France, Marcia Beth (1995) Olefin metathesis with group VIII transition metal complexes : mechanism, reactivity, and catalyst development. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-10122005-083645
Group VIII olefin metathesis catalysts are unusually functional group tolerant but are limited by their low reactivity and ill-defined nature. In order to address these concerns, mechanistic investigations of the Ru(H2O)6(tos)2-catalyzed ring-opening metathesis polymerization of norbornene and 7-oxanorbornene derivatives in aqueous media have been undertaken. Primarily through chain transfer studies and end group analysis, evidence supporting the intermediacy of ruthenium carbene species has been obtained. Furthermore, acyclic olefins have been shown to provide efficient molecular weight regulation during these polymerizations, allowing control of the polymer molecular weight and the identification of ring-opened units with well-defined functionalized end groups. The molecular weight regulation appears to occur by a standard chain-transfer mechanism. Methods of expanding the reactivity of group VIII metathesis catalysts to a wider variety of substrates have been developed. The polymerization of low-strain cyclic olefins such as cyclooctene was achieved with Ru(H2O)6(tos)2 in the presence of ethyl diazoacetate as an initiator. Such a finding indicates that the difficulties in polymerizing such monomers in the original system lies in the initiation and not in the propagation step. This result is an important indication that the development of more reactive group VIII systems is possible if the barrier to initiation can be overcome. In addition, several iridium based systems for the polymerization of low-stain olefins are presented. Furthermore, [(COE)2IrCl]/AgO2CCF3 was found to be an active catalyst for the simultaneous isomerization/olefn metathesis of acyclic olefins, including methyl oleate. This transformation is essentially a single-step analogue of the two-step Shell Higher Olefins Process. The reaction conditions can also be varied to favor more selective metathesis without accompanying isomerization. Finally, a number of new, isolable ruthenium carbene complexes have been prepared by alkylidene transfer from diazo compounds. Several of these species are active catalysts for the ring-opening metathesis polymerization of norbornene, and one such system appears to be living. This route offers a facile entry into complexes with catalytic activity identical to that observed with ruthenium carbenes prepared from the less accessible 3,3-diphenylcyclopropene. This method appears to be a general route into ruthenium carbene complexes.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||30 June 1994|
|Non-Caltech Author Email:||francem (AT) wlu.edu|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||14 Oct 2005|
|Last Modified:||26 Dec 2012 03:04|
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