Halophosphines with amines

Aminophosphines are mostly prepared by one of two routes the reaction of halophosphines (normally chlorophosphines) with amines or silylated amines (equation 32), or the... 

Organophosphorus compounds find wide use in the chemical industry as catalysts, intermediates, complexes, and end-use products. Arylphosphines and phosphine oxides are often produced by the reaction of a preformed Grignard reagent with a halophosphine or phosphine oxide. Yields are reduced by the production of unwanted side-reaction products such as biaryls. These unwanted products are reduced when the reaction is conducted under Barbier conditions. When alkyl and aryl halides are reacted with magnesium metal, a trihalophosphine or phosphine oxide, a metal halide or amine catalyst, in THE benzene mixtures, at reflux, good yields of phosphines or phosphine oxides are obtained [74]. For example, triphenylphosphine can be prepared in a 97.2% yield from the reaction of bromobenzene, trichlorophosphine, magnesium metal, aluminum chloride, and sodium chloride in THF-benzene at 70 80 C. 

Tervalent phosphorus acid derivatives are normally liquids or low-melting solids which can be purified by distillation, or sometimes by recrystallization from a non-polar solvent. Most are oxidized in contact with the atmosphere, and many are easily hydrolyzed, so they must be kept under an inert atmosphere (N2 or Ar) during all manipulations. Flasks should be predried and solvents dried and deoxygenated before use. Tervalent phosphorus acid derivatives are, with few exceptions, thermally stable and can be kept indefinitely in ampoules under an inert gas (many halophosphines dissolve stopcock grease and should not be kept in stoppered flasks for prolonged periods). Inert solvents are hydrocarbons, ethers and, for most compounds, dichloromethane, ethyl acetate and tertiary amines. Aminophosphines react vigorously with tetrachloromethane and slowly with trichloromethane, and most tervalent phosphorus acid derivatives are oxidized by dimethyl sulphoxide and react with alcohols. 

Methylphosphinite boranes react smoothly with organolithium reagents to afford the corresponding tertiary phosphine boranes, as will be discussed in the next section. However, phosphinite boranes are not electrophilic enough to react with other weaker nucleophiles such as alcohols, amines or thiols. More reactive precursors, capable of producing a wide variety of phosphorus compounds, were needed. In phosphorus chemistry halophosphines, and chlorophosphines 27 in particular, are essential synthons (Scheme 4.12) as nucleophilic (after transformation into metal phosphides 28) and electrophilic building blocks. 

---