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Highly efficient tetranuclear ZnII2LnIII2 catalysts for the Friedel–Crafts alkylation of indoles and nitrostyrenes
No full textWe demonstrate for the first time the high efficacy of tetranuclear ZnII2LnIII2 coordination clusters (CCs) as catalysts for the Friedel–Crafts (FC) alkylation of indoles with a range of trans-?-nitrostyrenes. The reaction proceeds in good to excellent yields (76%–99%) at room temperature with catalyst loadings as low as 1.0 mol
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Development of 3d-4f and Cu based catalytic methodologies
No full textThis thesis deals with the use of Schiff base, amyloid peptide and benzotriazole scaffolds to synthesise 3d-4f and copper complexes and hybrid materials, investigate their catalytic properties and develop novel cost-, time- and step-efficient methodologies for the domino ring-opening/electrocyclization reaction of furfural and amines for the synthesis of trans-4,5-diaminocyclopentenones and the corresponding Stenhouse salts, as well as the coupling of aldehyde, amine and alkyne for the synthesis of propargylamines, to replace existing catalytic protocols. Chapter 1 serves as a general introduction to the chemistry discussed in the thesis. The first part emphasises on the synthetic aspects of coordination complexes. A rationale regarding the selection of the employed ligands is presented. The second part presents an overview of methodologies in catalysis, related to the methodologies developed in the present thesis, towards the synthesis of the organic derivatives. Chapter 2 focuses on the synthesis and characterisation of a new bimetallic tetranuclear complex Ni2Dy2 and its use as a catalyst towards the domino ring-opening/electrocyclization reaction of furfural and amines. The present catalytic system surpasses the efficiency of other reported systems, and the scope and limitations are described. Chapter 3 describes the first amyloid fibril core decorated by a heterometallic entity. The tetranuclear 3d-4f entity is of the type Zn2Dy2. The functionalized assembly behaves as a Lewis acid and catalyses the ring-opening/electrocyclization reaction of furfural and amines at a nanoscale level. Chapters 4 describes the synthesis and characterisation of a CuII complex with the use of a Schiff Base ligand, and its use as a catalyst towards the A3 coupling reaction. Control experiments, cyclic voltammetry and theoretical studies shed light on the mechanism of the reaction, suggesting the formation of an in situ radical specie. Chapter 5 reports the synthesis and characterisation of a relatively unexplored, in coordination chemistry and catalysis, hybrid pyridine-benzotriazole based CuII complex and its use towards the A3 coupling reaction. Control experiments, cyclic voltammetry and theoretical calculations account for a detailed mechanistic pathway and the development of an efficient methodology. Chapter 6 provides an overall conclusion of this thesis while highlighting the contributions of this work to the reported literature and discusses some potential future directions. Finally, experimental and synthetic details, as well as crystallographic data, are presented in Chapter 7 and Chapter 8, respectively. The bibliography is presented in Chapter 9
Development of 3d-4f and Cu based catalytic methodologies
No full textThis thesis deals with the use of Schiff base, amyloid peptide and benzotriazole scaffolds to synthesise 3d-4f and copper complexes and hybrid materials, investigate their catalytic properties and develop novel cost-, time- and step-efficient methodologies for the domino ring-opening/electrocyclization reaction of furfural and amines for the synthesis of trans-4,5-diaminocyclopentenones and the corresponding Stenhouse salts, as well as the coupling of aldehyde, amine and alkyne for the synthesis of propargylamines, to replace existing catalytic protocols. Chapter 1 serves as a general introduction to the chemistry discussed in the thesis. The first part emphasises on the synthetic aspects of coordination complexes. A rationale regarding the selection of the employed ligands is presented. The second part presents an overview of methodologies in catalysis, related to the methodologies developed in the present thesis, towards the synthesis of the organic derivatives. Chapter 2 focuses on the synthesis and characterisation of a new bimetallic tetranuclear complex Ni2Dy2 and its use as a catalyst towards the domino ring-opening/electrocyclization reaction of furfural and amines. The present catalytic system surpasses the efficiency of other reported systems, and the scope and limitations are described. Chapter 3 describes the first amyloid fibril core decorated by a heterometallic entity. The tetranuclear 3d-4f entity is of the type Zn2Dy2. The functionalized assembly behaves as a Lewis acid and catalyses the ring-opening/electrocyclization reaction of furfural and amines at a nanoscale level. Chapters 4 describes the synthesis and characterisation of a CuII complex with the use of a Schiff Base ligand, and its use as a catalyst towards the A3 coupling reaction. Control experiments, cyclic voltammetry and theoretical studies shed light on the mechanism of the reaction, suggesting the formation of an in situ radical specie. Chapter 5 reports the synthesis and characterisation of a relatively unexplored, in coordination chemistry and catalysis, hybrid pyridine-benzotriazole based CuII complex and its use towards the A3 coupling reaction. Control experiments, cyclic voltammetry and theoretical calculations account for a detailed mechanistic pathway and the development of an efficient methodology. Chapter 6 provides an overall conclusion of this thesis while highlighting the contributions of this work to the reported literature and discusses some potential future directions. Finally, experimental and synthetic details, as well as crystallographic data, are presented in Chapter 7 and Chapter 8, respectively. The bibliography is presented in Chapter 9
Solvent-free synthesis and key intermediate isolation in Ni2Dy2 catalyst development in the domino ring-opening electrocyclization reaction of furfural and amines
No full textA solvent-free methodology that yields trans-4,5-diaminocyclopent-2-enones, main domains of natural products and variety of N-heterocycles, is described. The bimetallic catalyst [NiII2DyIII2L4(DMF)6] 2(OTf) 2(DMF) (1) promotes the domino reaction of furfural and amines, with loadings as low as 0.01%, under stirring or microwave assisted conditions to afford the corresponding frameworks in very good to excellent yields. Crystallographic and theoretical studies shed light on the exclusive formation of the trans-diastereoisomers via a 4π-conrotatory electrocyclization process elucidating the key step in the catalytic process
Shedding light on the use of Cu(II)-salen complexes in the A<sup>3</sup> coupling reaction
Full text linkOne Cu(II) complex, {Cu(II)L} (1S), has been synthesised, in two high yielding steps under ambient conditions, and characterised by single-crystal X-Ray diffraction (SXRD), IR, UV-Vis, circular dichroism (CD), elemental analysis, thermogravimetric analysis (TGA) and electron spray ionization mass spectroscopy (ESI-MS). This air-stable compound enables the generation, at room temperature and in open-air, of twenty propargylamines, nine new, from secondary amines, aliphatic aldehydes and alkynes with a broad scope with yields up to 99%. Catalyst loadings can be as low as 1 mol%, while the recovered material retains its structural integrity and can be used up to 5 times without loss of its activity. Control experiments, SXRD, cyclic voltammetry and theoretical studies shed light on the mechanism revealing that the key to success is the use of phenoxido salen based ligands. These ligands orchestrate topological control permitting alkyne binding with concomitant activation of the C–H bond and simultaneously acting as a template temporarily accommodating the abstracted acetylenic proton, and continuously generating, via in situ formed radicals and a Single Electron Transfer (SET) mechanism, a transient Cu(I) active site to facilitate this transformation. The scope and limitations of this protocol are discussed and presented
Polynuclear ampyrone based 3d coordination clusters
No full textThe use of the monoanionic Schiff base ligand (E)-4-(2-hydroxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one in transition (Co, Ni and Cu) coordination chemistry yields mono-, tetra- and pentanuclear Coordination Clusters with different structural motifs. An organic transformation occurs in the ligand in the Cu compound for which theoretical studies are presented. Solution studies, topological issues and magnetic studies are discussed. The present results demonstrate the richness of the coordination chemistry of this monoprotic organic ligand, which promotes the formation of high-nuclearity CCs
Dinucleating Schiff base ligand in Zn/4f coordination chemistry : synthetic challenges and catalytic activity evaluation
Full text linkFour Zn/4f polynuclear coordination clusters (PCCs) formulated as [ZnDyL2(CO3)2(NO3)2] (1), [ZnIIYIIIL(NO3)2(o-van) (MeOH)] (MeOH) [2 (MeOH)] and [ZnIILnIIIL(NO3)2Cl(EtOH)] where Ln is Dy (3) and Y (4) and where H2L is the dinucleating Schiff base ligand N,N'-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine and o-van is ortho-vanillin, were prepared and fully characterised for the first time. These air-stable heterometallic PCCs, obtained in high yields from commercially available materials, were shown to remain stable in solution in their dinuclear [ZnIILnIIIL] form. Their catalytic activity was evaluated in various catalytic transformations including the Friedel-Crafts alkylation of 2-acyl imidazoles with indoles
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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