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

Abstract

Electron-withdrawing substituents R in complexes [Ln M(PR2)] influence the P–M bond length due to a decreased σ-donation and enhanced π-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)2C6H3 were treated with Pd(F6acac)2 (F6acac = hexafluoroacetylacetonato) and Pd(acac)2 (acac = acetylacetonato). While the reaction of the phosphanes with Pd(F6acac)2 in all cases yielded the corresponding phosphido-bridged dinuclear palladium complexes [{(F6acac)Pd[µ-(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{µ-[P(C2F5)2]}}2] was obtained, while the reaction with (C6F5)2PH yielded a trinuclear palladium complex bridged by four phosphido units. All complexes were fully characterized, including X-ray crystallography.