SYNTHESIS AND CHARACTERIZATION OF NICKEL(II) COMPLEXES WITH SYMMETRICAL TETRADENTATE N2O2 NAPHTHALDIMINE LIGANDS - THEIR APPLICATION AS CATALYSTS FOR THE HYDROGENATION OF CYCLOHEXENE

Ni acetate reacts with naphthaldimines containing the N2O2 donor group to yield two types of complex. The first, of molecular formula Nit (L = naphthaldimine), is free of the anions in which the ligand behaves as a dibasic tetradentate towards one Ni ion. These complexes are all diamagnetic, having square planar geometry. In the second type, the li gand behaves either as a monobasic acid towards the Ni ion or as a neu tral molecule. These complexes are paramagnetic and exhibit a tetrahed ral configuration around the central metal ion. The metal chelates wer e characterized by elemental analyses (t.g.a. and d.t.a.), and by i.r. and u.v.-vis. spectroscopy. Magnetic moments were also measured. A se ries of Ni-II-Schiff base complexes were tested for their catalytic ac tivity ill the hydrogenation of cyclohexene with molecular Hz. The eff ects of the bridge length, amounts of solvent and cosolvent were studi ed. The use of H2O as a cosolvent greatly increases the yield of the r eaction product. The hydrogenation product yield is linearly related t o the dielectric constant of the medium.