Synthesis, structural investigations and ethylene polymerization of titanium complexes with tripodal oxazoline ligands

Article abstract of DOI:10.1007/s13738-014-0558-8

Abstract A series of tripodal nitrogen containing ligands including amidine and aminopyridines with extra oxazoline functionality were synthesized. The corresponding titanium complexes bearing such ligands were synthesized by diethylamine elimination rout

Full text of DOI:10.1007/s13738-014-0558-8

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0558-8
ORIGINAL PAPER
Synthesis, structural investigations and ethylene polymerization
of titanium complexes with tripodal oxazoline ligands
•
•
•
Muhammad Hafeez Sonja Lippert Tobias Bauer
Winfried P. Kretschmer
Received: 6 September 2014 / Accepted: 14 November 2014
Ó Iranian Chemical Society 2014
Abstract A series of tripodal nitrogen containing ligands
including amidine and aminopyridines with extra oxazoline
functionality were synthesized. The corresponding titanium
complexes bearing such ligands were synthesized by dieth-
ylamine elimination route. Diethylamidotitanium trichloride
[Et2NTiCl3] reacts with the functionalized anilines, 2-(4,4-
dimethyl-4,5-dihydrooxazol-2-yl)-N-(2-fluorophenyl)-aniline
(FOxH) and 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-(2-
methoxyphenyl)aniline (MeOOxH), the amidine(E)-N’-(2,6-
diisopropylphenyl)-N-(2-(4,4-dimethyl-4,5-dihydrooxazol-2-
yl)phenyl)benzimidamide ( Am OxH), and the aminopyri-
dines N-(2-(4,4-dimethyl-4,5-dihydro oxazol-2-yl)phenyl)-6-
(piperidin-1-yl)pyridin-2-amine (ApOxH) and N-(2-(4,4-
dimethyl- 4,5-dihydrooxazol-2-yl)phenyl)-6-(2,4,6-triisopro-
pyl phenyl)pyridin-2-amine (Ap*OxH), under diethylamine
elimination to form the corresponding titanium trichlorides
[FOxTiCl3], [MeOOxTiCl3], [AmOxTiCl3], [ApOxTiCl3]
and [Ap*OxTiCl3] in excellent yields. These compounds
were characterized by spectroscopic methods, and X-ray
crystal structure analysis (selected complexes). Furthermore,
their behavior in ethylene polymerization was explored. The
complexes show moderate activity towards ethylene if acti-
vated with MAO. The observed PEs were analyzed by HT-
GPC and were found to be of low molecular weight for the
amidinate AmOxTiCl3 but of very high one (Mp up to 3.5
million g/mol) for the aminopyridinate Ap*OxTiCl3 titanium
complex.
Keywords Amido ligands ꢀ Amidinates ꢀ
Aminopyridinates ꢀ N-ligands ꢀ Olefin polymerization ꢀ
Oxazoline ꢀ Titanium
Introduction
Amidinates (=Am) and Aminopyridinates (=Ap) of the
group 4 metals are promising alternatives to the widely
used metallocenes of these metals, for instance, in poly-
merization catalysis [1–9]. Both ligands are closely related
and show (mostly) a g2-coordination mode if coordinating
to early transition metals (Scheme 1) [10–12]. We have
recently used bulky aminopyridinates to stabilize titanium-
based polymerization catalysts [13].
These complexes were found to be highly active in eth-
ylene homo- and a-olefin copolymerization together with a
good response towards cyclic olefins when activated with
‘‘dry’’-methylaluminoxane (d-MAO), but were almost inac-
tive when free trimethyl aluminum (TMA) containing MAO
was used. We suspected that ligand transfer to aluminum as
observed earlier for aminopyridinates might be responsible
for the inactivity [14, 15]. To address the ligand transfer issue
the electron donating ability of the Ap ligands (Scheme 2)
was increased to significantly alter the rate of ligand transfer.
However, this approach leads to less stable catalysts with
regard to a ligand transfer to aluminum [16, 17].
We therefore thought that the introduction of an additional
linker (Scheme 3, left) in a ring closure position may solve
the ligand transfer problem and may lead to more stable
polymerization catalyst. A strong binding can be expected
from the oxazoline moiety (Scheme 3, right) [18, 19], which
was used before in group 4 metal chemistry [20–25].
M. Hafeez (&)
Department of Chemistry, University of Azad Jammu
and Kashmir, Muzaffarabad Azad Kashmir 13100, Pakistan
e-mail: smhafeezkhan@yahoo.com
S. Lippert ꢀ T. Bauer ꢀ W. P. Kretschmer
Amidine [26] and aminopyridine [22] bearing an oxaz-
oline moiety have been used earlier to stabilize palladium
¨
Lehrstuhl fu¨r Anorganische Chemie II, Universitat Bayreuth,
95440 Bayreuth, Germany
123

J IRAN CHEM SOC
Scheme 1 Binding mode of aminopyridinato (left) and amidinato
metal complex moiety;
(right) ligands ([M] = group
R = R’ = alkyl or aryl substituents)
4
Scheme 2 Mesomeric structures of 2,6-diaminopyridinato metal
complexes (R, R’, R’’ = alkyl substituents)
Scheme 4 Synthesis of oxazoline-substituted anilines, the bifunc-
tional tripodal ligands A (X = F) and B (X = OMe) and their
corresponding titanium complexes
Scheme 3 Ap ligands with a beneficial electron donating Atom in
chelating position (R = aryl substituents)
and zinc complexes. Herein, we report the synthesis of
novel amidine [26] and aminopyridine [22] bearing an
oxazoline moiety have been used earlier to stabilize pal-
ladium and zinc complexes. Herein, we report the synthesis
of novel aminopyridines, related anilines, and amidines
functionalized by an oxazoline side arm.
Furthermore, the synthesis of titanium complexes sta-
bilized by such ligands is reported as well as ethylene
polymerization studies with the selected of these
complexes.
Results and discussion
Synthesis and structural investigation
2-Oxazoline-substituted anilines can be easily synthesized
in higher yields by a zinc chloride catalyzed reaction of
isatoic anhydride with 2-aminoalcohols [23, 26–31]. Sub-
sequent reaction with 1-bromo-2-fluoro- or 1-bromo-2-
methoxybenzene in the presence of tris(dibenzilidineace-
Scheme 5 Synthesis of oxazoline functionalized aminopyridines C
and D and corresponding titanium complexes
(MeOOxH, B) in about 50–61 % isolated yield, respectively
[32–35]. Further reactions of the ligands A and B in toluene
with 1 equivalent diethylamido titanium trichloride give
under diethylamine elimination the corresponding titanium
complexes 1a and 1b as dark red crystals in good yields
(Scheme 4).
tone)dipalladium(0)/1,3
bis(diphenylphosphino)propane
(=DPPP) gives the fluorine and methoxy functionalized
tripodal anilines 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-
N-(2-fluorophenyl)-aniline (FOxH, A) and 2-(4,4-dimethyl-
4,5-dihydrooxazol-2-yl)-N-(2-methoxy-phenyl)
aniline
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J IRAN CHEM SOC
For the oxazoline-substituted aminopyridines, two dif-
ferent synthetic routes have been chosen. The recently
developed Ni(0)/2,20-bipyridine catalyzed amination [16]
of 2,6-dichloropyridine with 2-(4,4-dimethyl-4,5-di-
hydrooxazol-2-yl)aniline followed by a thermal amination
of the intermediate 6-chloro-N-(2-(4,4-dimethyl-4,5-di-
hydrooxazol-2-yl) phenyl) pyridin-2-amine (C1) with
piperidine gave N-(2-(4,4-dimethyl-4,5-dihydro oxazol-2-
(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl) benzimida-
mide (E, AmOxH) is easily available by a catalyst-free
reaction of (E)-N-(2,6-diisopropyl-phenyl)benzimidoyl
chloride with 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)ani-
line in the presence of triethylamine (Scheme 6). The
corresponding titanium complexes bearing such amipyrid-
inato or amidinato ligands were easily synthesized by the
above described reaction of free ligand with 1 equivalent of
dietylamido titanium trichloride in toluene under diethyl-
amine elimination (Schemes 6, 7). For the titanium com-
plexes ApOxTiCl3 (1c) and Ap*OxTiCl3 (1d) blue-green
crystals were observed while the relative AmOxTiCl3 (1f)
gave red cubes. All titanium complexes were characterized
yl)phenyl)-6-(piperidin-1-yl)pyridin-2-amine
(C2,
ApOxH) in an overall yield of 30 % (Scheme 5, right). For
the more bulky aminopyridine N-(2-(4,4-dimethyl-4,5-di-
hydrooxazol-2-yl)phenyl)-6-(2,4,6-triisopropyl
phenyl)pyridin-2-amine (D, Ap*OxH), a well-established
palladium(0) catalyzed arylation of anilines, starting from
2-bromo-6-(2,4,6-triisopropylphenyl)pyridine in 60 %
yield was used (Scheme 5, right) [36, 37].
1
by H and 13C NMR spectroscopy and elemental analysis.
For the selected compounds 1d and 1e, single crystal
structure analysis was carried out. Suitable crystals were
In contrast to the aminopyridines, the oxazoline func-
tionalized amidine (E)-N’-(2,6-diisopro-pylphenyl)-N-(2-
Fig. 1 Molecular structure of Id, hydrogen atoms are omitted for
˚
clarity, selected bond lengths (A) and bond angles (°): C5–N1
1.366(6), C1–N1 1.355(6), C1–N2 1.386(6), C23–N2 1.377(6), C22–
C23 1.412(7), C21–C22 1.441(7), C21–N3 1.296(6), C21–O1
1.354(6), N1–Ti1 2.135(4), N2–Ti1 2.016(4), N3–Ti1 2.079(4), av.
Cl–Ti1 2.31, Cl1–Ti1–Cl3 178.85(7), C6–C5–N1 119.3(5), C1–N2–
C23 127.4(4), N1–Ti1–N2 63.31(17), N2–Ti1–N3 84.37(16)
Scheme 6 Synthesis of oxazoline functionalized amidine E and
amidinato titanium trichloride 1e
+
-
Et NTi l
C 3
2
R
N
N
H
R
N
N
l
C
Et2NH
Ti
N
O
N
O
l
C
l
C
c
1d
,
2 D
,
1
C
Fig. 2 Molecular structure of Ie, hydrogen atoms are omitted for
˚
clarity, selected bond lengths (A) and bond angles (°): C19–N1
=
=
N
R
R
D
C2
1.447(4), C1–N1 1.327(4), C1–N2 1.355(4), C8–N2 1.388(4), C8–
C13 1.410(4), C13–C14 1.444(4), C14–N3 1.305(4), C14–O1
1.354(4), N1–Ti1 2.077(3), N2–Ti1 2.052(2), N3–Ti1 2.110(3), av.
Cl–Ti1 2.30, Cl1–Ti1–Cl3 171.77(4), N1–C1–N2 108.0(3), C1–N2–
C8 128.9(2), N1–Ti1–N2 63.40(9), N2–Ti1–N3 82.89(1)
Scheme 7 Synthesis of aminopyridinato titanium complexes 1c and
1d
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J IRAN CHEM SOC
obtained by slow cooling of saturated toluene solutions to
room temperature. The molecular structures of 1d and 1e
are presented in Figs. 1 and 2 respectively. X-ray crystal
structure analysis details are given in Table 1. The overall
symmetry of both complexes can best be described as
distorted octahedron with the three nitrogen and one
chlorine atom in the equatorial square plane.
Table 1 Crystallographic data for the compounds Id and Ie charac-
terized by single crystal X-ray structure analysis
Compound
Id
Ie
Formula
C31H44Cl3N3OTi
701.00
C30H34Cl3N3OTi
606.85
Formula weight
Crystal system
Space group
Monoclinic
P2(1)/n
Orthorhombic
P212121
10.3520(4)
16.5750(7)
17.1530(7)
90.0
In both complexes, all three N–Ti distances are fairly
˚
identical between 2.02 and 2.13 A with a slight elongation
˚
a [A]
15.6400(11)
10.12.60(7)
22.9120(14)
90.0
˚
b [A]
for N1–Ti in 1d and N3–Ti in 1e. This is in contrast to the
often observed amido pyridine form with a short Ti–Namido
distance and a long Ti–Npyridine one. For both the com-
plexes the Cl1–Ti–Cl3 angle is almost linear with stronger
deformation of 171.8° in 1e. The relative short Csp2–Nsp2
˚
c [A]
a [°]
b [°]
c [°]
101.280(5)
90.0
90.0
90.0
3
˚
˚
˚
Cell volume [A ]
3,558.5(4)
4
2,943.2(2)
4
single bond (1d, N2–C23 = 1.37 A; 1e, N2–C8 = 1.39 A)
together with the long Csp2-Csp2 aromatic bond (1d, C22–
Z
Crystal size [mm3]
0.17 9 0.15 9 0.14 0.30 9 0.24 9 0.14
˚
˚
C23 = 1.41 A; 1e, C8–C13 = 1.41 A) indicates a delo-
calization of the negative charge over the whole p-system
including the aryl and the lone pair of N3 in the oxazoline
moiety. Therefore, a high complex stability might be
expected.
Color
Density [gcm-3
T (K)
Blue
red
)
1.308
1.370
133(2)
1.71–24.60
4,943
3,885
349
133(2)
1.45–23.64
5,320
Theta range
Unique reflections
Olefin polymerization
Observed refl. [I [ 2rI] 2,684
No. of parameters
wR2 (all data)
414
To gain more insight into the stabilization of the electron-
deficient titanium metal center by the additional donor
functionality, the complexes were tested in ethylene
0.120
0.054
0.072
0.035
R value [I [ 2rI]
-1
Activity (kgPEmol h-1bar-)
Precat.a
T (°C)
mPol. (g)
Mn (kgmol-1
)
Mw/Mn
Table 2 Ethylene
polymerization
Entry
cat
1
Ic
Id
Id
Id
Id
Ie
Ie
Ie
70
30
50
70
50
50
50
80
0.22
0.28
0.13
0.03
0.08
–
22
28
13
3
2
7,840 (593,000)c
11,100 (593,000)c
9,400 (3,530,000)c
28.0
73.8
95.7
n.d.
n.d
3
a
4
5b
Precatalyst: 2.0 lmol; MAO:
1.0 mmol; toluene: 150 mL;
p = 2 bar; t = 15 min
8
n.d.
n.d
6
–
b
7b
8b
0.33
–
33
–
5,700
–
3.0
d-MAO
c
Mp of higher molecular
weight polymer fraction
–
Fig. 3 Molecular weight
distribution observed with
AmOxTiCl3 precatalyst (run 7)
Distribution Plot View
1,2
1,1
1
AmOxTiCl3-dMAO
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
100
1000
10000
100000
1e6
Extrapolated MW
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J IRAN CHEM SOC
Fig. 4 Molecular weight
distribution of PE observed with
ApOxTiCl3/MAO catalyst
system (run 1–3)
Distribution Plot View
0,65
0,6
Ap*OxTiCl3-MAO-30
Ap*OxTiCl3-MAO-50
Ap*OxTiCl3-MAO-70
0,55
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
0
100
1000
10000
100000
1e6
1e7
1e8
Extrapolated MW
polymerization in the presence of commercial and ‘‘dry’’-
methylaluminoxane (MAO) co-catalyst (Table 2).
dual manifold Schlenk line or in an argon-filled glove box
(Braun 120-G) with a high-capacity recirculator (\0.1 ppm
O2). Non-halogenated solvents were dried by distillation
from sodium wire/benzophenone. 2,6-Dichloropyridine,
2,20-bi-pyridine and piperidine were purchased from Alfa
Aesar. Nickel acetate and t-amyl alcohol were obtained
from Sigma Aldrich. 2-bromo-6-(2,4,6-triisopropyl-
phenyl)pyridine and titanium precursor (Et2NTiCl3) [41,
42] were prepared as described in literature. Deuterated
solvents were obtained from Cambridge Isotope Labora-
tories and were degassed, dried, and distilled prior to use.
NMR spectra were recorded with a Varian ARX at
400 MHz or Varian ARX 300 MHz and chemical shifts are
reported in ppm relative to the deuterated solvent. Ele-
mental analyses (CHN) were carried out using a Vario EL
III instrument. D-MAO was prepared by removal of all
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
C2D2Cl4 at 100 °C for 3 h before measuring. Gel perme-
ation chromatography (GPC) analysis was carried out on a
PL-GPC 220 (Agilent, Polymer Laboratories) high-tem-
perature chromatographic unit equipped with a DP and RI
detectors and two linear mixed-bed columns (Olexis,
13-micron particle size) at 150 °C using 1,2,4-trichloro-
benzene as the mobile phase. The samples were prepared
by dissolving the polymer (0.05 wt %, conc. = 1 mg/mL)
in the mobile phase solvent in an external oven and were
run without filtration. The molecular weight was referenced
Complexes 1a and 1b showed almost no ethylene con-
sumption, while for pre-catalyst 1c–1e, a low-to-moderate
activity was observed.
It is notable that the ethylene consumption was slow but
continuous over the whole run time. This indicates a slow but
stable polymerization catalyst. The enhancement of the catalyst
stability towards free trimethylaluminum (TMA) comes toge-
ther with probably blocking a coordination site by the additional
donating atom. Such low-to-moderate activity was observed
earlier for titanium complexes with planar tridentate ligands
[38–40]. It is also notable that for the amidinato titanium
compound 1e, mono-modal but low molecular weight PE was
observed (Fig. 3) while the aminopyridinato titanium congen-
ers yielded PE with a bimodal distribution including a very high
molecular weight fraction indicated by the peak molecular
weight of up to 3.5 million dalton (Mp Table 2; Fig. 4).
Conclusions
From the present studies, a series of conclusions can be
drawn. First, titanium complexes with novel tripodal ox-
azoline functionalized aminopyridines and amidines can be
synthesized by applying diethylamine elimination route.
Second, the higher stability towards ligand transfer can be
confirmed by observing an ethylene polymerization activ-
ity in the presence of free trimethylaluminum. Third, the
aminopyridinate Ap*OxTiCl3 produced very high molec-
ular weight polyethylene.
to polyethylene (Mw = 520–3,200,000 gmol-1
) and
polystyrene (Mw = 580–2,800,000 gmol-1) standards.
The reported values are the average of at least two inde-
pendent determinations. X-ray crystal structure analysis
was carried out at STOE IPDS II diffractometer equipped
with an Oxford Cryostream low-temperature unit. Structure
solution and refinement were accomplished using SIR97
[43] SHELXL-97 [44] and WinGX. Selected details of the
X-ray crystal structure analyses are listed in Table 1. CCDC-
1022674(compound Id) and CCDC-922730 (compound 1e)
Experimental section
Synthesis and structure analysis
All manipulations were performed with rigorous exclusion
of oxygen and moisture in Schlenk type glassware on a
123

J IRAN CHEM SOC
contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.
ccdc.cam.ac.uk/data_request/cif.
This mixture was dissolved in 60 mL toluene. 2-Fluoro-1-
bromobenzene (3.63 g, 2.3 mL, 21.0 mmol) was added to
this solution. The resulting solution was refluxed for
5 days. On cooling distilled water (50.0 mL) and diethyl
ether (50.0 mL) were added and the organic layer was
separated by solvent extraction. The inorganic layer was
washed three times with diethylether (3 9 20.0 mL). The
combined organic layers were washed with a saturated
sodium chloride solution and were dried over sodium sul-
fate. The volatiles were removed under vacuum and the
product was crystallized at -24 °C. Yield 3.0 g (50 %).
C17H17FN2O: calcd. C 71.80, H 6.03, N 9.86; found C
71.82, H 6.20, N 10.03. 1H NMR (300 MHz, CDCl3,
298 K): d = 1.35 (s, 6 H, H3,4), 4.02 (s, 2 H, H5),
6.79–7.27 (m, 3 H, H12,16,18), 7.27 (t, 1 H, H11), 7.81 (d, 1
H, H9), 6.89 (t, 1 H, H10), 7.03 (d, 1 H, H19), 10.54 (br. s. 1
H, NH) ppm. 13C NMR (75 MHz, CDCl3, 298 K):
d = 28.82 (C3,4), 68.13 (C2), 77.66 (C5), 111.35 (C19),
113.27 (C16), 116.11 (C10), 116.37 (C18), 117.63 (C17),
122.86 (C8), 124.36 (C12), 129.91 (C11), 132.02 (C9),
132.40 (C15), 145.18 (C13), 154.14 (C20), 162.17 (C7) ppm.
General description of ethylene polymerization
experiments with MAO
The catalytic ethylene polymerization reactions were per-
formed in a 250 mL glass autoclave (Buechi) in semi-batch
mode (ethylene was added by replenishing 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 pressure, the ethylene flow, the inner and the outer reactor
temperature and the stirrer speed were monitored continu-
ously. 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 desired temperature, stirred at
1,000 rpm and charged with 150 mL of toluene together
with MAO, as not mentioned differently in the text. After
pressurizing with ethylene to reach 2 bar total pressure, the
autoclave was equilibrated for 5 minutes. Subsequently,
1 mL of a 0.002 M catalyst stock solution in toluene was
injected to start the reaction. During the run, the ethylene
pressure was kept constant to within 0.1 bar of the initial
pressure by replenishing flow. After 15 min reaction time,
the reactor was vented and the residual aluminum alkyls
were destroyed by addition of 50 mL of ethanol. 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 subsequently in vac-
uum at 80 °C.
Synthesis of 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-
N-(2-methoxyphenyl)aniline (B)
The reactants; [2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)
aniline] (4.0 g, 21.0 mmol), tris[dibenzilideneacetondi-
palladium(0)] (0.381 g, 0.417 mmol), 1,3-bis(diphenyl-
phosphino)propane (0. 344 g, 0.837 mmol), sodium tertiary
butoxide (2.59 g, 27.0 mmol) were taken in a Schlenk tube
in a glove box.
Synthesis of ligands
Synthesis of 2-(4,4–dimethyl-4,5-dihydrooxazol-2-yl)-
N-(2-fluorophenyl)aniline (A)
This mixture was dissolved in 50.0 mL toluene. 1-bromo-2-
methoxybenzene (3.92 g, 2.6 mL, 21.0 mmol) was added
to this solution. The resulting solution was refluxed for
4 days. On cooling, distilled water (50.0 mL) and diethyl
ether (50.0 mL) were added and the organic layer was
separated by solvent extraction. The inorganic layer was
washed three times with diethyl ether (3 9 20.0 mL). The
combined organic layers were washed with a saturated
sodium chloride solution and were dried over sodium sul-
fate. The volatiles were removed under vacuum and the
product was crystallized at -24 °C. Yield 3.50 g (61 %).
C18H20N2O2 (296.36): calcd. C 72.95, H 6.80, N 9.55;
found C 72.78, H 6.95, N 10.07.1H NMR (300 MHz,
CDCl3, 298 K): d = 1.18 (s, 6 H, H3,4), 3.41 (s, 3 H, H21),
The reactants; [2-(4,4-dimethyl-4,5-dihydrooxazol-2-
yl)aniline] (4.0 g, 21.0 mmol), tris[dibenzilideneacetondi-
palladium(0)] (0.381 g, 0.417 mmol), 1,3-bis(diphenyl-
phosphino)propane (0.344 g, 0.837 mmol), sodium tertiary
butoxide (2.49 g, 25.93 mmol) were taken in a Schlenk
tube in a glove box.
123

J IRAN CHEM SOC
3.62 (s, 2 H, (d, 1 H, H12), 7.56 (t, 1 H, H17), 8.18 (d, 1 H,
H19), 10.97 (br. s. 1 H, NH) ppm. 13C NMR (75 MHz,
CDCl3, 298 K): d = 28.41 (C3,4), 55.27 (C21), 67.80 (C2),
77.07 (C5), 111.34 (C19), 111.92 (C16), 113.43 (C10), 116.88
(C12), 120.90 (C18), 121.63 (C17), 123.16 (C8), 130.24 (C9),
131.35 (C15), 132.05 (C11), 146.25 (C13), 152.36 (C20),
162.35 (C7) ppm.
Synthesis of 6-chloro-N-[2-(4,4-dimethyl-4,
The resultant solution was heated at 170 °C for 6 days.
5-dihydrooxazol-2-yl)phenyl)pyridin-2 amine] (C1)
After cooling, the reaction mixture was filtered. The sol-
vent was removed from filtrate under vacuum. The yellow
oil thus obtained was purified by the silica gel column
chromatography. The volatiles were removed under vac-
uum and the yellow oil was dissolved in 10.0 mL n-hexane
and crystallized at -24 °C. Yield 0.80 g (68 %).
C21H26N4O (350.46): calcd. C 71.97, H 7.48, N 15.99;
found C 72.40, H 7.37, N 15.70. 1H NMR (300 MHz,
CDCl3, 298 K): d = 1.32 (s, 6 H, H3,4), 1.36 (m, 6 H,
H22,23,24), 3.45 (t, 4 H, H21,25), 3.59 (s, 2 H, H5), 6.05 (d, 1
H, H18), 6.76 (t, 1 H, H17), 7.27–7.31 (m, 2 H, H9,11), 7.71
(d, 1 H, H12), 8.62 (d, 1 H,H18), 11.32 (br. s, 1 H, NH) ppm.
13C NMR (75 MHz, CDCl3, 298 K): d = 25.10 (C3,4),
25.63 (C23), 28.34 (C22,24), 46.72 (C21,25), 69.11 (C2),
75.30 (C5), 98.32 (C16), 100.71 (C18), 111.89 (C8), 118.37
(C12), 128.32 (C9), 129.70 (C11), 132.10 (C8), 138.79 (C17),
144.19 (C13), 154.70 (C15), 159.18 (C19), 162.77 (C7) ppm.
The reactants; [2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-
aniline] (3.80 g, 20. 0 mmol) and t-amylalcohol (0.352 g,
0.45 mL, 4.0 mmol) in 20.0 mL THF were added to a THF
suspension of NaH (0.720 g, 30.0 mmol). The resulting
mixture was heated at 65 °C for 2 h and 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 further heated for 2 h. To the
cool mixture 2,6-dichloropyridine (2.96 g, 20.0 mmol) and
styrene (0.11 mL, 0.099 g, 0.95 mmol) were added and the
reaction mixture was refluxed for 2 h. After cooling, water
(4.0 mL) and dichloromethane (100.0 mL) were added.
The reaction mixture was filtered over sodium sulfate and
the volatiles were removed from filtrate. The yellow oil
was purified by silica gel column chromatography and was
crystallized in n-hexane. Yield 2.50 g (40 %). C16H16-
ClN3O (301.77): calcd. C 63.66, H 5.35, N 13.93; found C
64.12, H 5.25, N 14.43. 1H NMR (300 MHz, CDCl3,
298 K): d = 1.37 (s, 6 H, H3,4), 4.01 (s, 2 H, H5), 6.63 (d, 1
H, H16), 6.92 (d, 1 H, H18), 7.21 (t, 1 H, H17), 7.39–7.41
(m, 2 H, H9, 10), 7.43 (d, 1 H, H12), 8.69 (d, 1 H, H9), 11.81
(br. s. 1 H, NH) ppm. 13C NMR (75 MHz, CDCl3, 298 K):
d = 28.82 (C3,4), 44.99 (C5), 68.11 (C2), 110.61 (C16),
112.21 (C18), 114.60 (C12), 117.84 (C10), 119.76 (C9),
129.38 (C11), 132.47 (C8), 139.30 (C13), 142.11 (C17),
149.24 (C15), 155.31 (C19), 162.43 (C7) ppm.
Synthesis of N-(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)
phenyl)-6-(2,4,6-triisopropyl-phenyl) pyridin-2-amine (D)
The reactants; 2-Bromo-6-(2,4,6-triisopropylphenyl)pyri-
dine (3.60 g, 10.00 mmol), aniline (1.90 g, 10.00 mmol),
sodium tert-butoxide (1.09 g, 11.30 mmol), tris(benzyl-
idenaceton) dipalladium(0) (0.17 g, 0.18 mmol) and 1,3-
bis(diphenylphosphino) propane (0.16 g, 0.36 mmol) were
transferred in a Schlenk vessel and suspended in 100 mL of
toluene.
Synthesis of N-[2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)
phenyl)-6-(piperidin-1-yl)pyridin-2-amine] (C2)
The resulting mixture was heated for 24 h at 95 °C. After
cooling down to room temperature, 50 mL of diethylether
together with 50 mL of water were added to quench the
reaction. The organic layer was separated and two times
washed with 25 mL of water. The water layer was once
extracted with 25 mL of diethylether and the combined
The reactants; 6-Chloro-N-(2-(4,4-dimethyl-4,5-dihydro-
oxazol-2-yl)phenyl)pyridin-2-amine (C1), (1.0 g, 3.32
mmol) and piperidine (0.868 g, 10.2 mmol, 1.0 ml) were
taken in a pressure tube containing 15.0 mL toluene.
123

J IRAN CHEM SOC
organic layers were dried over sodium sulfate. After
removal of all volatiles, the residue was extracted with
100 mL of hot n-hexane. The hexane solution was filtered
and stored at -30 °C to give colorless crystals of N-(2-
(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl)-6-(2,4,6-tri-
(m, 8 H, H3,4,5,6,7,10,21,23), 7.58 (br. s, 1 H, H22), 8.04 (d, 1
H, H12), 9.80 (br. s, 1 H, NH) ppm. 13C NMR (75 MHz,
CDCl3,
298 K):
d = 22.20
(C26,27,29,30),
24.10
(C26,27,29,30), 28.00 (C17,18), 28.70 (C25,28), 67.60 (C15),
77.40 (C16), 113.30 (C9), 119.20 (C11), 120.00 (C13),
123.10 (C21,22,24), 127.70 (C3,4,6,7), 129.30 (C6), 132.20
(C10), 135.00 (C2), 136.30 (C14), 138.10 (C20,24), 143.40
(C19), 145.80 (C8), 152.20 (C1), 162.20 (C14) ppm.
isopropylphenyl)
pyridin-2-amine
(1.90 g,
41 %).
C31H39N3O: calcd. C 79.28, H 8.37, N 8.95; found C 78.90,
H 8.30, N 8.60. 1H NMR (300 MHz, CDCl3, 298 K):
d = 1.04 (s, 6 H, H15,16), 1.24 (d, 18 H, H24,25,27,28,30,31),
2.60 (sept, 1 H, H23,26,29), 2.80 (sept, 1 H, H23,26,29), 3.00
(sept, 1 H, H23,26,29), 3.48 (s, 2 H, H13), 6.62 (m, 3 H,
H2,4,7), 6.91 (t, 1 H, H10), 7.09 (t, 1 H, H3), 7.13 (s, 2 H,
H19,21), 7.21 (d,1 H, H8), 8.02 (d, 1 H, H10), 9.33 (d, 1H,
HNH) ppm. 13C NMR (75 MHz, CDCl3, 298 K): d = 24.30
(C24,25,27,28,30,31), 28.30 (C15,16), 30.90 (C23,29), 34.80
(C26), 67.70 (C13), 77.00 (C14), 105.00 (C2), 110.20 (C4),
116.50 (C7), 118.40 (C9), 120.80 (C19,21), 129.40 (C10),
132.80 (C8), 136.80 (C3), 143.60 (C6), 146.80 (C18,20,22),
155.70 (C5), 158.70 (C1), 162.80 (C12) ppm.
Synthesis of complexes
General procedure
The complexes 1a–1e were synthesized by reacting to the
corresponding ligand with diethyl amido trianium tri-
chloride in equimolar ratios. All the reactions were car-
ried out in toluene and stirring was done for 12 h. Good
yields of 1a–1c were obtained at room temperature while
1d and 1e were obtained by heating the reaction mixture
at 50 °C for 12 h. All the complexes were extracted with
hexane and were crystallized at room temperature or at
-24 °C.
Synthesis of (E)-N’-(2,6-diisopropylphenyl)-
N-(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)
phenyl)benzimidamide (E)
Synthesis of [2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-(2
fluorophenyl)anilido]titanium trichloride (Ia)
The reactants; (E)-N-(2,6-diisopropylphenyl) benzimidoyl
chloride (2.15 g, 7.19 mmol) was dissolved in 25 mL of
toluene before successive 2-(4,4-dimethyl-4,5- di-
hydrooxazol-2-yl)aniline (1.37 g, 7.19 mmol) and trieth-
ylamine (1.30 mL, 0.94 mmol) were added.
Yield 0.290 g (66 %) C17H16Cl3FN2OTi (437.55): calcd. C
1
46.95, H 3.69, N 6.50; found C 46.95, H 3.51, N 7.09. H
NMR (300 MHz, C6D6, 298 K): d = 1.21 (s, 6 H, H3,4), 4.24
(s, 2 H, H5), 6.54–6.69 (m, 3 H, H12,16,18), 6.78 (t, 1 H, H10),
6.80–6.94 (m, 2 H, H 17,9), 7.95 (d, 1H, H19), 8.46 (t, 1H, H11)
ppm. 13C NMR (75 MHz, C6D6, 298 K): d = 27.76 (C3,4),
58.97 (C21), 80.95 (C5), 67.16 (C2), 114.01 (C19), 118.60
(C12), 122.58 (C18), 124.44 (C15), 127.52 (C17), 129.79 (C9),
130.33 (C16), 134.40 (C11), 143.22 (C10), 152.13 (C8), 153.80
(C13), 157.05 (C20), 166.04 (C7) ppm.
Synthesis of [2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-
(2-methoxyphenyl)anilido]titanium trichloride (Ib)
After refluxing for 2 h, the reaction mixture was poured
into 50 mL of water. The organic layer was separated and
washed two times with 25.00 mL water. The combined
water phase was extracted with 25.00 mL of diethylether.
The combined organic layer was dried with Na2SO4 and
filtered before all volatiles were removed. The residue was
recrystallized from ethanol (50.00 mL) to yield colorless
crystals (2.92 g, 89.50 %). C30H35N3O: calcd. C 79.43, H
Yield 0.285 g (63 %). C18H19Cl3N2O2Ti (449.37): calcd. C
1
48.07, H 4.26, N 6.23; found C 48.23, H 4.73, N 6.70. H
NMR (300 MHz, C6D6, 298 K): d = 1.21 (s, 6 H, H3,4), 2.81
(s, 3 H, H21), 4.24 (s, 2 H, H5), 6.39–7.10 (m, 5 H,
H9,16,17,18,19), 7.49 (t, 1 H, H10), 7.95 (t, 1 H, H11), 8.46 (d, 1
H, H12) ppm. 13C NMR (75 MHz, C6D6, 298 K): d = 28.41
(C3,4), 55.39 (C5), 58.75 (C21), 72.01 (C2), 111.29 (C10),
114.01 (C18), 117.36 (C11), 120.70 (C17), 122.92 (C12),
124.24 (C16), 125.10 (C9), 128.55 (C19), 131.43 (C13), 136.12
(C8), 143.22 (C15), 151.25 (C20), 156.28 (C7) ppm.
1
7.78, N 9.26; found C 79.30, H 7.65, N 9.70. H NMR
(300 MHz, CDCl3, 298 K): d = 0.89 (s, 6 H, H17,18), 1.23
(d, 12 H, H26,27,29,30), 3.34 (sept, 2 H, H25,28), 3.45 (s, 2 H,
H15), 6.80 (br. s, 1 H, H9), 6.93 (br. s, 1 H, H11), 7.00–7.15
123

J IRAN CHEM SOC
(C14), 136.10 (C20,24), 142.00 (C19), 143.20 (C8), 144.20
(C1), 163.30 (C14)ppm.
Synthesis of N-[2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)
phenyl)-6-(piperidin-1-yl)pyridin-2-amido]titanium
trichloride (Ic)
Acknowledgments We thank the Deutsche Forschungsgemeins-
chaft (DFG) SFB 840 for supporting this work. Corresponding author
thanks the University of Azad Jammu and Kashmir and the HEC
(Higher Education Commission) Pakistan for a scholarship. We thank
T. Bauer for his help in the X-ray lab.
Yield 0.310 g (61 %). C21H25Cl3N4OTi (503.43): calcd. C
50.16, H 5.00, N 11.13; found C 50.64, H 5.59, N 11.43. 1H
NMR (300 MHz, C6D6, 298 K): d = 1.07 (s, 6 H, H3,4),
1.20–1.42 (m, 6 H, H22,23,24), 3.43 (t, 4 H, H21,25), 3.51 (s, 2
H, H5), 6.17 (d, 1 H, H16), 6.36 (d, 1 H, H18), 6.80 (t, 1 H,
H17), 6.90 (t, 1 H, H10), 7.36 (t, 1 H, H11), 8.12 (d, 1 H,
H12), 9.17 (d, 1 H, H9) ppm. 13C NMR (75 MHz, C6D6,
298 K): d = 25.75 (C23), 26.45 (C3,4), 28.30 (C22,24),
45.48 (C21,25), 55.36 (C5), 67.90 (C2), 112.01 (C10), 113.52
(C18), 116.97 (C11), 120.9 l (C17), 121.68 (C12), 123.25
(C16), 130.30 (C19), 131.43 (C13), 132.40 (C9), 146.25
(C15), 152.36 (C7) ppm.
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123