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Several new neutral and cationic organopalladium complexes containing a P–N chelating ligand, 2-(diisopropylphosphinomethyl)-1-methylimidazole, have been synthesized and characterized. The neutral complexes [PdPh(I)(P–N)] 1 and [PdMe(I)(P–N)] 2 have been synthesized by oxidative addition of PhI and MeI, respectively to Pd(dba)₂ (dba = dibenzylideneacetone) in the presence of the P–N ligand. The cationic complexes [PdPh(PPh₃)(P–N)]BF₄ 3 and [PdMe(PPh₃)(P–N)]BF₄ 4 were obtained by adding an acetone solution of AgBF₄/PPh₃ to the corresponding neutral precursors 1 and 2, respectively. A cationic allyl complex, [Pd(η³-C₃H₅)(P–N)]Br 5, has also been prepared by oxidative addition of 3-bromopropene to Pd(dba)₂ in presence of the P–N ligand. Single crystal structure determinations have been carried out for 1, 4 and 5. Carbonylation of the metal–carbon bond in these new complexes was also studied. The neutral complexes 1 and 2 react smoothly with CO to give carbonylated products [Pd(C(O)Ph)I(P–N)] 6 and [Pd(C(O)Me)I(P–N)] 7, respectively. The methyl complex 2 reacted much faster than the phenyl complex 1. The cationic complexes 3 and 4 are inert and do not give any carbonylated product. However, in the case of the reaction of 3, evidence has been obtained for the formation of a CO-coordinated complex [PdPh(PPh₃)(CO)(P–N)]BF₄ 8 in which the P–N ligand temporarily acts as a monodentate phosphorus-bonded ligand. On the other hand, a cationic complex containing a weakly coordinating acetone molecule, [PdMe{(CD₃)₂CO}(P–N)]BF₄ 9, showed an enhanced reactivity toward CO and gave [Pd{MeC(O)}(CO)(P–N)]BF₄ 10.

Two new bidentate imidazolylphosphine P–N chelate ligands 2-(diphenylphosphinomethyl)-1-methylimidazole (PN^I) and 2-(diisopropylphosphinomethyl)-1-methylimidazole (PN^II) have been synthesized in good yields by treating R₂PCl (R = Ph or Prⁱ) 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 techniques. The structures of PN^I·HBr and two nickel(II) complexes, [Ni(PN^I)₂][BF₄]₂ 2 and [Ni(PN^II)₂][BF₄]₂·MeCN 4·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·MeCN they are trans to each other. The complex [NiCl₂(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]Cl₂, in aqueous and in methanolic solutions. However, complex [NiCl₂(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), [CoX₂(L)] (where X = Cl or Br), and cobalt(III) complexes, [Co(acac)₂(L)]ClO₄ (where acac = acetylacetonate, L = PN^I or PN^II), are tetrahedral and octahedral, respectively. A variable temperature ¹H and ³¹P 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)]ClO₄ and [Co(acac)₂(PN^II)]ClO₄ two protons of the backbone methylene group of the PN ligands are magnetically inequivalent.