A hydroboration route to geminal P/B frustrated Lewis pairs with a bulky secondary phosphane component and their reaction with carbon dioxide

The secondary aryl-P(H) phosphanyl substituted tert-butylacetylenes 7a,b (aryl: Mes or Mes*) undergo hydroboration with [HB(C6F5)(2)] to give the geminal vinylidene-bridged P/B Lewis pairs 8a,b. The treatment of 8a, b with benzonitrile, N-sulfinylaniline, and phenyl isothiocyanate, respectively, gives the addition products 12a,b, 13a,b, and 14 with proton transfer from the phosphorus to the more basic nitrogen site. The reaction of the FLPs 8a, b with carbon dioxide yields a doubly boron bonded addition product. The reaction of 8b with a conjugated ynone formally proceeded by trans-1,2-hydrophosphination of the alkyne at the geminal FLP framework to give the seven-membered heterocycle 21.