Titanium Carbenes: Reactions with Selected Carbonyl Compounds and Ring-Opening Metathesis Polymerization of Cyclic Olefins

Citation

Cannizzo, Louis Fiscel (1988) Titanium Carbenes: Reactions with Selected Carbonyl Compounds and Ring-Opening Metathesis Polymerization of Cyclic Olefins. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/x7cz-vr92. https://resolver.caltech.edu/CaltechTHESIS:01182013-080224143

Abstract

The reaction of "(C₅H₅)₂Ti=CH₂" with acid anhydrides and imides yielded several useful organic transformations, including stereoselective ring formation applicable to alkaloid synthesis. Further studies developed an in situ preparation of Tebbe's reagent for large-scale methylenation of ketones and esters. Additionally, the reaction of proton sources with titanacyclobutanes was briefly surveyed and found to give both ring-opened and carbene-trapped products.

The polymerization of strained cyclic olefins initiated by metal carbenes was investigated. Endcapping of polynorbornene produced by titanacyclobutanes was followed by UV and NMR. These analyses along with molecular weight measurements established the high efficiency of the endcapping reaction and the absence of polymer degradation during the reaction. The ring-opening polymerization of cyclopentene by titanacyclobutanes gave polymers that were close to being monodisperse. Kinetic studies showed that the rate of polymerization was first order in cyclopentene. Block copolymers (both A-B and A-B-A) containing monodispersed segments were synthesized with alternating "hard" and "soft" blocks. In these block copolymerization studies the polymerization of exo-dicyclopentadiene by titanacyclobutanes was shown to be a true "living" system. The polymerization of norbornene by the tungsten alkylidene, W(CHtBu)(NAr)[OCMe(CF₃)₂)₂ (Ar=2,6-diisopropylphenyl), was investigated and found not to be a living system. Finally, the heteroolefin, N-methyl-7-azabenzonorbornadiene, was ring-opened metathesis polymerized and the resulting polymer dehydrogenated and doped to give a conducting material (10^-3 to 10^-4 Scm^-1).

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