The reactivity of dibenzotetramethyltetraaza[14]annulene-Mn(II): functionalisation of manganese in a macrocyclic environment

Abstract

The present report deals with the one electron oxidation and the one- and two-electron reduction of [Mn(tmtaa)L], [L = THF, 1a; L = none, 1b; tmtaa = dibenzotetramethyltetraaza[14]annulene]. The former class of reactions led to the formation of a variety of functionalised Mn(III) species, [(tmtaa)Mn–X] [X = I, 2; X = Cl, 3; X = NCS, 5], including the cationic derivatives [Mn(tmtaa)(L)(L′)]BPh₄ [L = L′ = THF, 4a; L = L′ = DME, 4b; L = Py, L′ = none, 4c]. The magnetic properties of the Mn(III) derivatives are strongly dependent on the axial ligand. Reaction of 1a with NO gave [(tmtaa)Mn(NO)], 6, which takes up an axial pyridine leading to the diamagnetic [(tmtaa)Mn(NO)(Py)], 7. Complex 6 displays a peculiar magnetic behavior, which has been interpreted as a S = 0  S = 2 spin equilibrium with a ΔH_eff = 4.0 kJ mol⁻¹ and a ΔS_eff = 11.3 J mol⁻¹ K⁻¹ associated to the spin transition process. Reaction of 1 with sodium metal in DME leads to [Mn₂(μ₂-tmtaa)₂{Na·(DME)₂}₂], 8, while in THF [Mn₂(*tmtaa₂*)Na₄·(THF)₆], 9, is formed. Extended Hückel calculations have been performed for a better understanding of the magnetic and electronic properties of 6 and 9. The proposed structures have been supported by X-ray analyses of 3, 4b, 6, 8, and 9.