Nuclearity and coordination-mode control in Copper–Diphosphine complexes: From Cu(I)–BINAP to Cu(II)–BINAPO

Copper(I) diphosphine complexes are known to exhibit a strong tendency toward aggregation, often forming halide-bridged dinuclear species that hinder the isolation of well-defined mononuclear structures. Herein, we report a pyridine-driven strategy for nuclearity control in Cu(I)–BINAP halide systems, enabling the selective formation of mononuclear complexes of the type [CuX(L)(py)]. This pyridine effect is further supported by density functional theory (DFT) calculations, which indicate that pyridine coordination and Cu–X bond cleavage proceed in a concerted manner through two consecutive S N 2-like reactions. The methodology is applicable to both racemic and enantiopure BINAP, and extends to alternative diphosphine ligands such as DPEphos, revealing a clear correlation between ligand rigidity, bite angle, and deviation from ideal tetrahedral geometry (τ 4 ). Furthermore, the corresponding square-planar Cu(II)–BINAPO complex can be obtained either from BINAP under open-atmosphere Cu(OTf) 2 conditions or directly from preformed BINAPO, highlighting a coordination-mode switch from κ 2 P,P′ to κ 2 O,O′ binding. This result expands the limited examples of BINAPO coordination to first-row transition metals and provides new insight into the coordination versatility of oxidized diphosphine ligands in copper chemistry.