Phosphonium salts. II. The reaction of bis-phosphonium salts with metal hydrides

Abstract

Ethane-1,2-bis-phosphonium salts are cleaved by sodium hydride to phos- phines in 55-80% yields with loss of the two-carbon bridge. The reaction is independent of the substituents at the phosphorus atoms. The same reaction is observed with an ethene-1,2-bis-salt and with but- 2-ene-1,4-bis(triphenylphosphonium) dibromide. It is suggested that a phosphorane is formed which subsequently fragments in a manner analogous to alkaline hydrolysis.     Lithium aluminium .hydride behaves similarly but loss of the bridge is competitive with loss of benzyl groups, and yields are generally better (> 70%).