Halides anionic boranes

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 . 

Neutral carboranes and boranes react with transition-metal complexes forming metallocarboranes or metalloboranes, respectively. However, most metallocarboranes and metalloboranes are prepared from transition-metal halides and anionic carborane and borane species ( 6.5.3.4) or by reacting metal atoms and neutral boranes and carboranes. These reactions are oxidative addition reactions ( 6.5.3.3). 

Three kinds of B containing species may be used to react with metal halides cyclic compounds, carboranes and borane anions. The carboranes especially form an enormous number of complexes. 

There are many examples of borohydride compounds of these metals, e.g., Cu, Ag, Zn and Cd-BH as neutral and anionic complexes in which the mode of bonding of BH is dependent on the coordination number of the metaP. Higher borane anions also combine with Cu and Ag, yielding both neutral and anionic complexes. Although no borohydrides of Au are isolated, treatment of Au-halide complexes with, e.g., NaBH, is a standard method for the preparation of Au-cluster compounds Copper(I) hydride, first reported in 1844, has the ZnS structure [d(Cn-H) = 0.173 nm (1.73 A) d(Cu-Cu) = 0.289 nm (2.89 A)] and decomposes to the elements when heated. At >100°C the decomposition is explosive. 

Copper and Ag complexes of the higher boranes are prepared by reaction of the metal-halide complex with a borane anion, including " BjHg, B H, B H S, B,H(, BjqH(3 and Bj,Hj. Pentaborane(9) and hexaborane(lO) form the Cu complexes (PhjDjCuBjHg and (Ph3P)jCuBgH5 both are white, air-stable solids, formed in THF-CHjf Jlj from which they are precipitated by ether . ... 

The reaction of alkenes with borane, monoalkyl and dialkylboranes leads to a new organoborane (see 15-16). Treatment of organoboranes with alkaline H2O2 oxidizes trialkylboranes to esters of boric acid." This reaction does not affect double or triple bonds, aldehydes, ketones, halides, or nitriles that may be present elsewhere in the molecule. There is no rearrangement of the R group itself, and this reaction is a step in the hydroboration method of converting alkenes to alcohols (15-16). The mechanism has been formulated as involving initial formation of an ate complex when the hydroperoxide anion attacks the electrophilic boron... 

The thermal decomposition of a variety of tetramethylammonium salts of weak bases has been studied and the major product is generally the methylated anion 92>. The temperature required to decompose the bromide and chloride salts to trimethylamine and the methyl halide is near 360 °C and the products recombine on cooling. The fluoride salt decomposes at a much lower temperature (180 °C) and the products do not recombine 92>. Decomposition of the borohydride salt at 225 °C gives trimethylamine borane and methane 11h... 

Borane or carborane anions and Si halides form the Si—boron bond in >50% yield. ... 

Table 1. Borane Anions with Silicon Halides ...

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). 

Borane anion Tin halide T(°C) Time (h) Product Yield (7o) Ref. 

Although (7) reacts with methyl iodide and water predominantly at the a-carbon and with acetone mainly at the y-carbon, anion (8), which is readily prepared from the corresponding allyldimesityl-borane by treatment with mesityllithium or lithium dicyclohexylamide, reacts with both alkyl halides and... 

O Neill and Wade" consider the feasibility of deltahedral structures isoelec-tronic and isolobal with B H which are either neutral such as the B X halides, have a -2 charge such as the stable deltahedral borane anions or have a -4... 

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