Syntheses of new P-N ligands containing an imidazolyl group and their co-ordination behaviors toward nickel(II), cobalt-(II) and -(III)

摘要

Two new bidentate imidazolylphosphine P-N chelate ligands 2-(diphenylphosphinomethyl)-1-methylimidazole (PN~1) and 2-(diisopropylphosphinomethyl)-1-methylimidazole (PN~(II)) have been synthesized in good yields by treating R_2PCl (R = Ph or Pr~i) with 1-methyl-2-trimethylsilylmethylimidazole. Various types of nickel (II), cobalt-(II) and -(III) complexes have been prepared with these two ligands and characterized by physico-chemical techiques. The structures of PN~I centre dot HBr and two nickel (II) complexes, [Ni(PN~I)_2][BF_4]_2 and [Ni(PN~(II))_2] [BF_4]_2 centre dot MeCN 4 centre dot MeCN, have been studied by single crystal X-ray analyses. Both take planar structures with different configurations. In 2 the two phosphorus atoms are in cis position whereas in 4 centre dot MeCN they are trans to each other. The complex [NiCl_2(PN~I)] 1 adopts a five-co-ordinate dimeric structure with chloride bridges in the solid state and a monomeric square-planar structure, [Ni(PN~I)(solv)_2]Cl_2, in aqueous and in methanolic solutions. However, complex [NiCl_2(PN~(II))] 3 is diamagnetic and takes square-planar geometry around the metal ions both in the solid and solution states. The structures of cobalt (II), [CoX_2(L)] (where X=Cl or Br), and cobalt (III) complexes, [Co(acac)_2(L)]ClO_4 (where acac = acethylacetonate, L = PN~I or PN~(II)), are tetrahedral and octahedral, respectively. A variable temperature ~1H and ~(31)P NMR study of complexes 1 and 2 demonstrated the presence of dynamic motion of the PN-chelate ring (s). On the other hand, in the cobalt (III) complexes [Co(acac)_2(PN~I)]ClO_4 and [Co(acac)_2(PN~(II))]ClO_4 two protons of the backbone methylene group of the PN ligands are magnetically inequivalent.