Coordination chemistry of a bulky redox-active cyanomanganese carbonylligand: N-bound tetrahedral complexes of 3d metals

Abstract

The sterically hindered redox-active cyanomanganese carbonyl complex trans-[Mn(CN)(CO)(dppm)₂] acts as an N-donor ligand towards MCl₂ (M = Mn, Co or Ni) to give the cyanide-bridged tetrahedral (at M) complexes [Cl₂(thf)M(μ-NC)MnL_x] {L_x = (CO)(dppm)₂}. Displacement of the labile thf ligand by chloride ion affords anionic [Cl₃M(μ-NC)MnL_x]⁻ which is oxidised to [Cl₃M(μ-NC)MnL_x], containing two paramagnetic centres, tetrahedral M(II) and low spin octahedral Mn(II). The cobalt(II) complex [Cl₂(thf)Co(μ-NC)MnL_x] also undergoes thf substitution with neutral N-donor ligands to give [Cl₂L′Co(μ-NC)MnL_x] {L′ = 4,4′-bipy or (NC)Mn(PPh₃)(NO)(η-C₅H₄Me)}; the latter is oxidised to the mixed valence trimetallic cation [Cl₂Co^II{(μ-NC)Mn^IIL_x}{(μ-NC)Mn^I(PPh₃)(NO)(η-C₅H₄Me)}]⁺. X-Ray structural studies on [Cl₂(thf)M(μ-NC)MnL_x] (M = Co, Mn or Ni) and [Cl₃Mn(μ-NC)MnL_x] show distortion of the M–N–C angle to accommodate non-bonded interactions between the phenyl groups of the bulky Mn(dppm)₂ moiety and the ligands at the tetrahedral metal; distortions of the tetrahedral valence angles at the M^II centres of [Cl₂(thf)M(μ-NC)MnL_x] may in part be related to the weak binding of thf.