Pentamethylcyclopentadienyl Iron Complexes With Cooperative "Metal-Ligand" Reactivity

In classical transition metal catalysis,the ligand only acts as a spectator and all key transformations occur at the metal center.When the catalyst undergoes oxidative addition or reduction elimination,the valence state of metal center changes by two.Thus,metal catalyst in low-valence state is necessary in the catalytic cycle.In metalligand cooperative(MLC)catalysis,on the other side,both the metal and the ligand are directly involved in bond activation and formation.One of the most advantageous properties of MLC is that the catalytic reactions proceed efficiently at mild conditions under the cooperation of ligand with metal.Since the report of Shvo complex,research based on metal-ligand cooperative catalysis has obtained extensive attention.Chemists have developed many bifunctional catalysts for various reactions.In recent years,MLC catalysis based on iron has become attractive due to the low cost,easy availability and environmentally-benign properties.However,"Fe-S" cooperative catalysis is widely recognized in the active sites of[NiFe]hydrogenase and nitrogenase,catalytic reactions with "Fe-S" cooperation have not been reported yet.This thesis presents a series of bifunctional complexes based on Cp*Fe(Cp*?Me5C5-)with "Fe-S" or "Fe-N" as active center.The reactivities of these complexes towards organic substrates with unsaturated functionalities,such as epoxide,aryl alkyne and nitro groups,were investigated.In addition,catalysis based on these complexes were developed.The results were obtained as follows:1.A novel bifunctional complex containing "Fe-S" group[Cp*Fe(P-S)(NCMe)](Cp*=C5Me5-;P-S=1,2-Ph2C6H4S-,1)and a N2 bridged diiron complex[Cp*(PS)Fe]2(?-N2)(2)were synthesized and characterized by X-ray crystallography.Complex 2 can be obtained from the toluene solution of 1 bubbled with N2.Conversely,complex 1 was afforded when 2 was dissolved in MeCN.Bifunctional catalyst 1 reacts directly with the epoxide substrate through iron-thiolate cooperation and is capable of splitting C-O Bond of the aryl epoxide rings,affording ferrous-alkoxide intermediate 4.Intermediate 4 is able to react with HBpin to realize chemselective hydroboration of aryl epoxides.The structure of 4 was determined by X-ray diffraction analysis and NMR spectroscopy.The reactions of complex 1 with different boranes(THF-BH3,9BBN)produces B-H adductive complexes.However,1 cannot react with HBpin.Transition metal-catalyzed hydroboration reactions usually involve an initial step of B-H bond activation by the catalyst while our catalyst directly activate the epoxide substrate.This research expanded the application of "metal-ligand" cooperation.2.Complex 1 is active catalyst for C-N bond reductive coupling of aryl(hetero)nitro and olefins with(EtO)3SiH.Complex 1 catalyzed the sequential reaction of nitro and alkene reduction to produce secondary amines.It could realize the intermolecular C-N bond coupling of 2-nitrostyrene to afford indoles.The reaction intermediate,iron and nitroso coordinated complex[Cp*Fe(P-S)(?1-ArNO)](2),was successfully isolated.In addition,we found that radical reaction was involved in the catalysis through radical trapping experiments.Nitro compounds,the precursor of amine,can be used for C-N cross coupling,which could simplify synthetic process and improve the reaction efficiency.3.A "Fe-N" bifunctional complex[Cp*Fe(Ph2PC6H4NH)](5)was designed and synthesized.Complex 5 is able to react with a variety of aryl terminal alkyne(phenylacetylene,2-naphthylacetylene)to produce "iron-enamine" complexes(5a or 5b).By conducting deuterium-labeling experiments,we found that the complex activated terminal alkyne C-H bond via "Fe-N" cooperation.The study laid the foundation for iron-based alkyne activation and conversion,such as the dimerization of alkyne and the insertion reaction of CO2.Furthermore,we have also investigated its reactivity towards catalytic hydrogenation of ?,?-unsaturated aldehydes.