Titanium complexes stabilized by bulky electron-rich aminopyridinates and their application in ethylene and styrene polymerization

Article abstract of DOI:10.1002/ejic.201100843

A series of electron-rich aminopyridines with high electron density at the N_pyridine atom (due to an electron-donating mesomeric effect) was prepared by the Ni⁰/2,2′-bipyridine-catalyzed arylation of anilines, followed by an uncataly

Full text of DOI:10.1002/ejic.201100843

FULL PAPER
DOI: 10.1002/ejic.201100843
Titanium Complexes Stabilized by Bulky Electron-Rich Aminopyridinates and
Their Application in Ethylene and Styrene Polymerization
Muhammad Hafeez,[a] Winfried P. Kretschmer,[a] and Rhett Kempe*[a]
Keywords: Polymerization / Titanium / Amido ligands / N ligands
A series of electron-rich aminopyridines with high electron
density at the Npyridine atom (due to an electron-donating
mesomeric effect) was prepared by the Ni0/2,2Ј-bipyridine-
catalyzed arylation of anilines, followed by an uncatalyzed
amination reaction. Reacting 2,6-dichloropyridine with
1 equiv. of aniline in the presence of the Ni0/2,2Ј-bipyridine
catalyst gave exclusively N-(6-chloropyridin-2-yl)aniline.
Subsequent reaction with secondary alkylamines provided
electron-rich aminopyridines in which the lone pair of the
RRЈN substituent participates in the molecular π-system.
These aminopyridines react with [Et2NTiCl3] (Et = ethyl) and
undergo amine elimination to form simultaneously the corre-
sponding aminopyridinate (Ap) ligand-stabilized titanium
trichlorides [ApTiCl3] and Ap (diethylamido)titanium dichlo-
rides [Ap(Et2N)TiCl2]. The reaction presumably proceeds via
the reaction of the initially formed [ApTiCl3] with 2 equiv.
of the prereleased diethylamine to give the [Ap(Et2N)TiCl2]
complexes and diethylammonium chloride. Alternative se-
lective synthetic routes for both sorts of complexes are also
presented. These compounds were characterized by spectro-
scopic methods and X-ray diffraction analysis (selected com-
plexes). Furthermore, their behavior in ethylene and styrene
polymerization reactions was explored. The complexes show
high activity towards ethylene if activated with d-MAO
(‘‘dry” methylaluminoxane) but were almost inactive if d-
MAO was replaced with conventional MAO. The observed
polyethylene (PE) product was analyzed by NMR spec-
troscopy and found to be fully saturated, indicating a chain
transfer reaction to aluminum had occurred. Styrene was
polymerized in a highly syndiospecific fashion.
recently used bulky versions of these ligands to stabilize ti-
tanium based polymerization catalysts.[8] These complexes
were found to be highly active in ethylene homo- and α-
olefin copolymerizations, and also showed a good response
towards cyclic olefins when activated with d-MAO, but
were almost inactive when MAO that contained free tri-
methylaluminum (TMA) was used instead. We suspected
that ligand transfer to aluminum, as observed earlier for Ap
ligands, might be responsible for this inactivity.[9] An in-
crease or decrease in the electron-donating ability of the Ap
ligand should significantly alter the rate of ligand transfer,
and may lead either to more or less stable catalysts with
regard to a transfer to Al.
Introduction
Ap complexes of the group 4 metals are promising alter-
natives to the widely used metallocenes of these metals for
application in homogeneous catalysis, and especially in po-
lymerization catalysis.[1–4] The aminopyridinato ligands
mostly show η2-coordination modes when coordinating
with early transition metals (Scheme 1, left) and are related
to amidinato ligands (Scheme 1, right).[5] The lower sym-
metry of the Ap ligands in comparison to the related species
provides a higher ligand coordination flexibility that can be
advantageous for stabilizing catalytic intermediates.[1–3]
To increase the electron-donation ability of aminopyrid-
inato ligands one could introduce an amine substituent in
6 position of the pyridine ring. For details of the electron-
donating mesomeric effect see Scheme 2. If the lone pair of
Scheme 1. Binding mode of aminopyridinato (left) and amidinato
(right) ligands ([M] = group 4 metal complex; R, RЈ = substituent).
Titanium Ap complexes have been a focus of research
during the last decade.[6] Most of the ligands reported so
far have rather small steric demands and ligand redistri-
bution has been observed frequently. The application of
bulky aminopyridinates[7] can solve this problem, and we
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Scheme 2. Mesomeric structures of 2,6-diaminopyridinato ligands
(R, RЈ, RЈЈ = alkyl substituents).
Fax: +49-921-552-157
E-mail: kempe@uni-bayreuth.de
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Titanium Complexes Stabilized by Aminopyridinates
the RRЈN-substituent participates in the molecular π-sys-
tem, the electron density at the pyridine nitrogen atom will
increase and the six-electron-donating 4σ,2π Ap ligand may
possibly become an eight-electron-donating 4σ,4π ligand.
Herein, we report the synthesis of such Ap ligands
(Scheme 3), the synthesis of titanium complexes based on
the corresponding aminopyridinato ligands, and the appli-
cation of selected titanium complexes in ethylene and sty-
rene polymerization reactions. To the best of our knowl-
edge, mono-Ap-titanium complexes have never been em-
ployed in the polymerization of styrene before.
Scheme 4. Synthesis of aminopyridine ligands, for an explanation
of labels 1a–3b refer to Scheme 3 (A: RЈ = isopropyl and RЈЈ = H;
B: RЈ, RЈЈ = methyl).
ylammonium chloride salts. In a NMR experiment, a nearly
one to one ratio of both types of titanium complexes is
observed. Reaction of [ApTiCl3] with 2 equiv. of dieth-
ylamine gave the exclusive formation of [Ap(Et2N)TiCl2].
Furthermore, the addition of 1 equiv. of triethylamine to
the amine elimination reaction could drive the reaction
towards the selective formation of II1a–II3b (Scheme 5).
Such behavior was not observed for the earlier reported
bulky aminopyridines[8] that yielded [Ap(Et2NH)TiCl3]
complexes instead.
Scheme 3. Aminopyridines 1a–3b.
Results and Discussion
Ligand Synthesis
The ligand precursors N-(2,6-diisopropylphenyl)-(6-chlo-
ropyridin-2-yl)amine (A) and N-(2,4,6-trimethylphenyl)-(6-
chloropyridin-2-yl)amine (B) were synthesized in about
45% isolated yield by the reaction of 2,6-dichloropyridine
with the respective aniline derivative catalyzed by a Ni0/
2,2Ј-bipyridine catalyst system – a modified version of the
synthesis method developed by Fort and co-workers.[10]
Subsequent transition metal free thermal amination reac-
tions[11] of A and B were carried out successfully with piper-
idine, morpholine and pyrrolidine in toluene at 160 °C in
pressure tubes. After separation of the ammonium chloride
salt by filtration and removal of all volatiles from the reac-
tion mixtures, the residues were recrystallized from ethanol
to provide the corresponding N-(2,6-diisopropylphenyl)-6-
(N heterocycle)pyridin-2-amines [N heterocycle: piperidine
(1a); morpholine (2a); pyrrolidine (3a)] and N-(2,4,6-tri-
methylphenyl)-6-(N heterocycle)pyridin-2-amines [N het-
erocycle: piperidine (1b); morpholine (2b); pyrrolidine (3b)]
in good yields (Scheme 4).
Scheme 5. Synthetic routes to [ApTiCl3] and [Ap(Et2N)TiCl2] com-
plexes.
Synthesis and Structure of the Complexes
The N-6-(dialkylamino)pyridin-2-amines 1a–3b reacted
The selective synthesis of the [ApTiCl3] complexes I1a–
with [Et2NTiCl3] (Et = ethyl) in a 1:1 ratio in n-hexane un- I3b were carried out by the treatment of the corresponding
der amine elimination to form simultaneously the corre- aminopyridines with 1 equiv. of TiCl4 and triethylamine in
sponding Ap titanium trichlorides I1a–I3b and Ap-dieth- dichloromethane (Scheme 5), also by the alternative reac-
ylamido-titanium dichlorides II1a–II3b (Scheme 5). These tion of the lithiated aminopyridines with 1 equiv. of TiCl4
reactions probably proceed via the reaction of the initially in toluene (Scheme 6). For less bulky Ap ligands (electron-
formed [ApTiCl3] with 2 equiv. of the prereleased dieth- poor) the latter synthetic route selectively yielded [Ap2-
ylamine to give the [Ap(Et2N)TiCl2] complexes and dieth- TiCl2].[6]
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M. Hafeez, W. P. Kretschmer, R. Kempe
FULL PAPER
Scheme 6. Synthesis of the Ap titanium trichloride I1a.
All complexes were characterized by NMR spectroscopy
and elemental analysis. Single crystal structure analysis was
carried out for selected complexes. Suitable crystals for X-
ray analysis were obtained by slowly cooling saturated n-
hexane solutions of the complexes to –24 °C. The molecular
structures of complexes I2b, II1a, II2a and II3a are pre-
sented in Figures 1, 2, 3, and 4, respectively. X-ray crystal
structure analysis details are given in Table 1. The coordina-
tion of all four complexes is best described as a distorted
trigonal bipyramid with a pyridine moiety in one of the
apical positions.
Figure 3. Molecular structure of II2a, hydrogen atoms are omitted
for clarity, selected bond lengths [Å] and bond angles [°]: C5–N1
1.356(6), C5–N2 1.3576(6), C1–N2 1.357(6), C1–N3 1.396(6), N2–
Ti1 2.365(4), N3–Ti1 1.928(4), N4–Ti1 1.862(4), average Cl–Ti1
2.270(2), N1–C5–N2 117.8(4), N2–C1–N3 109.2(4), N2–Ti1–N3
62.01(2), Cl1–Ti1–Cl2 119.73(6), ΣЄ(N1) 353.1.
Figure 1. Molecular structure of I2b, hydrogen atoms are omitted
for clarity, selected bond lengths [Å] and bond angles [°]: C5–N1
1.358(3), C5–N2 1.360(6), C1–N2 1.393(3), C1–N3 1.392(3), N2–
Ti1 2.232(4), N3–Ti1 1.893(2), average Cl–Ti1 2.239(1), N1–C5–N2
119.4(2), N2–C1–N3 107.8(2), N2–Ti1–N3 64.9(1), ΣЄ(N1) 357.5.
Figure 4. Molecular structure of II3a, hydrogen atoms are omitted
for clarity, selected bond lengths [Å] and bond angles [°]: C5–N1
1.343(5), C5–N2 1.356(5), C1–N2 1.360(4), C1–N3 1.387(5), N2–
Ti1 2.241(3), N3–Ti1 1.961(3), N4–Ti1 1.858(3), average Cl–Ti1
2.294(2), N1–C5–N2 120.1(3), N2–C1–N3 107.8(3), N2–Ti1–N3
63.37(11), Cl1–Ti1–Cl2 98.05(4), ΣЄ(N1) 360.0.
of the N1 atoms together with the short C5–N1 distances
clearly indicates that the lone pair of the N1 atoms partici-
pate in the π-systems of the ligands. Despite their high elec-
tron-donating ability the aminopyridinato ligands discussed
herein still coordinate in their amido pyridine form with
short Ti–Namido distances within the range of 1.89–1.96 Å,
and long Ti–Npyridine distances of 2.24–2.37 Å.[2]
In the 1H NMR spectra of I1a–II3b the proton reso-
nances for the 3 and 5 position of the pyridine ring appear
between 4.6 and 5.6 ppm (Figure 5). These signals are fur-
ther up field than usually observed for pyridine or aromatic
protons, but is typical for olefinic ones. The mesomeric en-
hancement increases the electron-donating ability of the li-
Figure 2. Molecular structure of II1a, hydrogen atoms are omitted
for clarity, selected bond lengths [Å] and bond angles [°]: C5–N1
1.369(6), C5–N2 1.349(5), C1–N2 1.380(6), C1–N3 1.401(5), N2–
Ti1 2.342(4), N3–Ti1 1.931(4), N4–Ti1 1.864(4), average Cl–Ti1
2.284(2), N1–C5–N2 118.7(4), N2–C1–N3 108.2(4), N2–Ti1–N3
62.78(14), Cl1–Ti1–Cl2 122.66(7), ΣЄ(N1) 358.6.
The C5–N1 bond lengths of all four complexes are be- gand but weakens the ring current of the pyridine ring. The
tween 1.34–1.37 Å and are clearly shorter than expected for increased bond order for the C5–N1 bonds were also con-
a Csp2–Nsp3 (pyramidal) single bond (ca. 1.416 Å).[12] The firmed by low-temperature experiments that show coalesc-
calculated sums of all angles around the N1 atoms in these ence of the proton resonances of the piperidine, morpholine
complexes were between 353–360° confirming that these ni- and pyrrolidine rings at temperatures between –50 and
trogen atoms have an almost planar environment, which is –40 °C, which is a result of the increase in the rotation bar-
typical for an sp2-hybridized N atom. The sp2 hybridization riers.
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Titanium Complexes Stabilized by Aminopyridinates
Table 1. Crystallographic data for the compounds that were investigated by single crystal X-ray structure analysis.
Compound
I2b
II1a
II2a
II3a
III1a
Formula
C18H22Cl3N3OTi
450.50
monoclinic
P21/c
10.8790(6)
16.7640(6)
22.7520(7)
90
90.245(2)
90
4149.4(3)
8
0.55ϫ0.33ϫ0.25
block
C26H40Cl2N4Ti
527.42
C25H38Cl2N4OTi
529.39
C25H38Cl2N4Ti
513.39
monoclinic
P21/c
8.6580(5)
19.0580(11)
16.5830(9)
90
104.578(4)
90
2648.2(3)
4
0.41ϫ0.37ϫ0.21
plate
C24H36AlN3
393.54
monoclinic
P21/n
9.9850(7)
14.387(11)
16.428(11)
90
101.556(6)
90
2312.1(3)
4
0.38ϫ0.35ϫ0.28
block
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
triclinic
triclinic
¯
¯
P1
P1
8.454(5)
9.986(5)
16.898(5)
88.275(5)
83.266(5)
76.726(5)
1378.9(11)
2
9.7200(6)
10.0500(6)
16.7120(10)
103.060(5)
92.726(5)
117.817(4)
1384.17(16)
2
α [°]
β [°]
γ [°]
Cell volume [Å3]
Z
Crystal size [mm3]
Habit
0.30ϫ0.17ϫ0.16
prism
0.34ϫ0.33ϫ0.24
block
Colour
red
1.443
133(2)
orange
1.270
133(2)
red
1.270
133(2)
red
1.288
133(2)
colourless
1.131
133(2)
Density [gcm–3]
T [K]
Theta range
Unique reflections
Observed reflections [I Ͼ 2σI] 6203
1.51–25.62
7828
1.21–25.69
5202
2814
1.27–25.65
5221
3169
1.27–25.53
5001
2931
1.90–25.75
4378
3020
Parameters
wR2(all data)
R value [I Ͼ 2σ(I)]
475
0.109
0.039
298
0.123
0.070
304
0.203
0.074
295
0.131
0.053
255
0.107
0.048
Figure 5. Molecular structure of III1a, hydrogen atoms are omitted
for clarity, selected bond lengths [Å] and bond angles [°]: C5–N1
1.363(3), C5–N2 1.356(2), C1–N2 1.378(2), C1–N3 1.354(2), N2–
Al1 1.985(2), N3–Al1 1.901(2), average Al1–C 1.956(2), N1–C5–
N2 118.45(17), N2–C1–N3 108.09(16), N2–Al1–N3 69.35(7), C23–
Al1–C24 121.76(9), ΣЄ(N1) 359.6.
Scheme 7. Synthesis of III1a and ligand transfer reaction.
Olefin Polymerization and the Formation of ApAl
Complexes
amount III1a. We believe that this fast ligand transfer is the
Despite their enhanced electron-donating ability and the result of the intermediary formation of a hetero-bimetallic
increased stabilization of their electron-deficient metal cen- species (Scheme 7). Due to the extra amine function in 6
ters, the new complexes were found to be sensitive towards the position, not only is the electron-donating ability of the
trialkylaluminum compounds. When the complexes I1a– aminopyridinato ligand increased but also its tendency to
II3b were activated with commercial MAO almost no ethyl- form binuclear complexes, as is known for the dianionic
ene polymerization activity was observed. This is presum- 2,6-diaminopyridines analogues.[13] We independently syn-
ably due to the fast ligand transfer from titanium to alumi- thesized the Ap-containing dimethylaluminum complex
num.[9]
III1a by reacting the aminopyridine 1a with 1 equiv. of
To gain more insight into this behavior, we studied the TMA in toluene (Scheme 7). Removal of all volatiles from
stability of these complexes with respect to TMA in NMR the reaction mixture under reduced pressure gives the spec-
tube experiments. The NMR tubes were charged with troscopically pure product as a colorless solid. Crystalli-
40 μmol of I1a or II1a in 0.5 mL of deuterated benzene zation could be accomplished by very slow cooling of satu-
before 40 equiv. of TMA (160 μmol) was added to each rated warmed hexane solution of the product. The crystal
tube. The titanium complexes react fast with TMA forming structure of III1a is presented in Figure 5. Experimental de-
their corresponding methyl complexes, which after a short tails of the X-ray diffraction analysis can be found in
period decompose with the release of an NMR detectable Table 1.
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M. Hafeez, W. P. Kretschmer, R. Kempe
FULL PAPER
The structure of the complex III1a is mononuclear and place. This idea was supported by the observation that the
the Ap ligand is in a strained η2 coordination mode. η2- catalysts were active for only a few minutes, and the multi-
Coordinated Ap-aluminum complexes are still rare[14] and modality of the polymers suggested the existence of several
the first examples were published by Wang and co- active species in reaction solution. It is notable that the
workers.[15] Treatment of III1a (40 μmol in 0.5 mL of C6D6) average molecular weight of the polymers is quite high de-
with 2, 5, 10, 20, 40 and 100 equivalents of TMA revealed spite of the presence of low molecular weight PE material.
the existence of a second binuclear ApAl2 species in solu- The NMR investigation of the low molecular weight mate-
tion (Figure 6, Scheme 8). After the addition of 5 equiv. of rial revealed that all polymer chains are fully saturated, and
TMA to a III1a solution, the resonances of a new Al com- no olefinic proton resonances could be observed in the
plex (IV1a) become visible in the NMR spectrum of the spectra (Figure 7.). Such material could only emerge if the
solution, and after the addition of 100 equiv. of TMA this polymers were terminated with a metal, for example alumi-
seems to be the only Ap-containing species present. The num, before they were hydrolyzed by acidified ethanol. In
new complex shows three Al-CH3 resonances at –0.5 ppm comparison to the titanium complexes containing very
with an intensity ratio of 2:2:1. As a result of the Al coordi- bulky (classic) aminopyridinates,[8] we can say that the new
nation to N1, the piperidyl fragment stops rotating around catalysts produce PE with much higher molecular weights.
the C5–N1 bond; this is evidenced by the appearance of 10
Table 2. Details of the ethylene polymerizations.[a]
resonances in the NMR spectrum of the solution that can
be assigned to the now diastereotopic protons of the hetero- Entry Precat.[a]
cycle. Most likely, such a hetero-binuclear species will also
T
mPol.
Activity
Mw
Mw/Mn
[°C] [g] [kgPE molcat–1 h–1
]
[kg mol–1
]
be formed when [ApTiCl3] complexes are reacted with an
excess of TMA, allowing fast Ap ligand transfer from tita-
nium to aluminum to take place.
1
2
3
4
5
6
II1a
II1b
II2a
II2b
II3a
II3b
80 0.27
80 0.19
80 0.31
80 0.15
80 0.14
80 0.12
540
380
620
296
280
180
1275
729
482
1323
–
12.1
12.8
11.6
11.1
–
206
7.2
[a] Precatalyst: 2.0 μmol; d-MAO: 1.0 mmol; toluene: 150 mL; p =
2 bar; t = 15 min.
Figure 6. 1H NMR spectra (C6D6, 26 °C) of pure III1a, III1a with
40 equiv. TMA, and III1a with 100 equiv. TMA.
Figure 7. 1H NMR spectrum (C2Cl4D2, 120 °C) of PE obtained
with the II1a/d-MAO catalyst system. The spectrum was recorded
after acidic workup of the reaction mixture.
Scheme 8. Formation of the bimetallic aluminum complex IV1a.
Due to the promising results of amidinate titanium com-
Due to the sensitivity of the new titanium complexes to plexes[17,18] in syndiospecific styrene polymerization reac-
TMA, we switched the co-catalyst to dry methylalumin- tions, we became interested in the polymerization of this
oxane (d-MAO). When all the volatiles from the commer- monomer when catalyzed by the novel titanium compounds
cially bought MAO are removed, most of the free TMA described herein. The polymerization of styrene (2.0 mL) in
will also be removed. After activation of complexes II1a– toluene (10.0 mL) was carried out in sealed glass bottles
II3b with d-MAO, high polymerization activities[16] towards in a glove box. Subsequently, d-MAO (1.0 mmol) and the
ethylene were observed (Table 2). The complexes with the catalyst (2.0 μmol) were added, and the solution was stirred
more sterically demanding Ap ligands were found to be and heated to the desired temperature and kept at that tem-
more active. Despite the fact that the TMA content in the perature for for 90 min. The polystyrene (PS) product from
d-MAO is quite low, ligand transfer may still be taking each run was refluxed in acetone. The insoluble fraction
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Titanium Complexes Stabilized by Aminopyridinates
(more than 95%) was separated from solution and dried at
80 °C. The results from these experiments are presented in
Table 3.
Table 3. Details of the styrene polymerizations.[a]
Entry
Precat.[a]
T
mPol.
Activity
Mw
Mw/Mn
[°C] [g] [kgPS molcat–1 h–1
]
[gmol–1
]
9
II1a
30 0.02
60 0.04
90 0.06
30 0.01
60 0.02
90 0.05
30 0.03
60 0.06
90 0.12
30 0.01
60 0.02
90 0.05
30 0.02
60 0.03
90 0.04
30 0.01
60 0.02
90 0.03
30
40
110
26
42
100
66
110
240
20
40
90
36
52
76
24
32
46
310000
141000
57800
349500
137800
72700
94300
101700
68800
436300
109900
66100
235300
2046400
68200
1136600
300600
49500
19.0
11.3
4.2
18.0
9.0
3.6
1.5
1.6
2.2
11.2
6.4
3.7
129.5
18.2
2.0
27.5
25.6
4.0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
II1b
II2a
II2b
II3a
II3b
[a] Precatalyst: 2.0 μmol; d-MAO: 1.0 mmol; toluene: 10 mL; sty-
rene: 2.0 mL; t = 90 min.
The activity of all complexes increases as a function of
temperature, with maxima observed at 90 °C. As already
observed in the ethylene polymerization runs, complexes
containing sterically more demanding Ap ligands are more
active. The differences in catalytic activity of the complexes
are not as pronounced in styrene polymerizations as they
were in the ethylene polymerizations. The molecular weights
of the obtained polymers are quite high. However, the high
polydispersities of the polymers suggest that once again
more than one active species is formed during the reaction.
Figure 8. 1H (above) and 13C (below) NMR spectra (C2Cl4D2,
80 °C) of PS obtained with the II1a/d-MAO catalyst system.
of the titanium complexes confirm the increased electron-
donating ability of the novel Ap ligands, but did not show
a stronger coordination of these modified ligands to the
metal center. The ligands are sensitive to ligand exchange
reactions with TMA. Fourthly, the complexes described
herein are active in ethylene and styrene polymerizations.
Highly syndiotactic PS was produced. In the case of ethyl-
ene polymerization, high activities were observed and alu-
minum terminated PE for the low molecular weight prod-
ucts.
1
The tacticity of PS was studied by H and 13C NMR spec-
troscopy. The NMR spectra were collected at 80 °C and the
samples were prepared by dissolving 20 mg of the polymer
in deuterated tetrachloroethane. Selected spectra are pre-
sented in Figure 8. The proton spectrum shows typical reso-
nances[19] for syndiotactic PS with some traces of atactic
material, while the 13C spectrum only shows two singlet res-
onances corresponding to the methylene and methine car-
bon atoms, which indicates that the PS is a highly syndio-
tactic material.
Experimental Section
Conclusions
Synthesis and Structure Analysis: All manipulations were per-
formed with the rigorous exclusion of oxygen and moisture from
the systems by use of Schlenk type glassware on a dual manifold
Schlenk line, or in an argon filled glove box (Braun 120-G) fitted
with a high capacity recirculator (Ͻ 0.1 ppm O2). Nonhalogenated
solvents were dried by distillation with a sodium wire/benzophe-
none system. 2,6-Dichloropyridine, 2,2Ј-bipyridine, piperidine were
purchased from AlfaAesar. Nickel acetate and tert-amyl alcohol
were purchased from Acros. Morpholine, pyrrolidine and styrene
were purchased from Sigma Aldrich. The titanium precursor
(Et2NTiCl3) was synthesized by a method reported in the litera-
From the present study a series of conclusions can be
drawn; firstly, the novel 6-(N-heterocycle)-substituted ami-
nopyridines can be synthesized (with a large degree of vari-
ety) by Ni-catalyzed aryl aminations followed by thermal
amination reactions. Secondly, mono Ap titanium trichlo-
ride complexes can be synthesized by the reaction of
[TiCl4]/Et3N with the corresponding aminopyridine. Mixed
amido Ap complexes are selectively accessible by amine eli-
mination reactions involving [Et2NTiCl3], the aminopyr-
idine, and 1 equiv. of triethylamine. Thirdly, the structures ture.[20] Deuterated solvents were obtained from Cambridge Iso-
Eur. J. Inorg. Chem. 2011, 5512–5522
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M. Hafeez, W. P. Kretschmer, R. Kempe
FULL PAPER
tope Laboratories and were degassed, dried, and distilled prior to
use. NMR spectra were recorded with a 400 MHz Varian ARX, or
with a 300 MHz Varian ARX, and chemical shifts are reported in
ppm relative to the deuterated solvent. Elemental analyses (CHN)
were carried out with a Vario EL III instrument. d-MAO was pre-
pared by removal of volatiles from PMAO (4.9 wt.-% in Al). The
polymer samples for NMR spectroscopic measurements were pre-
pared by dissolving 15 mg of the polymer in 0.5 mL of C2D2Cl4
for 3 h at 100 °C before measurements were made. Gel permeation
chromatography (GPC) analysis was carried out on a PL-GPC 220
(Agilent, Polymer Laboratories) high temperature chromatographic
unit equipped with DP and RI detectors and two linear mixed bed
columns (Olexis, 13-micron particle size). GPC analysis were per-
formed at 150 °C and with 1,2,4-trichlorobenzene as the mobile
phase. The samples were prepared by dissolving the polymer (0.05
wt.-%, c = 1 mg/mL) in the mobile phase solvent in an external
oven, and the solutions were run without filtration. The molecular
weights of the samples were referenced to PE (Mw = 520–
3200000 gmol–1) and PS (Mw = 580–2800000 gmol–1) standards.
The reported values are the average of at least two independent
determinations. X-ray crystal structure analyses were carried out
with a STOE IPDS II diffractometer equipped with an Oxford
Cryostream low temperature unit. Structure solution and refine-
ment were accomplished with SIR97,[21] SHELXL-97[22] and
WinGX.[23] Selected details of the X-ray crystal structure analyses
are listed in Table 1.
ture for 90.0 min. The polymerization reaction was quenched by
the addition of ethanol (10.0 mL) acidified with HCl. The resultant
polymers were washed with ethanol and the atactic fraction of each
polymer was removed by heating the polymer sample in acetone at
60 °C for 2 h. The insoluble syndiotactic fraction was separated for
the mixture, and dried first at room temperature and then in an
oven at 80 °C for 12 h.
Synthesis of the Ligand Precursors
N-(2,6-Diisopropylphenyl)-(6-chloropyridin-2-yl)amine (A): 2,6-Di-
isopropylaniline (5.31 g, 5.70 mL, 30. 0 mmol) and tert-amyl
alcohol (0.352 g, 0.45 mL, 4.0 mmol) in THF (20.0 mL) were added
to a THF suspension of NaH (0.624 g, 26.0 mmol). The resulting
mixture was heated at 65 °C for 2 h and then cooled. 2,2-Bipyridyl
(0.94 g, 6.0 mmol) was added to the cool mixture followed by dried
Ni(OAc)2 (0.352 g, 2.0 mmol). The reaction mixture was heated for
a further 2 h then cooled. To the cool mixture 2,6-dichloropyridine
(2.96 g, 20.0 mmol) was added, and the reaction mixture was re-
fluxed for 2 h. After cooling, water (2.0 mL) and dichloromethane
(100.0 mL) were added to the mixture. The reaction mixture was
filtered through sodium sulfate and the volatiles were removed from
the filtrate. The resultant yellow oil was purified by silica gel col-
umn chromatography and recrystallized from n-hexane; yield 2.30 g
(40%). C17H21N2Cl (288.62): calcd. C 70.68, H 7.33, N 9.70; found
CCDC-838187 (for I2b), -838188 (for II1a), -838189 (for II2a),
-838190 (for II3a) and -838191 (for III1a) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
1
C 70.67, H 6.85, N 9.48. H NMR (C6D6, 298 K): δ = 1.04 (d, 12
H, H14,15,17,18), 3.16 (sept, 2 H, H13,16), 5.61 (d, 1 H, 1 H3), 6.33
(d, 1 H, H5), 6.62 (t, 1 H, H4), 6.91 (br. s, 1 H, NH), 7.01–7.21 (m,
3 H, H9,10,11) ppm. 13C NMR (C6D6, 298 K): δ = 23.73 (C14,15,17,18),
28.67 (C13,16), 103.76 (C3), 112.02 (C5), 124.22 (C9,11), 128.63 (C10),
133.71(C7), 135.12 (C8,12), 140.50 (C4), 148.18 (C2), 160.49 (C6)
ppm.
General Description of Ethylene Polymerization Experiments Per-
formed with d-MAO: The catalytic ethylene polymerization reac-
tions were performed in a 250 mL glass autoclave (Buechi) in semi-
batch mode (ethylene was added by replenishing the flow to keep
the pressure constant). The reactor was temperature and pressure
controlled and equipped with separated toluene, catalyst, and co-
catalyst injection systems. During a polymerization run the pres-
sure, the ethylene flow, the inner and the outer reactor temperature,
and the stirrer speed were monitored continuously. In a typical
semi-batch experiment, the autoclave was evacuated and heated for
1 h at 80 °C prior to use. The reactor was then brought to the
desired temperature, stirred at 1000 rpm and charged with 150 mL
of toluene together with d-MAO (54 mg, 1 mmol), unless men-
tioned different in the following text. After pressurizing with ethyl-
ene to reach 2 bar total pressure, the autoclave was equilibrated
for 5 min. Subsequently, 0.002 m catalyst stock solution in toluene
(1 mL) was injected into the autoclave to start the reaction. During
the run the ethylene pressure was kept constant to within 0.1 bar
of the initial pressure by replenishing the gas flow. After a 15 min
reaction time the reactor was vented and the residual aluminum
alkyls were destroyed by addition of 50 mL of ethanol to the reac-
tor. The polymeric product was collected, stirred for 30 min in
acidified ethanol, and rinsed with ethanol and acetone on a glass
frit. The polymer was initially dried in air and then in vacuo at
80 °C.
N-(2,4,6-Trimethylphenyl)-(6-chloropyridin-2-yl)amine (B): 2,4,6-
Trimethylaniline (4.05 g, 4.20 mL, 30.0 mmol) and tert-amyl
alcohol (0.352 g, 0.45 mL, 4.0 mmol) in THF (20.0 mL) were added
to a THF suspension of NaH (0.624 g, 26 mmol). The resulting
mixture was heated at 65 °C for 2 h then cooled. 2,2-Bipyridyl
(0.94 g, 6.0 mmol) was added to the cool mixture followed by dried
Ni(OAc)2 (0.35 g, 2.0 mmol). The reaction mixture was heated for
a further 2 h then cooled. To the cool mixture 2,6-dichloropyridine
(2.96 g, 20.0 mmol) was added, and the reaction mixture was re-
fluxed for 2 h. After cooling, water (2.0 mL) and dichloromethane
(120.0 mL) were added to the mixture. The reaction mixture was
filtered through sodium sulfate and volatiles were removed from
the filtrate. The resultant yellow oil was purified by silica gel col-
umn chromatography with dichloromethane as the eluent. Volatiles
were removed under vacuum and the product was recrystallized
from n-hexane at –24 °C; yield 2.0 g (41%). C14H15N2Cl (246.73):
calcd. C 68.13, H 6.13, N 11.36; found C 67.77, H 5.98, N 10.95.
1H NMR (400 MHz, C6D6, 298 K): δ = 2.02 (s, 6 H, H13,14), 2.15
(s, 3 H, H15), 5.61 (d, 1 H, H3), 6.15 (br. s, 1 H, NH), 6.33 (d, 1
H, H5), 6.65 (t, 1 H, H4), 6.73 (s, 2 H, H9,11) ppm. 13C NMR
Styrene Polymerizations: Styrene polymerizations were performed
in sealed glass bottles in a glove box. Styrene (2.0 mL) and d-MAO
(1 mmol) were added to a glass bottle containing toluene (7.0 mL).
The mixture was stirred for 10 min followed by the addition of
2.0 μmol of the desired catalyst. The temperature of the solution
was raised to 30 °C, 60 °C or 90 °C and then kept at this tempera-
5518
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 5512–5522

Titanium Complexes Stabilized by Aminopyridinates
(100 MHz, C6D6, 298 K): δ = 17.60 (C13,14), 20.38 (C15), 102.69
(C3), 111.65 (C5), 128.92 (C9,11), 135.36 (C10), 136.41 (C8,12), 139.13
(C7), 139.61 (C4), 149.51 (C2), 158.51 (C6) ppm.
(C14,15,17,18), 25.60 (C21,23), 28.72 (C13,16), 47.88 (C20,24), 86.64 (C3),
106.69 (C5), 124.07 (C9,11), 129.19 (C10), 141.22 (C8,12), 141.89 (C4),
150.35 (C7), 153.03 (C2), 157.48 (C6) ppm.
Synthesis of Ligands and Complexes
Synthesis of the Aluminum Complex III1a: Ligand 1a (0.337 g,
1.0 mmol) was dissolved in toluene (10.0 mL) before Me3Al (0.14 g,
2.0 mmol) was added. The solution was stirred at room tempera-
ture for 15 min, after which time all volatiles were removed under
reduced pressure. The remaining white solid was dissolved in boil-
ing hexane (10.0 mL), which was then slowly cooled to room tem-
perature over a period of 2 d. Colorless crystals were separated
from solution and dried in vacuo; yield 0.30 g (76%). C24H36AlN3
(393.54): calcd. C 73.25, H 9.22, N 10.68; found C 72.91, H 9.20,
N 10.70. 1H NMR (400 MHz, C6D6, 298 K): δ = –0.11 (s, 6 H,
HCH3-Al), 1.07–1.23 (m, 7 H, H14,15,17,18,21,22,23), 1.25–1.27 (d, 12 H,
H14,15,17,18), 2.97 (m, 4 H, H20,24), 3.55 (sept, 2 H, H13,16), 5.18 (d,
1 H, H3), 5.27 (d, 1 H, H5), 6.88 (t, 1 H, H4), 7.15 27 (t, 1 H, H10),
7.22 (d, 2 H, H9,11) ppm. 13C NMR (100 MHz, C6D6, 298 K): δ =
–8.76 (CCH3-Al), 24.22 (C14,15,17,18), 24.56 (C14,15,17,18), 24.83 (C22),
25.26 (C21,23), 28.40 (C13,16), 46.84 (C20,24), 92.46 (C3), 92.85 (C5),
124.13 (C9,11), 126.11 (C10), 143.06 (C8,12), 143.15 (C4), 146.15 (C7),
155.97 (C2), 165.99 (C6) ppm.
N-(2,6-Diisopropylphenyl)-6-(piperidin-1-yl)pyridin-2-amine (1a): Li-
gand precursor (6-chloropyridin-2-yl)-(2,6-diisopropylphenyl)-
amine (1.44 g, 5.0 mmol) and piperidine (0.85 g, 1.0 mL,
10.0 mmol) in toluene (10 mL) were heated for 3 d at 170 °C in a
pressure tube. The solution was filtered and volatiles were removed
under vacuum. The yellow oil thus obtained was purified by silica
gel column chromatography. After removing the volatiles the yellow
oil was then recrystallized from n-pentane at –80 °C; yield 1.5 g
(89%). C22H31N3 (337.25): calcd. C 78.28, H 9.26, N 12.46; found
1
C 77.93, H 9.79, N 12.16. H NMR (400 MHz, C6D6, 298 K): δ =
1.04 (d, 12 H, H14,15,17,18), 1.36 (m, 6 H, H21,22,23), 3.30 (sept, 2 H,
H13,16), 3.37 (t, 4 H, H20,24), 5.48 (d, 1 H, H3), 5.80 (d, 1 H, H5),
7.10 (t, 1 H, H4), 7.12–7.20 (m, 3 H, H9,10,11) ppm. 13C NMR
(100 MHz, C6D6, 298 K): δ = 23.30 (C14,15,17,18), 24.81 (C22), 25.62
(C21,23), 28.67 (C13,16), 45.63 (C20,24), 95.21 (C3), 96.24 (C5), 124.03
(C9,11), 128.20 (C10), 134.40 (C7), 139.15 (C4), 148.13 (C8,12), 158.89
(C2), 159.34 (C6) ppm.
N-(2,4,6-Trimethylphenyl)-6-(piperidin-1-yl)pyridin-2-amine
(1b):
Synthesis of the Dichloride II1a: Ligand 1a (0.337 g, 1.0 mmol) was
dissolved in n-hexane (15.0 mL). The ligand solution was added to
a light green n-hexane (15 mL) solution of (Et2N)TiCl3 (0.226 g,
1.0 mmol) at room temperature. The solution’s color changed from
light green to dark red. The resulting solution was stirred over-
night. The solution was filtered and the filtrate volume was re-
duced, and the product was crystallized from the solution at
–24 °C; yield 0.240 g (45%). C26H40Cl2N4Ti (527.10): calcd. C
Ligand precursor 6-chloro-N-mesitylpyridin-2-amine (1.23 g,
5.0 mmol) and piperidine (0.86 g, 1.0 mL, 10.0 mmol) in toluene
(10.0 mL) were heated for 3 d at 160 °C in a pressure tube. The
solution was filtered and volatiles were removed under vacuum.
The yellow oil thus obtained was purified by silica gel chromatog-
raphy with dichloromethane as the eluant. The volatiles were re-
moved under vacuum, and resultant yellow oil was recrystallized
from n-pentane at –80 °C; yield 1.30 g (88%). C19H25N3 (295.20):
calcd. C 77.23, H 8.53, N 14.23; found C 77.12, H 8.48, N 14.01.
1H NMR (400 MHz, C6D6, 298 K): δ = 1.30–1.40 (m, 6 H,
H18,19,20), 2.14 (s, 3 H, H15), 2.23 (s, 6 H, H13,14), 3.44 (t, 4 H,
H17,21), 5.47 (d, 1 H, H3), 5.61 (br. s, 1 H, NH), 5.93 (d, 1 H, H5),
6.79 (s, 2 H, H9,11), 7.03 (t, 1 H, H4) ppm. 13C NMR (100 MHz,
C6D6, 298 K): δ = 18.10 (C13,14), 20.64 (C15), 24.85 (C19), 25.53
(C18,20), 45.82 (C17,21), 93.61 (C3), 96.23 (C5), 129.03 (C9,11), 134.93
(C7), 135.32 (C10), 136.39 (C8,12), 138.91 (C4), 157.08 (C2), 159.17
(C6) ppm.
1
59.19, H 7.65, N 10.63; found C 59.67, H 7.40, N 10.17. H NMR
(400 MHz, C6D6, 298 K): δ = 0.79 (t, 6 H, HCH3–CH2–N–), 1.02–
1.20 (m, 12 H, H14,15,17,18,21,22,23), 1.39 (d, 6 H, H14,15,17,18), 3.33 (t,
4 H, H20,24), 3.46 (sept, 2 H, H13,16), 4.05 (q, 4 H, HCH3–CH2–N–),
4.87 (d, 1 H, H3), 5.66 (d, 1 H, H5), 6.80 (t, 1 H, H4), 7.14–7.27
(m, 3 H, H9,10,11) ppm. 13C NMR (100 MHz, C6D6, 298 K): δ =
12.23 (CCH3–CH2–N–), 24.40 (C14,15,17,18), 24.75 (C14,15,17,18), 25.53
(C22), 25.75 (C21,23), 28.20 (C13,16), 42.31 (CCH3–CH2–N–), 47.13
(C20,24), 101.47 (C3), 106.33 (C5), 123.70 (C9,11), 128.10 (C10),
140.74 (C8,12), 142.73 (C4), 147.88 (C7), 155.38 (C2), 158.55 (C6)
ppm.
Synthesis of the Dichloride II1b: Ligand 1b (0.148 g, 0.5 mmol) was
dissolved in n-hexane (10.0 mL). The ligand solution was added
drop wise to a light green n-hexane (10 mL) solution of (Et2N)-
TiCl3 (0.113 g, 0.5 mmol) at room temperature. The color of the
solution changed from light green to dark red. The resulting solu-
tion was stirred overnight. The solution was filtered, and the filtrate
volume was reduced, and the product was crystallized from the
solution at –24 °C; yield 0.215 g (47%). C23H34Cl2N4Ti (485.32):
calcd. C 56.90, H 7.06, N 11.55; found C 56.62, H 6.90, N 11.42.
1H NMR (400 MHz, C6D6, 298 K): δ = 0.80 (t, 6 H, HCH3–CH2–N–),
1.10–1.25 (m, 6 H, H18,19,20), 2.14 (s, 3 H, H15), 2.24 (s, 6 H, H13,14),
Synthesis of the Trichloride I1a: Ligand 1a (0.337 g, 1.0 mmol) was
dissolved in toluene (15.0 mL). nBuLi (0.625 mL, 1.0 mmol) was
added drop wise to the ligand solution at 0 °C, which was stirred
at room temperature for 2 h. The resultant mixture was added drop
wise to a toluene (15.0 mL) solution of titanium tetrachloride
(0.189 g, 1.0 mmol) at 0 °C. The resultant dark red solution was
stirred overnight. The solution was filtered, and the solution vol-
ume was reduced to 10.0 mL. The product was recrystallized from
toluene at –24 0 °C; yield 0.370 g (75%). C22H30Cl3N3Ti (490.47):
1
calcd. C 53.83, H 6.16, N 8.57; found C 53.45, H 5.86, N 8.40. H
NMR (400 MHz, C6D6, 298 K): δ = 1.20 (d, 6 H, H14,15,17,18), 1.35 3.38 (t, 4 H, H17,21), 3.98 (q, 4 H, HCH3–CH2–N–), 4.88 (d, 1 H, H3),
(m, 6 H, H21,22,23), 1.64 (d, 6 H, H14,15,17,18), 3.43 (t, 4 H, H20,24),
3.60 (sept, 2 H, H13,16), 4.75 (d, 1 H, H3), 5.75 (d, 1 H, H5), 6.91
5.62 (d, 1 H, H5), 6.80 (t, 1 H, H4), 7.13–7.25 (m, 3 H, H9,10,11
ppm. 13C NMR (100 MHz, C6D6, 298 K): δ = 12.58 (CCH3–CH2–N–),
)
(t, 1 H, H4), 7.14–7.27 (m, 3 H, H9,10,11) ppm. 13C NMR (100 MHz, 18.48 (C13,14), 20.90 (C15), 25.90 (C19), 28.20 (C18,20), 47.39
C6D6, 298 K):
δ
=
23.60 (C22), 24.04 (C14,15,17,18), 24.60 (CCH3–CH2–N–), 49.11 (C17,21), 87.70 (C3), 102.04 (C5), 122.40
Eur. J. Inorg. Chem. 2011, 5512–5522
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M. Hafeez, W. P. Kretschmer, R. Kempe
FULL PAPER
(C9,11), 128.10 (C10), 134.88 (C8,12), 138.74 (C4), 141.30 (C7), 157.10
C 72.68, H 7.80, N 14.14; found C 72.28, H 8.16, N 13.86. 1H
NMR (400 MHz, C6D6, 298 K): δ = 2.16 (s, 6 H, H13,14), 2.23 (s,
3 H, H15), 3.37 (t, 4 H, H18,20), 3.61 (t, 4 H, H17,21), 5.47 (d, 1 H,
H3), 5.74 (br. s, 1 H, NH), 5.93 (d, 1 H, H5), 6.79 (s, 2 H, H9,11),
7.03 (t, 1 H, H4) ppm. 13C NMR (100 MHz, C6D6, 298 K): δ =
18.38 (C13,14), 20.40 (C15), 45.86 (C17,21), 66.96 (C18,20), 95.03 (C3),
96.33 (C5), 122.40 (C9,11), 135.08 (C10), 136.64 (C8,12), 139.16 (C4),
141.50 (C7), 157.70 (C2), 159.48 (C6) ppm.
(C2), 159.48 (C6) ppm.
Synthesis of the Dichloride II2b: Ligand 2b (0.148 g, 0.5 mmol) was
dissolved in n-hexane (10.0 mL). The ligand solution was added
drop wise to a light green n-hexane (10.0 mL) solution of (Et2N)
TiCl3 (0.113 g, 0.5 mmol) at room temperature. The solution’s color
changed from light green to dark red. The resulting solution was
stirred overnight. The solution was filtered, the filtrate volume was
reduced, and the product was crystallized from solution at –24 °C;
yield 0.110 g (45%).
N-(2,6-Diisopropylphenyl)-6-(morpholino)pyridin-2-amine
(6-Chloropyridin-2-yl)-(2,6-diisopropylphenyl)amine
(2a):
(1.44 g,
5.0 mmol) and morpholine (0.87 g, 10.0 mmol) in toluene
(15.0 mL) were heated at 160 °C for 3 d in a pressure tube. The
solution was filtered and volatiles were removed under vacuum.
The yellow oil thus obtained was purified by silica gel column
chromatography with dichloromethane as the eluent. The volatiles
were removed under vacuum and the resultant yellow oil was
recrystallized from n-hexane at –24 °C; yield 1.45 g (85%).
C21H29N3O (339.23): calcd. C 74.29, H 8.62, N 12.38; found C
73.82, H 8.96, N 11.88. 1H NMR (400 MHz, C6D6, 298 K): δ =
1.09 (d, 12 H, H14,15,17,18), 3.34 (t, 4 H, H19,23), 3.38 (sept, 2 H,
H13,16), 3.48 (t, 4 H, H20,22), 5.48 (d, 1 H, H3), 5.74 (br. s, 1 H,
NH), 5.80 (d, 1 H, H5), 7.10 (t, 1 H, H4), 7.12–7.20 (m, 3 H,
H9,10,11) ppm. 13C NMR (100 MHz, C6D6, 298 K): δ = 23.92 (C
14,15,17,18), 28.54 (C13,16), 45.63 (C19,23), 66.76 (C20,22), 94.95 (C3),
96.24 (C5), 124.03 (C9,11), 128.20 (C10), 134.52 (C8,12), 139.15 (C4),
148.13 (C7), 158.59 (C2), 159.34 (C6) ppm.
Alternative Procedure for the Synthesis of II2b: Titanium tetrachlo-
ride (0.189 g, 1.0 mmol) was added to a Schlenk tube containing
dichloromethane (10.0 mL). Ligand 2b (0.297 g, 1.0 mmol) was dis-
solved in dichloromethane (10.0 mL). The ligand solution was
added drop wise to the titanium tetrachloride solution. The solu-
tion color changed from colorless to pink. Triethylamine (0.145 g,
0.20 mL, 1.40 mmol) was added to the solution, and changed the
color of the solution to dark red. The solution was stirred for 2 h.
Diethyamine (0.146 g, 0.22 mL, 2.20 mmol) was added to the solu-
tion. The resultant solution was stirred overnight. The solution was
filtered, the solvent was removed under vacuum, and the product
was extracted with, and recrystallized at –24 °C from, toluene; yield
0.110 g (45%). C22H32Cl2N4OTi (487.03): calcd. C 54.21, H 6.62,
N 11.50; found C 53.82, H 6.53, N 11.13. 1H NMR (400 MHz,
C6D6, 298 K): δ = 1.19 (t, 6 H, HCH3–CH2–N–), 2.10 (s, 6 H, H13,14),
2.20 (s, 3 H, H15), 3.38 (t, 4 H, H17,21), 3.64 (t, 4 H, H18,20), 3.96
(q, 4 H, HCH3–CH2–N–), 4.86 (d, 1 H, H3), 5.56 (d,1 H, H5), 6.80 (t,
1 H, H4), 6.86 (s, 2 H, H9,11) ppm. 13C NMR (100 MHz, C6D6,
298 K): δ = 11.10 (CCH3–CH2–N–), 18.42 (C13,14), 20.95 (C15), 25.53
(C17,21), 46.56 (CCH3–CH2–N–), 66.98 (C18,20), 92.76 (C3), 96.30 (C5),
122.40 (C9,11), 128.10 (C10), 134.88 (C8,12), 138.74 (C4), 141.30 (C7),
157.12 (C2), 159.48 (C6) ppm.
Synthesis of the Dichloride II2a: Ligand 2a (0.170 g, 0.5 mmol) was
dissolved in n-hexane (10.0 mL). The ligand solution was added
drop wise to a light green n-hexane (10.0 mL) solution of (Et2N)-
TiCl3 (0.113 g, 0.50 mmol) at room temperature. The solution’s
color changed from light green to dark red. The resulting solution
was stirred overnight. The solution was filtered, and the filtrate
volume was reduced, and the product was crystallized from the
solution at –24 °C; yield 0.125 g (47%). C25H38Cl2N4OTi (529.08):
calcd. C 56.70, H 7.24, N 10.59; found C 56.36, H 7.10, N 10.72.
1H NMR (400 MHz, C6D6, 298 K):
δ = 0.80 (t, 6 H,
HCH3–CH2–N–), 1.20 (d, 6 H, H14,15,17,18), 1.36 (d, 6 H, H14,15,17,18),
3.23 (t, 4 H, H19,23), 3.43 (sept, 2 H, H13,16), 3.50 (t, 4 H, H20,24),
3.96 (q, 4 H, HCH3–CH2–N–), 4.88 (d, 1 H, H3), 5.54 (d, 1 H, H5),
6.80 (t, 1 H, H4), 7.14–7.24 (m, 3 H, H9,10,11) ppm. 13C NMR
Synthesis of the Trichloride I2b: Titanium tetrachloride (0.189 g,
1.0 mmol) was added to a Schlenk tube containing dichlorometh-
ane (10.0 mL). Ligand 2b (0.297 g, 1.0 mmol) was dissolved in
dichloromethane (10.0 mL). The ligand solution was added drop
wise to the titanium tetrachloride solution. The color of the solu-
tion changed from colorless to pink. Triethylamine (0.141 g,
0.20 mL, 1.40 mmol) was added to the solution, and changed the
color of the solution to dark red. The resultant solution was stirred
overnight. The solution was filtered, the solvent was removed under
vacuum, and the product was extracted with, and recrystallized at
–24 °C from, toluene; yield 0.270 g (62%). C18H22Cl3N3OTi
(450.40): calcd. C 47.96, H 4.92, N 9.33; found C 47.70, H 4.85, N
9.14. 1H NMR (400 MHz, C6D6, 298 K): δ = 2.10 (s, 3 H, H15),
2.33 (s, 6 H, H13,14), 3.25 (t, 4 H, H17,21), 3.42 (t, 4 H, H18,20), 4.68
(d, 1 H, H3), 5.49 (d, 1 H, H5), 6.67 (t, 1 H, H3), 6.73 (s, 2 H,
H9,11). 13C NMR (100 MHz, C6D6, 298 K): δ = 17.98 (C15), 20.96
(C13,14), 47.05 (C17,21), 66.10 (C18,20), 87.34 (C3), 106.06 (C5),
128.02 (C10), 128.26 (C9,11), 129.61 (C10), 137.59 (C8,12), 142.19
(C7), 151.52 (C2), 153.57 (C6) ppm.
(100 MHz, C6D6, 298 K):
δ =
10.99 (CCH3–CH2–N–), 25.01
(C14,15,17,18), 25.42 (C14,15,17,18), 28.41 (C13,16), 42.60 (CCH3–CH2–N–),
47.37 (C19,23), 66.58 (C20,22), 92.20 (C3), 105.86 (C5), 124.32 (C9,11),
138.74 (C4), 140.24 (C7), 140.82 (C10), 143.65 (C8,12), 153.74 (C2),
159.69 (C6) ppm.
N-(2,4,6-Trimethylphenyl)-6-(morpholino)pyridin-2-amine (2b): Li-
gand precursor 6-chloro-N-mesitylpyridin-2-amine (1.47 g,
6.0 mmol) and morpholine (1.04 g, 12.0 mmol) in toluene
(10.0 mL) were heated at 170 °C in a pressure tube. The solution
was filtered and volatiles were removed under vacuum. The yellow
oil thus obtained was purified by silica gel column chromatography
with dichloromethane as the eluent. The volatiles were removed
under vacuum and the resultant yellow oil was recrystallized from
N-(2,6-Diisopropylphenyl)-6-(pyrrolidin-1-yl)pyridin-2-amine (3a):
Ligand precursor (6-chloro-pyridin-2-yl)-(2,6-diisopropylphenyl)-
amine (1.44 g, 5.0 mmol) and pyrrolidine (0.71 g, 0.82 mL,
10.0 mmol) in toluene (10.0 mL) were heated at 160 °C in a pres-
n-hexane at –24 °C; yield 1.50 g (85%). C18H23N3O (297.18): calcd. sure tube. The solution was filtered and volatiles were removed un-
5520 Eur. J. Inorg. Chem. 2011, 5512–5522
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Titanium Complexes Stabilized by Aminopyridinates
drop wise to a light green n-hexane (15.0 mL) solution of (Et2N)-
TiCl3 (0.226 g, 1.0 mmol) at room temperature. The color of the
solution changed from light green to dark red. The resulting solu-
tion was stirred overnight. The solution was filtered, the filtrate
volume was reduced, and the product was crystallized from solu-
tion at –24 °C; yield 0.220 g (46%). C22H32Cl2N4Ti (471.03): calcd.
C 56.05, H 6.85, N 11.89; found, C 56.13, H 7.36, N 11.65. 1H
NMR (400 MHz, C6D6, 298 K): δ = 0.78 (t, 6 H, HCH3–CH2–N–),
1.36–1.38 (t, 4 H, H17,18), 2.14 (s, 3 H, H15), 2.17 (s, 6 H, H13,14),
3.32 (t, 4 H, H16,19), 3.90 (q, 4 H, HCH3–CH2–N–), 5.49 (d, 1 H, H3),
5.64 (t, 1 H, H4), 5.74 (d, 1 H, H5), 6.79 (s, 2 H, H9,11) ppm. 13C
NMR (100 MHz, C6D6, 298 K): δ = 11.12 (CCH3–CH2–N–), 18.42
(C13,14), 20.95 (C15), 28.20 (C17,18), 42.50 (CCH3–CH2–N–), 46.26
(C16,19), 92.76 (C3), 96.30 (C5), 122.40 (C9,11), 128.10 (C10), 134.88
(C8,12), 138.74 (C4), 141.30 (C7), 157.10 (C2), 159.48 (C6) ppm.
der vacuum. The yellow oil thus obtained was purified by silica gel
column chromatography. The volatiles were removed under vacuum
and resultant yellow oil was recrystallized from n-pentane at
–80 °C; yield 1.35 g (83%). C21H29N3 (323.24): calcd. C 77.96, H
9.04, N 13.00; found C 77.42, H 8.96, N 12.78. 1H NMR
(400 MHz, C6D6, 298 K): δ = 1.10 (d, 12 H, H14,15,17,18), 1.49 (t, 4
H, H20,21), 3.31 (t, 4 H, H19,22), 3.41 (sept, 2 H, H13,16), 5.42 (d,1
H, H3), 5.70 (d, 1 H, H5), 5.84 (t, 1 H, H3), 7.02–7.22 (m, 3 H,
H9,10,11) ppm. 13C NMR (100 MHz, C6D6, 298 K): δ = 24.03
(C14,15,17,18), 25.22 (C20,21), 28.25 (C13,16), 46.29 (C19,22), 92.65 (C3),
96.04 (C5), 123.67 (C9,11), 128.20 (C10), 134.66 (C7), 138.36 (C4),
147.92 (C8,12), 157.15(C2), 158.73 (C6) ppm.
Reactions in NMR Tubes of the Complexes with TMA
(a) An NMR tube was charged with I1a (20 mg, 0.04 mmol), de-
uteriobromobenzene (0.5 mL) and TMA (115 mg, 1.60 mmol). Af-
terwards, the tube was sealed, shaken for 5 min, and then an NMR
spectrum was recorded. (b) An NMR tube was charged with II1a
(21 mg, 0.04 mmol), deuterio-bromobenzene (0.5 mL) and TMA
(115 mg, 1.60 mmol). Afterwards, the tube was sealed, shaken for
5 min, and then an NMR spectrum recorded. (c) NMR tubes were
charged with III1a (0.016 g, 40 μmol) and deuterio-bromobenzene
(0.5 mL) before TMA (6, 14, 29, 58, 115, and 289 mg, 0.08, 0.20,
0.40, 0.80, 1.60, and 4.0 mmol, respectively) was added. After-
wards, the tube was sealed, shaken for 5 min, and the NMR spectra
recorded (Figure 7).
Synthesis of the Dichloride II3a: Ligand 3a (0.323 g, 1.0 mmol) was
dissolved in n-hexane (15.0 mL). The ligand solution was added
drop wise to a light green n-hexane (15 mL) solution of (Et2N)-
TiCl3 (0.226 g, 1.0 mmol) at room temperature. The color of the
solution changed from light green to dark red. The resulting solu-
tion was stirred overnight. The solution was filtered, the filtrate
volume was reduced, and the product crystallized from solution at
–24 °C; yield 0.245 g (48%). C25H38Cl2N4Ti (513.08): calcd. C
1
58.47, H 7.46, N 10.92; found C 58.45, H 7.80, N 10.41. H NMR
(400 MHz, C6D6, 298 K): δ = 0.79 (t, 6 H, HCH3–CH2–N–), 1.10 (d,
6 H, H14,15,17,18), 1.18 (d, 6 H, H14,15,17,18), 1.34 (t, 4 H, H20,21),
3.32 (t, 4 H, H19,22), 3.40 (sept, 2 H, H13,16), 4.06 (q, 4 H,
HCH3–CH2–N–), 4.86 (d, 1 H, H3), 5.51 (d, 1 H, H5), 6.80 (t, 1 H,
H4), 7.14–7.27 (m, 3 H, H9,10,11) ppm. 13C NMR (100 MHz, C6D6,
Acknowledgments
We thank the Deutsche Forschungsgemeinschaft (DFG), SFB 840
for supporting this work. M. H. thanks the University of Azad
Jammu & Kashmir and the Higher Education Commission, Paki-
stan for a scholarship. We thank I. Haas, Dr. Ch. Döring, and T.
Bauer for their help in the X-ray laboratory.
298 K):
δ =
12.62 (CCH3–CH2–N–), 24.16 (C14,15,17,18), 24.58
(C14,15,17,18), 25.28 (C20,21), 28.45 (C13,16), 46.57 (CCH3–CH2–N–),
47.73 (C19,22), 92.42 (C3), 95.92 (C5), 123.53 (C9,11), 128.10 (C10),
134.52 (C8,12), 138.17 (C4), 147.77(C7), 157.00 (C2), 158.56 (C6)
ppm.
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the resultant yellow oil was recrystallized from n-pentane at –80 °C;
yield 1.50 g (89%). C18H23N3 (281.19): calcd. C 76.82, H 8.24, N
14.94; found C 76.63, H 8.10, N 14.73. 1H NMR (400 MHz, C6D6,
298 K): δ = 1.10 (t, 4 H, H17,18), 2.15 (s, 3 H, H15), 2.18 (s, 6 H,
H13,14), 3.30 (t, 4 H, H16,19), 5.70 (d, 1 H, H5), 5.81 (d, 1 H, H3),
6.79 (s, 2 H, H9,11), 7.12 (t, 1 H, H4) ppm. 13C NMR (100 MHz,
C6D6, 298 K): δ = 18.02 (C13,14), 20.55 (C15), 25.15 (C17,18), 46.17
(C16,19), 92.38 (C3), 95.95 (C5), 128.94 (C9,11), 135.17 (C7), 135.37
(C10), 136.33 (C8,12), 138.35 (C4), 157.10 (C2), 157.48 (C6) ppm.
Synthesis of the Dichloride II3b: Ligand 3b (0.281 g, 1.0 mmol) was
dissolved in n-hexane (15.0 mL). The ligand solution was added
Eur. J. Inorg. Chem. 2011, 5512–5522
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: August 11, 2011
Published Online: November 10, 2011
5522
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