Substituent effect on cyclopalladation of arylimines

The substituent effect on cyclopalladation of a series of substituted benzylidene-arylamines [(R2C6H3)NCCH2(ArXn), where R=H, Me, i-Pr, OH; Xn=H; 3,5-dimethoxyl; 3,5-difloro; 3,5-bis(2,6-dimethoxyphenyl); 4-chloro; 2-bromo; 2,4,6-trimethyl] by palladium(II) chloride under basic conditions was studied. As expected, cyclometallation takes place at the ortho position of the aryl ring resulting in formation of a five-member chelate ring. All metallated products have in chloro-bridged dipalladium [Pd2Cl2] structures except the one with R=OMe. A palladium species with mixed bridging ligand [Pd2(OH)Cl] was isolated due to the hydrogen-bonding interaction through the hydroxy ligand and the methoxy substituents. For the t-butyl substituted arylimine, cyclometallation does not occur because of the steric reason. In the case of R=OH, Xn=2,4,6-trimethyl, the cyclopalladation occurred at the benyzlic position forming a tetrameric palladium species. All the palladium complexes were characterized by both spectral and/or crystal structural analyses.