Exploring the coordination chemistry and reactivity of hemilabile N-alkylaminopyrazole ligands towards Pd(II)

Reaction of the N-alkylaminopyrazole (NN′N) ligands bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethyl-1-pyrazolyl)methyl]isopropylamine (bdmai) with [PdCl2(CH3CN)2] in a 1:1 M/L ratio in CH2Cl2 produces cis-[PdCl2(NN′N)] (NN′N = bdmae (1), bdmai (2)). The solid state structure of complex 1 was determined by X-ray diffraction studies. The bdmae ligand is coordinated through the two Npz atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition. Treatment of the corresponding ligand with [PdCl2(CH3CN)2] in 1:1 M/L ratio in the presence of AgBF4 and metathesis with NaBPh4 in CH2Cl2/CH3OH (3:1) gave [PdCl(bdmae)](BPh4) (3), and in the presence of NaBPh4 in CH2Cl2/CH3CN (3:1) gave [PdCl(bdmai)](BPh4) (4). Complexes 1 and 2 were again obtained when complexes 3 and 4 were heated under reflux in a solution of Et4NCl in acetonitrile. These Pd(II) compounds were characterised by elemental analyses, conductivity measurements, IR, 1H and 13C{1H} NMR, HMQC and NOESY spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.