Investigations into the Fundamental Organometallic Chemistry of Cobalt Complexes Supported by Anionic Pnp Pincer Ligands
Fundamental aspects of the coordination and organometallic chemistry of cobalt complexes have been explored using a series of compounds of the form CoXPNPtBu (PNPtBu = anion of 2,5-bis((di-tert-butylphosphino)methyl)pyrrole) and CoXdPNPtBu (dPNPtBu = anion of 2,5-bis((di-tert-butylphosphino)methylene)-2,5-dihydropyrrole). PNP and dPNP comprise a class of pyrrole-based anionic pincer ligands that enforce a rigid square-planar geometry at the Co center and can support a variety of Co oxidation states (CoI-CoIII) with varied spin configurations. The kinetic stability of these ligands, coupled with the steric protection afforded by the pendant tert-butyl groups, allow for the observation and isolation of monomeric, metastable CoPNP complexes that can serve as models for reactive intermediates. Chapter One provides a brief review on cobalt-containing pincer complexes, their reported applications, and introduces the PNP and dPNP ligands in this context. The isolation and reactivity of a PNP-supported cobalt hydride complex (Chapter Two), the preparation of dPNP via PNP dehydrogenation and its impact on electronic structure and reactivity (Chapter Three), and the preparation of CoPNP complexes featuring Co-N bonds (Chapter Four) are described in this document. Chapter Five describes the preparation of ruthenium complexes supported by Klaui's tripodal oxygen-based ligand and their chemistries with nitric oxide (NO).