Carbonylation Reactions of Intramolecular Vicinal Frustrated Phosphane/Borane Lewis Pairs

The intramolecular frustrated Lewis pair (FLP) Mes(2)PCH(2)CH(2)B(C6F5)(2) 4 adds cooperatively to carbon monoxide to form the five-membered heterocyclic carbonyl compound 5. The intramolecular FLP 7 contains an exo-3-B(C6F5)(2) Lewis acid and an endo-2-PMes(2) Lewis base functionality coordinated at the norbornane framework. This noninteracting FLP adds carbon monoxide in solution at -35 degrees C cooperatively to yield a five-membered heterocyclic FLP-carbonyl compound 8. In contrast, FLP 7 is carbonylated in a CO-doped argon matrix at 25 K to selectively form a borane carbonyl 9 without involvement of the adjacent phosphanyl moiety. The free FLP 7 was generated in the gas phase from its FLPH2 product 10. A DFT study has shown that the phosphonium hydrido borate zwitterion 10 is formed exergonically in solution but tends to lose H-2 when brought into the gas phase.