Metal-assisted syntheses and NMR characterization of square-planar Pd(II) and Pt(II) complexes with tridentate nitrogen-donor chelate ligands

The complexes [PtCl(NNNH)](OTf) (1H), [PdCl(NNNH)](OTf) (2H), [PdCl(NNNMe)](OTf) (2Me), [PdMe(NNNH)](OTf) (3H), [PdMe(NNNMe)](OTf) (3Me) and [PdMe(NNNPh)](OTf) (3Ph) {NNNH = (pyridin-2-ylmethylene)-quinolin-8-yl-amine; NNNMe = (1-pyridin-2-yl-ethylidene)-quinolin-8-yl-amine; NNNPh = (phenyl-pyridin-2-yl-methylene)-quinolin-8-yl-amine} were prepared by reacting a stoichiometric methanolic mixture of 8-aminoquinoline and an ortho-substituted aldehydo- or keto-pyridine {2-pyridinecarboxaldehyde, 2-acetylpyridine or 2-benzoylpyridine} with the proper Pt(II) or Pd(II) precursor in methanol. In the case of the 2 Me derivative, the addition of a stoichiometric amount of a Ag(I) salt to the reaction mixture was necessary to obtain the desired product. Information about the formation of these complexes are reported. In particular, NMR experiments allowed to observe the different reactivity of 8-aminoquinoline towards aldehydo- and keto-pyridines and the formation of the emiaminal ligand pyridin-2-yl-(quinolin-8-ylamino)-methanol NNN(H2O)H 4. Finally, the methanesulphonato-complex [Pd(η1-OSO2CH3)(NNNMe)](OTf) (5Me) was obtained by reacting the chloro-derivative 2Me with a stoichiometric amount of AgSO3CH3 in nitromethane.