MONO- AND DIHYDROPHOSPHORANES AND DIHYDROPHOSPHORANATES AS INTERMEDIATES In THE REACTION OF PHOSPHONIUM SALTS WITH LiAiH4

Reduction of tetraphenylphosphonium bromide with LiAlH(D)4 at room temperature affords first the monohydrophosphorane Ph4PH, then the dihydrophosphoranate anion Ph4PH2]− which decomposes to the dihydrophosphorane Ph3PH2, all of which are identified by 31PNMR. Reductions of other phosphonium salts appear to follow a similar path. At elevated temperatures none of these intermediates is observed and attempted isolation leads to extensive decomposition.