bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gold: Organometallic Chemistry
Authors: Schier Annette , Schmidbaur Hubert 
Published: March 2006

Abstract
Organogold chemistry reaches back to the beginning of the twentieth century, when Grignard compounds were first reacted with chloroauric acid. Since then, the number of organogold compounds has grown rapidly and now includes species with gold in various oxidation states (0, +1, +2, and +3) and with virtually all classes of organic substituents and ligands (alkyl, alkenyl, alkynyl, ylide, heteroaryl, ylide, carbonyl, isocyanide, carbenes, alkenes, alkynes, etc.). This development was possible owing to the discovery of many new synthetic pathways that reflect the general upsurge of organometallic chemistry in the last century and to the introduction of new physical and analytical methods as routine tools for the determination of composition and structure. Incentive and motivation for organogold research were also triggered by the emerging applications of gold and its compounds in medicine and pharmacology, as well as in many areas of modern technology, with material science and homogeneous and heterogeneous catalysis as the most prominent examples. The discovery of a novel type of bonding interactions, most common between low‐valent gold atoms with a closed‐shell electronic configuration (aurophilicity), has led to a rapid growth of the supramolecular chemistry of gold. The aggregation of mononuclear compounds to give dimers, oligomers, polymers, and clusters was found to induce novel photophysical properties (luminescence etc.), which attract widespread interest. In polynuclear compounds, aurophilic bonding is responsible for unique configurations and conformations of molecules, including clustering of gold atoms around hypercoordinate carbon atoms as one of the most curious phenomena.
Heterogeneous Catalysis by Metals
Authors: Ma Zhen , Zaera Francisco 
Published: March 2006

Abstract
Approximately 80% of the processes in the chemical industries require the use of catalysts. Because of that, catalysis generates annual global sales of about $1.5 trillion, and contributes directly or indirectly to approximately 35% of the world's GDP. Most catalytic processes are heterogeneous in nature, and often rely on the use of transition metal particles dispersed on high surface area supports. In this chapter, the basic chemical concepts behind heterogeneous metal catalysis are introduced. Examples are then provided for typical practical catalytic systems used in the generation of energy, the production of chemicals, the preparation of materials, and the cleaning of the environment. Finally, several promising new research directions related to the future development of heterogeneous metal catalysis are highlighted, in particular those associated with the designing and characterization of novel catalytic materials, the surface science of catalysis, high throughput catalyst testing, improved selectivities, and green chemistry.
Hydrogenation & Isomerization of Alkenes
Authors: Jardine Fred H. 
Published: March 2006

AbstractAlkenes are isomerized by complexes of late, second or third series transition metals. This occurs either by successive β‐hydride abstraction reactions or, more rarely, by a π–allylic mechanism. Both decyclization and annulation reactions of strained, cyclic hydrocarbons are catalyzed by these complexes. Palladium complexes are active catalysts for the Cope‐ and Claisen rearrangements. Homogeneous, catalytic hydrogenation can occur via three possible routes. Ruthenium complexes catalyze transfer hydrogenation. Catalyst modifications can be made to minimize by‐product formation during hydrogenation or deuteriation.
Hypervalent CompoundsBased in part on the article Indium: Inorganic Chemistry by Dennis G. Tuck which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Sean McGrady G. , Steed Jonathan W. 
Published: March 2006

Abstract
The chemistry of compounds formally exhibiting more than eight valence electrons is introduced and surveyed. The review covers the definition and representation of hypervalent bonding and its orbital description, including recent developments in electron localization function calculations. The synthesis and reactivity of hypervalent compounds is examined including their use in organic synthesis, along with the factors contributing to their stability. Techniques for determining the structures of hypervalent species are described, including gas‐phase electron diffraction and vibrational and NMR spectroscopic methods. Novel hypervalent intermediates and transition states are also surveyed, including recently appreciated inter‐ligand hypervalent interactions. Particular emphasis is placed on the important topic of pentacoordination. The review includes chemistry of the halogens, chalcogens, pnictides, noble gases, tin, silicon, and a variety of transition metals.
Intercalation Chemistry
Authors: Jacobson Allan J. , Nazar Linda F. 
Published: March 2006

AbstractThe term ‘intercalation’ refers to a process whereby a guest molecule or ion is inserted into a host lattice. The structure of the guest–host or intercalation compound is only slightly perturbed from the host structure and the reaction used to form the compound is reversible.In this chapter, the major classes of host lattice are classified by both dimensionality and electronic properties. In three‐dimensional systems, the sizes of the guest species are constrained by the dimensions of the host lattice. In lower dimensional systems, no such restriction exists and the strongly bonded layers or chains can adjust their separation freely to accommodate guest species of different sizes. With increasing guest size, the structural correlation between layers or chains is diminished and in the limiting case, complete separation of single layers or chains occurs in solution, resulting in the formation of colloidal dispersions.Insulating host lattices undergo reactions that involve ion exchange, acid–base chemistry, solvent exchange, and sorption of neutral molecules from the gas phase. The insulating hosts have a fixed concentration of ionic guests that remains unchanged throughout subsequent reactions. The conducting host lattices have the feature that the concentration of ionic guest species can be altered by oxidation or reduction of the host. The chemistry of most compounds involves reduction and cation intercalation with the major exceptions of graphite and some layered oxides, which can be both reductively intercalated with cations and oxidized with anion insertion.The present understanding of the mechanism of intercalation with particular emphasis on layered structures is reviewed. Reactions involve adsorption of guest species on host crystals, exchange or insertion at the host surface, the formation of intermediate stages in layered compounds, and transport within the host lattice. Macroscopic effects such as variations in crystal size, dislocations, stacking faults, and pore mouth blockage can strongly influence the reaction kinetics.The major classes of host lattices in each category and their chemical behavior are described. The insulating materials discussed include zeolites, clays, layered double hydroxides, acid phosphates, and layered oxides while graphite, C60, carbon nanotubes, transition metal chalcogenides, metal phosphorus trisulfides, metal oxyhalides, metal nitride halides, and metal oxides are the major examples of conducting hosts. In the case of metal oxides, examples of both reductive intercalation of lithium ions and oxidative intercalation of oxide ions are discussed. These two types of intercalation reactions are important for lithium batteries and high‐temperature superconductivity, respectively.
Lead: Organometallic ChemistryBased in part on the article Lead: Organometallic Chemistry by R. Bruce King which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Sharma Hemant K. , Pannell Keith H. 
Published: March 2006

AbstractAn update on the organometallic chemistry of lead since 1995 is presented. In particular the exciting chemistry associated with the synthesis, structure and reactivity plumbylenes, diplumbynes and related species are presented. In addition an extensive section on organolead transition metal complexes of is presented, an area not previously covered.
Mercury: Inorganic & Coordination ChemistryBased in part on the article Mercury: Inorganic & Coordination Chemistry by Gregory J. Grant which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Bebout Deborah C. 
Published: March 2006

Abstract

Mercury is one of the oldest known elements. The element exhibits surprisingly different chemistry from its congeners zinc and cadmium, and it is the only group 12 member without a known beneficial biological role. Unique properties associated with the element and its compounds have led to diverse applications. However, many of these are being phased out to minimize further increases in the environmental and atmospheric burden with this toxic heavy metal. Motivations to study the compounds and complexes of mercury include potential for discovery of novel properties such as high‐temperature superconductivity and improved understanding of its interactions in physiological systems. Valuable characterization of mercury‐containing compounds is possible with
199
Hg NMR techniques.

Mercury is the only group 12 member to have a stable monovalent state. Observed primarily in the oldest known and most common of all metal polycations, Hg
2
2+
, this metal–metal bonded species readily disproportionates into Hg
2+
and Hg
0
. Mercury(I) compounds, typically, have a linear structure of type XHgHgX. Halides, oxy salts, oxides, and coordination compounds with oxygen and weakly basic nitrogen‐donor ligands are best known for Hg
2
2+
.

The most prevalent ionization state of mercury, Hg
2+
, is a d
10
metal ion, which lacks strong coordination number and geometry preferences. As a result, structural characterization of its compounds by X‐ray crystallography is particularly critical. A wide range of halides, pseudohalides, and chalcogenides of Hg
2+
are known. The softness of Hg
2+
has led to an investigation of coordination, with a wide variety of sulfur ligands and physiological sulfur donors being assumed to be the most important. Mercury(II) typically has a stronger affinity for S‐, N‐, and P‐donors than any other divalent metal ion. However, Hg
2+
also has a tendency to undergo incredibly rapid ligand exchange. Recent studies have shown that sterically demanding multidentate ligand systems can suppress ligand exchange processes.
Mercury: Organometallic ChemistryBased in part on the article Mercury: Organometallic Chemistry by Richard C. Larock which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Rais Daniela , Vilar Ramón 
Published: March 2006

Abstract
Over the past 10 years, a wide range of new organomercury compounds have been prepared and their reactivity extensively studied, leading to interesting applications in organic synthesis. The solvomercuration of alkenes is still the most widely employed organometallic reaction of mercury, although there have been important advances in the use of the mercury‐mediated ring opening of cyclopropanes. Several structural investigations of organomercurials have been recently carried out providing detailed information on the connectivity of a wide range of mono‐ and polymercuric complexes. In this article, an overview of the most important advances on the organometallic chemistry of mercury between 1993 and 2003 will be provided.
Metathesis Polymerization Processes by Homogeneous Catalysis
Authors: Wagener Kenneth B. , Boncella James M. , Smith Dennis W. 
Published: March 2006

AbstractAlkene polymerization reactions proceeding by homogeneous metathesis catalysis are reviewed. Fundamental mechanistic aspects of these reactions are discussed with special emphasis on ring opening metathesis polymerization and acyclic diene metathesis polymerization chemistry.
Mixed Valence Compounds
Authors: Fackler John P. 
Published: March 2006

AbstractThe concept of mixed valence has referred to compounds in which a given element exists for an appropriate time in what can be described as more that one formal oxidation number. Clearly it is a formalism that has limited meaning when electron delocalization occurs on a timescale at or near the frequency of vibrations. The formalism that historically has been valuable, the Robin and Day classification, classifies such substances into three types depending upon an ability of experiment to identify well defined oxidation states. When electron transfer occurs readily between these mixed valence species, the concept of mixed valence may lose its meaning. These types of compounds are of considerable interest today since the nature of the bonding connecting the components influences significantly the electronic properties of the material. Understanding these factors is needed to help us develop and understand organic and ionic high‐Tcsuperconductors.
Nickel Enzymes & Cofactors
Authors: Ragsdale Stephen W. 
Published: March 2006

Abstract

This review covers the structure and function of the eight known Ni enzymes, with a focus on the chemistry and biology of the metallocenter. For the Ni redox enzymes, the Ni ion exhibits versatility in redox properties in exploiting the +3/+2 (superoxide dismutase and hydrogenase), the +2/+1 (hydrogenase, CO dehydrogenase, acetyl‐CoA synthase, and methyl‐CoM reductase), and perhaps even reaching the 0 (acetyl‐CoA synthase) states for the redox enzymes. On the other hand, the nonredox Ni enzymes (urease, glyoxylase‐I, aci‐reductone dioxygenase) apparently remain in the +2 state during catalysis. The Ni site(s) in these enzymes adopt a wide variety of coordination environments; some form mononuclear square planar or octahedral complexes, while others are homo‐ or hetero‐ (with iron) dinuclear with oxo or thiolato bridges and still others join heteromultinuclear clusters. Acetyl‐CoA synthase contains the most complex Ni metallocenter yet described, which is a [4Fe–4S]
2+
cluster bridged by a cysteine thiolate to a binuclear NiNi center. The three‐dimensional structures of all these enzymes are known and some (acetyl‐CoA synthase, aci‐reductone dioxygenase, CO dehydrogenase, and superoxide dismutase) have been determined in the past two years leading to a significant reinterpretation of spectroscopic results. In many Ni enzymes, density functional theory has begun to play a major role in assigning active‐site structures and testing mechanistic hypotheses.
Nickel: Inorganic & Coordination Chemistry
Authors: Collinson Simon R. , Schröder Martin 
Published: March 2006

AbstractThe general features and coordination chemistry of Ni0to NiIVand complexation to cyanide, N‐, P‐, O‐, S‐, and halide‐donor ligands are detailed. The reactivity of NiIIcomplexes in the template synthesis of macrocycles and for the oligomerization and polymerization of alkenes are highlighted. The stabilization of radical NiIand NiIIIcenters is related to the associated ligand types and metal‐ion stereochemistries. The supramolecular chemistry of NiIIincludes the formation of aggregates, framework polymers, and receptors. The structures of a number of Ni‐containing enzymes have been elucidated and the formation of low‐molecular weight complex mimics is discussed.
Nickel: Organometallic ChemistryBased in part on the article Nickel: Organometallic Chemistry by Clifford P. Kubiak which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Zargarian Davit 
Published: March 2006

Abstract
The organometallic chemistry of nickel has experienced rapid growth over the past decade. A number of exciting new areas have emerged, such as the reactivities of Ni(0)‐carbene complexes and the polymerization of olefins catalyzed by nickel complexes of nitrogen‐based ligands. In addition, the traditionally rich area of Ni‐catalyzed organic transformations has undergone major developments that have expanded the scope of their applications. These are the subjects of the present chapter.
Among the topics that will be discussed are the preparation, characterization, and reactivity studies of nickel complexes of allyl, cyclopentadienly, indenyl, and tris(pyrazolyl)borate ligands. The main structural and bonding properties of these complexes are presented and their major reactivities are outlined. Another topic of importance is the chemistry of the nickel complexes of hydride, alkyl, alkenyl, and silyl ligands. Hydrido and alkyl complexes of nickel are often involved in many catalytic processes of commercial importance, and so an in‐depth understanding of the fundamental reactivities of these complexes is crucial to expanding their practical applications. Silyl complexes are involved in the transformations of organosilicon compounds, and for this reason their basic reactivities and structural properties are of interest.
Zerovalent nickel complexes are also very important in the catalytic organic transformations. One of the most exciting developments in this area is the recent introduction of N‐heterocyclic carbene ligands. Ni complexes of these ligands have been shown to be important catalysts and reagents for a number of important organic transformations. Some of the practical methods for preparing Ni‐carbene complexes will be outlined, and the recently reported catalytic reactions promoted by these complexes will be described.

One of the most important areas of growth for the chemistry of nickel has been the polymerization and copolymerization of olefins. Thus, this chapter will describe the discovery of a family of diimine complexes that catalyze the polymerization of aliphatic olefins. A series of new and highly efficient catalysts were introduced in rapid progression, a great deal of new chemistry has been discovered, and a number of industrial processes have been developed on the basis of these nickel complexes. We will also discuss the emergence of new strategies for the efficient cross‐coupling of alkyl halides with organozinc and Grignard reagents, as well as the coupling of dienes with CO
2
.
Nitrogen Monoxide (Nitric Oxide): Bioinorganic Chemistry
Authors: Lancaster Jack R. , Giles Gregory I. 
Published: March 2006

AbstractIn only the last 20 years, Nitric oxide (NO, nitrogen monoxide), one of the smallest and simplest molecules in Nature, has been found to be involved in an astounding number of mammalian physiological and pathophysiological phenomena. The importance of NO as a messenger molecule in the cardiovascular system was recognized in 1998 by the awarding of the Nobel Prize in Physiology or Medicine and over 70000 papers have appeared involving NO in biology. The simplicity of its chemical structure stands in stark contrast to the complexity of its biological actions, including its “Janus‐faced” character as both beneficial and detrimental. This chapter is an overview of the history of this discovery, the fundamental chemistry of NO and its derivatives in the biological environment, and the multiple biological actions of NO.
Nitrogenase: Metal Cluster Models
Authors: Barrière Frédéric 
Published: March 2006

Abstract

This article reviews the synthesis and properties of inorganic clusters that model the iron–sulfur centers found in the nitrogenase enzyme. These sites are of the Fe
4
S
4
, Fe
8
S
7
, and MoFe
7
S
9
stoichiometry. The enzyme [Fe
4
S
4
]
2+/1+
center is well modeled by synthetic clusters bearing thiolate ligands at iron. However, the [Fe
4
S
4
]
0
state is stabilized in the enzyme and has not been reproduced in the laboratory so far. Recent progress in synthetic models of the Fe
8
S
7
P‐cluster is reported. One of its known structures can be obtained by self‐assembly from basic constituents, or synthesized in a stepwise fashion from smaller clusters yielding topological analogues. The most challenging cluster to model is the FeMo‐cofactor. This MoFe
7
S
9
center is the site of dinitrogen reduction to ammonia. The cluster also exists with vanadium or iron in place of molybdenum in alternative nitrogenases. It was shown only recently that the FeMo‐cofactor is centered on a light atom that is probably a nitrogen atom. Structural modeling of this center is limited. Only its molybdenum or heterometal end has been accurately modeled. Functional chemistry of good structural models, those with sulfur ligands and metal–metal bonds, only concerns the reduction of already partially reduced diazo substrates such as diazene or hydrazine.
Nitrogenase Catalysis & AssemblyBased in part on the article Nitrogenases & the Iron–Molybdenum Cofactor by Paul W. Ludden which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Hu Yilin , Schmid Benedikt , Ribbe Markus W. 
Published: March 2006

AbstractNitrogenases are metalloenzymes that catalyze biological N2fixation, in which dinitrogen is reduced to ammonia. The best‐characterized molybdenum nitrogenase is composed of the iron (Fe) protein that contains a [4Fe–4S] cluster and the molybdenum–iron (MoFe) protein that contains an [8Fe–7S] cluster (P cluster) and a [Mo–7Fe–9S–homocitrate] cluster (FeMo cofactor).The catalysis of molybdenum nitrogenase occurs in a series of steps. First, the reduced Fe protein binds 2MgATP, undergoes a conformational change, and forms a complex with the MoFe protein. Then, coupled with the hydrolysis of 2MgATP, one electron is transferred from the Fe protein to the MoFe protein within the complex. This is followed by complex dissociation, which allows the enzyme to start the next cycle of electron transfer. Once a sufficient amount of electrons is accumulated on the MoFe protein, substrate reduction takes place.The assembly of the molybdenum nitrogenase Fe protein involves thenifHand at least thenifS, nifU, andnifMgene products that are implicated in the [4Fe–4S] cluster assembly, while the assembly of the MoFe protein requires at least 15nifgene products and involves the biosynthesis and insertion of the FeMo cofactor into the MoFe protein.
Oxide Catalysts in Solid‐State ChemistryBased in part on the article Oxide Catalysts in Solid State Chemistry by Toshio Okuhara & Makoto Misono which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Okuhara Toshio , Kamiya Yuichi 
Published: March 2006

AbstractThis chapter deals with catalysis of metal oxides containing single elements and more than two metallic elements. The metal oxides catalyze typically selective oxidation and acid‐base reactions. The first section outlines factors controlling catalyst performance (activity, selectivity, and durability), which are categorized into geometric (crystal plane and surface defects) and material‐intrinsic factors. Catalysis of the metal oxides is illustrated in detail by examples such as BiMoO, MoVTeNbO, VPO, Perovskite‐type oxide, and heteropoly compounds. Catalyst performances of these metal oxides are discussed from the viewpoint of geometric aspects. For the heteropoly compounds, their synthetic methods, chemical properties, and porosities are also described. Solid acid and base catalysts are finally summarized.