Chemistry Reference
In-Depth Information
5
Well-Defined Transition Metal Catalysts
for Metathesis Polymerization
Michael R. Buchmeiser
5.1
Introduction
Quite late on (that is in the 1980s), metathesis polymerization has been added to
the armour of transition metal-catalyzed polymerizations. The mechanism of ring-
opening metathesis polymerization (ROMP) was elucidated by Dall'Asta et al. who
provided unambiguous evidence for the total cleavage of the double bond of the
starting monomer during polymerization [1]. The originally proposed mechanism
that suggested the existence of a metal carbene [2] was further supported by the
work of Katz et al. [3, 4]. Consecutive investigations mainly carried out by the
leading groups of Schrock et al. [5-7], Grubbs et al. [8-12] and Feast et al. [13-23]
initiated further research on that area [24]. The enormous potential of metathesis-
based polymerizations such as ROMP, acyclic diene metathesis polymerization
(ADMET polymerization), and alkyne polymerization in materials science was
soon recognized. In due course, enormous effort has been put into the develop-
ment of new, more efficient and selective catalytic systems, resulting in an im-
pressive variety of catalytic systems based on Ti, V, Nb, Ta, Cr, Mo, W, Re, Co, Rh,
Ir, Ru and Os [25-27].
This chapter will cover both the synthesis and basic principles of modern,
well-
defined
metal alkylidenes related to their use in ROMP, ADMET-polymerization
and alkyne metathesis polymerization. The term “well-defined” is limited to cata-
lytic systems, usually metal alkylidenes, that are characterized by a
uniform
and
stoichiometric
composition and for which the actual propagating species is well
known and characterized. Consequently, the entire chemistry of standard binary
or ternary systems such as WCl
6
/AlEt
2
Cl/ethanol has been neglected. Where ap-
plicable, general aspects of the preparation of advanced materials via ROMP and
alkyne-polymerization will be mentioned briefly.
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