Synthesis of triangular rhodium-silver clusters by the addition of silver electrophiles to electron-rich rhodium-rhodium bonds. X-ray crystal structure of [Rh2(η-C5H5)2(μ-CO)(μ-Ph2PCH2PPh2) (μ-AgO2CCH3)]

Rh2(η-C5H5) 2(μ-CO)(μ-dppm)] (1) [dppm = bis(diphenylphosphino)methane] reacts with silver acetate, trifluoroacetate, and diethyldithiocarbamate, AgY, to give the triangular mixed clusters [Rh2(η-C5H5) 2-(μ-CO)(μ-dppm)(μ-AgY)] (2, Y = CH3CO2; 3, Y = CF3CO2; 4, Y = (C2H5)2NCS2); the reactions occur by electrophilic attack of the silver salts on the electron-rich rhodium-rhodium bond of 1. Compounds 2-4 have been spectroscopically characterized; compound 2 has been also characterized by X-ray analysis. Crystals of 2 are orthorombic of space group Pnma with a = 14.426 (1) Å, b = 18.134 (2) Å, c = 12.614 (1) Å, and Z = 4. The structure was solved and refined to R and Rw values of 0.035 and 0.034 for the 1629 reflections with I ≥ 3σ(I). In the triangular Rh2Ag framework the two equivalent Rh-Ag distances are 2.730 (1) Å, and the Rh(1)-Rh(1′) bond distance is 2.751 (1) Å. The rhodium atoms are bridged by CO and dppm ligands and are symmetrically capped by η-cyclopentadienyl ligands. The cyclopentadienyl ligands are in cis position with an interplanar angle of 93.4 (3)° and are located in the less hindered side of the molecule. The acetate group is chelated to the silver atom [Ag-O(2) = 2.432 (7) Å; O(2)-Ag-O(2′) and O(2)-C(8)-O(2′) angles are respectively 51.0 (3)° and 123.7 (13)°]. The Ag, Rh(1), Rh(1′), O(2), and O(2′) atoms form a distorted square-planar pyramid with the silver atom in the apical position. The structural modification of 1 caused by the presence of the bridged AgO2CCH3 is discussed. Compound 1 reacts with silver malonate to give [{Rh2(η-C5H5)2(μ-CO) (μ-dppm)}2{μ-Ag2(CO2)2CH 2}] (5) in which two triangular Rh2Ag skeletons are joined by the bridged malonate group.