Boron-mercury bonds reactions with

These reactions usually proceed more slowly than the reactions of the corresponding alcohols or phenols with boron halides. In some cases, where direct reaction is too slow, the lead or mercury derivatives of thiols are used. Attempts to use the reactions of thiols with diboron trisulfide to prepare trialkylthioboranes have usually been unsuccessful, although analogous reactions with oxygen compounds are commonly used to prepare trialkoxyboranes. Formation of B-S bonds... 

Little experimental data on the photochemistry of compounds with B—0 bonds have been reported. Boron-hydride/oxygen mixtures are explosive. These explosions can be initiated by photochemical processes. Grimm and Porter have studied the photochemical decomposition of H2B2O3 using a low pressure mercury lamp. The UV spectrum of this compound is illustrated in Fig. 13. The rate of the reaction was increased when mercury was present as a photosensitizer. 

The reaction of heterocyclic lithium derivatives with organic halides to form a C-C bond has been discussed in Section 3.3.3.8.2. This cannot, however, be extended to aryl, alkenyl or heteroaryl halides in which the halogen is attached to an sp2 carbon. Such cross-coupling can be successfully achieved by nickel or palladium-catalyzed reaction of the unsaturated organohalide with a suitable heterocyclic metal derivative. The metal is usually zinc, magnesium, boron or tin occasionally lithium, mercury, copper, and silicon derivatives of thiophene have also found application in such reactions. In addition to this type, the Pd-catalyzed reaction of halogenated heterocycles with suitable alkenes and alkynes, usually referred to as the Heck reaction, is also discussed in this section. 

Although we have assigned a structure to the transition state so as to obtain the observed inversion, the coordination of solvent or chloride at boron and mercury is actually unknown. Ingold (1962) and Thorpe (1966) have suggested that SB2 reactions which go with inversion probably involve transition states in which bond formation lags bond 9... 

Oxidation of organoboranes to alcohols is usually effected with alkaline hydrogen peroxide. The reaction is of wide applicability and many functional groups are unaffected by the reaction conditions, so that a variety of substituted alkenes can be converted into alcohols by this procedure. Several examples have been given above. A valuable feature of the reaction is that it results in the overall addition of water to the double (or triple) bond, with a regioselectivity opposite to that from acid-catalysed hydration. This follows from the fact that, in the hydroboration step, the boron atom adds to the less-substituted carbon atom of the multiple bond. Terminal alkynes, for example, give aldehydes in contrast to the methyl ketones obtained by mercury-assisted hydration. 

One of the earliest methods for preparing aromatic boronic acids involved the reaction between diaryl mercury compounds and boron trichloride [198]. As organomer-curial compounds are to be avoided for safety and environmental reasons, this old method has remained unpopular. In this respect, trialkylaryl silanes and stannanes are more suitable and both can be transmetallated efficiently with a hard boron halide such as boron tribromide [199]. The apparent thermodynamic drive for this reaction is the higher stability of B-C and Si(Sn)-Br bonds of product compared to the respective B-Br and Si(Sn)-C bonds of substrates. Using this method, relatively simple arylboronic acids can be made following an aqueous acidic workup to hydrolyze the arylboron dibromide product [193]. For example, some boronic acids were synthesized more conveniently from the trimethylsilyl derivative than by a standard ortho-metallation procedure (entry 11, Table 1.3). 

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