Synthesis, Characterization And Photoresponsiveness Of Azophenyl Salicylaldehyde Schiff Base Palladium Complexes

Azophenylsalicylaldehyde Schiff bases are a class of compounds containing both nitrogen-nitrogen double bond groups（-N=N-）and imine groups（-C=N-）.These Schiff bases have large conjugated systems and exhibit good chemical and optical properties.They have photoisomerization phenomena.The structure of compounds can be converted from trans-structure to cis-structure by light irradiation.In the case of heating,cis-structure becomes trans-structure.The structure of salicylaldehyde Schiff base is very stable.After complexing with metal ions,salicylaldehyde Schiff base has been widely used in many fields,such as molecular switch,fuel dyeing,biomedicine,optical information storage,catalytic reaction and so on.Therefore,we synthesized azobenzylsalicylaldehyde Schiff base ligands,and then coordinated with palladium to form new complexes,in order to be expected to be applied in more fields.Firstly,we synthesized azobenzylsalicylaldehyde,p-fluoroazobenzyl-salicylaldehyde and p-nitroazobenzylsalicylaldehyde from salicylaldehyde,aniline,p-fluoroaniline and p-nitroaniline in ice bath.Then,under the protection of nitrogen,a new Schiff base ligand L₂-L₁₃3 was synthesized by the reaction of azobenzylsalicylaldehyde,p-fluoroazobenzylsalicylaldehyde and p-nitroazobenzyl-salicylaldehydewithaniline,2,6-dimethylaniline,2,6-diethylanilineand2,6-diisopropylaniline,respectively.Namely[C₆H₅N=CH（2-OH）C₆H₃N=NC₆H₅]（L₂）,[2,6-Me₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₅]（L₃）,[2,6-Et₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₅]（L₄）,[2,6-i-Pr₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₅]（L₅）,[C₆H₅N=CH（2-OH）C₆HN=NC₆H₄F]（L₆）,[2,6-Me₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₄F]（L₇）,[2,6-Et₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₄F]（L₈）,[2,6-i-Pr₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₄F]（L₉）,[C₆H₅N=CH（2-OH）C₆H₃N=NC₆H₄NO₂](L₁₀),[2,6-Me₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₄NO₂](L₁₁),[2,6-Et₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₄NO₂](L₁₂),[2,6-i-Pr₂C₆H₃N=CH（2-OH）C₆H₃N=NC₆H₄NO₂](L₁₃)。The reported compound[Pd（C,N-κ²-C₆H₄CH=NC₆H₃-2,6-i-Pr₂）（μ-Cl）]₂（1）was synthesized and reacted with the newly synthesized Schiff base ligand L₂-L₁₃derived from azobenzylsalicylaldehyde to synthesize a new palladium complex2-13.Namely[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅}]（2）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-Me₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅}]（3）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-Et₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅}]（4）,[Pd{C,N-κ²-C₆H₃CH=N C₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-i-Pr₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅}]（5）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅F}]（6）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-Me₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅F}]（7）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-Et₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅F}]（8）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-i-Pr₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅F}]（9）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅NO₂}]（10）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-Me₂C₆H₅N=CH-2-O-C₆H₃-5-N=N C₆H₅NO₂}]（11）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-Et₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅NO₂}]（12）,[Pd{C,N-κ²-C₆H₃CH=NC₆H₃-2,6-i-Pr₂}{N,O-κ²-2,6-i-Pr₂C₆H₅N=CH-2-O-C₆H₃-5-N=NC₆H₅NO₂}]（13）.The ligands L₂-L₁₃3 and complexes 2-13 were characterized by IR and ¹H NMR.The crystal structures of compounds 3 and 4 were determined by X-ray single crystal diffraction analysis.Finally,the ultraviolet spectra of the azobenzene salicylaldehyde Schiff base ligand and its palladium complexes were measured.It was found that the maximum absorption peak of the complexes shifted obviously compared with the ligands.The ligands L₂-L₅,L₉ and compounds 2-5,9 were irradiated by ultraviolet-visible light.The spectral data showed that the ligands changed from trans-configuration to cis-configuration after irradiation with 365 nm light source,and the complexes changed from trans-configuration to cis-configuration after irradiation with 405 nm light source.Compared with the ligands,the light response of the complexes was better.As the substituents change from H to-CH₃,-CH₂CH₃,-（CH）₂CH₃,the ligand ligands are more sensitive to light,while the complexes change little.Azophenylsalicylaldehyde Schiff base with-F and its palladium complex have better response to light than azobenzylsalicylaldehyde Schiff base without-F and its palladium complex.