Showing papers in "Chemical Society Reviews in 1999"
TL;DR: A number of polynuclear d10 transition metal complexes have been found to exhibit interesting luminescence properties, such as metal-to-ligand charge transfer, ligand to metal charge transfer and metal-centred to ligand-centered as discussed by the authors.
Abstract: A number of polynuclear d10 transition metal complexes have been found to exhibit interesting luminescence properties. The photoluminescence properties of polynuclear d10 metal complexes are highly diversified. In the presence of a wide range of bridging and ancillary ligands, the excited states of such complexes have been suggested to range from metal-to-ligand charge-transfer, ligand-to-metal charge-transfer, metal-centred to ligand-centred in nature. Recent work on the photophysical and photochemical properties, as well as the applications of this class of luminescent polynuclear d10 metal complexes will be described in this review article.
1,067 citations
TL;DR: The first salen ligand and Cu complex were discovered in 1889, and gradually the potential catalytic activity of subsequent salen species has been recognised, particularly in the case of achiral salen complexes in oxidation reactions.
Abstract: The first salen ligand and Cu complex were discovered in 1889, and gradually the potential catalytic activity of subsequent salen species has been recognised, particularly in the case of achiral salen complexes in oxidation reactions. The development of chiral salen metal complexes and catalysts in the last decade has however stimulated a very rapid growth in the chemistry and application of these species. The variety of asymmetric reactions in which particular chiral metal salen complexes are proving useful grows steadily, and there is no evidence of this growth slowing. This review summarises the key work and references on soluble chiral metal salen complex catalysts categorised according to the metal centre. It also describes the work to date on producing supported heterogeneous chiral analogues of some of these.
856 citations
TL;DR: In a recent review as discussed by the authors, the exceptional range of research avenues in supramolecular fullerene chemistry have been pursued during the past decade, which illustrates how molecular complexation of pristine fullerenes developed from solid state enclathration by π-electron-rich compounds to inclusion complexation by designed macrocyclic receptors in the liquid phase.
Abstract: This review documents the exceptional range of research avenues in supramolecular fullerene chemistry that have been pursued during the past decade. It illustrates how molecular complexation of pristine fullerenes developed from solid state enclathration by π-electron-rich compounds to inclusion complexation by designed macrocyclic receptors in the liquid phase. Progress in covalent fullerene functionalisation led to the development of spectacular supramolecular architectures including rotaxanes, catenanes, DNA complexes, diads and triads for photoinduced electron and energy transfer and ordered thin films. All of these molecular assemblies and supramolecular arrays feature distinct properties as a consequence of the presence of the fullerene components. Recent investigations hinting at potential technological applications of supramolecular fullerene, such as in sensorics, are highlighted.
656 citations
TL;DR: The concept of polarity reversal catalysis (PRC) was introduced in this paper to replace a single-step abstraction, that is slow because of unfavourable polar effects, with a two-step process in which the radicals and substrates are matched.
Abstract: The rates and selectivities of the hydrogen-atom abstraction reactions of electrically-neutral free radicals are known to depend on polar effects which operate in the transition state. Thus, an electrophilic species such as an alkoxyl radical abstracts hydrogen much more readily from an electron-rich C–H bond than from an electron-deficient one of similar strength. The basis of polarity-reversal catalysis (PRC) is to replace a single-step abstraction, that is slow because of unfavourable polar effects, with a two-step process in which the radicals and substrates are polarity-matched. This review explores the concept of PRC and describes its application in a variety of situations relevant to mechanistic and synthetic organic chemistry.
644 citations
TL;DR: In this article, the properties of metal clusters of one up to a few nanometers are discussed on the basis of numerous physical investigations in the course of the last few years, and the success of future applications of nanoclusters will strongly depend on the availability of three-, two-or one-dimensionalally organized materials.
Abstract: This article deals with some recent developments in metal and in semiconducting nanocluster science. Our studies on the properties, mainly of metal nanoclusters, with respect to future and also to current applications are reviewed, including a series of unpublished results. The general properties of metal clusters of one up to a few nanometers are discussed on the basis of numerous physical investigations in the course of the last few years. Quantum size effects open the door to novel future technologies. The success of future applications of nanoclusters will strongly depend on the availability of three-, two- or one-dimensionally organized materials. Our own very recent results are promising, but also indicate that much more work will be necessary. Much more realistic is the use of metal nanoclusters in heterogeneous catalysis. Finally, novel developments in generating semiconducting nanomaterials in transparent, nanoporous alumina membranes are discussed. CdS and GaN can easily be prepared inside the pores to give photoluminescent foils of unlimited size.
390 citations
TL;DR: More than 3200 known naturally occurring organohalogen compounds contain bromine as mentioned in this paper and more than 1600 contain indole alkaloids, which are produced by marine and terrestrial plants, marine animals (sponges, tunicates, bryozoans, gorgonians, sea hares, nudibranchs), bacteria, fungi, and some higher animals, including humans.
Abstract: Of the nearly 3200 known naturally occurring organohalogen compounds, more than 1600 contain bromine. These organobromines, which range in structural intricacy from the simple but enormously abundant bromoform (CHBr3) and bromomethane to the highly complex bryozoan bromine-containing indole alkaloids, are produced by marine and terrestrial plants, marine animals (sponges, tunicates, bryozoans, gorgonians, sea hares, nudibranchs), bacteria, fungi, some higher animals, and a few mammals including humans.
368 citations
TL;DR: In this article, a review of recent developments in the synthesis of scaffolds for novel forms of carbon made of a core π-system carrying alkyne appendages is presented.
Abstract: All-carbon materials with novel topologies are of interest in regard to their materials properties. These novel structures include graphite-like two-dimensional networks as well as fullerene-like three-dimensional cages. This article reviews recent developments in the synthesis of scaffolds for novel forms of carbon made of a core π-system carrying alkyne appendages, such as hexaethynylbenzene and its derivatives, pentaethynylcyclopentadienyl metal complexes, and tetraethynylcyclobutadiene metal complexes. Also included are the syntheses and properties of macrocyclic π-systems derived of these units which represent important substructures for the infinite lattices of novel carbon allotropes.
337 citations
TL;DR: In this paper, the lock-and-key principle associated with the preorganisation of rigid macropolycylic multidentate ligands tailored for one particular LnIII only partially fulfils these structural requirements.
Abstract: The variable and versatile co-ordination behaviour of lanthanide metal ions, LnIII, limits their selective introduction into organised molecular or supramolecular architectures. The design of lanthanide-based devices is thus a special challenge since their specific electronic, magnetic or spectroscopic properties result from a precise control of the co-ordination sphere around the metal ions. The lock-and-key principle associated with the preorganisation of rigid macropolycylic multidentate ligands tailored for one particular LnIII only partially fulfils these structural requirements. The development of less constrained macrocyclic ligands or macrocycles bearing pendant arms allows a smooth transition toward flexible (predisposed) receptors leading to the application of the induced fit principle in lanthanide co-ordination chemistry. According to this concept, programmed secondary non-covalent interstrand interactions (π-stacking, hydrogen bonds, electrostatic repulsion) assist the complexation process leading to an ultra-fine tuning of the metallic co-ordination sites. These two complementary approaches are discussed and evaluated for the design of organised mono-, di- and polymetallic lanthanide complexes together with the consideration of new semi-rigid multidentate podands which combine both aspects.
332 citations
TL;DR: Rotaxanes as mentioned in this paper are molecular architectures ideally suited for building integrated, multicomponent modular systems, displaying novel chemical and physical properties, and are particularly attractive for their photophysical and electronic properties as well as their dynamic behaviour.
Abstract: Rotaxanes are molecular architectures ideally suited for building integrated, multicomponent modular systems, displaying novel chemical and physical properties. In this new field of functional rotaxanes, those incorporating transition metals, which are incidentally used as synthetic templates, are particularly attractive for their photophysical and electronic properties as well as their dynamic behaviour. It is believed that they will provide, in the future, the basic elements for constructing nanoscale machines and motors.
278 citations
TL;DR: Fischer-type carbene complexes have received increasing interest as selective reagents in organic synthesis Apart from its electron-acceptor properties exploited in carbene ligand centered reactions, the metal carbonyl fragment provides a template for non-classical cycloaddition reactions as discussed by the authors.
Abstract: Over the past three decades Fischer-type carbene complexes have received increasing interest as selective reagents in organic synthesis Apart from its electron-acceptor properties exploited in carbene ligand centered reactions, the metal carbonyl fragment provides a template for non-classical cycloaddition reactions The most useful among them is the chromium-mediated benzannulation which allows a one-pot access to densely functionalized oxygenated arenes coordinated to a Cr(CO)3 fragment It is compatible with a variety of functional groups, occurs under mild conditions with remarkable chemo-, regio- and diastereoselectivity, and thus has considerable potential in the synthesis of complex targets and natural products
278 citations
TL;DR: In this paper, the application and potential of fluorous phase separation techniques for the recovery of soluble metal catalysts is discussed, which can be used to extract fluorous components from reaction mixtures.
Abstract: Fluorous solvents have limited miscibility with conventional organic solvents Combined with the fact that compounds functionalized with perfluorinated groups often dissolve preferentially in fluorous solvents this can be used to extract fluorous components from reaction mixtures This review discusses the application and potential of fluorous phase separation techniques for the recovery of soluble metal catalysts
TL;DR: In this paper, a review of recent progress in in inorganic zeolites, metalloorganic and organic networks including carbon nanotubes and condensed cyclodextrins is presented.
Abstract: Organic solid state and molecular architectures providing nano- or mesoporous space for the inclusion of guest species open up new opportunities for the synthesis of materials showing designed chemical and physical properties. Porous materials are reviewed by taking into account recent progress in inorganic zeolites, metalloorganic and organic networks including carbon nanotubes and condensed cyclodextrins. Various properties requiring a parallel alignment of close-packed guests are addressed. As a particular example of physical property design, spontaneous polarity formation in channel-type inclusion compounds is discussed.
TL;DR: A review of electron transfer studies can be found in this paper, where elegant synthetic model systems were used to address important fundamental questions and highlighted the increasing role of synthesis in modern physical chemistry research.
Abstract: Highlights of new findings in electron transfer studies, in which elegant synthetic model systems were used to address important fundamental questions, are briefly described. The selected examples include: (i) efficient long distance electron transfer mediated by hydrogen bonds; (ii) energy and electron transfer through the walls of hemicarcerands; (iii) the influence of internal electric fields on the rate of electron transfer in α-helical peptides; (iv) construction of a biomimetic proton pump driven by photoinduced electron transfer. The review underscores the increasing role of synthesis in modern physical chemistry research.
TL;DR: A range of water treatment methods which have been applied to removing microcystins from potable waters are reviewed.
Abstract: The incidence of cyanobacterial blooms in freshwaters, including drinking water reservoirs, has increased over the past few decades due to rising nutrient levels. Microcystins are hepatotoxins released from cyanobacteria and have been responsible for the death of humans as well as domestic and wild animals. Microcystins are chemically very stable and many processes have only limited efficacy in removing them. In this paper we review a range of water treatment methods which have been applied to removing microcystins from potable waters.
TL;DR: In this article, the surface chemistry of mineral particles and interface phenomena are reviewed with a focus on surface chemistry and interface properties, and an outline of the anatomy of the respiratory system and the etiology of the main diseases involved is also given.
Abstract: Some humans are often exposed to airborne mineral dusts at the workplace or in daily life. When inhaled, some kinds of mineral dusts can trigger a pathological response of the respiratory system. Silicosis (from silica dust) and asbestosis (from asbestos fibres) are the most commonly known diseases originating from inhaled mineral dusts; other examples are bronchogenic carcinoma and mesothelioma. Detailed knowledge of the chemical (and physical) factors underlying mineral dust toxicity is much needed in order to evaluate the relative risks from exposure to different kinds of materials, both natural and synthetic. These pathogenic factors have been reviewed, with a focus on the surface chemistry of mineral particles and interface phenomena. To facilitate understanding, an outline of the anatomy of the respiratory system and of the etiology of the main diseases involved is also given.
TL;DR: The addition of nucleophiles to carbon-carbon multiple bonds coordinated by Pd(II) is one of the most popular processes for palladium promoted organic transformations as mentioned in this paper, however, the palladium catalysed addition of pronucleophiles has not been investigated widely.
Abstract: The addition of nucleophiles to carbon–carbon multiple bonds coordinated by Pd(II) is one of the most popular processes for palladium promoted organic transformations. However, the palladium catalysed addition of pronucleophiles to carbon–carbon multiple bonds has not been investigated widely. The compounds (H–Nu) which are prone to form nucleophilic species (Nu–) on treatment with either base or transition metals are called pronucleophiles. The additions of carbon pronucleophiles (H–CR3, hydrocarbonation), nitrogen pronucleophiles (H–NR2, hydroamination), carboxyl pronucleophiles (H–OCOR, hydrocarboxylation) and sulfur pronucleophiles (H–S–, hydrosulfination) to C–C multiple bonds are catalysed by palladium complexes. The hydrocarbonation of allenes, enynes, alkynes and methylenecyclopropanes proceeds very smoothly in the presence of palladium catalysts to give the corresponding olefinic derivatives in good to high yields. The hydroamination of allenes, enynes and methylenecyclopropanes affords the corresponding allylic amines. The hydrocarboxylation of allenes gives the corresponding allylic carboxylates in high yields, and the hydrosulfination of allenes with tosylhydrazine produces the corresponding allylic tosylates.
TL;DR: In this review article, recent advances in the asymmetric Claisen rearrangement are described.
Abstract: Development of the asymmetric Claisen rearrangement is one of the challenging tasks in synthetic organic chemistry. There have been numerous reports of the asymmetric Claisen rearrangement based on the intramolecular chirality transfer using chiral substrates. On the other hand, reactions of achiral substrates with an external chiral activator have been studied during the last decade. In this review article, recent advances in the asymmetric Claisen rearrangement are described.
TL;DR: In this article, the role of silicon in the preparation of furan rings having a variety of substituent patterns has been reviewed, and a detailed review of the silicon placement on a ring can be found.
Abstract: Silanes have proven extremely useful for the synthesis of multi-substituted furan rings. Their judicious placement on a furan ring can be used to control either the placement of new groups around the furan ring or the silane can be directly replaced via an ipso-substitution. This paper will briefly review the role silicon has played in the preparation of furan rings having a variety of substituent patterns.
TL;DR: In this paper, the central carbon atom is stabilized by σ-donors and π-acceptors, as required for planar-tetracoordinate carbon atoms.
Abstract: Over the past years the number of examples of compounds containing a planar-tetracoordinate carbon atom has increased. However, the presence of a carbon atom with a 360° sum of angles does not imply that the species is a derivative of planar methane; there must be an appropriate electronic stabilization. In the case of complexes 21a and 21b the central carbon atom is indeed stabilized by σ-donors and π-acceptors, as required for planar methane.
TL;DR: The α-cyanomethyloxazolidine ring system has been integrated into piperidine and pyrrolidine structures providing chiral non-racemic building blocks as mentioned in this paper.
Abstract: The α-cyanomethyloxazolidine ring system has been integrated into piperidine and pyrrolidine structures providing chiral non-racemic building blocks Reaction conditions have been determined for regio- and stereoselective substitution of the ring atoms This review highlights the applications of the methodology for the diastereoselective synthesis of both natural and unnatural derivatives containing either the piperidine or the pyrrolidine ring as a substructure
TL;DR: In this paper, the authors suggest that, with careful control of the reaction conditions, fluorodenitration could well provide a viable industrial alternative for the formation of selectively fluorinated aromatic compounds.
Abstract: Selectively fluorinated aromatic compounds are of interest in many sectors. Of the methodologies used for their formation, halogen exchange is the only industrial rival to the diazonium based routes. Although many compounds can be formed by halogen exchange, the formation of meta-fluorinated species by this route is difficult. One possible method for overcoming this is fluorodenitration. Although traditionally plagued by side reactions, recent reports suggest that, with careful control of the reaction conditions, fluorodenitration could well provide a viable industrial alternative for the formation of selectively fluorinated aromatic compounds.
TL;DR: In this paper, a review of possible fermentation strategies, actual research activities and future research demands to enhance the use of renewable resources as a source of chemicals is presented, focusing on commodity chemicals, which have a considerable market volume or are believed to be key chemicals of the future.
Abstract: Current developments, especially in fermentation technologies, membrane technologies and genetic manipulation open new possibilities for the biotechnological production of market relevant chemicals from renewable resources. This article reviews possible fermentation strategies, actual research activities and future research demands to enhance the use of renewable resources as a source of chemicals. Special focus is put on commodity chemicals, which have a considerable market volume or which are believed to be key chemicals of the future.
TL;DR: In this paper, the tricarbonyl(η4-1,3-diene)iron complex is readily achieved by a 1-azabutadiene-catalyzed complexation of the free ligands.
Abstract: The protection of conjugated dienes by coordination to the tricarbonyliron fragment offers many potential applications of the resulting complexes to organic synthesis. The preparation of tricarbonyl(η4-1,3-diene)iron complexes is readily achieved by a 1-azabutadiene-catalyzed complexation of the free ligands. An asymmetric catalytic complexation of prochiral cyclohexa-1,3-dienes with pentacarbonyl-iron using chiral 1-azabutadienes affords chiral nonracemic complexes. The chiral tricarbonyliron complexes of acyclic butadienes represent versatile starting materials for the synthesis of a broad range of polyunsaturated natural products. Consecutive carbon–carbon and carbon–nitrogen bond formations of the tricarbonyliron–cyclohexa-1,3-diene complexes and arylamines provide many biologically active carbazole alkaloids and a tetracyclic subunit of the discorhabdin alkaloids. The iron-mediated [2+2+1] cycloaddition of trimethylsilylacetylenes and carbon monoxide affords stable 2,5-bis(trimethylsilyl)-substituted cyclopentadienones which are useful substrates for further cycloadditions.
TL;DR: In this article, the main approaches toward the stereoselective synthesis of planar chiral derivatives of (η6-benzene) tricarbonyl chromium(0) are summarized.
Abstract: Planar chiral (η6-arene) tricarbonyl chromium(0) complexes are well-studied compounds in synthetic organic chemistry. However, the number of investigations concerned with their application in asymmetric catalysis is rather low. This review aims to summarise the main approaches toward the stereoselective synthesis of planar chiral derivatives of (η6-benzene) tricarbonyl chromium(0) and to present recent applications of such complexes as ligands in enantioselective catalytic processes.
TL;DR: The host compound is the zeolite-type sodalite and the colour centres are S2 and S3, whose amount ratio determines the specific hue, varying from violet blue to blue to green.
Abstract: Blue minerals and gems have always been subjects of fascination to man. In particular lapislazuli is and was highly esteemed and also used as a precious stone and as a pigment. The host compound is the zeolite-type sodalite and the colour centres are S2– and S3–, whose amount ratio determines the specific hue, varying from violet blue to blue to green. But Se2– can also be substituted into the sodalite cages in high percentages, giving the pigment a brilliant red colour. It is even possible to incorporate the rather voluminous radical species Te2 and Te2– into the sodalite matrix. Because the otherwise unstable colour centres are completely screened from the atmosphere and isolated from each other in the cages, they can be fully characterised by various spectroscopic techniques.
TL;DR: In this article, the authors illustrate this philosophy by referring to the interplay that led to the confirmation of the dicopper site in haemocyanin and by speculating on the use of knowledge acquired concerning the dinuclear site in order to facilitate simulation of the functioning of the site.
Abstract: Just as it is possible to use coordination compounds to try and gain insight into the nature of metallobiosites so it is also possible to use the knowledge acquired through crystallography concerning the structure of a metallobiosite to try to develop new chemistry. The aim of this lecture was to illustrate this philosophy by referring to the interplay that led to the confirmation of the dicopper site in haemocyanin and by speculating on the use of knowledge acquired concerning the dinuclear site in urease to facilitate simulation of the functioning of the site.
TL;DR: In this paper, new methodologies for the synthesis of compound libraries are discussed based on new carbon-carbon bond-forming reactions on the solid phase (using polymer-supported silyl enol ethers), library preparation using polymer catalysts, and multi-component reactions in liquid phase.
Abstract: New methodologies for the synthesis of compound libraries are discussed. They are based on new carbon–carbon bond-forming reactions on the solid-phase (using polymer-supported silyl enol ethers), library preparation using polymer catalysts, and multi-component reactions in liquid phase. Development of new linker resins for efficient reactions on the solid-phase and a new method for the synthesis of monosaccharide libraries are also described.
TL;DR: In this paper, a variety of such examples involving the spin-1/2 nuclei 57Fe, 103Rh, and 187Os as well as the quadrupolar nuclei 51V, 53Cr, 55Mn, 59Co, and 91Zr are discussed.
Abstract: Transition metal NMR chemical shifts are readily measured by modern 1D and 2D pulse techniques and serve as a probe into electronic and steric effects of ligands and substituents in metal complexes. Quantitative correlations of metal chemical shifts with reaction rates and catalytic activities, both experimental and as a result of quantum chemical calculations, give new mechanistic insights and permit reactivity predictions and a screening of homogeneous catalysts. A variety of such examples involving the spin-1/2 nuclei 57Fe, 103Rh, and 187Os as well as the quadrupolar nuclei 51V, 53Cr, 55Mn, 59Co, and 91Zr are discussed.
TL;DR: In this paper, the metal binding properties of 1,3,5-triamino-1, 3, 5-trideoxy-cis-inositol (taci), a rigid, cyclohexane-based polyamino polyalcohol, are reviewed.
Abstract: Selective, tailored chelators are of importance in medicine for the treatment of metal intoxication, or to stabilise metal cations in diagnostic radiopharmaceuticals and paramagnetic contrast agents. In this report, the co-ordination chemistry of polyamines, polyalcohols, and polyamino-polyalcohols is examined and some general prerequisites for a successful design of tailored chelators are summarised. The metal binding properties of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci), a rigid, cyclohexane-based polyamino-polyalcohol, are reviewed. Concepts for the design of selective chelators which are based on the taci structure are presented, and the potential of such ligands for medical applications is briefly discussed.
TL;DR: An overview of the synthetic chemistry of low-valent chromium, presumably Cr(II) species, and highlights most of the recent developments can be found in this paper, where the introduction of milder protocols, catalytic versions, and the discovery of ligand tuning effects as a means of controlling carbanion selectivity.
Abstract: This article presents an overview of the synthetic chemistry of low-valent chromium, presumably Cr(II) species, and highlights most of the recent developments These organometallic reactions represent a convenient strategy for the construction of carbon–carbon bonds displaying unique elements of stereocontrol, chemoselectivity, and functional-group compatibility The introduction of milder protocols, catalytic versions, and the discovery of ligand tuning effects as a means of controlling carbanion selectivity, are the most salient improvements in this expansive field