N → P intramolecular stabilization of phosphenium ions and preparation of hypercoordinated phosphanes with unusual properties

Abstract

The reaction of ArLi 1 (Ar = [C 6H 3(CH 2NMe 2) 2-2,6]) with Ph 2PCl affords the phosphane 2 which, on treatment with HCl, gives rise to the monoprotonated ammonium salt 3, even in the presence of an excess of HCl. 2 reacts with MeI to give exclusively the phosphonium salt 4. Reaction of 1 with PhPCl 2 gives the stabilized phosphenium ion [ArPPh] +Cl − 6. This ion is reduced by LiAlH 4 in ArPHPh 9, which undergoes hydride abstraction on treatment with trityl cation, giving the same ionic phosphorus species. This unusual reaction is an example of increased reactivity of a P H bond resulting from hypercoordination at the phosphorus atom.