Entrapment of Lithium Salts by the Lithium Amidinate Li[(ⁿBu)C(N^tBu)₂]

Four novel complexes involving lithium amidinates and lithium salts have been synthesized and crystallographically characterized. Addition of anhydrous LiX (X = OH, Cl, Br, I) to Li[(nBu)C(NtBu)2] in THF afforded laddered aggregates in which two neutral lithium amidinates chelate one LiX unit. In the case of LiOH, LiCl, and LiBr, the ladders thus formed dimerize about their external LiX edges to form the complexes {(Li[(nBu)C(NtBu)2])2·LiX·THF}2 (X = OH, Cl, Br). When the added salt is LiI, however, dimerization is apparently prevented by solvation, producing the monomeric laddered aggregate {Li[(nBu)C(NtBu)2]}2·LiI·2THF. In all cases, the laddered structures have a distinctive, undulating shape imparted by the conformation of the [LiNLiX] units; each three-rung ladder is composed of contiguous cisoid and transoid four-membered rings. The moieties in the dimeric species are linked by a transoid [LiX]2 ring. In this way, Li[(nBu)C(NtBu)2] acts as a versatile “lithio ligand” capable of chelating a variety of neutral lithium salts through electrostatic interactions. Crystal data: 3, triclinic, space group P1̄, a = 13.142(4) Å, b = 13.239(4) Å, c = 11.425(2) Å, α = 94.30(2)°, β = 99.40(2)°, γ = 64.32(2)°, V = 1767(1) Å3, Z = 2; 4, monoclinic, space group P21/n, a = 13.514(5) Å, b = 11.619(6) Å, c = 24.020(8) Å, β = 99.78(4)°, V = 3717(3) Å3, Z = 4; 5, monoclinic, space group P21/n, a = 15.163(5) Å, b = 15.746(3) Å, c = 17.024(6) Å, β = 109.32(2)°, V = 3835.7(18) Å3, Z = 4; 6, monoclinic, space group P21/n, a = 12.306(6) Å, b = 18.276(8) Å, c = 19.000(6) Å, β = 96.61(4)°, V = 4245(3) Å3, Z = 4.