Tungsten with boron

Contact with boron, silicon, red phosphorus, sulfur, or arsenic, antimony or bismuth usually causes incandescence [1]. Solid potassium or molten sodium explode with the pentafluoride, and aluminium foil ignites on prolonged contact [2], Molybdenum and tungsten incandesce when warmed [3],... 

The above reaction is utilized in large-scale industrial production of methanol. Reaction with boron trichloride over a hot tungsten or tantalum filament yields boron and hydrogen chloride ... 

Tungsten also forms hard, crystalline refractory borides, such as WB2, W2B and WB when heated with boron in an electric furnace. Tungsten also forms a group of silicides, hard refractory compounds of compositions WSi2, WSis and W2Si3. These silicides are attacked by hydrofluoric-nitric acid mixture or by fused alkalies. 

CARBIDES. A binary solid compound of carbon and another element. The most familiar carbides are those of calcium, tungsten, silicon, boron, and iron (cemcntitc) Two factors have an important bearing on the properties of carbides (1) the difference in electronegativity between carbon and the second elemenl. and (2) whether the second element is a transition metal. Saltlike carbides of alkali metals are obtained by reaction with acetylene. Those ohlained from silver, copper, and mercury sails are explosive. See also Carbon and Iron Metals, Alloys, and Steels. 

It was also of interest to us how changes in the organic residue of the carbyne ligand influence the stability and the behavior of carbyne complexes. Hence, we treated with boron tribromide a series of pentacarbonyl-[methoxy (aryl) carbene tungsten (0) complexes which were substituted at... 

We could show further that not only methoxy(organo)carbene complexes react with boron trihalides in the above-mentioned sense. For instance, it was found that b aws-(bromo)tctracarbonyl(phenylcarbyne)chromium(0) and -tungsten(0) are also accessible from pentacarbonyl[hydroxy (phenyl)-carbene [[chromium (0) (02) and from pentacarbonyl[methoxycarbonyl-... 

An open question was also how pentacarbony 1 [[ethoxy (diethylamino) -carbene[]tungsten(0) would react with boron trihalides, since, as we have learned previously, in principle both the alkoxy and the amino group are removable. The answer was given by the exclusive formation of trans-(bromo)tetracarbonyl(diethylaminocarbyne)tungsten(0) (95), a com-... 

The synthesis of cyclopropyl carbyne complexes follows the general Fischer synthesis of carbyne complexes from alkoxycarbene complexes typical of transition metals of group 6 (Cr, Mo, W). Thus, addition of cyclopropyllithium to chromium and tungsten hexacar-bonyl followed by alkylation of the acylmetallate intermediate with triethyloxonium fluo-roborate gave cyclopropyl ethoxycarbene complexes which, upon subsequent reaction with boron tribromide at -25 °C, afforded the corresponding /ra 5 -bromotetracarbonyl cyclopropylcarbyne complexes (equation 91). However, whereas the monotungsten... 

Boron Trichloride. Boron trichloride is prepared commercially by the chlorination of boron carbide (equation 15). Direct chlorination of boric acid or a sodium borate in the presence of carbon is an alternative method. Most of the boron trichloride produced is converted to filaments of elemental boron by chemical vapor deposition (CVD) on tungsten wire in a hydrogen atmosphere. Numerous laboratory preparations of boron trichloride have been reported. One of the most convenient is the halogen exchange reaction of aluminum chloride with boron trifluoride or a metal fluoroborate. 

Ignidon on contact with boron-containing materials, iodine, finely divided refractory materials (e.g., asbestos, glass wool, sand, tungsten carbide), fluorinated polymers (with flowing trifluoride). 

Flammable by chemical reaction. A powerful oxidizer. Explosive reaction with hydrazine. Reacts violently or ignites with H2SO4 + acetone, hydroxylamine, ethylene glycol (above 100°C). Forms pyrotechnic mixtures with boron + silicon, iron (ignites at 1090°C), tungsten (ignites at 1700°C). Reacts with sulfuric acid to form the strong oxidant chromic acid. Used in... 

The cycloaddition reactions of chiral 2-amino-l, 3-dienes with Fischer-type carbene complexes have been examined by Barluenga et al. Reactions with tungsten vinyl carbene complexes A and with boron-nitrogen-chelated chromium complexes B lead very selectively to cyclohexanone derivatives. However, when employing chromium vinyl carbene complexes in acetonitrile at room temperature in these reactions, cycloheptadienes were obtained selectively by cyclopropanation and subsequent Cope rearrangement. 

Fourteen new tricarbonylchromium complexes of benzodiazaboroles, phenyl-boranes and related compounds have been prepared and characterired. In all compounds n.m.r. data indicate that the Cr(CO)8 moiety is bonded to the benzo and phenyl rings. New types of co-ordination compounds of chromium, molybdenum, and tungsten with phosphino-aminoboranes of general formula (COsMPRSBRS, (CO)4M(PRia)aBR , and (CO)3M(PRS)B have been synthesized. Suitably substituted carbonyl compounds of the same metals reportedly react with l-phenyl-4,5-dihydroborepin (35) to yield stable complexes in which the boron atom apparently participates in metal-ligand bonding. "... 

The boron so obtained is an amorphous powder. It can be obtained in the crystalline state by reducing the vapour of boron tribromide with hydrogen, either in an electric arc or in contact with an electrically-heated tungsten filament ... 

---