O ₂ Activation at a Low-Valent P-Center: Isolation of a Cyclic Alkyl(Amino) Carbene (cAAC)-Phosphonate-Supported Dicationic Cu(II) ₆ Cluster

Herein, we explore the coordination behavior and O₂-activation of molecular diphosphorus (P₂) in the presence of CuX (X = Cl, Br), unraveling the phosphinidene nature of low-valent phosphorus atoms. Both mono- and dicuprated P₂ complexes with general formula [(cAAC)₂P₂(CuX)<i>_n</i>] (cAAC = cyclic alkyl(amino) carbene, <i>n</i> = 1, X = Cl (<b>2a</b>-<b>2b</b>), Br (<b>2c</b>); <i>n</i> = 2, X = Cl (<b>3a</b>-<b>3b</b>), Br (<b>3c</b>)) are isolated in the solid state. Aerial oxidation of bis-cAAC-supported P₂ in the presence of Cu(I) ions afforded the paramagnetic dicationic Cu(II)₆ cluster [Cu₆^II(Cy-cAAC-PO₃)₄O₂Cl₂][CuCl₂]₂ (<b>4</b>), stabilized by cAAC-phosphonate ligands with μ³-P atoms. EPR studies revealed the <i>in situ</i> generation of a P-centered monoradical intermediate upon exposure of the monocuprated P₂ to atmospheric oxygen, followed by oxidation of Cu(I) to Cu(II). All complexes are structurally characterized by single-crystal X-ray diffraction. Quantum chemical calculations are performed to explore the nature of chemical bonding and the electron density distribution of <b>2</b> and <b>3</b>. Mulliken spin density calculations revealed the open-shell nature of cluster <b>4</b>, featuring the Cu(II) ions, which was further supported by XPS, EPR, and magnetic measurements.