Facile anaerobic oxidative dehydrogenation promoted by bases: The case of copper-2,4-dihydro-1H-benzo[d][1,3]oxazine complexes

Two new 2,4-dihydro-1H-benzo[d][1,3]oxazines (L1 and L2) were prepared by condensation of 2-quinolinecarboxaldehyde and 2-amino-benzyl alcohols and tested as N,N’-bidentate ligands toward CuCl2. Treatment of the resulting copper(II) derivatives with Et3N promoted an oxidative dehydrogenation yielding the corresponding copper(I) [Cu(L-ox)Cl] complexes, 2, (L-ox = 4H-benzo[d][1,3]oxazine). The [Cu(L2-ox)Cl] species, 2b, was characterized by single crystal X-ray diffraction, showing a trigonal geometry at the metal center and reacted with PPh3 and CO, affording [Cu(L2-ox)(PPh3)Cl], 4b, and [Cu(L2-ox)(CO)Cl], 6b, respectively. The latter species, stable in the solid state, was structurally characterized by diffraction methods and showed tetrahedral coordination of the Cu(I) ion.