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Organotitanium and Niobium Chemistry. I. Structure and Reactivity of a Titanium Ethylene Complex. II. Reactivity of Decamethyl Niobocene Derivatives


Cohen, Steven Alan (1982) Organotitanium and Niobium Chemistry. I. Structure and Reactivity of a Titanium Ethylene Complex. II. Reactivity of Decamethyl Niobocene Derivatives. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3DDT-0252.


The synthesis and X-ray diffraction study of bis(pentamethylcyclopentadienyl) ethylene titanium (I) are reported. This complex represents the first example of an isolable ethylene adduct of a group IV metal, a key intermediate in Ziegler-Natta olefin polymerization schemes. While treatment of I with ethylene leads to only traces of polymer after months, I participates in a wide range of stoichiometric and catalytic reactions. These include the catalytic conversion of ethylene specifically to butadiene and ethane and the catalytic isomerization of alkenes. Detailed studies have been carried out on the stoichiometric reactions of I with nitriles and alkynes. At low temperatures, nitriles react to form metallacycloimine species which more slowly undergo a formal 1,3-hydrogen shift to generate metallacycloeneamines. The lowest energy pathway for this rearrangement is an intramolecular hydrogen shift which is sensitive to the steric bulk of the R substituent. The reactions of I with alkynes yield metallacyclopentene complexes with high regioisomer selectivity. Carbonylation of the metallacyclopentene (η-C5Me5)2TiC(CH3)=C(CH3)CH2CH2 under relatively mild conditions cleanly produces the corresponding cyclopentenone and [C5(CH3)5]2Ti(CO)2. Compounds derived from CO2 and acetaldehyde have also been isolated.

The synthesis and characterization of bis-(η-pentamethylcyclopentadienyl) niobium(III) tetrahydroborate (II) are described and a study of its temperature-dependent proton NMR spectroscopic behavior is reported. The complex is observed to undergo a rapid intramolecular averaging process at elevated temperatures. The free energy of activation, ΔG = 16.4 ± 0.4 kcal/mol, is calculated. The reinvestigation of a related compound, bis(η-cyclopentadienyl)niobium(III) tetrahydroborate, established ΔG = 14.6 ± 0.2 kcal/mol for the hydrogen exchange process. The tetrahydroborate complex, II reacts with pyridine and dihydrogen to yield (η-C5Me5)2NbH3 (III). The reactivity of III with CO and ethylene is reported.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Titanium, ethylene, niobium, metallacycle, organometallic
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.
  • Marsh, Richard Edward
  • Grubbs, Robert H.
Defense Date:4 February 1982
Record Number:CaltechTHESIS:02132014-115308678
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8075
Deposited By: Benjamin Perez
Deposited On:14 Feb 2014 23:19
Last Modified:15 May 2020 23:41

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