Synthesis,Structures And Catalytic Performance Of Transition Metal-Carboxylate Coordination Compounds

Coordination polymers or metal-organic frameworks（MOFs）refer to a class of coordination polymers with one-,two-or three-dimensional network structures formed by bonding metal ions with organic bridging ligands.As a new class of functional molecular materials,coordination polymers have attracted a widespread attention because of their excellent,interesting properties,and easy post-synthetic modification.Such compounds that are composed of metal ions and organic ligands have combine some characteristics of both inorganic and organic materials,and may feature unique properties.Therefore,the design,synthesis,structure and properties of coordination polymer molecular materials represent one of particularly active research fields in recent years.Currently,coordination polymers can be used as adsorbents,sensors and probes,as well as bioactive materials.In addition,these compounds can act as powerful catalysts in a diversity of organic transformations,including Henry reaction,Knoevenagel condensation,silylation,alcohol oxidation and alkane functionalization reactions.Considering that these reactions require a harsher reaction environment,there is an important trend to develop heterogeneous catalysts capable of providing high catalytic activity under mild conditions.In the present work,17 novel metal-organic compounds were successfully prepared by reacting,under hydrothermal conditions,3,3’-dihydroxy-（1,1’-biphenyl）-4,4’-dicarboxylic acid（H₄L₁）,4,4’-dihydroxy-（1,1’-biphenyl）-3,3’-dicarboxylic acid（H₄L₂）or 4,4’-（pyridine-3,5-diyl）dibenzoic acid（H₂pdba）with different metal ions and a series of auxiliary ligands.All the products were fully characterized by standard methods and their catalytic properties were investigated in detail in a series of model reactions.Chapter 1:Catalysts are indispensable for many chemical reactions.This chapter briefly describes common Lewis acidic or basic catalysts that are widely used in Knoevenagel condensation,silylation reaction,Henry reaction,coupling of CO₂ with epoxides,and oxidation of cyclohexane.Chapter 2:The main ligands,3,3’-dihydroxy-（1,1’-biphenyl）-4,4’-dicarboxylic acid（H₄L₁）or 4,4’-dihydroxy-（1,1’-biphenyl）-3,3’-dicarboxylic acid（H₄L₂）were reacted with transition metal ions（Co（II）,Mn（II）,Zn（II）,Cd（II）or Cu（II））and auxiliary ligands（2,2’-bipyridine,4,4’-bipyridine or phenanthroline）under hydrothermal conditions to obtain 9 coordination polymers with novel structures.The crystal structures of the compounds were determined by single crystal X-ray diffraction,and supported by a series of standard characterization techniques,including PXRD,FTIR,and TGA.The solid-state emission properties of organic ligands（H4L1and H4L2）and compounds 1-9 were also investigated.The synthesized compounds 1-9 were used as catalysts to promote the Henry reaction.Among them,[Zn（μ2-H2L1）（2,2’-bipy）（H2O）]n（3）exhibited a particularly high catalytic activity when using4-nitrobenzaldehyde as a model substrate to produceβ-nitroalcohol,with a conversion rate of up to 89%.In addition,the effects of catalyst loading,different reaction times,different solvents,different substrate ranges,and recycling on the yields of Henry reaction products were investigated.Chapter 3:Mixtures of the main ligand,4,4’-（pyridin-3,5-diyl）dibenzoic acid（H₂pdba）,auxiliary ligand（2,2’-bipyridine,pyridine,1,10-phenanthroline or 2,2’-biimidazole）and M（II）（M=Co,Mn,Ni or Cu）chloride salts were subjected to hydrothermal synthesis,resulting in 8 new coordination compounds 10-17.The composition,structure,and thermal stability of compounds 10-17 were studied by elemental analysis,infrared spectroscopy,single crystal X-ray diffraction,powder XRD,and thermogravimetric analysis.Analysis of the structural characteristics of the compounds indicates that compounds 10-17 are 2D coordination polymers except{[Cu₂（μ₃-pdba）₂（bipy）]·2H₂O}_n（13）that has a 3D metal-organic framework structure.It should be noted that compound 15 is a mixed-valence 2D coordination polymer.We applied compounds 10-17 in the Knoevenagel condensation reaction of benzaldehyde and malononitrile.One of the compounds（13）revealed a particularly high catalytic activity with product yields up to 99%.In addition,we also examined different reaction parameters,including catalyst content,reaction times,solvent type to determined the optimal conditions for the reaction.Under these conditions,we further investigated the substrate scope of the Knoevenagel condensation reaction between benzaldehyde with malononitrile.