Synthesis and N-H reductive elimination study of dinuclear ruthenium imido dihydride complexes.

Diruthenium imido dihydride complexes [(CpRu)(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) (1a-d). Reductive elimination of the N-H bond from 2a-c in the presence of arene yields the amido hydride complexes [(CpRu)(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 {(CpRu)(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 [(CpRu)(2)(μ-NHPh)(μ-H)(μ-η(2):η(2)-C(7)H(8))] with the tetranuclear complex [(CpRu)(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.