Steric effects in pyrazole palladium(II) compounds: Synthetic, structural, and theoretical studies of a highly distorted octahedral palladium(II) pyrazole compound

Abstract

Carbamoyl pyrazole compounds of palladium(II) chloride of the type [PdCl2L2] (where L=C3H3N2CONR2 or C5H7N2CONR2; R=CH3, C2H5 or iC3H7) have been synthesized and characterized by IR, 1H NMR, ES-MS, elemental analysis and single crystal X-ray diffraction methods. The centrosymmetric structure of [PdCl2(C3H3N2CON{C2H5}2)2] (2) shows that the palladium(II) ion is surrounded by two pyrazolyl nitrogen and two chlorine atoms in a square planar arrangement and the two nitrogen atoms of the carbamoyl group are weakly bonded to the metal centre in axial positions. In the centrosymmetric structure of [PdCl2(C5H7N2CON{C2H5}2)2] (5), the palladium(II) ion is surrounded by two pyrazole nitrogen and two chlorine atoms form a square planar arrangement and the two oxygen atoms of the carbamoyl group are weakly bonded to the metal centre in axial positions. The ligands are bonded through the soft pyrazole nitrogen to palladium(II) chloride in mutually trans positions. The carbamoyl pyrazole groups displayed an anti conformation. Theoretical studies on compound 5 show that the axial interactions involve donation from the filled pz orbital of the oxygen atom to the dxz orbital of the palladium(II) ion.