Design,Synthesis And Catalytic Application Of Ferrocenylpyrdine Palladacycle Catalyst

Palladium complexes are often used as catalysts in the cross coupling of C-C and C-X,and show excellent catalytic performance.With the development of the green chemistry,palladium catalyst is required to catalyze cross coupling reaction efficiently under mild conditions in air and green solvent.In the traditional palladium catalytic reaction,phosphine ligands or carbene ligands need to be added to improve the catalytic activity of the catalyst.However,these two ligands have some disadvantages,such as environmental toxicity,spontaneous combustion,reactionhas to be carried out under an inert gas environment and aproticsolvents.Nitrogen-containing ligands are always used to replace phosphine ligands and carbene ligands.There are two problems in the use of nitrogen-containing ligands:1.How to obtain nitrogen-containing ligands with strong electron donating ability;2.How to improve the catalytic activity of palladium precatalyst with nitrogen-containing ligands.Therefore,the design,synthesis and application of ferrocenylpyridine palladacycle catalyst in catalytic reactions were studied in this paper.1. In view of the excellent electron donating ability of[C^N]monoanion bidentate ligands composed of carbon anion and nitrogen atom,three kinds of ferrocenylpyridine compounds were synthesized and characterized in this paper.They were2-ferrocenylpyridine（1）,3-ferrocenylpyridine（2）and 4-ferrocenylpyridine（3）.It was verified by electrochemistry and DFT calculation that the distance between ferrocenyl group and nitrogen atom in pyridine could influenced the isolated electron delocalization of nitrogen atom.The electron cloud density of ferrocenyl would be changed by the distance.Through the experiments and references,the electron delocalization made it form an electron rich coordination region between two electron donor units（carbon anion and lone pair electron of nitrogen atom）.Therefore,2-ferrocenylpyridine（1）[C^N]monoanionic bidentate ligands would be strong donor ligands.The ferrocenylpyridine palladacycle complexes would beresearch objects.2. Seven 2-ferrocenylpyridine palladacycle complexes Pd Cl{[（η⁵-C₅H₅）]Fe[（η⁵-C₅H₃）]-2-Py}（PPh₃）（1）,Pd Cl{[（η⁵-C₅H₅）]Fe[（η⁵-C₅H₃）]-2-Py}（Py）（2）,Pd Cl{[（η⁵-C₅H₅）]Fe[（η⁵-C₅H₃）]-2-Py}（4-Py Fc）（3）,Pd Cl{[（η⁵-C₅H₅）]Fe[（η⁵-C₅H₃）]-2-Py}（4-Py Ph）（4）,Pd Cl{[（η⁵-C₅H₅）]-Fe[（η⁵-C₅H₃）]-2-Py}（4-^tBu Py）（5）,Pd Cl{[（η⁵-C₅H₅）]Fe[（η⁵-C₅H₃）]-2-Py}（4-Me Py）（6）and Pd Cl{[（η⁵-C₅H₅）]Fe[（η⁵-C₅H₃）]-2-Py}（4-Me OPy）（7）were synthesized by using dichlorobis-（2-ferrocenylpyridine）palladiumdimer as precursor and pyridine derivatives as ancillary ligands,and were characterized by Elemental analysis,FT-IR,MS and NMR,respectively.The molecular structures of complexes（1-5）were determined by single crystal X-ray diffraction,the structure of square-planar palladium center were slightly influenced by the ancillary ligand.The¹³C NMR of ferrocenyl carbon（Pd-C）shifted from 97.72 ppm to 98.39 ppm which was used as an indicator in different electron donating ability of ancillary ligands.The catalytic performance of seven complexes for the Suzuki-Miyaura reaction of iodobenzene and phenylboronic acidwere evaluated in inert and air environment.The isolated yields of the product biphenyl are 50%-96%.The higher p Ka of ancillary ligands should create a stronger metal-ligand bond,increasing the stability,which further demonstrates that the ancillary ligands change the catalyst.The more electron-donating ligands will have a lower dissociation rate from Pd（II）/Pd（0）and thus significantly retard the formation of active species and diminish reactivity to coupling product.The catalytic activities of the complex（1）is lower in air.In order tointerpret the deactivation of catalyst（1）,an in-situ ³¹P NMR experiment was carried out in air for the catalytic process.Furthermore,the effect of ancillary ligands were explored preliminarily in the catalytic mechanism.3. In order to expand the application of 2-ferrocenylpyridine palladacycle complexes in cross coupling reaction and synthetise the ferrocenyl heterocyclic compounds,the Copper-free Sonogashira reaction of 2-iodoaniline with ferrocenylacetylene was catalyzed by complex 2.The important intermediate2-ferrocenethynylanilines（1a）was synthesized.When we used 2-ferrocenethynylanilines（1a）as reactant and Na Au Cl₄·2H₂O（5%）as catalyst to prepare 2-ferrocenylindole（2a）,we were surprised to find that an novel compound 3,3’-ferrocenylbiindoles（3a）,was obtained simultaneously.The 3a were characterized by Elemental analysis,FT-IR,MS,NMR and X-ray single crystal diffraction,respectively.The reactant-substitution reaction,in-situ HNMR characterization,XPS,EPR characterization and theory calculations were carried out to interpret why the 3a were obtained in one pot.The results showed that the hydroperoxyl radical played a key role in the reaction processes,it induced synthesis of 3a.