less industrial interest in this homogeneous Ziegler catalyst because of the low
polymerization activity.
The most investigated homogeneous catalyst systems are based on bis(cyclopentadienyl)titanium(IV), bis(cyclopentadienyl)zirconium(IV), tetrabenzyltitanium, vanadium chloride, and trialkylaluminum or alkylaluminum halides as cocatalysts.
Subsequent research on these and other systems with various alkyl groups has been
conducted by Patat and Sinn [4], Shilov [5], Henrici-Olive ´ and Olive ´ [6], Reichert
and Schoetter [7], and Fink et al. [8].
The polymerization of olefins, promoted by homogeneous Ziegler catalysts
based on biscyclopentadienyltitanium(IV) or analogous compounds and aluminum
alkyls, is accompanied by a series of other reactions such as alkylation, hydrogen
transfer, and reduction that greatly complicate the kinetic interpretation of the
polymerization. It was found that the polymerization takes place primarily into a
Ti–C bond where the titanium exists as the titanium(IV) alkyl cation formed by
alkylation and dissociation (1) and (2) [8–11]:
C 5 H 5
ð
Þ 2 TiCl 2 þ AlR 2 Cl ! C 5 H 5
ð
Þ 2 TiRCl þ AlRCl 2
(1)
C 5 H 5
ð
Þ 2 TiRCl þ AlRCl 2 ! C 5 H 5
ð
Þ 2 TiR
Â
à þ þ AlRCl 3
½
À
(2)
In the case of β-hydrogen transfer by ethyl alkylated titanium complexes,
Ti–CH 2 –CH 2 –Ti units are formed (3), which are unstable and decompose within
some seconds into titanium(III) species and ethene (4) [12, 13]:
2 Cp 2 Ti Cl
ð ÞCH 2 ÀCH 3 ! Cp 2 Cl
ð ÞTiÀCH 2 ÀCH 2 ÀTi Cl
ð ÞCp 2 þCH 3 ÀCH 3 (3)
Cp 2 Cl
ð ÞTi À CH 2 À CH 2 À Ti Cl
ð ÞCp 2 ! 2 Cp 2 TiCl þ CH 2 ¼ CH 2
(4)
The bridged titanium complexes as well as the reduced titanium(III) species
are polymerization inactive. Analogous zirconium complexes have been used to
isolate intermediates and to study alkyl exchange and β-hydrogen transfer because
zirconium is less easily reduced than titanium [14, 15]. Sinn and Kolk isolated a stable
Cp 2 (Cl)Zr–CH 2 –CH 2 –Zr(Cl)Cp 2 complex [16]. Zirconium–aluminum alkyl
complexes with unusual bonding angles (75.9
) between the bridging angles were
obtained (Fig. 1), showing the force in these complexes [17]. It looks like an ethene is
complex bonded between two zirconium complexes, but NMR measurements show
that the chemical C–C bond of the bridge (bond length 0.151 nm) is normal.
In the Institute of Technical and Macromolecular Chemistry at the University of
Hamburg we investigate these side reactions, especially the hydrogen transfer
reactions. The main goal of the research is to be able to engineering the polymer
reaction. The kinetics of polymer reactions are studied as well as the analysis of
polymers and different side pathways. In the Hamburg Institute, research groups for
polymer synthesis and characterization, polymer physics, and polymer recycling
work together [18, 19].
Methylaluminoxane: Key Component for New Polymerization Catalysts
3
polymerization activity.
The most investigated homogeneous catalyst systems are based on bis(cyclopentadienyl)titanium(IV), bis(cyclopentadienyl)zirconium(IV), tetrabenzyltitanium, vanadium chloride, and trialkylaluminum or alkylaluminum halides as cocatalysts.
Subsequent research on these and other systems with various alkyl groups has been
conducted by Patat and Sinn [4], Shilov [5], Henrici-Olive ´ and Olive ´ [6], Reichert
and Schoetter [7], and Fink et al. [8].
The polymerization of olefins, promoted by homogeneous Ziegler catalysts
based on biscyclopentadienyltitanium(IV) or analogous compounds and aluminum
alkyls, is accompanied by a series of other reactions such as alkylation, hydrogen
transfer, and reduction that greatly complicate the kinetic interpretation of the
polymerization. It was found that the polymerization takes place primarily into a
Ti–C bond where the titanium exists as the titanium(IV) alkyl cation formed by
alkylation and dissociation (1) and (2) [8–11]:
C 5 H 5
ð
Þ 2 TiCl 2 þ AlR 2 Cl ! C 5 H 5
ð
Þ 2 TiRCl þ AlRCl 2
(1)
C 5 H 5
ð
Þ 2 TiRCl þ AlRCl 2 ! C 5 H 5
ð
Þ 2 TiR
Â
à þ þ AlRCl 3
½
À
(2)
In the case of β-hydrogen transfer by ethyl alkylated titanium complexes,
Ti–CH 2 –CH 2 –Ti units are formed (3), which are unstable and decompose within
some seconds into titanium(III) species and ethene (4) [12, 13]:
2 Cp 2 Ti Cl
ð ÞCH 2 ÀCH 3 ! Cp 2 Cl
ð ÞTiÀCH 2 ÀCH 2 ÀTi Cl
ð ÞCp 2 þCH 3 ÀCH 3 (3)
Cp 2 Cl
ð ÞTi À CH 2 À CH 2 À Ti Cl
ð ÞCp 2 ! 2 Cp 2 TiCl þ CH 2 ¼ CH 2
(4)
The bridged titanium complexes as well as the reduced titanium(III) species
are polymerization inactive. Analogous zirconium complexes have been used to
isolate intermediates and to study alkyl exchange and β-hydrogen transfer because
zirconium is less easily reduced than titanium [14, 15]. Sinn and Kolk isolated a stable
Cp 2 (Cl)Zr–CH 2 –CH 2 –Zr(Cl)Cp 2 complex [16]. Zirconium–aluminum alkyl
complexes with unusual bonding angles (75.9
) between the bridging angles were
obtained (Fig. 1), showing the force in these complexes [17]. It looks like an ethene is
complex bonded between two zirconium complexes, but NMR measurements show
that the chemical C–C bond of the bridge (bond length 0.151 nm) is normal.
In the Institute of Technical and Macromolecular Chemistry at the University of
Hamburg we investigate these side reactions, especially the hydrogen transfer
reactions. The main goal of the research is to be able to engineering the polymer
reaction. The kinetics of polymer reactions are studied as well as the analysis of
polymers and different side pathways. In the Hamburg Institute, research groups for
polymer synthesis and characterization, polymer physics, and polymer recycling
work together [18, 19].
Methylaluminoxane: Key Component for New Polymerization Catalysts
3