Tungsten-Promoted Pyridine Ring Scission: The Selective Formation of η2-Cyanine and η2-Merocyanine Complexes and Their Derivatives

Nucleophiles capable of four-electron donation (e.g., anilines, enolates) add to C2 of the N-acetylpyridinium (NAPy) ligand of TpW(NO)(PMe3)(NAPy)(OTf) and induce a Zincke−König-like ring scission to generate 3,4-coordinated acetamidotrienes or 1-azatrienes with 3Z,5E stereochemistry. This ring opening is driven by the enhanced π-acidity of the cyanine, relative to its purported dihydropyridine predecessor, which stabilizes the π-base {TpW(NO)(PMe3)}. X-ray data of the indoline-derived analogue (2) indicates that metal coordination disrupts the donor−acceptor (i.e., amide−iminium) conjugation in the cyanine ligand. Photolysis of 2 in the presence of indoline liberates a further derivatized cyanine.