Reactions with Boron Compounds

Nitrogen trifluoride and diborane do not react at room temperature and pressures up to 8 atm (under these conditions, B2H6 and PF3 give the adduct FaP-BHa) [1]. At 145°C, yellow solids deposit in the reaction tube but no volatile products are produced [2]. NF3-B2H6 mixtures are explosive when handled as liquids [1]. 

Passing nitrogen trifluoride at 615°C over B2O3 produces about a 90% yield of NOBF4 (based on NF3 reacted), plus NO, NO2, and N2O [3]  

Vapor pressure measurements on the system NF3-BF3 at 158.95 K (triple point of HCl) show large deviations from Raoult s law, however, there is no evidence for acid-base association between the two components [5]. Very weak association resulting from small van der Waals forces was observed for NF3and BF3 below 148 K and for NF3and BCI3 below 173 Kby means of infrared spectroscopy [6]. 

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He then joined Professor Vaultier s team from the University of Rennes 1 for his postdoctoral studies, where he worked on conversions of organophosphorus compounds in reactions with boron compounds. 

Rate constants have been measured for the reactions of boron compounds with a series of bromomethanes and bromofluoromethanes. Previously it was shown that the reactivity of the chlorine in chlorofluoromethane is substantially reduced by increasing fluorine substitution. The corresponding decrease in the reactivity of bromolluoromethane u as not observed [ifS]. 

These coupling reactions can also be done with boronate esters activated by conversion to ate reagents by reaction with alkyllithium compounds.279 For example, analogs of leukotrienes have been synthesized in this way. 

Perlmutter used an oxymercuration/demercuration of a y-hydroxy alkene as the key transformation in an enantioselective synthesis of the C(8 ) epimeric smaller fragment of lb (and many more pamamycin homologs cf. Fig. 1) [36]. Preparation of substrate 164 for the crucial cyclization event commenced with silylation and reduction of hydroxy ester 158 (85-89% ee) [37] to give aldehyde 159, which was converted to alkenal 162 by (Z)-selective olefination with ylide 160 (dr=89 l 1) and another diisobutylaluminum hydride reduction (Scheme 22). An Oppolzer aldol reaction with boron enolate 163 then provided 164 as the major product. Upon successive treatment of 164 with mercury(II) acetate and sodium chloride, organomercurial compound 165 and a second minor diastereomer (dr=6 l) were formed, which could be easily separated. Reductive demercuration, hydrolytic cleavage of the chiral auxiliary, methyl ester formation, and desilylation eventually led to 166, the C(8 ) epimer of the... 

Re NB(C6F5)3 Cl4(H20)] anion (54) is obtained as its [Bu4N]" salt in good yields,the trimeric compound [(H20)Br4ReNReBr4ReBr4N(H20)] (55) is the product of the reaction with boron tribromide. Both compounds are paramagnetic and have been characterized by EPR spectroscopy. The spectral parameters indicate a decrease of the coupling constants... 

Tetrahydrofuran itself can be opened using either the stoichiometric or the catalytic version of arene-promoted lithiation, but both cases need the activation by boron trifluoride. The catalytic reaction was performed by treating the solvent THF 324 with the complex boron trifluoride-etherate and a catalytic amount (4%) of naphthalene. The intermediate 325 was formed. Further reaction with carbonyl compounds and flnal hydrolysis yielded the expected 1,5-diols 326 (Scheme 95), which could be easily cyclized to the corresponding substituted tetrahydropyrans under acidic conditions (concentrated FlCl). 

Bora-substituted aza macrocycles are formed by reaction of oxime complexes with boron compounds, e.g. (32) and (33) are formed with boron trifluoride. 

Under mild conditions, isosorbide (3) is converted into 1,6-dichloro-1,6-dideoxy-D-glucitol (147) by reaction with boron trichloride (Scheme 41). Compound 147, which was not isolated in pure form, was allowed to react with benzaldehyde to afford 2,4-(3-benzylidene-1,6-dichloro-1,6-dideoxy-D-glucitol (148) and 2,4 3,5-di-O-benzylidene-1,6-dichloro-1,6-dideoxy-D-glucitol (149). By this method, the two tetrahydrofuran rings are cleaved in a very mild manner.218... 

The greater part of the modification studies of silica with boron compounds has been directed towards achieving an understanding of the surface structure of silica and silica based adsorbents, utilizing the quantitative reactions with boron containing probe molecules. Because hydroxyl type specificity occurred in some reactions, boron compounds were used to make a distinction between isolated and vicinal surface hydroxyls. Diborane was even utilized as a probe to distinguish surface silanols from hydration water.6,7... 

The following overview of the modification reactions of silica with boron compounds will be focused on B2H6 and BX3 (X = Cl and F). 

The redistribution reaction in lead compounds is straightforward and there are no appreciable side reactions. It is normally carried out commercially in the liquid phase at substantially room temperature. However, a catalyst is required to effect the reaction with lead compounds. A number of catalysts have been patented, but the exact procedure as practiced commercially has never been revealed. Among the effective catalysts are activated alumina and other activated metal oxides, triethyllead chloride, triethyllead iodide, phosphorus trichloride, arsenic trichloride, bismuth trichloride, iron(III)chloride, zirconium(IV)-chloride, tin(IV)chloride, zinc chloride, zinc fluoride, mercury(II)chloride, boron trifluoride, aluminum chloride, aluminum bromide, dimethyl-aluminum chloride, and platinum(IV)chloride 43,70-72,79,80,97,117, 131,31s) A separate catalyst compound is not required for the exchange between R.jPb and R3PbX compounds however, this type of uncatalyzed exchange is rather slow. Again, the products are practically a random mixture. 

Fluoride anion strongly interacts with various inorganic and organic boron and silicon compounds. These reactions are the basis for several fluoride sensors. Interaction of fluoride with boron compounds results in electron density redistribution and may also induce structural changes. Formation of fluoride complex by ferrocene derivative (Figure 16.19a) results in a decrease of oxidation potential by 200 mV... 

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... 

DOT CLASSIFICATION Forbidden SAFETY PROFILE A powerful oxidant which explodes above 140°C. Explosive reaction with boron. Hypergolic reaction with dimethyl hydrazine or other strong organic bases. Forms powerfully explosive mixtures with nitrogen containing organic compounds (e.g., 2-nitroaniline). Upon decomposition it emits toxic fumes of NOx. See also NITRO COMPOUNDS. 

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