A series of d6 non-noble transition metal complexes are designed and studied computationally for the hydrogenation of CO2 to formic acid. Catalysts with a metal of weaker electronegativity and lower...
N-heterocyclic Carbene (NHC) and carbonyl (CO) ligands are generally regarded as innocent ligands in bifunctional catalysts. However, their non-innocent roles in cooperation as Lewis acid sites due to their π-accepting...
The quantitative Lewis acidity of N‐heterocyclic iod(az)olium salts is helpful for their further application in organic chemistry. The acidity scales of different N‐Heterocyclic iodonium salts (NHISs) in acetonitrile are investigated using Density functional theory (DFT) studies. There are a total of 121N‐Heterocyclic iodonium salts that have been designed by combining N‐heterocyclic and iodonium salt structures in this research. Theoretical calculations systematically established the 31P NMR chemical shifts of NHISs, and the relative Lewis acidity scale was derived. The Lewis acidity trend is analyzed and explained by the natural population analysis (NPA) charges, molecular electrostatic potential, and the interaction between the iodonium center and the N‐heterocyclic substituents. This study is expected to provide a practical quantitative theoretical scale for the understanding and design of hypervalent iodine(III) reagents with versatile Lewis acidity.
To understand the unprecedented difference between 6-endo and 5-exo selectivity in hypervalent iodine (III) promoted fluorocyclization of unsaturated carboxylic acids or alcohols by difluoroiodotoluene, density functional theory (DFT) studies have been performed to systematically compare both the previous proposed “fluorination first and cyclization later” mechanism and the alternative “cyclization first and fluorination later” mechanism. Our results revealed that the selectivity is mechanism-dependent. The unsaturated alcohol prefers the fluorination first and the 6-endo-tet cyclization later pathway, leading to the experimentally observed 6-endo ether product. In contrast, the unsaturated carboxylic acid plausibly undergoes the 5-exo-trig cyclization first and the fluorination later to the experimentally observed 5-exo lactone product. The pKa property of the functional group of the substrate is found to play a key role in determining the reaction mechanism. The provided insights into the mechanism-dependent selectivity should help advance the development of fluorocyclization reactions with hypervalent iodine reagents.
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