The sterically expanded octamethyloctahydrodibenzofluorene moiety, C29H38
(Oct), has been incorporated into ansa-metallocenes and constrained geometry catalysts
(CGC's). Utilization of this sterically expanded version of fluorene has resulted in solidstate
anomalies for both systems.
The ansa-metallocenes Me2C(n5-C5H4) (n5-C29H36)MCl2, M = Zr, Hf and
Me2C(n5-C5H4)(n5-C29H36)ZrBn2 demonstrate crystal motifs expected for ansametallocenes
while Me2C(n5-C5H4)(n5-C29H36)MMe2, M=Zr, Hf exhibit diffuse
diffraction, a phenomenon that is extremely unusual for organometallic complexes. This
crystalline anomaly is the result of a disorder restricted to two dimensions caused by the
rare pillared motif of the system. The best solution for this system consists of parallel
and anti-parallel pillars present in a 60:40 ratio.
The solid state anomaly observed for the Oct-CGC's occurs on a molecular level.
The parent Oct-CGC, Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2, demonstrates an
unprecedented n1 ligation to the fluorenyl-based ring. Systematic derivatization of this
system via halide substitution, alkylation, and exchange of Zr for Hf has revealed that the n1 ligation persists for systems with small substituents on the metal center capable of
retaining a coordinated ether.
It is hypothesized that the unusual structure of this new Oct-CGC results in
Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2/MAO (MAO = methylaluminoxane) being six
times more active in the homopolymerization of 1-octene than ethylene. When
compared to the prototypical Ti-CGC Me2Si(n5-C5Me4)(n1-N-tBu)TiCl2/MAO, the Oct-CGC is 85 times more reactive in the homopolymerization of 1-octene and 52 times
more active in the copolymerization of 1-octene and 4-methyl-1-pentene. The high
reactivity of the Oct-CGC towards alpha-olefins results in the observation of an unyielding
comonomer effect in the copolymerization of these olefins with ethylene.
In addition, the Oct-CGC is perhaps the most syndioselective catalyst known.
With an enantiofacial selectivity of 99.7% and a remarkably high activity towards alpha-olefins, the Oct-CGC is capable of producing the highest melting syndiotactic
polypropylene (Tm = 165oC, annealed = 174oC) reported thus far. The high activity and
syndioselectivity of the Oct-CGC can be extended to the production of syndiotactic
poly(4-methyl-1-pentene) with the highest melting point thus far reported (Tm = 215oC).
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3106 |
| Date | 12 April 2006 |
| Creators | Irwin, Levi Jacob |
| Contributors | Miller, Stephen A. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 8226770 bytes, electronic, application/pdf, born digital |
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