Carbon-boron system

The discovery of 1 (1), in 1970, opened a new and fascinating chapter of organometallic chemistry. This cation was the first compound derived from the hypothetical borabenzene 2 and the first complex of a classical boron-carbon ligand. Since then approximately 100 borabenzene derivatives, mainly complexes of 3d metals, have been characterized. Other unsaturated boron-carbon systems have been shown to act as ligands to metals (2). This development has also strongly stimulated the challenging quest for the simple species 2-5. 

Rogl, P. and G. Eftenberg Phase Diagrams of Ternary Metal-Boron-Carbon Systems, ASM International, Materials Park, OH. 1998. 

Elliott RP, Van Thyne RJ (1961) The boron-carbon system. Final Technical Report ARF 2200-12, US Atomic Energy Commission Lowell CE (1967) J Am Ceram Soc 50 142... 

Although only a few phase diagrams of the R-boron-carbon systems [R = Y (Bauer and Nowotny 1971), Eu (Schwetz et al. 1979), Gd (Smith and Grilles 1967), and Ho (Bauer et al. 1985)] have been published, several studies on the formation of the... 

Along the EUB6-B4C section again the formation of the solid solution EuBg- Q occurs, but no ternary compound was found. The isothermal section of the tentative phase diagram of the europium-boron-carbon system at 1500°C has been deduced (see fig. 17). To give a better overview, the Eu(B, C)g and i2+xCz-x solid solution has not been included within the diagram. 

Rog] Rogl, R, Niobium-Boron-Carbon , in Phase Diagrams of Ternary Metal-Boron-Carbon Systems", Effenberg, G., (Ed), ASM-Intl, MSI, 197-213 (1998) (Review, Ciys. Strueture, Experimental, Phase Diagram, 25)... 

A remarkable variety of compounds in the Ca-(B,C,N) system has opened a window for research in related fields. With the elements boron, carbon and nitrogen, substance classes such as borocarbides, boronitrides, and carbonitrides can be considered to contain anionic derivatives of binary compounds B4C, BN, and C3N4. Until now, most compounds in these substance classes have been considered to contain alkali, alkaline-earth, or lanthanide elements. Lanthanide borocarbides are known from the work of Bauer [1]. Lanthanide boronitrides represent a younger family of compounds, also assigned as nitridoborates [2] following the nomenclature of oxoborates. 

This review will restrict itself to boron-carbon multiple bonding in carbon-rich systems, as encountered in organic chemistry, and leave the clusters of carboranes rich in boron to the proper purview of the inorganic chemist. Insofar as such three-dimensional clusters are considered at all in these review, interest will focus on the carbon-rich carboranes and the effect of ring size and substituents, both on boron and carbon, in determining the point of equilibrium between the cyclic organoborane and the isomeric carborane cluster. A typical significant example would be the potential interconversion of the l,4-dibora-2,5-cyclohexadiene system (7) and the 2,3,4,5-tetracarbahexaborane(6) system (8) as a function of substituents R (Eq. 2). 

Various diboriodilithiomethanes of type 225 were synthesized by Bemdt and coworkers, adding different aryllithium compounds to the boron-carbon bonds of compounds 224a-e (Scheme 77) . The dilithium compounds have been characterized in the solid state by X-ray structural analysis. 225a-e adopt the structure of a 1,3-diborataallene system, where lithium-diethyl ether units are bridging the twisted B-C-B axis from both sides. 

The boron atom dominates the reactivity of the boracyclic compounds because of its inherent Lewis acidity. Consequently, there have been very few reports on the reactivity of substituents attached to the ring carbon atoms in the five-membered boronated cyclic systems. Singaram and co-workers developed a novel catalyst 31 based on dicarboxylic acid derivative of 1,3,2-dioxaborolane for the asymmetric reduction of prochiral ketones 32. This catalyst reduces a wide variety of ketones enantioselectively in the presence of a co-reductant such as LiBH4. The mechanism involves the coordination of ketone 32 with the chiral boronate 31 and the conjugation of borohydride with carboxylic acid to furnish the chiral borohydride complex 34. Subsequent transfer of hydride from the least hindered face of the ketone yields the corresponding alcohol 35 in high ee (Scheme 3) <20060PD949>. 

These structures would be unusual because of borons great reluctance to form double bonds in normal chemical systems. Doubly bonded boron-oxygen systems have been mentioned in the literature, however (9), as have certain hyperconjugated systems (2) involving boron and carbon. 

This article covers only a part of the chemistry of boron. Boron-carbon compounds are covered in other articles in this volume see Boron Organoboranes Boron Metallacarbaboranes, and Boron Polyhedral Carboranes). The main subject of the latter two articles, and the separate one on Boron Hydrides is the extensive chemistry of the multicenter bonded boron-hydride systems. This area has been a major focus of boron research for the past 60 years. There is some direct overlap between the two articles Borides Solid-state Chemistry and Borates Solid-state Chemistry, and this more general one covering the inorganic chemistry of boron. Boron-Nitrogen Compounds are also covered separately. These articles should be consulted for more detailed discussions of the structure, bonding, and properties of borides, solid-state borates, and boron-nitrogen compounds. 

The selected value is an average based on the equilibrium data summarized below. Drowart and co-workers have used the Knudsen effusion-mass spectrometric technique to determine the vapor equilibria over the systems SiC-graphite ( ), SiC-silison (2 ) and boron-carbon-silicon (3). 3rd law analysis of the partial pressures of C Si and Si lead to the concordant values -1 ... 

Included in the term nonoxide ceramics are all non-electrically conducting materials in the boron-carbon-silicon-aluminum system. The industrially most important representatives, apart from carbon (see Section 5.7.4), are silicon carbide (SiC), silicon nitride (Si3N4), boron carbide (B4C), boron nitride (BN) and aluminum nitride (AIN). 

The acid-hase pair with the second highest concentration and a pK near the pH of seawater is horic acid (Table 4.1). The carbonate system and boric acid turn out to be by far the most important contributors to the acid-base chemistiy of seawater, but they contrast greatly in their reactivity in the ocean carbon is involved in all metabohc processes and varies in concentration from place to place, whereas borate is conservative and maintains a constant ratio to salinity. The equih-brium reaction and total boron, Bj, equations are ... 

Aluminum, boron, carbon, iron, nitrogen, oxygen, phosphorus, sulfur and titanium are the common impurities in the SoG-Si feedstock. Arsenic and antimony are frequently used as doping agents. Transition metals (Co, Cu, Cr, Fe, Mn, Mo, Ni, V, W, and Zr), alkali and alkali-earth impurities (Li, Mg, and Na), as well as Bi, Ga, Ge, In, Pb, Sn, Te, and Zn may appear in the SoG-Si feedstock. A thermochemical database that covers these elements has recently been developed at SINTEF Materials and Chemistry, which has been designed for use within the composition space associated with the SoG-Si materials. All the binary and several critical ternary subsystems have been assessed and calculated results have been validated with the reliable experimental data in the literature. The database can be regarded as the state-of-art equilibrium relations in the Si-based multicomponent system. 

E. Rudy, Ternary phase equilibria in transition metal-boron-carbon-silicon systems. Part V. Compendium of phase diagram data. Tech. Rep. AFML-TR—Air Force Mater. Lab. (US.) AFML-TR-65-2 (1969). 

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