Syntheses,Structures And Catalytic Properties Of A Series Of Copper(?) And Cobalt(?) Coordination Compounds Constructed From Multifunctional Carboxylic Acids

Coordination chemistry is an important branch of inorganic chemistry,which has seen in recent years a tremendous development due to very diverse and widespread applications of different coordination compounds?complexes and coordination polymers?in various areas,including sensing,molecular recognition,gas storage and adsorption,drug delivery,and catalysis.For example,coordination compounds are notable catalysts for the oxidation of alkanes and alcohols,the Henry reaction,coupling reactions,the Knoevenagel condensation reaction,and the hydrogenation of aldehydes and ketones,among other organic transformations.In particular,the development of new catalytic systems for the mild and efficient oxidation of alkanes and more reactive substrates such as alcohols has been of high importance given the widespread use of the obtained oxidation products.Hence,the main goal of the present work has consisted in exploring different multifunctional carboxylic acids for the preparation of new copper and cobalt coordination compounds,followed by an evaluation of their catalytic performance in the mild oxidative functionalization of saturated hydrocarbons and alcohols.Herein,six carboxylic acid ligands,namely 5-?2'-carboxyphenyl?nicotinic acid?H₂cpna?,biphenyl-2,4,4'-carboxylic acid?H₃btc?,4-?5-carboxypyridin-2-yl?isophthalic acid?H₃cpic?,2-?4-carboxypyridin-3-yl?terephthalic acid?H₃cptc?,5-?4-carboxyphenoxy?nicotinic acid?H₂cpna?,and 5-?3,4-dicarboxyphenyl?picolinic acid?H₃dppa?were selected as building blocks for the hydrothermal synthesis of new coordination compounds.Eight products featuring new structures and excellent catalytic performance have been obtained,isolated and fully characterized by standard methods,including by the single crystal X-ray diffraction.Then,the obtained Cu and Co compounds have been investigated as catalysts for the oxidation of alkanes or alcohols under mild conditions.The content of this thesis is divided into three chapters,which are briefly described below.Chapter 1 briefly introduces the development of coordination chemistry and the definition of coordination polymers.It also discusses in detail the synthetic methods for different coordination compounds and the factors affecting their structures.In addition,extensive applications of the relevant compounds are highlighted.Chapter 2 describes the use of copper???ions and different carboxylic acid ligands?H₂cpna,H₃btc?,H₃cpic,H₃cptc)along with pyridine-based auxiliary ligand such as 1,10-phenanthroline?phen?for the hydrothermal generation of four new copper???coordination compounds 1-4,namely{[Cu??₃-cpna??phen?]·H₂O}_n?1?,{[Cu??-Hbtc??phen?]·H₂O}_n?2?,{[Cu??₃-Hcpic??phen?]·2H₂O}_n?3?,and[Cu₆??-Hcptc?₆?phen?₆]·6H₂O?4?.These compounds have been structurally characterized,showing that 1-3 are all one-dimensional coordination polymers,while complex 4 is a discrete hexanuclear copper complex.Magnetic properties of these compounds have been studied,indicating a weak antiferromagnetic interaction between the adjacent Cu???centers in 1-3 and a ferromagnetic interaction in 4.In addition,compounds 1-4have been used to catalyze the oxidation of alkanes.Under mild conditions of normal pressure and50°C and using H₂O₂ as an oxidant,1-4 can effectively catalyze the oxidation of C₆-C₈cycloalkanes.In particular,compound 1 can efficiently catalyze the oxidation of cyclohexane without the need for an acid promoter,resulting in the formation of cyclohexanol and cyclohexanone?total yields up to 20%,based on cyclohexane?.At the same time,the corresponding mechanism has been proposed.Such a level of yields is remarkable in the field of mild oxidation of alkanes considering their high inertness.Chapter 3 describes the hydrothermal preparation of cobalt???compounds assembled from H₂cpna and H₃dppa as main building blocks,along with auxiliary ligands such as1,10-phenanthroline?phen?or 4,4?-bipyridine?4,4?-bipy?.Four new cobalt???compounds 5-8have been obtained,namely:[Co??₄-cpna??H₂O?₂]_n?5?,[Co??₃-cpna??phen??H₂O?]_n·nH₂O?6?,[Co₃??₄-dppa?₂?H₂O?₆]_n·2nH₂O?7?,and[Co₃??₅-dppa?₂??-4,4?-bipy??H₂O?₂]_n·4nH₂O?8?.Compounds 5 and 8 have a three-dimensional MOF structure,while 6 and 7 are two-dimensional coordination polymers.The magnetic properties of 5-7 have been investigated revealing an magnetic interaction between neighboring Co centers,while there is a ferromagnetic interaction in8.In addition,under the conditions of normal pressure and low temperature of 50?and using ^tBuOOH as an oxidant,compounds 5-8 act as catalysts for the oxidation of 1-indanol,cyclohexanol and fenchyl alcohol.Compound 6 has shown the highest activity?up to 45%yield?in the oxidation of 1-indanol to 1-indanone.Finally,products 5–8 broaden a still very small number of coordination polymers driven by the present type of multifunctional pyridine-carboxylic acids?H₂cpna,H₂dppa?.