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 Ru2(DPhF)4N3 (1a, DPhF = N,N′-diphenylformamidinate) and Ru2(D(3,5-Cl2)PhF)4N3 (1b, D(3,5-Cl2)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 N2 and isolation of Ru2(D(3,5-Cl2)PhF)3NH(C13H6N2Cl4) (3b), in which a nitrogen atom has been inserted into one of the proximal aryl C–H bonds of a D(3,5-Cl2)PhF ligand. A similar C–H insertion product is obtained upon thawing a frozen CH2Cl2 solution of the nitride complex Ru2(DPhF)4N (2a), formed via photolysis at −196 °C of 1a to yield Ru2(DPhF)3NH(C13H10N2) (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 Ru2(D(3,5-Cl2)PhF)4N3, and by Arrhenius/Eyring analysis of the conversion of Ru2(DPhF)4N to its C–H insertion product, respectively. These data are used to develop a detailed, experimentally validated DFT reaction pathway for N2 extrusion and C–H functionalization from Ru2(D(3,5-Cl2)PhF)4N3. 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.