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

The La 2+ complex [K(18-crown-6)(OEt 2 )][Cp″ 3 La] ( 1 ) [Cp″ = C 5 H 3 (SiMe 3 ) 2 -1,3], can be synthesized under N 2, but in the presence of KC 5 Me 5, 1 reduces N 2 to the (N═N) 2– product [(C 5 Me 5 ) 2 (THF)La] 2 (μ-η 2:η 2 -N 2 ). 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 Y 2+ complex could be isolated using this logic, Cp′ 3 Y ( 2 ) (Cp′ = C 5 H 4 SiMe 3 ) was synthesized from YCl 3 and KCp′ and reduced with KC 8 in the presence of 18-crown-6 in Et 2 O at −45 °C under argon. EPR evidence was consistent with Y 2+ and crystallization provided the first structurally characterizable molecular Y 2+ complex, dark-maroon-purple [(18-crown-6)K][Cp′ 3 Y] ( 3 ).