Effect of ortho-substituents on the stereochemistry of 2-(o-substituted phenyl)-1H-imidazoline–palladium complexes

Palladium complexes composed of [Pd(Ln)2Cl2] (n = 1, 2, 3, 4, 6), [L5a]2[PdCl4] and [Pd(L5b)2], where L1 = 4,5-dihydro-2-phenyl-1H-imidazole (=2-phenyl-1H-imidazoline), L2 = 2-(o-fluorophenyl)-1H-imidazoline, L3 = 2-(o-methylphenyl)-1H-imidazoline, L4 = 2-(o-tert-butylphenyl)-1H-imidazoline, L5a = 2-(o-hydroxyphenyl)-1H-imidazolinium, L5b = 2-(1H-imidazolin-2-yl)phenolate, and L6 = 2-(o-methylphenyl)-1H-imidazole, were synthesized. Molecular structures of the isolated palladium complexes were characterized by single crystal X-ray diffraction analysis. The effect of ortho-substituents on the phenyl ring on trans-chlorine geometry was noted for complexes [Pd(L1)2Cl2] 1a and 1b, [Pd(L2)2Cl2] 2 and [Pd(L6)2Cl2] 6, whereas cis-chlorine geometry was observed for [Pd(L3)2Cl2] 3 and [Pd(L4)2Cl2] 4. PdCl2 reacts with 2-(o-hydroxyphenyl)-1H-imidazoline in DMF to give [L5a]+ and [L5b]– so that [L5a]2[PdCl4] 5a and [Pd(L5b)2] 5b were obtained. In complex 5b, as an N,O-bidentate ligand, two ligands L5b coordinated with the central Pd(II) ion in the trans-form. The coordination of PdCl2 with 2-(o-hydroxyphenyl)-1H-imidazolines in solution was investigated by NMR spectroscopy.