Diruthenium Naphthalene and Anthracene Complexes Containing a Doubly Linked Dicyclopentadienyl Ligand

The reaction of cis-{(η5-C5H3)2(CMe2)2}­Ru2(CO)4Br2 with naphthalene affords
the syn-facial [cis-{(η5-C5H3)2(CMe2)2}­Ru2(μ-η6,η6-C10H8)]­[OTf]2, (22+), a complex that appears to be two electrons
short of the
18-electron rule. Density functional theory (DFT) calculations suggest
that the Ru atoms satisfy their missing valence by a combination of
a weak metal–metal bond and sharing electrons from the central
π bond of the naphthalene. The one-electron reduction of 22+ yields 2+, a Class II mixed-valence complex, while the two-electron
reduction of 22+ causes a hapticity
change from η6 to η4 on one of the
naphthalene rings and yields cis-{(η5-C5H3)2(CMe2)2}­Ru2(μ-η6,η4-C10H8) (20), a zwitterionic complex. The DFT calculations predict that
the Cs isomer of 20 is 4.69 kcal/mol lower in energy than the C2v isomer, which is a transition
state. Reaction of cis-{(η5-C5H3)2(CMe2)2}­Ru2(CO)4Br2 with anthracene affords the
analogous syn-facial anthracene complex, [cis-{(η5-C5H3)2(CMe2)2}­Ru2(μ-η6,η6-C14H10)]­[OTf]2, (4), and the tetranuclear dianthracene complex,
[cis-{(η5-C5H3)2(CMe2)2}­Ru2(μ-η6,η6-C14H10)]2[OTf]4, (5). 22+, 20, and 5 were structurally characterized by X-ray diffraction.