bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of Reaction of Organometallic Complexes
Authors: Atwood Jim D. , Rosenberg Edward 
Published: March 2006

AbstractAn overview of the mechanistic features of organometallic reactions is presented. The primary mechanistic types discussed are ligand substitution, oxidative addition, reductive elimination, and electron transfer. Each reaction pathway is discussed within the context of the common electron counts encountered for most organometallic complexes. Examples of how these common reaction pathways extend to polynuclear complexes are also presented. Although reasonable generalizations with regard to overall reaction rates and stepwise mechanisms using the electron count formalism can be made, many recent reports point out that the details of ligand and metal center structure can override these general trends. A considerable amount of quantitative rate data is provided and computational methodologies for understanding the observed rates are discussed.
MetalloregulationBased in part on the article Metalloregulation by Robert P. Hausinger which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Rouault Tracey A. , Philpott Caroline C. 
Published: March 2006

AbstractMetalloregulation refers to the concept that living organisms from bacteria to mammals must orchestrate the processes of metal import, utilization, sequestration, and export to optimize availability of metals for use in metabolism. Metals are required for the function of many proteins, but metals can also be toxic because free metal ions may react with protein, nucleic acid, and lipid contents of cells. In general, metals are transported across membranes by specific unidirectional transporters, and cells and organisms regulate the abundance of specific transporters and metal sequestration proteins to meet their needs. Changes in abundance result mainly from changes in either the rate of transcription, the stability of mRNA, the translation rate, or the stability of the metal protein. Complex regulatory frameworks exist to govern metal homeostasis in virtually all cells and organisms. Usually a central component of a successful regulatory network is a protein that registers metal availability by directly binding the metal ion that requires regulation. Metal binding then drives a change in function of the central regulatory protein, which usually has multiple regulatory targets that include transporters, chaperone proteins, sequestration molecules, and others. In this chapter, we focus on the main regulatory proteins of iron homeostasis in bacteria, yeast, plants, and mammals, and those involved with regulation of zinc homeostasis in bacteria and yeast. We describe the sensing mechanism and targets of the bacterial transcription factor, fur, and the yeast transcription factors known as Aft 1 and 2. In mammals, we focus on the sensing and regulatory mechanisms utilized by iron regulatory proteins (IRPs) and on the role of the peptide hormone hepcidin in physiologic regulation of iron metabolism. In zinc homeostasis, we focus on the bacterial transcription factors Zur and Znt 1, and the yeast transcription factor, Zap1. References for regulation of copper, manganese, and nickel metabolism are cited for further reading. Nature has produced a wide variety of solutions to the important question of how cells and organisms can ‘sense’ their metal status and modify gene expression to ensure that metals are appropriately available for use in metabolism.
MetallothioneinsBased in part on the article Metallothioneins by Milan Vašák & Jeremias H. R. Kägi which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Vašák Milan , Romero‐Isart Núria 
Published: March 2006

Abstract

Metallothionein (MT) is a generic name for a superfamily of ubiquitous low molecular weight cysteine‐ and metal‐rich proteins or polypeptides possessing sulfur‐based metal clusters. In these compounds, clusters are usually formed through the preferential coordination of d
10
metal ions by an array of closely spaced cysteine thiolate ligands. Their preservation in an increasing number of three‐dimensional structures of these proteins signifies the importance of this structural motif. The versatile and striking chemical reactivity of clusters in MTs and their unprecedented dynamics make this class of proteins highly unusual. A primary role of MTs has not been identified, and remains elusive, as further functions continue to be discovered.
Mixed Donor LigandsBased in part on the article Mixed Donor Ligands by Nikolay N. Gerasimchuk & Kristin Bowman‐James which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Lawrance Geoffrey A. 
Published: March 2006

Abstract
Mixed donor ligands are extremely common and are linear, branched, or cyclic molecules that contain at least two different donor groups capable of chelation to metal ions by those groups as polydentate ligands. The most common donor atoms met are N, O, S, and P, although other donors such as group 14 elements (including C) are known. Whereas mixed donor ligands are considered classically to involve groups with different donor atoms (such as N from an amine and O from a carboxylate), different classes of donor groups of one type of donor atom (such as pyridine and amine groups) also effectively produce mixed donor ligands. The coordination chemistry of mixed donor ligands is very extensive; all metal ions form mixed donor complexes, and the number of isomers possible for complexes with mixed donors is usually greater than with symmetrical ligands of comparable denticity.
Molybdenum: Inorganic & Coordination Chemistry
Authors: McCleverty Jon A. 
Published: March 2006

Abstract
The inorganic and coordination chemistry of molybdenum is described, being presented according to ligands and/or donor atom set (halides, cyanides, ligands containing O, S, Se, Te, N, P, or As‐donor atoms) and are discussed in relation to oxidation state. Special mention is made of metal–metal bonded dinuclear species, a brief description of polyoxoanionic species is given, and tri‐ and tetranuclear cluster compounds and some species of higher nuclearity containing chalcogenide atoms are described.
Molybdenum: Organometallic ChemistryBased in part on the article Molybdenum: Organometallic Chemistry by M. David Curtis which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Flower Kevin R. 
Published: March 2006

Abstract
This article considers only compounds that contain a direct molybdenum‐to‐carbon bond. Because of the size of the topic and the large number of publications each year, the article gives a general overview of major current areas of interest in molybdenum‐centered organometallic chemistry. The material is presented in three major sections: σ‐ligand‐containing complexes, which covers alkyl‐, carbonyl‐, halocarbonyl‐, alkylidenes‐, and alkylidyne complexes, heavier group 14 analogs of alkylidene and alkylidyne complexes; π‐ligand‐containing complexes, which covers alkene‐, polyene‐, alkyne‐, phosphaalkyne‐containing complexes, along with π‐bound cyclic organic systems such as cyclobutadiene, cyclopentadienyl, and arenes; polymetallic complexes and multiply bonded systems are also discussed. Each section considers the major methods of preparation of compounds containing that ligand class and surveys the major types of reaction they undergo, both metal‐ and ligand‐centered, along with the factors that influence the products that form. Where data is available, solid‐state structural data are presented to aid in the discussion of the material presented.
Niobium & Tantalum: Inorganic & Coordination Chemistry
Authors: Hubert‐Pfalzgraf Liliane G. 
Published: March 2006

Abstract

The chemistry of niobium and tantalum ranges from oxidation states +V to −III with no species of oxidation state −II known so far. The chemistry of those oxophilic metals is dominated by their highest oxidation states, V and IV. Pentahalides especially chlorides are the most usual starting material. They form numerous complexes especially with hard donors and are used for access not only to pentavalent metal alkoxides, amides, thiolates, and so on but also to most molecular species in lower oxidation states. Oxo species are formed quite easily by O‐donor abstraction reactions or adventitious hydrolysis. Pentavalent alkoxides are active in various catalytic processes and are useful precursors for access to oxide ceramics such as ferroelectrics via the formation of heterometallic species. The most relevant results in organometallic chemistry of Nb and Ta have been obtained with ancillary, bulky aryloxide or siloxide ligands. Niobium is more prone to reduction than tantalum. Chalcogenides and chalcogenohalides are often one–dimensional solids and display a rich structural and synthetic chemistry. Numerous trispyrazolylborate derivatives of Nb and Ta have been reported for oxidation states V to I. The development of the nonaqueous chemistry of those elements in intermediate oxidation states has become an active and fruitful area. Species based on MM or MM multiple bonds, the latter especially for Nb, have been characterized. The NbNb triple bond (2.20 Å) is much shorter than the MM distance in the metal. Tri‐ or divalent species are able to promote CE (E = O, S, N) cleavage and thus to generate novel ligands because of the trend of Nb and Ta to form multiple ME bonds and attain their highest oxidation states. CC coupling reactions are observed with unsaturated ligands (alkynes, nitriles, etc.). M
III
η
2
‐alkyne complexes have a metallocyclopropene character; they can react with unsaturated organic molecules via stoichiometric reactions. The reservoir of electrons of the MM bond is also of interest for activation of small molecules such as N
2
, H
2
, CO, and so on. Tri or tetradentate N,N; N,P; or N,O ligands have been used to stabilize dimeric dia or paramagnetic dinitrogen complexes. The bridging, highly activate N
2
ligand is amenable to functionalization in some cases, and cleavage into nitrides has been observed. The chemistry of reduced Nb and Ta halides is rich in clusters with nonintegral oxidation states (between III and I). Hexanuclear clusters dominate the aqueous chemistry for these oxidation states. One of their potential applications could be their use as contrasting agents. The species in the lowest oxidation states are essentially based on carbonyl ligands.
Nitrides: Transition Metal Solid‐State ChemistryBased in part on the article Nitrides: Transition Metal Solid State Chemistry by Peter Ettmayer & Walter Lengauer which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Lengauer Walter , Eder Alexander 
Published: March 2006

Abstract

Basic properties and properties interesting for applications of transition metal nitrides are presented in this article. Starting from crystal chemistry, bonding, and preparation, the article also briefly discusses analytical chemistry of chemical and physical nitrogen analysis and standardization as well as thermodynamics. Updated portions of phase diagrams of group 4–6 transition metals with nitrogen are presented. A substantial part is devoted to the solid‐state properties because they make nitrides interesting for application. The presentation of these properties includes hardness, thermal expansion, nitrogen diffusivity, thermal properties, electrical conductivities, superconductivities, and elastic properties. Several of these properties are given as a function of temperature and composition. The topic is closely connected to article (
see
Carbides: Transition Metal Solid‐state Chemistry).
Noble Gases: Inorganic ChemistryBased in part on the article Noble Gases: Inorganic Chemistry by Boris Žemva which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Atwood David A. 
Published: March 2006

Abstract
The noble gas (Ng) elements have a rich reaction chemistry despite having a filled valence shell that would indicate otherwise. Halide compounds, usually with fluorine, and various oxides are common. There is also a growing class of carbon and nitrogen derivatives. A wide range of neutral and cationic noble gas compounds can be formed as long as the added elements, or combinations of elements, possess sufficient electron affinity. The range of compounds, along with characterization data and brief bonding descriptions will be presented for each element. Many of the compounds serve as starting materials for other derivatives, including the rapidly growing field of noble gas containing transition metal complexes. For example, there is now a broad range of salts containing transition metals. The article will conclude with a brief overview of the many unusual and disparate applications being found for these elements.
Noncrystalline Solids
Authors: Adam Jean‐Luc , Lucas Jacques 
Published: March 2006

Abstract
This review deals with the formation and physical properties of noncrystalline materials in oxide and nonoxide systems. Structural aspects are also developed. Oxide materials are silica‐based glasses, borate, and phosphate glasses, while nonoxide systems include halide and chalcogenide glasses. They are described in terms of chemical compositions and thermal and optical properties. Special attention is paid to the unique properties of nonoxide glasses for infrared‐light transmission and rare earth emissions. Some applications in the fields of infrared optics, infrared fiber sensors, fiber lasers, and amplifiers are shown. In a special section, the formation and properties of metallic glasses are presented, with special focus on chemical, magnetic, and mechanical properties.
Nucleic Acid–Metal Ion Interactions
Authors: Kazakov Sergei A. , Hecht Sidney M. 
Published: March 2006

Abstract

Nucleic acids (DNA and RNA) are actually salts (or complexes) of metal ions from a chemical point of view. It is impossible to separate the behavior of DNA and RNA from their interactions with metal ions. Metal ions are usually required to promote and stabilize functionally active or native conformations of nucleic acids, as well as to mediate nucleic acid‐protein interactions. However, certain metal ions can also cause structural transformation of nucleic acids, and induce their chemical modification and cleavage. Metal‐nucleic acid interactions are involved in nucleotide biochemistry; genetic information storage and transfer, and control of gene expression, as well as in mutagenesis and carcinogenesis. However, in most cases, it is not currently clear whether the observed effects actually result from direct metal ion‐nucleic acid interaction, since other species, such as specific proteins, may be mediators between the metal ion and the nucleic acid in these processes
in vivo
. Interest in metal‐nucleic acid interactions is also enhanced by studies of the mechanisms of antitumor activity of certain platinum metal compounds, finding metal ions in crystal structure of natural RNA molecules, studies of the mechanism of RNA catalysis and possible involvement of metal ions in origin of life, as well as by the use of metal ions as structural probes of nucleic acids and as biotechnology tools. This article does not attempt to be comprehensive, but rather presents selected examples to illustrate key facets of metal ion‐nucleic acid interaction. The focus is on the chemical and structural properties of both nucleic acids and metal ions relevant to their interactions. Nucleic acid‐metal interactions can be either nonspecific or dependent on the chemical nature, sequence, and structure of nucleic acids. However, the specificity of these interactions is dependent on structural and chemical properties of both the nucleic acids and the metal ions. Both nucleic acids and metal ions exhibit considerable complexity in their interactions, and such interactions could affect the chemical and biochemical properties of both species.
Oligomerization & Polymerization by Homogeneous Catalysis
Authors: Hlatky Gregory G. 
Published: March 2006

AbstractThe 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.
Osmium: Organometallic Chemistry
Authors: Shapley Patricia A. 
Published: March 2006

Abstract
Organometallic complexes of osmium include those with sigma bonds between the metal and the organic moiety, such as metal–alkyl complexes, or π bonds, such as metal–alkene complexes. The osmium alkyl complexes include homoleptic alkyls and complexes with ancillary carbonyl, cyclopentadienyl, arene, or alkene ligands. Because osmium complexes are stable in higher oxidation states than either ruthenium or iron, oxidative addition of CH bonds to form alkylidene and alkylidyne complexes is very common. Metal–ligand bonds also tend to be stronger in osmium complexes than in complexes of the lighter elements of this group. Because of the stability of OsOs bonds, there are many bimetallic and cluster complexes of osmium and these species have an extensive reaction chemistry. Selective oxidation reactions of unsaturated organic molecules dominates the catalytic chemistry of this metal. Mechanistic studies on the activation of molecular oxygen and oxygen transfer reactions by organoosmium complexes have provided insights into catalytic oxidation chemistry.
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: March 2006

AbstractOrganophosphorus 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: March 2006

Abstract

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.
Peptide–Metal InteractionsBased in part on the article Peptide–Metal Interactions by Justin K. Moran & Claude F. Meares which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Meares Claude F. 
Published: March 2006

Abstract
Copper–peptide complexes have been the most extensively studied of all the metal–peptide complexes. Copper(II) is the most important oxidation state in copper–peptide complexes, although copper(III) can be stabilized by coordination to peptides. The deprotonated peptide nitrogens help stabilize the higher oxidation state of copper; therefore the more deprotonated peptide nitrogens, the more stable the copper(III) complex. The copper(II) complexes of GlyGlyProGly and (GlyGlyProGly)2 are very similar. At low pH, both peptides bond through the amino nitrogen and carbonyl oxygen of the first peptide linkage. The peptides GlyGlyProLys and (GlyGlyProLys)2 initially form 1N complexes with copper(II). With luteinizing hormone‐releasing hormone the copper(II) is coordinated via the imidazole nitrogen and two deprotonated peptide nitrogens. With angiotensin II, the copper(II) is bonded via the imidazole nitrogen of the histidine residue and two deprotonated peptide nitrogens. The dipeptide TyrPro bonded copper(II) through the amino nitrogen and the peptide carbonyl. Since there was no ionizable hydrogen on the peptide nitrogen, there was no bonding by the peptide nitrogen. The copper(II)AVP (vasopressin analog) complex is one of the most stable 4N copper–peptide complexes known. Owing to their similarities, nickel(II)–peptide complexes are usually studied along with copper(II) complexes. In neutral to acidic solutions, the nickel is coordinated through the amino nitrogen and the carbonyl oxygen (1N). When the pH is raised to 9.0, nickel(II) substitutes for a peptide hydrogen, and the coordination changes. In NiH1L complexes of cysteine‐containing dipeptides, the nickel is coordinated via the amino and deprotonated peptide nitrogens and the thiol group. Zinc‐peptide complexes are less stable. With the dipeptides Ala–His and Gly–His at high pH, zinc(II) was shown to form complexes coordinated through the amino nitrogen, deprotonated peptide nitrogen, and the imidazole nitrogen. Unlike copper(II), both palladium(II) and platinum(II) are soft acceptors and as such are expected to coordinate to soft donors like sulfur and aromatic nitrogen donors in residues such as Met and His, and deprotonated peptide nitrogens. Early investigations of metals showed that divalent metals such as copper(II), cobalt(II), and nickel(II) could catalyze the hydrolysis of amino acid esters. Mechanisms of cobalt(III)‐mediated peptide‐bond cleavage have been investigated; because cobalt(III) complexes bind to the N‐terminal amino acid residue of peptides, only the N‐terminal peptide bond is hydrolyzed. Complexes containing iron can cleave peptide bonds, as can complexes of palladium or platinum.