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 ($η$4—$η$6), less is known about the chemistry of their $η$2 analogues. Herein, we describe a general method for synthesizing 5,6-$η$2-(1-azatriene) tungsten complexes via a 6$π$-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 $η$2-dihydropyridine and $η$2-1-azatriene complexes, both of which were prepared as single regio- and stereoisomers.