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

A versatile synthetic procedure is described for the synthesis of previousl y unreported heteroleptic Cr(diimine)(3)(3+) complexes. The method takes ad vantage of the excellent leaving group characteristics of the trifluorometh anesulfonate (triflate) ligand, CF3SO3-, and involves refluxing a precursor cis-[Cr(diimine)(2)(CF3SO3)(2)]CF3SO3 complex with an alternative free dii mine ligand in a non-coordinating solvent such as CPI,CI, or CH,CN. The syn thesis 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-phananthroline, bpy 2,2' -bipyridine, TMP = 3,4,7,8-1,10-phenanthroline, and DPPZ = dipyridophenazin e). Capillary electrophoresis studies have proven an especially valuable ai d in determining the presence or absence of diimine ligand scrambling land 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 volt ammetry data are also presented for these heteroleptic systems, and Also co mparisons are made with known values for the homoleptic parent species Cr(b py)(3)(3+), Cr(phen)(3)(3+) and Cr(TMP)(3)(3+). Also reported is the synthe sis of these three homoleptic complexes via the appropriate cis-[Cr(diimine )(2)(CF3SO3)(2)]CF3SO3 precursor species. The procedure is an attractive al ternative to the widely employed literature method for homoleptic systems i nvolving the preliminary formation of air sensitive Cr(II) complexes. (C) 2 001 Elsevier Science B.V. All rights reserved.