Carbonylation Reactions of Intramolecular Vicinal Frustrated Phosphane/Borane Lewis Pairs

The
intramolecular frustrated Lewis pair (FLP) Mes2PCH2CH2B­(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-PMes2 Lewis base functionality coordinated at the norbornane
framework. This noninteracting FLP adds carbon monoxide in solution
at −35 °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 H2 when brought into the gas phase.