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Synthetic, Structural and Mechanistic Studies of Interactions of Carbon, Nitrogen, and Oxygen Nucleophiles with Bis-Pentamethylcyclopentadienyl Zirconium and Hafnium Derivatives

Citation

Moore, Eric Jan (1984) Synthetic, Structural and Mechanistic Studies of Interactions of Carbon, Nitrogen, and Oxygen Nucleophiles with Bis-Pentamethylcyclopentadienyl Zirconium and Hafnium Derivatives. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/18vn-5737. https://resolver.caltech.edu/CaltechTHESIS:04082013-141952473

Abstract

The reactivity of permethylzirconocene and permethylhafnocene complexes with various nucleophiles has been investigated. Permethylzirconocene reacts with sterically hindered ketenes and allenes to afford metallacycle products. Reaction of these cummulenes with permethylzirconocene hydride complexes affords enolate and σ-allyl species, respectively. Reactions which afford enolate products are nonstereospecific, whereas reactions which afford allyl products initially give a cis-σ-allyl complex which rearranges to its trans isomer. The mechanism of these reactions is proposed to occur either by a Lewis Acid-Lewis Base interaction (ketenes) or by formation of a π-olefin intermediate (allenes).

Permethylzirconocene haloacyl complexes react with strong bases such as lithium diisopropylamide or methylene trimethylphosphorane to afford ketene compounds. Depending on the size of the alkyl ketene substituent, the hydrogenation of these compounds affords enolate-hydride products with varying degrees of stereoselectivity. The larger the substituent, the greater is the selectivity for cis hydrogenation products.

The reaction of permethylzirconocene dihydride and permethylhafnocene dihydride with methylene trimethylphosphorane affords methyl-hydride and dimethyl derivatives. Under appropriate conditions, the metallated-ylide complex 1, (η5-C5(CH3)5)2Zr(H)CH2PMe2CH2, is also obtained and has been structurally characterized by X-ray diffraction techniques. Reaction of 1 with CO affords (η5-C5(CH3)5)2Zr(C,O-η2-(PMe3)HC=CO)H which exists in solution as an equilibrium mixture of isomers. In one isomer (2), the η2-acyl oxygen atom occupies a lateral equatorial coordination position about zirconium, whereas in the other isomer (3), the η2-acyl oxygen atom occupies the central equatorial position. The equilibrium kinetics of the 2 → 3 isomerization have been studied and the structures of both complexes confirmed by X-ray diffraction methods. These studies suggest a mechanism for CO insertion into metal-carbon bonds of the early transition metals.

Permethylhafnocene dihydride and permethylzirconocene hydride complexes react with diazoalkanes to afford η2-N,N'-hydrazonido species in which the terminal nitrogen atom of the diazoalkane molecule has inserted into a metal-hydride or metal-carbon bond. The structure of one of these compounds, Cp*2Zr(NMeNCTol2)OH, has been determined by X-ray diffraction techniques. Under appropriate conditions, the hydrazonido-hydride complexes react with a second equivalent of diazoalkene to afford η'-N-hydrazonido-η2-N,N'-hydrazonido species.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Grubbs, Robert H.
Thesis Committee:
  • Bercaw, John E. (chair)
  • Evans, David A.
  • Collins, Terrence J.
  • Grubbs, Robert H.
Defense Date:30 June 1983
Record Number:CaltechTHESIS:04082013-141952473
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:04082013-141952473
DOI:10.7907/18vn-5737
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7586
Collection:CaltechTHESIS
Deposited By: John Wade
Deposited On:08 Apr 2013 21:47
Last Modified:16 Apr 2021 22:58

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