Macrocycle ligand modifications in the pursuit of nickel-oxygen complexes
Date
2010
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
The utility of small molecules lies in the ability to alter the structure of the
molecule and examine the spectroscopic characteristics as well as the reactivity of the
complex. Small molecules are often used to probe mechanistic questions on much
more complicated systems, such as enzymes. In 1996 a new form of superoxide
dismutase was discovered which had nickel in the active site of the enzyme. This
discovery sparked renewed interest in nickel-oxygen chemistry. Small molecules
were used to probe different nickel-oxygen structure types and their spectroscopic
characteristics, though complete understanding of the implications when altering the
small molecules has yet to develop.
This thesis addresses macrocycle ligand modifications, the varying ways of
synthesizing nickel-oxygen complexes, and the reactivity of the nickel-oxygen adducts
with exogenous substrates. The work presented herein, describes the synthesis and
characterization of [Ni(tmcyclen)(CO)](OTf). Subsequent oxygen activation by
[Ni(tmcyclen)(CO)](OTf) lead to the formation of ”side-on” nickel(III) peroxo
complex as determined by electronic absorption spectroscopy, electron paramagnetic
resonance spectroscopy, and mass spectroscopy. Alternatively, the complex can be
synthesized from nickel(II) and reduced oxygen reagents, H2O2 or KO2. Reactivity
studies of the [Ni(tmcyclen)(O2)](OTf) with phosphines, sulfides, olefins, activated CH bonds, and substituted phenols were investigated. The reactivity studies completed
on the “side-on” nickel(III)-peroxo complex shed light on the electronic characteristics
of the complex. This thesis represents the first time a “side-on” nickel(III)-peroxo
complex is synthesized from monovalent nickel and dioxygen.