UBC Undergraduate Research

Rapid Synthesis of Ligand-Based Radicals from Chromium(II) Compounds Desnoyer, Addison


The existence of metal complexes that contain ligand-based radicals has been known for years, yet has mainly been regarded as a spectroscopic oddity. More recently, the effects of these redox non-innocent ligands on the reactivities of first-row transition metals during catalytic processes has been examined. In an effort to study the reactivities of some of these complexes, a series of octahedral Cr(III) complexes with both redox innocent and non-innocent ligands was synthesized. The square planar Cr(II) compound Cr(DPM)2 was found to be an excellent single electron reductant for a variety of neutral diimines to give the corresponding octahedral Cr(DPM)2(LX•) complexes. In addition, the use of a variety of Cr(II) compounds as single electron reductant prior to protonolysis of the resulting Cr(bpy) complex with a variety of ligands of the form H(R,R’-acac) was found to give the corresponding Cr(R,R’-acac)2(bpy•) complex, allowing for greater tuning of the ancillary ligands. The radical complexes were found to be intensely coloured and air sensitive, and were primarily characterized by UV/vis spectrophotometry. In addition, the complex Cr(DPM)2(bpy•) was found to rapidly and quantitatively react with trityl bromide via an outer-sphere single electron transfer mechanism, generating the trityl radical and the cationic Cr(DPM)2(bpy) complex.

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