Aryl C-H amination by diruthenium nitrides in the solid state and in solution at room temperature: experimental and computational study of the reaction mechanism.

Diruthenium azido complexes Ru(2)(DPhF)(4)N(3) (1a, DPhF = N,N'-diphenylformamidinate) and Ru(2)(D(3,5-Cl(2))PhF)(4)N(3) (1b, D(3,5-Cl(2))PhF = N,N'-bis(3,5-dichlorophenyl)formamidinate) have been investigated by thermolytic and photolytic experiments to investigate the chemical reactivity of the corresponding diruthenium nitride species. Thermolysis of 1b at ~100 °C leads to the expulsion of N(2) and isolation of Ru(2)(D(3,5-Cl(2))PhF)(3)NH(C(13)H(6)N(2)Cl(4)) (3b), in which a nitrogen atom has been inserted into one of the proximal aryl C-H bonds of a D(3,5-Cl(2))PhF ligand. A similar C-H insertion product is obtained upon thawing a frozen CH(2)Cl(2) solution of the nitride complex Ru(2)(DPhF)(4)N (2a), formed via photolysis at -196 °C of 1a to yield Ru(2)(DPhF)(3)NH(C(13)H(10)N(2)) (3a). Evidence is provided here that both reactions proceed via direct intramolecular attack of an electrophilic terminal nitrido nitrogen atom on a proximal aryl ring. Thermodynamic and kinetic data for this reaction are obtained from differential scanning calorimetric measurements and thermal gravimetric analysis of the thermolysis of Ru(2)(D(3,5-Cl(2))PhF)(4)N(3), and by Arrhenius/Eyring analysis of the conversion of Ru(2)(DPhF)(4)N to its C-H insertion product, respectively. These data are used to develop a detailed, experimentally validated DFT reaction pathway for N(2) extrusion and C-H functionalization from Ru(2)(D(3,5-Cl(2))PhF)(4)N(3). The diruthenium nitrido complex is an intermediate in the calculated reaction pathway, and the C-H functionalization event shares a close resemblance to a classical electrophilic aromatic substitution mechanism.

Aryl C-H bond amination by an electrophilic diruthenium nitride.

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.