Synthesis and structural characterization of bis-chelate Pd(II) complexes derived from substituted di-(2-pyridyl)methane ligands

Bis-chelate complexes of palladium(II) derived from dipyridyl ligands of general formula [Pd(L)2](BF4)2 (L = (C5H4N)2C(OH)2, (C5H4N)2CH(OH), (C5H4N)2CH(Cl), (C5H4N)2CH(S2CNEt2) and (C5H4N)2CH(S-C5H4N)) have been synthesized and characterized by elemental analyses, X-ray diffraction, vibrational, and NMR spectroscopy. Crystal structures of the complexes [bis-{di-(2-pyridyl)dihydroxymethane}palladium(II)]tetrafluoroborate (1), [bis-{di-(2-pyridyl)hydroxymethane}palladium(II)]tetrafluoroborate (2), [bis-{di-(2-pyridyl)chloromethane}palladium(II)]tetrafluoroborate (3), [bis-{di-(2-pyridyl)-N,N′-diethyldithiocarbamatemethane}palladium(II)]tetrafluoroborate (4) and [bis-{di-(2-pyridyl)-2-pyridylsulfanylmethane}palladium(II)]tetrafuoroborate (5) displayed to the substituted di-2-pyridylmethane ligands in a bidentate coordination mode to the palladium atom with the formation of six-membered chelate rings. In these complexes, the palladium atom showed a distorted square planar local geometry. Crystal structures of the complexes 3–5 displayed the –Cl, –S2C(NEt)2 and –S-C5H4N groups on the bridge carbon atom in a flagpole position, which is stabilized by weak intramolecular interactions of type Pd⋯Cl (for 3) and Pd⋯S (for 4 and 5). However, in 2 the crystallographic data showed to the major conformer containing the –OH group in a bowsprit position, displaying an intramolecular Pd⋯H interaction.

Synthesis and structural characterization of five bis-chelate complexes of Pd(II) of type [Pd(L)2](BF4)2 (L = (C5H4N)2C(OH)2 (1), (C5H4N)2CH(OH) (2), (C5H4N)2CH(Cl) (3), (C5H4N)2CH(S2CNEt2) (4), and (C5H4N)2CH(S-C5H4N) (5) are reported. Crystal structures of 1–5 displayed a bidentate coordination mode of the free ligands toward palladium atom with the formation of six-membered chelate rings in a boat conformation. X-ray diffraction and NMR data for the complexes 3–5 showed to the major conformer in a flagpole position; in 2 the predominant bowsprit conformer in solution and solid state is observed.Figure optionsDownload as PowerPoint slideHighlights
► Five bis-chelate complexes of Pd(II) of type [Pd(L)2](BF4)2 are reported.
► Six-membered chelate rings in a boat conformation are obtained.
► Intramolecular Pd⋯Cl or Pd⋯S interactions enhance the flagpole conformer.
► In the bowsprit conformer an intramolecular Pd⋯H interaction is observed.
► By X-ray diffraction and NMR the major conformer was identified.