Alkene Addition of Frustrated P/B and N/B Lewis Pairs at the [3]Ferrocenophane Framework
Résumé
o-Vinyl/α-NRR′-substituted [3]ferrocenophane derivatives (R = R′ = Me (8), R = H, R′ = tBu (11), R = R′ = H (13)) were prepared via a Wittig olefination route starting from the corresponding aldehyde. The NMe2 group was further exchanged for Pmes2 (9). The bulky α-substituents NHtBu and Pmes2 form frustrated Lewis pairs with B(C6F5)3 that undergo cooperative intramolecular addition reactions to the adjacent alkene. In the case of 13 stable Lewis pair adduct (14) formation is observed instead. The corresponding α-dimesitylphosphino[3]ferrocenophanyl-substituted butadiene (16) and acrolein (23) derivatives were synthesized via multistep synthetic pathways. Upon treatment with B(C6F5)3, intramolecular 1,4-addition of the frustrated Lewis pairs to the adjacent doubly unsaturated moieties takes place to yield the zwitterionic products 17 and 24, respectively. The complexes 9, 10, 12, 16, 17, 20, 22, and 23 were characterized by X-ray diffraction.