Several novel Pd(II), Pt(II) and Pt(IV) dimers containing 1,2-bis(diphenylphosphino)acetylene (dppa) as bridging ligand have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy (195Pt{1H}, 31P{H1H}), IR spectroscopy, elemental analyses and melting points. The X-ray structures of the former reported complexes [Pd2Cl4(dppa)2] (1) and [Pt2Cl4(dppa)2] (2) are given for the first time: 1: monoclinic, for 6432 observed reflections ( for 2332 observed reflections (1>3σ(1)). These two X-ray structures are discussed with respect to the former given ambiguous interpretation of the X-ray structure of [PtPdCl4(dppa)2]. Replacement of the chlorides in 1 or 2 by iodides leads to [Pd2I4(dppa)2] (3) or [Pt2I4(dppa)2] (4). 4 is also fully characterized by an X-ray structure analysis for the first time: 4: monoclinic, for 4698 observed reflections (1>3σ(1)).
The X-ray structures of 1,2 and 4 reveal different orientations of the dppa bridges due to metal-phosphorus dπ-dπ back bonding leading to different angles between the square-planar coordination units, respectively. Replacement of the chlorides in 1 by NO2− leads to [Pd2(NO2)4(dppa)2] (5), whereas in 2 only one chloride can be substituted by NO2− and [Pt2Cl3(NO2) (dppa)2] (6) is formed. A similar reaction of 2 with 2,2′-bipyridine (bipy) produces [Pt2Cl2(dppa)2(bipy)](BF4)2 (7). Oxidation of 2 by chlorine gives the Pt(IV) dimer [Pt2Cl8(dppa)2] (8). An equimolar amount of PdCl2 reacts with one triple bond of 2 leading to [Pt2PdCl6(dppa)2] (9). an analogous manner [Pd4Cl8(dppa)2] (10) is formed from 1 and two equimolar amounts of PdCl2. The stability and reactivity of complexes 1–10 are discussed with respect to the X-ray structures of 1,2,4 and [PtPdCl4(dppa)2].