X-RAY PHOTOELECTRON-SPECTRA OF BINUCLEAR PALLADIUM-PALLADIUM-BONDED COMPLEXES AND THEIR INSERTION PRODUCTS

X-ray photoelectron spectroscopic (XPS) data have been obtained for the binuclear Pd(I) complexes Pd2(dpm)2Cl2 and Pd2(dam)2Cl2 (dpm = bis(diphenylphosphino)methane and dam = bis(diphenylarsino)methane) and products resulting from the insertion of carbon monoxide, methyl isocyanide, sulfur dioxide, and atomic sulfur into the metal-metal bond. The insertion of these small molecules into the Pd-Pd bond results in either no change or modest increases in the Pd 3d5/2 binding energies (ΔEB of 0.0 to +0.6 eV) while the Cl 2p3/2, P 2p3/2, or As 3d binding energies of the attendant ligands remain constant. The largest Pd 3d5/2 binding energy shifts arise from insertion of SO2. When observable, the binding energies of atoms in the inserted ligands decrease, sometimes substantially (0.9-2.5 eV), compared with those of their precursors. The small binding energy shifts of the Pd 3d levels are reasonable because only half of the charge donated to the inserted ligand comes from each half of the dipalladium complex. Similarly the binding energy shifts of the atoms of the inserted ligands (compared to those of their free, neutral precursors) become smaller, where detectable, as the number of atoms which compose the ligand increases. Nitrogen Is binding energies for bridging methyl isocyanide in Pd2(dpm)2 (m-CNCH3)C12 and [Pd2(dpm)2( μ-CNCH3)(CNCH3)2](PF6)2 are ~1 eV lower than those for terminal methyl isocyanide. For comparison, XPS data are also presented for [Pd2(CNCH3)6](PF6)2, [Pd(CNCH3)4](PF6)2, Pd(CNCH3)2I2, and [Pt2(CNCH3)6](BF4)2, which contain only terminal, linearly bound CNCH3 ligands. © 1979, American Chemical Society. All rights reserved.