Synthesis characterization of polyamide metallodendrimers and their catalytic activities in ethylene oligomerization

Article abstract of DOI:10.1007/s10562-010-0393-1

Nickel complexes with aromatic amine terminated first generation (G1) and second generation (G2) polyamide dendrimers {POA-(NH₂)_n (n = 6 or 12, POM = Polyamide)} were synthesized. All the synthesized dendrimers and metallodendrimers

Full text of DOI:10.1007/s10562-010-0393-1

Catal Lett (2010) 138:171–179
DOI 10.1007/s10562-010-0393-1
Synthesis Characterization of Polyamide Metallodendrimers
and their Catalytic Activities in Ethylene Oligomerization
•
Tansir Ahamad Saad M. Alshehri
•
S. F. Mapolie
Received: 19 April 2010 / Accepted: 6 June 2010 / Published online: 24 June 2010
Ó Springer Science+Business Media, LLC 2010
Abstract Nickel complexes with aromatic amine termi-
nated first generation (G1) and second generation (G2)
polyamide dendrimers {POA-(NH2)n (n = 6 or 12, POM =
Polyamide)} were synthesized. All the synthesized den-
drimers and metallodendrimers were characterized by ele-
mental and spectral analysis. These novel dendritic
complexes were evaluated as catalyst precursors in the
oligomerization of ethylene, using methylaluminoxane
(MAO) as an activator at two different pressure and different
Al/M (M = Zn) ratio. In the case of 1 atm pressure of eth-
ylene, and 500:1 and 1,000:1 Al/Ni molar ratio, for C1 and
C2 respectively display higher catalytic activity towards
ethylene polymerization. Oligomerization using the gener-
ation 1 dendrimer complex, C1 yields short chain oligomers
whereas those obtained from the generation 2 dendrimer
catalyst, C2 resulted in longer chain products with molecular
weights up to 9.54 9 104 and 9.86 9 104 g/mol at 1 and
5 atm respectively.
structures for the larger systems [1]. These novel macro-
molecules functionalized with transition metals have
inspired many researchers to develop new materials and
several applications have been explored, catalysis being
one of them [2]. The recent impressive strides in synthetic
procedures increased the accessibility of functionalized
metallodendrimers, resulting in a rapid development of
dendrimer chemistry. The potential interest of metallo-
dendrimers as catalyst, arise mainly from their ability to
combine the advantage of homogenous and heterogeneous
catalyses in one system, more ever their shape and sized
make them more suitable for recycling than soluble poly-
mer supported catalyst [3–5]. The multiple sites located at
their surfaces may afford reaction rates comparable to
those shown in homogenous systems due to the accessi-
bility for the substrate [6]. Recently there have been several
reports detailing the application of metallodendrimers as
catalysts. In a number of instances, some sort of dendritic
effect has been observed, Mapolie et al. [7] report nickel
complexes based on Periphery-functionalized dendrimers
salicylaldime ligand as catalysts for the vinyl polymeriza-
tion of norbornene. When comparing the effect of dendri-
mer generation on activity, the second generation catalysts
were found to be more active than the first generation
catalysts. De la Mata et al. reported the use of titanium-
containing carbosilane dendrimers as catalysts for the
polymerization of ethylene. Using these metallodendrimers
as catalyst precursors, polyethylene with high molecular
weight and low polydispersity was produced [8]. The
dendritic nature of the catalyst also resulted in a higher
degree of crystallinity in the polymers obtained. The
Periphery-functionalized dendrimers have their ligand
systems, and thus the metal complexes, at the surface of the
dendrimer. The transition metals will be directly available
for the substrate, in contrast to core-functionalized systems,
Keywords Ethylene Á Oligomerization Á Catalyst Á
Dendrimers Á Complexes
1 Introduction
Metallodendrimers are well-defined, highly branched, there
dimensional macromolecules with characteristic globular
T. Ahamad Á S. M. Alshehri (&)
Department of Chemistry, King Saud University, PO Box 2455,
Riyadh 11451, Kingdom of Saudi Arabia
e-mail: alshehri@ksu.edu.sa
S. F. Mapolie
Department of Chemistry and Polymer Science, University of
Stellenbosch, Private Bag X1, Matieland 7602, South Africa
123

172
T. Ahamad et al.
for example, in which the substrate has to penetrate the
dendrimer prior to reaction [9]. This accessibility allows
reaction rates that are comparable with homogeneous sys-
tems. On the other hand, the periphery-functionalized
systems contain multiple reaction sites and ligands, which
results in extremely high local catalyst and ligand
concentrations [10]. This inspireed us to synthesize
periphery-functionalized metallodendrimer precatalysts for
the polymerization of olefin. Herein we selected amino
functionalized dendrimers as a ligand support these den-
drimers were modified into metallodendrimes with transi-
tion metal ions. This article describes the preparation and
characterization of the Ni metallodendrimers, as precata-
lyst using [PDA-(NH)2]6 [PDA-(NH)2]12 and abbreviated
as C1 (nickel complex of first generation) and C2 (nickel
complex of second generation) respectively. The compar-
ison study of the metallodendrimers for ethylene poly-
merization upon activation with MAO at different pressure.
[11]. The yellow powder of 1,3,5 tris(3,5 dinitrophenyl)
benzamide [PAD-(NO2)6] was prepared by the reaction of
1,3,5-benzene tricarboxylchloride with 3,5 dinitroaniline in
acetone in 1:3 molar ratio in good yield. PAD-(NO2)6 can
be purified simply by precipitation in NaHCO3 aqueous
in quantitative yield. The formation and isolation of
PAD-(NO2)6 were confirmed by IR, elemental analysis, 1H
NMR, and 13C NMR spectroscopy as shown Figs. 1 and 2.
The IR spectrum of PAD-(NO2)6 showed strong absorption
at 1,650 cm-1 characteristic to C=O stretching of amide
group and terminal nitro groups at 1,588 and 1,290 cm-1
.
The reduction of PAD-(NO2)6 by employing SnCl2 and
concentrated hydrochloric acid successfully afforded the
desired 1,3,5 tris(3,5 diaminophenyl) benzamide {PAD-
(NH2)6} as a first generated dendrimers. The FTIR spec-
trum of {PAD-(NH2)6} show a strong peak at 3,410 cm-1
due to terminal amino groups [12]. The proton signals at d
4.36 indicate the presence of NH2 group hydrogen. The
12-amine-terminated second generation polyamide was
synthesized when PAD-(NH2)6 react with 3,5-dinitro-
benzolyl chloride in acetone under nitrogen atmosphere in
75% yield, then the similar reduction of (5) as used in the
synthesis of first generation dendrimers. The structures of
PAD-(NH2)12 was also characterized by elemental analy-
2 Results and Discussion
A general synthetic route for the first and second genera-
tion dendrimeric ligands PAD-(NH2)6 and PAD-(NH2)12 is
shown in Scheme 1. The PAD-(NH2)6 and PAD-(NH2)12
were prepared using ammonium formate and commercial
Zinc Powder as a reducing agent from their corresponding
PAD-(NO2)6 and PAD-(NO2)12 according to the literature
1
1
sis, IR, H NMR, and 13C NMR. The H NMR spectra of
PAD-(NO2)12 show proton signals for the internal branches
amide and outer branch amide at 10.20 and 10.01 ppm
respectively [13]. The terminal amino protons show
Scheme 1 Synthesis of first
generation dendrimers and their
nickel complexes
O2N
NO2
NH
O
Cl
O
O2N
NO2
acetone
reflux
+
NH
NO2
O
Cl
O
O
NO2
O2N
NH
O
Cl
NO2
NO2
SnCl /HCl
2
Cl
Cl
Ni
H2N
NH2
H2N
NH2
NH
NH
O
O
NiCl2
H2
N
NH
NH2
NH
O
O
H2
N
O
Cl
O
H2N
NH
NH
Ni
NH2
N
Cl
H2
Ni
Cl
NH2
NH2
Cl
(C )
1
123

Synthesis Characterization of Polyamide Metallodendrimers
173
Fig. 1 H NMR spectra of first
and second generation
dendrimers
resonance signals at 4.82 ppm. Scheme 2 shows the syn-
thetic route for metallodendrimers of Ni with PAD-(NH2)6
and PAD-(NH2)12. The metal complexes were synthesized
via simple complexation reaction of metal salts with first
and second generation dendrimers in ethanol (Scheme 3).
The Nickel complexes were isolated as green colour
powder in good yields. The formation of metal complexes
was supported by UV–Vis, FTIR, and elemental analysis.
The results of elemental analysis revealed that the metal
ions attached to the aromatic amine groups via coordina-
tion-covalent bonds and containing two chloride ions with
each metal ions. In IR spectra of the complexes the NH
stretching at 3,405–3,410 cm-1 shifted to the lower fre-
quency when compare with their parental dendrimeric
ligands [14]. In the metallodendrimers C1 and C2, the new
strong peak at 530 cm-1 is due to the M-N stretch of the
bond formed during coordination of Ni via terminal amino
group. Although the MALDI-TOF MS measurement of C1
and C2 provide a clear spectrum and indicated its formation
and isolation as shown in Fig. 3.
the effect of Al/Ni ratios which ranged from 50:1 to
2,000:1 molar ratios on the activities of precatalyst first
generation C1 and second generation C2 for ethylene
polymerization at room temperature. The activities of the
C1 and C2 expressed as turn over frequencies (TOF) and
given in Table 1 with 1 atm pressure of ethylene. The
oligomeric products were weighed after evaporation of the
solvent. C1 showed optimum catalyst activity at an Al:Ni
ratio of 500:1 while C2 showed optimum activity at an
Al:Ni ratio of 1,000:1 when the reaction were carried out
with 1 atm pressure of ethylene. As shown in Table 2. the
higher polymerization activity was observed at an Al:Ni
ratio of 1,000:1 for both catalysts. It is also observed that
the ethylene concentration significantly affect the catalytic
behaviour of the metallodendrimers. In comparison with
the result obtained with 1 atm pressure of ethylene, the
distribution of oligomers formed at 5 atm of ethylene
pressure shift to higher carbon number of olefins. The
oligomers obtained from our C1 catalyst and C2 catalyst,
were analyzed using gas chromatography (GC). The GC
analysis was done on the residues after evaporation of the
solvent. This was done after we confirmed that no low
boiling point oligomers were present in the reaction med-
ium. From the results it would appear that at low levels of
Polymerizations of ethylene were conducted at 1 and 5
atmospheric pressure of ethylene in toluene using first
generation and second generation metallodendrimers, and
methylaluminoxane (MAO) as co-catalyst. We investigated
123

174
T. Ahamad et al.
Fig. 2 C NMR spectra of first
and second generation
dendrimers
Al, the chain transfer process from the active Ni centre to
the Al is much more rapid than chain growth. This results
in relatively shorter oligomer chains being formed. At these
low Al concentrations, largely C10 and C12 oligomers were
obtained, with C10 being more dominant. At very high
levels of Al longer chain oligomers were obtained. From
our results we observe that our two dendrimer systems give
very different types of oligomeric products. Oligomeriza-
tion using the generation 1 dendrimer complex, C1 yields
short chain oligomers whereas those obtained from the
generation 2 dendrimer catalyst, C2 resulted in longer chain
products with molecular weights up to 9.54 9 104 and
9.86 9 104 g/mol at 1 and 5 atm respectively. The overall
activity of the generation 2 catalyst is significantly higher
than that of the generation 1 catalyst. It should however be
noted that the optimum activity for the generation 2 cata-
lyst is obtained at Al concentrations that are twice as high
than those used in reactions of the generation 1 catalyst. A
possible reason for this difference in behaviour of the
two catalysts in respect of the amount of co-catalyst used
could be due to differences in the architecture of the two
dendrimeric catalysts [15]. The generation 1 catalyst, C1
has three amide units within its internal structure, while
the generation 2 catalyst, C2 has six amide units. In both
cases these amide, being Lewis base sites, are potential
positions for the binding of the Lewis acidic organoal-
uminium co-catalyst. It is thus thought that the co-cata-
lyst as shown Scheme 2 MAO, first binds to these Lewis
basic sites before it becomes involved in the activation
of the metal centre. It is well known that N-donor
molecules form adducts with Lewis acidic Aluminium
complexes [16–18]. Since the C2 has more N-donor sites
it will react with a larger amount of the aluminum alkyl
than the C1. It therefore requires larger amounts of co-
catalyst before the optimum activity is reached for the
C2 system.
123

Synthesis Characterization of Polyamide Metallodendrimers
175
NO2
Scheme 2 Synthesis of second
generation dendrimers and their
nickel complexes
H2N
NH2
NO2
O
NO2
O2N
NO2
NH
NH
O
NH
O2N
NO2
O
O
acetone
reflux
+
NO2
NH
NH
NH2
O
Cl
O
O
O
O
H2N
NH
NO2
NH2
NH
NH
O
NH2
NH
NH
O2N
O
NH
O
NH
O
O2N
NO2
O2N
NO2
SnCl /HCl
2
NH2
NH2
O
NH2
NH
NH
H2N
NH2
O
NH2
NH
O
O
NH2
NH
NH
Cl
Cl
O
NH2
NiCl
2
O
NH
NH
NH
Ni
H2N
H3C
O
NH
O
O
NH2
NH
O
H2N
NH2
H2N
NH2
while C2 produces higher molecular weight products which
were waxy in nature (100%). This behaviour of catalyst C1
and C2 can be used in petrochemical industries.
NH
CH
NH
Cl
2
2
3
MAO
Ni
Ni
CH
Cl
3
NH
NH
2
2
MAO
4 Experimental Section
+
NH
CH
3
2
4.1 Materials and Methods
-
[MAO CH ]
3
+
Ni
Manipulations of air and moisture sensitive compounds
were performed under a nitrogen atmosphere using stan-
dard Schlenk techniques. Toluene was refluxed over
sodium-benzophenone and distilled under argon prior to
use. Methylaluminoxane (MAO, a 1.46 M solution in tol-
uene) and other chemicals were purchased from Sigma-
Aldrich. Infrared spectra were recorded on a Perkin Elmer
Paragon 1000 PC FT-IR spectrophotometer, using KBr
plates. 1H NMR (400 MHz) and 13C NMR (100 MHz)
spectra were recorded on a Varian XR200 spectrometer,
using tetramethylsilane as an internal standard. MALDI-
TOF Mass spectra were recorded using a KMPACT
MALDI mass spectrometer (Shimadzu Kratos) in positive
mode. Gas chromatography analysis was carried out on a
Varian CP-3800 using a HP PONA column. The yield of
oligomers was calculated by referencing to the mass of the
solvent on the basis of the prerequisite that the mass of
each fraction was approximately proportional to its
NH
2
Scheme 3 Mechanism of MOA as a co-catalyst
3 Conclusion
In this study, we have successfully synthesized two new
metallodendrimers and used as a catalysts for ethylene
oligomerization in the presence of MAO (co-catalyst). The
catalytic activities were found to be sensitive to the pres-
sure, co-catalyst to catalyst ratio. The best co-catalyst to
catalyst ratio is 1,000:1, at this ratio C2 exhibit higher
activity then C1, but at 500:1, Al:Ni ratio C2 show slightly
lower catalytic activity than C1. The type of molecular
oligomers formed is also dependent on the nature of the
catalyst generation. The C1 support the formation of short
chain oligomers within the C10–C20 (50–60%) diesel range,
123

176
T. Ahamad et al.
Fig. 3 MLDI-TOF-MS
of C1 and C2
integrated area in the GC trace Dodecane was used as an
internal standard. Gel permeation chromatography was
performed on a Polymer Laboratories GPC220 instrument
using polystyrene standards.
250 mL round bottom flask in 100 mL of ethanol. The
resulting yellow colour solution was allowed to reflux for
6 h under nitrogen. After the mixture was cooled to room
temperature was distilled off under reduced pressure, and
the residue was dissolved in hexane resulting precipitate
was filtrated and washed off several time. The desired
compound [1,3,5-tris(3,5-dinitrophenyl) benzamide)] was
obtained as a yellow solid powder in 70% yield after
purification by column chromatography (silica gel, 3/1
(v/v) petroleum ether/ethyl acetate). Mp: 190 °C. FTIR
(KBr, cm-1): 1110, 1340, 1560, 1588, 1615, 1710, 3265;
1H NMR (400 MHz, DMSO, TMS, d): 10.46 (s, 3H,
4.2 Synthesis
4.2.1 Synthesis of 1,3,5-Tris(3,5-Dinitrophenyl)
Benzamide (1)
1,3,5-Benzene tricarboxylchloride (2.65 g, 0.1 mol) and
3,5-dinitroaniline (2.74 g, 0.3 mol) were mixed in a
123

Synthesis Characterization of Polyamide Metallodendrimers
177
Table 1 Oligomerization of 1 atm of ethylene with C1–C2/MAO
Entry
Catalyst
Al/Ni (mol)
Oligomer distribna (%)
Activityb
Mcw (9104) (g/mol)
PDI (Mw/Mn)
C10/RC
C12/RC
C14/RC
C16?/RC
1
C1
C1
C1
C1
C1
C1
C2
C2
C2
C2
C2
C2
50
100
62
58
26
2
37
30
50
43
4
1
8
14
7
6
–
4
–
–
–
–
–
–
425
982
–
–
2
4
–
–
3
200
10
1356
2450
1845
1536
110
–
–
4
500
48
–
–
5
1000
2000
50
–
90
–
–
6
–
–
100
16
6.12
–
1.42
–
7
–
–
8
100
–
–
100
100
100
100
100
460
7.52
7.78
8.24
9.54
7.65
1.76
1.94
1.49
1.65
1.47
9
200
–
–
812
10
11
12
500
–
–
1427
3250
2600
1000
2000
–
–
–
–
General condition: 5 lmol of catalyst; 30 min; room temperature, 30 mL of toluene
a
Determined by GC; RC signifies the total amounts of oligomers
b
TOF: 103 g of polyethylene produced per mol of Ni per hour per bar
c
Determined by GPC
Table 2 Oligomerization of 5 atm of ethylene with C1–C2/MAO
Entry
Catalyst
Al/Ni (mol)
Oligomer distribna (%)
Activityb
Mcw (9104) (g/mol)
PDI (Mw/Mn)
C10/RC
C12/RC
C14/RC
C16?/RC
1
C1
C1
C1
C1
C1
C1
C2
C2
C2
C2
C2
C2
50
100
59
53
21
–
32
21
30
10
–
9
–
420
840
–
–
2
14
19
53
–
12
–
–
3
200
20
1295
1920
2360
1820
230
–
–
4
500
37
–
–
5
1000
2000
50
–
100
100
100
100
100
100
100
100
6.86
7.42
7.86
8.12
8.65
9.22
9.86
8.02
1.46
1.56
1.84
1.88
1.56
1.64
1.76
1.52
6
–
–
–
7
–
–
–
8
100
–
–
–
500
9
200
–
–
–
960
10
11
12
500
–
–
–
1590
3280
2430
1000
2000
–
–
–
–
–
–
General condition: 5 lmol of catalyst; 30 min; room temperature, 30 mL of toluene
a
Determined by GC; RC signifies the total amounts of oligomers
b
TOF: 103 g of polyethylene produced per mol of Ni per hour per bar
c
Determined by GPC
NHCO), 7.12 (s, 3H, ArH), 6.96 (s, 3H, ArH), 6.42 (s, 6H,
ArH). Anal. Calcd for C27H15N9O15 (705.46): C, 45.97; H,
2.14; N, 17.87. Found: C, 45.95; H, 2.13; N, 17.89.
and refluxed for 30 min. Cool the flask and add a solution
of sodium hydroxide in 100 cm3 of water to re-dissolve the
initial precipitate. Add 3 g of powdered sodium chloride to
the mixture, shake to dissolve, and then transfer the liquid
to a separating funnel and 10 mL of chloroform. The
separated organic mixture was washed off several times
with water. The solvent was evaporated at reduced pres-
sure, and the desired compound 2 was obtained as a brown
4.2.2 Synthesis of First-Generation Dendritic Ligand (2)
To a solution of 1 (3.52 g, 50 mmol in 30 mL of acetone)
and Sn (7.64 g), conc. HCl (60 mL) was drop wised added
123

178
T. Ahamad et al.
colours powder in 54% yield after purification by column
chromatography (silica gel, 3/1 petroleum ether/ethyl ace-
tate). Mp: 245 °C, FTIR (KBr, cm-1): 1511, 1556, 1596,
the reaction mixture was allowed to stir under reflux for
24 h forming a green precipitate. The precipitate was fil-
tered off by vacuum filtration and washed extensively with
ethanol to afford C1 as a green solid in 80% yield. Mp:
245 °C, FTIR (KBr, cm-1): 1515, 1550, 1584, 1620, 1680,
3374. Anal. Calcd for C27H27N9O3Ni3Cl6 (914.35): C,
35.47; H, 2.98; N, 13.79; Cl, 23.26; Ni, 19.26. Found: C,
35.47; H, 2.98; N, 13.79, Cl, 23.26, Ni, 19.26.
1
1622, 1680, 3409. H NMR (400 MHz, DMSO, TMS, d):
9.84(s, 3H, NH–CO), 6.81 (s, 3H, ArH), 6.52 (s, 6H, ArH),
6.21 (s, 3H, ArH) and 4.83 (s, 12H, Ar–NH2); 13C NMR
(100 MHz, DMSO, TMS): 102.3, 128.4, 134.9, 136.8, and
174.8 ppm. ESI-MS (m/z): 526.23 (M ? H?). Anal. Calcd
for C27H27N9O3 (525.56): C, 61.70; H, 5.18; N, 23.99.
Found: C, 61.71; H, 5.17; N, 23.98.
4.2.6 Synthesis of Generation 2 Dendritic Nickel
Complex (C2)
4.2.3 Synthesis of Second Generation Nitro Group
Terminated Dendrimers (3)
To a solution of the PAD-(NH2)12 dendrimeric ligand
(6.65 g, 5 mmol) in ethanol (10 mL) was added nickel
chloride hexahydrate (7.60 g, 30 mmol) and the mixture
stirred under reflux for 24 h. The solvent was evaporated
via rotary evaporation to give a green residue. The residue
was then dissolved in dichloromethane (15 mL) and the
solution was filtered by gravity and dried to afford complex
C2 as a green solid in 76% yield. Mp: 348 °C. FTIR (KBr,
cm-1): 1110, 1342, 1560, 1556, 1582, 1648, 1712, 3260;
C69H39N21O9Ni6Cl12 (2083.77): C, 39.77; H, 1.89; N,
14.12; Cl, 20.42; Ni, 16.90. Found: C, 39.78; H, 1.88; N,
14.14, Cl, 20.43, Ni, 16.91.
To a solution of 2 (5.26 g, 10 mmol) in chloroform
(100 mL) was added 1,3-dinitrobenzoyl chloride (13.99 g,
60 mmol) and the mixture was refluxed under nitrogen,
with stirring at 70 °C for 5 h resulting yellow colour
mixture found. The process of reaction was monitored by
TLC using CH2Cl2 and hexane as eluent. After completion
of the reaction the solvent was removed under reduced
pressure and washed off several time using water, and
obtained as a yellow brown powder in 60% yield. Mp:
275 °C. FTIR (KBr, cm-1): 1115, 1342, 1560, 1558, 1588,
1
1650, 1720, 3245; H NMR (400 MHz, DMSO, TMS, d):
Acknowledgments We would like to thanks the College of Science
Research centre, King Saud University, for financial support under
Grant No. CHEM/2010/10 and vice reactor of King Saud University.
9.81 (s, 3H, NH–CO), 9.76 (s, 6H, NH–CO), 7.27 (s, 9H,
ArH), 6.84 (s, 3H, ArH), 6.62 (s, 6H, ArH), and 6.25 (s,
12H, ArH). 13C NMR (100 MHz, DMSO, TMS): 104.2,
112.5, 114.2, 129.8, 133.3, 135.4, 137.2, 145.2, 171.8 and
174.1 ppm. Anal. Calcd for C69H39N21O33 (1690.17): C,
62.29; H, 4.77; N, 22.11. Found: C, 62.30; H, 4.78; N,
22.10.
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4.2.4 Synthesis of Second Generation Dendritic Ligand (4)
Using the same procedure as for the synthesis of 3 was
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1
1562, 1560, 1586, 1652, 1721, 3265; H NMR (400 MHz,
DMSO, TMS, d): 4.82 (s, 48H, NH2), 10.10 (s, 3H,
NH–CO), 9.82 (s, 6H, NH–CO), 7.18 (s, 9H, ArH), 6.82
(s, 3H, ArH), 6.48 (s, 6H, ArH), and 6.21 (s, 12H, ArH).
13C NMR (100 MHz, DMSO, TMS): 103.2, 110.8, 115.4,
123.8, 134.2, 136.0, 138.4, 147.0, 170.6 and 173.2 ppm.
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