Masked Divalent Reactivity of Heterobimetallic Lanthanide Isocarbonyl Complexes.

A new rare-earth reduction system is described in which trivalent yttrium and dysprosium react as though present in their unstable divalent oxidation state. This masked divalent reactivity is achieved using the isocarbonyl-bridged dimers [( M)(μ-Fp)] (M=Y, 1; M=Dy, 1; Cp=1,2,4-C BuH; Fp=CpFe(CO)), where the reducing electrons originate from the bridging [Fp] ligands. The reactivity of 1 and 1 is showcased by reducing the N-heterocycles 2,2'-bipyridyl (bipy), phenazine (phnz) and hexaazatrinaphthylene (HAN) to give corresponding mono-, di- and tri-metallic rare-earth complexes, respectively, with the heterocyclic ligands present in their singly, doubly and triply reduced forms, respectively. The dynamic magnetic properties of the dysprosium compounds are described. Compound 1 is a single-molecule magnet (SMM) with an appreciable energy barrier of 449(17) cm, whereas [( Dy)(μ-phnz)] (3) is not an SMM because of a strong, competing equatorial crystal field. Surprisingly, [( Dy)(HAN)] (4) is also not an SMM, the origins of which are traced to the impact of the tert-butyl substituents on the dysprosium centre and its interaction with the radical [HAN] ligand.