Incorporation of Ru-2(O2C(CH2)(6)CH3)(4) into extended chains: Interaction of Ru-2(O2C(CH2)(6)CH3)(4) with pyrazine, 4-cyanopyridine, TCNE, and p-benzoquinone

In attempts to form extended chains Ru-2(O2C(CH2)(6)CH3)(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)](2) 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-4h 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.