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 complexes [PdCl(η3-2-XC3H4){Ph3PC(H)COR}][R = Me, X = H (1) or Me(2); R = Ph, X = H (3) or Me (4)] have been obtained in high yields by treatment of the dimers [{PdCl(η3-2-XC3H4)}2] with the keto-stabilized ylides Ph3PC(H)COMe [ampp, (acetylmethylene)triphenylphosphorane] and Ph3PC(H)COPh [bmpp, (benzoylmethylene)triphenylphosphorane] in CH2Cl2 solution. They have been characterized by analytical data, i.r., low-temperature 1H and 31P-{1H} n.m.r., and for complex (2) also by 13C n.m.r. spectroscopy. Spectroscopic evidence indicates that complexes (1)–(4) in solution at low temperature are present as two diastereoisomeric forms arising from co-ordination on the metal centre of the asymmetric ylidic carbon atom and of the η3-allyl ligand. In CH2Cl2 solution at room temperature the complexes are in equilibrium with their reagents. Reaction with PPh3 and [AsPh4]Cl gives [ PdCl(η3-2-XC3H4)(PPh3)] and [AsPh4][PdCl2-(η3-2-XC3H4)], respectively, and the free ylide. The X-ray crystal structure of complex (2) was determined showing that, in the solid state, only one diastereoisomer is present. The crystals are monoclinic, space group P21/n with a= 9.668(3), b= 14.879(4), c= 16.226(3)A, β= 99.85(2)°, and Z= 4. Final full-matrix least-squares refinement, based on 3 063 reflections, converged to R= 0.031. The keto-stabilized ylide ligand is C bonded to the metal with a Pd–C distance of 2.193(3)A.

Synthesis and Characterization of Palladium(II)-η3-Allyl-Ylide Complexes. X-Ray Crystal Structure of (PdCl(η3-2-MeC3H4)(Ph3PC(H)COMe)).

Structure of a sigma-carboranyl complex of platinum(ii), 1-((p-n-pr3)pt(p-n-pr2chch2ch3))-2-c6h5-1,2-(sigma-b10c2h10), an unusual metal-phosphine bonding

The iridium complex {H2[graphic omitted]H2Me][(P)–NMe2]}[(P)–NMe2=o-(diphenylphosphino)-N,N-dimethyl aniline] formed by intramolecular C-H oxidative addition, as shown by X-ray analysis, behaves as a chemoselective catalyst in hydrogen transfer reduction of α,β-unsaturated ketones to unsaturated alcohols.

Intramolecular Activation of a N-Methyl C-H Bond by an Electron Rich Iridium Centre: A Novel Chemoselective Reduction Catalyst.

The crystal structure of a fully silver-exchanged heulandite is reported. The freshly prepared monoclinic crystals, space group C2/m, have cell parameters a= 17.736(9), b= 18.104(9), c= 7.447(6)A, β= 116.2(1)°, Z= 1, and formula Ag7.3Al7.2Si28.8O72·18H2O (from electron microprobe analysis). The final R index was 0.068 using 1 602 independent reflections in the least-squares refinement. X-Ray analysis results suggest that Ag+ has exchanged two sites CS(1) and CS(2) already occupied by Ca2+ and Na+ in the natural heulandite. Furthermore, a new site, CS(3), with a low occupancy has been ascribed to Ag2+. However, the total amount of silver ions (4.1 per unit cell) detected from X-ray refinement is significantly smaller than that derived from chemical analysis. This suggests that the remainder of the Ag+ ions are spread out in the zeolite pores. Since crystals after long exposure in air darken, a second crystal structure analysis was carried out using a crystal of (Ag)heu exchanged under different conditions and after exposure to air for two months. No significant difference was found with the above results.

Giorgio Nardin

Papers

Synthesis and Characterization of Palladium(II)-η3-Allyl-Ylide Complexes. X-Ray Crystal Structure of (PdCl(η3-2-MeC3H4)(Ph3PC(H)COMe)).

Structure of a sigma-carboranyl complex of platinum(ii), 1-((p-n-pr3)pt(p-n-pr2chch2ch3))-2-c6h5-1,2-(sigma-b10c2h10), an unusual metal-phosphine bonding

Intramolecular Activation of a N-Methyl C-H Bond by an Electron Rich Iridium Centre: A Novel Chemoselective Reduction Catalyst.

Location of cations in metal ion-exchanged zeolites. part 2. crystal structures of a fully silver-exchanged heulandite

Kristallstruktur und polymere natur von zink(ii)- und kobalt(ii)-dialkyl(aryl)-thiophosphinaten