Addition of silver electrophiles to an electron-rich rhodium-rhodium bond. Synthesis and x-ray crystal structure of the [Rh2(η-C5H5)2(μ-CO)(μ-Ph2PCH2PPh2)(μ-AgOPF2O)], a triangular rhodium-silver cluster with the difluorophosphate ion coordinated to the silver atom

[Rh2(η-C5H5) 2(μ-CO)(μ-dppm)] (1) [dppm = bis(diphenylphosphino)methane] reacts with AgX (X = BF4 -, PF6 -, ClO4 -) to give [Rh2Ag(η-C5H5) 2(μ-CO)(μ-dppm)]X (2a-c); in solution the complexes 2a-c are very unstable. During these experiments using, by accident, an old and humid sample of AgPF6, the neutral compound [Rh2(η-C5H5)2(μ-dppm) (μ-AgOPF2O)] (3) was obtained; the same compound is also obtained by reacting 1 with silver difluorophosphate. The compound 3 has been spectroscopically and structurally characterized. It crystallizes in the space group Pnma; the cell dimensions are a = 14.471 (1) Å, b = 18.042 (2) Å, c = 12.772 (1) Å, V = 3334.5 Å3, and Z = 4. The structure has been refined to R = 0.051 and Rw = 0.048 for the 1281 reflections with I ≥ 3σ(I). In the triangular Rh2Ag framework the two Rh-Ag distances [2.689 (2) Å] are equivalent, and the Rh-Rh bond [2.750 (3) Å] is lengthened by 0.067 Å on silver adduct formation. The rhodium atoms are bridged by the CO and the dppm ligands; each rhodium atoms is further coordinated to the η5-cyclopentadienyl ligand. The structural features of the bridging dppm and CO groups remain essentially the same as in 1. The cyclopentadienyl ligands are in cis position. The difluorophosphate ion is O bonded to silver atom [Ag-O(S) = 2.12 (2) Å] and shows the phosphorus atom tetrahedrally coordinated.