title: Effects of pendant ligand binding affinity on chain transfer for 1-hexene polymerization catalyzed by single-site zirconium amine bis-phenolate complexes.
abstract: The kinetics of 1-hexene polymerization using a family of five zirconium amine bis-phenolate catalysts, Zr[tBu-ON(X)O]Bn2 (where X = THF (1), pyridine (2), NMe2 (3), furan (4), and SMe (5)), has been investigated to uncover the mechanistic effect of varying the pendant ligand X. A model-based approach using a diverse set of data including monomer consumption, evolution of molecular weight, and end-group analysis was employed to determine each of the reaction specific rate constants involved in a given polymerization process. The mechanism of polymerization for 1-5 was similar and the necessary elementary reaction steps included initiation, normal propagation, misinsertion, recovery from misinsertion, and chain transfer. The latter reaction, chain transfer, featured monomer independent β-H elimination in 1-3 and monomer dependent β-H transfer in 4 and 5. Of all the rate constants, those for chain transfer showed the most variation, spanning 2 orders of magnitude (ca. (0.1-10) × 10(-3) s(-1) for vinylidene and (0.5-87) × 10(-4) s(-1) for vinylene). A quantitative structure-activity relationship was uncovered between the logarithm of the chain transfer rate constants and the Zr-X bond distance for catalysts 1-3. However, this trend is broken once the Zr-X bond distance elongates further, as is the case for catalysts 4 and 5, which operate primarily through a different mechanistic pathway. These findings underscore the importance of comprehensive kinetic modeling using a diverse set of multiresponse data, enabling the determination of robust kinetic constants and reaction mechanisms of catalytic olefin polymerization as part of the development of structure-activity relationships.
authors.affiliation: Brown Laboratory, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, USA.
authors.forename: D Keith
authors.initials: DK
authors.lastname: Steelman
authors.forename: Silei
authors.initials: S
authors.lastname: Xiong
authors.forename: Paul D
authors.initials: PD
authors.lastname: Pletcher
authors.forename: Erin
authors.initials: E
authors.lastname: Smith
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Switzer
authors.forename: Grigori A
authors.initials: GA
authors.lastname: Medvedev
authors.forename: W Nicholas
authors.initials: WN
authors.lastname: Delgass
authors.forename: James M
authors.initials: JM
authors.lastname: Caruthers
authors.forename: Mahdi M
authors.initials: MM
authors.lastname: Abu-Omar