In attempts to form extended chains Ru(2)(O(2)C(CH(2))(6)CH(3))(4) (1) was reacted with both simple coordination and redox-active bridging ligands. The simple coordination ligands, pyrazine (pz) and 4-cyanopyridine (4-cp), coordinated in the axial sites of the diruthenium complex. With the symmetric ligand pyrazine, the polymer [1(pz)](n)() was isolated. With the asymmetric ligand 4-cp, the pyridine nitrogen coordinated preferentially and the bis-adduct 1(4-cp)(2) was isolated. Solution UV/visible and NMR studies indicated that pi-interactions between the Ru-Ru pi and ligand pi orbitals were occurring in both cases. Mole ratio and continuous variation studies of 1 with pyrazine and 4-cp indicated that these axial ligands were labile and that a number of solution species existed. When 1 was reacted with TCNE, redox reactions occurred. Solid-state IR and solution NMR studies also showed that both 1(TCNE) (2) and [1](2)TCNE (3) contained diruthenium carboxylate cores which no longer possessed the D(4)(h)() paddle-wheel geometry. With p-benzoquinone, redox reactions occurred upon coordination to give [1(+)][SQ(-)(*)] (4), which contained an undisrupted oxidized diruthenium tetracarboxylate core. Formation of 4 was reversible in solution, with 1 and p-benzoquinone being favored at higher temperatures.
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Wesemann et al. (1997) studied this question.
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