bluuebunny/crossref_metadata_2025 huggingface dataset:
Oligomerization & Polymerization by Homogeneous Catalysis
Authors: Hlatky Gregory G.
Published: December 2011

The metal‐catalyzed oligomerization and polymerization of alkenes by homogeneous metal complexes has not only provided extraordinary insights into the chain‐growth process, it has also become of increasing commercial importance in delivering products of greater purity or improved properties. Novel materials not accessible using conventional heterogeneous catalysts can now be synthesized. Metals are no longer constrained to certain functions (titanium for polymerization, nickel for oligomerization) but span the range of molecular weights and polymer structures. This review discusses the fundamentals of chain‐growth polymerization catalyzed by homogeneous complexes and new developments in the field.
Organic Synthesis using Transition Metal Carbonyl Complexes
Authors: Söderberg Björn C. G.
Published: December 2011

Synthetic transformations using transition metal carbonyl carbene, arene, diene, and alkyne complexes are discussed. Reaction of synthetic importance and applications in organic total synthesis are included.
Osmium: Inorganic & Coordination Chemistry
Authors: Collinson Simon R. , Schröder Martin
Published: December 2011

The general features and coordination chemistry of Os are discussed in the context of the use of different ligand types to stabilize complexes of OsVIIIthrough to Os−II. The complexation chemistry with cyanide, N‐, P‐, O‐, S‐, and halide‐donor ligands is detailed. The asymmetric dihydroxylation and aminohydroxylation of alkenes, general coordination chemistry with macrocyclic and open chain ligands, porphyrin complexes, photophysical properties and electrochemistry of OsIIcomplexes of heterocyclic ligands and comparisons to their RuIIanalogues, and electron transfer in heterobimetallic and dendrimer complexes of OsIIare all highlighted.
Oxidation Catalysis by Transition Metal Complexes
Authors: Crabtree Robert H.
Published: December 2011

Oxidation catalysis is reviewed with emphasis on radical versus nonradical pathways, autoxidation, and mechanistic studies. Bioinorganic model catalysts are discussed, including the distinction between monooxygenase and dioxygenase pathways. Some organic synthetic applications as well as applications to green chemistry are discussed. Finally some organometallic oxidation catalysts are discussed.
Oxygen: Inorganic ChemistryBased in part on the article Oxygen: Inorganic Chemistry by Donald T. Sawyer which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Bharara Mohan S. , Atwood David A.
Published: December 2011

The present review will provide a systematic and complete coverage of the formation, chemical properties, and reactivity of a wide range of common oxygen‐containing species. These include dioxygen, ozone, hydrogen peroxide, oxide, superoxide, and hydroxide, as well as the radical forms of most of these species.
P‐Donor LigandsBased in part on the article P‐Donor Ligands by Charles A. McAuliffe & Anthony G. Mackie which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Schier Annette , Schmidbaur Hubert
Published: December 2011

Organophosphorus compounds of various types are among the most important classes of ligands in the coordination chemistry of the transition elements. This is particularly true for the tertiary phosphines R3P, which are known to stabilize complexes of metals in low oxidation states, while secondary and primary phosphines, R2HP and RPH2, are less common. The donor properties and the stereochemistry can be tuned by using carefully designed substitution patterns. More recently, organophosphorus compounds with low‐coordinate phosphorus atoms have also been employed as ligands in metal complexes. These include mainly phosphaalkenes and phosphaalkynes, phosphinidenes, diphosphenes, phosphinines, phosphonium cations, and even elemental phosphorus.
Palladium: Organometallic Chemistry
Authors: William Suggs J.
Published: December 2011

Four oxidation states of palladium are encountered in organometallic chemistry. In order of importance, they are Pd
II
, Pd
0
, Pd
IV
, and Pd
I
. With the reduction of palladium from Pd
II
to Pd
0
, the metal changes its reactivity from electrophile to nucleophile. Ligands π‐bound to Pd
II
, such as π‐allyl, alkene, and alkyne, show enhanced reactivity toward nucleophiles, particularly less basic nucleophiles such as malonates. Pd
0
species, such as (PR
3
)

n

Pd, are powerful nucleophiles. They undergo oxidative addition to alkyl, aryl, and vinyl halides to produce LnPd
II
‐R species. If the R group is an alkyl group with β‐hydrogens, a beta‐elimination of H usually takes place, giving a palladium hydride and an alkene. If the R group is aryl or vinyl, the species does not undergo beta‐elimination. Instead, if a second R′ group is bonded to the palladium center, reductive elimination can take place, forming R–R′. Alternatively, the PdR bond can add across an unsaturated group, such as an alkene, forming a new carbon–carbon bond. New carbon–palladium bonds can also form through transmetalation. Organotin, organoboron, organosilicon (and other main group and transition metal organometallic reagents) will react with Pd
II
halides to give new Pd
II
‐R bonds and R
3
SnX (or analogous) species. Because Pd
II
‐C bonds are neither very strong nor very weak (on the order of 160 kJ mol
−1
), palladium can catalyze many organic reactions. For example, in the Suzuki reaction, an aryl boronic acid (ArB(OH)
2
) and an aryl halide (Ar′X) are coupled to form a biaryl, Ar–Ar′. The mechanism involves a Pd
0
species undergoing oxidative addition to the Ar′X, forming L

n

Pd
II
Ar′(X), then transmetalation giving a L
n
Pd
II
Ar(Ar′) and, finally, reductive elimination forming Ar–Ar′ and regenerating L

n

Pd
0
. Palladium‐catalyzed reactions are increasingly being used in the synthesis of high value‐added chemicals such as pharmaceuticals. With basic, hindered phosphine ligands, such as P(
t
‐Bu)
3
, Pd
0
reagents undergo oxidative addition even with aryl chlorides, and new reactions, such as the arylation of amines (ArX + HNR
2
giving ArNR
2
) are possible.
Paramagnetic Organometallic Complexes
Authors: Leznoff Daniel B. , Mund Garry
Published: December 2011

The synthesis, characterization, and reactivity of paramagnetic (or open‐shell) organometallic species are described. Many stable complexes featuring transition metals, lanthanides, and actinides have been reported. These systems, which are exceptions to the 18‐electron rule (or 16‐electron rule), are increasingly being used in the catalytic realm, and also have different reactivity patterns compared to their diamagnetic counterparts due to the presence of the unpaired electrons. The formation and subsequent stability of paramagnetic organometallic complexes in violation of the 18‐electron rule can be explained via molecular orbital theory in terms of (1) the use of π‐donor ligands (as opposed to the ubiquitous π‐acceptor ligands usually found in organometallic chemistry); (2) kinetic stabilization with sterically demanding ligands; (3) partially filled molecular orbitals being nonbonding or slightly antibonding/bonding. Although metallocene‐based complexes are probably the most well studied of all paramagnetic organometallic complexes, homoleptic σ‐alkyl complexes and other non‐Cp systems have also been explored. Such non‐Cp ancillary ligands include amido‐, alkoxo‐, and thiolato‐ligands, β‐diketiminate ligands, and tris(pyrazolylborate) ligands. f‐electron organometallic systems also utilize a similar range of ligands, but due to their larger size, they can accommodate more sterically congested coordination spheres; for example, Cp*3M complexes can be prepared, and they show unusual reactivity pathways.

Open‐shell organometallic molecules are known to span a range of electron counts from 8–20. Nineteen‐electron organometallic complexes are of particular interest with respect to the location of the extra electron residing primarily on the metal or on the ligand (in this case, the complex is referred to as an 18 + δ system).

The discussion of short‐lived paramagnetic organometallic systems revolves around 17‐ and 19‐electron radicals, and their use in catalytic processes and as ‘super reducing agents.’ Many reactivity pathways for such organometallic radicals (or ‘metalloradicals’) have been identified.

Characterization tools for paramagnetic organometallic complexes, such as NMR and ESR spectroscopy, DFT calculations, and magnetic measurements are presented. Variable temperature NMR studies and2H NMR can be of significant use in interpreting paramagnetic NMR spectra. Solid‐state NMR spectroscopy of paramagnetic organometallic systems is still in its infancy. The applications of paramagnetic organometallic complexes span many areas including catalysis (e.g. olefin polymerization), synthetic organic chemistry, and the development of molecule‐based magnetic materials.
Phosphorus–Nitrogen CompoundsBased in part on the article Phosphorus–Nitrogen Compounds by Robert H. Neilson which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Haiduc Ionel
Published: December 2011

Phosphorus displays several oxidation states (+II,+III, +IV, and+V) and coordination numbers (from one to six), and with nitrogen (also two‐, three‐, and four‐coordinate) can form a broad variety of compounds (purely inorganic or organo‐N‐ or ‐P‐substituted). In addition to mononuclear PN compounds, many short‐chain, polymeric, and cyclic compounds based on molecular skeletons formed by PN alternation are known. There are numerous classes of phosphorus–nitrogen compounds, and this article makes an attempt to introduce the most important ones in the limited space available by selecting what seem to be the most illustrative examples from a very rich chapter of chemistry.
Phosphorus: Organophosphorus Chemistry
Authors: Engel Robert , Cohen JaimeLee Iolani
Published: December 2011

The chemistry associated with compounds bearing at least one carbon–phosphorus bond has been surveyed. This survey has been organized on the basis of the coordination about the phosphorus center, beginning with monocoordinated phosphorus and continuing through hexacoordinated phosphorus. Preparations, stereochemistry, and reactivity are principal topics considered.
Photochemistry of Transition Metal Complexes: TheoryBased in part on the article Photochemistry of Transition Metal Complexes: Theory by Jeffrey I. Zink which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Daniel Chantal
Published: December 2011

The most significant developments in quantum chemistry and wave packet dynamics that provide the theoretical tools to study the electronic spectroscopy and photoreactivity of transition metal complexes are presented. The difficulties inherent to this class of molecules as well as the degree of maturity of the theoretical approaches are discussed. Recent applications in the chemistry of transition metal complexes are selected to outline and to illustrate the necessity for a strong interplay between theory and experiments.
Platinum: Inorganic & Coordination Chemistry
Authors: Crabtree Robert H. , Torrens Hugo
Published: December 2011

The articlePlatinum: Inorganic & Coordination Chemistryincludes some historical highlights related to this metal as well as some properties and uses of platinum. Its inorganic and coordination chemistry is illustrated briefly through some specific chemical compounds and reactions. Binary compounds with halides, chalcogen, and related ligands are described. Platinum oxidation states 0 to IV are deal with on separated headings: compounds of Pt(0) predominantly with phosphine ligands; complexes of ‘monovalent’ platinum with PtPt bonds; Pt(II) with a large range of ligands; ‘trivalent’ platinum compounds and finally Pt(IV) bound to a variety of donor atoms. Nearly 70 references help the reader to follow specific topics.
Platinum: Organometallic ChemistryBased in part on the article Platinum: Organometallic Chemistry by Charles M. Lukehart which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Chen Jwu‐Ting
Published: December 2011

This article aims to describe the prominent advances of organoplatinum chemistry in the latest decade. Recent development in this field has been much advanced with the design of new ancillary ligands as well as new organic ligands. For the former, the polydentate cyclometallated ligands, tridentate pincer ligands, nitrogen‐donor ligands, and aminocarbenes are discussed. For the latter, in addition to the synthesis and structure of new organoplatinum compounds, a noteworthy growth is to exploit some of these compounds for luminescent materials. The content in this regard is brief since it has been covered as an independent article of this volume. Organoplatinum species with unprecedented bonding modes or new organometallic functionalities are discussed separately. The progress of nano sciences prompts the conceptual revolution in the whole frontier line of chemical research. Organoplatinum chemistry has been contributing in a profound way to construction of the new substances of large skeletons. Exploration starting from clusters and molecular assemblies to organometallic polymers, particularly with rational design, is addressed. Reactions involving the SiH, SiSi, CH, and CC bond formation or cleavage are crucial to hydrosilylation and alkane functionalization respectively. Platinum‐silylene chemistry accounts for a major breakthrough in synthetic chemistry. As to platinum‐hydrides that are mainly concerned in Pt(IV)‐state and are key intermediates in alkane activation, their syntheses and structures are discussed in Section 5. Platinum(IV)‐alkyls are the theme of Section 6. The reaction mechanisms of Pt(II)/Pt(IV) involving aqueous CH activation and other reactions or catalysis involving organoplatinum are summarized at the end.
Polynuclear Organometallic Cluster Complexes
Authors: Keister Jerome B.
Published: December 2011

The title refers to molecular compounds containing three or more transition metal atoms and hydrocarbyl ligands as a part of the metal–carbon cluster core. Because the chemistry of trimetallic clusters is the most well developed, these examples are to be stressed. Selected examples are presented to illustrate the principles of structure and bonding of organometallic clusters, synthetic approaches, and chemical reactions, including ligand substitution, oxidative addition, intramolecular insertion, protonation of metal–metal bonds and coordinated ligands, nucleophilic attack on coordinated ligands, and ligand fluxionality. The chemistry of these clusters is exemplified by trimetallic clusters containing hydrocarbon fragments of one, two, or three carbon atoms. While, many of the features of cluster chemistry are common with those of organometallic complexes containing a single metal atom, there are notable differences in structures and reactivities owing to the tendencies of ligands to bridge between two or more metal atoms and for ligands bound to only a single metal atom to undergo facile intramolecular migrations between metal atoms. These distinctions give rise to the ‘metal‐cluster‐metal surface analogy’ in which structural and spectroscopic features of organometallic clusters are used as models for hydrocarbons chemisorbed on metal surfaces.
Polyoxometalates
Authors: Pope Michael T.
Published: December 2011

The elements of groups 5 and 6, especially vanadium, molybdenum, and tungsten in their highest oxidation states, form a vast range of polyoxoanions that can incorporate most other positive‐valent elements of the periodic table. The first examples of these complexes were discovered in the latter half of the nineteenth century, but it is only within the last few decades that the extraordinary variety and numbers of polyoxoanion structures, properties, and applications have begun to be recognized. The field has historically been divided into isopoly‐ and heteropolyanions according to whether one or more than one type of positive‐valent element is incorporated, respectively. The largest variety of isopolyanions is found with V, Mo, and W, and the results of speciation studies in aqueous solution are summarized. The structures of heteropolyanions are dependent upon the coordination demands of the heteroatom, and the major types based on 4‐, 6‐, 8‐, and 12‐coordination are described. In virtually every case, the V, Mo, and W atoms (addenda atoms) occupy MO6octahedra with one or two (cis) unshared oxygen atoms. Such octahedra share vertices and edges with their neighbors. Structures in which one or more (adjacent) MO6octahedra have been ‘removed’ can be prepared by the control of solution pH, and the resulting lacunary anions are used as precursors to generate new, larger structures and derivatives. Since the addenda atoms are in their highest oxidation states (d0), many polyoxoanions can reversibly accept variable numbers of electrons to yield mixed‐valence heteropoly ‘blues’ (d0,d1) with delocalized hopping electrons and ‘browns’ (d0,d2) with metal–metal bonds. Several strategies for the synthesis of derivatized and functionalized polyoxoanions with organic and organometallic groups are reviewed since this has been a major thrust in the field in recent years. Also, a recent development has been the discovery of extremely large polyoxoanions with 100 + metal atoms that are readily prepared and are stable in aqueous solution. Examples are the mixed‐valence polymolybdate wheels (Mo154and Mo176) and tungstate(VI) assemblies (W184Ln16). Polyoxoanions have long been used in analytical chemistry, and their use as heterogeneous and homogeneous acid and oxidation catalysts continues to be developed. Other applications, especially in structural biology (imaging, crystallographic phasing) and medicine (antiviral and antitumoral agents) are also important.
Polyphosphazenes
Authors: Allcock Harry R.
Published: December 2011

Polyphosphazenes comprise the largest class of inorganic polymers. During the past 10 years, new synthetic developments have arisen that allow carefully tailored macromolecules to be assembled with precise chain lengths and with access to star geometries and a range of hybrid phosphazene‐organic polymer systems. This has stimulated research in the use of polyphosphazenes in biomedicine, optoelectronics (photonics), lithium battery technology, and fuel cell membranes, as well as in new elastomers and hydrogels.
Quasicrystals
Authors: King R. Bruce
Published: December 2011

Quasicrystals are solid materials exhibiting diffraction patterns with apparently sharp spots containing symmetry axes such as fivefold or eightfold axes, which are incompatible with the three‐dimensional periodicity associated with crystal lattices. Many such materials are aluminum alloys that exhibit diffraction patterns with fivefold symmetry axes; such materials are called icosahedral quasicrystals. The location of atoms in quasicrystals requires the use of six‐dimensional crystallography. However, a polyhedral shell structure using a number of polyhedra of icosahedral symmetry provides a three‐dimensional model for the structure of many icosahedral quasicrystals.
Rhodium: Inorganic & Coordination Chemistry
Authors: Jardine Fred H.
Published: December 2011

The element and its binary compounds are discussed, including specific discussions of the range of available oxidation states. Complexes of Rhodium(I), (II), and (III) receive attention, together with a discussion of nitrosyl complexes.
Ruthenium: Organometallic ChemistryBased in part on the article Ruthenium: Organometallic Chemistry by Ulrich Koelle which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: White Rosemary E. , Hanusa Timothy P.
Published: December 2011

In the slightly more than half a century that the organometallic chemistry of ruthenium has had time to develop, it has become clear that the metal's position as the ‘middle child’ of the Group 8 metals is richly reflected in its organometallic derivatives. That is, despite many similarities in the compounds of the iron–ruthenium–osmium triad, addition and elimination reactions of ruthenium, for example, are slower than those of iron but are more facile than those of osmium. Similarly, complexes with hydride and alkyl bonds are generally more stable for ruthenium than for iron, but the ruthenium compounds are often unstable or highly fluxional compared to analogous osmium species. Carbonyl cluster complexes are an important feature of organoruthenium chemistry, and mixed‐ligand carbonyl species with high nuclearity are known, in some cases with more than 10 ruthenium atoms. Interstitial carbides and nitrides are often encountered in ruthenium clusters, and carbonyl hydrides are of interest as hydroformylation catalysts (conversion of alkenes to aldehydes). The cyclopentadienyl ligand is found extensively throughout organoruthenium chemistry, and with a decomposition temperature around 600°C, the sandwich complex ruthenocene Ru(C
5
H
5
)
2
is among the most stable organometallic compounds known. The stability of ruthenocene and its derivatives allow them to be incorporated as labels into biomolecules such as peptides. Ruthenocene derivatives have also been studied as potential second‐order nonlinear optical materials, and they have played a central role in the development of 30 valence electron triple‐decker cations of the iron group. The high ligand field stabilization of Ru
II
enables combinations of π‐acceptor ligands together with even the hardest σ‐donors, such as carbonate, sulfate, or nitrate, and hence Ru
II
carbonyl and phosphine complexes are known with myriad coligand combinations having O, N, or S binding functionalities. In particular, the ability of the (η‐arene)Ru moiety to bind N‐ and O‐ligands has been used to complex various amines, imines, Schiff bases, and amino acids to generate diastereomeric salts, which can serve as chiral catalysts; they are valuable in stereoselective organic syntheses and in the production of biologically active compounds.
Semiconductor Interfaces
Authors: Tan Ming X. , Bansal Ashish , Lauermann Iver , Shreve Gary A. , Lewis Nathan S.
Published: December 2011

This article describes the properties of semiconductors that are responsible for the operation of rectifiers, transistors, photovoltaic devices, and light emitting. The penetration of the electric field and the electric potential into a bulk semiconductor phase yields a nonuniform carrier concentration in the sample, and produces contacts that either attract or repel specific types of charge carriers. Chemical control over these electric fields is crucial to the technology of semiconductor contacts. In principle, such control can be established through a simple variation in the electrochemical potential of the contacting phase. In practice, this ideal model often does not apply, and other factors influence or completely determine the interfacial electric field strength. The application of these principles is described for semiconductor/semiconductor, semiconductor/metal, semiconductor/liquid, and semiconductor/polymer contacts, making the approach valuable for understanding the operational principles of a variety of technologically important semiconductor devices.
Semiconductors
Authors: Stanton Colby E. , Nguyen SonBinh T. , Kesselman Janet M. , Laibinis Paul E. , Lewis Nathan S.
Published: December 2011

The structural, electronic, optical, and electrical properties of semiconductors are treated within a common framework. The bonding in the lattice determines the band structure of the solid, which is used to describe the chemical, optical, and electrical properties of the semiconductor. These concepts enable this process to be understood from a qualitative, chemically based viewpoint.
Short‐Lived Intermediates
Authors: Almond Matthew J. , Jenkins Samantha L.
Published: December 2011

Methods for the generation and detection of short‐lived intermediates are discussed. These include flow systems (where a steady‐state concentration of the intermediate is monitored), flash photolysis (where the intermediate is studied in real time using a very fast detection method), and matrix isolation (where the intermediate is preserved by trapping in a solid, inert host at low temperature and where conventional spectroscopic methods are used for detection). Many of the classical experiments utilizing these methods are described, but the relevance to modern chemical studies is also emphasized. The spectroscopic methods used to detect short‐lived intermediates are considered. These include nuclear magnetic resonance (NMR), electron spin resonance (ESR), microwave, infrared (IR), Raman, and ultraviolet‐visible absorption and emission spectroscopies. It is shown that IR remains the method of choice for matrix‐isolation experiments whereas flash photolysis work tends to rely mainly upon electronic spectroscopic techniques. The use of IR spectroscopy, using tunable lasers, for flash photolysis work (at least for slightly longer‐lived intermediates) is discussed. Finally two case studies are considered in detail. These are the photolysis of metal carbonyls and the formation of unusual main group compounds at high temperatures. These studies exemplify the procedures that have been used to investigate short‐lived intermediates in inorganic chemistry.
Silicon: Inorganic Chemistry
Authors: Lickiss Paul D.
Published: December 2011

Silicon is an element of vital importance in many areas of modern synthetic chemistry, the electronics industry and in materials science. This article attempts to summarize the many types of important inorganic derivatives of silicon but excludes the chemistry of silicates and zeolites, which are covered in separate articles. The isolation of elemental silicon from sand is described together with the various methods of purification of the element for use in the semiconductor industry. A brief description of the occurrence of silicon in biology is also given. The bulk of the article deals with compounds of silicon organized according to coordination number. One‐coordinate compounds are short‐lived intermediates and are described briefly. Two‐coordinate compounds, silylenes, have become increasingly important in recent years as are transition metal complexes in which they act as ligands. The use of bulky substituents has allowed stable silylenes to be isolated and their chemistry is described. Three‐coordinate compounds comprise radicals, cations, anions, and silanes (compounds containing a double bond to Si). These species are also generally short‐lived and reactive. The bulk of the article deals with four‐coordinate compounds and is organized according to the substituents at silicon. The industrially important hydrosilanes and halosilanes are described together with the mixed halohydrosilanes and the less common pseudohalosilanes. Alkoxysilanes are also industrially important and these are discussed with other oxygen derivatives such as esters and silanols. Compounds containing SiN bonds are also common and have interesting structural features. The preparation and structures of transition metal complexes containing silyl ligands is described. This is followed by a description of compounds containing silicon with coordination number five or six. The final section describes the analytical methods for the determination of the composition and structure of inorganic silicon compounds. Compounds containing SiC bonds are excluded throughout.
Silicon: Organosilicon Chemistry
Authors: Sakurai Hideki
Published: December 2011

An overview of the chemistry of organosilicon compounds from the first synthesis in 1863 to the latest results is presented. After an introduction, classes of compounds and nomenclature are briefly described. Synthesis of organosilicon compounds is then disucssed systematically. Characteristic points of structure and bonding of organosilicon compounds, including tetrahedral and polyhedral compounds are described. Important σ–π conjugation (sigma‐pi conjugation) and σ*–π conjugation (sigma*‐pi conjugation) in organosilicon compounds are discussed in relation to structure and reactions. Reactions of organosilicon compounds are classifed into ionic and hemolytic (nonionic) reactions and various reactive intermediates including silyl radicals, silylium ions (silyl cations), silyl anions, and silylenes are described. Recent developments in kinetic stablization of these reactive intermediates are then summarized. In relation to kinetic stablization, silicon‐containing multiple bonds, silaaromatics, and silicon polyhedranes are described. Lastly, two important applications of organosilicon compounds, namely polymers and organic synthesis, are described briefly.
Silver: Inorganic & Coordination ChemistryBased in part on the article Silver: Inorganic & Coordination Chemistry by W. Ewen Smith which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Mak Thomas C. W. , Zhao Xiao‐Li
Published: December 2011

The present review is a complete rewrite of the original article in the first edition. The new version provides concise and up‐to‐date information on the inorganic and coordination compounds of silver in oxidation states ranging from subvalent to Ag(IV). Literature coverage is extended to October 2004, and pertinent references are listed for the convenience of the interested reader.

The presentation is organized under the following headings: 1. Introduction; 2. Subvalent silver compounds; 3. Silver(I) compounds (under subheadings: 3.1 Halides and pseudohalides; 3.2 Phosphorus donor ligands; 3.3 Nitrogen donor ligands; 3.4 Oxygen donor ligands; 3.5 Chalcogen donor ligands; 3.6 Silver‐rich compounds); 4. Silver(II) compounds; 5. Silver(III) and silver(IV) compounds; 6. Catalysis. The structural features of the compounds are described, and specific examples are illustrated with five figures.

For the most important +1 oxidation state of silver, particular emphasis is placed on recent highlights and advances in new areas such as double and multiple salts of silver, silver(I) polyhedra with encapsulated acetylenediide (C
2
2−
) species (symbolized as C
2
@Ag

n

), argentophilic Ag(I)⋯Ag(I) interaction in supramolecular assembly, halide‐centered Ag

n

cages, mixed‐metal clusters, and silver‐rich chalcogenide supercluster complexes. Modern application of inorganic silver catalysts, of both achiral and chiral types, to organic synthesis is presented with selected examples from the recent literature.
Stereochemical Nonrigidity of Organometallic Complexes
Authors: Faller John W.
Published: December 2011

Compounds that undergo intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges are described as stereochemically nonrigid. Analysis of 1D and 2D NMR spectra as a function of temperature often allow the rates, as well as the mechanisms of interconversion of conformers or isomers, to be determined. Examples were selected to illustrate the importance of stereochemical nonrigidity in reactivity and the potential for affecting stereochemistry in the products of reactions.
Sulfur: Inorganic Chemistry
Authors: Woollins J. Derek
Published: December 2011

The inorganic chemistry of sulfur is described. Oxides and oxy‐anions, halides are reviewed.
Sulfur: Organic PolysulfanesBased in part on the article Sulfur: Organic Polysulfanes by Ralf Steudel & Monika Kustos which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Atwood David A. , Zaman M. Kamruz
Published: December 2011

Organic polysulfanes are compounds of the type RSnR with n > 2. They may be chain‐like or cyclic. The organic residues (alkyl or aryl) are linked to the sulfur atoms via carbon atoms. In the literature these compounds are often termed as organic polysulfides, but the IUPAC recommended nomenclature is polysulfanes. Sulfur‐rich organic polysulfanes can be viewed as intermediates between organic and inorganic compounds. On one hand, they are characterized by organic substituents R, which terminate the sulfur chain or close this chain to form a ring. On the other hand, compounds with sulfur chains of three or more sulfur atoms are ‘inorganic’ enough to attract the interest of inorganic chemists who have contributed much to this area. Organic polysulfanes with up to 16 sulfur atoms in the molecules have so far been obtained as pure substances, but species with up to 35 sulfur atoms in a chain or ring have been prepared in mixtures. Organic polysulfanes play an important role not only in basic research and industry, they are also found as natural products in organisms and occur in the inanimate nature. The main importance of organic polysulfanes comes, however, from their role in the large scale industrial vulcanization of natural and synthetic rubber. In this article, the preparation, structure, modern analysis, basic reactions, natural occurrence, biological activity, and practical importance of organic polysulfanes with three or more neighboring sulfur atoms in a chain or ring have been presented.
Technetium: Organometallic ChemistryBased in part on the article Technetium: Organometallic Chemistry by Ronald J. Clark which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Rochon Fernande D.
Published: December 2011

The chemistry of organometallic technetium compounds is discussed along with its application in the field of nuclear medicine. Several99mTc radiopharmaceuticals are presently used in hospitals using a99Mo−99mTc generator to prepare the starting material [99mTcO4]−. The isotope99mTc is a γ‐ray emitter. The most common organometallic radiopharmaceutical is [Tc(MIBI)6]+, where MIBI is an isonitrile ligand.99mTc can be produced only at the tracer level and it disintegrates to the longer life isotope99Tc, which has a half‐life of 2.12 × 105years. The chemistry of technetium has been studied with the latter isotope, which is commercially available. But it emits weak β−particles and special precautions must be taken in the laboratories in order to avoid health problems.

Most of the publications in the literature on organometallic Tc compounds contain the ligands CO, isonitriles or the cyclopentadienyl ion. These π‐accepting ligands usually bind to Tc in a low oxidation states. Tc‐CO compounds are the ones who have been most studied. Binary compounds and a great variety of mixed‐ligands complexes are discussed. The new complex ion [Tc(CO)3(H2O)3]+is particularly important, since a kit was recently developed for its preparation. It should open a new field for the development of99mTc radiopharmaceuticals. It can bind to biomolecules like proteins, peptides, and antibodies which have very specific targets.

Several Tc‐cyclopentadienyl complexes have the sandwich or the piano stool structures. The arene compounds should have similar structures, but the latters have not been much studied yet. No Tc‐arene compound seem to have been characterized by crystallographic methods yet. But more recently, interest in the arene complexes has increased because of its potential use in nuclear medicine. Isonitriles or isocyanides and cyanide ligands are bonded to Tc through the C atom. A few crystal structures on mixed‐ligand isonitrile Tc complexes were determined and the segment TcCNC is linear. Fewer cyanide Tc compounds were studied. Finally a few Tc‐alkyl compounds have been reported.
Thallium: Organometallic ChemistryBased in part on the article Thallium: Organometallic Chemistry by William S. Rees, Jr. & Gertrud Kräuter which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Pike Robert D.
Published: December 2011

The organometallic chemistry of thallium(I) is dominated by cyclopentadienyl complexes. These may be polymeric through bridging Cp arrangements or oligomeric as a result of Tl⋯Tl contacts. ThCp complexes are easily prepared and are highly useful Cp‐transfer agents. There are two known Tl(I) organometallics with direct TlC σ‐bonds; one is monomeric and the other is tetrameric due to Tl⋯Tl contact. A variety of Tl(I) π‐complexes are recognized. Bonding in the latter tends to be fairly weak.

Two R2TlTlR2dimers (R = silyl group) are known, but no such Tl(II) complexes are known for carbon ligands. The chemistry of organothallium(III) compounds is more extensive, encompassing such species as R3Tl, R2TlX, RTlX2(X = anionic ligand), and complexes of these species with additional ligands. A wide array of X‐ray crystal structures for Tl(III) complexes reveals monomeric, oligomeric, and polymeric arrangements, with bridging ligands being very common.

Thallium compounds are highly toxic and should be handled with great care. Volatile Tl species are of use in the chemical‐vapor deposition of superconducting phases. Finally, Tl(III) salts are fairly important reagents in organic syntheses, especially in oxidations and in ring expansion and contraction reactions.
Tin: Organometallic Chemistry
Authors: Wardell James L. , Spencer Gavin M.
Published: December 2011

Frankland produced the first organometallic tin compound, Et
2
SnI
2
, in 1849. Since that time a wide range of tin compounds containing SnC bonds have been prepared. This article will detail the synthesis and characterization of these compounds. This will include a description of tetraorganotin compounds, halides, pseudohalides, hydrides, tin‐tin bonded compounds, radicals, group 15, and group 16 derivatives. The industrial and environmental aspects of these compounds will also be discussed.
Transition Metal Carbonyls: Infrared Spectra
Authors: Timney John A.
Published: December 2011

The number, pattern, and position of the CO‐stretching absorptions (ν(CO)) of transition metal carbonyls gives considerable information about molecular structure, symmetry, and bonding. This article deals with the processing of the basic data (number, frequency, and intensity of ν(CO) bands) to give useful information about carbonyl‐containing organometallic compounds via an ‘energy factored force field’ (EFFF). The reasons why the EFFF works so well and the relationships between different types of force constant within the EFFF are examined. The application of these force constants in elucidating molecular structure is discussed, together with the very successful ligand effect model that enables chemists to predict ν(CO) frequencies with remarkable accuracy.
Tungsten: Organometallic ChemistryBased in part on the article Tungsten: Organometallic Chemistry by Andreas Mayr which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Pamplin Craig B. , Hayton Trevor W. , Legzdins Peter
Published: December 2011

This article surveys the organometallic chemistry of tungsten in a systematic manner according to the various types of complexes known to contain tungsten–carbon bonds. The first section deals with complexes having the inorganic ligands CO (carbonyl), CNR (isocyanide), and CN (cyanide) in the metal's coordination sphere. The second and by far the largest section considers tungsten complexes containing organic ligands. This section is divided into subsections dealing with compounds having η1‐hydrocarbyl ligands (i.e. alkyl and aryl complexes, vinyl and alkynyl complexes, carbene complexes, and carbyne complexes), η2‐hydrocarbon ligands (i.e. alkene complexes and alkyne complexes), η3‐hydrocarbon ligands (i.e. allyl complexes), η4‐hydrocarbon ligands (i.e. diene complexes), η5‐hydrocarbon ligands (i.e. cyclopentadienyl complexes), and η6‐hydrocarbon ligands (i.e. arene complexes). Within each category of complex, the material is generally presented in the following order: common methods of synthesis of these complexes, their characteristic physical properties, and their representative chemical properties. The latter are usually illustrated by examples taken from the literature published since 1992, the final year of coverage by the first edition of the Encyclopedia of Inorganic Chemistry. Other articles in the current encyclopedia also cover some aspects of this chemistry, most notably, alkene and alkyne metathesis reactions mediated by organotungsten complexes, the organometallic chemistry of di‐ and polynuclear tungsten complexes, and tungsten compounds containing main group element ligands. Consequently, these topics are not specifically discussed in this article.
Vanadium in Biology
Authors: Wever Ron , Renirie Rokus , Hasan Zulfiqar
Published: December 2011

In this article, the role of vanadium in a number of biological systems will be discussed. The metal oxide (vanadate) is present as the prosthetic group in the haloperoxidases, enzymes that are able to oxidize halides in the presence of hydrogen peroxide to hypohalous acids. The bromoperoxidases seem to be involved in the production of the huge amounts of brominated compounds formed by several seaweeds. The enzymes have unusual properties in terms of stability and structural organization. X‐ray structures at high resolution are available now for four vanadium haloperoxidases and details of the events occurring at the active site during catalysis are known. The metal oxide binds peroxide in a side‐on fashion and seems to acts as a Lewis acid in polarizing the bound peroxide for further nucleophilic attack by an incoming halide. These enzymes are also able to mediate in the presence of hydrogen peroxide, the enantioselective sulfoxidation of organic sulfides yielding chiral sulfoxides with high enantiomeric excess. The active site of the haloperoxidases is very similar to that found in acid phosphatases that hydrolyze phosphate monoesters and there is some evidence that the haloperoxidases have evolved from the phosphatases. Vanadium is found in the vanadiumIIIstate in certain blood cells of tunicates (Ascidians) under very acidic conditions. Despite many studies, there is no clue as to the physiological role of the metal and there are many questions regarding the mechanism of accumulation and reduction of the metal in these organisms. The metal also seems to be used as an electron sink by certain bacteria under anaerobic conditions. Furthermore, vanadium is accumulated in Amanita species. These toadstools contain up to 10 mM of a vanadiumIVcompound with very special structure in which the vanadiumIVis eightfold coordinated in an unusual geometry. Although the compound has been reported to carry out redox reactions, the physiological function is elusive.
Zinc:DNA‐Binding Proteins
Authors: Pennella Mario A. , Giedroc David P.
Published: December 2011

Zinc‐containing nucleic acid‐binding proteins are ubiquitous in nature and interact with all types of nucleic acids, including ssDNA, duplex DNA, and RNA. The primary role played by these Zn(II) coordination complexes is to provide local or global stability to these proteins that function in transcriptional regulation, DNA metabolism, and nucleic acid packaging. These proteins are now broadly designated as zinc finger (zf) proteins. Six structural classes of zf proteins are discussed here that are distinguished from one another on the basis of the secondary and tertiary structure of the zf domain, the nature of the ligating side chains (Cys and/or His), and the linear spacing of amino acid ligands in the primary structure. These structural zinc sites are compared with metalloregulatory zinc coordination complexes found in metal‐sensing transcriptional regulatory proteins that control zinc homeostasis in bacteria (e.g.E. coliZurR and ZntR;S. aureusCzrA;SynechococcusSmtB), lower eukaryotes (S. cerevisiaeZap1), and mammalian cells (MTF‐1). Structural and functional comparisons of the bacterial zinc sensors with homologous sensors specific for other transition metal ions (e.g. Cu, Ni, Mn) and xenobiotics (e.g. Cd, Pb, and Hg) suggest that coordination number and therefore geometry are primary determinants of metal selectivity of metal sensor proteins in vivo.
Zinc: Inorganic & Coordination ChemistryBased in part on the article Zinc: Inorganic & Coordination Chemistry by Reg H. Prince which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Burgess John , Prince Reg H.
Published: December 2011

Alloys and salts of zinc have been known for many centuries; commercial production of the metal dates from early in the eighteenth century. Of the several million tons now produced annually, by electrolytic and smelting processes, much is used in alloys, in batteries, in corrosion prevention, and in the manufacture of a range of compounds with various uses. In particular, zinc oxide and zinc chloride have a large number of uses, detailed in this article. Zinc sulfide is both one of the main zinc ores and the archetype for the two main structural forms of 4:4‐coordinated structures (zinc blende and wurtzite). Many zinc compounds and complexes have interesting structural, spectroscopic, optical, magnetic, and conductivity properties, some of which are of actual or potential value in technical and industrial applications. Zinc‐containing species have also proved valuable in synthesis and self‐assembly of a range of supramolecular structures. Both in the solid state and in solution zinc exhibits a range of coordination numbers, though tetrahedral and, especially in solution, octahedral stereochemistries dominate. Zinc forms a variety of complexes, especially with nitrogen, oxygen, sulfur, and halide donor ligands. Many of these complexes show high stability, but they are generally labile in solution. Zinc plays an essential role in biology, being a key constituent of at least 200 metalloproteins. It is an essential element in human nutrition, but toxic in large quantities. Many zinc complexes have been synthesized as biochemical models; a few zinc salts are used in dietary supplements.
Zinc: Organometallic ChemistryBased in part on the article Zinc: Organometallic Chemistry by Gerard Parkin which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Grévy Jean‐Michel
Published: December 2011

Since the discovery of the first organozinc compounds by Sir Edward Frankland in 1849, the organometallic chemistry of zinc made remarkable advances and organozinc species have become essential tools for organic chemists. During the past decade, numerous new and modified procedures for the preparation of the title compounds have been published, rendering their synthesis easier, faster, and less expensive and giving higher yields. The coordination chemistry of organozinc derivatives has been subject of further interest and various intra‐ and intermolecular complexes with different donor ligands have been structurally characterized by X‐ray crystallography and spectroscopic methods. The accumulation of molecular structures, physicochemical studies, and computational calculations has led to a better understanding of the organozinc chemistry, and consequently to the design of new derivatives for specific applications. Even if the development of areas like the chemistry of organozinc anions and cations is still in its early stage, these compounds, which exhibit properties different than those of the parent organometallic species, appear to have promising applications in synthesis and catalytic reactions. During the past ten years, the chemistry of organo‐gem‐dizincio derivatives has also been the subject of much interest and progress. These reagents can form two carbon–carbon bonds in a one‐pot reaction and with high stereoselectivity. They became key reagents for organic chemists who want to combine multiple transformations in one operation. The importance of organometallic compounds of zinc can be seen in the growing number of their applications in synthesis. They are used in many reactions such as substitutions, additions to carbonyl compounds and unsaturated systems, cyclopropanations, and polymerizations. Furthermore, as a result of their low reactivity, they tolerate a wide variety of functionalities and perform most of the transformations with high regio‐ and enantioselectivity. After spending more than half a century in the shade of Grignard and organolithium reagents, organozinc reagents are becoming more and more important in modern chemistry.