Synthesis of new palladium(II) compounds with several bidentate nitrogen-donor ligands: Structural analyses by 1H and 13C{1H} NMR spectroscopy and crystal structures

Synthesis and Characterization of New N-Alkylamino-3,5-diphenylpyrazole Ligands and Reactivity Toward PdII and PtII. Study of the cis–trans Isomerization

In this paper, the synthesis and characterization of two new N-alkylaminopyrazole ligands, 1-[2-(ethylamino)ethyl]-3,5-diphenylpyrazole (dpea) and 1-[2-(octylamino)ethyl]-3,5-diphenylpyrazole (dpoa) are reported. The reaction of these ligands with [MCl2(CH3CN)2] (M = PdII, PtII) affords the following square planar complexes: cis-[MCl2(NN′)] (M = PdII: NN′ = dpea, 1; dpoa, 2; M = PtII: NN′ = dpea, 3; dpoa, 4). Reaction of [PdCl2(CH3CN)2] and dpea or dpoa in 1:2 M:NN′ molar ratio, in the presence of NaBF4, yields complexes [Pd(NN′)2](BF4)2 (NN′ = dpea, [5](BF4)2); dpoa, [6](BF4)2). The solid-state structures of complexes 1, 3, and [5](BF4)2 have been determined by single-crystal X-ray diffraction methods. In complexes 1 and 3, the dpea ligand is coordinated through the Npz and Namino atoms to the metallic centre, which completes its coordination with two chlorine atoms in a cis disposition. For complex [5](BF4)2, the crystal structure consists of cations involving a [Pd(Npz)2(Namino)2]2+ core with a cis disposition of the two dpea ligands in a square-planar geometry and BF4 – anions. Theoretical calculations were carried out to optimize the geometries of the cis and trans isomers of the [Pd(dpea)2]2+ cation and of the [Pd(dpea)2](BF4)2 complex. The results show that the trans isomer is the most stable for [Pd(dpea)2]2+, in contrast with the cis stereochemistry observed in the crystal structure of [Pd(dpea)2](BF4)2. The calculations also predict that in acetonitrile solution, the dissociation of this complex into the corresponding ions is thermodynamically favourable. The cis–trans isomerization process of [Pd(dpea)2]2+ in acetonitrile solution has been studied by NMR spectroscopy at different temperatures. These experimental results confirm that the trans isomer is the thermodynamically most stable form of the complexes [5](BF4)2 and [6](BF4)2.

Synthesis and Characterization of New Palladium(II) Complexes Containing N-Alkylamino-3,5-diphenylpyrazole Ligands. Crystal Structure of [PdCl(L2)](BF4) {L2 = Bis[2-(3,5-diphenyl-1-pyrazolyl)ethyl]ethylamine}

In this paper, the synthesis of two new N,N′,N-ligands, bis[2-(3,5-diphenyl-1-pyrazolyl)ethyl]amine (L1) and bis[2-(3,5-diphenyl-1-pyrazolyl)ethyl]ethylamine (L2) is reported. These ligands form complexes with the formula [PdCl(N,N′,N)]Cl when reacting with [PdCl2(CH3CN)2] in a 1:1 metal-to-ligand molar ratio. Treatment of these ligands with [PdCl2(CH3CN)2] in a 1:1 metal-to-ligand molar ratio in the presence of AgBF4 or NaBF4 gave [PdCl(N,N′,N)](BF4) complexes. These PdII complexes were characterized by elemental analyses, conductivity measurements, mass spectrometry, and IR, 1H, and 13C{1H} NMR spectroscopies. The X-ray structure of the complex [PdCl(L2)](BF4) has been determined. The metal atom is coordinated by two azine nitrogen atoms and one amine nitrogen atom of the aminopyrazole ligand. The distorted square planar coordination is completed by one chlorine atom. In this complex, intermolecular π–π stacking interactions are present.