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 [(Cpttt2M)(μ‐Fp)]2 (M = Y, 1Y; M = Dy, 1Dy; Cpttt = 1,2,4‐C5tBu3H2; Fp = CpFe(CO)2), where the reducing electrons originate from the bridging [Fp]– ligands. The reactivity of 1Y and 1Dy 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 1Dy is a single‐molecule magnet (SMM) with an appreciable energy barrier of 449(17) cm–1, whereas [(Cpttt2Dy)2(m‐phnz)] (3Dy) is not an SMM because of a strong, competing equatorial crystal field. Surprisingly, [(Cpttt2Dy)3(HAN)] (4Dy) 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]3– ligand.