Synthesis, Characterization, and Evaluation of Novel Bis(imino)pyridine Cobalt Compounds in the Metal Catalyzed Hydroboration of Olefins

Abstract

Improved methods for the hydroboration of olefins have vast implications for the fields of organic and inorganic chemistry. The high cost and environmental concerns of using precious metals, such as Rh and Ir, have prompted our research on base metals as viable catalyst alternatives. Our lab has recently discovered that bis(imino) pyridine (PDI) iron dinitrogen and cobalt monomethyl complexes can catalyze the hydroboration of a range of terminal, internal, and geminal alkenes with anti-Markovnikov selectivity. Fundamental studies suggested that the reactivity could benefit from increasing the electron richness of the metal center. Therefore, I synthesized and characterized a novel (PDI)cobalt catalyst with dimethylamino substituents on the ligand. Electrochemical measurements revealed that this complex is more electron rich than unsubstituted PDIcobalt complexes but more electron poor than pyrrolidinyl substituted compounds. The hydroboration reactivity of this novel catalyst with a series of olefins proved to be proportional to the electron donating ability of the ligand system, consistent with our hypothesis. Deuterium labeling experiments suggested a similar mechanism to the standard cobalt catalysts. I also explored the synthesis of other (PDI)cobalt complexes with electrondeficient ligands to further probe trends in electron donating ability and hydroboration reactivity.