J. Appl. Cryst.の発刊に際して

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Polyoxometalates (POMs) are discrete anionic metaloxygen clusters which can be regarded as soluble oxide fragments. They exhibit a great diversity of sizes, nuclearities, and shapes. They are built from the connection of {MOx} polyhedra, M being a d-block element in high oxidation state, usually VIV,V, MoVI, or WVI.1 While these species have been known for almost two centuries, they still attract much interest partly based on their large domains of applications. They play a great role in various areas ranging from catalysis,2 medicine,3 electrochemistry,4 photochromism,5 to magnetism.6 This palette of applications is intrinsically due to the combination of their added value properties (redox properties, large sizes, high negative charges, nucleophilicity...). Parallel to this domain, the organic-inorganic hybrids area has followed a similar expansion during the last 10 years. The concept of organic-inorganic hybrid materials * To whom correspondence should be addressed. E-mail: dolbecq@ chimie.uvsq.fr. Chem. Rev. 2010, 110, 6009–6048 6009

Hybrid Organic−Inorganic Polyoxometalate Compounds: From Structural Diversity to Applications

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

The trans-influence: its measurement and significance

The chemistry of halogen-dimethyl sulfoxide-ruthenium(II) complexes with the general formula RuX/sub 2/(DMSO)/sub 4/ (X = Cl, Br) is reported. In particular the synthesis and x-ray structure of trans-RuCl/sub 2/(DMSO)/sub 4/ are described and compared with those of the already known cis-RuCl/sub 2/(DMSO)/sub 4/ and trans-RuBr/sub 2/(DMSO)/sub 4/. The structure op a new crystal form of cis-RuCl/sub 2/(DMSO)/sub 4/ is also reported. While the cis isomers are thermodynamically more stable and form from the trans species a photochemically driven cis to trans isomerization reaction is observed in dimethyl sulfoxide solution. Kinetic parameters for the thermal trans to cis isomerization reactions for trans-RuCl/sub 2/(DMSO)/sub 4/ and trans-RuBr/sub 2/(DMSO)/sub 4/ are reported. In chloroform solution the complexes, and in particular the trans isomers, tend to release a dimethyl sulfoxide molecule to give pentacoordinated Ru(II) complexes. However, in aqueous solution, while the cis complexes immediately release one DMSO, the trans ones release two. In both cases, this step is followed by the slow dissociation of a halide ion. For the chloro derivatives the dissociation is completely inhibited at physiological chloride concentrations. Preliminary results from pharmacological tests show that trans-RuCl/sub 2/(CMSO)/sub 4/ is more active than the cis isomer against Lewis lung carcinoma, a metastasizingmore » murine tumor. A remarkable dependence of activity on the halogen nature (Cl > Br) is also observed. 33 refs., 4 figs., 9 tabs.« less

cis- and trans-dihalotetrakis(dimethyl sulfoxide)ruthenium(II) complexes (RuX2(DMSO)4; X=Cl, Br): synthesis, structure, and antitumor activity

The dicopper(II) complex with the ligand N,N,N‘,N‘,N‘‘-pentakis[(1-methyl-2-benzimidazolyl)methyl]dipropylenetriamine (LB5) has been synthesized and structurally characterized. The small size and the quality of the single crystal required that data be collected using synchrotron radiation at 276 K. [Cu2(LB5)(H2O)2][ClO4]4:  platelet shaped, P1, a = 11.028 A, b = 17.915 A, c = 20.745 A, α = 107.44°, β = 101.56°, γ = 104.89°, V = 3603.7 A3, Z = 2; number of unique data, I ≥ 2σ(I) = 3447; number of refined parameters = 428; R = 0.12. The ligand binds the two coppers nonsymmetrically; Cu1 is coordinated through five N donors and Cu2 through the remaining three N donors, while two water molecules complete the coordination sphere. Cu1 has distorted TBP geometry, while Cu2 has distorted SP geometry. Voltammetric experiments show quasireversible reductions at the two copper centers, with redox potential higher for the CuN3 center (0.40 V) and lower for the CuN5 center (0.17 V). The complex binds azide in the ter...

Tyrosinase Models. Synthesis, Structure, Catechol Oxidase Activity, and Phenol Monooxygenase Activity of a Dinuclear Copper Complex Derived from a Triamino Pentabenzimidazole Ligand.

Structural aspects of metal complexes with some tetradentate schiff bases

Dinuclear copper(II) complexes with the new ligand 1,6-bis[[bis(1-methyl-2-benzimidazolyl)methyl]amino]-n-hexane (EBA) have been synthesized, and their reactivity as models for tyrosinase has been investigated in comparison with that of previously reported dinuclear complexes containing similar aminobis(benzimidazole) donor groups. The complex [Cu2(EBA)(H2O)4]4+, five-coordinated SPY, with three nitrogen donors from the ligand and two water molecules per copper, can be reversibly converted into the bis(hydroxo) complex [Cu2(EBA)(OH)2]2+ by addition of base (pKa1 = 7.77, pKa2 = 9.01). The latter complex can also be obtained by air oxidation of [Cu2(EBA)]2+ in methanol. The X-ray structural characterization of [Cu2(EBA)(OH)2]2+ shows that a double μ-hydroxo bridge is established between the two Cu(II) centers in this complex. The coordination geometry of the coppers is distorted square planar, with two benzimidazole donors and two hydroxo groups in the equatorial plane, and an additional, lengthened and sev...

Giorgio Nardin

Papers

cis- and trans-dihalotetrakis(dimethyl sulfoxide)ruthenium(II) complexes (RuX2(DMSO)4; X=Cl, Br): synthesis, structure, and antitumor activity

Tyrosinase Models. Synthesis, Structure, Catechol Oxidase Activity, and Phenol Monooxygenase Activity of a Dinuclear Copper Complex Derived from a Triamino Pentabenzimidazole Ligand.

Structural aspects of metal complexes with some tetradentate schiff bases

Mechanistic, Structural, and Spectroscopic Studies on the Catecholase Activity of a Dinuclear Copper Complex by Dioxygen

X-ray structural chemistry of cobalamins