The role of a redox-active non-innocent ligand in additive-free C-C Glaser-Hay and Suzuki coupling reactions by an -aminophenol palladium() complex

• Published in: RSC advances Vol. 13; no. 5; pp. 3278 - 3289
• Main Authors: Pakpour, Fatemeh, Safaei, Elham, Azami, S. Mohammad, Wojtczak, Andrzej, Kaldunska, Karolina
• Format: Journal Article
• Published: 20.01.2023
• DOI: 10.1039/d2ra07252a

A novel mononuclear palladium complex with 2-(3,5-di- tert -butyl-2-hydroxyphenyl amino) benzonitrile as a non-innocent ligand (abbreviated as Pd II L 2 NIS ) was synthesized, and characterized by IR, UV-Vis, 1 H and 13 C NMR spectroscopies and elemental analysis. The crystal structure clearly showed that the metal center was in a square planar environment. The bond lengths obtained from X-ray structure analysis revealed that both ligands are in the o -iminobenzosemiquinone radical form. The neutral complex showed strong absorptions in the NIR region, corresponding to the ILCT (intra-ligand charge transfer). Catalytic tests performed for the coupling reaction of terminal alkynes showed that the palladium Pd II L 2 NIS complex acts as a highly effective catalyst for the base-free C-C coupling reactions, leading to diyne derivatives with excellent yields. The Pd II L 2 NIS complex in ethanol, as a green solvent, is demonstrated to be an exceptionally active phosphine-free catalyst for the Suzuki reaction of aryl iodides and bromides. The reaction can be carried out under mild conditions (room temperature) with high yields without using a microwave or phosphine ligands. This catalyst exhibits an interesting application of redox non-innocent ligands, the electron reservoir behavior, which makes it needless to use additional reagents. The theoretical calculation provides more details about the complex structure, molecular orbitals, and electronic state. A palladium complex of non-innocent ligand a was synthesized, and characterized by IR, UV-Vis, 1 H and 13 C NMR spectroscopies and elemental analysis.