Metallocene-mediated olefin polymerization: The effects of distal ligand perturbations on polymer stereochemistry

New group IV compounds containing a 9-dialkylaminofluorenide ligand have been prepared. Their properties and reactivity have been investigated. For example, single crystal X-ray analysis of the metallocene (9-(N,N-dimethylamino)fluorenyl) ₂ZrCl₂ (4) reveals a bonding mode that includes a zirconium-nitrogen bond. In combination with methylaluminoxane (MAO), several aminofluorenide complexes afford atactic polypropylene.; A statistical model has been developed that quantifies the unidirectional site epimerization probability, ϵ, for singly- and doubly-bridged C₁-symmetric metallocene polymerization catalysts. The unidirectional site epimerization model allows deconvolution of the site sequence probability and the stereochemical probability for producing a given pentad.; Highly stereoregular syndiotactic polypropylene is obtained with the catalyst systems Ph₂C(Oct)(C₅H₄)ZrCl ₂/MAO (8/MAO) (Oct = octamethyloctahydrodibenzofluorenyl, C₂₉H₃₆) and Me₂C(Oct)(C₅H ₄)ZrCl₂/MAO (12/MAO). Melting temperatures as high as 153°C or 154°C are found for the thermally quenched polymers. Distal ligand perturbations are demonstrated to have a dramatic effect on polymer stereochemistry.; Polypropylenes that are isotactic-hemiisotactic or syndiotactic-hemiisotactic can be made with proper R substituent selection in the catalyst system Me ₂C(Flu)(3-R-C₅H₃)ZrCl₂/MAO or Me ₂C(Oct)(3-R-C₅H₃)ZrCl₂/MAO, where Flu = fluorenyl (C₁₃H₈). The prepared polymers have been subjected to a statistical model which suggests that the metallocenes have one highly selective site (99%) and one site of variable selectivity which is highly dependent on the nature of the R substituent and whether the metallocene contains the Flu or Oct ligand.; Control of the tacticity of isotactic-hemiisotactic polypropylene, as quantified by the parameter α, is achieved by proper R substituent selection in the catalyst system R′₂C(3-R-C₅H ₃)(C₁₃H₈)MCl₂/MAO. For R = 2-adamantyl, R′ = Ph, and M = Zr or Hf, α is approximately 0.60 and the polypropylene obtained is elastomeric. Its properties are rationalized by the statistical existence of isotactic stereoblocks among an otherwise amorphous hemiisotactic medium.; For the C₁-symmetric polymerization catalyst Me₂C(3-t-butyl-C₅H₃)$$(9-C₁₃H₈)ZrCl₂/MAO, evidence gathered here supports an alternating mechanism in which both sites of the metallocene wedge are utilized for monomer insertion. For an Oct-containing catalyst system with a cyclopentadienyl substituent of R = 2-methyl-2-adamantyl, unprecedentedly high isotacticity (>99% [mmmm]) is observed for a fluorenyl-based metallocene catalyst. Melting temperatures for such isotactic polymers can be as high as 167°C (T_p = 0°C).