A Manganese-based Full-function Model For The [FeFe]-Hydrogenase

In the past few decades,the consumpation of fossil fuels has resulted the serious environmental problem,we must develop and build sustainable,carbon-free energy systems.H₂ is considered as an important energy carrier and has a wide range of applications due to its features of zero emission and no pollution.It can be produced by reducing protons during electrocatalysis by structural design of catalysts.In the past few decades,iron,cobalt,nickel complexes have received special attention.Although manganese is one of the most abundant elements in the earth’s crust after iron and titanium,it has been seldom exploited and utilized.Therefore,this dissertation intends to take transition metal manganese as catalytic active center and take the key functional structure of[Fe Fe]-hydrogenase in nature as inspiration to construct the electron relay and proton transfer group matching with manganese metal center,and make them cooperate with each other to explore the design method of HER catalyst under low overpotential and high rate.In this dissertation,two kinds of bipyridine carbonyl manganese complexes with excellent performance were successfully designed as the complete structural models of[Fe Fe]-hydrogenase.The specific research work includes the following two series:1.With pyridine-quinolone carbonyl manganese complex as the parent structure,the aniline and benzamide groups were introduced to the o-position of one of the pyridine groups to construct the second coordination environment,which was inspired by the amine in the natural[Fe Fe]-hydrogenase.The structure of the products was characterized by FTIR,1H NMR,MS and X-ray single crystal diffraction,and results show that the prepared Y1 and Y2 have the same structure as the designed target.Using the aniline tetrafluoroborate as a proton source,the catalytic rate of complex Y1 exceed 10,000 s^-1 at?.45V(vs.Fc^+/0),which is comparable to[Fe Fe]-hydrogenase.Although the overpotential is 700 m V,both experimental results and DFT calculations confirm that the framework structure of the complex is a suitable proton reduction catalyst.2.In order to further regulate the collaboration of key functional structures and prepare catalysts with low overpotential,the complex J1-J5 with different electron reservoir groups and proton relay groups was prepared in this chapter.It was found that the catalytic overpotential of J1 was only 120 m V and the catalytic rate was 242.5 s^-1 in the presence of3M phenol.As a result,the first main reason is that the p Ka of phenol perfectly matches the alkalinity of the central metal,the Mn-H bond is neither too strong nor too weak.Secondly,the potential difference of pyridine-quinoline ligand and the metal center are appropriate,providing a mild electronic compensation,which is helpful for the dissociation of hydrogen.The complex not only fully simulates the three key parts of[Fe Fe]-hydrogenase,but also enables them to transfer protons and electrons through coupling.This is the first time to use an artificial model to control the motion of electrons and protons.