FACILE SYNTHESES AND INTERCONVERSIONS BETWEEN SIMPLE PHOSPHIRANIUM AND PHOSPHIRENIUM SALTS

The first phosphiranium salt, 1-methyl-1-phenylphosphiranium triflate (1), has been isolated in 73% yield from the reaction between 1-phenyl phosphirane and methyl triflate in benzene. The crystal and molecular structures of 1 have been determined. The phosphiranium ion in 1 under goes ring opening with water to give (+/-)-ethylmethylphenylphosphine oxide, and reacts with primary alcohols to give (+/-)-alkoxyethylmethy lphenylphosphonium ions. Treatment of 1 with dimethyl- or methylphenyl acetylene in dichloromethane affords over one week the corresponding s ubstituted phosphirenium salts in high yield. Phosphirenium salts can also be prepared in high yields by reacting a chloraolkylaryl- or chlo rodiarylphosphine and an alkyne with thallium(I) triflate in dichlorom ethane. The crystal and molecular structures of 1,2,3-trimethyl-1-phen ylphosphirenium triflate have been determined. The reaction of chlorom ethylphenylphosphine with thallium(I) triflate in the absence of an al kyne leads to an unstable phosphinophosphonium triflate that undergoes rapid chloride exchange and/or pyramidal inversion at phosphorus unde r ambient conditions, as determined by variable temperature NMR spectr oscopy.