Coordination of a diphosphine-phosphine oxide to Au, Ag and Rh: when polyfunctionality rhymes with versatility.

Gold, silver and rhodium complexes of the diphosphine-phosphine oxide DPPO = {[o-iPr(2)P-(C(6)H(4))](2)P(O)Ph} have been prepared and characterized. Thanks to its polyfunctional character, DPPO features versatile coordination properties. According to crystallographic data, only one phosphine moiety is engaged in coordination towards (AuCl) and [RhCl(nbd)]. However, NMR data indicate fluxional behavior in solution, as the result of the exchange between the free and coordinated phosphines around the metal. Chelating coordination via the two phosphine sites is observed towards (Au(+)) and (AgCl) with PMP bite angles varying from 122° to 159°. According to X-ray and theoretical analyses, the oxygen atom of the central phosphine oxide moiety points towards the metal but does not interact significantly with it. Tridentate coordination via the two phosphines as well as the oxygen atom of DPPO occurs with [Rh(CO)(+)], leading to an original PO(P)P pincer structure.