Anions boron-containing

FIGURE 9.5 Anionic boron-containing amino acids. (Adapted from M. Ya. Berzina et al. mannscript in preparation.)... 

Figure 7. Structures of anionic boron-containing aminoacids.

Diborane reacts with ammonia to form an ionic compound (there are no other products). The cation and anion each contain one boron atom, (a) Predict the identity and formula of each ion. (b) Give the hybridization of each boron atom, (c) Identify the type of reaction that has occurred (redox, Lewis acid-base, or Bronsted acid-base). 

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. 

Closely related to, but distinct from, the anionic boron and aluminum hydrides are the neutral boron (borane, BH3) and aluminum (alane, A1H3) hydrides. These molecules also contain hydrogen that can be transferred as hydride. Borane and alane differ from the anionic hydrides in being electrophilic species by virtue of the vacant p orbital and are Lewis acids. Reduction by these molecules occurs by an intramolecular hydride transfer in a Lewis acid-base complex of the reactant and reductant. 

Even before the discovery of the katapinands vide supra), work upon bidentate Lewis acid hosts suggested the possibility of chelation of anionic sjjecies by acyclic-boron-containing ligands such as BF2CH2CH2BF2. In many ways mul-... 

Various neutral and, especially, anionic boron species are well known as ligands in transition metal complexes. In the majority of cases, however, one or more H, N or other basic atom of the boron compounds is coordinated to the transition metal (e.g. Chapters 13.8, 13.6 and 19). In the last 20 years, however, several complexes containing boron-transition metal bonds have been prepared with ligands such as sBX, -BX2 or BX3 (Table 14). 

Ogner [1] has described an automated analyser method for the determination of boron-containing anions in plants. This is based on the formation of a fluorescent complex between these anions and carminic acid at pH 7. The plant tissues are ashed at 550 °C and the residue dissolved in 0.5 N hydrochloric acid prior to adjustment to pH 6-7 with sodium carbonate solution. The solution is excited at 470 nm and fluorescence intensities measured at 585 nm. Interferences by the reaction of some cations with carminic acid are overcome by passing the solution through an ion exchange column to exchange the cations for sodium ions. Analytical recoveries of boron anions were in the range 98-104%. The detection limit of the method was 5 xg/l boron. 

A/dm2, Ni2+ ions discharge into Ni-B° occurs with enhance polarization in comparison with discharge into Ni°. The breaking of the Ni2+ ions discharge rate, when Ni-B° is electrodeposited (at the E< - 0,75), is connected with this alloy surface coverage by the adsorbed dope boron containing anions. So, for example, cathodic polarization at the ik = 2 AJ dm2 maintained the value 30 mV, and at the ik = 4 A/ dm2 - 45 mV. 

Treatment of Cp2ZrCl2 with LiAlH4 and then HsGaNMes or reaction of the preformed hydride Cp2ZrH2 with H3 AINMes affords the heterobimetallic complex (15). Boron-containing heterobimetallic complexes (16) can be prepared by reaction of metallocene dichlorides with the cyclic hydroborate anion [H2BC5H10] then reduction of MX l bond with LiH. 

Most of the publications dealing with heterocycles contain nuclear magnetic resonance (NMR) data. While H and NMR data are the most important, NMR data are particularly relevant to boron-containing heterocyles. The H, B, and NMR data of unsaturated, anionic, and transition metal 7t-coordinated rings are useful probes of their electronic structures. 

Although technically a heteroelement rather than a metal, some interesting Lewis acidic receptors for anions have been based on boron-containing systems. The first evidence for this type of anion receptor was published in 1967, one of the earliest examples of anion binding. Compound 21, when compared with 22, exhibited a chelate effect in the binding of methoxide anions (3). 

The most versatile route to Ge—boron-containing species is from Ge halides and boron hydride anions, products embracing both oxidation states of Ge, inorganic and mono-, di-, and triorganogermyl derivatives, as well as borane and carborane substrates (Table 1) (cf. 5.3.7.3.2 for the analogous Si-based reactions). 

The nature and concentration of boron-containing compounds affect substantially the film formation process, chemical and phase composition, structure and surface morphology of the resultant films. The ability of compounds to be a source of boron depends on either kinetic stability (i.e. the symmetry of anion) in the case of higher boranes or B-N bond strength for the borane complexes. 

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