B—halogen bonds

There have been many halogenation reactions of I-CB9FI10- and its derivatives to form anions with B-halogen bonds (F, Cl, Br, and I) 88,93,177-181 hydroxyl derivative 6-HO-l-Ph-l-CB9H8 was made from 1-Ph-1-CB9H9 ... 

Figure 1.24 Examples of closed shell interactions (a) Aurophilic interactions in [Au2( J.-C1) (PPh3)2] (C104), (b) halogen bonding in pyridine—I-CCR and I5 and (c) secondary bonding in [ HgCl(C6H4N2Ph) 2].

There are few useful reactions in which new B—H bonds are formed. Although the formation of boranes from the protolysis of borides or the reduction of boron compounds with Hj, either in electrical discharges or in the presence of active metals, have historical importance, these methods have no importance or utility today. Indeed, the preparation of boranes is so dominated by the single common starting material, the tetrahydroborate ion, that the only important reactions in which B—H bonds are formed are those in which hydride ion either reduces species with B—O or B-halogen bonds to form boranes or adds to trifunctional boron compounds to form hydroborates. 

B-Trihaloborazines are more thermally stable than (HNBH)j, and they decompose only if heated above their melting points. They are hydrolyzed rapidly, however (the fluoroborazine least rapidly), owing to the typical hydrolytic instability of B-halogen bonds, whereas (HNBHjj is hydrolyzed only slowly at room temperature. 

The numerous results presented here for different La-Lb interactions show that at least few common characteristics may be indicated for them especially for the Lewis acid bond being in contact with the Lewis base center. This is the A-H bond for the A-H... B hydrogen bonds and for the A-H... H-B dihydrogen bonds as well as the A-X bond for the A-X...B halogen bonds. Scheme 9.4 shows selected characteristics of the A-Y...B La-Lb interaction, where B is the Lewis base center while A-Y is the bond of the Lewis acid unit. 

Figure 18 2D frameworks sustained by (a) carboxylic acid dimers and (b) halogen bonds between iodines atoms. " ... 

Methods of producing B —C bonds include hydroboration, nucleophilic displacement at a boron atom in BX., (X = halogens or B(0R>3) by e.g. a Grignard reagent, and a psewiio-Friedel-Crafts reaction with an aromatic hydrocarbon, BX3, and AICI3. 

Different types of halogen bonding as they occur in the interaction of small molecules have been reviewed. In all cases studied so far, the halogen bond turned out to have a number of characteristic properties reminiscent of the well-known hydrogen bond. The best investigated cases are those in which a dihalogen XY interacts with a Lewis base B. 

This chapter is restricted to a discussion of halogen-bonded complexes B XY that involve a homo- or hetero-dihalogen molecule XY as the electron acceptor and one of a series of simple Lewis bases B, which are chosen for their simplicity and to provide a range of electron-donating abilities. Moreover, we shall restrict attention to the gas phase so that the experimental properties determined refer to the isolated complex. Comparisons with the results of electronic structure calculations are then appropriate. All of the experimental properties of isolated complexes B- XY considered here result from interpreting spectroscopic constants obtained by analysis of rotational spectra. 

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