Using internal electrostatic fields to manipulate the valence manifolds of copper complexes.

A series of tetradentate tris(phosphinimine) ligands (Ptren) was developed and bound to Cu to form the trigonal pyramidal, -symmetric cuprous complexes [Ptren-Cu][BAr ] () (PR = PMe, PMePh, PMePh, PPh, PMe(NEt), BAr = B(CF)). Electrochemical studies on the Cu complexes were undertaken, and the permethylated analog, , was found to display an unprecedentedly cathodic Cu/Cu redox potential (-780 mV Fc/Fc in isobutyronitrile). Elucidation of the electronic structures of density functional theory (DFT) studies revealed atypical valence manifold configurations, resulting from strongly σ-donating phosphinimine moieties in the -plane that destabilize 2 (d /d ) orbital sets and uniquely stabilized (d ) orbitals. Support is provided that the stabilizations result from intramolecular electrostatic fields (ESFs) generated from cationic character on the phosphinimine moieties in Ptren. This view is corroborated 1-dimensional electrostatic potential maps along the -axes of and their isostructural analogues. Experimental validation of this computational model is provided upon oxidation of to the cupric complex [Ptren-Cu][OTf] (), which displays a characteristic Jahn-Teller distortion in the form of a see-saw, pseudo- -symmetric geometry. A systematic anodic shift in the potential of the Cu/Cu redox couple as the steric bulk in the secondary coordination sphere increases is explained through the complexes' diminishing ability to access the ideal -symmetric geometry upon oxidation. The observations and calculations discussed in this work support the presence of internal electrostatic fields within the copper complexes, which subsequently influence the complexes' properties a method orthogonal to classic ligand field tuning.