Paramagnetic tetrahedral dinitrosyliron complexes containing redox-active cyanomanganese ligands

Abstract

The redox-active cyanomanganese ligands trans-[Mn(CN)(CO)₂{P(OEt)₃}(dppm)](dppm = Ph₂PCH₂PPh₂), cis-[Mn(CN)(CO)₂(PEt₃)(dppe)](dppe = Ph₂PCH₂CH₂PPh₂) and trans-[Mn(CN)(CO)(dppm)₂] reacted with [{Fe(µ-I)(NO)₂}₂] in CH₂Cl₂ to give the heterobinuclear complexes [FeI{(µ-NC)MnL_x}(NO)₂]{L_x=trans-(CO)₂[P(OEt)₃](dppm)1, cis-(CO)₂(PEt₃)(dppe)2 and trans-(CO)(dppm)₂3}; the molecular structure of 3 is consistent with a tetrahedral iron(–I) centre bound to octahedral manganese(I) by a near linear Mn–CN–Fe bridge. The ESR spectra of complexes 1–3 are very similar to those of the tetrahedral Fe^–1 complex [FeI₂(NO)₂]^–. Complexes 1–3 reacted with PPh₃ in the presence of TIPF₆ to give [Fe(PPh₃){(µ-NC)MnL_x}(NO)₂][PF₆]{L_x=trans-(CO)₂[P(OEt)₃](dppm)5⁺, cis-(CO)₂(PEt₃)(dppe)6⁺ and trans-(CO)(dppm)₂7⁺} which were also prepared from [Fe(PPh₃)₂(NO)₂][PF₆] and the appropriate cyanomanganese ligand in a 1 : 1 ratio; the related cation [Fe(PPh₃){(µ-NC)MnL_x}(NO)₂]⁺{L_x=trans-(CO)₂[P(OPh)₃](dppm)8⁺} was generated in solution. The ESR spectra of complexes 6⁺–8⁺ showed hyperfine coupling to N(O), P, N(C) and Mn, suggesting a structure similar to that of [Fe(PPh₃)(OPPh₃)(NO)₂]⁺ with some delocalisation through the cyanide bridge to manganese. Treatment of 2 equivalents of trans-[Mn(CN)(CO)₂{P(OEt)₃}(dppm)] or cis-[Mn(CN)(CO)₂(PEt₃)(dppe)] with [Fe(PPh₃)₂(NO)₂][PF₆] gave the heterotrinuclear complexes [Fe{(µ-NC)MnL_x}₂(NO)₂][PF₆]{L_x=trans-(CO)₂[P(OEt)₃](dppm)9⁺ and cis-(CO)₂(PEt₃)(dppe)10⁺} which may also be prepared from the reaction of 1 with trans-[Mn(CN)(CO)₂{P(OEt)₃(dppm)] or 2 with cis-[Mn(CN)(CO)₂(PEt₃)(dppe)] in the presence of TIPF₆. Complexes 1–10⁺, which contain diamagnetic Mn^I and paramagnetic Fe^–I centres, undergo oxidation and reduction at a platinum electrode in CH₂Cl₂. The Mn^II derivatives 3⁺ and 7²⁺ and the Fe^–II complex 7 have been generated in solution by ferrocenium ion oxidation or cobaltocene reduction respectively.