Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 135, Issue 24, Pages 8882-8895Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja400338e
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Funding
- European Research Council
- Deutsche Forschungsgemeinschaft [SFB 858]
- Fonds der Chemischen Industrie
- NRW Forschungsschule Molecules and Materials
- National Science Foundation [CHE-0840453]
- ACS Petroleum Research Fund (PRF) [51971-ND3]
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Hydroboration of dimesitylnorbornenylphosphane with Piers' borane [HB(C6F5)(2)] gave the frustrated Lewis pair (FLP) 4 in good yield. It has the -PMes(2) 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 S. 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 P-31/B-11 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 H-1 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.
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