Macrocycle ligand modifications in the pursuit of nickel-oxygen complexes
Trujillo, Joliene Renee
University of Delaware
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.