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(SiMe3)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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)