Investigations of transition metal catalysts for the hydration of cyanohydrins and ligand effects in aqueous molybdocene chemistry
Loading...
Date
2008-09
Authors
Ahmed, Takiya Janice, 1980-
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Efforts toward developing improved methods of synthesizing acrylamides are ongoing. Several homogeneous organometallic and coordination complexes have proven useful in catalytic acrylonitrile hydration; however, none of these complexes have been tested in the hydration of cyanohydrins used to synthesize substituted acrylamides.
This dissertation describes the reactivity of molybdocene and Pt phosphinito nitrile hydration catalysts toward cyanohydrin substrates and the effect of Cp ring substituents on aqueous molybdocene chemistry. Chapter I identifies the motivation for developing a transition metal-catalyzed process for cyanohydrin hydration and the strategy used to improve on the reactivity of molybdocene catalysts. Chapter II reports the effect of cyclopentadienyl ring substituents on the electronic and geometric structure, solution behavior, and hydrolytic activity of molybdocenes.
To examine the effect of Cp ring substituents, ansa -molybdocenes containing the fragment {C 2 Me 4 (C 5 H 4 ) 2 }Mo 2+ were compared to non-bridged molybdocenes containing (C 5 H 5 ) 2 Mo 2+ and (C 5 H 4 Me) 2 Mo 2+ . Addition of a tetramethylethylene-bridge decreases the electron density on the Mo center and exerts a small effect on the structure of the metallocene. However, the catalytic activity of the molybdocene catalysts is unchanged or slowed because of counteractive effects on the bound nucleophile and electrophile.
Although adding substituents to the Cp rings did not change the catalytic activity of the molybdocene, the substituents led to significant changes in the equilibrium behavior. The equilibria have practical consequences that warrant investigation. Chapters III and IV chronicle the effect of Cp ring substituents on the monomer-dimer equilibria and the acidity of the molybdocene complexes, respectively. Interestingly, the monomer-dimer equilibrium established by ansa -{C 2 Me 4 (C 5 H 4 ) 2 }Mo(OH)(OH 2 ) + exhibits a strong solvent dependence. New equilibrium schemes are reported for the ansa and non- ansa complexes.
Chapter V describes the reactivity of the molybdocene and Pt phosphinito catalysts toward cyanohydrins. Both catalysts gave unsatisfactory results; however, the à à à à à ±-hydroxy substituent of cyanohydrins facilitates nitrile hydration. The low reactivity exhibited by these systems was due to liberation of hydrogen cyanide from the cyanohydrin leading to acute poisoning of either catalyst. As discussed in Chapter VI, this study will expedite the innovation of new catalysts that are better suited to overcome the challenges associated with cyanohydrin hydration. This dissertation includes previously published and unpublished co-authored material.
Description
xx, 204 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
Keywords
Inorganic chemistry, Molybdocene, Ligand effects, Cyanohydrins, Hydration, Transition metal catalysts