3‐Aryl Substituted 1‐Methylquinolinium Salts as Carbene Precursors

Abstract

1‐Methylquinolinium salts substituted at the C3 position with phenyl, naphthalen‐1‐yl, phenanthren‐9‐yl, and pentaphenyl phenyl as well as aryl ethynyl substituents were prepared. The phenyl, naphthalen‐1‐yl, and phenanthren‐9‐yl substituents are in conjugation with the quinolinium ring, and the sterically crowded pentaphenyl phenyl residue causes a propeller‐type molecule possessing a calculated dihedral angle between aryl substituent and the quinolinium ring of approximately 54°. The different influences of the substituents including the aryl ethynyl residues on the π‐architecture is well reflected in their frontier orbital profiles, their spectroscopic properties, and in their ability to form N‐heterocyclic carbenes. The latter were generated from the C3‐aryl substituted quinolinium salts and trapped as sulfur and selenium adducts, whereas the aryl ethynyl substituted derivatives failed to undergo the NHC generation under the conditions applied. 77Se NMR measurements of the corresponding selenones reveal that quinolin‐2‐ylidenes are electron poor carbenes with strong π‐acceptor character.