Polychlorinated Biaryl Heterocycles as Potential Ligands. Reactions between Octachloro-1,10-phenanthroline and -2,2′-bipyridine with Copper(I) and Other Metal Ions

Abstract

C hlorinated A rom atics, C opper C om pounds, C rystal Structure, Electrochem istry, H eterocycles Perchlorinated derivatives o f the com m on a -d iim in e chelate ligands 2,2'-bipyridine and 1,10-phenanthroline w ere synthesized and tested fo r their coordination behavior tow ards metal ions. O ctachloro-l.lO -ph en an th ro lin e (ocp) was o b tained via chlorination with P C I5 under pressure (300°C, 18 h). It fails to form stable com plexes w ith e.g. Fe2+, M n2+, Ru2+, N i2+, Z n 2+ or Cd~+, but yields com plex cations [M (ocp)2]+ w ith M = Cu, Ag. The crystal structure an aly sis o f the red tetrafluoroborate o f the copper(I) com plex cation reveals a distorted tetrahedral coordination at the metal w ith a slight tendency tow ards the trigonal-pyram idal arrangem ent; two essentially planar ligands w ith sm all bite angles intersect at alm ost right angle. Relative to conventional bis( 1,10-phenanthroline)copper(I) com plexes with sim ilar structures, [C u(ocp)2]+ has oxidation and reduction potentials shifted positively by about 1 V which leaves the energy o f the m ain M LC T absorption features little changed. A ttem pts to synthesize R u C h (o c p )2 in D M F produced as substituted product a sym m etrical b is(dim ethylam ino)-hexachloro-l,10-phenanthroline w hich can be oxidized electrochem ically in tw o steps. In contrast to ocp, octachloro-2,2'-bipyridine (ocb) show ed no detectable com plexation with C u+ and a very neg ative reduction potential, most probably due to its inability to exhibit a low -energy coplanar conform ation.Transition metal complexes with perhalogenated ligands have been investigated as potential oxida tion catalysts [1], The reason is the lower activation of C-Hal vs. C-H bonds in highly oxidized interme diates towards dissociation, Hal+ ions being much poorer leaving groups than H+. Examples include especially macrocyclic ligands such as the por phyrins [1], Small perchlorinated aromatic ligands were also used to investigate unusual and normally very reactive oxidation states such as Pt(III) [2].Perhalogenated derivatives of the standard adiimine chelate ligands 2,2'-bipyridine (bpy) and 1, 10-phenanthroline (phen) have not yet been systematically studied although the parent com pounds and their organosubstituted derivatives were employed as ligands in arrangements for oxidation catalysis [3]. In particular, (1,10-phenanthroline)copper(I) complexes with their low-lying metal(d)-to-ligand(7r*) charge transfer * R eprint requests to Prof. Dr. W. Kaim.(MLCT) excited states have received wide attention because of their long-standing application in ana lytical chemistry [4] and their more recent uses as "chemical nucleases" in site-specific DNA cleavage [51 and as photoactivated catalysts [6]. The struc tures of such molecules are also of relevance for supramolecular chemistry, e.g. for the synthesis of catenates and knotted molecules [7], for the under standing of the coordination and functioning of cop per centers in proteins [8] and for potential medical applications [9],...

Structural Flexibility of the Hydrogen-Free Acceptor Ligand Octachloro-1,10-phenanthroline in Its Complexes with d10 Metal Ions

“…The basic structural arrangements observed in the three d 10 metal complexes (Cu I , Ag I , Hg II ) and the crystalline free ligand ocp are not untypical for phenanthrolines and their coordination compounds. ,, There are the characteristically 4a,e,f,12,24 distorted tetrahedral structures of the [M(ocp) 2 ] + cations, the weak binding of the chelate ligand to slightly bent Cl−Hg−Cl (162°), and π/π interaction of individual aromatic molecules in crystals of the free ligand. In agreement with the increasing length of the coordinative bond in the series copper(I) (2.04 Å), silver(I) (2.35 Å), and mercury(II) (2.61 Å), the bite angle N−M−N decreases considerably from 78.8° 12 via 68.2° to 61.2° (Tables and ). Bond lengths and angles of free or coordinated ocp are also typical for phenanthrene-derived molecules, one typical such feature being the small C(15)−C(16) distance of about 1.36 Å, which indicates a particularly high double-bond character.…”

“…Materials. Octachloro-1,10-phenanthroline (ocp) and [Ag(ocp) 2 ](PF 6 ) were synthesized as described previously …”

“…The crystal structure analysis of the red tetrafluoroborate of the copper(I) complex revealed a distorted tetrahedral coordination, two virtually planar ocp ligands intersecting at almost a right angle. In contrast to ocp, octachloro-2,2‘-bipyridine showed no detectable complexation with Cu + or other metal ions, most probably due to its inability to exhibit a low-energy cis -coplanar conformation …”

“…In another such attempt at modification we recently presented a first systematic study directed at the coordination behavior of the perchlorinated derivatives of the common α-diimine chelate ligands 2,2‘-bipyridine and 1,10-phenanthroline …”

“…In this contribution we now describe the crystal structures of the d 10 metal compounds [Ag(ocp) 2 ](PF 6 )·CH 2 Cl 2 and Cl 2 Hg(ocp)·2.5C 6 H 6 and of the metal-free ligand. The results will be compared with those of the copper(I) compound [Cu(ocp) 2 ](BF 4 ) reported recently, and the remarkable structural variety will be assessed using ab initio calculations of ocp at the 6-31G** level. Similar basis sets have been used recently in calculations of polychlorinated aromatic hydrocarbon molecules …”