Synthesis of bis-1,3-(benz)azoles catalyzed by palladium-PEPPSI complex-based catalysts and the study of photophysical properties

Many biologically potent molecules have been identified to consist of benzo [b]azoles skeleton that are regarded to be the most important drug targets. Specifically, bis-benzo azoles have been the privileged conjugated structures due to their broad applications in environmental catalysis, and synthesis of various polymers, advanced materials, ligands, and natural products. Considering the significant features, different approaches have been attempted to synthesize such molecules via C-H activations by utilizing the transition metal complexes. In this study, we have developed facile and efficient Pd-based N-heterocyclic carbene (NHC) complexes, i.e., Pd-PEPPSI (Palladium-Pyridine Enhanced Pre-catalyst Preparation Stabilization and Initiation) catalysts that could successfully activate C-H bond and construct C-C bond between two 1,3-(benz)azoles via intermolecular oxidative homo-coupling reaction. The prepared Pd NHC catalysts were characterized by NMR and XPS. Pd NHCs concern about the special electronic and steric factors as the strong σ-donating and poor π-accepting properties of these nuclei renders great diversity in the field of transition metal catalysis as ancillary ligands and catalysts. Key factors of this methodology include low catalyst load, good substrate scope (even with sterically hindered substituted components), but no necessity of any extraneous ligands/oxidants and working at ambient reaction conditions with good to excellent yields of the products. Further, the targeted bis azole molecules have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and cyclic voltammetric (CV) studies. The fluorescence and absorption spectra of a few of the synthesized compounds revealed that the electron-donating groups present on N-substituent dictate the absorption and emission bands.

WEPA: a bio-derived medium for added base, π-acid and ligand free Ullmann coupling of aryl halides using Pd(OAc)2

A bio-derived sustainable medium based on water extract of pomegranate ash (WEPA) has, for the first time, been developed for the homocoupling of aryl halides under palladium-assistance. Avoiding the requirement of an external base, ligand and π-acid, the use of the proposed renewable medium offers remarkable attributes like wide substrate scope, good to nearly quantitative yields of biphenyls with exceptional chemoselectivity and scale up viability.

Aminoborylation/Suzuki-Miyaura tandem cross coupling of aryl iodides as efficient and selective synthesis of unsymmetrical biaryls

Sequential borylation of a first aryl iodide using a dialkylaminoborane followed by a Suzuki-Miyaura cross coupling of second aryl iodide ended up with an efficient, selective and practical synthesis of unsymmetrical biaryls. This tandem coupling shows a wide range of applicability.