Boron, diboron compounds 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... 

Diboron tetrachlorides undergo a variety of reactions, including facile additions to aUcenes similar to hydroboration (equation 20). The reactions of boron subhalides, particularly B2CI4, with organic and organometallic compounds, have been studied in some detail. 

Most workers have presumed that the addition reaction proceeds via TT-donation from the olefin into the vacant/) orbitals of the diboron compound (55). Stereochemical evidence (discussed more fully below. Section III,B) is in general agreement with such a four-center mechanism, and there is as yet no convincing evidence for an alternative. The involvement of the boron p orbitals is clearly indicated by the lack of reactivity of B2Cl4-base complexes as well as by the failure to obtain addition with compounds such as the aminodiborons in which the coordinative saturation at the boron atoms can be removed or reduced by pir-pn bonding. 

Two further methods of preparing organoboron compounds have been the subject of fairly recent detailed study, namely, reaction of boron halides with hydrocarbons and addition of boron hydrides to olefins. For instance, arylboron dihalides are formed when boron trihalides are heated with aromatic hydrocarbons, aluminum chloride, and aluminum powder,217 and phenyl-boron dibromide has been prepared analogously.218 Further, boron halides such as diboron tetrachloride and tetrafluoride add to olefins, yielding bis-(dichloroboryl) and bis(difluoroboryl) compounds 219... 

Diboron compounds are a part of a relatively unexplored class of compounds. Their main use is for p-boration reactions where a boron centre is rendered nucleophilic with the use of a metal catalyst or a Lewis base to form a sp -sp diboron compound. The reactivity of these... 

Cross-coupling reactions 5-alkenylboron boron compounds, 9, 208 with alkenylpalladium(II) complexes, 8, 280 5-alkylboron boron, 9, 206 in alkyne C-H activations, 10, 157 5-alkynylboron compounds, 9, 212 5-allylboron compounds, 9, 212 allystannanes, 3, 840 for aryl and alkenyl ethers via copper catalysts, 10, 650 via palladium catalysts, 10, 654 5-arylboron boron compounds, 9, 208 with bis(alkoxide)titanium alkyne complexes, 4, 276 carbonyls and imines, 11, 66 in catalytic C-F activation, 1, 737, 1, 748 for C-C bond formation Cadiot-Chodkiewicz reaction, 11, 19 Hiyama reaction, 11, 23 Kumada-Tamao-Corriu reaction, 11, 20 via Migita-Kosugi-Stille reaction, 11, 12 Negishi coupling, 11, 27 overview, 11, 1-37 via Suzuki-Miyaura reaction, 11, 2 terminal alkyne reactions, 11, 15 for C-H activation, 10, 116-117 for C-N bonds via amination, 10, 706 diborons, 9, 167... 

Diboron tetrafluoride can be prepared from BF3 and elemental boron at 1850°C, a reaction that first produces BF (a compound that can be isolated by condensation at -196°C), which reacts with BF3 to give B2F4 and unstable higher boron fluorides such as B Fi2. 

Other reported binary boron sulfides include subvalent B12S, a black crystalline material prepared by a high-temperature reaction of amorphous boron with elemental sulfur, and BS, which has been studied spectroscopically in an electric discharge. A vapor-phase dimer, (BS)2, was identified, and a refractory condensed form of BS was reported from the reaction of elemental boron with sulfur at 1850°C and a pressure of 94 500 atmospheres. Boron disulfide, BS2, has been identified in the gas phase and appears to be the primary compound present in the vapor phase over diboron trisulfrde or elemental boron and sulfur. 

Usually, boronic acids are synthesized by reaction of an aryl magnesium or aryl lithium compound with a borate ester [6]. However, in the case of 4-bromo-benzonitrile, a metal-organic intermediate would react with the nitrile group. Aryl boronic acids could be also synthesized by palladium-catalyzed reaction using diboron reagents [7]. This method would certainly tolerate the cyano func-tionahty, but the diboron reagents are very expensive. 

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