Borohydride anion

The salt sodium borohydride NaBH4 has an ionic bond between ] and the anion BH4 What are the H—B—H angles in the borohydride anion J... 

As a second example of dihydrogen bonding, let us consider the borohydride anion (BH4-) in complexation with water (as analyzed by Jackson53),... 

Although it has been generally believed that molecules would never be found in icosahedral (Ih) symmetry (31, 32), we now know that such is not the case. There are at least three molecules possessing icosahedral symmetry. These are the borohydride anion (33) dodecahedrane, C20H20 (34), and the... 

Aluminum forms a number of borohydride anions with 3c-2e bonds, e.g., [AlH (BH4)4-n] (n = 0, 1, 2, 3). The anion [Al(i72-BH4)4] is a rare example of 8-coordinate Al111.22 Lithium aluminum hydride reacts with ammonium salts and amines to give Al amides 23... 

This new reagent is an active reducing agent and reduces cyclic and bicyclic ketones with supcrstcreoselectivity. Thus reduction of 2-mcthylcyclohexanone (I) gives rw-2-methylcyclohexanol in 99.3 (, purity. Note that reduction with lithium trimethoxy-aluminum hydride alone yields (2) in 69% yield. Thus increasing the size of the alkyl substituents on boron enhances the stereoselectivity of the borohydride anion. Even... 

As indicated in Fig. 4.31, the overall result is the same as that of an insertion reaction, the difference being that insertion gives rise to a syn-addition and formation of a vacant site, and nucleophilic attack to an anti-addition. There is ample proof for the anti fashion the organic fragment can be freed from the complex by treatment with protic acids and the organic product can be analyzed. Suitably substituted alkenes will show the anti or syn fashion of the addition. Hydrides can be added anti to an alkene by taking a borohydride anion as the nucleophile and adding that to a coordinated, and thus activated, alkene. 

The borohydride anion BH4 is an effective and important reducing agent. 

We have investigated the solvolytic stability and reactivity of polymer-bound borohydrides and have evaluated these materials in several applications such as solvent purification, arsine generation, and metal reduction. These polymer-bound borohydrides offer several advantages over sodium or tetraethylammonium borohydride. The primary advantages are the convenience of use and the minimal introduction of ionic species or organic by-products into the treated bulk media. With the polymer-bound borohydrides, the cation is bonded covalently to the insoluble resin while the borohydride anion or its oxidation product (borate) is retained by ionic bonding. Typically, boron at levels of less than 5 ppm is the only impurity introduced into the treated medium. 

Hutchins et al. have since reported that the disulfonimides undergo nucleophilic displacement with borohydride anion in HMPT to give hydrocarbons. In the case of di-p-toluenesulfonimides temperatures of 150-175° and a twofold excess of borohydride are used in order to obtain reasonable reaction times. 

Synkinetic assemblies of quinones in bulk water include monolayer vesicles, where a negatively charged large quinone carboxylate is localized outside and a fatty acid carboxylate group inside. Upon addition of sodium borohydride exactly 50% of the quinone is reduced to the hydroquinone, because the borohydride anion cannot pass the membrane to react inside quinone headgroups (Scheme 7.2.6) (Fuhrhop, 1990). 

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