Revisiting Formal Copper(III) Complexes: Bridging Perspectives with Quasi-d¹⁰ Configurations

The formal Cu(III) complex [Cu(CF₃)₄]¹⁻ has often served as a paradigmatic example of challenging oxidation state assignment – with many reports proposing conflicting descriptions. Here we report a computational analysis of this compound, employing Energy Decomposition Analysis and Intrinsic Bond Orbital Analysis. We present a quasi-d¹⁰ perspective of the metal centre, resulting from ambiguities in d-electron counting. The implications for describing reactions which undergo oxidation state changes, such as the formal reductive elimination from the analogous [Cu(CF₃)₃(CH₂Ph)]¹⁻ complex (Paeth et al. J. Am. Chem. Soc. 2019, 141, 3153), are probed. Electron flow analysis finds that the changes in electronic structure may be understood as a quasi-d¹⁰ to d¹⁰ transition at the metal centre, rendering this process essentially redox neutral. This is reminiscent of a previously studied formal Ni(IV) complex (Steen et al., Angew. Chem. Int. Ed. 2019, 58, 13133–13139), and indicates that our description of electronic structure has implications for the understanding of elementary organometallic reaction steps.