Synthesis of 1-Azatriene Complexes of Tungsten: Metal-Promoted Ring-Opening of Dihydropyridine

For nearly a century, chemists have explored how transition-metal complexes can affect the physical and chemical properties of linear conjugated polyenes and heteropolyenes. While much has been written about higher hapticity complexes (η⁴–η⁶), less is known about the chemistry of their η² analogues. Herein, we describe a general method for synthesizing 5,6-η²-(1-azatriene) tungsten complexes via a 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe₃)}. This study includes detailed spectroscopic and crystallographic data for the η²-dihydropyridine and η²-1-azatriene complexes, both of which were prepared as single regio- and stereoisomers.