Master of Science
Blacquiere, Johanna M.
Two new cationic Fe(II) PR2NR'2 complexes, [Fe(Cp*)(PR2NPh2)(MeCN)]PF6 (R = cyclohexyl, 3a) and [Fe(Cp*)(PR2NPh2)(MeCN)]PF6 (R = phenyl, 3b), were synthesized and characterized. The catalytic activity for intramolecular hydrofunctionalization was tested using the benchmark substrate 2-ethynylaniline (EA) and both catalysts effectively produced indole (Ind). The selectivity of catalysis was also tested using 2-ethynylbenzyl alcohol (EBA) and both catalysts formed only the endo product isochromene (IC). These complexes represent the first well-defined Fe(II) catalysts that are endo selective for the hydrofunctionalization of alkynes. An Fe(II) vinylidene complex, [Fe(Cp*)(PR2NPh2)(=C=CHPh)]PF6 (R = cyclohexyl, 7), was also characterized that suggests an analogous intermediate is responsible for catalytic selectivity. Catalyst decomposition was also probed and a likely off-cycle deactivation product was identified. On-cycle intermediates were potentially identified and proposed as resting-state species in the catalytic cycle. Preliminary studies were attempted to assess activity and selectivity on a small scope of substrates, but more optimization will be required.
Summary for Lay Audience
Two iron compounds were made for the first time that were based on similar ruthenium compounds previously known. These iron compounds are catalysts that help to cause chemical reactions for making rings containing carbon atoms and either oxygen or nitrogen atoms. The ring size that the catalysts make is consistent and controlled by carefully designing the structure around the metal to do reactions in a specific way. These catalysts are the first ones made with iron that can make rings in a certain way that previously has been done with expensive metals. A similar iron compound was also made that showed how the catalyst was able to make the correct size of rings, and another compound was found that was likely the catalyst breaking down. Understanding how the catalyst works and how it breaks down will help find ways to improve performance and lifetime. There could be a large reduction in the cost of catalysts if abundant metals like iron can continue to be used in well-designed compounds to do the jobs of precious metals.
Bridge, Benjamin, "Iron(II) Metal-Ligand Cooperative Catalysts for Endo-Selective Intramolecular Hydrofunctionalization" (2020). Electronic Thesis and Dissertation Repository. 7257.