Date of Award
Doctor of Philosophy (PhD)
The development of both palladium and nickel catalysis over the past several decades has led to the ability to perform a multitude of C-C coupling, C-Heteroatom coupling, and C-H functionalization reactions. These reactions typically utilize a catalytic cycle involving Pd0/II/IV and Ni0/II. While using these types of catalytic cycles one can create a multitude of different hard to make bonds, it is always important to keep expanding what we view as potential catalytic intermediates to keep developing new cycles capable of new transformations. One such way to expand our knowledge of these catalytic cycles is to look at the oxidation states that are less commonly observed in catalysis. This typically involves PdI/III and NiI/III/IV . Studying these rare oxidation states allows us to determine if they have the potential to either take part in current catalytic cycles, or develop new ones that take advantage of these oxidation states. Our group has previously synthesized various PdIII and NiIII complexes with the support of N,N’- dialkyl-2,11-diaza[3.3](2,6)pyridinophane (RN4). This ligand has allowed for the isolation and characterization of these complexes that are typically seen as unstable letting us study their reactivity. First, we investigated the effects of ligand flexibility on the stabilization of PdIII complexes by synthesizing several ligands. The “flexible” ligands had a 1,4,7-triazacyclononane framework and the “rigid” ligands had a diazabicylononanone framework. Seeing that the flexible 1,4,7- triazacyclononane ligands seemed to be better at stabilizing the high valent palladium, we continued using it to synthesize organometallic nickel complexes. These complexes proved very easy to oxidize allowing NiII/III/IV oxidation states to be isolated and fully characterized. The oxidative reactivity was studied for these three nickel complexes looking at oxidative addition with organic halides, aerobic oxidation, and most interestingly photolysis that resulted in much faster reductive elimination from the NiIV species. Lastly, we investigated the ligand modifications that can be done to either stabilize or destabilize high valent NiIII species using a N,N’-dialkyl-2,11- diaza[3.3](2,6)pyridinophane ligand that was modified to observe the effect on differing amounts of steric bulk and electronic effects. Studying these rare high valent complexes is important so we can continue to expand the scope of what catalytic transformations we can use to improve our daily lives.
Chair and Committee
Liviu M. Mirica
John R. Bleeke, William E. Buhro, Sophia E. Hayes, Nigam P. Rath,
Watson, Michael Benjamin, "Oxidative C-C Bond Formation Reactivity of High Valent Nickel and Palladium Complexes" (2017). Arts & Sciences Electronic Theses and Dissertations. 1152.