Multifaceted Lewis Acidity of a High‐Valent Cu(III) Hydroxide Complex

Copper(III) compounds are of crucial importance in biological systems and aerobic oxidative processes, whereas their Lewis acidity, a key reactivity feature, is barely studied. Herein, we report the multifaceted reactivity of the copper(III) hydroxide tetramer [Cu(CF 3 ) 2 (OH)] 4 with amide or phosphine oxide Lewis bases to give biologically relevant dimeric bis(µ 2 ‐hydroxy)dicopper(III) adducts with different types of metal‐ligand coordination. Oxidation state localized orbital (OSLO) analysis of dimeric copper(III) hydroxide species supports the high oxidation state of copper. Addition of chloride or bromide Lewis bases to cubane [Cu(CF 3 ) 2 (OH)] 4 leads to the formation of unstable adducts with µ 2 ‐Cl or µ 2 ‐Br coordination, where the tetrameric heterocubane scaffold is preserved. The Lewis acidity of the tetrameric hydroxide was evaluated using DFT calculations and Gutmann‐Beckett analysis and compared to the elusive and hypothetical inorganic and organometallic copper(III) species. Accordingly, the Lewis acid strength increases in the order PyCu(CF 3 ) 3 ∼ [Cu(CF 3 ) 2 (OH)] 4 < Cu(CF 3 ) 2 OH < Cu(CF 3 ) 3 ∼ CuF 3 < Cu(C 6 F 5 ) 3 < Cu(OTeF 5 ) 3 .