Diborane adducts

Olefins may be obtained by elimination from the organoboron intermediates formed from enol derivatives and diborane. " As in the reaction with a,jS-unsaturated ketones (section IX), the conversion is carried out in two parts first formation of the diborane adduct and second, decomposition in refluxing acetic anhydride. 

Nonbonded complexes. The equilibrium constants, enthalpies, and entropies for the weak complexation of pyrazine with dichloromethane, chloroform, or carbon tetrachloride have been determined from changes in the n — 77 absorptions of solutions at various concentrations (in cyclohexane) and temperatures 568 similar data for pyrazine-aromatic hydrocarbon complexes were obtained from variations in the H NMR chemical shift values.1037 The spectral effects of complexation with borane have been studied in the pyrazine diborane adduct and its methyl derivatives.254... 

Piperazine- and triethylenediamine-monoborane (but not diborane) adducts of BH2F, BHF2, and BF3 are produced by displacement reactions between the diamine and the Me3N-fluoroboranes. H and B n.m.r., and i.r. data were given for these new species. ... 

Bicyclo[7,3,0]dodecane-l,5-diol was obtained by treatment of the diborane adduct of cyclododecatriene, cis,cis,trflns-perhydro-96-boraphenylene, with bromine and water in the presence of sunlight followed by oxidation. ... 

Borane does not exist as such, but a donor molecule can break up diborane and form an adduct, thus ... 

Despite the fact that many boron hydride compounds possess unique chemical and physical properties, very few of these compounds have yet undergone significant commercial exploitation. This is largely owing to the extremely high cost of most boron hydride materials, which has discouraged development of all but the most exotic appHcations. Nevertheless, considerable commercial potential is foreseen for boron hydride materials if and when economical and rehable sources become available. Only the simplest of boron hydride compounds, most notably sodium tetrahydroborate, NajBHJ, diborane(6), B2H, and some of the borane adducts, eg, amine boranes, are now produced in significant commercial quantities. 

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

The yellow compound BsF 2 appears to have a diborane-like structure (112) and this readily undergoes symmetrical cleavage with a variety of ligands such as CO, PF3, PCI3, PH3, ASH3 and SMe2 to give adducts L.B(BF2)3 which are stable at room temperature in the absence of air or moisture. 

X = alkyl, H, halogen, etc. They are usually colourless, crystalline compounds with mp in the range 0-100° for X = H and 50-200° for X = halogen. Synthetic routes, and factors affecting the stability of the adducts have already been discussed (p. 165 and p. 198). In cases where diborane undergoes unsymmetrical cleavage (e.g. with NH3) alternative routes must be devised ... 

Like iminoboranes, imine-adducts of boron compounds have only recently been prepared and investigated. The adduct obtained from the reaction of diphenylketimine and diborane readily loses hydrogen, even at 20°, to form 1,3,5-diphenylmethylborazine 41) ... 

Hydroboration, the addition of a boron-hydrogen bond across an unsaturated moiety, was first discovered by H. C. Brown in 1956. Usually, the reaction does not require a catalyst, and the borane reagent, most commonly diborane (B2H6) or a borane adduct (BH3-THF), reacts rapidly at room temperature to afford, after oxidation, the /AMarkovnikov alkene hydration product. However, when the boron of the hydroborating agent is bonded to heteroatoms which lower the electron deficiency, as is the case in catecholborane (1,3,2-benzodioxaborole) 1 (Scheme 1), elevated temperatures are needed for hydroboration to occur.4 5... 

Two carborane cations, zV/ -2,3,4,5,6-McsC5BBr+ and the tentatively proposed arachno-N ci WX I71, were reported. The identity and pyramidal structure of the pentacarbaborane cation was determined by X-ray crystallography.112 The small arachno-carborane was detected on the basis of ab initio computations and 11B NMR data in the mixture from reaction of the 2-propyl cation with diborane.113 Two neutral adducts based on the pentacarbaborane cation, ///V/9-2,3,4,5,6-McsCsBBKCI2 (R = Cl or SiClj), were made from MesCsSiMe3 or (MesCs Si with B2CI4, respectively.114 The BCI3 adduct was structurally characterized by X-ray crystallography. 

Obviously, the basic site in KB5H8 is its basal B-B single bond and, therefore, reactions with Lewis acids are to be expected. A typical example is the reaction with diborane in ether at —78 °C which generates via its //-adduct (3c2e-BBB bond) the nido-undeca-hexaborate(l—), B6Hn, by cluster expansion. This anion can be proto nated to B Hn [53],... 

This adduct begins to decompose to diborane and H3PBH2Br at -45 °C The latter compound is stable up to 0 °C. At this temperature it polymerises slowly by splitting off hydrogen ... 

With ethyl iodide, ethylphosphine and phosphine are formed. The reaction with excess silyl bromide results in the formation of silylphosphine. Silylphosphine, like methylphosphine, forms an adduct with diborane... 

Diborane forms stable adducts with many electron donors ... 

Boron trichloride is used as a catalyst in polymerization reactions. Other applications include refining of alloys soldering flux and as a component in certain fire extinguishers. It also is used to prepare boron libers and other boron compounds including diborane, sodium borohydride and several adducts. 

PES of, 16 78, 81 reaction with diborane, 16 276 trifluoroacetate, 17 9, 10 trihalides, 21 147-172, see also specific compounds adducts... 

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