Synthesis and Structural Analysis of Palladium(II) Complexes Containing Neutral or Anionic C2-Symmetric Bis(oxazoline) Ligands: Effects of Substituents in the 5-Position

Abstract

A series of neutral and cationic palladium(II) complexes containing C2-symmetric bis(oxazoline) (BOX) ligands, (BOX)PdCl2 (2a-d), (BOX)Pd(Me)Cl (3a-d), and [(BOX)PdMe(2,6-Me2C5H3N)]+PF6- (4a-d) [BOX: 2,2′-(2-propylidene)bis{(4R)-4-phenyl-5,5-dimethyl-2-oxazoline}, 2,2′-methylenebis{(4R)-4-phenyl-5,5-dimethyl-2-oxazoline}, 2,2′-methylenebis{(4R)-4,5,5-triphenyl-2-oxazoline}, and 2,2′-methylenebis{(4R,5S)-4,5-diphenyl-2-oxazoline}], were prepared, and their structures were determined by X-ray crystallography. It was found that substituents at the 5-position (Ph, Me) in addition to substituents on the bridgehead carbon directly affect the structure around palladium, especially the BOX bite angle and the dihedral angles between the phenyl rings at the 4-position and the N2Pd plane. Treatment of the bridged methylene proton in the BOX ligand (1b-d) with KH afforded the anionic BOX ligand; also, the neutral Pd complexes, (BOX)PdMe(2,6-Me2C5H3N) (5b-d), could thus be prepared by reaction with Pd(Me)Cl(cod) (cod = 1,5-cyclooctadiene); 5b-d showed strong coordination to Pd, as demonstrated by X-ray crystallographic analysis.