Dendritic β-diketiminato titanium and zirconium complexes: Synthesis and ethylene polymerisation

Article abstract of DOI:10.1016/j.jorganchem.2004.10.041

The cyclopentadienyl(β-diketiminato)titanium and zirconium chlorides (η⁵-C₅H₅)MCl₂(CH(C(NC ₆H₄-4-OR)CH₃)₂) (M = Ti (4-dend), Zr (5-dend)), where R corresponds to the f

Full text of DOI:10.1016/j.jorganchem.2004.10.041

Journal of Organometallic Chemistry 690 (2005) 939–943
www.elsevier.com/locate/jorganchem
Dendritic b-diketiminato titanium and zirconium
complexes: synthesis and ethylene polymerisation
*
Roman Andres , Ernesto de Jesus, F. Javier de la Mata, Juan C. Flores, Rafael Gomez
´
´
´
´
´ ´ ´ ´
Departamento de Quımica Inorganica, Universidad de Alcala, Campus Universitario, E28871 Alcala de Henares, Madrid, Spain
Received 29 June 2004; accepted 25 October 2004
Available online 24 November 2004
Abstract
The cyclopentadienyl(b-diketiminato)titanium and zirconium chlorides (g5-C5H5)MCl2(CH(C(NC6H4-4-OR)CH3)2) (M = Ti (4-
dend), Zr (5-dend)), where R corresponds to the first generation carbosilane dendron (dendritic wedge) Si(CH2CH2SiMePh2)3, have
been synthesised. After activation with methylaluminoxane, the activity of 4-dend and 5-dend as catalysts for ethylene polymerisa-
tion has been determined and compared with that of the non-dedritic counterpart (g5-C5H5)MCl2(CH(C(NC6H5)CH3)2) (M = Ti
(4), Zr (5)).
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Diketiminato ligands; Dendrimers; Titanium; Zirconium; Substituent effects
1. Introduction
nyl(b-diketiminato) complexes of titanium and zirco-
nium containing carbosilane dendritic wedges of first
generation linked to the b-diketiminato ligand [4]. The
location of the dendritic wedges in the complexes here
described has been chosen in such a way that little steric
hindrance should be expected in the close environment
of the metal center.
A large number of reports published on metallodend-
rimers [1] deal with catalysis [2]. The location of the
transition metal within the dendritic framework (core,
branches, or periphery) is a critical issue in the design
of such catalysts. When one or more dendritic wedges
are incorporated to ligands, their metal complexes can
benefit from the local environment created by the
wedges to which focal point are linked. In a previous pa-
per [3], we observed significant modifications on the
molecular weight distributions of polymers when tita-
nium metallocenes with dendritic substituents at the
cyclopentadienide ligands were used in ethylene polym-
erisation. This fact, which was accompanied by a
decreasing in activity, was interpreted as a result of the
space filling produced by the wedges in the vicinity of
the metal centres. In this paper, we describe the synthesis
and ethylene polymerisation of mixed cyclopentadie-
2. Results and discussion
The synthetic route to the metal complexes is de-
picted in Scheme 1. The hydroxyphenyl b-diketimine 2
was synthesised through the classical method based on
the condensation of a primary amine (4-aminophenol)
with a b-diketone (2,4-pentanedione) [5], a multistep
process involving the enaminoketone intermediate 1. A
carbosilane dendron was attached to the para position
of each diketimine phenyl ring via phenolysis of Si–Cl
bonds at the focal point with the hydroxy protons of 2
in the presence of triethylamine. The protonolysis was
quantitative (1H NMR evidence) but dendritic b-diketi-
mine 3-dend was isolated as a yellow solid (melting over
*
Corresponding author. Tel.: +34 91 885 4677; fax: +34 91 885
4683.
´
E-mail address: roman.andres@uah.es (R. Andres).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.10.041

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R. Andres et al. / Journal of Organometallic Chemistry 690 (2005) 939–943
940
OH
H
CaSO4
O
O
O
N
H
H2N
OH
+
THF, Reflux
N
N
1
3
HO
NH2.HCl
EtOH
N
N
Cl
Cl
M
HO
OH
HO
OH
M = Ti (4)
Zr (5)
H
N
H H
NEt3
THF
N
N
N
2
Cl
Si
ClSi(CH2CH2SiMePh2)3
NEt3, THF
Si
Si
Si
O
N
N
Cl
Cl
M
Si
Si
(η5-C5H5)TiCl2
NEt3, THF
Si
Si
Si
O
Si
O
Si
Si
M = Ti (4-dend)
Zr (5-dend)
O
Si
H
Si
N
N
Si
Si
3-dend
Scheme 1.
15 ꢁC) in only a 48% yield after workup, due to its high
solubility in most common organic solvents (see Section
4). Both b-diketimines 2 and 3-dend, which are depicted
in Scheme 1 with localised bonds for simplicity, are bet-
ter described by a symmetrically hydrogen-bonded
structure consistent with the chemical shift equivalence
of the two methyl groups, and the large low-field shift
of the N–H proton [6].
Mixed cyclopentadienyl(b-diketiminato) complexes
of titanium (4-dend) and zirconium (5-dend) were ob-
tained by direct reaction of (g5-C5H5)MCl3 (M = Ti,
Zr) with dendritic b-diketimine 3-dend, in the presence
of triethylamine as Lewis base to promote the protono-
lysis of the metal–chloride bond. Complexes are isolated
in high yield as red (4-dend) or pale-yellow (5-dend) oily
products. Similar procedures have been used for the
preparation of related complexes (titanium 4, and the al-
ready reported [7] zirconium 5), which were synthesised
as reference for the ethylene polymerisation studies de-
scribed below.
the solid state for the indenyl analogue of 5 [7]. How-
ever, the CH shift in 5 is similar to that found in other
related complexes with r coordination, may be indicat-
ing a facile p ! r interconversion in solution [7].
The renewed interest in b-diketiminato transition me-
tal complexes is partially due to the ability of this ligand
to stabilise coordinatively unsaturated complexes [5]
that function as catalysts in, e.g., non-metallocene olefin
polymerization [9]. Recent reports have demonstrated
that mixed cyclopentadienyl(b-diketiminato)zirconium
complexes as 5, be have as single-site catalyst for the
polymerisation of ethylene [10]. Table 1 summarises
our results obtained with complexes 4-5 after activation
with an excess of methylaluminoxane (MAO). These
catalysts are far from the performance of the metallo-
cene complexes (g5-C5H5)2MCl2 (M = Ti, Zr) [3].
However, dendritic catalyst 4-dend and 5-dend displayed
Table 1
Ethylene polymerization results with complexes 4–5 and 4–5-denda
Precatalyst
Yield (mg)
Activity (kgPE/molM h)
b–Diketiminato ligands adopt a diversity of bonding
modes in their coordination to metals ranging from g2–
2r (4e) to g5–p (6e) in mononuclear complexes. The
similarity of the NMR chemical shifts for the methine
protons [8] in diketiminato complexes 4–5 (5.37 (4)
and 5.42 (4-dend), 5.22 (5) and 5.23 ppm (5-dend)) may
be consistent with the g5 coordination mode found in
4
4-dend
22
76
4
53
182
10
5
5-dend
10
24
a
Conditions: MAO cocatalyst, Al/M = 1000, 1.25 lmol of catalyst
dissolved in 50 ml of toluene, 20 min, 293 K, 1 bar of constant
monomer pressure.

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R. Andres et al. / Journal of Organometallic Chemistry 690 (2005) 939–943
941
slightly higher activities than non dendritic complexes 4
and 5.
washed with THF (4 · 50 ml) and reacted with an excess
of triethylamine (3 ml) in THF (50 ml). The reaction
mixture was stirred overnight and filtered off. The solu-
tion was evaporated in vacuo to dryness and the residue
was extracted with a mixture of THF/Pentane (ca. 15 ml,
1:5 v/v). After evaporation of solvents, compound 2 (2.5
g, 34%) was obtained as an orange solid, sometimes con-
taminated by small amounts of 4-aminophenol. Anal.
Calc. for C17H18N2O2: C, 72.32; H, 6.43; N, 9.92.
3. Conclusion
A b-diketiminato ligand has been incorporated to the
focal point of two carbosilane dendrons, and used for
the preparation of the corresponding cyclopentadie-
nyl(b-diketiminato)titanium and zirconium complexes.
The dendritic catalysts show an increased activity com-
pared to their non dendritic analogues. Further studies
are in progress.
1
Found: C, 72.45; H, 6.49; N, 9.89. H NMR (CDCl3/
CD3OD 5:1 v/v): d 6.64 (center of an AA0BB0 spin sys-
tem, 8H, C6H4), 4.67 (s, 1H, CH), 1.80 (s, 6H, CH3),
NH and OH not observed, probably due to exchange
with CD3OD. 13C NMR (CDCl3/CD3 OD 5:1 v/v): d
159.9 (CH3CN), 152.8 (C6H4, C4), 137.5 (C6H4, C1 (car-
bon linked to N)), 124.0 (C6H4, C2,3), 115.0 (C6H4, C3,5),
95.7 (CH), 20.1 (CH3).
4. Experimental
4.1. Reagents and general techniques
4.4. Synthesis of MeC(NHC6H4-4-OR)CHC(NC6H4-4-
OR)Me, R = Si(CH2CH2SiMePh2)3 (3-dend)
General techniques are described in [3]. (g5-
C5H5)TiCl3 [11], ClSi(CH2CH2SiMePh2)3 [3] and 3 [12]
were prepared according to literature procedures.
Chemical shifts (d, ppm) are relative to SiMe4 and were
measured by internal referencing to the deuterated sol-
An excess of triethylamine (1.0 ml) was added to a
solution of b-diketimine 2 (0.382 g, 1.35 mmol) and
ClSi(CH2CH2SiMePh2)3 (2.00 g, 2.70 mmol) in THF
(50 ml). After stirring for 2 h, the solvent and the excess
of triethylamine were removed by evaporation in vacuo
to dryness, and the residue was extracted with cold THF
(20 ml, 0 ꢁC). The resulting solution was concentrated
up to 2 ml and, after addition of pentane (20 ml), cooled
at ꢀ30 ꢁC overnight. The yellow oil that separated at the
bottom of the Schlenk was dried in vacuo after carefully
removal of the supernatant solution with a syringe. The
above process (dissolution, cooling, removal and drying)
was repeated several times until crystallization of a yel-
low compound (1.1 g, 48%) that remains permanently
solid below its melting point (ca. 15 ꢁC). Anal. Calc.
for C107H118N2O2Si8: C, 76.10; H, 7.04; N, 1.66. Found:
1
vent (13C and residual H resonances), or by the substi-
tution method from the 29Si resonance of SiMe4.
4.2. Synthesis of MeC(NHC6H4-4-OH)CHC(O)Me (1)
2,4-Pentanedione (9.0 ml, 88 mmol) was added to a
mixture of 4-aminophenol (9.6 g, 88 mmol) and calcium
sulphate (5 g) in THF (100 ml). The reaction mixture
was refluxed for 24 h. Then, the CaSO4 was separated
by filtration, the solution was concentrated up to 50
ml, and pentane (30 ml) was added. The white solid pre-
cipated was filtered and dried in vacuo to yield 13.3 g
(79%) of pure 1. Anal. Calc. for C11H13NO2: C, 69.09;
H, 6.85; N, 7.32. Found: C, 69.13; H, 6.90; N, 7.37%.
1H NMR (CDCl3): d 12.22 (m, 1H, NH), 8.25 (broad
s, 1H, OH), 6.85 (center of an AA0BB0 spin system,
4H, C6H4), 5.14 (d, 1H, CH, 4J = 0.45 Hz), 2.09 (s,
1
C, 76.15; H, 7.10; N, 1.69%. H NMR (C6D6): d 13.12
(s, 1H, NH), 7.47 (m, 24H, SiC6H5), 7.15 (two multiplets
overlapping, 36H, SiC6H5), 6.75 (center of an AA0BB0
spin system, 8H, C6H4), 4.84 (s, 1H, CH), 1.84 (s, 6H,
CH3CN), 1.09 and 0.86 (m, 24H, SiCH2H2Si), 0.46 (s,
18H, SiCH3). 13C NMR (C6D6): d 159.8 (CH3CN),
152.2 (C6H4, C4), 140.1 (C6H4, C1 (carbon linked to
N)), 124.5 (C6H4, C3,5), 120.2 (C6H4 C2,6), 97.3 (CH),
20.6 (CH3CNH), 129.4 (C6H5, C4), 137.2 (C6H5, C1
(carbon linked to Si)), 134.9 (C6H5, C2,6), 128.2 (C6H5,
C3,5), 5.9 and 5.2 (SiCH2CH2Si), ꢀ4.9 (SiCH3). 29Si
NMR (C6D6): d 19.1 (s, 2Si), ꢀ5.6 (s, 6Si).
4
3H, CH3CO), 1.89 (d, 3H, CH3NH, J = 0.36Hz). 13C
NMR (CDCl3): d 195.6 (CO), 162.9 (CH3CNH), 155.3
(C6H4, C4), 130.2 (C6H4, C1 (carbon linked to N)),
126.7 (C6H4, C2,6), 116.1 (C6H4, C3,5), 96.7 (CH), 28.6
(CH3CO), 19.7 (CH3CNH).
4.3. Synthesis of MeC(NHC6H4-4-OH)CHC(NC6H4-4-
OH)Me (2)
Enaminoketone 1 (5.0 g, 26 mmol), 4-aminophenol
hydrochloride (3.8 g, 26 mmol), calcium sulphate (10
g), and dry ethanol (100 ml) were introduced into a
200 ml ampoule fitted with a PTFE stopcock, and
heated in an oil bath for 72 h at 90 ꢁC. Subsequently,
the solvent was removed in vacuo and the residue
4.5. Synthesis of (g5-C5H5)MCl2(CH(C(NC6H4- 4-OR)-
CH3)2), R = Si(CH2CH2SiMePh2)3)
4-dend (M = Ti). An excess of triethylamine (0.020
ml, 0.14 mmol) was added to a mixture of b-diketimine
3-dend (0.100 g, 0.060 mmol) and (g5-C5H5)TiCl3 (0.013

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R. Andres et al. / Journal of Organometallic Chemistry 690 (2005) 939–943
942
g, 0.060 mmol) in toluene (20 ml), and stirred for 8 h.
Subsequently, the solution was filtered and evaporated
in vacuo to dryness to yield 4-dend as a spectroscopically
pure, red oil (0.095 g, 85%). Anal. Calc. for
in agreement with those previously reported by Rahim
et al. [7].
4.7. Ethylene polymerisation
C
112H122N2O2Si8Cl2Ti: C, 71.87; H, 6.57; N, 1.50.
1
Found: C, 71.95; H, 6.60; N, 1.47%. H NMR (C6D6):
d 7.49 (m, 24H, SiC6H5), 7.18 (two multiplets overlap-
ping, 36H, SiC6H5), 6.80 (center of an AA0BB0 spin sys-
tem, 8H, C6H4), 6.25 (s, 5H, C5H5), 5.42 (s, 1H, CH),
1.68 (s, 6H, CH3CN), 1.10 and 0.92 (m, 24H, SiCH2H2
Si), 0.47 (s, 18H, SiCH3). 13C NMR (C6D6): d 161.4
(CH3CN) 154.2 (C6H4, C4), 148.3 (C6H4, C1 (carbon
linked to N)), 125.2 (broad, C6H4, C2,6) 120.1 (C6H4,
C3,5), 122.6 (C5H5), 99.9 (CH), 22.7 (C3 CNH), 129.6
(C6H5, C4), 137.0 (C6H5, C1 (carbon linked to Si)),
134.8 (C6H5, C2,6), 128.3 (C6H5, C3,5), 6.0 and 5.4
(SiCH2CH2Si), ꢀ4.8 (SiCH3). 29Si NMR (C6D6): d
19.9 (s, 2Si), ꢀ5.7 (s, 6Si).
A 250 ml flask charged with toluene (50 ml) and
equipped with a magnetic stirrer was four times evacu-
ated and refilled with pre-dried ethylene gas. Keeping
the flask pressurised with ethylene (1 bar) and stirred at
room temperature, a toluene solution of MAO, 0.83 ml,
1.5 M was syringed through a septum. After 5 min, a
toluene solution of the catalyst (0.50 ml, 2.5 mM) was
injected into the flask with simultaneous starting of a
stopwatch. The polymerization was quenched 20 min
later by closing the ethylene feeding, release of the over-
pressure and addition of acidified methanol (4% v/v
HCl). The mixture was stirred for 6H and the polymer
was filtered, washed with copious amounts of methanol,
and dried in an oven to constant weight.
5-dend (M = Zr). This complex was obtained as a
pale-yellow oil in 90% yield by a similar procedure of
that described in detail for 4-dend. Anal. Calc. for
C
112H122N2O2Si8Cl2Zr: C, 70.25; H, 6.42; N, 1.46.
Acknowledgements
1
Found: C, 70.45; H, 6.49; N, 1.43%. H NMR (C6D6):
d 7.48 (m, 24H, SiC6H5), 7.18 (two multiplets overlap-
ping, 36H, SiC6H5), 6.80 (center of an AA0BB0 spin sys-
tem, 8H, C6H4), 6.23 (s, 5H, C5H5), 5.22 (s, 1H, CH),
1.73 (s, 6H, CH3CN), 1.08 and 0.86 (m, 24H, SiCH2H2-
Si), 0.46 (s, 18H, SiCH3). 13C NMR (C6D6): d 164.2
(CH3CN) 154.1 (C6H4, C4), 144.1 (C6H4, C1 (carbon
linked to N)), 125.4 (C6H4, C2,6), 120.3 (C6H4, C3,5),
91.4 (CH), 22.3 (C3CN), 129.6 (C6H5, C4), 137.0
(C6H5, C1 (carbon linked to Si)), 134.8 (C6H5, C2,6),
128.2 (C6H5, C3,5), 117.3 (C5H5), 6.0 and 5.3
(SiCH2CH2Si), ꢀ4.9 (SiCH3). 29Si NMR (C6D6): d
19.8 (s, 2Si), ꢀ5.7 (s, 6Si).
We gratefully acknowledge financial support from the
´
y Tecnologıa (Project
DGI-Ministerio de Ciencia
´
BQU2001-1160 and FEDER-Programa Ramon y Cajal),
and Comunidad de Madrid (Project 07N/0078/2001).
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added to a THF solution of b-diketimine 3 (0.200 g,
0.80 mmol) and (g5-C5H5)TiCl3 (0.175 g, 0.80 mmol).
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was added to the solution until precipitation of a red so-
lid that was filtered and dried in vacuo to yield 4 (0.300
g, 86%). Anal. Calc. for C22H22N2Cl2Ti: C, 61.00; H,
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´ ´
´
[3] R. Andres, E. de Jesus, F.J. de la Mata, J.C. Flores, R. Gomez,
1
5.12; N, 6.47. Found: C, 60.85; H, 5.10; N, 6.43%. H
NMR (C6D6): d 7.10 (m, 4H, C6H5), 6.92 (two multi-
plets overlapping, 6H, C6H5), 6.17 (s, 5H, C5H5), 5.33
(s, 1H, CH), 1.61 (s, 6H, CH3). 13C NMR (C6D6): d
161.3 (CH3CN) 154.4 (C6H5, C1 (carbon linked to N)),
129.0 (C6H5, C3,5), 126.4 (C6H5, C4), 124.0 (broad,
C6H5, C2,6), 122.6 ( C5H5), 99.9 (CH), 22.5 (CH3).
5 (M = Zr). Complex 5 was prepared by the same
procedure above described for 4, and obtained as a
pale-yellow solid in 90% yield. Spectroscopic data are
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[4] Some authors state that 4-dend and 5-dend should not be
denominated as dendritic complexes if there is not a way to go
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observation. In fact, we have developed a simple procedure for
preparing ClSi(carbosilane) dendrons of higher generations that
should allow the synthesis of similar metal complexes of second
´
and higher generations. Andres et al. (manuscript in preparation).
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