Calcium complexes of noninnocent α-diimine ligands

A series of calcium compounds with α-diimine ligands, [L ^-Ca-(μ₂-Cl)(THF)₂]₂ (1, L = L^iPr; 2, L = L^Mes), [(L^iPr)^2- ₂CaK₂(THF)]_n (3), [(L^Mes) ^2-Na(THF)₂]₂Ca (4), and [Ca(L ^iPr)^2-Li(THF)(μ₃-Cl)Li(THF) ₂(μ₃-Cl)]₂ (5), where L^iPr = [(2,6-ⁱPr₂C₆H₃)NC(Me)]₂ and L^Mes = [(2,4,6-Me₃C₆H₂)NC(Me)] ₂, have been synthesized by the reaction of the lithium, sodium, or potassium salts of the reduced ligands (L^- or L^2-) with calcium chloride. Single-crystal X-ray diffraction analyses reveal that compounds 1 and 2 are isostructural dinuclear compounds bridged by chloride ions, compound 3 forms a left-handed 2₁ helical structure, while 4 features a metallocene-like structure, and 5 forms a laddered aggregate. The ligand exists as the doubly reduced dianionic form in 3-5 and appears as the radical anion in compounds 1 and 2. The coordination modes of the alkali metal and calcium ions in these complexes are discussed.