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 AgAsF 6 with R 2 PCH 2 PR2 (R = Ph or Me) in a 2:3 ratio in MeNO 2 or Me 2 CO produces the new compounds [Ag 2 (R 2 PCH 2 PR 2 ) 3 ](AsF 6 ) 2 , which have been isolated in good yield. The analogous 107 Ag-enriched compounds are produced using 107 AgAsF 6 . The 2:3 compounds have interesting variable temperature 31 P nmr spectra which have been studied in detail using the 107 Ag-enriched compounds. The 31 P nmr spectra of [ 107 Ag 2 (Ph 2 PCH 2 PPh 2 ) 3 ](AsF 6 )2:[ 107 Ag2(Me 2 PCH 2 PMe 2 ) 3 ](AsF 6 )2 mixtures at ambient probe temperature show the formation of the mixed ligand binuclear cations [ 107 Ag 2 (Ph 2 PCH 2 PPh 2 ) 3−x (Me 2 PCH 2 PMe 2 ) x ] 2+ (x = 1 or 2). By analogy, the two parent complexes also contain binuclear cations, and the limiting low temperature 31 P nmr spectra of these can be interpreted in terms of the manxane structure, [ 107 Ag(μ-R 2 PCH 2 PR2) 3 107 Ag] 2+ . With increase in temperature, the 31 P 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 R 2 PCH 2 PR 2 . This type of exchange has not been observed previously for these ligands. With Me 2 CO as solvent, an approximate value of the enthalpy of activation for exchange is 59 kJ mol −1 for [ 107 Ag((μ-Ph 2 PCH 2 PPh 2 ) 3 107 Ag] 2+ and 50 kJ mol −1 for [ 107 Ag(μ.-Me 2 PCH 2 PMe 2 ) 3 107 Ag] 2+ .