Diastereoselectivity in the self-assembly of As₂L ₂Cl₂ macrocycles is directed by the As-π interaction

The As-π interaction, in conjunction with reversible As-thiolate bond formation, is used to direct the self-assembly of dinuclear As₂L ₂Cl₂ (L = a dithiolate) macrocycles that exist as equilibrium mixtures of both syn and anti diastereomers. The diastereomeric excess of these self-assembly reactions is controlled in a predictable manner by prudent choice of different achiral, isomeric ligands. A general method for the preparation of As₂L₂Cl₂ macrocycles is established, and strategies to control the diastereoselective self-assembly of regioisomeric macrocycles in solution and the crystalline state are described. A mechanism for the interconversion between diastereomers (a slow process on the NMR time scale) is suggested, and variable-temperature NMR spectroscopic data show that the diastereomeric excess (de) decreases with increasing temperature. anti-As₂(L^2,6)₂Cl₂ crystallizes in monoclinic space group P2₁/n with a = 6.3949(13), b = 19.675(4), c = 10.967(2) Å, β = 106.817(3)°, and Z = 2. anti-As ₂(L^1,5)₂Cl₂ crystallizes in monoclinic space group P2₁/c with a = 6.813(4), b = 19.085(12), c = 10.277(6) Å, β = 107.788(10)°, and Z = 4. syn-As ₂(L^1,4)₂Cl₂·CHCl₃ crystallizes in triclinic space group P1 with a = 19.313(4), b = 19.923(4), c = 24.508(5) Å, α = 78.110(4)°, γ = 78.860(5)°, γ = 89.183(5)°, and Z = 12. As₂(L^1.4)₂Cl ₂·C₆H₆ crystallizes in monoclinic space group P2₁/n with a = 10.3332(7), b = 34.375(2), c = 17.8593(12) Å, β = 98.9650(10)°, and Z = 8.