Boron compounds Subject

To date, the most extensively studied polyboron hydride compounds in BNCT research have been the icosahedral mercaptoborane derivatives Na2[B22H22SH] and Na [(B22H22S)2], which have been used in human trials with some, albeit limited, success. New generations of tumor-localizing boronated compounds are being developed. The dose-selectivity problem of BNCT has been approached using boron hydride compounds in combination with a variety of deUvery vehicles including boronated polyclonal and monoclonal antibodies, porphyrins, amino acids, nucleotides, carbohydrates, and hposomes. Boron neutron capture therapy has been the subject of recent reviews (254). 

Boron rods provide an alternative wood preservative, which is considered safe for people and the environment. They are made of boron compounds that have been subjected to high temperatures to form water-soluble, glassllke rods. These rods are Inserted Into drilled holes In the wood, strategically positioned where decay is most likely the holes are then plugged to keep the rods In place. When the wood becomes wet, boric acid is released, which prevents fungal decay. Boron pastes have a similar effect. Manufacturers of boron rods are seeking to make these rods available for home use. 

In a series of papers some thieno fused boron compounds have been subjected to structure determination by X-ray methods. Thus the bis(dithienoborepinyl) ether (26 R = C10H6BS2O) has dimensions close to those of the isoelectronic dithienotropylium ion (74ACS(B)998>. The borepin ring is almost planar, and the B—C bond length was found to be 1.533 A. 

For the last four decades, there has been an exponential increase in the synthesis and usage of a number of organic and inorganic boron compounds in industry and academia. Due to the explosive growth of heterocyclic boron-containing compounds, this topic is covered as a separate chapter here. Previously, the subject of this chapter was covered in a subsection of Chapter 4.24 in CHEC-II(1996) (Sections 4.24.1.3.6 and 4.24.1.3.7). This chapter covers as much literature as possible, but the space restraints did not permit a comprehensive coverage of all literature. 

Names used in this cumulative Subject Index for Volumes XVI and XVII, as well as in the text, are based for the most part upon Nomenclature of Inorganic Chemistry, Definitive Rules 1970 Report of the Commission on the Nomenclature of Inorganic Chemistry of the International Union of Pure and Applied Chemistry, Butterworths, London, 1971 [see Pure Appl. Chem. 27(1), 1-110] also on the Tentative Rules of Organic Chemistry—Section D and Nomenclature of Inorganic Boron Compounds [Commission on Nomenclature of Inorganic Chemistry, IUPAC, published in Pure Appl. Chem. 30(3 -4), 683 - 710 (1972)]. All of these rules have been approved by the ACS Committee on Nomenclature. Conformity with approved organic usage is also one of the aims of the nomenclature used here. 

Despite the multitude of well characterized boron compounds, the knowledge of azole derivatives of boron is still rather limited. For example, only three C-borylated pyrazoles are known. Although N-borylated pyrazole derivatives are considerably more abundant, until most recently these were restricted to compounds containing only four-coordinate boron. Of these, the poly(l-pyrazolyl)borate anions have been a bonanza for the coordination chemist, since the steric and electronic features of these ions render them as extremely useful (polydentate and chelating) ligands. However, recent studies of the chemistry of boron derivatives of pyrazoles have provided for some noteworthy developments and a survey of such compounds and their chemistry appears to be a timely subject. 

The rapid development of carborane chemistry is mainly due to their practical applications. For instance, the potential utility of carborane polymers as gaskets, O-rings, and electrical connector inserts has been reported. Their functionality for solvent extraction of radionuchdes as well as the potential medicinal value of the isoelectronic and isostructural boron analogues of biologically important molecules has been the subject of many review articles. For example, a number of boron compounds have been found to possess anti-inflammatory and antiarthritic activity in animal model studies. Boron compounds have also been implicated in studies designed to probe the importance of the so-called anionic subsite of acetylcholine esterase and Ach receptors. But, by far the most interesting practical apphcations of carboranes are in areas of boron neutron capture therapy (BNCT) and supramolecular assembly. 

The coordination chemistry of boron was reviewed some time ago and the structure and properties of compounds of the general formula BX3 L, where X and L can be one of a wide variety of substituents and electron pair donors, respectively (15). Indeed, the reactions of tricoordinate boron compounds in general are thought to proceed via addition of the reaction partner in a Lewis acid-base reaction to yield a tetracoord-inate intermediate that then undergoes further reaction. Stable tetra-coordinate boron compounds are subject to ligand displacement reactions for which a variety of mechanisms obtain (16). The coordination chemistry of transition metals is vast and includes not only structimal facts (17) but considerable information on the mechanistic behavior of these species as well (18). In our brief comparison we will restrict ourselves to low oxidation state chemistry and group 16 metals (19). 

Much of the early work on the B shifts of simple ter- and tetra-covalent boron compounds, complexes, and some simple borane derivatives, has been reviewed by Emsley et al. The review of B shifts by Schaeffer,although published earlier, is a more comprehensive account of this particular subject, although the text is primarily concerned with borane derivatives. Since the last review, there have been only very brief articles dealing with some particular aspect of the B resonance investigations these articles are mentioned in the appropriate sections of the accompanying text. 

This review, concerned with reactivity of the boranes with no attempt to make the references exhaustive, has demonstrated the current and intense activity in this area of chemistry. The reader may already have recognized that nearly 60% of the references quoted refer to work published in this field during the last five years. With the application of new methods of preparation and separation, it is evident that boron compounds will be described in increasing numbers. Meanwhile, it is hoped that the subject matter reviewed here will be of help to research workers and teachers alike. 

Boric oxides, boric acids, and metal borates are of primary importance in any discussion of boron chemistry since these include essentially all boron minerals and the vast majority of boron compounds produced and used worldwide on a weight basis. Reviews of this chemistry and the commercial aspects of this general subject are available. ... 

The Suzuki coupling was developed by Professor Akira Suzuki of Hokkaido University. The Suzuki coupling uses a boron compound (R-BYj) and an alkenyl, aryl, or alkynyl halide or triflate (RX) as the carbon sources, with a palladium salt as the catalyst. Bromides and iodides are the most commonly used halides chlorides are less reactive. Alkyl halides can sometimes be used but are subject to elimination. A base is also required. The boron compound can be a borane (R jB), a borate ester (R B(OR)2), or a boric acid (R B(OH)2), where R is alkyl, alkenyl, or aryl. The general reaction is shown in the following scheme, where X is halide or triflate and Y is alkyl, alkoxyl, or OH. A list of the types of components that can be used is given in Table 24.1. This reaction is one of the principal methods now used to prepare biaryls. 

Boric acid solution is stored externally to the aimex building to a total quantity of 132 tonnes (Environmental Report Tables 2.9.3 and 2.9.6, reference 14.4). Boric acid is not subject to regulation under COMAH. Boric acid (i.e., a compound of boron) is subject to regulation as a List n substance in Groundwater Directive (Reference 14.24) and should be prevented from escaping thereby causing pollution. 

Boron compounds such as borax and boric acid are well known fire retardants for cellulosic products [1]. However, the use of boron compounds such as zinc borate, ammonium pentaborate, boric oxide, and other metallo-borates in the plastics industry has become prominent only since the late 1970s. This entry will review the manufacturing, chemical and physical properties, end-use applications, as well as modes of action of major boron compounds as fire retardants in polymers. The subject is also mentioned in the section entitled Flame retardants inorganic oxide and hydroxide systems. ... 

In general, elemental boron and boron compounds have been the subject of many studies involving propulsion systems due to the very high heats of combustion. However, due to some combustion problems, the theoretical benefits of boron and its compounds have rarely been delivered. The main limitations for boron combustion are (i) ignition delay due to the presence of an oxide layer on the surface of... 

This chapter attempts to provide a critical review of the work carried out on alkaline fuel cell, which directly uses hydrogen rich liquid fuel and oxygen or air as an oxidant. The subjects covered are electrode materials, electrolyte, half-cell analysis and single cell performance in alkaline medium. Koscher et al. (2003) brought out elaborate review work on direct methanol alkaline fuel cell. Earlier Parsons et al. (1988) reviewed literature on anode electrode where, the oxidation of small organic molecules in acid as well as in alkaline conditions was considered. A review work on electro-oxidation of boron compounds was done by Morris et al. (1985). However, in this chapter use of three specific fuels, e.g., methanol, ethanol and sodium borohydride in alkaline fuel cell is discussed. 

Boron subhaHdes are binary compounds of boron and the halogens, where the atomic ratio of halogen to boron is less than 3. The boron monohaUdes, BCl, [20583-55-5] bromoborane(l) [19961-29-6] BBr, and iodoborane(l) [13842-56-3] BI, are unstable species that have been observed spectroscopicaHy when the respective ttihaUdes were subjected to a discharge (5). Boron dihaUde radicals have been studied, and stmctural and thermochemical data for these species ( BX2) have been deduced (5). 

The chemistry and stereochemistry of aminoboranes containing the siLicon—nitrogen—boron linkage have been the subject of numerous studies. Many of these compounds are useful precursors to other B—N systems including diboryl-amines (45) and B—H substituted aminoboranes (46). A series of... 

Gauthier et al. <2005JOC5938> elaborated a synthetic route to 148, which is an important biologically active compound. These authors found that 147 can be subjected directly to cross-coupling process with the appropriate boronic acid, and there is no need for the halogenation of 147 to an intermediate for this cross-coupling. The product 148 was obtained in kilogram quantities in almost quantitative yield. 

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