Oxygenation of heterodinuclear di(µ-phenoxo) CoIIMII (M = Mn, Fe or Co) complexes having a “Co(salen)” entity in a macrocyclic framework†

Abstract

Heterodinuclear di(µ-phenoxo) Co^IIM^II complexes [CoM(L)(AcO)]ClO₄ (M = Mn 1, Fe 2 or Co 3) and [CoM(L)(NCS)]ClO₄ (M = Mn 4, Fe 5 or Co 6) have been obtained where L^2– is a heterodinucleating macrocycle derived by the 2∶1∶1 condensation of 2,6-diformyl-4-methylphenol, ethylenediamine and diethylenetriamine and has a “salen”-like N₂O₂ metal-binding site and a “saldien”-like N₃O₂ site sharing the phenolic oxygens. The CoM(AcO) complexes 1 and 3 show reversible oxygenation at 0 °C in dmf, whereas 2 is irreversibly oxidized under the same conditions. The structures of the dioxygen adducts of 1 and 3 have been determined by X-ray crystallography. In that of 1, [{CoMn(L)(AcO)}₂(O₂)][ClO₄]₂·4CH₃CN oxy-1, the Co resides in the “salen” site and the Mn in the “saldien” site. An exogenous acetate group bridges the two metal ions in the η¹∶η¹ mode together with the two phenolic oxygens. The peroxo group bridges two {CoMn(L)(AcO)} molecules at the Co forming a Co–O–O–Co linkage. The peroxo O(1)–O(2) bond distance is 1.416(5) Å and the Co(1)· · ·Co(2) intermetallic separation is 4.359(1) Å. The geometry about the Co is pseudo octahedral with a peroxo oxygen and an acetate oxygen at the axial sites and the Mn has a distorted six-co-ordination. The dioxygen adduct of 3, [{Co₂(L)(AcO)}₂(O₂)][ClO₄]₂· 4CH₃CN oxy-3, is isomorphous with oxy-1: the peroxo O(1)–O(2) bond distance is 1.415(4) Å and the Co(1)· · ·Co(3) intermetallic separation is 4.3527(8) Å. Within the CoM(NCS) complexes 4–6, 4 shows reversible oxygenation at –30 °C, whereas irreversible oxidation is observed for 5 and 6.