Synthesis,structure Of Magnesium Complexes With Chiral Binaphthyl Ligand And Their Use As Catalysts For Asymmetric Hydrophosphonylation

Chiral phosphonates and their derivatives have a wide range of uses in the fields of medicine,iochemistry and materials due to their potential biological activity and rich chemical properties.Asymmetric hydrophonylation is an efficient method for construc-tion of C-P bond,leading to formation of chiral phosphonates.The targets of this paper are to synthesis a series of efficient magnesium complexes,and to investigate their application in asymmetric hydrophosphonylation of aromatic aldehydes and ketones.In this paper,a series of chiral binaphthyl ligands have been designed and successfully prepared from(R)-2,2'-hydroxy-1,1'-binaphthy,including 3-position monosubstituted binaphthol ligands(4a-4g),3,3'-position bissubstituted binaphthol ligands(7a-7h)and 3,3'-position bissubstituted phosphorylamide ligands(11a-11 e,17a-17e).Then reaction of these ligands with Mg(NMe2)2,MgBu2 and Mg[N(TMS)2]2generates a range of magnesium complexes.The steric hindrance of the ligands plays an important role in the formation of magnesium complexes.For example,treatment of ligand 4d or 4e with equimolar amount of Mg[N(TMS)2]2 gives a chiral dinuclear bis-ligated complexes(4d)2Mg2(THF)2(17)and(4e)2Mg2(THF)2(18).While under the similar reaction conditions,the bulky ligand 7d reacts with equimolar amount of Mg[N(TMS)2]2 gives a mono-nuclear metal complex(7d)Mg(THF)2(21).All of the ligands and complexes were confirmed by various spectra,elmental analysis and nuclear magnetic resonance,and some of them were also determined by X-ray diffraction.These chiral complexes are active catalysts for the asymmetric hydrophosphonylation of aromatic aldehydes and ketones,giving the corresponding ?-hydroxyphosphonates in high yield with poor enantioselectivity.In addition,we found that the magnesium complexes with 3,3'-disubstituted binaphthyl ligands are active catalysts for 1,4-addition of phosphates to ?,?-unsaturated ketones with moderate enantioselectivity.The catalytic enantioselectivity of such transformations depends strongly on the steric hindrance of the ligands.