Differences in the Reactivity of Geminal Si−O−P and Al−O−P Frustrated Lewis Pairs

The new oxygen‐bridged geminal Si/P Frustrated Lewis Pair (FLP) tBu(2)P−O−Si(C(2)F(5))(3) (2) is able to reversibly bind carbon dioxide at ambient temperature. We compared its reactivity towards benzil, but‐3‐en‐2‐one, nitriles and phenylacetylene to that of the Al/P FLP tBu(2)P−O−AlBis(2) (Bis=−CH(SiMe(3))(2)) (1). When reacted with benzil, both, 1 and 2, form the 1,2‐addition product, but in the Si/P FLP 2, the second carbonyl function additionally binds to the silicon atom. With but‐3‐en‐2‐one 2 forms the 1,2‐addition product, while 1 binds in 1,4‐position. The reaction with acetonitrile yielded an unexpected etheneimine adduct for both systems, while only 1 reacted with tert‐butylnitrile. With benzonitrile and acrylonitrile, 2 showed reversible addition to the C≡N bond and 1 forms a stable adduct with benzonitrile. Solely 1 shows reactivity towards phenylacetylene affording a mixture of the CH deprotonation adduct tBu(2)P(H)−O−AlBis(2)(CCPh) and the FLP −C≡C 1,2‐addition adduct under ring formation. All compounds were characterized by multinuclear NMR spectroscopy, XRD and elemental analysis.