Complexes of ligands derived from 1,8-dihydroxynaphthalene. Synthesis and crystal structures of a palladium and a copper complex

Abstract

A simplified synthesis has been elaborated for 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene, H₂daddn, whose di-Schiff base derivatives in principle offer binuclear metal complexes with potentially useful geometrical features; only mono-Schiff base products, however, are formed upon condensation with the mono-primary amines 2-aminomethylpyridine, 2-aminoethylpyridine or N,N-dimethylethylenediamine in either metal-free reactions or in the presence of Pd²⁺ or Cu²⁺. The X-ray crystal structures of two metal derivatives of H₂daddn have been determined. Crystals of [PdL(N₃)](in which L is the monoanion formed by proton loss from a phenolic group in the mono-Schiff base from H₂daddn and 2-aminoethylpyridine) are monoclinic, space group P2₁/c, with a= 11.220(1), b= 12.910(2), c= 14.521(2)Å and β= 92.540(9)°; at convergence R= 0.030 for 3398 reflections [I > 2σ(I)]. The Pd is essentially square planar with one N₃^– ligand, L acting as a tridentate chelating ligand which has a pronounced fold. The intact phenolic OH is hydrogen-bonded to the adjacent deprotonated and co-ordinated phenoxy centre. Crystals of [Cu(daddn)(en)]·MeOH (en = ethylenediamine) are orthorhombic, space group Pbca, with a= 14.515(2), b= 16.596(3) and c= 16.406(3)Å; at convergence R= 0.046 for 1158 reflections [I > 3σ(I)]. An approximately square O₂N₂ arrangement around the Cu is provided by a bidentate daddn^2– on one side and a bidentate ethylenediamine on the other; the molecules are present in pairs in which a phenoxide atom in one molecule is weakly bonded [Cu ⋯ O 2.848(12)Å] to the Cu in its neighbour.