Synthesis and Structural Characterization of Lithium Thiolates: Dependence of Association and Aggregation on Donor Hapticity and Ligand Size and Synthesis of the First Trimeric Lithium Thiolate [Li(THF)SR]₃ and the Solvent-Separated Ion Pair [Li(12-crown-4)₂][SR] (R = 2,4,6-tBu₃C₆H₂)¹

The synthesis and structural characterization of several lithium thiolates are reported. Formation of discrete species can be achieved by careful variation of ligand size and donor hapticity, as exemplified by the monomeric formulation of Li(PMDTA)STrityl (PMDTA = N,N,N',N'',N''-pentamethyldiethylenetriamine, Trityl = CPh₃), 1, and Li-(PMDTA)STrip, 2 (Trip = 2,4,6-iPr₃C₆H₂), versus the dimeric species [Li(THF)₂STrityl]₂, 3, and [Li(TMEDA)-STrip]₂, 4 (TMEDA = N,N,N'N'-tetramethylethylenediamine). By control of the stoichiometry of the donor, the first trimeric lithium thiolate [Li(THF)SMes*]₃, 5 (Mes* = 2,4,6-tBu₃C₆H₂), exhibiting a six-membered ring system and rare three-coordinate lithium centers, becomes available. In contrast, use of a crown ether leads to the isolation of the monomeric contact ion pair Li(12-crown-4)STrityl, 6, while employing the cumbersome - SMes* ligand allows for the isolation of the first solvent-separated lithium thiolate [Li(12-crown-4)₂][SMes*], 7. All compounds were prepared by reacting the respective thiols with nBuLi in the presence of various donor adjuncts. The target molecules were characterized using ¹H NMR and IR spectroscopy and melting point criteria. Crystal structure analysis was employed to determine solid state structures. Crystal data are as follows. 1: Cu Kα (λ = 1.541 78 Å) at 130 K, a = 12.152(3) Å, b = 15.260(3) Å, c = 14.764(5) Å, β = 106.90(2)°, V = 2619.6(12) ų, Z = 4, monoclinic, space group P2₁/c, 2526 reflections (I > 2σ(I)), R = 0.064. 2: Cu Kα (λ = 1.541 78 Å) at 228 K, a = 15.805(7) Å, b = 9.206(4) Å, c = 18.923(7) Å, β= 99.74(3)̊, V = 2714(2) ų, Z = 4, monoclinic, space group P2₁/n, 2047 reflections (I > 2σ(I)), R = 0.085. 3: Mo Kα (λ = 0.710 73 Å) at 213 K, a = 13.141(3) A, b = 12.381(2) Å, c = 14.664(3) Å, β = 94.84(3)°, V = 2377.3(8) ų, Z = 2, monoclinic, space group P2₁/n, 2622 reflections (I > 2σ(I)), R = 0.052. 4: Cu Kα (λ = 1.541 78 Å) at 130 K, a = 18.906(4) Å, b = 9.516(2) Å, c = 25.617(5) Å, β = 92.75(3)°, V = 4603(2) ų, Z = 4, monoclinic, space group I2/a, 2390 reflections (I > 2σ(I)), R = 0.067. 5: Mo Kα (λ = 0.710 73 Å) at 213 K, a = 9.991(2) Å, b = 17.934(4) Å, c = 20.314(4) Å, α = 83.36(3)°, β= 76.74(3)°, γ = 76.72(3)°, V = 3440.4(12) ų, Z = 2, triclinic, space group P1, 6397 reflections (I > 2.5σ(I)), R = 0.063, 6: Mo Kα (λ = 0.710 73 Å) at 213 K, a = 10.542(2) Å, b = 12.821(3) Å, c = 18.729(4) Å, β = 102.22(3)°, V = 2474.0(9) ų, Z = 4, monoclinic, space group P2₁/c, 4206 reflections (I > 2σ(I)), R = 0.086. 7: Mo Kα (λ = 0.710 73 Å) at 213 K, a = 10.134(2) Å, b= 19.800(4) Å, c = 18.423(4) Å, β = 93.15(3)°, V = 3691.0(13) ų, Z = 4, monoclinic, space group P2₁/n, 4088 reflections (I > 2σ(I)), R = 0.092.