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Bis(thiophenolate)pyridine Pincer Ligands and Trivalent Zirconocene Complexes Relevant to Earlv Transition Metal Polymerization Catalysts

Citation

Lenton, Taylor Nichole Baker (2014) Bis(thiophenolate)pyridine Pincer Ligands and Trivalent Zirconocene Complexes Relevant to Earlv Transition Metal Polymerization Catalysts. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FPP5-0461. http://resolver.caltech.edu/CaltechTHESIS:09242013-191401866

Abstract

Two major topics are covered: the first chapter is focused on the development of post-metallocene complexes for propylene polymerization. The second and third chapters investigate the consequences of diisobutylaluminum hydride (HAliBu2) additives in zirconocene based polymerization systems.

The synthesis, structure, and solution behavior of early metal complexes with a new tridentate LX2 type ligand, bis(thiophenolate)pyridine ((SNS) = (2-C6H4S)2-2,6-C5H3N) are investigated. SNS complexes of Ti, Zr, and Ta having dialkylamido coligands were synthesized and structurally characterized. The zirconium complex, (SNS)Zr(NMe2)2, displays C2 symmetry in the solid state. Solid-state structures of tantalum complexes (SNS)Ta(NMe2)3 and (SNS)TaCl(NEt2)2 also display pronounced C2 twisting of the SNS ligand. 1D and 2D NMR experiments show that (SNS)Ta(NMe2)3 is fluxional with rotation about the Ta N(amide) bonds occurring on the NMR timescale. The fluxional behavior of (SNS)TaCl(NEt2)2 in solution was also studied by variable temperature 1H NMR. Observation of separate signals for the diastereotopic protons of the methylene unit of the diethylamide indicates that the complex remains locked on the NMR timescale in one diastereomeric conformation at temperatures below -50 °C.

Reduction of Zr(IV) metallocenium cations with sodium amalgam (NaHg) produces EPR signals assignable to Zr(III) metallocene complexes. Thus, chloro-bridged heterobinuclear ansa-zirconocenium cation [((SBI))Zr(μ-Cl)2AlMe2]+B(C6F5) (SBI = rac-dimethylsilylbis(1-indenyl)), gives rise to an EPR signal assignable to the complex (SBI)ZrIII(μ-Cl)2AlMe2, while (SBI)ZrIII-Me and (SBI)ZrIII(-H)2AliBu2 are formed by reduction of [(SBI)Zr(μ-Me)2AlMe2]+B(C6F5) and [(SBI)Zr(μ-H)3(AliBu2)2]+B(C6F5)4¯, respectively. These products are also formed, along with (SBI)ZrIII-iBu and [(SBI)ZrIII]+ AlR4¯ when (SBI)ZrMe2 reacts with HAliBu2, eliminating isobutane en route to the Zr(III) complex. Studies concerning the interconversion reactions between these and other (SBI)Zr(III) complexes and reaction mechanisms involved in their formation are also reported.

The addition of HAliBu2 to precatalyst [(SBI)Zr(µ-H)3(AliBu2)2]+ significantly slows the polymerization of propylene and changes the kinetics of polymerization from 1st to 2nd order with respect to propylene. This is likely due to competitive inhibition by HAliBu2. When the same reaction is investigated using [(nBuCp)2Zr(μ-H)3(AliBu2)2]+, hydroalumination between propylene and HAliBu2 is observed instead of propylene polymerization.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Pincer Ligands, Trivalent Zirconocene, Metallocene, Polypropylene
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bercaw, John E.
Thesis Committee:
  • Agapie, Theodor (chair)
  • Stoltz, Brian M.
  • Fu, Gregory C.
  • Bercaw, John E.
Defense Date:10 September 2013
Record Number:CaltechTHESIS:09242013-191401866
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:09242013-191401866
DOI:10.7907/FPP5-0461
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/om300789hDOIArticle adapted for ch. 2
http://dx.doi.org/10.1021/ja403170uDOIArticle adapted for ch. 3
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7961
Collection:CaltechTHESIS
Deposited By: Taylor Lenton
Deposited On:02 Oct 2013 17:55
Last Modified:11 Apr 2019 17:46

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