Reactions of Small Molecules Facilitated by Metal-Acceptor Interactions

Citation

Suess, Daniel Leif Migdow (2013) Reactions of Small Molecules Facilitated by Metal-Acceptor Interactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Q4B0-AG41. https://resolver.caltech.edu/CaltechTHESIS:05302013-182601874

Abstract

The role of metal-acceptor interactions arising from M–BR₃ and M–PR₃ bonding is discussed with respect to reactions between first-row transition metals and N₂, H₂, and CO. Thermally robust, S = 1/2 (TPB)Co(H₂) and (TPB)Co(N₂) complexes (TPB = tris(2- (diisopropylphosphino)phenyl)borane) are described and the energetics of N2 and H2 binding are measured. The H2 and N2 ligands are bound more weakly in the (TPB)Co complexes than in related (SiP₃)M(L) complexes (SiP₃ = tris(2- (diisopropylphosphino)phenyl)silyl). Comparisons within and between these two ligand platforms allow for the factors that affect N₂ (and H₂) binding and activation to be delineated. The characterization and reactivity of (DPB)Fe complexes (DPB = bis(2- (diisopropylphosphino)phenyl)phenylborane) in the context of N₂ functionalization and E–H bond addition (E = H, C, N, Si) are described. This platform allows for the one-pot transformation of free N₂ to an Fe hydrazido(-) complex via an Fe aminoimide intermediate. The principles learned from the N₂ chemistry using (DPB)Fe are applied to CO reduction on the same system. The preparation of (DPB)Fe(CO)₂ is described as well as its reductive functionalization to generate an unprecedented Fe dicarbyne. The bonding in this highly covalent complex is discussed in detail. Initial studies of the reactivity of the Fe dicarbyne reveal that a CO-derived olefin is released upon hydrogenation. Alternative approaches to uncovering unusual reactivity using metal- acceptor interactions are described in Chapters 5 and 6, including initial studies on a new π-accepting tridentate diphosphinosulfinyl ligand and strategies for designing ligands that undergo site-selective metallation to generate heterobimetallic complexes.

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