The Design And Synthesis Of Copper And Cobalt Complexes For Water Splitting And Transfer Hydrogenation

Energy issues as one of the top ten global problems has been attracted more and more attention in recent years.Pursuit of sustainable clean energy instead of fossil energy is around the corner.Hydrogen is known as a green energy,is seen as a substitute for fossil fuels.One way in which chemistry can be used to provide hydrogen is through the development of artificial photosynthesis systems,which allow for the conversion of the energy of sunlight into useful chemical energy by water splitting.Photosensitizer plays the most important role in this method.In this article we used heteroleptic copper photosensitizers which have nitrogen ligand and phosphine ligand as the structure model,designed and synthesized a series of1,10-phenanthroline derivatives as nitrogen ligands.The activity of these copper photosensitizers for the water splitting system was studied by in-situ method.Alkenes are useful building blocks in organic synthesis.The transition-metal catalyzed semi-hydrogenation of alkynes to alkenes is a very important reaction to obtain alkenes.We designed and synthesized a new type of pincer ligands,the corresponding cobalt complexes were obtained,and applied to the transfer hydrogenation of alkynes.In the first,2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline and aryl aldehyde were used as the starting materials,acetic anhydride was used as the solvent,seven2,9-（E）-diarylvinyl-1,10-phenanthroline derivatives（A-G）were obtained by adole condensation with yield 50-68 %.Using 4,7-bis（4-bromophenyl）-1,10-phenanthroline as raw material,reaction with secondary amine,then organic lithium,two2,9-diisopropyl-1,10-phenanthroline derivatives（H,I）were obtained,yield was 34 %,42 % respectively.Starting from 4,7-di（[1,1’-biphenyl]-4-yl）-1,10-phenanthroline,using organic lithium as the nucleophilic reagent,4,7-di（[1,1’-biphenyl]-4-yl）-2,9-diisopropyl-1,10-phenanthroline（J）was synthesized.The copper photosensitizers were synthesized by in situ method in water reduction system,using 1,10-phenanthroline derivatives as nitrogen ligands,Xantphos（I）and Thixantphos（II）as phosphine ligands,together with Cu（MeCN）₄PF₆,THF:TEA:H₂O=4:3:1（10 mL）as solvent,Fe₃（CO）₁₂ as reduction catalyst.Their photocatalytic activity of hydrogen generation from water splitting and photophysical properties were explored and discussed.The results show that 4,7 positons bearing tertiary amine groups can lower the activity.The copper complexes containing Thixantphos（II）and nitrogen ligands（A-G）show the ability in water reduction,electron-withdrawing groups can improve the activity,fluorescence enhancement effect of fluoride was tested by fluorescence analysis spectral.When nitrogen ligands（J）and Thixantphos（II）were chose as the as nitrogen ligand,phosphine ligands respectively,photosensitizer has the best activity,TON number up to 1034.Last,we designed and synthesized four new NNP-pincer ligand（L1-L4）with moderate yield,together with two existing PNP-pincer,six pincer cobalt complexes（I-VI）were obtained by coordination with CoCl₂.Using substituented iodine benzene and benzene acetylene as raw material,a series of substituented diphenyl acetylene（1b-1m）were synthesized by Sonogashira couping with yield 74⁹9 %,used as substrates.After screening pincer cobalt catalysts,solvents,hydrogen source,the optimum reaction conditions were determined as follows: substrate（0.5 mmol）H₃NBH₃（0.5 mmol）,pincer cobalt catalyst（III,1 mol %）,MeOH（2 mL）,50 oC,16 h.Under the optimum conditions,the substrate suitability was tested,the results show that almost all substrate（except the nitro）were hydrogenated in high yields（> 90%）and excellent chemo-and regio-selectivity,the type and the postion of substituentgroups have no obvious effect.