Calix[n]arenes are well known polyphenol macrocyclic structures which offer several advantages over other molecular systems including their relatively easy functionalization at their lower- and upper-rims, the presence of hydrophobic cavities, and the presence of flexible core/scaffolds that can be modified for target substrate binding. Their application in the design and synthesis of new ligands for metal ions is of current ongoing interest in supramolecular chemistry due to the roles that these ions play in biological, environmental, and chemical processes.<br/>NHCs (N-heterocyclic Carbenes) rank among the most powerful ligands for transition metal catalyzed chemical transformations. Mesoionic carbenes (MICs) are a new class of ligands that have received considerable attention as they have been postulated as better sigma donors compared to their classical NHC counterparts. Owing to their synthetic versatility, a vast family of metal complexes bearing MICs has been reported in the literature, usually targeting their application in homogeneous catalysis. The increasing interest on cleaner chemical processes has risen attention in multi-metallic complexes owing to their superiority in terms of enhanced reactivity and selectivity compared to their monometallic counterparts. In recent years, our group has shown that multinuclear metal complexes of MICs can be used to generate highly potent catalysts for C-C cross-coupling reactions, hydrosilylations, cycloaddition reactions, among others.<br/>Designing conceptually new carbon-donor ligands, incorporating their strong donation properties, and developing hybrid platforms stabilized by macrocyclic frameworks (such as calixarenes) are current research topics in our research lab. In the present work, we describe the synthesis of novel hybrid calixarene-NHC/MIC architectures and their use as ligands for the stabilization of transition metal complexes. The structural diversity in solution and solid state of all new complexes and their preliminary catalytic activities will be discussed.

Hybrid calixarene-NHC/MIC ligands as versatile platforms for multimetallic species

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ACS Fall 2022

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