Dicopper Complexes with Anthyridine-Based Ligands: Coordination and Catalytic Activity

Two new anthyridine-based ligands, 5-phenyl-2,8-bis(2-pyridinyl)-1,9,10-anthyridine (L-3) and 5-phenyl-2,8-bis(6'-bipyridinyl)-1,9,10-anthyridine (L-4), were designed for accommodation of dimetallic systems with the metal ions separated by similar to 5 angstrom. Complexation of Cu(ClO4)(2) with L-3 and L-4 provided the corresponding dicopper complexes [{Cu-2(L-3)(H2O)(4)(CH3CN)(2)}(ClO4)(4)] (3) and [{Cu-2(L-4)-(mu-ClO4)(2)}(PF6)(2)] (4) respectively. Both complexes were characterized by spectroscopic methods, and the detail structural features were further confirmed by X-ray crystallography. Structural analyses of 3 and 4 reveal the Cu center dot center dot center dot Cu distances in the complexes being 4.9612(7) and 5.013 (2) angstrom, respectively. Both complexes are active in the catalytic oxidation of benzyl alcohols into the corresponding aldehydes. Furthermore, complex 4 appears to be a good catalyst for the oxidative coupling of primary alcohols into the corresponding esters with the use of hydrogen peroxide as the oxidant in an aqueous medium. The possible cooperative interactions between the metal ions during the catalysis are discussed.