Kinetic studies of acetate exchange in trans-4-acetoxy-[η3-(1,2,3)-cyclohexenyl]palladium complexes. Relevance for asymmetric 1,4-oxidation reactions
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Contributors
Abstract
The acetate/acetate-d3 exchange reaction of the ring-bonded acetate of bis(4-acetoxy-[η3-(1,2,3)-cyclohexenyl]palladium acetate-d3 complexes 1a-c was studied in acetic acid solutions using 1H NMR spectroscopy. The reactions followed first-order kinetics in palladium, and the rates were highly affected by the presence of methanesulfonic acid or lithium acetate. The nature of the substituent in the 2-position of the complex was found to have a large impact on the reaction rate. Complexes 1a-c are observed intermediates in the benzoquinone-assisted palladium(II)-catalyzed 1,4-diacetoxylation reaction of 1,3-dienes. Complex 1b was treated with stoichiometric amounts of the enantiomerically pure ligand (S)-(+)-2-(4′-fluorophenylsulfinyl)-1,4-benzoquinone 4 under conditions where no exchange reaction occurs. Kinetic resolution was observed, implying that the two enantiomers of 1b reacted to trans-1,4-diacetoxy-2-phenyl-2-cyclohexene with different rates. Attempts to demonstrate dynamic kinetic resolution in stoichiometric reactions between 1b and 4 were unsuccessful. The major reason for this is presumably that with lithium acetate the equilibrium reaction between the two enantiomers of 1b is too slow compared to the chiral benzoquinone-induced attack of acetate to give the products. Under very acidic conditions the decomposition of the (π-allyl)palladium complex is faster than benzoquinone-induced product formation. This scenario is in full agreement with our observed rates.
Details
Original language | English |
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Pages (from-to) | 3367-3375 |
Number of pages | 9 |
Journal | Organometallics |
Volume | 21 |
Issue number | 16 |
Publication status | Published - 5 Aug 2002 |
Peer-reviewed | Yes |
Externally published | Yes |
External IDs
ORCID | /0000-0001-8423-6173/work/171062638 |
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