A Versatile Synthetic Approach to Rhodium(III) Diimine Metallointercalators: Condensation of o-Quinones with Coordinated cis-Ammines

Abstract

A new route to the preparation of rhodium(III) diimine complexes which bind DNA by intercalation was developed by condensation of coordinated ammine ligands with o-quinones. Starting from cis-[Rh(L∧L)2(NH3)2]3+ (L∧L: 2,2‘-bipyridine or 1,10-phenanthroline) and the appropriate quinones the ligands 9,10-phenanthrenequinone diimine (phi) and 5,6-chrysenequinone diimine (chrysi) were introduced in high yields. The reactions are completed within hours at ambient temperature in MeCN/water mixtures, 0.1 M in NaOH. Experiments with enantiomerically pure Δ-[Rh(phen)2(NH3)2]3+ and 9,10-phenanthrenequinone showed that the configuration at the metal center is retained during the course of the reaction. Condensation of rhodium(III) tetraammine starting material with 9,10-phenanthrenequinone allows the selective introduction of one or two phi ligands, depending on the reaction conditions. The ability to incorporate specifically only one phi ligand makes this a promising approach for the synthesis of tris(heteroleptic)...