Beiträge zur Chemie des Bors, 198 Über die Reaktion von Amino‐imino‐boranen mit Dioxaphospholanen, Dioxarsolanen und Dioxastibolanen

Contributions to the Chemistry of Boron, 198. ‐ Reactions of Amino‐imino‐boranes with Dioxaphospholanes, Dioxarsolanes, and Dioxastibolanes (tert‐Butylimino)(2,2,6,6‐tetramethylpiperidino)borane (1) inserts into the exocyclic PX bond of 2‐methoxy‐ and 2‐(dimethylamino)‐1,3,2‐dioxaphospholanes, while ring expansions to the seven‐membered dioxazaphosphaborepanes 4 and 5 are observed with fluoro‐, chloro‐, bromo‐, and methyl‐dioxaphospholanes and their benzo derivatives. These decompose at elevated temperatures producing the (tetramethylpiperidino)dioxaborolane 12 and benzodioxaborole 20, respectively, and diazadiphosphetidine derivatives. Insertion into the exocyclic bond occurs also between 1 and methoxy‐benzodioxarsole (16) and ‐benzodioxastibole (17). The chloro derivatives, however, react with 1 to give 20 and (tBuN = ECl)2 (E = As, Sb) products. (2,6‐Diisopropylphenylimino)(2,2,6,6‐tetramethylpiperidino)borane (6) behaves similarly with the exception that 2‐chloro‐1,3,2‐benzodioxaphosphole yields the exocyclic insertion product. It appears from these experiments that the insertion into the exocyclic bond of the heterocyclic compounds yields kinetically controlled products, while ring expansion followed by expulsion of a dioxaborolane is thermodynamically controlled.