Preparation Of Iron,cobalt And Nickel Tripyridine Amine Complexes And Application To Photocatalytic CO₂ Reduction And Dehydrogenation Reaction

Tripyridine amine?TPA?and its derivatives are polypyridyl compounds,which possess tetradentate coordination ability and easy to obtain metal complexes combined with transition metals.These complexes have received wide attention and application due to they can be used as models to simulate the catalytic process of biological enzymes in organisms.Tripyridine amines transition metal complexes also can be used as catalysts in the catalytic system,such as photocatalytic CO₂ reduction reaction.Up to now,the most transition metal complexes photocatalysts are mainly based on noble metals.In this work,we introduce the non-noble transition metal iron,cobalt,and nickel as the catalytic metal center and tripyridine amine as ligands to synthesize seven different complexes.The complexes of c₁ and c₂ were obtained by using TPA and anhydrous FeCl2,CoCl2 as precursors.The compound of b?bis?2-methylpyridyl??4-?diethylphosphonate?-2-methylpyridyl?amine?was obtained by introducing the diethyl phosphite group in the TPA group.Then the obtained ligand was coordinated with anhydrous FeCl2,CoCl2 and NiCl2 respectively to obtain the complexes b₁,b₂ and b₃.After that a bromine atom was introduced into the parent TPA to obtain the compound of a?bis?2-methylpyridyl??4-bromo-2-methylpyridyl?amine?and then coordinated with anhydrous FeCl2 and CoCl2 to obtain the complexes a₁ and a₂,respectively.The seven complexes were analyzed by IR and UV-Vis absorption spectra respectively.The photocatalytic CO₂ reduction efficiencies were investigated.Several experimental conditions,such as photosensitizer,sacrificial agent,solvent,amount of catalyst and sacrificial agent,were optimized.In this paper,we also studied the photocatalytic dehydrogenation of Hantzsch 1,4-dihydropydines and its derivatives.Several complicated and expensive catalysts such as Pt complexes,Pd/C and other catalysts have been reported as catalysts for dehydrogenation of Hantzsch1,4-dihydropyridine.In this paper,we introduced cadmium sulfide?CdS?as a photosensitizer and nickel phosphide?Ni₂P?as a co-catalyst to establish a photocatalytic Hantzsch1,4-dihydropyridine dehydrogenation system and the resulting dehydrogenation product were e1-e5 with a high yield.The main conclusions are as follows:???For the iron complexes of a₁?b₁?c₁,b₁ were chosen as the main research objects and selected ruthenium pyridine?[Ru?bpy?3]2+?as photosensitizer,propylene carbonate?PC?as solvent.When the amount of catalyst was 0.15 mM and the sacrificial agent / solvent = 1:5 the results reached the best efficiency.Under the optimum conditions,the peak area of CO was measured by gas chromatography and the TON was calculated after 10 hours of irradiation.Based on the results,b₁ demonstrated the best catalytic efficiency and the peak area of CO was 122207?TON= 112.7?.For a₁,the peak area of CO is 3521 and the TON value is 3.2.However for c₁,the TON value is 2.Herein,a₁ and c₁ can not be used as efficient catalysts for this reaction.???For the ingredients of cobalt complexes a₂,b₂,c₂,b₂,[Ru?bpy?3]2+ was selected as the photosensitizer,PC as the solvent?sacrificial agent / solvent = 1:6?and the amount of the catalyst is 0.1 mM.Under the optimized conditions,b₂ showed the best catalytic rate.The CO integral area was 16221 and the TON value was 22.8.The TON values of a₂ and c₂ were 5.5 and 4.26,respectively.When introduced b₃ as the catalyst,the CO peak area was 4921 and the TON was 6.9.Herein,the rate of b₃ was far less than that of b₁.???Ni₂P / CdS hybrid could act as a photocatalyst for dehydrogenation of Hantzsch 1,4-dihydropyridine derivatives?d1-d5 has hydrogen atoms in one and four positions?.1 mol of H2 can be obtained and get the product e1-e5 with a yield of85%-99%.For d6,due to the hydrogen on the nitrogen atom is replaced by methyl,the hydrogen can not be taken off and the photocatalytic reaction cannot occur.