol−1
)
Tmc (°C)
1
2
3
4
5
6
7
8
1a (o-tBu, p-Me)
1a (o-tBu, p-Me)
1a (o-tBu, p-Me)
2a (o,p-tBu2)
1000
1000
5000
1000
1000
5000
1000
1000
1000
1000
5000
1000
1000
5000
1000
1000
5000
1000
1000
5000
1000
1000
1000
1000
100
120
120
100
120
120
100
120
100
120
120
100
120
120
100
120
120
100
120
120
100
120
100
120
63
111
158
92
142
277
66
378
666
948
552
852
1662
396
456
468
768
1272
1176
1542
2376
1920
2082
4170
372
504
582
288
384
*
133.4
134.6
133.7
132.5
133.6
133.7
135.2
134.5
133.8
134.2
133.2
133.6
134.2
134.7
134.6
133.7
134.5
132.8
133.6
135.2
—
18.2
7.73
*
2a (o,p-tBu2)
14.4
5.34d
18.8
6.88
21.4
8.18
2.73
25.1
14.0
8.32
25.5d
9.54d
6.33d
*
15.4
9.85
18.3
6.32
55.1
46.4
2a (o,p-tBu2)
3a (o,p-cumyl2)
3a (o,p-cumyl2)
4a (o-CPh3, p-Me)
4a (o-CPh3, p-Me)
4a (o-CPh3, p-Me)
7a (o,p-Cl2)
7a (o,p-Cl2)
7a (o,p-Cl2)
8a (o,p-Br2)
8a (o,p-Br2)
76
78
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
128
212
196
257
396
320
347
695
62
84
97
48
64
8a (o,p-Br2)
9a (o-tBu, p-Me)
9a (o-tBu, p-Me)
9a (o-tBu, p-Me)
10a (o,p-cumyl2)
10a (o,p-cumyl2)
8b (o-, p-Br2)
133.9
134.3
—
64
51
384
306
8b (o-, p-Br2)
a Conditions: toluene as solvent, [Cat.] = 0.04 μmol mL−1, Vtotal = 25 mL, MMAO as cocatalyst, 1 MPa of ethylene, 10 min. b Intrinsic viscosity was
determined in decahydronaphthalene at 135 °C by Ubbelohde viscometer technique, and the viscosity average molecular weights were calculated
using the relation:96 [η] = 6.67 × 10−4Mη0.67, in unit of 104 g mol−1; * insoluble. c Determined by DSC at a heating rate of 10 °C min−1 d Mw and
.
Mw/Mn were determined by GPC, using 1,3,5-trichlorobenzene as solvent at 160 °C, in unit of 104 g mol−1. For entry 6, Mw = 4.92 × 104 g mol−1
,
Mw/Mn = 16.8; for entry 15, Mw = 34.8 × 104 g mol−1, Mw/Mn = 16.4; for entry 16, Mw = 10.1 × 104 g mol−1, Mw/Mn = 10.2; for entry 17, Mw = 7.25 ×
104 g mol−1, Mw/Mn = 13.7.
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Table 2 Ethylene polymerization catalyzed by complex 8a under different conditionsa
Entry
Cat. (μmol mL−1
)
Temp. (°C)
Al/Ti
Yield (mg)
Activity (kg (mol-Ti h)−1
)
Mηb (104 g mol−1
)
Tmc (°C)
25
26
8a (0.04)
8a (0.04)
8a (0.04)
8a (0.04)
8a (0.04)
8a (0.04)
8a (0.04)
8a (0.02)
8a (0.02)
8a (0.004)
8a (0.04)
8a (0.04)
30
50
80
1000
1000
1000
1000
1000
1000
2000
1000
123
133
162
318
394
462
487
238
644
74
738
798
972
*
*
134.4
133.8
133.5
132.0
133.6
135.2
133.9
134.6
133.9
135.2
133.4
133.8
27
40.7
9.60
5.76
2.68
8.59
12.8
9.94
13.6
22.3
9.38
28d
29d
30d
31
120
140
160
120
120
120
120
100
120
954
1182
1386
2922
2856
15 456
8880
2148
2202
32
33e
34e
35
5000
5000
1000/100 f
1000/100 f
358
367
36
a In toluene, 25 mL, MMAO as cocatalyst, 1 MPa of ethylene, 10 min. b Mη measured by the Ubbelohde calibrated viscometer technique,
* insoluble. c Determined by DSC. d In 1,3,5-trimethylbenzene, 50 mL. e 5 min. f Al(MMAO)/AlAliBu3/Ti = 1000/100/1.
Table 3 Ethylene polymerization catalyzed by complexes 5e–8ea
Activity
Entry
Cat.
Temp. (°C)
Al/Ti
Yield (mg)
(kg (mol-Ti h)−1
)
Mηb (104 g mol−1
)
37
38
39
40
41
42
5e (o-Cl, p-tBu)
5e (o-Cl, p-tBu)
5e (o-Cl, p-tBu)
6e (o-Br, p-tBu)
7e (o,p-Cl2)
25
50
80
50
50
50
1000
1000
1000
1000
1000
1000
311
606
512
362
515
162
207
404
341
241
343
110
3.48
3.25
3.06c
0.96
25.2
5.56
8e (o,p-Br2)
a Solvent: toluene, 25 mL; MMAO as cocatalyst, [Cat.] = 0.12 μmol mL−1, 0.5 MPa of ethylene, 30 min. b Mη measured by the Ubbelohde calibrated
viscometer technique. c Mw and Mw/Mn were determined by GPC, using 1,3,5-trichlorobenzene as solvent at 160 °C, in unit of 104 g mol−1. For
entry 39, Mw = 13.6 × 104 g mol−1, Mw/Mn = 34.8.
the bromo group.97 However, the space effect of the ortho- and h)−1, while the activity of zirconium complex 8b is only 306 kg
para-substituents of the phenolate ring is complicated for alkyl (mol-Ti h)−1, suggesting that the zirconium complex is mark-
or aralkyl substituted complexes 1a–4a. Complex 4a with an edly less thermally stable than the titanium analogues.
ortho-trityl group on the phenolate ring exhibits higher activity
It is found that the molecular weights of the resultant poly-
than complex 3a with o,p-cumyl groups, but is less active than mers are closely dependent on the structure of the catalysts. In
complex 2a with o,p-tert-butyl groups at 120 °C (entries 2, 5 general, increasing the steric hindrance of the substituents in
and 10). At present we do not have a reasonable explanation, it the ligand framework results in an obvious decrease of the
is tentatively suggested that probably a cooperative effect of the molecular weights of the obtained polymers.98 Under
steric bulkiness and the electronic nature of these substituents the polymerization conditions of Al/Ti = 1000 and 120 °C, with
might be responsible for this unusual phenomenon. Moreover, the variation of the ortho-substituent of the phenolate ring
the substituents on the pendant aryl ethyl group of the ligand from tert-butyl (1a, 2a and 9a) to cumyl (3a, 10a) and CPh3
also have a slight impact on the catalytic activity of the corres- (4a), a sharp decrease of Mη values of the resulted polyethyl-
ponding titanium complex. When two H atoms of the pendant enes from 144–182 kg mol−1 to 63.2–81.8 kg mol−1 could be
aryl ring are replaced by tert-butyl and methyl groups separ- observed (entries 2, 5, 8, 10, 19, 22, respectively). It is also the
ately (9a and 10a), reduced activities of 504 kg (mol-Ti h)−1 case for the polymers obtained by complexes 7a and 8a
and 384 kg (mol-Ti h)−1 are produced in comparison to those (entries 13, 16). Although being less active than titanium ana-
of complexes 1a and 3a (entries 19 and 22 vs. entries 2 and 8). logues zirconium complex 8b provides polyethylenes with
It seems that although the pendant aryl group is located far much higher molecular weights of 464–551 kg mol−1 at high
away from the metal center according to the X-ray diffraction temperatures of 100–120 °C. Furthermore, polyethylenes with
studies, it does exhibit a certain influence on the polymeri- very broad molecular weight distributions (Mw/Mn = 10.2–16.8)
zation likely by hindering the coordination/insertion of ethyl- are obtained as indicated by the GPC measurements for
ene monomer.
typical polymer samples (entries 6, 15, 16 and 17), which
In comparison to the high activities of titanium analogues suggest the presence of multiple active species. From the 1H
at high temperatures, zirconium trichloride complex 8b is sig- NMR spectra of these titanium complexes, the existence of
nificantly less active. At 120 °C, with a Al/M molar ratio of isomers is conclusive. The variable temperature 1H NMR study
1000, titanium complex 8a shows an activity of 2082 kg (mol-Ti of complex 2a further indicates the somewhat rigid configur-
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ation of these complexes at high temperature. Therefore, the group in the ligand framework of these complexes might play
widely distributed GPC traces might be a result of multiple a crucial role in stabilizing the active species during the
active sites of different nature generated from different polymerization, although it isn’t coordinated to the metal in
isomers, although possible species generated from some the precatalyst. It is worthy of note that, under similar con-
decomposition pathways might not be ruled out. Moreover, ditions, using 8a–MMAO as the catalytic system for ethylene
the obtained PEs possess melting points in the range polymerization, a higher activity of 2082 kg (mol-Ti h)−1 could
133–136 °C, typical for linear polyethylene.97
be reached in toluene than that in trimethylbenzene (entry 16
The polymerization temperature also exerts a crucial influ- vs. 28). Similar phenomena have also been reported in the lite-
ence on the catalytic activities of these titanium and zirconium rature recently.83 It is conceivable that the polarity and the
trichloride complexes. As illustrated in Fig. 6, with the increase steric bulkiness of the solvent molecule might be the likely
of the polymerization temperature from 30 °C to 120 °C, the factors.
activities of titanium complexes 1a–4a, 7a and 8a increase to a
It is noticeable that the polymerization temperature influ-
great extent, so for complexes 9a and 10a from 80 to 120 °C. ences the molecular weights of the resultant polymers remark-
For instance, in the presence of MMAO, the most active tita- ably. Polyethylenes obtained at lower temperatures (<100 °C)
nium complex 8a displays a moderate activity of 738 kg (mol-Ti are in general insoluble in decahydronaphthalene at 135 °C,
h)−1 toward ethylene polymerization at 30 °C, while nearly a indicative of the ultra-high-molecular-weight nature, especially
three-fold increase of the activity could be obtained at 120 °C for polymers obtained by complexes 1a, 2a and 9a with less.
(2082 kg (mol-Ti h)−1). As for zirconium complex 8b, the
As observed for most of the catalytic olefin polymerization
optimal temperature is around 80 °C, at which the highest systems, the activity of these titanium complexes toward ethyl-
activity of 678 kg (mol-Zr h)−1 could be obtained with a Al/Zr ene polymerization is also influenced by the molar ratio of
molar ratio of 1000. All these indicate the superior thermal Al/Ti. With the increase of Al/Ti ratio from 1000 to 5000, the
stability of this series of titanium trichloride complexes. To activity of complex 8a is increased from 2082 kg (mol-Ti h)−1 to
have further insight into the thermal stability of these tita- 4170 kg (mol-Ti h)−1 (entries 16 and 17). A similar trend is also
nium complexes, ethylene polymerizations catalyzed by the found for the other complexes. According to literature reports,
8a–MMAO catalytic system were carried out at higher tempera- with MAO as cocatalyst, the addition of a small amount of
tures of 120–160 °C in trimethylbenzene. As depicted by the alkyl aluminium could normally enhance the catalytic activity
data in Table 2, an increasing tendency of the activities could of the corresponding system.99,100 Therefore, the same strategy
still be observed with the temperature elevating from 120 °C to was adopted for ethylene polymerizations catalyzed by 8a–
160 °C (from 954 kg (mol-Ti h)−1 to 1386 kg (mol-Ti h)−1
,
MMAO at 100 and 120 °C, as expected the addition of 100
entries 28–30), suggesting that the in situ formed catalytic equiv. of AliBu3 slightly increased the activity from 1920 kg
species are quite stable even at a high temperature of 160 °C. (mol-Ti h)−1 and 2082 kg (mol-Ti h)−1 to 2148 kg (mol-Ti h)−1
Tang’s group reported83 that, in the presence of MMAO, tita- and 2202 kg (mol-Ti h)−1, respectively (entry 15 vs. 35 and 16
nium trichloride complexes supported by tridentate amino- vs. 36). The influence of the Al/Ti molar ratio on the polymer
phenolate ligand [O−N(H)X] (X = S, P) showed high activity molecular weight was also investigated. The results shown in
toward ethylene polymerization at 90 °C. However, a further Tables 1 and 2 indicate that, in general, under otherwise the
increase of polymerization temperature led to a decline of the same conditions, the molecular weight of the obtained PE
activity. Therefore, it is conceivable that the additional OMe decreases dramatically with the increase of the Al/Ti molar
ratio. From the 1H NMR spectrum of a typical polyethylene
sample obtained by 8a at 120 °C, no obvious alkenyl hydrogen
signals could be detected, implying that the dominant termin-
ation process is chain transfer to aluminum17,101,102 instead of
the β-hydride elimination reaction.101
Moreover, the catalytic activity depends on the catalyst con-
centration. For 8a, the effect of catalyst concentration on
activity was studied in the range of 0.04 to 0.004 μmol mL−1
,
the highest activity of 15 456 kg (mol-Ti h)−1 was obtained with
a catalyst concentration of 0.02 μmol mL−1 (entry 33).
For a comparison purpose, titanium isopropoxide com-
plexes 5e–8e were tested as precatalysts for the polymerization
of ethylene using MMAO as the cocatalyst, and the results are
illustrated in Table 3. For 5e–MMAO, when the Al/Ti molar
ratio is 1000, changing polymerization temperature from 25 to
80 °C, the highest activity of 404 kg (mol of Ti h)−1 is achieved
at 50 °C (entries 37–39). This trend demonstrates that the tita-
nium isopropoxide complexes are less thermally stable than
the corresponding trichloride complexes. Meanwhile, much
Fig. 6 The influence of polymerization temperature on the catalytic
activities of complexes 1a–4a, 7a–10a and 8b (polymerization con-
ditions: toluene as solvent, [Cat.] = 0.04 μmol mL−1, MMAO as cocatalyst,
1 MPa of ethylene pressure, 10 min).
12670 | Dalton Trans., 2014, 43, 12663–12677
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lower activities are obtained by these titanium isopropoxide dried over calcium hydride before use. CDCl3 was distilled
complexes in comparison to titanium trichloride analogues from CaH2 and stored under argon. 3-tert-Butyl-2-methoxy-5-
under similar conditions. Among complexes 5e–8e, complex methylbenzaldehyde, 2-chloro-4-tert-butylphenol, 2-bromo-4-
5e with a chloro group on the ortho-position of the phenolate tert-butylphenol, 2,4-dibromo-6-bromomethyl phenol, and pro-
ring is most active and exhibits significantly higher activity ligands L1–3H, L7H, L9H, and L10H were prepared according to
than 6e with an ortho-bromo group for ethylene polymerization literature procedures.85–87 TiCl4(THF)2 and ZrCl4(THF)2 were
at 50 °C (entry 38 vs. 40). A similar order is also found for com- prepared according to literature procedures.103 1,3,5-Trimethyl-
plexes 7e and 8e. On the other hand, when compared with benzene was purchased from Acros and distilled with sodium
complex 7e with chloro groups on both ortho- and para-posi- before use. AliBu3, n-BuLi, TiCl4, and ZrCl4 were purchased
tions of the phenolate ring, the activity of complex 5e with a from J&K, Aldrich or Acros. 1H and 13C NMR spectra were
para-tert-butyl group is slightly higher. It brings an ambivalent recorded on
a
Bruker AVANCE-400 (1H: 400 MHz, 13C:
situation for understanding the effect of substituents, either 100 MHz) spectrometer at room temperature unless otherwise
by steric effect or by electronic effect. We tentatively suggest stated. Elemental compositions were determined by an
that different influences of the ortho- and para-substituents EA-1106 elements analyzer. The melting points of the com-
might be involved. In addition, the observed very broad poly- pounds were measured by WRS-1B digital melting point tester
dispersity indices of the polymer sample obtained by 5e and reported without correction. The molecular weights of the
(Mw/Mn = 34.8, entry 39) indicated the presence of multiple polyethylenes were measured in decahydronaphthalene at
active sites in these catalyst systems, which might be due to 135 °C by a Ubbelohde viscometer according to the following
1
the fluxional nature of this series of titanium isopropoxide equation:96 [η] = (6.77 × 10−4)Mη0.67. The H NMR spectrum of
complexes above 0 °C.
a typical polymer sample was recorded on a Varian 400 NMR
spectrometer at 100 °C using a mixed solvent of o-dichloroben-
zene and C6D6 (4 : 1). The melting temperatures (Tm) of poly-
mers were measured by differential scanning calorimetry
(DSC) (V2.3C TA) at a heating rate of 10 °C min−1 from −20 to
Conclusions
A series of novel titanium and zirconium complexes supported 200 °C. Molecular weights and molecular weight distributions
by tetradentate aminophenolate ligands in tridentate, cis-O, N, N of the polyethylenes were measured on a PL-GPC 220 instru-
chelating mode were prepared and characterized. In the pres- ment at 160 °C with 1,2,4-trichlorobenzene as the eluent.
ence of MMAO, these complexes show moderate to high activi-
Synthesis of proligands and titanium and zirconium
complexes
ties in catalyzing ethylene polymerization and afford high
molecular weight polymers with broad molecular weight distri-
butions. Moreover, the active species generated in situ from
2-{[(2-(Dimethylamino)ethyl)(2-methoxybenzyl)amino]methyl}-
titanium trichloride complexes upon treatment with MMAO 4-methyl-6-tritylphenol (L4H). To a solution of 2-methoxyben-
possess unusual thermal stability even at high temperatures of zaldehyde (4.08 g, 30.0 mmol) in ethanol (30 mL) was added
120–160 °C. In comparison to titanium trichloride complexes, N,N-dimethyl-1,2-ethanediamine (3.9 mL, 30 mmol), and the
zirconium trichloride complexes and titanium isopropoxide mixture was refluxed for 12 h. After cooling the reaction
complexes are less active and thermally stable. The electronic mixture to 0 °C, NaBH4 (2.27 g, 60 mmol) was slowly added.
properties and steric hindrances of the substituents of the The solution was refluxed for another 12 h and then cooled to
ligands remarkably affect the catalytic activities of these com- room temperature. The reaction was quenched with 20 mL of
plexes, and complex 8a with bromo groups on both the ortho- water and all the volatiles were evaporated. The resulting
and para-positions of the phenolate ring of the ligand exhibits viscous residue was extracted with petroleum ether
the highest activity among them. The highest activity for ethyl- (3 × 30 mL). The combined organic phase was dried over anhy-
ene polymerization was achieved as 15 456 kg (mol-Ti h)−1 at drous MgSO4 and filtered. The filtrate was evaporated in vacuo
120 °C by complex 8a. These results and the easy modification to afford a light yellow oil. 4-Methyl-2-tritylphenol (10.5 g,
feature of these complexes are helpful in developing efficient 30.0 mmol) and paraformaldehyde (1.80 g, 60.0 mmol) were
catalysts having potentially industrial applications.
added to the solution of the above light yellow oil in ethanol
(30 mL). The reaction mixture was refluxed for 12 h and then
cooled to ambient temperature. All the volatiles were evapo-
rated to give a white solid, which was recrystallized with a
mixture of solvents (PE/EA = 5 : 1) to afford the target proli-
gand L4H as colorless crystals (9.96 g, 56.6%). mp:
Experimental
General considerations
All air- and/or moisture-sensitive compounds were manipu- 138.3–139.5 °C. (Found: C, 81.73; H, 7.34; N, 4.68. Calc. for
lated using standard Schlenk techniques or in a glovebox C39H42N2O2: C, 82.07; H, 7.42; N, 4.91%); δH (400 MHz, CDCl3)
under an argon atmosphere. Solvents for air- and moisture- 10.63 (1 H, bs, ArOH), 7.34–7.07 (16 H, m, ArH), 6.93–6.71
sensitive reactions, for example, toluene, THF, and n-hexane (5 H, m, ArH), 3.64 (2 H, s, ArCH2N), 3.58 (3 H, s, ArOCH3),
were refluxed with sodium–benzophenone and distilled prior 3.53 (2 H, s, ArCH2N), 2.45–2.35 (2 H, m, N(CH2)2N), 2.22–2.12
to use under argon. Dichloromethane and triethylamine were (2 H, m, N(CH2)2N), 2.15 (3 H, s, ArCH3), 2.01 (6 H, s, N(CH3)2).
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δC (100 MHz, CDCl3) 158.0, 154.2, 146.4, 133.7, 131.5, 131.3, in vacuo to give a light yellow oil. 2,4-Dibromo-6-(bromo-
131.1, 130.6, 128.9, 128.6, 127.3, 126.9, 126.1, 125.5, 125.2, methyl)phenol (10.34 g, 30.00 mmol) and triethylamine
122.9, 120.4, 110.2, (all ArC), 63.4 (ArCPh3), 57.8 (OCH3), 56.0 (4.5 mL) were added to the solution of the above light yellow
(N(CH2)2N), 55.1 (N(CH2)2N), 52.6 (ArCH2N), 50.4 (ArCH2N), oil in THF (30 mL) under argon. The reaction mixture was
45.4 (N(CH3)2), 21.0 (ArCH3).
stirred for 3 h in the dark, and then the solvent was evaporated
4-tert-Butyl-2-chloro-6-{[(2-(dimethylamino)ethyl)(2-methoxy- to dryness and the brown crude product was purified by
benzyl)amino]methyl}phenol (L5H). Proligand L5H was syn- chromatography (PE/EA = 4 : 1) and then recrystallization with
thesized in the same manner as that for L4H with 2-chloro- petroleum ether. The target product L8H was isolated as col-
4-tert-butylphenol (5.54 g, 30.0 mmol) as the starting material. ourless crystals (9.97 g, 70.4%). mp: 138.3–139.5 °C. (Found: C,
After work-up, a light yellow oil was obtained, which was puri- 48.03; H, 5.20; N, 5.84. Calc. for C19H24Br2N2O2: C, 48.33; H,
4
fied by chromatography (PE/EA = 4 : 1) and then recrystalliza- 5.12; N, 5.93%); δH (400 MHz, CDCl3) 7.53 (1 H, d, J = 2.2 Hz,
3
3
tion with absolute alcohol. The target product L5H was ArH) 7.23 (1 H, t, J = 7.4 Hz, ArH), 7.15 (1 H, d, J = 7.4 Hz,
4
3
isolated as colorless crystals (6.29 g, 51.8%). mp: ArH), 7.07 (1 H, d, J = 2.2 Hz, ArH), 6.88 (1 H, t, J = 7.4 Hz,
107.1–108.4 °C. (Found: C, 68.00; H, 8.19; N, 6.59. Calc. for ArH), 6.83 (1 H, d, 3J = 7.4 Hz, ArH), 3.78 (3 H, s, ArOCH3), 3.64
C23H33ClN2O2: C, 68.21; H, 8.21; N, 6.92%); δH (400 MHz, (2 H, s, ArCH2N), 3.60 (2 H, s, ArCH2N), 2.56 (2 H, t, 3J =
CDCl3) 11.20 (1 H, bs, ArOH), 7.26–7.17 (3 H, m, ArH), 6.5 Hz, N(CH2)2N), 2.48 (2 H, t, 3J = 6.5 Hz, N(CH2)2N), 2.13
3
6.93–6.86 (2 H, m, ArH), 6.84 (1 H, d, J = 8.1 Hz, ArH), 3.81 (6 H, s, N(CH3)2). δC (CDCl3, 100 MHz) 158.2, 154.4, 134.1,
(3 H, s, ArOCH3), 3.72 (2 H, s, ArCH2N), 3.65 (2 H, s, ArCH2N), 131.7, 131.3, 129.2, 126.5, 125.1, 120.3, 111.4, 110.5, 109.8 (all
3
3
2.58 (2 H, t, J = 6.6 Hz, N(CH2)2N), 2.48 (2 H, t, J = 6.6 Hz, ArC), 56.0 (N(CH2)2N), 56.0 (N(CH2)2N), 55.2 (ArOCH3), 53.1
N(CH2)2N), 2.14 (6 H, s, N(CH3)2), 1.26 (9 H, s, ArC(CH3)3). (ArCH2N), 49.9(ArCH2N), 45.1 (N(CH3)2).
δC (100 MHz, CDCl3) 158.1, 151.2, 141.9, 131.6, 128.9, 125.9,
2-{[(3-tert-Butyl-2-methoxy-5-methylbenzyl)(2-(dimethyl amino)-
125.4, 124.6, 123.8, 120.3, 120.2, 110.4, (all ArC), 57.1 (OCH3), ethyl)amino]methyl}-4-methyl-6-tritylphenol (L11H). Proligand
56.4 (N(CH2)2N), 55.2 (N(CH2)2N), 53.0 (ArCH2N), 50.4 L11H was synthesized in the same manner as for that L4H
(ArCH2N), 45.3 (N(CH3)2), 34.0 (ArC(CH3)3), 31.5 (ArC(CH3)3).
with 3-tert-butyl-2-methoxy-5-methylbenzaldehyde (6.18 g,
2-Bromo-4-tert-butyl-6-{[(2-(dimethylamino)ethyl)(2-methoxy- 30.0 mmol) as the starting material. The target product L11H
benzyl)amino]methyl}phenol (L6H). Proligand L6H was syn- was obtained as a colourless crystals (8.76 g, 45.6%). mp:
thesized in the same manner as that for L4H with 2-bromo-4- 137.5–138.7 °C. (Found: C, 81.99; H, 8.23; N, 4.34. Calc. for
tert-butylphenol (6.67 g, 30.0 mmol) as the starting material. C44H52N2O2: C, 82.46; H, 8.18; N, 4.37%); δH (400 MHz, CDCl3)
After work-up, a light yellow oil was obtained, which was puri- 10.46 (1 H, bs, ArOH), 7.26–7.09 (15 H, m, ArH), 6.96 (1 H, d,
fied by chromatography (PE/EA = 4 : 1) and then recrystalliza- 4J = 1.6 Hz, ArH), 6.89 (1 H, s, ArH), 6.81 (1 H, s, ArH), 6.69
tion with absolute alcohol. The target product L6H was (1 H, s, ArH), 3.63 (2 H, s, ArCH2N), 3.59 (3 H, s, ArOCH3), 3.55
isolated as colourless crystals (7.90 g, 58.6%). mp: (2 H, s, ArCH2N), 2.36–2.28 (2 H, m, N(CH2)2N), 2.25–2.20 (2 H,
142.3–143.4 °C. (Found: C, 61.46; H, 7.30; N, 6.26. Calc. for m, N(CH2)2N), 2.17 (6 H, s, ArCH3), 1.97 (6 H, s, N(CH3)2), 1.35
C23H33BrN2O2: C, 61.47; H, 7.40; N, 6.23%); δH (400 MHz, (9 H, s, ArC(CH3)3). δC (100 MHz, CDCl3) 156.5, 154.0, 146.2,
4
CDCl3) 11.06 (1 H, bs, ArOH), 7.38 (1 H, d, J = 2.2 Hz, ArH), 142.0, 133.7, 132.4, 131.1, 130.7, 130.5, 129.2, 129.1, 125.2,
4
7.26–7.18 (2 H, m, ArH), 6.93 (1 H, d, J = 2.2 Hz, ArH), 6.89 126.8, 126.8, 126.2, 123.0 (all ArC), 63.3 (CPh3), 62.3 (OCH3),
(1 H, t, 3J = 7.4 Hz, ArH), 6.84 (1 H, d, 3J = 8.2 Hz, ArH), 3.82 (3 57.7 (N(CH2)2N), 55.7 (N(CH2)2N), 52.1 (ArCH2N), 49.9
H, s, ArOCH3), 3.73 (2 H, s, ArCH2N), 3.65 (2 H, s, ArCH2N), (ArCH2N), 45.1 (N(CH3)2), 34.7 (ArC(CH3)3), 31.1 (ArC(CH3)3),
3
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2.58 (2 H, t, J = 6.8 Hz, N(CH2)2N), 2.48 (2 H, t, J = 6.8 Hz, 21.2 (ArCH3), 20.9 (ArCH3).
N(CH2)2N), 2.13 (s, 6H, N(CH3)2), 1.25 (s, 9H, ArC(CH3)3).
L1TiCl3 (1a). A solution of L1H (0.769 g, 2.00 mmol) and tri-
δC (100 MHz, CDCl3) 158.1, 152.2, 142.5, 131.6, 128.9, 128.8, ethylamine (0.6 mL, 4 mmol) in 30 mL of THF was added
125.4, 125.3, 123.7, 120.3, 110.5, 109.9, (all ArC), 57.4 (OCH3), dropwise via a syringe to a mixture of TiCl4(THF)2 (0.644 g,
56.4 (N(CH3)2), 55.2 (N(CH3)2), 53.0 (ArCH2N), 50.5 (ArCH2N), 2.00 mmol) in 20 mL of THF which was pre-cooled to −78 °C
45.4 (N(CH3)2), 34.0 (ArC(CH3)3), 31.5 (ArC(CH3)3).
2,4-Dibromo-6-{[(2-(dimethylamino)ethyl)(2-methoxybenzyl)- warmed to room temperature and stirred for 24 h. The result-
amino]methyl}phenol (L8H). To
solution of 2-methoxy- ing dark red suspension was filtered. All the volatiles of the fil-
with a liquid nitrogen–alcohol bath. The mixture was then
a
benzaldehyde (4.08 g, 30.0 mmol) in ethanol (30 mL) was trate were removed in vacuo, and the residue was re-dissolved
added N,N-dimethyl-1,2-ethanediamine (3.9 mL, 30 mmol), in toluene (100 mL) and filtered. The red solution was concen-
and the mixture was refluxed for 12 h. After cooling the reac- trated to 50 mL and kept at −20 °C. The target complex 1a was
tion mixture to 0 °C, NaBH4 (2.27 g, 60 mmol) was slowly collected as red solids after filtration and drying (0.884 g,
added. The solution was refluxed for another 12 h and then 82.2%). 1a was characterized to be a mixture of isomers, the
cooled to room temperature. The reaction was quenched with molar ratio of cis-1a/trans-1a = 10 : 1. mp: 211.5–212.4 °C.
20 mL of water and all the volatiles were evaporated. The (Found: C, 56.96; H, 6.79; N, 4.44. Calc. for C24H35Cl3N2O2-
resulting viscous residue was extracted with petroleum ether Ti·(0.6C7H8): C, 57.11; H, 6.76; N, 4.72%); NMR spectroscopic
3
4
(3 × 30 mL). The combined organic phase was dried over an- data for cis-1a: δH (400 MHz, CDCl3) 7.41 (1 H, td, J = 8.3, J =
hydrous MgSO4 and filtered. The filtrate was evaporated 1.7 Hz, ArH), 7.21 (1 H, dd, 3J = 7.5, 4J = 1.7 Hz, ArH), 7.08
12672 | Dalton Trans., 2014, 43, 12663–12677
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(s, 1H, ArH), 7.02 (1 H, t, J = 7.5 Hz, ArH), 6.97 (1 H, d, J = 126.6, 125.8, 125.6, 120.7, 120.6, 111.2 (all ArC), 61.9 (OCH3),
8.3 Hz, ArH), 6.67 (1 H, s, ArH), 5.45 (1 H, d, 2J = 14.5 Hz, 58.9 (N(CH2)2N), 57.6 (N(CH2)2N), 55.4 (ArCH2N), 54.9
2
2
ArCH2N), 4.60 (1 H, d, J = 14.5 Hz, ArCH2N), 4.21 (1 H, d, J = (ArCH2N), 48.6 (N(CH3)2), 48.5 (N(CH3)2), 42.9 (C(CH3)2Ph),
14.5 Hz, ArCH2N), 3.94–3.81(1 H, m, N(CH2)2N), 3.81 (3 H, s, 42.4 (C(CH3)2Ph), 34.9 (C(CH3)2Ph), 30.9 (C(CH3)2Ph), 30.9
OCH3), 3.59 (1 H, d, 2J = 14.5 Hz, ArCH2N), 3.11 (3 H, s, (C(CH3)2Ph), 26.0 (C(CH3)2Ph).
N(CH3)2), 2.85–2.74 (1 H, m, N(CH2)2N), 2.67–2.56 (1 H, m,
L4TiCl3 (4a). Complex 4a was synthesized in a similar
N(CH2)2N), 2.60 (3 H, s, N(CH3)2), 2.26 (3 H, s, ArCH3), manner to that described for 1a, using proligand L4H (1.143 g,
2.30–2.21 (1 H, m, N(CH2)2N), 1.55 (9 H, s, C(CH3)3). 2.00 mmol), triethylamine (0.6 mL, 4 mmol), and TiCl4(THF)2
δC (100 MHz, CDCl3): 159.0, 157.6, 137.6, 135.2, 134.0, 130.8, (0.644 g, 2.00 mmol) as starting materials. After crystallization
129.8, 128.9, 127.5, 120.4, 120.6, 111.3 (all ArC), 61.4 (OCH3), in toluene, pure cis-4a was obtained as red crystals (0.527 g,
59.2 (N(CH2)2N), 57.6 (N(CH2)2N), 55.5 (ArCH2N), 55.0 36.4%). mp: 197.2–198.1 °C. (Found: C, 64.03; H, 5.82; N, 3.47.
(ArCH2N), 50.9 (N(CH3)2), 48.5 (N(CH3)2), 35.0 (C(CH3)3), 30.3 Calc. for C39H41Cl3N2O2Ti: C, 64.70; H, 5.71; N, 3.87%); NMR
(C(CH3)3), 21.0 (ArCH3).
spectroscopic data for cis-4a: δH (400 MHz, CDCl3) 7.44–7.37
L2TiCl3 (2a). Complex 2a was synthesized in a similar (1 H, m, ArH), 7.34–7.11 (1 6H, m, ArH), 7.02 (1 H, t, 3J =
manner to that described for 1a, using L2H (0.853 g, 7.4 Hz, ArH), 6.95 (1 H, d, J = 9.2 Hz, ArH), 6.93 (1 H, d, J =
3
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2.00 mmol), triethylamine (0.6 mL, 4 mmol), and TiCl4(THF)2 2.5 Hz, ArH), 6.80 (1 H, s, ArH), 5.28 (1 H, d, 2J = 14.5 Hz,
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2
(0.644 g, 2.00 mmol) as the starting materials. Red crystals ArCH2N), 4.80 (1 H, d, J = 14.5 Hz, ArCH2N), 4.25 (1 H, d, J =
were obtained (0.819 g, 70.6%), which were characterized to be 14.5 Hz, ArCH2N), 3.77 (3 H, s, ArOCH3), 3.67–3.57 (1 H, m,
a mixture of two isomers, the molar ratio of cis-2a/trans-2a = N(CH2)2N), 3.57 (1 H, d, 2J = 14.5 Hz, ArCH2N), 2.73 (3 H, s,
10 : 2. mp: 178.5–180.2 °C. (Found: C, 57.96; H, 7.31; N, 4.32. N(CH3)2), 2.56–2.43 (1 H, m, N(CH2)2N), 2.49 (1 H, d, J = 13.2
Calc. for C27H41Cl3N2O2Ti·(0.4C7H8): C, 58.04; H, 7.22; N, Hz, N(CH2)2N), 2.19 (3 H, s, ArCH3), 1.87 (1 H, d, J = 13.2 Hz,
2
2
4.54%); NMR spectroscopic data for cis-2a: δH (400 MHz, N(CH2)2N), 1.20 (3 H, s, N(CH3)2). δC (100 MHz, CDCl3) 159.0,
3
CDCl3) 7.44 (1 H, t, J = 7.6 Hz, ArH), 7.30 (1 H, s, ArH), 7.25 157.4, 135.2, 133.9, 133.2, 133.0, 131.0, 130.6, 130.3, 129.8,
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(1 H, d, J = 8.0 Hz, ArH), 7.06 (1 H, t, J = 7.6 Hz, ArH), 6.99 127.6, 127.4, 125.9, 125.6, 120.6, 120.5, 111.2 (all ArC), 63.6
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(1 H, d, J = 8.0 Hz, ArH), 6.78 (1 H, s, ArH), 5.48 (1 H, d, J = (CPh3), 61.8 (OCH3), 59.0 (N(CH2)2N), 57.5 (N(CH2)2N), 55.4
14.6 Hz, ArCH2N), 4.62 (1 H, d, 2J = 14.6 Hz, ArCH2N), 4.22 (ArCH2N), 55.1 (ArCH2N), 48.6 (N(CH3)2), 47.9 (N(CH3)2), 21.1
2
(1 H, d, J = 14.6 Hz, ArCH2N), 3.95–3.84 (1 H, m, N(CH2)2N), (ArCH3).
2
3.82 (3 H, s, OCH3), 3.62 (1 H, d, J = 14.6 Hz, ArCH2N), 3.12
Attempted synthesis of L6TiCl3 (6a). Complex 6a was syn-
(3 H, s, N(CH3)2), 2.88–2.77(1 H, m, N(CH2)2N), 2.62 (3 H, s, thesized in a similar manner to that described for 1a, using
N(CH3)2), 2.68–2.58 (1 H, m, N(CH2)2N), 2.28–2.21 (1 H, m, proligand L6H (0.899 g, 2.00 mmol), triethylamine (0.6 mL,
N(CH2)2N), 1.56 (9 H, s, C(CH3)3), 1.25 (9 H, s, C(CH3)3). 4 mmol), and TiCl4(THF)2 (0.644 g, 2.00 mmol) as starting
δC (100 MHz, CDCl3): 159.0, 157.3, 147.1, 137.0, 135.3, 130.7, materials. The product collected through crystallization, giving
129.3, 125.2, 123.8, 120.6, 120.4, 111.2 (all ArC), 61.8 (OCH3), 6a as red–orange powder (0.181 g, 15.0%). (Found: C, 44.32; H,
59.2 (N(CH2)2N), 57.6 (N(CH2)2N), 55.5 (ArCH2N), 55.1 5.37; N, 4.71. Calc. for C23H32BrCl3N2O2Ti: C, 45.84; H, 5.35;
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(ArCH2N), 51.1 (N(CH3)2), 48.6 (N(CH3)2), 35.3 (C(CH3)3), 34.7 N, 4.65%); δH (400 MHz, CDCl3) 7.48 (1 H, d, J = 2.0 Hz, ArH),
(C(CH3)3), 31.4 (C(CH3)3), 30.3 (C(CH3)3).
7.46–7.40 (1 H, m, ArH), 7.29–7.24 (1 H, m, ArH), 7.10–7.03
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L3TiCl3 (3a). Complex 3a was synthesized in a similar (1 H, m, ArH), 6.99 (1 H, d, J = 8.1 Hz, ArH), 6.88 (1 H, d, J =
manner to that described for 1a, using proligand L3H (1.102 g, 2.0 Hz, ArH), 5.44 (1 H, d, J = 14.5 Hz, ArCH2N), 4.70 (1 H, d,
2
2.000 mmol), triethylamine (0.6 mL, 4 mmol), and TiCl4(THF)2 2J = 14.8 Hz, ArCH2N), 4.21 (1 H, d, 2J = 14.5 Hz, ArCH2N),
(0.644 g, 2.00 mmol) as starting materials. After crystallization 3.95–3.75(2 H, m, N(CH2)2N), 3.82 (3 H, s, ArOCH3), 3.62 (1 H,
2
in toluene, pure cis-3a was obtained as red crystals (0.712 g, d, J = 14.8 Hz, ArCH2N), 3.12 (3 H, s, N(CH3)2), 2.63 (3 H, s,
50.6%). mp: 238.6–239.7 °C. (Found: C, 62.68; H, 6.56; N, 3.97. N(CH3)2), 2.65–2.58 (1 H, m, N(CH2)2N), 2.25–2.18 (1 H, m,
Calc. for C37H45Cl3N2O2Ti: C, 63.13; H, 6.44; N, 3.98%); NMR N(CH2)2N), 1.24 (9 H, s, Ar(CH3)3).
spectroscopic data for cis-3a: δH (400 MHz, CDCl3) 7.40 (1 H,
L7TiCl3 (7a). Complex 7a was synthesized in a similar
td, 3J = 8.1 Hz, 4J = 1.8 Hz, ArH), 7.34–7.28 (5 H, m, ArH), manner to that described for 1a, using proligand L7H (0.767 g,
7.24–7.16 (6 H, m, ArH), 7.09 (1 H, t, 3J = 7.3 Hz, ArH), 7.02 2.00 mmol), triethylamine (0.6 mL, 4 mmol), and TiCl4(THF)2
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(1 H, t, J = 7.3 Hz, ArH), 6.94 (1 H, d, J = 8.1 Hz, ArH), 6.77 (0.644 g, 2.00 mmol) as starting materials. Pure cis-7a was
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(1 H, d, J = 1.8 Hz, ArH), 5.34 (1 H, d, J = 14.6 Hz, ArCH2N), obtained as red–orange powder (0.642 g, 59.8%). mp:
2
2
4.57 (1 H, d, J = 14.6 Hz, ArCH2N), 4.11 (1 H, d, J = 14.6 Hz, 189.4–190.6 °C. (Found: C, 48.83; H, 5.18; N, 4.33. Calc. for
ArCH2N), 3.76 (3 H, s, OCH3), 3.70–3.59 (1 H, m, N(CH2)2N), C19H23Cl5N2O2Ti·(0.9C7H8): C, 49.05; H, 4.91; N, 4.52%); NMR
3.54 (1 H, d, 2J = 14.6 Hz, ArCH2N), 2.81 (3 H, s, N(CH3)2), spectroscopic data for cis-7a δH (400 MHz, CDCl3) 7.46–7.38
2.63–2.53 (1 H, m, N(CH2)2N), 2.49–2.41 (1 H, m, N(CH2)2N), (1 H, m, ArH), 7.33 (1 H, d, 3J = 2.2 Hz, ArH), 7.20 (1 H, dd, 3J =
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2.09 (3 H, s, N(CH3)2), 2.03–1.95 (1 H, m, N(CH2)2N), 1.67 (6 H, 7.4 Hz, J = 2.2 Hz, ArH), 7.03 (1 H, t, J = 7.4 Hz, ArH), 6.98
s, C(CH3)2Ph), 1.46 (3 H, s, C(CH3)2Ph), 1.40 (3 H, s, (1 H, d, J = 8.3 Hz, ArH), 6.90 (1 H, d, J = 2.2 Hz, ArH), 5.38
C(CH3)2Ph). δC (100 MHz, CDCl3) 158.9, 156.9, 150.0, 146.0, (1 H, d, 2J = 14.5 Hz, ArCH2N), 4.67 (1 H, d, 2J = 14.9 Hz,
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136.4, 135.4, 130.6, 129.4, 128.1, 127.9, 126.7, 126.6, 126.6, ArCH2N), 4.22 (1 H, d, J = 14.5 Hz, ArCH2N), 3.87–3.76 (1 H,
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m, N(CH2)2N), 3.82 (3 H, s, OCH3), 3.57 (1 H, d, J = 14.9 Hz, (11 H, m, ArH), 7.08 (1 H, t, 3J = 7.2 Hz, ArH), 6.80 (1 H, s,
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ArCH2N), 3.12 (3 H, s, N(CH3)2), 2.60 (3 H, s, N(CH3)2), ArH), 6.69 (1 H, s, ArH), 5.25 (1 H, d, J = 14.6 Hz, ArCH2N),
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2.68–2.51 (2 H, m, N(CH2)2N), 2.94–2.21 (1 H, m, N(CH2)2N). 4.57 (1 H, d, J = 14.6 Hz, ArCH2N), 4.23 (1 H, d, J = 14.6 Hz,
δC (100 MHz, CDCl3) 158.8, 154.3, 135.1, 131.1, 130.2, 129.4, ArCH2N), 3.75 (3 H, s, OCH3), 3.63–2.43 (1 H, m, N(CH2)2N),
128.6, 128.4, 122.1, 120.7, 120.1, 111.4 (all ArC), 60.1 (OCH3), 3.32 (1 H, d, 2J = 14.6 Hz, ArCH2N), 2.80 (3 H, s, N(CH3)2),
58.8 (N(CH2)2N), 57.7 (N(CH2)2N), 55.6 (ArCH2N), 55.5 2.53–2.42 (1 H, m, N(CH2)2N), 2.42–2.34 (1 H, m, N(CH2)2N),
(ArCH2N), 49.7 (N(CH3)2), 48.2 (N(CH3)2).
2.31 (3 H, s, N(CH3)2), 2.08 (3 H, s, ArCH3), 2.04–1.96 (1 H, m,
L8TiCl3 (8a). Complex 8a was synthesized in a similar N(CH2)2N), 1.67 (3 H, s, C(CH3)2Ph), 1.66 (3 H, s, C(CH3)2Ph),
manner to that described for 1a, using proligand L8H (0.944 g, 1.45 (3 H, s, C(CH3)2Ph), 1.38 (3 H, s. C(CH3)2Ph), 1.35 (9 H, s,
2.00 mmol), triethylamine (0.6 mL, 4 mmol), and TiCl4(THF)2 C(CH3)3). δC (100 MHz, CDCl3) 158.5, 157.0, 150.1, 150.0,
(0.644 g, 2.00 mmol) as starting materials. Pure cis-8a was 146.3, 143.7, 136.4, 133.5, 132.8, 129.7, 129.7, 128.2, 128.0,
obtained as red crystals (0.695 g, 55.6%). mp 186.9–187.8 °C. 126.8, 126.7, 126.6, 125.9, 125.7, 125.2 (all ArC), 63.3 (OCH3),
(Found: C, 37.16; H, 4.41; N, 3.80. Calc. for C19H23Br2Cl2N2O2- 61.6 (N(CH2)2N), 59.1 (N(CH2)2N), 58.4 (ArCH2N), 55.0
Ti·(0.1C7H8): C, 37.28; H, 3.78; N, 4.41%). NMR spectroscopic (ArCH2N), 48.5 (N(CH3)2), 48.0 (N(CH3)2), 43.0 (C(CH3)2Ph),
4
data for cis-8a: δH (400 MHz, CDCl3) 7.65 (1 H, d, J = 2.0 Hz, 42.4 (C(CH3)2Ph), 35.0 (C(CH3)3), 34.5 (C(CH3)2Ph), 31.1
3
ArH), 7.42 (1 H, t, J = 7.3 Hz, ArH), 7.22–7.17 (1 H, m, ArH), (C(CH3)3 and C(CH3)2Ph overlapped), 30.9 (C(CH3)2Ph), 26.0
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7.08 (1 H, d, J = 2.0 Hz, ArH), 7.03 (1 H, t, J = 7.3 Hz, ArH), (C(CH3)2Ph), 21.2 (ArCH3).
6.98 (1 H, d, 3J = 8.3 Hz, ArH), 5.37 (1 H, d, 2J = 14.5 Hz, L8ZrCl3 (8b). Complex 8b was synthesized in a similar
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ArCH2N), 4.69 (1 H, d, J = 14.5 Hz, ArCH2N), 4.23 (1 H, d, J = manner to that described for 1a, using proligand L8H (0.944 g,
14.5 Hz, ArCH2N), 3.80 (3 H, s, OCH3), 3.86–3.75 (1 H, m, 2.00 mmol), triethylamine (0.6 mL, 4 mmol), and ZrCl4(THF)2
N(CH2)2N), 3.57 (1 H, d, 2J = 14.5 Hz, ArCH2N), 3.12 (3 H, s, (0.750 g, 2.00 mmol) as starting materials. Pure cis-8b was
N(CH3)2), 2.61 (3 H, s, N(CH3)2), 2.68–2.52 (2 H, m, N(CH2)2N), obtained as colourless crystals (0.531 g, 42.5%). mp:
2.28–2.19 (1 H, m, N(CH2)2N). Due to the poor solubility of 234.3–235.6 °C. (Found: C, 36.50; H, 3.83; N, 3.69. Calc. for
complex 8a in CDCl3, the 13C NMR spectrum could not be C19H23Br2Cl3N2O2Zr·(0.3C7H8): C, 36.39; H, 3.68; N, 4.02%);
obtained.
NMR spectroscopic data for cis-8b: δH (400 MHz, CDCl3) 7.63
L9TiCl3 (9a). Complex 9a was synthesized in a similar (s, 1H, ArH), 7.50–7.37 (1 H, m, ArH), 7.31–7.12 (2 H, m, ArH),
manner to that described for 1a, using proligand L9H (0.910 g, 7.11–6.88 (2 H, m, ArH), 5.31 (1 H, d, J = 14.5 Hz, ArCH2N),
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2.00 mmol), triethylamine (0.6 mL, 4 mmol), and TiCl4(THF)2 4.62 (1 H, d, J = 14.5 Hz, ArCH2N), 4.27 (1 H, d, J = 14.5 Hz,
(0.644 g, 2.00 mmol) as starting materials. Red crystals were ArCH2N), 3.84 (3 H, s, OCH3), 3.92–3.72(1 H, m, N(CH2)2N),
isolated (0.518 g, 42.6%), which was characterized to be a 3.58 (1 H, d, 2J = 14.5 Hz, ArCH2N), 3.03 (3 H, s, N(CH3)2),
mixture of two isomers, the molar ratio of cis-9a/trans-9a = 2.70–2.59 (2 H, m, N(CH2)2N), 2.48 (3 H, s, N(CH3)2), 2.32–2.24
10 : 1. mp: 226.7–227.5 °C. (Found: C, 58.98 H, 7.62; N, 3.92. (1 H, m, N(CH2)2N). Due to the poor solubility of the complex
Calc. for C29H45Cl3N2O2Ti·(0.4C7H8): C, 59.24; H, 7.53; N, 8b in CDCl3, the 13C NMR spectrum could not be obtained.
4.34%); NMR spectroscopic data for cis-9a: δH (400 MHz,
L5Ti(OiPr)3 (5e). Ti(OiPr)4 (0.40 mL, 1.3 mmol) was added
CDCl3) 7.21 (1 H, s, ArH), 7.07 (1 H, s, ArH), 6.86 (1 H, s, ArH), dropwise via a syringe to the solution of proligand L5H
6.61 (1 H, s, ArH), 5.43 (1 H, d, 2J = 14.6 Hz, ArCH2N), 4.56 (0.520 g, 1.28 mmol) in 10 mL of dry toluene. The mixture was
(1 H, d, 2J = 14.6 Hz, ArCH2N), 4.27 (1 H, d, 2J = 14.6 Hz, stirred at room temperature for 3 h. Then all the volatiles were
ArCH2N), 3.84–3.73 (1 H, m, N(CH2)2N), 3.82 (3 H, s, OCH3), removed in vacuo, and the residue was re-dissolved in n-hexane
3.40 (1 H, d, 2J = 14.6 Hz, ArCH2N), 3.11 (3 H, s, N(CH3)2), (10 mL) and filtered. The pale yellow solution was concen-
2.72–2.61 (1 H, m, N(CH2)2N), 2.59–2.49 (1 H, m, N(CH2)2N), trated to 5 mL and kept at −20 °C. Complex 5e was isolated as
2.56 (3 H, s, N(CH3)2), 2.34 (3 H, s, ArCH3), 2.26 (3 H, s, colourless crystals (0.490 g, 60.9%). (Found: C, 60.93; H, 8.31;
ArCH3), 2.29–2.19 (1 H, m, N(CH2)2N), 1.55 (9 H, s, C(CH3)3), N, 4.45. Calc. for C32H53ClN2O5Ti: C, 61.09; H, 8.49; N, 4.45%);
3
1.36 (9 H, s, C(CH3)3). δC (100 MHz, CDCl3) 158.4, 157.8, 143.7, δH (CDCl3, 400 MHz) 7.44 (1 H, t, J = 8.0 Hz, ArH), 7.29 (2 H,
137.7, 134.0, 133.9, 132.7, 129.9, 129.7, 128.9, 127.6, 125.2 (all m, ArH), 7.09 (1 H, t, 3J = 7.4 Hz, ArH), 7.03 (1 H, d, 3J = 8.0 Hz,
ArC), 63.4 (OCH3), 61.2 (N(CH2)2N), 59.6 (N(CH2)2N), 58.4 ArH), 6.65 (1 H, s, ArH), 5.02 (4 H, br, ArCH2 and CH(CH3)2
(ArCH2N), 55.2 (ArCH2N), 50.6 (N(CH3)2), 47.9 (N(CH3)2), 35.1 overlapped), 4.28 (2 H, br, ArCH2), 3.88 (3 H, s, CH3OAr),
(C(CH3)3), 35.0 (C(CH3)3), 31.1 (C(CH3)3), 30.4 (C(CH3)3), 21.1 3.53–3.25 (2 H, br, NCH2CH2N and ArCH2 overlapped), 2.42
(ArCH3), 21.1 (ArCH3).
(9 H, br, N(CH3)2 and NCH2CH2N overlapped), 1.31 (18 H, br,
L10TiCl3 (10a). Complex 10a was synthesized in a similar CH(CH3)2), 1.26 (9 H, s, C(CH3)3). δC (CDCl3, 100 MHz) 159.3,
manner to that described for 1a, using proligand L10H 156.0, 138.1, 135.0, 129.5, 126.0, 125.3, 124.6, 122.8, 121.5,
(1.242 g, 2.00 mmol), triethylamine (0.6 mL, 4 mmol), and 120.1, 111.1 (all ArC), 59.1 (CH3O), 57.1 (ArCH2N), 55.3
TiCl4(THF)2 (0.644 g, 2.00 mmol) as starting materials. Pure (N(CH2)2N), 53.0 (N(CH3)2), 45.8 (N(CH3)2), 33.8 (C(CH3)3), 31.6
cis-10a was obtained as red–orange crystals (0.565 g, 36.5%). (C(CH3)3), 26.2 (CH(CH3)2).
mp: 271.2–273.0 °C. (Found: C, 64.89; H, 7.13; N, 3.62. Calc.
L6Ti(OiPr)3 (6e). Complex 6e was synthesized in a similar
for C42H55Cl3N2O2Ti: C, 65.16; H, 7.16; N, 3.62%); NMR spec- manner to that described for 5e, using proligand L6H (1.15 g,
troscopic data for cis-10a: δH (400 MHz, CDCl3) 7.34–7.12 2.56 mmol), and Ti(OiPr)4 (0.80 mL, 2.60 mmol) as starting
12674 | Dalton Trans., 2014, 43, 12663–12677
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materials. Pure 6e was obtained as colourless crystals (1.15 g, radiation (λ = 0.71073 Å) at 298 K. These structures were solved
62.3%). (Found: C, 56.76; H, 7.79; N, 4.25. Calc. for by direct methods, using Fourier techniques, and refined on
C32H53BrN2O5Ti: C, 57.06; H, 7.93; N, 4.16%); δH (CDCl3, F2 by a full-matrix least-squares method. All calculations were
3
4
400 MHz) 7.37 (2 H, br, ArH), 7.22 (1 H, dd, J = 7.4 Hz, J = performed using the SHELXTL program.104,105
3
4
1.6 Hz, ArH), 7.02 (1 H, td, J = 7.4 Hz, J = 0.9 Hz, ArH), 6.97
3
4
Ethylene polymerization
(1 H, d, J = 8.2 Hz, ArH), 6.62 (1 H, d, J = 2.5 Hz, ArH), 4.87
(4 H, br, ArCH2 and CH(CH3)2 overlapped), 4.20 (2 H, br,
ArCH2), 3.81 (3 H, s, CH3OAr), 3.33 (2 H, br, NCH2CH2N and
ArCH2 overlapped), 2.34 (9 H, br, N(CH3)2 and NCH2CH2N over-
lapped), 1.24 (18 H, br, CH(CH3)2), 1.19 (9 H, s, C(CH3)3).
δC (CDCl3, 100 MHz) 159.3, 156.8, 138.6, 135.0, 129.5, 129.0,
126.2, 124.4, 122.8, 120.1, 112.5, 111.1 (all ArC), 59.3 (CH3O),
57.1 (ArCH2N), 55.3 (N(CH2)2N), 53.0 (N(CH3)2), 45.8 (N(CH3)2),
33.8 (C(CH3)3), 31.6 (C(CH3)3), 26.3 (CH(CH3)2).
Toluene and MMAO (2.5 M in toluene) were introduced to a
thoroughly dried 50 mL steel autoclave equipped with a mag-
netic stirrer. The autoclave was placed in a bath at the desired
temperature for 10 min, and saturated with ethylene (1.5 atm).
The polymerization reaction was started by adding a toluene
solution of the desired catalyst precursor with a syringe to
bring the total volume of the solution to 25 mL. The vessel was
pressurized to 10 atm with ethylene immediately, and the
pressure was kept by continuous feeding of ethylene. The reac-
tion mixture was stirred at the desired temperature. After the
polymerization was carried for a certain time interval, the
reactor was cooled to room temperature and then the
polymerization reaction was quenched with 3% HCl in ethanol
(50 mL). The precipitated polymer was filtered, washed with
water and ethanol, and then dried overnight in a vacuum oven
at 60 °C to constant weight.
L7Ti(OiPr)3 (7e). Complex 7e was synthesized in a similar
manner to that described for 5e, using proligand L7H (0.490 g,
1.28 mmol), and Ti(OiPr)4 (0.40 mL, 1.3 mmol) as starting
materials. Pure 7e was obtained as colourless crystals (0.480 g,
62.3%). (Found: C, 55.31; H, 7.34; N, 4.62. Calc. for
C28H44Cl2N2O5Ti: C, 55.36; H, 7.30; N, 4.61%); δH (CDCl3,
400 MHz) 7.36 (1 H, t, 3J = 7.8 Hz, ArH), 7.16 (2 H, m, ArH),
6.97 (2 H, m, ArH), 6.63 (1 H, s, ArH), 5.23 (1 H, s, ArCH2),
4.84–4.94 (3 H, br, CH(CH3)2), 4.28 (1 H, d, 2J = 12.6 Hz,
ArCH2), 4.05 (1 H, d, 2J = 12.6 Hz, ArCH2), 3.80 (3 H, s,
CH3OAr), 3.38 (1 H, m, CH2CH2), 3.16 (1 H, d, 2J = 12.6 Hz,
ArCH2), 2.66 (3 H, s, N(CH3)2), 2.35 (2 H, m, NCH2CH2N), 2.12
(3 H, s, N(CH3)2), 1.93 (1 H, m, NCH2CH2N), 1.30–1.10 (18 H,
br, CH(CH3)2). δC (CDCl3, 100 MHz) 159.1, 157.4, 134.8, 129.7,
128.5, 128.1, 126.1, 123.0, 122.0, 120.1, 118.0, 110.9 (all ArC),
58.2 (CH3OAr), 56.9 (N(CH2)2N), 55.2 (CH(CH3)2), 52.9
(N(CH3)2), 45.7 (N(CH3)2), 26.2 (CH(CH3)2).
Notes and references
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ArH), 7.00–6.94 (2 H, m, ArH), 6.78 (1 H, d, J = 2.5 Hz, ArH),
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X-ray crystallography
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