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(N)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, H2O). 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.