Synthesis and complexation characteristics of phenanthroline and bipyridine diols

Abstract

Neocuproine (2,9-dimethyl-1,10-phenanthroline) 1 was converted to achiral and chiral tetradentate phenanthroline diols 3a-c by addition to benzophenone, adamantanone and camphor, respectively. Analogously 6,6'-dimethyl-2,2'-bipyridine 2 was converted to diol 7a on base-induced addition to benzophenone. Reactions with benzophenone and adamantanone proceeded smoothly although small amounts of mono adducts were also formed. Functionalization of 1 with (R)-camphor failed under the standard conditions. However, conversion of the lithio derivative 5 to the cerium chloride derivative 6 and subsequent reaction with (R)-camphor led to the phenanthroline diol 3c. Complexes of the diols 3 and 7 with zinc and copper were prepared. Xray analysis of the zinc complex 20 of diol 7a revealed a five coordinate zinc ion that is firmly embedded in the ligand. X-ray analysis of the Cu(acac)2 complex 21 of diol 7a unexpectedly revealed this to be an acetate bridged di-copper species. This copper complex forms on recrystallization from ethyl acetate. The initial acac-complex apparently hydrolyses the ethyl acetate to provide the bridging acetate found in the di-copper complex 21. From 4,7-dichloro-2,9-dimethyl-1,10-phenanthroline 13 a "doubly armed" derivative 18 was prepared by substitution with two tetraethylene glycol "arms" followed by suitable derivatisation. A bridged derivative 19 was prepared by ring closure with an amine of the ditosylated tetraethylene glycol derivative. Attempts to prepare copper complexes of 18 and 19 were inconclusive.