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theses

The understanding of small molecule activation by transition metal complexes is key for many fields of study such as organic and inorganic chemistry. Since their initial report in the 1960’s, pincer-ligated (meridional bound tridentate ligands) complexes have demonstrated a rich chemistry for the activation of small molecules. This thesis will focus on new reactivity of known pincer-ligated complexes as well as the synthesis and reactivity of novel pincer-ligated transition metal complexes. The addition of aryl O-H bonds to olefins (hydroaryloxylation) and cleavage of those C-O bonds (dehydroaryloxylation) have been examined using pincer-ligated iridium complexes. The mechanism of this reaction was determined by experimental (kinetic studies, KIE expt, competition and resting state studies etc.) and computational DFT analysis. The addition of aryl N-H bonds to olefins was not successful catalytically and was determined to have an overall larger energetic barrier by DFT computations. Novel pincer-ligated osmium complexes were synthesized. These complexes are isoelectronic to (tBuPCP)Ir, one of the most active alkane dehydrogenation catalysts known. The reactivity of these complexes was examined to see how they compared to their isoelectronic iridium analogues. These complexes were treated with olefins, carbon monoxide and nitrogen. Additionally they were tested for the dehydrogenation of alkanes and alcohols and the hydrogenation of olefins and ketones. Recent reports have shown that pincer ligated metal complexes are capable of cleaving dinitrogen to form metal nitrides. Novel pincer-ligated rhenium and molybdenum complexes were synthesized in order to study their activity for dinitrogen cleavage. Synthesis of the pincer-ligated metal chlorides was achieved with further study required to test their reactivity with dinitrogen. Finally new pincer complexes were developed to improve or demonstrate new reactivity. Three approaches were taken when examining new ligands. The first was incorporation of a positive charge away from the metal center in the ligand structure. The second was use of a PPP ligand with the potential for metal-ligand cooperativity. The third was using established ligand frameworks with metals not traditionally used for alkane dehydrogenation. Complexes for each of these strategies were synthesized and characterized.

ETD_8713

Ph.D.

Includes bibliographical references

by Nicholas Lease

doi:10.7282/T34X5C8P

ETD doctoral

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