Reductive Functionalization with Cobalt Complexes Containing Pyrrole-diphosphine Pincer Ligands
First-row transition metal pincer complexes have recently become a popular target for catalyst development in the areas of C–H bond functionalization, cross-coupling, and olefin hydrofunctionalization. We were able to design a series of cobalt complexes capable of accessing different oxidation states with the PNP pincer ligand based on 2,5-bis(dicyclohexylphosphinomethyl)pyrrole (CyPNP) and to examine their reactivity towards fundamental organometallic reactions, as well as catalytic organic transformations. Our studies demonstrate that Co(PNP) systems are active towards reductive functionalization, including aldehyde decarbonylation, alkene hydrogenation, alkyne semi-hydrogenation, and hydrosilylation. Different mechanisms for these transformations have been proposed involving CoIII, CoII, and CoI species. This dissertation focuses on the underlying detail of the catalytic mechanisms and the isolation of relevant intermediates that occur in this chemistry. Results based on both stoichiometric reactions and catalytic studies were investigated to demonstrate a role for several different oxidation states of cobalt in these transformations.