New reactions and reagents for phosphorus-carbon bond-formation

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.