Chiral Pd-, Cu- and Ni-chelates and their utilities as catalysts in allylic acetoxylation of alkenes
1994; Science Press; Volume: 91; Issue: 3 Linguagem: Inglês
10.1016/0304-5102(94)00037-9
ISSN1873-3131
AutoresYang Hu, Masood A. Khan, Kenneth M. Nicholas,
Tópico(s)Asymmetric Hydrogenation and Catalysis
ResumoA series of chiral ML★2 complexes of Pd, Cu and Ni [L★=2-trifluoroacetylcamphorato (tfacam), (R)-N-α-methylbenzylsalicylaldimine, 2-(2′-phenolato)-4-substituted-oxazoline (phenox)] have been prepared and characterized, including X-ray structures of Pd(tfacam)2 (1) and Pd(4-Ph-phenox)2 (3a). The Pd- and Cu-chelates are active (pre) catalysts for the allylic acetoxylation of alkenes. The yields and chemoselectivities in these reactions are high but little enantioselectivity (0–5%) was found. Several mechanistic probes, including tests of the stability of the product and PdL★2 under the reaction conditions, the product distribution from the acetoxylation of D-1-cyclohexene, and the low acetolysis reactivity of L★Pd(η3-allyl), indicate the intervention of (η3-allyl)-Pd intermediates in the catalytic process in which either or both L★ groups dissociate or at least dechelate in the product-forming step.
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