One-pot generation of a tris-cationic homobimetallic planar-chiral ruthenacycle

The "one-pot" generation of a tris-cationic homobimetallic racemic planar-chiral ruthenacyclic ruthenium sandwich complex from a reaction of the metal-free chelating ligand with the (-⁶-benzene) dichloridoruthenium(II) dimer in acetonitrile is reported. This unexpected complex, which was characterized by structural X-ray diffraction analysis, is the product of a multistep process entailing first the cycloruthenation of the ligand, a ligand exchange reaction, and eventually the site-selective π-bonding of a bis-cationic [(-⁶-benzene)Ru]²⁺ moiety to a monocationic ruthenacyclic intermediate. Investigations of the underlying electronic structure and bonding scheme by resorting to quantum chemical methods of the density functional theory have revealed the key role played by the electron-donating NMe₂ substituent, which enables the a priori antagonistic π-coordination of the in situ-formed cationic ruthenacycle by a dicationic (-⁶-arene) ruthenium(II) moiety. Experimental evidence indicates indeed that, in the absence of such an electron-donating group at the metalacycle, the π-coordination of the [(-⁶-benzene)Ru] ²⁺ cannot take place.