Structure and Electrochemistry of Heterobimetallic Ferrocenecarboxylatoruthenium(II) Complexes

The mixed-valent diruthenium complexes [Ru2(μ-O2CR)4L2](PF6) (where R = CH3, L =
H2O or R = Fc (ferrocenyl), L = MeOH) were reacted with the three diphosphine (dpp) ligands
bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), and 1,3-bis(diphenylphosphino)propane (dppp) to yield, via a disassembly reaction, the monoruthenium(II) complexes [Ru(η2-O2CR)(dpp)2](PF6) (R = CH3 and dpp = dppm (1), dpp = dppe
(2), dpp = dppp (3); R = Fc and dpp = dppm (4), dpp = dppe (5), dpp = dppp (6)). All six
complexes were characterized by elemental analysis, IR and NMR (1H and 31P) spectroscopy,
cyclic and Osteryoung square wave voltammetry, and X-ray crystallography. Complexes 4−6
are rare examples of structurally characterized ruthenium complexes with η2-bound
ferrocenecarboxylate ligands, and they are unique in displaying a metal and an organometallic center. The electrochemical measurements reveal an essentially reversible ruthenium-centered redox process for complexes 2 and 3, which becomes irreversible in the presence of
the ferrocenyl group in complexes 4−6. The iron-centered redox process in complexes 4−6
is chemically reversible. The separation between these redox processes is large (>1.0 V),
leading to a stable “mixed-valent” state, and increases in the potential separation of these
two redox processes over the separation seen between the redox potentials of the isolated
ruthenium and ferrocenecarboxylate fragments may indicate the possibility of metal−metal
interactions. A mechanism for the disassembly process, exploited in the synthetic procedure,
is postulated.