Electronic control in frustrated Lewis pair chemistry: adduct formation of intramolecular FLP systems with –P(C6F5)2 Lewis base components†
2-Propenylbis(pentafluorophenyl)phosphane adds Piers’ borane [HB(C6F5)2] with anti-Markovnikov orientation to yield the intramolecular vicinal frustrated P/B Lewis pair 10. The FLP 10 adds pyridine, acetonitrile or alkyl isocyanides to form simple boron Lewis acid adducts 11–14, all of which were characterized by X-ray diffraction. The FLP 10 reacts with trans-cinnamic aldehyde to give a boron carbonyl adduct 15 that was characterized by an X-ray crystal structure analysis. In contrast, the geminal FLP (C6F5)2P–CHEt–B(C6F5)2 (3) undergoes 1,2-carbonyl addition reactions with benzaldehyde or trans-cinnamic aldehyde to yield the respective five-membered heterocyclic products (7, 8, both characterized by X-ray diffraction). The FLP 10 undergoes 1,2-P/B addition to p-tolylacetylene and to 2-methylbutenyne, respectively, to yield the corresponding six-membered heterocyclic products 17 and 18, respectively (both were characterized by X-ray diffraction).