Coordination Chemistry of an Unsymmetrical Naphthyridine-Based Tetradentate Ligand toward Various Transition-Metal Ions

An unsymmetrical ligand, 2-(2-pyridinyl)-7-(pyrazol-1-yl)-1,8-naphthyridine (L-5) was prepared for the construction of a series of dinuclear complexes. Treatment of L-5 with [Ru-2(mu-OAc)(4)Cl] followed by anion metathesis afforded [(L-5)(mu-OAc)(3)Ru-2](PF6) (3). Reaction of L-5 with 2 equiv. of Ni(OAc)(2) provided [Ni-4(L-5)(2)(mu-OH)(4)(CF3COO)(2)](CF3COO)(2) (5). Reaction of [Re-2(CO)(8)(CH3CN)(2)] with L-5 in a refluxing chlorobenzene solution gave a mixture of dirhenium (6) and monorhenium (7) complexes. The monocobalt complex 8 was obtained from complexation of L-5 with CoCl2. These new complexes were characterized by elemental analysis and spectroscopic techniques. The structures of complexes 3, 5 and 8 were further confirmed by X-ray crystallography. Nickel complex 5 was evaluated as a catalyst for reduction reactions involving the conversion of ester functionalities into their corresponding alcohols.