Cationic copper (I) complexes with bulky 1,4-diaza-1,3-butadiene ligands – Synthesis, solid state structure and catalysis

• Two bulky 1,4-diaza-1,3-butadiene ligands were synthesized.
• Ligand 2 formed homoleptic and ligand 3 formed heteroleptic copper(I) complexes.
• Solid state structures of all the ligand s 2-3 and copper(I) complexes 3-5 were established.
• Complexes 3-5 were tested as catalyst for the coupling reaction of o-iodophenol and phenyl acetylene.

We report the full characterization of two glyoxal-based ligands N,N bis(diphenylmethyl)-1,4-diaza-1,3-butadiene ligand (DADPh2, 1) and more bulky N,N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand (DADPh3, 2) by the condensation reaction of glyoxal and diphenylmethanamine and triphenyl-methanamine respectively. The copper (I) complex of composition [Cu(DADPh2)2]PF6 (3) having two neutral bidentate N,N bis(diphenyl-methyl)-1,4-diaza-1,3-butadiene ligand was prepared by the reaction of [Cu(CH3CN)4]PF6 and 1 in 1:2 ratio in dichloromethane. In a similar reaction with N,N bis(triphenylmethyl)-1,4-diaza-1,3-butadiene ligand (2) and [Cu(CH3CN)4]PF6 in dichloromethane yielded corresponding heteroleptic copper (I) complex [Cu(DADPh3)(CH3CN)2]PF6 (4). Another copper (I) complex [Cu(DADPh2)(PPh3)]PF6 (5) can also be obtained by the one pot reaction involving ligand 1, [Cu(CH3CN)4]PF6 and triphenylphosphine. Solid state structures of all the five compounds were established by single crystal X-ray diffraction analysis. The solid state structures of the copper complexes 3–5 reveal a distorted tetrahedral geometry around the copper (I) centers. The copper complexes 3–5 were tested as catalysts for the coupling reaction of o-iodophenol and phenyl acetylene and it was observed that complex 4 exhibits the highest catalytic activity.