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Showing papers in "Accounts of Chemical Research in 1989"


Journal ArticleDOI
TL;DR: In this article, a modular assembly approach is proposed to integrate light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients into single molecular assemblies or on separate electrodes in photelectrochemical cells.
Abstract: The goal of artificial photosynthesis is to use the energy of the sun to make high-energy chemicals for energy production. One approach, described here, is to use light absorption and excited-state electron transfer to create oxidative and reductive equivalents for driving relevant fuel-forming half-reactions such as the oxidation of water to O2 and its reduction to H2. In this “integrated modular assembly” approach, separate components for light absorption, energy transfer, and long-range electron transfer by use of free-energy gradients are integrated with oxidative and reductive catalysts into single molecular assemblies or on separate electrodes in photelectrochemical cells. Derivatized porphyrins and metalloporphyrins and metal polypyridyl complexes have been most commonly used in these assemblies, with the latter the focus of the current account. The underlying physical principleslight absorption, energy transfer, radiative and nonradiative excited-state decay, electron transfer, proton-coupled elec...

1,260 citations


Journal ArticleDOI
TL;DR: In this paper, the authors provide a concise resume of magnetic phenomena, report briefly on the different strategies that have been developed up to the moment for designing molecular magnetic materials, and then summarize their own approach and the main results obtained in this area.
Abstract: Molecular materials are characterized by being made up by discrete molecules. This structural property gives in principle many possibilities, to modulate the bulk electrical, magnetic, and optical properties of the material by choosing appropriately the constituent molecules. At the same time, however, it is a challenge to develop synthetic strategies that allow the control of the spatial distribution of the molecules in the lattice. In fact, the bulk properties are always determined by cooperative interactions between the constituent molecules, which consequently must be assembled in the lattice in such a way as to maximize the bulk response. In this Account we provide a concise resume of magnetic phenomena, report briefly on the different strategies that have been developed up to the moment for designing molecular magnetic materials, and then summarize our own approach and the main results that have been obtained in this area.

764 citations





Journal ArticleDOI
TL;DR: In this paper, a comparative evaluation of the relative equilibrium constants and rates of reaction for both alkane and arene hydrocarbon activation has been provided for the first time, based on a series of homogeneous rhodium organometallic complexes.
Abstract: Alkanes are among the most abundant and unreactive of all organic compounds. Industrial use of these resources often relies upon free-radical activation of carbon-hydrogen bonds, often at high temperatures, thereby limiting the selectivities that can be achieved in any functionalization reaction. Consequently, the selective activation of C-H bonds by homogeneous transition-metal compounds has been a topic that has been of great interest to the organometallic community for many years. In this Account, mechanistic studies with a series of homogeneous rhodium organometallic complexes are summarized that provide for the first time a comparative evaluation of the relative equilibrium constants and rates of reaction for both alkane and arene hydrocarbon activation.

407 citations


Journal ArticleDOI
TL;DR: The most widely studied diplatinum(II) complex is Pt{sub 2} as discussed by the authors, which contains bridging (P,P-bonded) pyrophosphito ligands.
Abstract: The most widely studied diplatinum(II) complex is Pt{sub 2}({mu}-P{sub 2}O{sub 5}H{sub 2}){sub 4}{sup 4{minus}} (abbreviated Pt{sub 2}), which contains bridging (P,P-bonded) pyrophosphito ligands. The excited-state chemistry exhibited by Pt{sub 2} is probably the richest of all d{sup 8}-d{sup 8} complexes. Photophysical studies confirm that the properties of the photoactive excited state are a manifestation of d{sup 8}-d{sup 8} metal-metal interactions. This report looks at the photochemistry of Pt{sub 2}, because the observed reactions with substrates include rare examples of atom abstractions in addition to electron transfer and other well-studied inorganic excited-state processes.

394 citations



Journal ArticleDOI
TL;DR: In this article, the authors limit themselves to those methods in which motion along the reaction coordinate is the key dynamic variable that can be controlled as reactants approach and measured as the products recede.
Abstract: For species as simple as atomic transition-metal ions, organometallic transformations usually involve multistep processes. These transformations have been studied with the entire arsenal of experimental techniques developed for the study of ion-molecule chemistry: conventional tandem mass spectrometry, flowing afterglow (FA) techniques, and ion cyclotron resonance (ICR) mass spectrometry and its Fourier transform adaptation (FT-ICR). In this Account, the authors limit ourselves to those methods in which motion along the reaction coordinate is the key dynamic variable that can be controlled as reactants approach and measured as the products recede. In our laboratories, guided ion beam techniques have been developed and highly refined for studies of the variation of reaction probabilities with E{sub T}. Complementing this work are measurements of product kinetic energy release distributions (KERDs).

291 citations


Journal ArticleDOI
TL;DR: In this paper, the pyrrole group is used for electrocatalytic polymerization of polypyrrolic polymers, which can be applied to a wide range of applications, including bio-and electroanalysis, microelectronics, and electroreleasing devices.
Abstract: The concept of altering the chemical structure of an electrode surface with a view to controlling the course of an electrochemical reaction was pioneered some 15 years ago by Lane and Hubbard. This promising new areas of electrochemistry rapidly attracted interest, the major objective being to tailor spectifically the electrode material in such a way as to promote the desired electrochemical reaction. The possibility of making electrodes with specific chemical, electrochemical, or optical surface properties gave rise to numerous possible applications of these modified electrodes in the fields of electro- and photocatalysis, electrosynthesis, electroanalysis, molecular devices, and electrochromism. Among the numerous chemical functions that could undergo electrochemical polymerization, the pyrrole group is exceptionally convenient for carrying out the coating of electrode surfaces by nonpassifying polymer films containing catalytic and/or redox active centers. Furthermore, polypyrrolic films are characterized by a long-term chemical stability, which allows their productive use in various applications. An account of this topic, mainly devoted to electrocatalytic applications, will be given here. A few typical extra examples, including bio- and electroanalysis, microelectronics, and electroreleasing devices, are also presented to emphasize the versatility of this type of polymeric coating.

280 citations


Journal ArticleDOI
TL;DR: A rich cluster chemistry of organotin compounds has recently emerged based on Sn-O-Sn and Sn-S-Sn bonding formed in reactions of stannonic acids with carboxylic and phosphorus-based acids as participating ligands as mentioned in this paper.
Abstract: A rich cluster chemistry of organotin compounds has recently emerged based on Sn-O-Sn and Sn-S-Sn bonding formed in reactions of stannonic acids with carboxylic and phosphorus-based acids as participating ligands. In the development of the underlying chemistry, it was discovered that some members exhibit catalytic activity on transesterification and potentially in polymerization processes. Further, as new cluster compositions were uncovered, analogies became apparent with other cluster chemistries, particularly those involving aluminum-nitrogen and iron-sulfur systems. What follows is a description of the emerging cluster chemistry of these interesting new classes of organotin compounds, their interconversions, and possible applications.


Journal ArticleDOI
TL;DR: The concept of coherent control of chemical reactions has been introduced in this article, where the authors provide an overview of the concepts underlying coherent control for chemical reactions and their application to chemical reactions.
Abstract: Manipulating the yield of chemical reactions is at the heart of chemistry, and controlling reactions by using lasers has been a goal for decades. Recently, we demonstrated how this goal could be achieved. An appreciation of this approach, termed coherent control of chemical reactions, opens up new avenues in chemistry by introducing a world of chemical control based upon previously unutilized quantum effects. The purpose of this Account is to provide an introduction to the concepts underlying coherent control of chemical reactions. It is organized as follows: Section 2 reviews some fundamental concepts in the application of quantum mechanics to chemical reactions; these may be skipped by the reader who is well versed in collision theory. Section 3 deals directly with control of chemical reactions whereas sections 4 and 5 provide overview summary remarks.



Journal ArticleDOI
TL;DR: In this paper, the C-H bond of a terminal methyl group of an alkyl chain can be oxidatively added to the anchored transition-metal ion M{sup +} (Scheme II).
Abstract: Gas-phase experiments with naked transition-metal ions offer a unique opportunity to probe, in the absence of any solvation, ion-pairing, and/or ligand effects, the intrinsic properties of reactive organometallic species and to evaluate the potential role these remarkable transients play in the initial steps of the activation of C-H and C-C bonds. Not surprisingly, this topic is of fundamental interest in catalysis and has attracted considerable attention in the last decade. The authors and later others, have recently demonstrated that remote functionalization can be achieved in the gas phase for quite a variety of flexible substrates including aliphatic nitriles, isonitriles, amines, alcohols, ketones, alkynes, and allenes, respectively. Specifically, we have shown that the C-H bond of a terminal methyl group of an alkyl chain can be oxidatively added to the anchored transition-metal ion M{sup +} (Scheme II). The insertion is followed by a {beta}-hydrogen shift (5 {yields} 6) or {beta}-cleavage of the C-C bond (5 {yields} 7) to generate intermediates from which eventually reductive elimination of H{sub 2} of ligand detachment occurs. This discussion will be confined to recent results from our laboratory. While most of the data will be concerned with the chemistry of aliphatic nitriles, the reactions of alkynesmore » with bare transition-metal ions will be briefly mentioned.« less




Journal ArticleDOI
TL;DR: In this paper, a triplet-derived flexible chain Biradical intermediates are considered, where the radical centers are close together and two processes ensue: ISC in a given conformation produces a singlet biradical in the same conformation and internal rotation gives rise to chain dynamics, which changes the end-to-end distance.
Abstract: A large number of thermal and photochemical reactions proceed via biradical intermediates. Typically, a biradical generated in the triplet state must first undergo intersystem crossing (ISC) to the singlet biradical before forming products. This presents one of the major challenges of photochemistry; to understand a reaction in which the molecule must hop from one potential energy surface to another. In this Account we are concerned with triplet-derived flexible chain biradicals, and Scheme I shows the important processes. A triplet precursor (e.g., an {sup 3}n, {pi}* ketone) cleaves with conservation of spin to produce a triplet biradical in a set of conformations where the radical centers are close together. Two processes ensue: ISC in a given conformation produces a singlet biradical in the same conformation, and internal rotation gives rise to chain dynamics, which changes the end-to-end distance.


Journal ArticleDOI
TL;DR: Indirect detection allows one to monitor species that normally do not give a response as mentioned in this paper, and it has grown from an intellectual curiosity to become an extremely useful tool for monitoring species.
Abstract: Indirect detection allows one to monitor species that normally do not give a response. It has grown from an intellectual curiosity to become an extremely useful tool. For volume displacement, polarimetry gives the best results. For charge displacement, ion chromatography and capillary zone electrophoresis are ideal situations for applying indirect fluorescence detection. LOD surpasses all but the most specialized detection schemes. Future developments in systems specially designed for indirect detection should make these schemes even more powerful.





Journal ArticleDOI
TL;DR: In this paper, data is presented on some of the significant structure-property relations in the various cuprate superconductors, distilled from the recent literature and substantially based on their own contributions to this area.
Abstract: High-temperature superconductivity constitutes the most sensational discovery of recent times. Since these new superconductors are complex metal oxides, chemistry has had a big role to play in the investigations. For the first time, stoichiometry, structure, bonding, and such chemical factors have formed central themes in superconductivity, an area traditionally dominated by physicists. These oxide superconductors have given a big boost to solid-state chemistry. In this Account, data is presented on some of the significant structure-property relations in the various cuprate superconductors, distilled from the recent literature and substantially based on our own contributions to this area. We shall first present the essential features of the La{sub 2-x} (Ca, Sr, Ba){sub x} CuO{sub 4} and LnBa{sub 2}Cu{sub 3}O{sub 7} systems and then discuss the bismuth and thallium cuprate superconductors.