Synthesis and characterization of heteroleptic Cr(diimine)3 3+ complexes

A versatile synthetic procedure is described for the synthesis of previously unreported heteroleptic Cr(diimine)3 3+ complexes. The method takes advantage of the excellent leaving group characteristics of the trifluoromethanesulfonate (triflate) ligand, CF3SO3 −, and involves refluxing a precursor cis-[Cr(diimine)2(CF3SO3)2]CF3SO3 complex with an alternative free diimine ligand in a non-coordinating solvent such as CH2Cl2 or CH3CN. The synthesis and characterization of the heteroleptic systems Cr(phen)2(bpy)3+, Cr((phen)(bpy)2 3+, Cr(phen)2(TMP)3+, Cr(phen)(TMP)2 3+, and Cr(phen)2(DPPZ)3+ are reported (where phen=1,10-phenanthroline, bpy=2,2′-bipyridine, TMP=3,4,7,8-1,10-phenanthroline, and DPPZ=dipyridophenazine). Capillary electrophoresis studies have proven an especially valuable aid in determining the presence or absence of diimine ligand scrambling (and for establishing purity in general). With the exception of Cr(phen)(bpy)2 3+, these syntheses proceed with essentially no diimine ligand scrambling, even when carried out in the presence of excess entering diimine. UV–Vis absorption and emission spectra, and excited state lifetime and cyclic voltammetry data are also presented for these heteroleptic systems, and comparisons are made with known values for the homoleptic parent species Cr(bpy)3 3+, Cr(phen)3 3+, and Cr(TMP)3 3+. Also reported is the synthesis of these three homoleptic complexes via the appropriate cis-[Cr(diimine)2(CF3SO3)2]CF3SO3 precursor species. The procedure is an attractive alternative to the widely employed literature method for homoleptic systems involving the preliminary formation of air sensitive Cr(II) complexes.