期刊
ORGANOMETALLICS
卷 29, 期 6, 页码 1479-1486出版社
AMER CHEMICAL SOC
DOI: 10.1021/om9010966
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资金
- National University of Singapore [R 143-000-327-133]
Four imidazolium (5a/b) and benzimidazolium (6a/b) salts with hemilabile alkyl-aryl thioether functions have been prepared via a straightforward and modular pathway in order to compare their reactivities toward palladation. Reaction of 5a/b with Pd(OAc)(2) gave complex product Mixtures, whereas 6a/b afforded the desired bis(benzimidazolin-2-ylidene) complexes 8a/b in good yields. The difference in reactivities of benzimidazole versus imidazole derivatives was attributed to the presence of additional acidic protons at C4/5 positions of the imidazolium ring, leading to competing and unselective deprotonation reactions. The milder Ag-NHC transfer reaction, oil the other hand, provided either mono- or bis(imidazolin-2-ylidene) complexes (9 or 7a/b) in good yields depending on the ligand:metal ratio. The interesting hemilability in monocarbene complex 9 was investigated by spectroscopy and thioether displacement reaction with PPh(3), yielding the mixed NHC-PPh(3) complex 10 in high yields. An initial comparative catalytic study also reveals that the mixed-donor complex 10 exhibits the highest activity among the complexes tested.
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