Synthesis, Study, and Catalysis of New Dimethyl-Phosphine Ligands
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Two new general synthetic routes to phosphines were developed. The first method described directly converts phosphonates to phosphine oxides using organometallic nucleophiles. This reaction proceeds through a five-coordinate phosphorus intermediate. The second synthetic method uses a deprotonated secondary phosphine oxide for nucleophilic addition to an alkyl halide to form a tertiary phosphine oxide. This reaction proceeds through a standard SN2 mechanism, however in extreme cases a competitive electron transfer reaction was observed. These syntheses were used to make a new dimethyl phosphine (MeJPhos). This phosphine was used as a ligand for metal complexes and compared against a series of structurally related (JohnPhos) phosphines. MeJPhos was found to be the strongest electron donor in the series MeJPhos, EtJPhos, iPrJPhos, CyJPhos, and tBuJPhos. These ligands were then used to study structural effects of ligands on Buchwald-Hartwig cross-coupling catalysis. It was found that only tBuJPhos performed catalytically. This observation is likely due to the smaller steric profile of the other JohnPhos ligands. Specifically, it is the inability to perform the reductive elimination step of the catalytic cycle that prevents turnover. Ozonolysis was used to oxidize alkenes to aldehydes directly. Typically with ozonolysis, a secondary ozonide is formed as the product that must be chemically reacted in a subsequent step. By trapping out the immediate chemical precursor to the secondary ozonide with water, the formation of secondary ozonides was avoided. This method produced aldehydes directly from aryl alkenes in good to excellent yields. This dissertation includes previously published and unpublished co-authored material.