Structural features and reactions of a geminal frustrated phosphane/borane Lewis pair

• Hydroboration of a (C6F5)2P-substituted alkyne gave a frustrated Lewis pair.
• The geminal frustrated Lewis pair (FLP) adds to carbonyl compounds.
• The FLP adds to terminal and internal acetylene derivatives.

[Bis(pentafluorophenyl)phosphanyl]phenylacetylene (4) undergoes a regioselective hydroboration reaction with HB(C6F5)2 to yield the geminal frustrated Lewis pair 5 that bears pairs of strongly electron-withdrawing C6F5 substituents at both boron and phosphorus. The X-ray crystal structure analysis has revealed that there is no direct P–B interaction in 5. This has been confirmed by both solid state and solution NMR spectroscopy. The “non-interacting” geminal FLP 5 undergoes 1,2-P/B addition reactions to carbonyl compounds (benzaldehyde, trans-cinnamic aldehyde), to the CN bond of phenylisocyanate and to the CC triple bonds of several alkynes (1-pentyne, phenylacetylene, 4-octyne). The frustrated Lewis pair 5 and several reaction products were characterized by X-ray diffraction.

Hydroboration of a bis(pentafluorophenyl)phosphanylalkyne with Piers' borane yields a geminal P/B frustrated Lewis pair that shows no appreciable phosphane/borane interaction. It adds to a variety of π-systems to form the respective five-membered heterocyclic products.Figure optionsDownload as PowerPoint slide