Synthesis and characterization of tris(heteroleptic) diimine complexes of chromium(III)

A preparative procedure of potentially wide applicability is described for the synthesis of previously unreported tris(heteroleptic) [Cr(diimine)3]3+ complexes. The synthetic scheme involves the sequential addition of three different diimine ligands, and employs CrCl3 · 6H2O as the initial Cr(III) reagent. The synthesis and characterization of the complexes [Cr(TMP)(phen)(diimine′)]3+ are reported (where TMP = 3,4,7,8-tetramethyl-1,10-phenanthroline, phen = 1,10-phenanthroline; and diimine′ is either bpy = 2,2′-bipyridine, Me2bpy = 4,4′-dimethyl-2,2′-bipyridine, 5-Clphen = 5-chloro-1,10-phenanthroline, or DPPZ = dipyridophenazine). Chiral capillary electrophoresis and electrospray mass spectrometry were essential aids in determining the presence or absence of diimine ligand scrambling. Utilizing emission and electrochemical data obtained on these compounds, the oxidizing power of the lowest lying excited state (2Eg(Oh)) was calculated, and was found to vary in a systematic fashion with diimine ligand type.

Graphical abstractA versatile procedure is described for the synthesis of tris(heteroleptic) diimine complexes of Cr(III). Capillary electrophoresis and electrospray mass spectroscopy confirm the absence of diimine ligand scrambling. Emission and electrochemical investigations of the [Cr(diimine)3]3+ products demonstrate that their excited state oxidizing power varies systematically with diimine ligand type.Figure optionsDownload full-size imageDownload as PowerPoint slide