Intramolecular electron transfer in linear trinuclear complexes of copper(I), silver(I) and gold(I) bound to redox-active cyanomanganese ligands

The reaction of [Cu(NCMe)(4)][PF6] with 2 equivalents of [Mn(CN)L(x)]{L(x) = (CO)(dppm)(2), cis- or trans-(CO)(2)[P(OR)(3)](dppm) (R = Ph or Et, dppm = Ph(2)PCH(2)PPh(2))} in CH2Cl2 gave [Cu{mu-NC)MnL(x)}(2)][PF6]. With 2 equivalents of [Mn(CN)L(x)] in toluene, AgPF6 gave [Ag{(mu-NC)MnL(x))(2)](+) {L(x) = cis- or trans-(CO)(2)[P(OR)(3)](dppm) (R = Ph or Et)} but in CH2Cl2 cis-[Mn(CN)(CO)(2)(PEt(3))(dppe)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) or trans-[Mn(CN)(CO)(dppm)(2)] and AgX (X = BF4-, PF6- or SbF6-) gave the tricationic manganese(II) complexes [Ag{(mu-NC)Mn(CO)(dppm)(2)}(2)][PF6](3) and [Ag{(mu-NC)MnL(x)}(2)]X(3) {L(x) = trans-(CO)(2)(PEt(3))(dppe)]; the complexes [Ag{(mu-NC)MnL(x)}(2)][PF6](3) {L(x) = trans-(CO)(2)[P(OR)(3)](dppm) (R = Ph or Et)} were prepared directly from Ag[PF6] and trans-[Mn(CN)(CO)(2){P(OR)(3)}(dppm)][PF6] (R = Ph or Et) in CH2Cl2. Treatment of [AuCl(tht)] (tht = tetrahydrothiophene) with [Mn(CN)L(x)] in CH2Cl2 in the presence of Tl[PF6] yielded [Au{(mu-NC)MnL(x)}(2)][PF6] {L(x) = (CO)(dppm)(2), cis- or trans-(CO)(2)[P(OR)(3)](dppm) (R = Ph or Et)}. X-Ray structural studies on [Ag{(mu-NC)MnL(x)}(2)][PF6] {L(x) = trans-(CO)(2)[P(OPh)(3)](dppm)}, [Au{(mu-NC)MnL(x)}(2)][PF6] {L(x) = trans-(CO)(2)[P(OEt)(3)](dppm)}, and [Ag{(mu-NC)MnL(x)}(2)][PF6](3) [L(x) = (CO)(dppm)(2)] showed, in each case, near linear Mn-CN-M'-NC-Mn skeletons (M' = Ag or Au); the Mn-P and P-substituent bond lengths are consistent with octahedral Mn-I and Mn-II centres in the monocations and trication respectively. Each of the complexes [M'{(mu-NC)MnL(x)}(2)][PF6] {M' = Cu or Au, L(x) = (CO)(dppm)(2); M' = Cu or Ag, L(x) = trans-(CO)(2)[P(OR)(3)](dppm) (R = Ph or Et)} showed one reversible two-electron oxidation wave at a platinum electrode in CH2Cl2; the trication [Cu{(mu-NC) Mn(CO)(dppm)(2)}(2)](3+) was generated in solution by controlled potential electrolysis of [Cu{(mu-NC)Mn(CO)(dppm)(2)}(2)](+), and [Au{(mu-NC)Mn(CO)(dppm)(2)}(2)][PF6](3) was prepared by chemical oxidation of [Au{(mu-NC)Mn(CO)(dppm)(2)}(2)][PF6] with [Fe(cp)(2)][PF6] (cp = eta-C5H5) in CH2Cl2. Magnetic and ESR spectroscopic studies provided further evidence for the presence of two isolated low-spin Mn-II centres in the trications [Ag{(mu-NC)MnL(x)}(2)](3+) {L(x) = (CO)(dppm)(2), trans-(CO)(2)[P(OR)(3)](dppm) (R = Ph or Et) or trans-(CO)(2)(PEt(3))(dppe)}. By contrast, [Au{(mu-NC)MnL(x)}(2)](+) {L(x) = trans-(CO)(2)[P(OR)(3)](dppm) (R = Et or Ph)} showed two reversible one-electron oxidation waves corresponding to the stepwise formation of di- and trications. Electrolytic oxidation of [Au{(mu-NC)MnL(x)}(2)](+) in tetrahydrofuran, or chemical oxidation with [N(C6H4Br-p)(3)](+) or [Fe(eta-C(5)H(4)COMe)(cp)](+) in CH2Cl2, gave solutions of [Au{(mu-NC)MnL(x)}(2)](2+) {L(x) = trans-(CO)(2)[P(OEt)(3)](dppm)}, IR spectroscopic and voltammetric studies on which are compatible with weak interaction between the two manganese centres in the mixed-valence dication.