Cummins Project
New Reactions and Reagents for Phosphorus-Carbon Bond-Formation, Michael Baily Geeson (2020)
Experimental apparatus used to hydrogenate (—)-terpinen-4-ol.
ABSTRACT
Chapter 1 takes the format of an “Outlook” and sets forth the case for developing sustainable methods in the synthesis of phosphorus-containing compounds. Methods used by nature for phosphorus-carbon bond-formation, or in the chemistry of other elements such as silicon, are discussed as model processes for the future of phosphorus in chemical synthesis.
Chapter 2 describes the discovery of [TBA][P(SiCl3)2], prepared from [TBA]3[P3O9]-2H2O and trichlorosilane. The bis(trichlorosilyl)phosphide anion is used to prepare compounds that contain P–C, P–O, P–F, and P–H bonds in a method that bypasses white phosphorus (P4), the traditional route to organophosphorus compounds.
Chapter 3 extends the phosphate precursors to [TBA][P(SiCl3)2] from trimetaphosphate to crystalline phosphoric acid. Balanced equations are developed for the formation of [TBA][P(SiCl3)2] from phosphate sources and the byproducts are identified as hexachlorodisiloxane and hydrogen gas. Extension of trichlorosilane reduction to bisulfate provides improved access the known trichlorosilylsulfide anion, [TBA][SSiCl3]. This anion was used as a thionation reagent to prepare thiobenzophenone and benzyl mercaptan from benzophenone and benzyl bromide, respectively.
Chapter 4 describes the synthesis of neutral phosphine, HP(SiCl3)2, obtained by protonation of [TBA]1 with triflic acid. HP(SiCl3)2 is a highly efficient reagent for photochemical hydrophosphination of terminal alkenes. The phosphorus-silicon bonds in the hydrophosphination products can be functionalized to provide compounds of the general formulae: RPCl2, RPH2, [RP(R’)3]Cl, RP(O)(H)(OH), and RP(O)(OH)2.
Chapter 5 describes a method to prepare phosphiranes (three-membered rings that contain a phosphorus atom) from anthracene-based phosphinidene precursors and styrenic olefins. The phosphinidene transfer reaction requires an organoiron and fluoride catalyst. The resulting phosphirane is prepared in good yield (73%) with high stereoselectivity (>99%). Experimental investigations into the mechanism point toward the intermediacy of an iron-coordinated fluorophosphide species.
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