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

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.