Deprotonated 5-acetylmethyl-1,2,4-oxadiazoles as bidentate chelating ligands for the synthesis of palladium(II) and copper(II) complexes

Neutral bis-chelate complexes M(L)₂ (M = Pd(II); LH = 3-R-5-acetylmethyl-1,2,4-oxadiazole: R = Me 1a, Et 1b, Bn 1c, Ph 1d, 4-Tol 1e; M = Cu(II); LH = 3-R-5-acetylmethyl-1,2,4-oxadiazole: R = Me 2a, Et 2b, Bn 2c, Ph 2d, 4-Tol 2e) were synthesized in moderate to good yields (61–87%) by the reaction of the corresponding 5-acetylmethyl-1,2,4-oxadiazole with Na₂[PdCl₄] or CuCl₂·2H₂O in the presence of sodium tert-butoxide as a base. The complexes were characterized by IR (1a–e and 2a–e) and ¹H and ¹³C{¹H} NMR spectroscopy (1a–e), electrospray ionization high-resolution mass spectrometry (ESI-HRMS; 1a–e and 2a–e), and powder X-ray diffraction analysis (2a–e). Compounds 1a–e and 2a–e are also characterized by single-crystal X-ray diffraction data. Their coordination geometries and supramolecular organization differ significantly depending on the nature of the metal center and the substituent R.