Nickel(II), palladium(II), platinum(II) and platinum(IV) complexes of cis-1,2-bis(diphenylphosphino)ethene and nitrogen-containing heterocycles or sulfur ligands

Article abstract of DOI:10.1016/S0020-1693(97)06041-6

Several novel Ni(II), Pd(II), Pt(II) and Pt(IV) complexes containing the diphos ligand cis-1,2-bis(diphenylphosphino)ethene (cis-dppen) have been prepared and characterized by X-ray diffraction methods. NMR spectroscopy (¹⁹⁵Pt{¹H}, ³¹P{¹H}, ³¹C{¹H}, ¹H), fast atom bombardment mass spectrometry, IR spectroscopy, elemental analyses, and melting points. In the case of [PtCl₂(cis-dppen)] (1) a second crystal modification was found and definitely characterized by an X-ray structure analysis: monoclinic, P2₁/n, Z=4, a = 8.312(1), b = 14.578(2), c = 19.868(4) A, β = 91.27(1)°, R = 0.028 for 3862 observed reflections (1>3σ(1)). In contrast to the former reported X-ray structure of the other modification of 1, which shows a complete coplanarity of the coordination plane and the ethene bridge, this coplanarity is slightly disturbed by a crystal packing effect in the second modification of 1. Nevertheless, both conformations are dominated by a π bonding interaction. Furthermore, the X-ray structures of the recently prepared complexes [Pt(cis-dppen)(bipy)](PF₆)₂ (2) and [Pt(cis-dppen) (phen)](BF₄)₂ (3), where bipy and phen are 2,2′-bipyridine and 1,10-phenanthroline, respectively, are given for the first time: 2: monoclinic, P2₁/c, Z = 4, a = 12.649(3), b = 26.114(5), c= 14.665(3) A, β = 111.62(3)°, R = 0.057 for 4260 observed reflections (1> 3σ(1)); 3: monoclinic, P2₁, Z = 2, a = 8.779(2), b = 17.297(3), c = 13.059(3) A, β = 93.79(3)°, R = 0.045 for 3589 observed reflections (1>3σ(1)). These two X-ray structures are the first examples of square-planar structures of Pt(II) complexes containing bipy or phen together with phosphines. The different conformations of 2 and 3 are of interest with respect to the known differences between bipy and phen in photo-activation processes. The reaction of 1 with an equimolar amount of anhydrous Na₂S leads to the dimer [Pt₂(μ₂-S)₂(cis-dppen)₂] (4). A similar treatment of 1 with the phosphoniodithioformate S₂CPCy₃, where Cy is cyclohexyl, produces the dimer [Pt₂(μ₂-S) (μ₂-S₂CPCy₃) (cis-dppen)₂ (BF₄)₂ (5). However, the reactions of [MCl₂(cis-dppen)] (M = Ni, Pd) with anhydrous Na₂S give the trinuclear complexes [M₃(μ₃-S)₂ (cis-dppen)₃] X₂ (M = Ni, X^- = PF₆ (6); M = Pd, X^- = BF₄ (7)). In the case of 1 Na₂S · 9H₂O is needed to produce the corresponding Pt(II) complex [Pt₃(μ-S)₂(cis-dppen)₃]Cl₂ (8). Interestingly, treatment ot [NiCl₂ (cis-dppen)] with S₂CPCy₃ leads to the unexpected mononuclear compound [Ni(CS₂)₄(cis-dppen)](BF₄)₂ (9). Oxidation of [Pt(cis-dppen)₂]Cl₂ by chlorine gives the mononuclear complex [PtCl₂(cis-dppen)₂]Cl₂ (10). The common feature of the compounds 1-10 is the presence of cis-dppen as a chelating ligand. The goal of this article is to reveal possible π bonding interactions due to the unsaturated nature of this diphos ligand.