On Educational psychology: A cognitive view.

The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.

Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3

However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.

Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.

A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

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Aerobic Copper-Catalyzed Organic Reactions

2.4.2. Interpenetrated Ladders 711 2.4.3. Unusual Motifs of Ladders 713 2.4.4. Properties of Ladderlike Chains 713 2.5. Rotaxane Polymers 714 2.5.1. 1D Polyrotaxanes 714 2.5.2. 2D Polyrotaxanes 715 2.5.3. 3D Polyrotaxanes 716 2.5.4. Hydrogen-Bonded Polyrotaxanes 716 2.6. Ribbon/Tape Polymers 717 2.7. Metal Cluster As Building Blocks for 1D CP 718 2.7.1. Metal Carboxylate Clusters 718 2.7.2. Metal Halide Clusters 719 2.7.3. Metal Chalcogenide Clusters 720 2.7.4. Polyoxometalate Clusters 721 2.7.5. Single Molecular Magnets as Building Blocks 722

One-Dimensional Coordination Polymers: Complexity and Diversity in Structures, Properties, and Applications

Over the past few decades, supramolecular chirality in discrete metallosupramolecular architectures has received considerable attention. In this review, a comprehensive summary of discrete, chiral coordination-driven structures, including helices, metallacycles, metallocages, etc., is presented. Although chirality can be introduced prior to, during or even after the coordination self-assembly process, this review puts major emphasis on the more recent development of metallosupramolecular architectures from chiral components, where chirality arises from the enantiopure or racemic scaffolds (bridging or auxiliary ligand). Special attention will be paid to homochiral metallo-assemblies using achiral components where chirality is obtained as a consequence of the twisting of the ligands. Additionally, the potential applications of homochiral metallosupramolecular architectures are also discussed. We hope that this review will be of interest to researchers attempting to design new elaborate homochiral metallosupramolecular architectures with even greater complexity and potential for functions such as chiral recognition, enantiomer separation, asymmetric catalysis, nonlinear sensors, and devices.

Chiral metallosupramolecular architectures

Four new homochiral metal–organic framework (MOF) isomers, [Zn(l-LCl)(Cl)](H2O)2 (1), [Zn(l-LBr)(Br)](H2O)2 (2), [Zn(d-LCl)(Cl)](H2O)2 (3), and [Zn(d-LBr)(Br)](H2O)2 (4) [L = 3-methyl-2-(pyridin-4-ylmethylamino)butanoic acid], have been synthesized by using a derivative of l-/d-valine and Zn(CH3COO)2·2H2O. A three-periodic lattice with a parallel 1D helical channel was formed along the crystallographic c-axis. Molecular rearrangement results in an unprecedented zeolitic unh-topology in 1–4. In each case, two lattice water molecules (one H-bonded to halogen atoms) form a secondary helical continuous water chain inside the molecular helix. MOFs 1 and 2 shows different water adsorption properties and hence different water affinity. The arrangement of water molecules inside the channel was monitored by variable-temperature single-crystal X-ray diffraction, which indicated that MOF 1 has a higher water holding capacity than MOF 2. In MOF 1, water escapes at 80 °C, while in 2 the same happens at a much lower te...

Helical water chain mediated proton conductivity in homochiral metal-organic frameworks with unprecedented zeolitic unh-topology.

Helix inside a Helix: Encapsulation of Hydrogen‐Bonded Water Molecules in a Staircase Coordination Polymer

Amino acid-containing reduced Schiff bases as the building blocks for metallasupramolecular structures

The copper(II) complexes of the Schiff-base ligands H 2 Sams and H 2 Saes and the reduced Schiff-base ligands H 2 Sam and H 2 Sae formed between salicylaldehyde and aminomethanesulfonic acid or 2-aminoethanesulfonic acid (taurine) have been synthesized in moderate yields. The solid-state structures of the five dinuclear complexes, [Cu 2 (Sams) 2 (H 2 O 2 ] (1), [Cu 2 (Sam) 2 (H 2 O) 2 ].H 2 O (2), [Cu 2 (Saes) 2 (H 2 O) 2 ].2H 2 O (3), [Cu 2 (Sae) 2 ].2H 2 O (4), and [Cu 2 (Sae) 2 (DMF) 2 ].2DMF (5), have been determined by X-ray crystallography, showing that the Cu I I centers have distorted square-pyramidal geometry. The Schiff-base copper complexes 1 and 3 have hydrogen-bonded 2D sheet structures while the reduced Schiff-base complexes 4 and 5 display a 2D coordination network and a hydrogen-bonded 2D structure respectively. All these complexes have been investigated for their catecholase activity and activity measurements have been compared with those of dinuclear copper(II) complexes of similar ligands obtained with carboxylate analogues of the corresponding sulfonic acids; these studies show that 4 has significantly higher activity. Further, a strong antiferromagnetic interaction between Cu I I ions in dimeric complexes 1 [J = -9.04(2) cm - 1 ], 3 [J = -272(4) cm - 1 ), and 4 [J = -237(4) cm - 1 ] has been observed.

Copper(II) Complexes of Schiff-Base and Reduced Schiff-Base Ligands: Influence of Weakly Coordinating Sulfonate Groups on the Structure and Oxidation of 3,5-DTBC

A series of dinuclear Cu II complexes of reduced Schiff bases from substituted salicylaldehydes and amino acids have been synthesized and characterized. They are: [Cu 2 (Rscp11) 2 -(H 2 O) 2 ) {H 2 RScp11 = 1-[(2-hydroxy-5-R-benzyl)amino]cyclopentane-1-carboxylic acid; R = H (1), Cl (2), CH 3 (3), OH (4)), [Cu 2 (Rsch11) 2 (H 2 O) x ] {H 2 RSch11 = 1-[(2-hydroxy-5-R-benzyl)amino]cyclohexane-1-carboxyhc acid; R = H and x = 1 (5), R = Cl and x = 2 (6), R = CH 3 and x = 2 (7)), [Cu 2 (RSch12) 2 -(H 2 O) 2 ] {H 2 RSch12 = 2-[(2-hydroxy-5-R-benzyl)amino]cyclo-hexane-1-carboxylic acid; R = H (8), CH 3 (10) and [Cu 2 (ClSch12) 2 ]·2H 2 O (9)}, [Cu 2 (Diala5) 2 (H 2 O) 2 ]·H 2 O [H 3 -Diala5 = N-(2,5-dihydroxybenzyl)-L-alanine] (11), [Cu 2 -(Diala4) 2 (H 2 O) 2 ]·H 2 P [H 3 Diala4 = N-(2,4-dihydroxybenzyl)-L-alanine] (12), and (Cu 2 (Diala3) 2 (H 2 O) 2 ]·H 2 O [H 3 Diala3 = N-(2,3-dihydroxybenzyl)-L-alanine] (13). They were isolated and characterized by chemical and spectroscopic methods. Single crystal X-ray crystallographic studies have revealed that [Cu 2 (Scp11) 2 (MeOH) 2 ] (la), [Cu 2 (ClScp11) 2 (DMF)-(H 2 O)]·MeCN (2a), [Cu 2 (MeScpll) 2 (MeOH) 2 ]·2MeOH (3a), [Cu 2 (ClSchll) 2 (MeOH) 2 ]·2MeOH (6a), [Cu 2 (ClSch12) 2 ]· 2MeOH (9a), and [Cu 2 (Diala4) 2 (DMSO) 2 ]·2DMSO·2 acetone (12a) have 1D hydrogen-bonded polymeric structures while 4 has a 3D hydrogen-bonded network structure. Complex 8 displays a 2D coordination polymeric network structure. The complexes 1-13 have been investigated as functional models for the catechol oxidase by employing 3,5-di-tert-butylcatechol as a model substrate. Electron-withdrawing substituents reduced the activity while electron-donating substituents enhanced the activity. Variable-temperature magnetic studies conducted on compound 8 suggest the presence of strong inter-dimer antiferromagnetic coupling.

Synthesis, Structures and Catecholase Activity of a New Series of Dicopper(II) Complexes of Reduced Schiff Base Ligands

This study explored undergraduate students’ understanding of the chemistry topic of thermodynamics using a 4-tier diagnostic instrument, comprising 30 questions, and follow-up interviews. An additional objective of the study was to assess the utility of the 4-tier instrument for use in studies on alternative conceptions (ACs) as there has been no study done on it since its introduction in the literature in the year 2010. A total of 296 students majoring in Chemistry at a university in Singapore participated in this study—88 students in the preliminary study, 102 students in the pilot study and 106 students in the main study. This article reports on the results obtained with students in the main study; their age ranges from 20 to 22 years. Comprising answer and reason tiers plus associated confidence ratings, the 4-tier diagnostic instrument enabled the eliciting of 34 ACs harbored by the undergraduates as well as the strengths of these ACs. Of concern to note is that even for questions which were answered...

Bellam Sreenivasulu

Papers

Helix inside a Helix: Encapsulation of Hydrogen‐Bonded Water Molecules in a Staircase Coordination Polymer

Amino acid-containing reduced Schiff bases as the building blocks for metallasupramolecular structures

Copper(II) Complexes of Schiff-Base and Reduced Schiff-Base Ligands: Influence of Weakly Coordinating Sulfonate Groups on the Structure and Oxidation of 3,5-DTBC

Synthesis, Structures and Catecholase Activity of a New Series of Dicopper(II) Complexes of Reduced Schiff Base Ligands

University Students’ Understanding of Chemical Thermodynamics