Reductive Elimination of S ₂ N ₂ and Se ₂ N ₂ from Heavy Main Group Dithia- and Diselenadiazoles: A DFT Evaluation

Thermal decomposition pathways for cyclotrithiazenes Ph 3 EN-S 3 N 3 (E = P, As) have been examined by density functional theory methods. While open-chain derivatives S-ax -Ph 3 ENSNS formed by the initial release of c -N 2 S can isomerize to cyclic dithiadiazoles N-ax -Ph 3 ES 2 N 2, subsequent reductive elimination of S 2 N 2 is only kinetically and thermodynamically favored for E = As. Investigations of heavier pnictogen-based dithiadiazoles Ph 3 ES 2 N 2 (E = Sb, Bi) as precursors of S 2 N 2 indicate that the hypervalent five-coordinate antimony derivative is too stable, but the corresponding bismuth-based heterocycle has a much lower barrier for release of S 2 N 2 and more favorable overall energetics. Extension to the corresponding diselenadiazoles R 3 ESe 2 N 2 (E = Sb, Bi) suggests that the bismuth derivative may serve as a benign source of Se 2 N 2 . Exploration of heavy heteroatoms from other periodic groups indicates that Pb(IV)-based derivatives are not effective, but Te(IV)-based materials are potentially superior to the Bi(V) systems. Collectively, the results indicate that thermal release of S 2 N 2 and Se 2 N 2 from heavy hypervalent atom dithia- and diselenadiazoles, either in solution or solid state, may afford facile and safe synthetic routes to these fragile rings and their polymeric analogues (SN) x and (SeN) x . The relative energetics of the formation of the two polymers are compared through molecular dynamics (MD) calculations.