Preparation of (L)(N,N‘-ethylenebis(salicylideneaminato))- (1,3-butadien-2-yl)cobalt(III) Complexes and Their Utilization in Facile and Regioselective Diels−Alder Reactions

Dark green (N,N‘-ethylenebis(salicylideneaminato)cobalt(I) (Co(salen)) anions underwent smooth S<INF>N</INF>2‘ reactions with allenic electrophiles in the presence of added ligands (L) to give (L)(salen)(1,3-butadien-2-yl)cobalt(III) complexes (L = pyr, DMAP, H<INF>2</INF>O). The cobalt dienyl complexes prepared were fully characterized and then treated with a range of dienophiles to give Diels−Alder cycloaddition adducts. The cobalt−carbon bonds in Diels−Alder adducts were cleaved by utilizing straightforward chemical reactions which allowed recovery of cobalt in a reusable form as well as demetalated cycloadduct.