Synthesis And Studies Of Metal Complexes With Sulfurcontaining Pyridine Ligands For Catalytic Hydrogen Evolution

With the rapid development of society and economy,the worldwide energy shortages and environmental pollution are becoming increasingly serious.The development of sustainable clean energy is an important issue facing society today.Due to the characteristic of high gravimetric energy density and pollution-free,hydrogen energy is expected to replace traditional fossil fuels in the future.Noble metal such as platinum have good catalytic activity for hydrogen production reaction,but its low abundance and high cost have limited its application in the large-scale industries production.Therefore,there is an urgent need to develop efficient non-noble metal catalysts.With the characteristics of robust catalytic activity,long catalytic lifetimes and low cost,molecular catalysts possess the potential advantages of catalytic hydrogen evolution.The works are following:1?Five complexes,[Ni?mpo?₂?PPh₃?]1?mpo:2-mercaptopyridine N-oxide?,[?bpte?Fe Cl₂]2?bpte:S,S?-bis?2-pyridylmethyl?-1,2-thioethane?,[?bpte?Cu Cl₂]3,[?bptb?Co Cl₂]4?bptb:S,S?-bis?2-pyridylmethyl?-1,2-thiobenzene?and[?bptb?Co Br₂]5 are synthesized and characterized by using Single Crystal X-ray Diffraction,Powder X-ray Diffraction,Nuclear Magnetic Resonance,Infrared Spectroscopy,UV-visible Spectroscopy and X-ray Photoelectron Spectroscopy.2?Investigations of catalytic behaviors of complexes 1-5 for hydrogen generation:?1?Catalytic behaviors of the nickel complex,1 for hydrogen generation.The nickel complex,[Ni?mpo?₂?PPh₃?]1,is synthesized by reaction of 2-mercaptopyridine N-oxide sodium salt with?PPh₃?₂Ni Cl₂.Together with Cd S nanorods?NRs?as photosensitizer?PS?and ascorbic acid as sacrificial electron-donor?SED?in a heterogeneous photocatalytic system,complex 1 can provide hydrogen with a turnover number?TON?of 8365 mol H₂?mol cat?^-1 during 70 h of irradiation and an average apparent quantum yield?AQY?of 16.05%.Moreover,electrochemical studies show that complex 1 also can electrocatalyze hydrogen evolution from neutral water-acetonitrile?3:2?phosphate buffer solution with a turnover frequency?TOF?of 103 mol H₂?mol cat?^-1h^-1 and a Faradaic efficiency of 87%at an overpotential?OP?of 837.6 m V.?2?The impact of central metal centers on catalytic behaviors of complexes supported by bpte for hydrogen productionThe N₂S₂-type ligand,bpte is obtained by the reaction of 2-?chloromethyl?pyridine hydrochloride and ethanedithiol.[?bpte?Fe Cl₂]2 and[?bpte?Cu Cl₂]3 are provided by reactions of bpte with Fe Cl₂ and Cu Cl₂,respectively.Complex 2 can photocatalyze hydrogen evolution with a TON of 10709 mol H₂?mol cat?^-1 during 90 h of light irradiation and an average AQY of 23.21%.Complex 3 only achieves a TON of 2519 mol H₂?mol cat?^-1 during 40 h of light irradiation,and the average AQY is 8.66%.Electrochemical studies show that under an OP of837.6 m V,complex 2 and complex 3 can afford 246.8 mol H₂?mol cat?^-1h^-1and 159.4 mol H₂?mol cat?^-1h^-1 from neutral aqueous phosphate buffer solution with a Faradaic efficiency of92.17%and 89.47%,respectively.The result shows that the catalytic efficiency of the iron complex is better than the copper complex with the same ligand.?3?The effect of ligands on catalytic behaviors of the cobalt complexes for hydrogen generationThe reaction of 2-?chloromethyl?pyridine hydrochloride with 1,2-benzenedithiol affords the N₂S₂-type ligand,bptb.The reactions of bptb with Co Cl₂and Co Br₂ to form the cobalt complexes,[?bptb?Co Cl₂]4 and[?bptb?Co Br₂]5,respectively.Under the heterogeneous photocatalytic system,complex 4 and complex 5 can afford 23826 mol H₂?mol cat?^-1 and 19417mol H₂?mol cat?^-1 during 90 h of light irradiation with an average AQY of 24.10%and 23.62%,respectively.Under an OP of 837.6 m V,complex 4 and complex 5 are found to be highly active electrocatalysts for hydrogen generation with a TOF of 1200.6 mol H₂?mol cat?^-1h^-1 and 872.4mol H₂?mol cat?^-1h^-1 from neutral aqueous buffer solution and a Faradaic efficiency of 96.0%and 94.2%,respectively.The results indicate that the catalytic efficiency for hydrogen evolution of the cobalt complex with chlorine is higher than that with bromine.