Palladium(II) and platinum(II) complexes of cis-1,2-bis(diphenylphosphino)ethene: completely planar structures due to π bonding in the case of platinum(II)

Article abstract of DOI:10.1016/0020-1693(95)04682-Y

Several novel Pd(II) and Pt(II) complexes contaning the diphos ligand cis-1,2-(diphenylphosphino)ethene (cis-dppen) have been prepared and characterized by X-ray diffraction methods. NMR spectroscopy (195)Pt{(1)H}, (31)P{(1)H}), IR spectroscopy, elemental analyses and melting points. In contrast to the former reported and directly available compounds [PtCl2(cis-dppen)] (1) and [Pd(cis-dppen)2](BPh4)2 (3), an intermediate is formed in the synthesis of [PtCl2(cis-dppen)] (2). It is shown that this intermediate is of type [Pt(cis-dppen)2](2+). Both 2 and [Pt(cis-dppen)2](BPh4)2 (4) are fully characterized by X-ray structure analyses: 2: monoclinic, P21/m, a=8.507(2), b=18.236(4), c=11.205(2)?, β=105.25(3)°, R=0.052 for 3070 observed reflections (I>3σ(I)); 4: monoclinic, P21/c, a=10.718(2), b=17.283(3), c=24.549(5)?, β=99.25(3)°, R=0.028 for 5588 observed reflections (I>3σ(I)). In 2 and 4 the Pt atoms show square-planar coordinations, where in both casesthe ethene bridges are stricly coplanar with the coordination planes. T his gives strong evidence of a πbonding interaction including the ethene bridges. Replacement of the chlorides in 1 and 2 by 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to the square-planar compounds [Pd(cis-dppen)(bipy)](BPh4)2 (5), [Pt(cis-dppen)(bipy)](PF6)2 (6), [Pd(cis-dppen)(phen)] (7) and [Pt(cis-dppen)(phen)](BF4)2 (8). Similar reaction with NO2(1-) produce [Pd(NO2)2(cis-dppen)] (9), [Pt(NO2)2(cis-dppen)] (10) and [PtCl(NO2)(cis-dppen)] (11). From Pd(CN)2 and cis-dppen [Pd(CN)2(cis-dppen)] (12) is formed. The stability and reactivity of complexes 1-12 are discussed with respect to the known non-planar X-ray structures of [PtCl2(dppe)], where dppe is 1,2-bis(diphenylphosphino)ethane, and [Ni(cis-dppen)2](ClO4)2.