New Insights in Frustrated Lewis Pair Chemistry with Azides

摘要

The geminal frustrated Lewis pair (FLP) tBu_2PCH_2BPh_2 (1) reacts with phenyl-, mesityl-, and tert-butyl azide affording, respectively, six, five, and four-membered rings as isolable products. DFT calculations revealed that the formation of all products proceeds via the six-membered ring structure, which is thermally stable with an N-phenyl group, but rearranges when sterically more encumbered Mes-N_3 and tBu-N_3 are used. The reaction of 1 with Me_3Si- N_3 is believed to follow the same course, yet subsequent N_2 elimination occurs to afford a four-membered heterocycle (5), which can be considered as a formal FLP-trimethylsilylnitrene adduct. Compound 5 reacts with hydrochloric acid or tetramethylammonium fluoride and showed frustrated Lewis pair reactivity towards phenylisocyanate.