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.