Boron halides BX3 and

Equation 13.28 shows the usual synthesis of BF3 excess H2SO4 removes the H2O formed. Boron trifluoride fumes 

Pure tetrafluoroboric acid, HBF4, is not isolable but is commercially available in Et20 solution, or as solutions formulated as [H30][BF4]4H20. It can also be formed by reaction 13.30. 

Tetrafluoroboric acid is a very strong acid, and mixtures of HF and BF3 are extremely strong proton donors, although not quite as strong as those of HF and SbFs (see Section 9.7). Salts containing the [Bp4] ion are frequently encotmtered in synthetic chemistry. The [BF4] ion (like [PF5] coordinates very weakly, if at all, to metal centres and is often used as an innocent anion to precipitate cations. For a discussion of the stability of KBF4 with respect to KF - - BF3, see Section 6.16. 

To what point group does [BF4] belong Explain why [Bp4] has two IR active T2 vibrational modes. 

Boron trifluoride forms a range of complexes with ethers, nitriles and amines. It is commercially available as the adduct Et20 BF3 (13.11). Being a liquid at 298 K, this is a convenient means of handling BF3 which has many applications as a catalyst in organic reactions, e.g. in Friedel-Crafts alkylations and acylations. 

6 Halides and complex halides Boron halides BX3 and B2X4 

Equation 13.28 shows the usual synthesis of BF3 excess H2SO4 removes the H2O formed. Boron trifluoride fumes strongly in moist air and is partially hydrolysed by excess H2O (equation 13.29). With small amounts of H2O at low temperatures, the adducts BF3-H20 and BF3-2H20 are obtained. 

B2O3 + 3CaF2 + 3H2SO4 — 2BF3 -b 3CaS04 -b 3H2O 

Tetrafluoroboric acid is a very strong acid, and mixtures of HF and BF3 are extremely strong proton donors, although not quite as strong as those of HF and SbF5 (see Section 8.7). Salts containing the [BF4] ion are frequently encountered in 

33) coordinates very weakly, if at all, to metal centres and is often used as an innocent anion to precipitate cations. For a discussion of the stability of KBF4 with respect to KF + BF3, see Section 5.16. 

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In pursuit of alternative methods of isocyanate production, the results of investigations with simple boron halides, BX3 (X = Cl, Br), in converting carbamate esters to isocyanates of industrial importance were reported. Additionally, it has previously been shown that BX3 can be generated in the production of benzyl esters by reaction of trialkyl borates with benzylic halides and CO in the presence of catalytic quantities of Pd° or Rh [244-246]. This offers the rather attractive option of two concomitant processes achieving commercially valuable ends, together with constant recycling of boron. 

Boron forms two simple series of lower halides, BX3 and B2X4(X2B—BX2). The highly reactive trihalides are volatile covalent compounds whose molecules have the expected trigonal planar geometry. The molecules of the other series are also planar in the solid state however, in the gaseous state, the chloride and the bromide... 

Actually the halides all do have the formula BX3, and show no tendency to associate, while the simplest hydride, B2H6, has not begun to dissociate into 2BH3 at a temperature at which it begins to lose hydrogen. If BH3 were given an electronic formula with an electron-pair bond between boron and each H... 

Analysis for boron, halide, free halogen, and silicon is carried out by standard methods following hydrolysis of BX3 (11,79). Specifications for BC13 and BBr3 supplied by Kerr-McGee Corp. are given in Table 2. 

The halides participate as terminal and bridge ligands and can be included in inner and external spheres of this kind of complex. A few examples of compounds with such terminal ligands are the boron ammines [BX3 NH3], [BX2(NH3)2]X, BX(NH3)3]X2, and [B(NH3)4]X3 (X = F, Cl, Br, I). Halides form part of many mixed-ligand carbonyl complexes, for example, Fe(CO)4I2 and polyhalide anions with various elements [4], In this respect, the structure of the anion [Re2Clx]2 provides important information the Re — Re bond is present and the chlorine atoms have a bridge function [4]. 

Boron halides have the general formula BX3 and have a trigonal planar structure. 

The boron halides have the expected formula, BX3. Boron trifluoride can be made by heating boric oxide, calcium fluoride and concentrated sulfuric acid ... 

All 20 of the possible boron trihalide adducts of NMcs have been detected (halogen exchange to give the mixed halide species only occurs when an excess of BX3 is present). In contrast to the free boron trihalides and their O-donor adducts, the iV-donor adducts allow isolation of the individual... 

He (I) photoelectron spectra of mixed halides of boron, BX X 3 , where X, X = Q or F, n = 1 or 2, have been recorded and assigned, using the results of studies of mixtures of BX3+BX3. The mixed halides were present in essentially... 

The structure of BX3 molecules. The boron atom is s/) -hybridized. Some evidence exists that some n bonding may occur between the unhybridized 2p orbital of the boron and the filled (shaded) np orbitals of the halides. 

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