Bis(2-phenylethyl)-nacnac: A Chiral Diketiminate Ligand and Its Copper Complexes

The chiral diketiminate ligand bis-N,N′-(2-phenylethyl)-2,4-diiminopentane, 1H, was synthesized in good yields in a one-step reaction from chiral amine and acetylacetone. Reaction of 1Li(THF) with N-bromosuccinimide yielded the succinimide-substituted ligand 2H. Copper complexes were obtained by reaction of the ligand with a basic copper source in the presence of coordinating Lewis bases, and 1Cu(NCMe), 1Cu(DMAP), 1Cu(PPh₃), 1Cu(2,6-xylyl isonitrile), 2Cu(PPh₃), and 2Cu(2,6-xylyl isonitrile) have been prepared and, for the most part, characterized by X-ray diffraction studies. Compared to their more common analogues with aromatic substituents on N, 1 and 2 seem to be more basic (1 > 2) and sterically more demanding (2 > 1). Their copper complexes are less stable than those of aryl-substituted diketiminates and tend to decompose by disproportionation, most probably after dissociation of the coordinated Lewis base. Despite the rotational freedom around the N−R* bond, the complexes are sterically rigid, a necessary requirement for potential applications in enantioselective catalysis.