Diboron compounds

Diboron compounds with alkylamino or alkyloxy substituents are prepared from the appropriate halogenoborane derivative using active metals " ... 

In addition, the reactions of dialkoxyboranes, such as pinacolborane, with aryl halides and base have been reported.182,183 The yields are lower for reactions of this reagent in some cases than they are for reactions of the diboron reagent, but good yields are obtained from aryl bromides in most cases. Dialkoxyboranes are less expensive than the analogous diboron compounds, but the diboron compound is very stable thermally and is stable in air. 

Although not fitting exactly into the scope of this book, the iridium catalyzed borylation of five membered heterocycles through C-H bond activation also deserves mentioning. A recent report by Miyaura disclosed the reaction of bis(pinacolato)diboron with heteroaromatic systems, where thiophene, fiirane and pyrrole were converted to their 2-boryl derivatives with good selectivity (6.86.), The yields presented refer to the diboron compound since the heterocycles were used in excess in all cases. Indole, benzofurane and benzothiophene were monoborylated with similar efficiency.116... 

This chapter will concentrate primarily on features of the chemistry of diboron compounds of particular interest from the organometallic point of view. While our limited scope does not permit a comprehensive review of all aspects of diboron chemistry, we will initially survey some general features of the subject, with emphasis on unique synthetic aspects and on properties particularly characteristic of compounds containing a simple electron-pair bond between boron atoms. Previously, we published several review articles provided some aspects on boron chemistry,8 16 and including natural boron-containing compounds.17,18... 

Synthesis of diboron compounds may involve either reductive coupling reactions of monoboron derivatives to form the boron-boron bond,19 or reactions of compounds possessing preformed B2 fragments.20... 

The earliest synthesis of characterized diboron compounds was the preparation of B2C14 by Stock,1 using an electric discharge between zinc electrodes immersed in liquid BC13. Many discharge procedures have been reported for the synthesis of B2C14.21 26 Structures of some halogenated diboranes, 1, 2, and 3 are shown in Fig. 1. Diborane(6) 3 (or diboron hexahydride) has been reviewed.27 31... 

Synthesis of diboron compound 164 via bisdiboranes has been demonstrated by Wrackmeyer and Kehr.103 Organoboration of tetra(alk-ynyl)stannanes leads to the spiro-cyclic compound in high yield, which reacts with MeBBr2, i-PrBBr2, and PhBCl2 in dichloromethane between —78... 

Boron compounds, subvalent, 193-194 Boron-containing compounds, See also Diboron compounds Boryl complexes, 165 Borylene complexes bridged, 166-176 molecular structure data, 172 reactivity, 170-171 spectroscopic and structural aspects, 172-176... 

Diboron compounds, 193-250 miscellaneous reactions, 234-243 preparation, 194-206 properties of, 193... 

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