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 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe(3))}. 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.