Structure and Electrochemistry of Various Diruthenium(II,III) Tetrametallocenecarboxylates

A series of mixed-valent diruthenium(II,III) tetrametallocenecarboxylates of the form Ru2(μ-O2C(X)C5H4MCp)4Cl, where M = Fe(II) and X = nothing (1), −CH2− (2), −CH2CH2− (3),
−CHCH− (5), M = Ru(II) and X = nothing (6), and the corresponding dechlorinated alcohol
di-adducts [Ru2(μ-O2C(X)C5H4MCp)4(ROH)2](PF6), where M = Fe(II), R = ethyl or 1-propyl,
and X = nothing (7), −CH2− (8), −CH2CH2− (9), and −CHCH− (10), and M = Ru(II) and
X = nothing (11), were synthesized and characterized. In addition, the partially substituted
complex with the tentative formula Ru2(μ-O2CCH3)3(μ-O2C(X)C5H4FeCp)4Cl, where X = −CH2CH2CH2− (4), was partially characterized. Complex 7 was structurally characterized
previously, and the structures of complexes 10 and 11 are reported here. The complexes
differ significantly in the orientation of the metallocenyl rings with respect to each other.
An extension of the electrochemical studies that previously revealed evidence of ferrocenyl−ferrocenyl communication in complex 7 shows that this interaction is absent as the X group
is lengthened and saturated, but a small degree of communication is still present in complex
10, which contains an unsaturated, conjugated, spacer. The trend in the ferrocenyl-based
redox process for complexes 7−10 mimics that of the corresponding free acids. No interactions
are seen in the ruthenocenyl derivative (11) due to the irreversibility of its ruthenocenyl-centered redox processes.