Boron halides anionic

The above-discussed anionic ligands are the most important ones from the viewpoint of redox properties. For the sake of completeness, we can also consider the redox behavior of halides and boron. Halides stable in water are the simple... 

A theoretical (AMI molecular orbital) treatment of boron analogues of the katapinand series as well as macrotricyclic compounds related to 16 has also recently appeared. As with the ammonium-based host molecules the macrotricyclic hosts containing four boron atoms exhibited a greater degree of anion specificity as a consequence of the rigidity of their binding sites. In all cases, size selective complexation of halide anions was observed with accompanying decreases in B - B distances and partial sp -> sp rehybridization. ... 

The pathway followed by the reaction is depicted in Figure B4.1. Methoxide anion adds to the a-haloalkenylborane generated by hydroboration of the haloalkyne, and induces migration of an alkyl group from the boron atom to the alkenyl carbon atom. The migration displaces halide anion from the alkenyl carbon atom and the centre is inverted. Finally protonolysis of the carbon-boron bond by acetic acid releases the (/f)-alkcne. 

The first literature example of a mercury based receptor (32) for anions was analogous to the chelating boron receptor discussed earlier. The crystal structure indicated that two molecules of Compound 32 asociate with one chloride ion, which sits in a four-coordinate binding site. Solution studies, however, gave results indicative of 1 l binding for halide anions (94, 95). This simple... 

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). 

Table 1. Germanium Halides with Boron Hydride Anions ...

Phosphorus pentahalide complexes contain phosphonium cations and boron tetrahalide anions, for example, PCI4 BCI4 (Chapter 2.6). Phosphonium borohydrides, R4P BjH., can be prepared from phosphonium halides and sodium borohydride. On hydrolysis they give phosphine boranes. Salts with phosphonium cations and boron-containing anions are formed in other reactions (6.379) and (6.531). 

Boron-stabilized anions have again been put to use in C—C bond-forming processes, an example of which is provided by the reaction of the anion (74) with electrophiles. Alkyl halides give substituted boronic esters, whereas aldehydes are converted to predominantly ci5-alkeneboronic esters, in contrast to the condensation of diborylmethide ions with aldehydes (mainly trans-). A useful homologation of carbonyl compounds to aldehydes involves reaction with the anion (75), to give alkeneboronic esters (76), followed by oxidation. ... 

In some cases, fluorination was photoaccelerated in the reaction of aryl diazonium salts in the presence of etherated boron trifluoride [221], Photodecomposition of diazonium salts in the presence of other halide anions (bromide or chloride) was in practice not explored [222,223]. Although aryl iodides can be obtained thermally from diazonium and iodonium precursors, some photoinduced syntheses were also reported [224,225]. The reaction seemed to involve aryl radicals [225] in the former case and aryl cations in the latter one [224],... 

The formation of boron-group IB bonds succeeds in two ways by transfer of a boryl group from metal-boron compounds to other metals, and by reaction of anionic boranes or carboranes with transition-metal halides. 

The synthesis of compounds containing boron-group IIB bonds also occurs by two pathways. The most convenient method is using anionic borane or carboranc species, as in the group-IB case, to react with Zn, Cd, or Hg halides. Moreover, reactions between organometallic compounds (Zn, Cd) with unchanged boranes arc also realized, so Zn and Cd decaboranes, e.g., MB H 2 n solvent (M = Zn, Cd), result from reactions of decaborane(14) with MRj . 

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. 

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