Tuning low-coordinate metal environments: High spin d⁵–d⁷ complexes supported by bis(phosphinimino)methyl ligation

Treatment of FeCl₂ with the lithium derivative of [CH₂(Ph₂P═NC₆H₂Me₃-2,4,6)₂] in THF and crystallisation from Et₂O gave the ‘ate’ complex [(CH(Ph₂PNC₆H₂Me₃-2,4,6)₂)Fe(μ-Cl)₂Li(THF)(OEt₂)] in which the iron is four-coordinate and the chlorides bridge to lithium. Treatment of [M(N(SiMe₃))₂] (M = Mn, Fe, Co) with [CH₂(Ph₂P═NC₆H₂Me₃-2,4,6)₂] in toluene afforded the complexes [(CH(Ph₂PNC₆H₂Me₃-2,4,6)₂)MN(SiMe₃)₂] which all feature essentially planar N(1)–N(2)–N(3)–M coordination. The carbanionic character of the bis(phosphinimino)methyl ligand results in close C(1)–M contacts in both the Mn and Co complexes effectively raising the coordination number to four. The analogous iron compound is strictly three-coordinate as demonstrated by X-ray crystallography and ⁵⁷Fe Mössbauer. However protonolysis of this compound with Ph₃COH yields the iron alkoxide [(CH(Ph₂PNC₆H₂Me₃-2,4,6)₂)FeOCPh₃] that features a close C(1)–Fe contact of 2.375 Å. Although the iron centre in this complex is only marginally pyramidalised by this contact, its ⁵⁷Fe Mössbauer spectrum indicates a significant perturbation to the local electronic environment at the metal.