title: Noninteracting, vicinal frustrated P/B-Lewis pair at the norbornane framework: synthesis, characterization, and reactions.
abstract: Hydroboration of dimesitylnorbornenylphosphane with Piers' borane [HB(C6F5)2] gave the frustrated Lewis pair (FLP) 4 in good yield. It has the -PMes2 Lewis base attached at the 2-endo position and the -B(C6F5)2 group 3-exo oriented at the norbornane framework. The vicinal FLP 4 was shown by X-ray diffraction and by spectroscopy to be a rare example of an intramolecular noninteracting pair of a Lewis acid and Lewis base functionality. The FLP 4 rapidly splits dihydrogen heterolytically at ambient temperature to yield the phosphonium/hydrido borate zwitterion 5. It adds to the carbonyl group of benzaldehyde and to carbon dioxide to yield the adducts 6 and 7, respectively. Compounds 5-7 were characterized by X-ray diffraction. Compound 4 adds to the S═O function of sulfur dioxide to give a pair of diastereomeric heterocyclic six-membered ring products due to the newly formed sulfur chirality center, annulated with the norbornane skeleton, which were investigated by (31)P/(11)B single and double resonance solid state NMR experiments. Compound 8 was also characterized by X-ray diffraction. The FLP 4 undergoes a clean N,N-addition to nitric oxide (NO) to give a norbornane annulated five-membered heterocyclic persistent FLP-NO aminoxyl radical 12 (characterized, e.g., by X-ray diffraction and EPR spectroscopy). Additionally, the FLP radical was characterized by (1)H solid state NMR spectroscopy. The radical 12 undergoes a H-atom abstraction reaction with 1,4-cyclohexadiene to yield the respective diamagnetic FLP-NOH product 13, which was also characterized by X-ray diffraction and solid state NMR spectroscopy.
authors.affiliation: Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstr. 40, 48149 Münster, Germany.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Sajid
authors.forename: Gerald
authors.initials: G
authors.lastname: Kehr
authors.forename: Thomas
authors.initials: T
authors.lastname: Wiegand
authors.forename: Hellmut
authors.initials: H
authors.lastname: Eckert
authors.forename: Christian
authors.initials: C
authors.lastname: Schwickert
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen
authors.forename: Allan Jay P
authors.initials: AJ
authors.lastname: Cardenas
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Warren
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
authors.forename: Constantin G
authors.initials: CG
authors.lastname: Daniliuc
authors.forename: Gerhard
authors.initials: G
authors.lastname: Erker