Synthesis of Boron-Carbon Ring Compounds

Abstract

A procedure for the preparation of simple mixed trialkylborane compounds has been devised. n-Butyldiethylborane and di-n-butylethylborane have been prepared. AI kyl group exchange has been shown to occur when a Grignard reagent is allowed to react with tri-n-butylborane or di-n-butylchloroborane. In one attempt to prepare α,ω-bis(di-n-butylboryl)-alkanes, 1,4-bis(di-n-butylboryl)butane apparently was isolated. This reaction could not be repeated. Failure to isolate α,ω-bis(di-n-butylboryl)alkanes has been attributed to either disproportionation of this product or to exchange of alkyl groups during the reaction. As a result of this, two boron-carbon ring compounds, 1-n-butylboracyclopentane and 1-n-butylboracyclohexane, have been prepared.All reactions were conducted under anhydrous conditions with the maintenance of a nitrogen atmosphere at all times.Boron analyses were determined by oxidation with hydrogen peroxide, accord ing to the method of Erickson (#).Molecular weights were determined cryoscopically by measuring the freezing point depressions of benzene solutions. n-Butyldiethylborane from Di-n-butylchloroboraneTo a cold (0°C.) ethereal Grignard solution prepared from 12.0 grams (0.5 gramatom) of magnesium and 55.0 grams (0.5 mole) of ethyl bromide were added drop wise 40.0 grams (0.25 mole) of di-n-butylchloroborane (1), dissolved in an equal volume of ether. The reaction mixture, after being heated to reflux for 2 hours, was hydrolyzed at 0°C. with a 10% solution of hydrochloric acid. The ethereal layer was washed with water, 5% sodium bicarbonate solution, and again with water, and finally was dried over anhydrous magnesium sulfate. After the ether had been removed in vacuo, distillation of the residue gave 8.8 grams (28%) of n-butyldiethylborane, boiling point, 45° to 46°C. (15 mm.).Analysis. Calculated for C8H19B: boron, 8.75; molecular weight, 126. Found: boron, 7.73; molecular weight, 125, 126. In addition, 5.5 grams of an impure liquid, boiling point 63° to 73° C. (15 mm.), and 9.5 grams (21%) of tri-n-butylborane were collected.During the course of this work, it became necessary to find a solvent for the

Preparation of Alkylmagnesium Reagents from Alkenes through Hydroboration and Boron–Magnesium Exchange

“…[9] Thus, early attempts to realize a boron-magnesium exchange reaction by addition of ordinary alkylmagnesium reagents to trialkylboranes 2 were not successful owing to incomplete transfer of the alkyl substituents from boron to magnesium. [10] A significant advance was reported by Murahashi and Kondo, who observed complete boron-magnesium exchange of trialkylboranes upon reaction with a 1,5dimagnesium reagent (Scheme 1) with concomitant formation of the spiro [5,5]boron-ate [11] 4 a as the proposed byproduct. [12] However, the method suffers from three major limitations: First the method is limited to the generation of primary alkylmagnesium reagents starting from mono-substituted alkenes, because the boron-magnesium exchange reaction is inhibited owing to steric hindrance.…”

Preparation of Alkylmagnesium Reagents from Alkenes through Hydroboration and Boron–Magnesium Exchange

“…Thus, early attempts to realize a boron–magnesium exchange reaction by addition of ordinary alkylmagnesium reagents to trialkylboranes 2 were not successful owing to incomplete transfer of the alkyl substituents from boron to magnesium 10. A significant advance was reported by Murahashi and Kondo, who observed complete boron–magnesium exchange of trialkylboranes upon reaction with a 1,5‐dimagnesium reagent (Scheme ) with concomitant formation of the spiro[5,5]boron‐ate11 4 a as the proposed byproduct 12.…”

The development of borane fuels

“…Although the mechanisms for the reactions resulting from the pyrolysis of diborane are not completely understood, it is known that the higher boranes are obtained from the pyrolysis of diborane. The mechanism by which these boranes are formed is controversial, but experimental evidence indicates that the unstable tetraborane and pentaborane(ll) are formed along with the stable pentaborane (9). There is evidence that pentaborane(ll) can be converted to pentaborane(9) at low temperatures (4).…”

“…For example, decaborane will react with a methyl Grignard reagent in accordance with the following equations (34). have been prepared in which R is a butyl or a phenyl group (9,38).…”