Boron halides bonding

A series of Rh and Ir complexes is also basic enough to add boron halides, although the metal-boron bonds are weak, e.g., dppe and PPh3-Rh complexes serve as electron-pair bases when they react with BF3 and BCI3 . Table 1 summarizes the results. 

In 6.5.2.1 it is shown that BF3 and BCI3 add to phosphine Pt complexes without cleaving the B—X bond. In contrast, aryl and alkyl boron halides are added oxidatively with phosphine Pt complexes - ... 

N.m.r. studies are reported on the triethylphosphine and trisdi-methylaminophosphine complexes with boron halides, and triethylphos-phine complexes with aluminium chloride. A correlation of Sp with the number of phosphorus ligands in metal carbonyl complexes has led to a qualitative rationalization of 8p in terms of a- and 7r-bonding. ... 

It should be clear that we can expect boron to form three equivalent covalent bonds with 120° bond angles. As a result, boron halides have the following trigonal planar structure (D3h symmetry). 

In addition to functioning as Lewis acids, boron halides undergo many other types of reactions. As is typical of most compounds containing covalent bonds between a nonmetal and a halogen, the boron halides react vigorously with water to yield boric acid and the corresponding hydrogen halide. 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Boron halides have also been shown to insert into B—B bonds to give initial products with the new boryl moiety in a bridge position (80). 

Boron-sulfur bonds, addition, to alkynes, 10, 778 Boron trihalides, in boron compound synthesis, 9, 146 Boron-zinc exchange and copper-catalyzed substitutions, 9, 518 for organozinc halide preparation, 9, 89 Borostannylation, enynes, 10, 334... 

Among the boron halides, B4CI4 is of interest as both B4H4 and B411 do not exist. Figure 13.3.7 shows the molecular structure of B4CI4, which has a tetrahedral B4 core consolidated by four terminal B-Cl 2c-2e bonds and four BBB 3c-2e bonds on four faces. This structure is further stabilized by a-n interactions between the lonepairs of Cl atoms and BBB 3c-2< bonds. The... 

Treatment of l,10-distannacyclodeca-2,8,ll,17-tetrayne 100 with electrophiles leads to cleavage of the Sn-C bonds. The reaction of 100 with three different boron halides giving rise to the formation of acetylene derivatives 286 is summarized in Scheme 48 <1997MGM573>. 

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