2-ELECTRON AND ONE-ELECTRON REDUCTION OF THE INDENYL COMPLEX [MN(ETA(5)-C9H7)(CO)(3)] AND REVERSIBLE COUNTERION-CONTROLLED COMPROPORTIONATION OF [MN(ETA(5)-C9H7)(CO)(3)] AND [MN(ETA(3)-C9H7)(CO)(3)](2-) TO GIVE [MN(ETA(5)-C9H7)(CO)(3)](-)

Two-electron reduction of [Mn(eta(5)-C9H7)(CO)(3)] (3) gives a dianion formulated as the ring-slipped indenyl complex [Mn(eta(3)-C9H7)(CO)(3)](2-) (4(2-)), and protonation of the activated indenyl ligand in 4(2-) in the presence of naphthalene yields the eta(4)-naphthalene complex [Mn(eta(4)-C10H8)(CO)(3)](-) (6(-)). One-electron reduction of 3 leads to a mixture of 3, 4(2-), and the monoanionic species [Mn(eta(5)-C9H7)(CO)(3)](-) (5(-)). Subsequent addition of 18-crown-6 (18-C-6) gives a solution of 5(-) alone (IR), and we propose that 18-C-6 complexation of K+ perturbs solution ion pairing, which would be expected to stabilize 4(2-), sufficiently to induce 3 and 4(2-) to comproportionate to 5(-). This equilibrium can be shifted back toward 3 and 4(2-) by addition of 10 equiv of NaPF6 to induce disproportionation of 5(-). The formulation of 5(-) as [Mn(eta(5)-C9H7)(CO)(3)](-) is supported by EPR spectra (a symmetrical sextet, [g] = 1.986, [a](Mn-55) = 31 G) and susceptibility measurements. The importance of disproportionation of 5(-) in its chemistry is demonstrated by the reaction of [K(18-C-6)]5 with Bu(3)SnH to give [K(18-C-6)][Mn(eta(5)-C9H7)(Co)(2)(SnBu(3))] ([K(18-C-6)]7) in 34% yield together with 3 (41%). Equimolar formation of 7(-) and 3 suggests that 5(-) disproportionates in this reaction to 3 and 4(2-) and that 4(2-) then reacts with Bu(3)SnH to form 7(-). Independent experiments establish that Bu(3)SnH reacts with 4(2-) to give 7(-) (60% by IR). Treatment of 3 with excess [K(18-C-6)]-[SnBu(3)] gives [K(18-C-6)]7 in 35% yield, establishing that 7(-) could be formed from 4(2-) via 3. Treatment of 5(-) with O-2, CO2, the trityl dimer, or H2O2 gives 3 quantitatively. Cyclic voltammograms of 3 in THF exhibit two successive one-electron reductions (as confirmed by chronocoulometry) at (E(a) + E(c))/2 = -1.95 and -2.20 V vs SCE. The small difference between these potentials suggests marked stabilization of the final reduction product 4(2)-by an eta 5 - eta 3 hapticity shift concomitant with the second reduction and also supports eta(5)-indenyl ligation in the first reduction product 5(-).