Study On The Synthesis And Electrochemical Properties Of Iron & Nickel Dithiolate Complexes And Related Carbon Nanotube Hybrids

The increasing energy demand and the severely limited fossil fuels have triggered great interest in the development of clean and sustainable energy.In nature,two kinds of the iron-and nickel-containing metalloenzymes(namely,[FeFe]-and[NiFe]-hydrogenases)have been found,whose active sites can efficiently catalyze the reversible conversion of protons into H2.In this context,many efforts have been devoted to developing the biomimetic chemistry of[FeFe]-and[NiFe]-hydrogenase active sites,aiming to find a efficient hydrogen-evoluting non-noble metal molecular catalyst,i.e.,the iron-and nickel-bearing dithiolate complexes that are still lowly catalytically active to date.Thus,in this thesis,three new series of mononuclear Ni,dinuclear Fe2,and trinuclear NiFe2 dithiolate complexes with aminodiphosphine ligands PCNCP were designed and prepared,wherein their molecular structures and electrochemical properties are studied and compared.Meanwhile,a deep insight into the electrocatalytic performance of the iron sulfur cluster functionalized carbon nanotube hybrids has been carried out in aqueous medium.The meaningful results are as follows:1.In this thesis,a total of twenty-five novel compounds were synthesized,in which the crystal structrues of thirteen compounds were further determined.More importantly,the electrochemical and electrocatalytic properties of nineteen new iron&nickel dithiolate complexes and one known diiron dithiolate cluster covalently-attached carbon nanotube hybrid,which are regared as the biomimetic models of[FeFe]-and[NiFe]-hydrogenases,have been investigated and compared by means of cyclic voltammetry(CV).2.Two new aminodiphosphine ligands(PCNCP)(Ph2PCH2)2X(X=NCH2C5H4N-p(1)and NCH2C6H5(2))and four mononuclear Ni chloride salts[{(Ph2PCH2)2X}NiCl2](X=NCH2C5H4N-p(3),NCH2C6H5(4),NCH2CHMe2(5),and CH2(6))were firstly prepared.Further treatment of the as-obtained salts 3-6 with ethanedithiol in the presence of triethylamine at room temperature resulted in the formation of four new mononuclear Ni dithiolate complexes[{(Ph2PCH2)2X}Ni(SCH2CH2S)](X=NCH2C5H4N-p(7),NCH2C6H5(8);NCH2CHMe2(9),and CH2(10)).All the as-prepared compounds 1-10 are characterized by elemental analysis and nuclear magnetic resonance(NMR,1H and 31P)spectroscopy as well as by X-ray crystallography for 4,7-10.In order to further explore the ability of these mononuclear Ni complexes 7-10 to capture protons when reducing protons,their protonations and electrochemical proton reduction were carried out in the presence of trifluoroacetic acid(TFA).The protonation result displays that the room temperature reactions of complexes 7-10 with excess TFA formed dinuclear Ni(?)-Ni(?)dication complexes[{(Ph2PCH2)2X}2Ni2(?-SCH2CH2S)](CF3CO2)2(X=NCH2C5H4N-p(11),NCH2C6H5(12),NCH2CHMe2(13),CH2(14))and N-protonated mononuclear Ni(?)monocation complexes[{(Ph2PCH2)2N(H)R} Ni(SCH2CH2S)]-(CF3CO2)(R=CH2C5H4N-p(15),CH2C6H5(16),CH2CHMe2(17)),respectively.These above-protonated products 11-17 have been characterized by high-resolution electrospray ionization mass spectroscopy(HRESI-MS)as well as NMR(1H,31P)and especially by X-ray crystallography for 14.In addition,the electrocatalytic behaviors of mononuclear Ni complexes 7-10 are studied and compared through CV technique.This finding indicates that the fully protonated products 11-14 are responsible for the electrocatalytic proton reduction to H2 by 7-10,respectively 3.Three new series of mononuclear Ni complexes Ni(SCH2CH2S){(Ph2PCH2)2NR}(R=CMe3(18)and CH2CH2CH2CH3(19)),dinuclear Fe2 complexes Fe2(?-SCH2CH2S)-(CO)4{?2-(Ph2PCH2)2NR}(R=CH2CHMe2(20),CMe3(21),and CH2CH2CH2CH3(22))and trinuclear NiFe2 complexes Fe2(CO)6(?3-S)2Ni{(Ph2PCH2)2NR}(R=CH2CHMe2(23),CMe3(24),and CH2CH2CH2CH3(25))with chelating aminodiphosphines(labeled PCNCP=(Ph2PCH2)2NR)are described.All the as-prepared complexes 18-25 are characterized by elemental analysis,FT-IR,and NMR(1H,31P)spectroscopies as well as by X-ray crystallography.In order to further investigate the effect of different metal cluster cores on the electrochemical performances of hydrogenase-inspired models,the electrochemistry of complexes 9,18-25 has been studied and compared by using CV This outcome suggests that three series of complexes 9/18/19,20-22 and 23-25 have the distinct abilities of the electrocatalytic proton reduction in the presence of acetic acid(HOAc)as a proton source4.The electrochemistry of a known diiron dithiolate cluster functionalized single-walled carbon nanotube hybrid denoting as ADT-f-SWCNTs loaded on glassy carbon electrode and carbon paper as working electrodes are described.Some results are as follows:(?)hybrid ADT-f-SWCNTs has a more positive reduction potential in pure water relative to organic solvent.(?)In contrast to precursor ADT loaded on the aforementioned electrodes,hybrid ADT-f-SWCNTs shows the better electrocatalytic H2 evolution ability,strongly indicating that introduction of carbon nanotubes can promote fast electron transfer and thus improve catalytic performance.(?)the comparison for the electrocatalytic efficiency of hybrid ADT-f-SWCNTs coated on the aforementioned electrodes has shown that the TOF value of ADT-f-SWCNTs on glassy carbon electrode reaches 9444 s-1 whereas that of ADT-f-SWCNTs on carbon paper is only 722.2 s-1,suggesting that this kind of diiron dithiolate cluster functionalized carbon nanotube hybrids like ADT-f-SWCNTs is proper to load on glassy carbon electrode as working electrode for efficient catalytic H2 evolution.