Molecular Routes to Metal Carbides, Nitrides, and Oxides. 2. Studies of the Ammonolysis of Metal Dialkylamides and Hexamethyldisilylamides

Ammonolysis of metal amides M(NR 2 ) n, where M = a group 4, 5, or 6 transition metal, M 2 (NMe 2 ) 6, where M = Mo, W, and metal hexamethyldisilylamides M(N(SiMe 3 ) 2 ) n, where M = Ti, V, Cr, Mn, Co, Cu, La, Y, and Sn have been carried out in hydrocarbon solvents. The initially formed products are hydrocarbon-insoluble powders wherein the metal retains its original oxidation state. Elemental analysis of these powders reveals a dramatic loss of NR 2 ligands as evidenced by relatively low C and H content. Thermogravimetric analysis coupled with mass spectroscopy indicates that these powders readily eliminate amine (HNR 2 ) and ammonia to form metal nitrides upon heating, typically in the temperature range 200−400 °C. Upon further heating, redox reactions may occur with the evolution of N 2 gas leading to more thermodynamically stable nitrides or the metal, i.e., where M = Fe, Co, Cu. The nitrogen content of the nitrides has been shown to be derived from ammonia and not from the parent amide. Ammonolyses of mixtures of metal amides have been studied, and the resultant powders have been shown to give, upon heating, either a mixture of the metal nitrides, nitride solid solutions, e.g., (Nb,Ta)N and (Ti,V)N or, for the later transition elements, metal alloys. The metal nitrides and metal alloys were characterized by XRD and SEM/EDAX.