Halo-carbonyl complexes of platinum(II) and palladium(II)

The mononuclear and binuclear square-planar complexes of palladium(II) and platinum(II) cis-PtCl2(CO)2 (1), trans- Pt2Cl4(CO)2 (2), cis-PtBr2(CO)2 (3), and cis-Pd2Cl4(CO)2 (4), have been prepared by new synthetic procedures and some of them (2, 3, and 4) structurally characterised by X-ray diffraction methods. In the mononuclear platinum derivatives, cis-PtX2(CO)2, X=Cl, Br, the molecules are arranged in columns, the Pt⋯Pt separation being 3.378 Å (X=Cl) or 3.65 Å (av., X=Br). The chloride-bridged dinuclear chloro-carbonyl complexes M2Cl4(CO)2, M=Pd, Pt, contain terminal chloride and carbonyl groups, trans for the platinum derivative 2, but, unexpectedly, cis for the corresponding palladium compound 4. Packing is based on intermolecular C⋯X or Pt⋯Pt interactions, as a function of the nature of the halide. The carbonylation at atmospheric pressure and room temperature of the tetrahalo complexes of platinum(II) in the presence of AlX3 as halide scavenger leads to [PtX3(CO)]− or PtX2(CO)2, depending on the Pt/AlX3 molar ratio. The crystal and molecular structural data of [NBu4][PtBr3(CO)] (5), show the anion to have substantially identical Pt–Br bond distances, the CO ligand performing no trans influence.