Metal tetrahydroborates

Boron Triiodide. Boron ttiiodide is not manufactured on a large scale. Small-scale production of BI from boron and iodine is possible in the temperature range 700—900°C (70—72). Excess I2 can be removed as Snl by reaction with Sn, followed by distillation (71). The reaction of metal tetrahydroborates and I2 is convenient for laboratory preparation of BI (73,74). BI can also by synthesized from B2H and HI in a furnace at 250°C (75), or by the reaction of B with excess Agl or Cul between 450—700°C, under vacuum (76). High purity BI has been prepared by the reaction of I2 with mixtures of boron carbide and calcium carbide at elevated temperatures. 

Unsymmetrical cleavage of B2H by metal hydrides gives metal tetrahydroborate salts, also called metal borohydrides or hydroborates. 

The alkali metal tetrahydroborates are ionic, white, crystalline, high-melting solids that are sensitive to moisture but not to oxygen. Group 3 and transition metal... 

In contrast to the interstitial hydrides, where the metal lattice hosts the hydrogen atoms on interstitial sites, the desorption of the hydrogen from the complex hydride leads to a complete decomposition of the complex hydride and a mixture of at least two phases is formed. For alkali metal tetrahydroborates and tetrahydroaluminates, the decomposition reaction is described according to the following equation ... 

For alkaline earth metal tetrahydroborates and tetrahydroaluminates, the decomposition reaction is described according to the following equations ... 

The physical and chemical properties of the tetrahydroborates show more contrasts than the salts of nearly any other anion. The alkali metal salts are the most stable. In dry air, NaBH4 is stable at 300°C and in vacuo to 400°C with only partial decomposition. In contrast, several tetrahydroborates, including the titanium, thallium, gallium, copper, and silver salts, are unstable at or slightly above ambient temperatures. The chemical and physical properties of the tetrahydroborates are closely related to molecular structure. Sodium tetrahydroborate, which is typical of the alkali metal tetrahydroborates except for the lithium salt, has a face-centered cubic (fee) crystal lattice which is essentially ionic and contains the tetrahedral [BHJ- anion. The tetrahydroborates of the polyvalent metals are in many cases the most volatile derivatives of these metals known. Aluminum tris(tetrahydroborate)... 

The chemistry of transition-metal tetrahydroborate complexes has been the subject of numerous investigations over the last few years, which have focused primarily upon the unusual bonding and fluxional characteristics such compounds possess. The synthetic application of these complexes as reducing agents for unsaturated... 

Boron Tribromide and Boron Triiodide. Boron tribromide is prepared commercially in relatively small quantities by the bromination of boron carbide, and its commercial use is limited. No commercial use for boron triiodide has been reported. Laboratory quantities of boron tribromide can be prepared by the reaction of aluminum bromide with boron trifluoride or a metal fluoroborate. Boron triiodide can be prepared in small quantities by the reaction of boron or a metal tetrahydroborate with iodine. 

A metathesis reaction is a convenient route to lanthanide tetrahydroaluminate and lanthanide tetrahydroborate complexes. Using tetrahydroaluminate complexes as the hydride source, a number of structurally characterized lanthanide tetrahydroaluminate complexes are prepared via metathesis reactions in the presence of an excess of a Lewis base (Equation 8.24) [79]. Metathesis reaction of organolanthanide chlorides with alkali metal tetrahydroborate generates the corresponding lanthanide tetrahydroborate. The same reaction with sodium hydride in THE is reported to afford a lanthanide hydride however, no molecular structure for the hydride has been presented up till now. 

While many metal tetrahydroborate complexes have been prepared and studied,1 little is known concerning metal organohydroborate chemistry. 

Alkali-metal tetrahydroborates reduce oxyarsenic(III) species in H O to ASH3 in high yields . Potassium tetrahydroborate in base, when added dropwise to aq acid (HjSO j), reacts as ... 

Reactions of complex hydrides with Sb compounds are effective for stibine syntheses. Metal tetrahydroborate reductions of Sb compounds in both HjO and nonaqueous media occur. Dropwise addition of a basic [Sb(OH) ] -KBH, soln to aqueous acid forms SbHj in 95% yield ... 

Alkali-metal tetrahydroborates in ethers reduce SbClj ... 

Metal tetrahydroborates and tetrahydroaluminates can react with coordinated unsaturated organic molecules without ligand displacement ... 

In a review of the mechanisms of homogeneous reductions of inorganic species by tetrahydroborates, Hanzlik was able to compare the mechanism of the redox process proper with the homo- and hetero-geneous oxidation of alkali-metal tetrahydroborates.30... 

Coordination Modes and Hydride Exchange Dynamics in Transition Metal Tetrahydroborate Complexes... 

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