A series of neutral and cationic
palladium(II) complexes containing
C
2
-symmetric
bis(oxazoline) (BOX) ligands, (BOX)PdCl
2
(
2a
–
d
), (BOX)Pd(Me)Cl (
3a
–
d
), and [(BOX)PdMe(2,6-Me
2
C
5
H
3
N)]
+
PF
6
–
(
4a
–
d
) [BOX: 2,2′-(2-propylidene)bis{(4
R
)-4-phenyl-5,5-dimethyl-2-oxazoline}, 2,2′-methylenebis{(4
R
)-4-phenyl-5,5-dimethyl-2-oxazoline}, 2,2′-methylenebis{(4
R
)-4,5,5-triphenyl-2-oxazoline}, and 2,2′-methylenebis{(4
R
,5
S
)-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 N
2
Pd
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-Me
2
C
5
H
3
N) (
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.