Synthesis, Characterization and Application of Pincer Complexes for C – C Coupling

Abstract

Inorganic chemistry has gone through a colossal transformation and breakthroughs in the scientific field. The work of Alfred Werner in the development and understanding of coordination chemistry helped significantly to establish the importance of ligands in defining the properties of a central metal ion. Phosphine donor ligands and their chelates were developed as efficient new catalysts for organic transformations. In the midst of these developments, a meridional tridentate ligand emerged out of the initial work of Shaw and van Koten which unveiled and paved way to the pincer ligand as a strong contributor to the then established field of Inorganic chemistry. Pincer complexes possess unique metal bound structures which defines their desirable catalytic activity in organic transformations. Pincer compounds find major application as homogeneous catalysts and forms a major and an important segment of organometallic and coordination compounds. The present research work is focused on synthesizing non-palladium pincer complexes with ‘P’ and ‘N’ based donors for cross-coupling of aryl halides with phenylboronic acid. In our effort to provide an alternative to the costly Pd-catalyzed reactions, this study has credited a substantial materialization of nonprecious metal catalysts for the Suzuki cross coupling reactions. The basic approach of research study was to synthesize pincer complexes as homogeneous catalysts for Suzuki coupling reactions. A very good catalytic efficiency was observed with the four series of pincer complexes synthesized and their fruitfulness motivated us to heterogenize the selective complexes to achieve recovery and reusability of the otherwise disposable active components. Six of the complexes displaying high catalytic activity were chosen and immobilized on aminofunctionalized solid substrate of graphene oxide and applied again as catalysts in the coupling reaction and their recovery and reusability was demonstrated. The ease of synthesis, use of nonprecious metals as an alternative to the expensive palladium metal, low catalyst loading, mild reaction conditions, good coupling yield, catalyst recovery through immobilization are few of the key attractions of the proposed catalytic system.