NICKEL(II), PALLADIUM(II), PLATINUM(II) AND PLATINUM(IV) COMPLEXES OFCIS-1,2-BIS(DIPHENYLPHOSPHINO)ETHENE AND NITROGEN-CONTAINING HETEROCYCLES OR SULFUR LIGANDS

Several novel Ni(II), Pd(II), Pt(II) and Pt(IV) complexes containing t he diphos ligand cis-1,2-bis(diphenylphosphino) ethene (cis-dppen) hav e been prepared and characterized by X-ray diffraction methods, NMR sp ectroscopy ((PtH)-Pt-195-H-1}, P-31{H-1}, C-13{H-1}, H-1), fast atom b ombardment mass spectrometry, IR spectroscopy, elemental analyses, and melting points. In the case of [PtCl2(cis-dppen)] (1) a second crysta l modification was found and definitely characterized by an X-ray stru cture analysis: monoclinic, P2(1)/n, Z = 4, a = 8.312(1), b = 14.578(2 ), c = 19.868(4) Angstrom, beta = 91.27(1)degrees, R = 0.028 for 3862 observed reflections(I> 3 sigma(I)). In contrast to the former reporte d X-ray structure of the other modification of 1, which shows a comple te coplanarity of the coordination plane and the ethene bridge, this c oplanarity is slightly disturbed by a crystal packing effect in the se cond modification of 1. Nevertheless, both conformations are dominated by a pi bonding interaction. Furthermore, the X-ray structures of the recently prepared complexes [Pt(cis-dppen)(bipy)] (PF6)(2) (2) and [P t(cis-dppen)(phen)](BF4)(2) (3), when bipy and phen are 2,2'-bipyridin e and 1,10-phenanthroline, respectively, are given for the first time: 2. monoclinic, P2(1)/c, Z = 4, a = 12.649(3), b = 26.114(5), c = 14.6 65(3) Angstrom, beta = 111.62(3)degrees, R = 0.057 for 4260 observed r eflections (I> 3 sigma(I)); 3. monoclinic, P2(1), Z = 2, a = 8.779(2), b = 17.297(3), c = 13.059(3) Angstrom, beta = 93.79(3)degrees, R = 0. 045 for 3589 observed reflections (I>3 sigma(I)). These two X-ray stru ctures are the first examples of square-planar structures of Pt(II) co mplexes containing bipy or phen together with phosphines. The differen t conformations of 2 and 3 are of interest with respect to the known d ifferences between bipy and phen in photoactivation processes. The rea ction of 1 with an equimolar amount of anhydrous Na2S leads to the dim er [Pt-2(mu(2)-S)(2)(cis-dppen)(2)] (4). A similar treatment of 1 with the phosphoniodithioformate S2CPCy3, where Cy is cyclohexyl, produces the dimer [Pt-2(mu(2)-S) (mu(2)-S2CPCy3) (cis-dppen)(2)](BF4)(2) (5). However, the reactions of [MCl2(cis-dppen)] (M=Ni, Pd) with anhydrous Na2S give the trinuclear complexes [M-3(mu(3)-S)(2)(cis-dppen)(3)]X-2 (M = Ni, X-= PF6- (6), M = Pd, X-= BF4- (7)). In the case of 1 Na2S . 9H(2)O is needed to produce the corresponding Pt(II) complex [Pt-3(mu (3)-S)(2)(cis-dppen)(3)] Cl-2 (8). Interestingly, treatment of [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)]Cl -2 by chlorine gives the mononuclear complex [PtCl2(cis-dppen)(2)]Cl-2 (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 pos sible pi bonding interactions due to the unsaturated nature of this di phos ligand. (C) 1998 Elsevier Science S.A. All rights reserved.