Polychlorinated biaryl heterocycles as potential ligands. Reactions between octachloro-1,10-phenanthroline and -2,2'-bipyridine with copper(I) and other metal ions

Per-chlorinated derivatives of the common alpha-diimine chelate ligands 2,2-'-bipyridine and 1,10-phenanthroline were synthesized and tested for their coordination behavior towards metal ions. Octachloro-1,10-phenanthroline (ocp) was obtained via chlorination with PCl5 under pressure (300 degrees C, 18 h). It fails to form stable complexes with e.g. Fe2+, Mn2+, Ru2+, Ni2+, Zn or Cd2+, but yields complex cations [M(ocp)(2)](+) with M = Cu, AE. The crystal structure analysis of the red tetrafluoroborate of the copper(I) complex cation reveals a distorted tetrahedral coordination at the metal with a slight tendency towards the trigonal-pyramidal arrangement; two essentially planar ligands with small bite angles intersect at almost right angle. Relative to conventional bis(1,10-phenanthroline)copper(I) complexes with similar structures, [Cu(ocp)(2)](+) has oxidation and reduction potentials shifted positively by about 1 V which leaves the energy of the main MLCT absorption features little chan ed. Attempts to synthesize RuCl2(ocp)(2) in DMF produced as substituted product a symmetrical bis(dimethylamino)-hexachloro-1,10-phenanthroline which can be oxidized electrochemically in two steps. In contrast to ocp, octachloro-2,2'-bipyridine (ocb) showed no detectable complexation with Cu and a very negative reduction potential, most probably due to its inability to exhibit a low-energy coplanar conformation.