Synthesis and single-molecule magnet properties of a trimetallic dysprosium metallocene cation

The dimetallic fulvalene-bridged dysprosium complex [{Dy(Cp*)(μ-BH(4))}(2)(Fv(tttt))] (1, Cp* = C(5)Me(5)) is converted into the trimetallic borohydride-bridged species [{Dy(Cp*)(Fv(tttt))}(2)Dy(μ-BH(4))(3)] (2). In turn, 2 is reacted with a silylium electrophile to give [{Dy(Cp*)(μ-BH(4))(Fv(tttt))}(2)Dy][B(C(6)F(5))(4)] ([3][B(C(6)F(5))(3)]), the first trimetallic dysprosocenium cation. Compound [3][B(C(6)F(5))(3)] can also be formed directly from 1 by adding two equivalents of the electrophile. A three-fold enhancement in the effective energy barrier from 2 to 3 is observed and interpreted with the aid of ab initio calculations.