Synthesis of 31P nmr spectroscopic study of [Ag(μ-R2PCH2PR2)3Ag]2+ (R = Me or Ph). Observation of an intramolecular "end-over-end" exchange of bridging R2PCH2PR2

Abstract

Reaction of AgAsF6 with R2PCH2PR2 (R = Ph or Me) in a 2:3 ratio in MeNO2 or Me2CO produces the new compounds [Ag2(R2PCH2PR2)3](AsF6)2, which have been isolated in good yield. The analogous 107Ag-enriched compounds are produced using 107AgAsF6. The 2:3 compounds have interesting variable temperature 31P nmr spectra which have been studied in detail using the 107Ag-enriched compounds. The 31P nmr spectra of [107Ag2(Ph2PCH2PPh2)3](AsF6)2:[107Ag2(Me2PCH2PMe2)3](AsF6)2 mixtures at ambient probe temperature show the formation of the mixed ligand binuclear cations [107Ag2(Ph2PCH2PPh2)3-x-(Me2PCH2PMe2)x:]2+ (x = 1 or 2). By analogy, the two parent complexes also contain binuclear cations, and the limiting low temperature 31P nmr spectra of these can be interpreted in terms of the manxane structure, [107Ag(μ-R2PCH2PR2)3107Ag]2+. With increase in temperature, the 31P nmr spectra of the parents provide evidence for an intramolecular exchange process which is faster for R = Ph than for R = Me and which is shown to involve "end-over-end" exchange of bridging R2PCH2PR2. This type of exchange has not been observed previously for these ligands. With Me2CO as solvent, an approximate value of the enthalpy of activation for exchange is 59 kJ mol-1 for [l07Ag(μ-Ph2PCH2PPh2)3107Ag]2+ and 50 kJ mol-1 for [107Ag(μ-Me2PCH2PMe2)3107Ag]2+.