The reactions of tetramethyldiborane with ammonia and trimethylamine



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The high vacuum technique was used to study the reactions of tetramethyldiborane with the Lewis bases ammonia and trimethylamine. These reactions have been confirmed to proceed at ambient temperatures as follows: Me[lowered 4]B[lowered 2]H[lowered 2] + 2NH[lowered 3] = 2H[lowered 2] + 2Me[lowered 2]BNH[lowered 2] Me[lowered 4]B[lowered 2]H[lowered 2] + 2Me[lowered 3]N = 2Me[lowered 2]BHNMe[lowered 3] The reaction of the diammoniate of tetramethyldirborane with trimethylamine displaces ammonia at -80[degrees] in amounts greater than one mole of ammonia per mole of the diammoniate. The First mole of ammonia is readily displaced and the remainder is slowly displaced with trimethylamine. The data indicates that the net stoichimetric reaction at room temperature for the displacement of one mole of ammonia is Me[lowered 4]B[lowered 2]H[lowered 2][dot]2NH[lowered 3] + NMe[lowered 3] = H[lowered 2] + Me[lowered 2]BNH[lowered 2] + Me[lowered 2]BHNMe[lowered 3] + NH[lowered 3] Comparisons are made for the structure of the diammoniate of tetramethyldiborane with the three proposed structures for the diammoniate of diborane. The results of the trimethylamine displacement studies are best correlated with the structure (Me[lowered 2]B(NH[lowered 3])[lowered 2]+)(H[lowered 2]BMe[lowered 2]-) which is comparable to that proposed by Parry and coworkers for the diammoniate of diborane. Two unsuccessful attempts to prepare aminotetramethyldiborane from the products of the tetramethyldiborane-ammonia system are discussed. The hydrolysis of the methyl derivatives of boric acid to produce methane is shown to be appreciable at temperatures above 110[degrees]. A vapor pressure-composition curve is given for the ammonia-trimethylamine system.