Ligand Design For Iron Or Cobalt-catalyzed Asymmetric Hydrofunctionalization Of Ketones And Alkenes

Chirality is a basic property of three-dimensional objects,which is widely existed in nature.Preparation of chiral compounds with high optical activity is of great importance and has attracted much attention from the chemist.Asymmetric transition-metal catalysis is one of the most efficient methods.However,most of these reactions are focused preponderantly on the use of noble metals with high price and toxic,such as Pd,Ru,Ir,Rh,Pt et.al.Earth-abundant transition metals,iron and cobalt,are cheap and less toxic,which meet the requirements of sustainable development and green chemistry and have drawn more and more attention from chemist.Cobalt has received continuous ever-growing attention during the last two decades.This interest may attribute to the low rates for the ?-hydride elimination and the high affinity of cobalt to carbonyl groups,carbon-carbon ?-bonds and carbon-nitrogen ?-bonds.At present,chiral salen,porphyrin,bisphosphine and oxazoline ligands have occupied most of the ligands used in the enantioselective cobalt-catalyzed transformations and their successful application in enantioselective cobalt-catalyzed transformations indicates the potential application of cobalt as a green catalyst on the asymmetric catalysis.However,the reaction types involved in the enantioselective cobalt-catalyzed transformations are still limited compared to noble metal catalysis.There existed some problems to be solved:1)How to design novel and efficient chiral ligands for cobalt catalysis using a scientific strategy?2)How to find suitable ligands for cobalt to expand the reaction scope of cobalt-catalyzed highly efficient asymmetric hydrofunctionalization of olefins or ketones.Meanwhile,iron,as the second most abundant metal in the earth crust,is cheap,commercially available,relatively nontoxic.Undoubtedly,iron catalysis is more environmentally benign and sustainable compared with other metal catalysis.Part ?:Based on the theory of hard and soft acids and bases,the directing group strategy and the framework of aminophenyl-2-oxazolines,three types of novel anionic chiral ligands,namely iminophenyl oxazolinylphenylamines(IPOPA),oxazolinylphenyl quinolinylamines(OPQA)and imidazoline phenyl picoliamide(ImPPA),were designed and prepared.Anionic chiral ligands are more stable than the complexes from neutral ligands.Compared to the typical anionic chiral ligands containing oxazoline,these ligands are highly non-symmetrical on geometry,which makes it convenient for us to fine tune the steric and electronic properties of the ligand through modification on the backbone.Pant ?:Enantioselective cobalt-catalyzed hydrosilylation of aryl ketones.Using IPOPA as ligand,an efficient cobalt-catalyzed highly enantioselective hydrosilylation of ketones was realized,delivering a series of chiral secondary alcohols.The reaction was performed under mild conditions with an excellent tolerance to various functional groups and low catalyst loading(0.5 mol%).Part ?:Studies on the iron-catalyzed,Markovnikov selective hydroboration of styrenes.A highly eficient iron-catalyzed hydroboration of styrene was developed by employing readily available oxazolinylphenyl picolinamide ligands.This reaction has a good regioselectivity and could be carried out in gram scale.Part ?:Iron or Cobalt-catalyzed asymmetric hydroboration of alkenes.Using OPQA and OPPA as ligands,an iron-catalyzed asymmetric hydroboration of styrene was investigated.However,the highest ee valuable of hydroboration product was 65%.Meanwhile,a cobalt-asymmetric hydroboration of alkenes was also studied by employing OPQA,OPPA and ImPPA as ligands.A highly regio-and enantioselective cobalt catalyzed asymmetric Markovnikov hydroboration of styrenes and?-substituted styrenes were developed and a possible mechanism was proposed.Part ?:Experimental section.The general procedures for the experiments and compounds characterization in this dissertation were described.