Design,assembly and Asymmetric Catalytic Properties of Chiral Biphenol-based Metal-organic Frameworks

Author:Mo Ke

Supervisor:cui yong

Database:Doctor

Degree Year:2018

Download:30

Pages:159

Size:9054K

Keyword:

The field of chiral metal-organic frameworks(MOFs)represents a burgeoning area with versatile applications in various aspects,such as enantioselective recognition and separation,heterogeneous catalysis,and chiral optics.In this thesis,two axially C2-symmetric biphenol-derived tetracarboxylate linkers were synthesized and utilized to build porous crystalline materials.These materials are well characterized by SCXRD,PXRD,EA,IR,and TGA,etc.They were applied to asymmetric heterogeneous catalysis.The thesis includes five chapters as follows:In Chapter 1,a brief introduction summarized research history and recent furits including the synthesis strategies of chiral MOFs and their applications in chiral resolution,enantioselective separation and chiral sensing.The challenges and opportunities remained in thesis area together with overviews of the thesis topic and research progress were also presented and discussed.In Chapter 2,an axially C2-symmetric 1,1′-biphenol ligand H4L1 was synthesized and used to build a homochiral porous MOF(R)-1 with Zn2+through self-assembly.After exchanging one proton of the dihydroxyl group for Li(I)ions,the framework can be a highly efficient and recyclable heterogeneous catalyst for asymmetric cyanation of aldehydes with up to>99%ee.The material can be recycled and reused for several times without any apparent loss of enantioselectivity.Compared with the homogeneous counterpart,the MOF catalyst exhibits significantly enhanced catalytic activity and enantioselectivity,especially at a low catalyst/substrate ratio,due to that the rigid framework could stabilize the catalytically active monolithium salt of biphenol against its free transformation to catalytically inactive and/or less active assemblies in reactions.The synthetic utility of the cyanation was demonstrated in the synthesis of(S)-bufuralol with 98%ee.In Chapter 3,a chiral porous MOF(S)-2 with 1D nanosized channels and accessibly chiral hydroxyl auxiliaries has been assembled with an cadmium carboxylate chains and chiral tetracarboxylate ligands derived from 1,1′-biphenol derived.After post-modificated by InBr3,this framework exhibits outstanding heterogeneous catalytic activity for asymmetric alkynylation of aldehydes and trifluoromethyl ketones,affording up to 95%conversion and 99%ee.After five catalytic runs,the activity and selectivity of the material were retained and the metal leaking was very low.EXAFS studies demonstrated that In(III)has the different coordination environment between homogenous and heterogenous system.This difference may lead to MOF catalyst have higher activity and enantioselectivity.The synthetic utility of the approach was demonstrated in the synthesis of(S)-efavirenz with 99%ee from the obtained enantioenriched propargylic alcohols.In Chapter 4,1,1′-biphenol derived tetracarboxylate ligand H4L2 was synthesizedand used to build a homochiral MOF(S)-3,which is constructed by a rare zirconium clusters.After postsynthetic modification by P(NMe2)3 followed by metalated with Rh,this framework exhibits outstanding heterogeneous catalytic activity for asymmetric alkynylation of a variety of aldehydes in up to 95%yield,99%b/l and 99%ee.Compared with the homogeneous counterpart,the MOF catalyst exhibits significantly enhanced catalytic activty and selectivity,due to the stabilization of acitive mono(phosphoramidite)-Rh intermediate by preventing disproportion reactions/ligand exchanges in catalysis.The catalyst can be recycled and reused with negligible loss of efficiency and enantioselectivity,and the recovered remained structurally intact.In the Chapter 5,a brief summary of this thesis was made and an outlook of this thesis was given.