AM2Net Advanced Macromolecular Materials By Transition Metal Catalysis; Group 2: "Post Metallocene Catalysis"; Post-metallocene polymerization catalysts for alpha-olefins and dienes

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The present proposal aims at a deeper mechanistc understanding of the role of trivalent titanium alkyl intermediates in the "constrained geometry" titanium catalysts and the so-called Lovacat catalytsts, both industrially used for the random copolymerization of ethylene with 1-octene. We seek to elucidate, by synthetic and mechanistic studies using functionalized cyclopentadienyl ligands, the relationship between single-site catalysts containing tetravalent titanium centers and those containing trivalent titanium centers. In analogy to the highly efficient mono(cyclopentadienyl)titanium(III) catalysts for the syndiospecific polymerization of styrene, we attempt to develop polymerization catalysts for alpha-olefins, 1,3-diene, and styrene. As diamagnetic model compounds the synthesis of isoelectronic scandium complexes containing the same functionalized cyclopentadienyl ligands with amido and amino donors will be attempted. Linked bis(phenolate), bis(amido), and phenoxyimine ligands, incorporating hemilabile donor functions, will be tested as new types of ancillary ligand systems for the complexation of the electrophilic trivalent metal centers scandium, titanium, and aluminum. Bimetallic derivatives containing titanium and aluminum within the same ligand set may lead to useful models for the heterogeneous Ziegler catalysts and to catalysts more tolerant to polar functional groups. Trivalent titanium complexes may also result in catalysts switchable between insertion and controlled radical chain propagation mechanisms. Such metal based initiators bear considerable potential for the rational synthesis of new macromolecular architectures such as block copolymers with nonpolar and polar segments.