Some ary I-substituted bis( phosphinatcs) and bis(phosphine oxides) with tetra-and hcxamethylcne bridgcs, which arc not casily acccssible by conventional chemical methods. were synlhcsized hy palladium-catalyzed formation of thc carbonphosphorus hood.
Because of their potential as organoextractants in hydrometallurgy and as fire retardants, bis(phosphinates) and bis(phosphine oxides) have received a great deal of attention from industry. In addition, bis(phosphines) formed by reduction of the corresponding bis(phosphine oxides) are important ligands in homogeneous catalysis.
However, only few methods are known for their preparation. Early in 1959, Kosolapoff et a].') reported the synthesis of bis-(phosphine oxides) with polymethylene bridges, by reaction of phosphinyl chloride with twofold Grignard reagents. Soon afterwards, the same authors also described the synthesis of bis(phosphine ox- ides) by the reaction of 0,O-diethyl phosphonate with ditosylate and excess Grignard reagent *). Both methods obviously suffer from the limitation that functional groups, which are attacked by the Grignard reagent, may not be present. With regard to the preparation of bis(phosphinates), both the Arbusov reaction of dialkyl phenylphosphonite with alkyl dibromide3s4) and the Michaelis-Becker reaction of sodium phenylphosphinate with alkyl dichloride ' 1 have been reported. In both methods, phenyldichlorophosphine is generally employed as the precursor of the phosphonite and is usually obtained by the action of phosphorus trichloride on benzene in the presence of anhydrous aluminum trichloride. However, this route has the disadvantage that the orientation of the PC12 group in the benzene ring is often not controllable if there is already a substituent present in the benzene ring. The existing methods are thus not applicable to the synthesis of bis-(phosphinates) with a phenyl substituent bearing a functional group.