Organocopper(III) Spiro Complexes: Synthesis, Structural Characterization, and Redox Transformation

Reductive elimination of Cu­(III) intermediates is often proposed as a key step in many copper-catalyzed or -mediated formation of C–C or C–heteroatom bonds. However, there still lacks concrete evidence on this key step, mainly because Cu­(III) complexes are usually too unstable to be isolated and structurally characterized. In this work, novel organocopper­(III) spiro complexes and their analogous organocopper­(I) spiro complexes were synthesized and structurally characterized. Single-crystal X-ray structural analysis revealed that the spiro Cu­(III) atom adopted a distorted square-planar geometry while its corresponding spiro Cu­(I) atom was tetrahedrally coordinated. A redox transformation between these spiro Cu­(I) and Cu­(III) complexes was experimentally observed by reacting with reductants or oxidants, respectively. As concrete evidence, the organocopper­(III) spiro compounds were found to form C–C bonds intramolecularly via reductive elimination.