Synthesis and Evaluation of Thioether-Based Tris-Melamines as Components of Self-Assembled Aggregates Based on the CA·M Lattice

Two new tris-melamine derivatives, triazine-thio-M3 (5) (C3N3-2,4,6-[SCH2C6H4-3-N(CH2C6H4-4-C(CH3)3)COC6N3-2-NHC3N3(NH2)(NHCH2CH2C(CH3)3)-5-Br]3) and benzene-thio-M3 (6) (C6H3-1,3,5-[SCH2C6H4-3-N(CH2C6H4-4-C(CH3)3)COC6H3-2-NHC3N3(NH2)(NHCH2CH2C(CH3)3)-5-Br]3), were synthesized by reactions of 2,4,6-trithiocyanuric acid and 1,3,5-trimercaptobenzene with a bromobenzyl melamine derivative 19 (BrCH2C6H4-3-N(CH2C6H4-4-C(CH3)3)COC6H3-2-NHC3N3(NH2)(NHCH2CH2C(CH3)3)-5-Br). These two compounds formed stable and structurally well-defined 1 + 3 supramolecular aggregates with neohexyl isocyanurate (R'CA) (9) as shown by NMR spectroscopy and gel permeation chromatography. 1H NMR competition experiments indicated that the stability of triazine-thio-M3·(R'CA)3 (1) was similar to that of benzene-thio-M3·(R'CA)3 (2). The order of stabilities of tris-melamine-based 1 + 3 complexes was hubM3·(R'CA)3 (3) > triazine-thio-M3·(R'CA)3 (1) ∼ benzene-thio-M3·(R'CA)3 (2) > flexM3·(R'CA)3 (4). Computational simulations were also carried out on triazine-thio-M3·(R'CA)3 and hubM3·(R'CA)3 fully solvated in CHCl3. Values of DP (the deviation from planarity of the cyanuric acid and melamine rosette) obtained from these simulations correlated correctly with the observed stabilities and suggested a structural reason why triazine-thio-M3·(R'CA)3 was less stable than hubM3·(R'CA)3.