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%).

Stability of ionic liquids in Brønsted-basic media

“…Gallagher reported that ethylene and vinylene-bridged bis(phosphonium) salts treated with sodium hydride once again exhibited a concerted decomposition of both phosphonium centers to yield two phosphines, a proton and ethylene or acetylene gas. 136 The mechanism most likely proceeds according to that shown in Fig. 30, which is analogous to that observed for the alkaline hydrolysis of similar salts.…”

“…30). 136 As observed for alkaline hydrolysis of phosphonium salts, benzyl and phenyl groups leave preferentially over alkyl groups, reflecting the order of anionic stability. 137,138 Conversely, Gough and Trippett noted an exception to this rule, as isopropyltriphenylphosphonium iodide yielded triphenylphosphine after treatment with LiAlH 4 .…”

“…31: Reduction of ethylene-bridged bis(phosphonium salts) according to Brophy and Gallagher. 136 Methyl substituents are shown for visual clarity.…”

Tetrasulfonated 1,2‐Bis(diphenylphosphanyl)ethane as a Building Block for the Synthesis of Disulfonated Alkyldiphenylphosphanes

“…For the cleavage step, the bis‐phosphonium salt was introduced into a suspension of LiAlH 4 in anhydrous tetrahydrofuran (THF) and this mixture was refluxed for 24 h. The use of LiAlH 4 resulted in a reductive cleavage accompanied by the loss of ethylene and H 2 . The mechanism of the cleavage is described in Scheme by analogy with the mechanism proposed for DPPE 10. After the cleavage, a treatment was necessary to eliminate the excess of LiAlH 4 and to recover the water‐soluble phosphane.…”

“…The desired water‐soluble phosphanes can be obtained by alkylation then cleavage of DPPETS. This strategy uses the capacity of the quaternary bis‐phosphonium salts of 1,2‐bis(diphenylphosphanyl)ethane (DPPE) to be cleaved by lithium aluminium hydride (LiAlH 4 ) producing an alkyldiphenylphosphane with loss of the carbon bridge between the two phosphorus atoms 10. We report here the synthesis of five new disulfonated alkyldiphenylphosphanes ( 1–5 ; Scheme ) by using this new methodology.…”