ABSTRACT
Diruthenium imido dihydride complexes [(Cp*Ru)(2)(µ-NAr)(µ-H)(2)] (Ar = Ph (2a), p-MeOC(6)H(4) (2b), p-ClC(6)H(4) (2c), 2,6-Me(2)C(6)H(3) (2d); Cp* = η(5)-C(5)Me(5)) have been synthesized by hydrogenation of the corresponding bis(amido) complexes [Cp*Ru(µ-NHAr)](2) (1a-d). Reductive elimination of the N-H bond from 2a-c in the presence of arene yields the amido hydride complexes [(Cp*Ru)(2)(µ-NHAr)(µ-H)(µ-η(2):η(2)-arene)] containing a π-bound arene. The rate and kinetic isotope effect for this reaction are consistent with a mechanism involving initial rate-determining reductive elimination of an N-H bond to produce the coordinatively unsaturated amido hydride species {(Cp*Ru)(2)(µ-NHAr)(µ-H)} (A) followed by rapid trapping of this species by an arene. The existence of A is also supported by the reversible interconversion of [(Cp*Ru)(2)(µ-NHPh)(µ-H)(µ-η(2):η(2)-C(7)H(8))] with the tetranuclear complex [(Cp*Ru)(4)(µ(4)-NHPh)(µ-NHPh)(µ-H)(2)] (4), a dimerization product of A through a µ(4)-NHPh bridge. DFT calculations provide structures of A and transition states for the N-H reductive elimination. Two distinct reaction pathways are found for the N-H reductive elimination, one of which involves direct migration of a µ-hydride to the µ-NAr ligand, and the other involves formation of a transient terminal hydride species.
