Carbonyl halides of the Group VIII transition metals. VII. Reactions of palladium(I) halocarbonyls with Bis(diphenylphosphino)methane and Bis(diphenylarsino)methane and the crystal and molecular structures of these derivatives

Abstract

The reactions of Pd(CO)X (X = Cl, Br) with bis(diphenylphosphino)methane (dpm) and its arsenic analogue, dam, have been investigated. The iodo complexes were prepared indirectly. Ligand dpm gives complexes of the formula [Pd(dpm)X]₂. With dam, the nature of the product depends upon the identity of the halogen; with X = Cl, Br the products are [Pd(dam)X]₂CO, but the iodo derivative is [Pd(dam)I]₂. N.m.r. spectroscopy suggests that [Pd(dam)I]₂ has a structure different to the dpm complexes.     [Pd(dam)Cl]₂CO,3C₆H₁₄ is tetragonal, space group P4_I, a 22.0458(1), c 14.4345(1) Ǻ containing four dimer units per unit cell. The structure was refined to R 0.096 and R_w 0.097 for 1698 independent reflections. The crystals are molecular being composed of discrete dimeric molecules of the complex and solvent. The palladium coordination is approximately square planar with two trans arsenic atoms, terminal halogen and the bridging carbonyl group which is common to both metal environments. There is no twist about the Pd-Pd axis so the Pd,As, unit is planar. The Pd-Pd distance of 3.274(8) Ǻ is too long for a direct metal-metal bond. However, the compound is diamagnetic so spin pairing must occur through the unusual carbonyl bridge.