Synthesis and Reactivity of a Ruthenium(III) Bis(anilide) Dimer by Oxidative Addition of an N,N‘-Disubstituted Hydrazine

The RuIII bis(anilide) dimer [Cp*RuCl(μ-NHPh)]2 (1a) is formed upon reaction of (Cp*RuCl)4 with
1,2-diphenylhydrazine in benzene. An X-ray crystal structure shows a centrosymmetric (Ci) dimer with
a planar Ru2N2 core. Reaction of (Cp*RuCl)4 with a mixture of PhNHNHPh and TolNHNHTol gives
only the homodimers 1a and [Cp*RuCl(μ-NHTol)]2 (Tol = p-tolyl). The lack of crossover indicates that
cleavage of the hydrazine N−N bond is an intramolecular process. In polar solvents such as acetonitrile,
the Ci dimer 1a isomerizes to the C2v isomer 1b, in which the anilido substituents are cis across the
Ru2N2 core. Both isomers appear to be kinetic products of the synthesis, but 1b isomerizes to 1a in the
benzene solvent. In the presence of 1a, 1,2-diphenylhydrazine disproportionates into azobenzene and
aniline, and labeling studies show that this occurs without participation of the anilido ligands of 1a.
Complex 1a shows slow exchange of the anilide ligands with toluidine (H2NTol) by NMR spectroscopy
and is unreactive toward methanol, triethylphosphine, styrene, and phenylacetylene. The addition of silver
triflate and phenylacetylene to 1a leads to a new species, assigned as the acetylene complex [{Cp*Ru(μ-NHPh)}2(μ-η2:η2-PhC⋮CH)](OTf)2 (6a).