Synthesis of a Crystalline Molecular Complex of Y²⁺, [(18-crown-6)K][(C₅H₄SiMe₃)₃Y]

The La2+ complex [K(18-crown-6)(OEt2)][Cp″3La] (1) [Cp″ = C5H3(SiMe3)2-1,3], can be synthesized under N2, but in the presence of KC5Me5, 1 reduces N2 to the (NN)2– product [(C5Me5)2(THF)La]2(μ-η2:η2-N2). This suggests a dichotomy in terms of ligands that optimize isolation of reduced dinitrogen complexes versus isolation of divalent complexes of the rare earths. To determine whether the first crystalline molecular Y2+ complex could be isolated using this logic, Cp′3Y (2) (Cp′ = C5H4SiMe3) was synthesized from YCl3 and KCp′ and reduced with KC8 in the presence of 18-crown-6 in Et2O at −45 °C under argon. EPR evidence was consistent with Y2+ and crystallization provided the first structurally characterizable molecular Y2+ complex, dark-maroon-purple [(18-crown-6)K][Cp′3Y] (3).