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Mechanistic and Reactivity Studies of Bent Metallocene Complexes of Niobium and Tantalum


Trimmer, Mark S. (1989) Mechanistic and Reactivity Studies of Bent Metallocene Complexes of Niobium and Tantalum. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/bads-b915.


A variety of olefin hydride complexes of niobium and tantalum has been prepared in order to study their reactivity and to gain insight into organometallic reaction mechanisms. Examination of a series of ethylene and propylene complexes of niobocene (Cp₂Nb; Cp = η⁵-C₅H₅), permethylniobocene (Cp*₂Nb; Cp* = η⁵-C₅(CH₃)₅), tantalocene, and permethyltantalocene has indicated that there are both large electronic and steric effects deriving from the metal (and its ancillary ligands) in the olefin insertion (β-migratory insertion) process. Furthermore, a thermodynamic and kinetic analysis has been completed for a series of substituted styrene complexes of niobocene in order to better understand the important electronic properties of the olefin. The results are in accord with a concerted four-center process with only moderate charge development.

The special case of β-migratory insertion of a hydride ligand into coordinated benzyne has also been studied for the permethyltantalocene system. The coordinatively unsaturated (sixteen electron) phenyl tautomer, which is made accessible by the facile benzyne hydride insertion reaction, readily reacts with a variety of ligands, L, to afford Cp*₂ Ta(C₆H₅)L complexes (L = CO, O₂, NC≡R, :CH₂, H₂, etc.). This family of compounds exhibits interesting reactivity (a-migratory insertion, O₂ activation, and reductive elimination) which is discussed in some detail.

Finally a series of paramagnetic seventeen electron Cp*₂ TaX₂ (X = halide, alkyl, hydride) complexes, and the corresponding cationic and anionic species, have been prepared and studied. The odd electron neutral complexes exhibit surprising thermal stability and undergo very little reactivity. While the chemistry of the anionic compounds is almost completely dominated by their potent reducing power, that of the cations is quite diverse and amenable for study. Therefore the syntheses and reactivity (1,2-eliminations, ligand insertions, and deprotonation reactions) of these coordinatively unsaturated sixteen electron species are presented.

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):
  • Bercaw, John E.
Thesis Committee:
  • Gray, Harry B. (chair)
  • Bercaw, John E.
  • Chan, Sunney I.
  • Grubbs, Robert H.
Defense Date:8 September 1988
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-85ER13431
Shell Companies FoundationUNSPECIFIED
Record Number:CaltechTHESIS:08232013-111400988
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7935
Deposited By: Benjamin Perez
Deposited On:26 Aug 2013 14:41
Last Modified:22 Dec 2021 23:58

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