Steric and electronic influence on Cu–Cu short contacts in β-thioketiminato tricopper(i) clusters†

Abstract

A series of β-thioketiminate copper(I) complex trimers [LCu^I]₃ were synthesized by modifying the ligand framework with electron-withdrawing groups (F and Cl) or electron-donating groups (ⁱPr and Me) at the N-aryl ring as well as with CF₃ groups on the chelating backbone. This ligand modification significantly impacts the enhancement of Cu⋯Cu short contacts, which can be rationalized by using steric and electronic factors of the chelated ligand. We observed that this intramolecular cuprophilicity among [LCu^I]₃ complexes is primarily governed by the size of N-aryl ortho-substituents. These findings were well supported by X-ray crystallography, Raman spectroscopy, and Mayer bond order analysis. The electronic effects induced by the ligand modification on the LCu^I fragment were investigated using CO and 2,4,6-CNC₆H₂Me₃ as probe molecules. Corroborated by the FTIR and CV measurements, our results reveal that the β-thioketiminate SN chelators induce more pronounced changes in the electronic character of the LCu^I fragment due to the presence of CF₃ groups on the chelating backbone in comparison with the F or Cl substituents on the N-aryl ring.