Journal
ADVANCED SYNTHESIS & CATALYSIS
Volume 353, Issue 18, Pages 3403-3414Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adsc.201100481
Keywords
C?O bond formation; mechanistic DFT study; palladium; reductive elimination; triphosphanes
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Funding
- CNRS
- ANR [ANR-09-CP2D-03 CAMELOT]
- Region Bourgogne [PARI-SMT8]
- Singapore-MIT Alliance
- Grants-in-Aid for Scientific Research [21590025, 23710261] Funding Source: KAKEN
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The present study highlights the potential of robust tridentate ferrocenylphosphanes with controlled conformation as catalytic auxiliaries in C?O bond formation reactions. Air-stable palladium triphosphane systems are efficient for selective heteroaryl ether synthesis by using as little as 0.2 mol% of catalyst. These findings represent an economically attractive and clean etherification of functionalized phenols, electron-rich, electron-poor and para-, meta- or ortho-substituted substrates, with heteroaryl chlorides, including pyridines, hydroxylated pyridine, pyrimidines and thiazole. The etherification tolerates very important functions in various positions, such as cyano, methoxy, amino, and fluoro groups, which is useful to synthesize bioactive molecules. DFT studies furthermore demonstrate that triphosphane ligands open up various new pathways for the C?O reductive elimination involving the third phosphane group. In particular, the rate for one of these new pathways is calculated to be about 1000 times faster than for reductive elimination from a complex with a similar ferrocenyl ligand, but without a phosphane group on the bottom Cp-ring. Coordination of the third phosphane group to the palladium(II) center is calculated to stabilize the transition state in this new pathway, thereby enhancing the reductive elimination rate.
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