Oxidative C-C bond formation and C-N bond cleavage catalyzed by complexes of copper(i) with acridine based (E N E) pincers (E = S/Se), recyclable as a catalyst

Copper(i) complexes of 4,5-bis((phenylthio/seleno)methyl)acridine, [CuLBr] (C1 and C2) (L = L1/L2; pincer type (E N E) ligand), were synthesized and found to be thermally stable, and moisture and air insensitive. The complexes and ligands were characterized by multinuclei NMR and single crystal X-ray diffraction. In both complexes C1 and C2, ligands L1 and L2 coordinate with Cu in a pincer mode furnishing two six-membered chelate rings, with the distorted tetrahedral geometry of donor atoms around Cu. The Cu-S and Cu-Se bond lengths (angstrom) are 2.2482(17)-2.2979(16) and 2.3603(14)-2.4177(13) respectively. These complexes served as efficient catalysts for cross dehydrogenative coupling of unactivated tertiary amines with unactivated terminal alkynes, and cleavage of the benzylic (C-N) bond of N,N dimethylbenzylamines under oxidative solvent-free conditions. The reactions were found to be highly selective, and no over-oxidation to acid was observed. A low catalytic loading of 1.0 mol% was good enough to bring about both these transformations with recyclability up to five times.