The template effect of palladium(II): Synthesis, characterization, and crystal structures of 2,4-substituted 1,3,5-triazapentadienatopalladium(II) complexes

The reaction of LiN(SiMe₃)₂ with two equivalents of 2-, 3-, or 4-cyanopyridine followed by the addition of half an equivalent of [PdCl₂(PhCN)₂] gives neutral 1,3,5-triazapentadienato complexes of the general formula [Pd{HNC(Py)NC(Py)NH}₂] (Py = 2-pyridyl 1, 3-pyridyl 2, 4-pyridyl 3). When the above reaction was carried out with benzonitrile and then 3- or 4-cyanopyridine was added followed by half an equivalent of [PdCl₂(PhCN)₂] neutral unsymmetrical 1,3,5-triazapentadienato complexes of the general formula [Pd{HNC(Ph)NC(Py)NH} ₂] (Py = 3-pyridyl 4, 4-pyridyl 5) were obtained. When LiN(SiMe ₃)₂ was treated with one equivalent of benzonitrile in THF, followed by the addition of a quarter of an equivalent of anhydrous palladium chloride and workup in air, the trinuclear complex tetrakis(benzamidinato)bis(2,4-diphenyl-1,3,5-triazapentadienato) tripalladium(II) (6) was obtained as yellow crystals in 19% yield. All complexes were fully characterized by elemental analysis, ¹H NMR spectroscopy, and mass spectrometry. The solid-state structures of compounds 2, 3, and 6 were determined by X-ray crystallography. Structural analyses revealed that the 2,4-bis(pyridyl)-1,3,5-triazapentadienyl ligands in 2 and 3 behave as didentate ligands to form six-membered rings with the metal ion. For 6, the 2,4-diphenyl-1,3,5-triazapentadienyl ligands also behave as didentate ligands to form six-membered rings with the metal ion, whereas the amidinato ligands behave as bridging didentate ligands.