The reaction of a mixture of isomers of 4,4,8,8-tetramethyl-tetrahydro-s-indacene (1) with Ru 3 -(CO) 12 afforded cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (CO) 4 , (2) in 68% yield. Reaction of 2 with Br 2 gave cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (CO) 4 Br 2 (3) in 88% yield. Reaction of 3 with AgOTf yields cis-[{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (CO) 4 (μ-Br)][OTf] (4), while reaction of 3 with Me 3 NO and AgOTf yields cis-[{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (CO) 2 (MeCN) 2 (μ-Br)][OTf] (5). Reaction of 3 under more forcing conditions with AgOTf in MeCN gave cis-[{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (CO) 2 (MeCN) 4 ][OTf] 2 (6), while a MeCN/C 6 H 6 solvent combination afforded cis-[{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (η 6 -C 6 H 6 ) 2 ][OTf] 2 (7) in a 64% yield. Removal of the benzene ligands in 7 can be accomplished by first adding Hto the coordinated benzene ligands to afford cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (η 5 -C 6 H 7 ) 2 (10). Subsequent protonation of 10 in MeCN afforded [cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (MeCN) 6 ][OTf] 2 (8) in 88% yield. Structural data for 4, 5, 7, and 10 are reported.

The reaction of cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }-Ru 2 (CO) 4 Br 2 with naphthalene affords the syn-facial [cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (μ-η 6 ,η 6 -C 10 H 8 )][OTf] 2 , (2 2+ ), a complex that appears to be two electrons short of the 18electron 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 2 2+ yields 2 + , a Class II mixed-valence complex, while the two-electron reduction of 2 2+ causes a hapticity change from η 6 to η 4 on one of the naphthalene rings and yields cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (μ-η 6 ,η 4 -C 10 H 8 ) (2 0 ), a zwitterionic complex. The DFT calculations predict that the C s isomer of 2 0 is 4.69 kcal/mol lower in energy than the C 2v isomer, which is a transition state. Reaction of cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (CO) 4 Br 2 with anthracene affords the analogous syn-facial anthracene complex, [cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (μ-η 6 ,η 6 -C 14 H 10 )][OTf] 2 , (4), and the tetranuclear dianthracene complex, [cis-{(η 5 -C 5 H 3 ) 2 (CMe 2 ) 2 }Ru 2 (μ-η 6 ,η 6 -C 14 H 10 )] 2 [OTf] 4 , (5). 2 2+ , 2 0 , and 5 were structurally characterized by X-ray diffraction.