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)MnLx}(NO)2]{Lx=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)MnLx}(NO)2][PF6]{Lx=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)MnLx}(NO)2]+{Lx=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)MnLx}2(NO)2][PF6]{Lx=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 MnI and paramagnetic Fe–I centres, undergo oxidation and reduction at a platinum electrode in CH2Cl2. The MnII derivatives 3+ and 72+ and the Fe–II complex 7 have been generated in solution by ferrocenium ion oxidation or cobaltocene reduction respectively.