Conversion of tris(isopropylamino)borane to polyborazines. Thermal degradation to boron nitride

Thermolysis of tris(isopropylamino)borane (1) and its reaction with ammonia were investigated. Compound 1 exhibited good thermal stability resulting in almost complete evaporation during its thermogravimetric analysis under Ar up to 1000 degrees C. Refluxing of 1 for 42 h at 250 degrees C produced its conversion into the expected B,B',B''-tris(isopropylamino)-N,N',N''-triisopropylborazine (2), and into the new intermediate [(NHPri)(2)B]2NPri (3), both found in low concentrations. Reaction of 1 with ammonia at room temperature resulted in spontaneous transamination, cyclization and polycondensation reactions leading first to B,B',B''-tris(isopropylamino)borazine (4), and subsequently to polyborazines. In spite of the high carbon content of 1, its pyrolysis at 1000 degrees C under NH3 led to the formation of boron nitride containing less than 1% carbon.