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

Abstract Palladium complexes composed of [Pd(Ln) 2 Cl 2 ] ( n  = 1, 2, 3, 4, 6), [ L5a ] 2 [PdCl 4 ] and [Pd( L5b ) 2 ], where L1  = 4,5-dihydro-2-phenyl-1 H- imidazole (=2-phenyl-1 H -imidazoline), L2  = 2-( o -fluorophenyl)-1 H- imidazoline, L3  = 2-( o- methylphenyl)-1 H- imidazoline, L4  = 2-( o - tert -butylphenyl)-1 H- imidazoline, L5a  = 2-( o -hydroxyphenyl)-1 H -imidazolinium, L5b  = 2-(1 H -imidazolin-2-yl)phenolate, and L6  = 2-( o- methylphenyl)-1 H- 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 ) 2 Cl 2 ] 1a and 1b , [Pd( L2 ) 2 Cl 2 ] 2 and [Pd( L6 ) 2 Cl 2 ] 6 , whereas cis -chlorine geometry was observed for [Pd( L3 ) 2 Cl 2 ] 3 and [Pd( L4 ) 2 Cl 2 ] 4 . PdCl 2 reacts with 2-( o -hydroxyphenyl)-1 H -imidazoline in DMF to give [ L5a ] + and [ L5b ] – so that [ L5a ] 2 [PdCl 4 ] 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 PdCl 2 with 2-( o -hydroxyphenyl)-1 H -imidazolines in solution was investigated by NMR spectroscopy.