Ruthenium pincer complexes: Ligand design and complex synthesis

• Definitions of pincer ligands and their nomenclature are presented.
• Modification of the pincer backbone to control steric and electronic properties.
• Design of pincer ligands based on pyridine, benzene, etc. for ruthenium pincer complexes (RPCs).
• Synthesis of RPCs via direct metallation, C/SiH bond activation, trans-metallation, and trans-cyclometallation.
• Key RPC structures affect the catalyst behavior in catalytic hydrogenation reactions.

Active transition–metal complexes based on relatively inexpensive metals are considered to be a desirable method for sustainable human industrial growth. Considering their cost efficiency, ruthenium complexes are gaining increasing attraction, instead of palladium, rhodium, and iridium. Among the ruthenium complexes, ruthenium pincer complexes (RPCs) have received much attention due to their outstanding performance. Various strategies have been developed for pincer ligand design and RPC synthesis, which indicate that ligand design is a key feature of pincer chemistry. In addition, electronic and steric effects, hemilability, non-innocent behavior, and the flexibility of the pincer ligand have significant effects on the catalytic performance of RPCs in hydrogenation and dehydrogenation reactions.

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