Boron-metal compounds

Some interesting photochemical reactions involving metalloboranes and metallo-carboranes have been reported. These include synthesis, isomerization and complexa-tion reactions. Gaines and Hildebrandt have used the following process to synthesize a metalloborane  

They have also demonstrated a reversible photochemical conversion from a tridentate to a bidentate B3H8 (Fig. 14). Fehlner has achieved a photochemical carborane synthesis by irradiating mixtures of B4H8Fe(CO)3 and dimethylacetylene. Products of the reactions include (CH3)4C4B4H4 and (CH3)8C8B4H4. Leyden and co-workers have observed two examples of metalloborane isomerization reactions initiated by light  

Franz and coworkers reported the photochemical synthesis of a metalloborane from a carborane and Fe(CO)s (reaction 54). 

Open circles = Fe Closed circles = C Lined circles = B o = H Dotted circles = O 

Finally, two complexation reactions have been reported  

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In 1970, the synthesis of the orange-red sandwich cation 1 from cobaltocene and PhBCl2 (1) marked a further starting point in the chemistry of boron metal compounds. The presence of a planar benzenoid C5H5B ligand moiety in 1 was deduced from XH and UB NMR data (1). This was made ironclad by two X-ray structure determinations which revealed typical centrosymmetric sandwich structures for the 19-e complexes Co(C5H5BOMe)2 (6) (21,22) and Co(C5H5BMe)2 (7) (22) as shown in Fig. 1. 

CHR) , formed, e g. from the reaction of diazomethane and alcohols or hydroxylamine derivatives in the presence of boron compounds or with metal compounds. Poly-methylene is formally the same as polyethene and the properties of the various polymers depend upon the degree of polymerization and the stereochemistry. 

The alkylation of pyridine [110-86-1] takes place through nucleophiUc or homolytic substitution because the TT-electron-deficient pyridine nucleus does not allow electrophiUc substitution, eg, Friedel-Crafts alkylation. NucleophiUc substitution, which occurs with alkah or alkaline metal compounds, and free-radical processes are not attractive for commercial appHcations. Commercially, catalytic alkylation processes via homolytic substitution of pyridine rings are important. The catalysts effective for this reaction include boron phosphate, alumina, siHca—alurnina, and Raney nickel (122). 

Tetrahydroborates. The tetrahydroboranes constitute the most commercially important group of boron hydride compounds. Tetrahydroborates of most of the metals have been characterized and their preparations have been reviewed (46). The important commercial tetrahydroborates are those of the alkah metals. Some properties are given ia Table 4. 

Reactions between anionic species containing one or more group-IIIB elements (particularly boron) and complexes of transition-metal halides are used to produce an immense number of ionic boron-containing compounds. For this reason a strong selection factor must be made. 

Reduction of a metal compound and boron halide with hydrogen... 

Reduction of a metal oxide or other metal compound using C, B or boron carbide... 

The early sixties saw a broad and intense interest in the making of the heretofore unknown molecular compounds with a boron-metal bond (8). In 1963, the first compounds with boron-metal [Pg.200]

Another very useful rule for classifying the structures of polyboranes and hetero-boranes as well as many metal boron cluster compounds and their derivatives has been developed by Rudolph, Williams, Mingos and Wade (see Chapter 1.1.2) [4]. Today these are generally termed the Wade rules. They can be derived from the structures and electronic requirements of closed polyhedral boranes, such as an octahedron or an icosahedron, which are present in the anions B6H62 and B,2 H, 22. Since there are only exopolyhedral B-H bonds the number of electron... 

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

The fuels are finely powdered metals (2.0-10.0 g) among which titanium, zirconium, manganese, tungsten, molybdenum and antimony are very common. Sometimes, non-metal powders such as boron and silicon (for fast burning delays), binary alloy powders such as ferrosilicon, zirconium-nickel, aluminum-palladium and metal compounds such as antimony sulfide, calcium silicide etc. are also used. 

The present chapter includes commercially available organic chemicals. Most of the organo- phosphorus, boron, silicon, alkali metal compounds and metal ion salts are in Chapter 4. Naturally occurring commercially available organic compounds of use in biochemistry, molecular biology and biology are included in Chapter 5. Abbreviations of words and some journal names are listed in Chapter 1, pages 1 and 2. 

There are a number of other important boron cage compounds as well as structurally similar metal atom cluster molecules that are not closed polyhedra. Generally, these may be regarded as derived from closed polyhedra by removal of one or two vertices. The diagram below illustrates how removal of one or two vertices generates the so-called nido and arachno relatives of a closo octahedral structure. 

Boron Cage Compounds 789 Metal Clusters 807 Conclusion 819... 

Some chirally modified metallic compounds (or combined systems) containing lithium (20d, g, o, p), boron (30), or titanium (31, 32) also... 

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