Synthesis and Structures of New Mixed-Metal Lanthanide/Magnesium Allyl Complexes

The reaction of LnI3(THF)n (Ln = La, n = 4; Ln = Y, n = 3.5) with 3 equiv of allylMgI in
THF/1,4-dioxane proceeds in moderate yields to give the unexpected mixed-metal complexes
[Ln(η3-C3H5)3(μ-C4H8O2)·Mg(η1-C3H5)2(μ-C4H8O2)1.5]∞ (Ln = La 1, Y 2). By contrast, samarium
iodide gives a salt containing a new allyl-bridged anion, [Mg(THF)6][Sm2(η3-C3H5)6(μ-η3:η3-C3H5)]2·toluene (3), while neodymium iodide affords [Mg(THF)6][Nd(η3-C3H5)4]2·2THF (4)
under the same reaction conditions. On reaction with a mild proton acid such as the diketimine 2-(2,6-diisopropylphenyl)amino-4-(2,6-diisopropylphenyl)imino-2-pentene, 3 is converted
into [Mg(THF)6][Sm(η3-C3H5)4]2·2THF (5), alongside Sm(η3-C3H5)2{κ3-HC(MeCNC6H3iPr2-2,6)2}. The solid-state structures of 1 and 2 contain distorted trigonal-bipyramidal lanthanide
centers with three η3-allyl ligands and distorted trigonal-bipyramidal magnesium centers
with two η1-bonded allyls. Both metal centers are connected by bridging 1,4-dioxane molecules
building a planar polymeric network. By contrast, 3 and 5 consist of well-defined discrete
ions. Complex 3 contains an unprecedented type of binuclear anion containing two samarium
centers bridged by an η3:η3-allyl ligand, while the anion in 5 has distorted tetrahedral
geometry.