Immobilized rare-earth metal complex

Figure 12.4 Oxygenated heteroqrcles used for ring-opening polymerization by immobilized rare-earth metal complexes.

Immobilization of Rare-Earth Metal Alkoxide and -Diketonate Complexes... 

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

Solution grafting has been the predominant approach for the immobilization of rare-earth metal precatalyst components [288]. The identification of the catalytically active surface species, commonly formed upon interaction with organoaluminum compounds, is difficult and assisted by molecular model complexes. Several types of support materials including magnesium chloride [289], silica [290], and organic (co-)polymers [291,292], were examined both in the gas-phase and the slurry polymerization of 1,3-dienes. 

Let us briefly summarize the state of the art in the polymerization of other monomer groups in the presence of polymer-boxmd metal complexes. Considerable progress has been achieved in polymerization of dienes, namely, butadiene and isoprene, catalyzed by macromolecnlar complexes based on rare earth halides [114], Co-oligomerization of 1,3-butadiene and CO2 with immobilized palladium complexes (phosphynated PS as macromolecnlar ligand) [115] and polymerization of acetylene monomers with immobilized complexes of Mo(V), W(VI), and Pd(II) have been developed though they have not been investigated intensively. 

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