Phosphido-Bridged Di- and Trinuclear Palladium Complexes from Electron-Poor Phosphanes R2PH (R = C2F5, C6F5, (CF3)2C6H3)

Electron-withdrawing substituents R in complexes [L-n M(PR2)] influence the P-M bond length due to a decreased sigma-donation and enhanced pi-back-bonding, leading to an increased Lewis acidity of the metal ion and therefore strengthening the M-L bond to electron-rich ligands L. This influences the Lewis acidity and the redox behavior of corresponding transition-metal complexes, which is important for the design of optimized catalytic systems. To investigate this effect, the electron-poor phosphanes R2PH with R = C2F5, C6F5, 2,4-(CF3)(2)C6H3 were treated with Pd(F(6)acac)(2) (F(6)acac = hexafluoroacetylacetonato) and Pd(acac)(2) (acac = acetylacetonato). While the reaction of the phosphanes with Pd(F(6)acac)(2) in all cases yielded the corresponding phosphido-bridged dinuclear palladium complexes [{(F(6)acac)Pd[mu-(PR2)]}(2)], the compounds obtained in the reaction with Pd(acac)(2) were structurally more diverse. For R = C2F5, the dinuclear palladium complex [{(acac)Pd{mu-[P(C2F5)(2)]}}(2)] was obtained, while the reaction with (C6F5)(2)PH yielded a trinuclear palladium complex bridged by four phosphido units. All complexes were fully characterized, including X-ray crystallography.