Thermolysis of the terminal azido Ru(2)(D(3,5-Cl(2))PhF)(3)N(3) (3, D(3,5-Cl(2))PhF = N,N'-bis(3,5-dichlorophenyl) formamidinate) cleanly produces Ru(2)[(D(3,5-Cl(2))PhF)(3)(D(3,5-Cl(2)-2-NH)PhF)] (4), which is proposed to result from insertion of a nitrido N atom into a ligand aryl C-H bond. This mechanism is supported by differential scanning calorimetry and thermogravimetric analysis results, which show the two-step reaction to be exothermic by -215 kJ mol(-1), in agreement with results from density functional theory calculations. This is the first example of electrophilic insertion of a terminal nitride into an aromatic C-H bond.