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Synthetic, reactivity, and mechanistic studies relevant to olefin oligomerization and polymerization

Citation

Agapie, Theodor (2007) Synthetic, reactivity, and mechanistic studies relevant to olefin oligomerization and polymerization. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-04092007-132543

Abstract

Chapters 2 and 3 present synthetic, structural, and mechanistic studies relevant to the selective trimerization of ethylene to 1-hexene using a chromium diphosphine catalyst system. The studied diphosphines, PNPL=(o-L-C6H4)2PN(Me)P(o-L-C6H4)2, display a PNP backbone with phosphine-aryl groups ortho-substituted with ethers, amines, or thioethers (L=OMe, NMe2, or SMe). Chromium(0) and chromium(III) complexes have been prepared, characterized structurally, and tested for catalytic activity, highlighting the importance of the pendant ether groups. A chromacyclopentane model complex, (PNPO4)Cr(o,o-biphenyldiyl)Br, has been isolated using the parent phosphine system (PNPO4, L=OMe). Starting with this model system, the olefin trimerization reaction has been investigated using trans-, cis-, and gem-d2-ethylene as well as mixtures of C2D4 and C2H4. The selectivity of alpha-olefin insertion into the chromacyclopentane mimic and that of beta-H elimination from chromacycloheptanes have been studied. The relative rates of insertion of terminal and internal olefins into the chromacyclopentane moiety have been measured. Chapters 4, 5, and 6 present synthetic studies of tantalum, titanium, and zirconium complexes supported by a new tridentate bisphenolate framework, along with applications to olefin polymerization and mechanistic studies of organometallic transformations based on these architectures. The utilized ligand framework involves a bisphenol connected at the ortho positions via semirigid, ring-ring (sp2-sp2) linkages to a flat ring (pyridine, thiophene, furan, or benzene). These ligands were found to coordinate to metals in a mer fashion to give a variety of binding geometries. A tantalum system supported by the benzene bridged bisphenolate was found to undergo intramolecular CH activation faster than metal-alkyl protonolysis by a pendant phenol, un unprecedented process for early metals. An alpha-H abstraction reaction has afforded access to a tantalum benzylidene supported by the pyridine linked bisphenolate. Isotope labeling studies and variable temperature kinetics measurements were used to investigate the mechanisms of these transformations. Group 4 complexes supported by the present bisphenolates were found to have interesting catalytic behavior for the propylene polymerization and oligomerization, upon activation with excess MAO. The propylene polymerization activity of present zirconium complexes is excellent, exceeding 106 g polypropylene / (mol Zr • h), in some cases. Chapter 7 presents the synthesis and study of group 3 dialkyl complexes supported by tetradentate L2N-phenolates (L = S, N, O). These complexes were found to undergo a non-dissociative ligand exchange process in solution. The mechanism of this process was studied by using variable temperature NMR spectroscopy.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:alkylidene; CH bond activation; ethylene trimerization; fluxional process; nonmetallocene catalysts; olefin polymerization
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Awards:The Herbert Newby McCoy Award, 2007
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bercaw, John E.
Thesis Committee:
  • Grubbs, Robert H. (chair)
  • Gray, Harry B.
  • Bercaw, John E.
  • Peters, Jonas C.
Defense Date:22 January 2007
Record Number:CaltechETD:etd-04092007-132543
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-04092007-132543
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5181
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:19 Apr 2007
Last Modified:26 Dec 2012 03:15

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