Monomeric M(ii) (M = Fe, Co, Ni) complexes supported by bulky aryloxide ligands tethered to an arene functionality; synthesis, electrochemistry and study of the M(ii)–arene interaction

Abstract

The aminolysis reaction between MN′′₂ (N′′ = N(SiMe₃)₂; M = Fe, Co, Ni) and the neutral pro-ligand 6,6′-(1,4-phenylenebis(propane-2,2-diyl))bis(2,4-di-tert-butylphenol) (LH₂) affords the low coordinate, isomorphous, monomeric bis-aryloxide complexes (2-M) (M = Fe, Co, Ni). Their molecular structures all feature a basal arene functionality, poised to interact with the metal centre, anchored by two sterically encumbering pendant aryloxide arms. Complexes (2-M) show metal–arene interactions with decreasing strength from (2-Ni), to (2-Co) and finally to (2-Fe). The M–arene interactions were evaluated by a combination of SC-XRD studies, supported by computational investigation and IR spectroscopic characterisation of basal–arene C–C stretches in the absence and the presence of THF in their coordination sphere. The mono-THF adducts (2-Fe·THF) and (2-Co·THF) were also synthesised, isolated and structurally characterised, showing that the M–arene interaction is disrupted upon THF coordination. Cyclic voltammetry (CV) studies of (2-Fe) and (2-Co) show reversible M²⁺/M⁺ reduction waves in non-coordinating solvent, and more complex redox chemistry upon THF coordination with (2-Fe·THF) and (2-Co·THF) in THF.