Diels-Alder route to norbornane derived vicinal phosphane/borane frustrated Lewis pairs for the metal-free catalytic hydrogenation of α, β-unsaturated ketones

• Published in: Journal of organometallic chemistry Vol. 899; pp. 120879 - 120888
• Main Authors: Wölke, Christian, Daniliuc, Constantin G., Kehr, Gerald, Erker, Gerhard
• Format: Journal Article
• Language: English
• Published: LAUSANNE Elsevier B.V 30.10.2019; Elsevier
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Diels-Alder reaction; Frustrated Lewis pairs; Metal-free hydrogenation; Physical Sciences; Science & Technology; α,β-unsaturated ketones; Metal-free hydrogenation; Diels-Alder reaction; Frustrated Lewis pairs; α,β-unsaturated ketones; HETEROLYTIC DIHYDROGEN ACTIVATION; REDUCTION; STEREOSELECTIVITY; ELECTRONIC CONTROL; CHEMISTRY; alpha,beta-unsaturated ketones; BIS(PENTAFLUOROPHENYL)BORANE
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2019.120879

The [4+2] cycloaddition reaction of the (dimesitylphosphino)cyclopentadienes 5a,b with N-phenylmaleimide gave the norbornene derivative 9. Its reduction with LiAlH4 produced the N-phenylpyrrolidino-annulated system 10. Treatment with Piers' borane gave the respective P/B FLP 12 as the major product, which cleaved dihydrogen under mild conditions to yield the phosphonium/hydrido borate product 14. Reaction of the phosphino-norbornene 10 with 2 M equiv. of Piers’ borane [HB(C6F5)2] followed by exposure to dihydrogen eventually gave the HB(C6F5)2 adduct 15. This served as a catalyst for the hydrogenation of a series of chalcone derivatives. The system requires a pre-activation period before becoming active for the conjugated enone hydrogenation. [Display omitted] •The [4+2] cycloaddition reaction of the (dimesitylphosphino)cyclopentadienes 5a,b with N-phenylmaleimide followed by reduction gave product 10.•Treatment with Piers' borane gave the respective P/B FLP 12 as the major product, which cleaved dihydrogen under mild conditions to yield the phosphonium/hydrido borate product 14.•Reaction of the phosphino-norbornene 10 with 2 M equiv. of Piers' borane [HB(C6F5)2] followed by exposure to dihydrogen eventually gave the HB(C6F5)2 adduct 15.•This served as a catalyst for the hydrogenation of a series of chalcone derivatives.•The system requires a pre-activation period before becoming active for the conjugated enone hydrogenation.