Etherification of Functionallzed Phenols with Chloroheteroarenes at Low Palladium Loading: Theoretical Assessment of the Mole of Triphosphane Ligands in C-O Reductive Elimination

摘要

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 tri-phosphane systems are efficient for selective hetero-aryl 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, pyri-midines 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 studiesfurthermore 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.