Boron halides reduction

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

Reduction of boron oxide or boron halides by metals... 

S. by Reduction of Boron Oxide or Boron Halides with Metals... 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Boron may be prepared by several methods, such as chemical reduction of boron compounds, electrolytic reduction in nonaqueous phase, or by thermal decomposition. Many boron compounds including boron oxides, borates, boron halides, borohydrides, and fluoroborates can be reduced to boron by a reactive metal or hydrogen at high temperatures ... 

Reduction of boron halides might be expected to produce bourne. BH,. However, it is impossible to isolate the monomer, all syntheses resulting in diborane. 

Boron(Bor in Ger Rus, Bore in Fr, Boro in Ital Span), B, at wt 10.82 occurs in two forms blk monoclinic crysts yel or brn amor powd mp 204( > bp 3930°, d 2.33(cryst), 1.73(amor) sol in nitric and sulfuric acids and in most molten metals insdl in w, ale, ether solns of caustic alkalies. The element boron was isolated in 1808 by Gay-Lussac Thenard who reduced boron oxide(B2C>3) with K by heating it in an iron tube. Sir Humphrey Davey independently obtd the same product and called the element "boron . This element is not found free in nature, but occurs in the form of borates boric acid. It can be prepd by the reduction of the oxide, borates or boron halides... 

One of the prominent synthetic protocols for the preparation of diazaborolines 323 involves the reaction of lithiated diamides 324 with boron halides and subsequent elimination of lithium halide salt. Another protocol involves synthesis via cyclocondensation of 1,2-diimines 325 with alkylboron halides to yield the diazaborolium salts 326 that undergo reduction with sodium amalgam yielding the diazaborolines 323 in high yield (Scheme 53) <2005EJI4715>. 

Reduction of a Metal Oxide and Boron Halide with Hydrogen... 

Zirconium and hafnium diboride have been studied less extensively. Zirconium diboride potentially is useful as a coating for solar absorbers [242]. These compositions can be prepared either by hydrogen co-reduction of the metal and boron halides [242], or by the decomposition of the metal tetrakis(tetrahydroborates) M(BH4)4 [241]. 

P-Rhombohedral boron The p-rhombohedral variety of boron, also called the high-temperature form, is prepared either by reduction of a boron halide with hydrogen on a substrate heated to a temperature above approximately 1400° C, or by solidification of liquid boron, or by annealing (a-rh.) boron beyond the (a-rh.) - (p-rh.) transformation point. That means, the a-rhombohedral boron ° transforms by 1200° C into the more stable solid p-boron. The p-rh. boron is composed of much complicated Bi2(B6)i2 polyhedra. " The structure of p-boron consists of B12 icosahedra and B28 subunits which can be regarded as triplex icosahedra. The lattice constants of p-rhombohedral boron are (a =10.145 A, a = 65° 17 space... 

The initial experiments carried out by Hurd (158) were complicated because hydrogen was admixed with the boron halides passed through the reduction chamber. 

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