Synthesis of Triisocyanomesitylene β‑Diketiminato Copper(I) Complexes and Evaluation of Isocyanide π-Back Bonding

Abstract A new 2,4,6-triisocyanomesitylene ligand was synthesized and along with 1,4-isocyanobenzene utilized to prepare unique N-aryl-N′-alkylpyridyl β-diketiminato copper(I) complexes. Crystallographic characterization of 2,4,6-triisocyanomesitylene, dinuclear and trinuclear copper isocyanide complexes were carried out to elucidate their structural features. The FT-IR spectroscopic analysis of the prepared copper(I) isocyanide complexes show the CN stretching frequencies experience a significant red shift relative to those of the free ligands, indicating that π-back bonding interaction exist between copper(I) centers and isocyanide moieties. DFT based frontier molecular orbital analysis demonstrated that the enhanced π-back bonding is a consequence of the π-accepting abilities of the 1,4-diisocyanobenzene and 2,4,6-triisocyanomesitylene ligands.