Synthesis, Characterization, and Fluxional Behavior of a 34 Electron Homochiral Dimetallic Complex with an Unsupported Hydride Bridge between Two Ru Atoms

The binuclear η6-benzene cycloruthenated
complex 2, which bears an unsupported bridging hydride
ligand, was
synthesized by treating the monomeric cationic cycloruthenated (R)-(+)-1-(1-naphthyl)­ethylamine 1 with potassium
hydroxide under biphasic conditions and then with an alcoholic solvent.
Alternatively, compound 2 was prepared from an equimolar
amount of compound 1 and the homologous monomeric hydrido
complex 3. The crystal structure of 2 revealed
π-stacking interactions between the naphthyl groups of each
cyclometalated amine; the hydride ligand is bent, with a Ru–H–Ru
angle of 145.3(10)°. Compound 2 is fluxional as
shown by variable-temperature NMR analysis. DFT analysis of homochiral 2 and of its hypothetical heterochiral counterpart 2* revealed that dispersion-based π–π interactions
between the cyclometalated ring are not the only interactions that
must be taken into account to rationalize the conformational preference
for 2. Indeed, the overall dispersion-based interactions
between all the ligands of the connected metallacycles provide an
additional 5 to 6 kcal/mol of stabilization energy for 2 regardless whether the π-stacking interactions between the
naphthyl rings exist or not.