Synthesis and catalytic applications of NHC-metal complexes supported on -butylcalix[4]arene frameworks

• Published in: New journal of chemistry 2024-08, Vol.48 (31), p.1421-1428
• Main Authors: Ruiz-Mendoza, Francisco J, Campos-Dominguez, Emmanuel, Álvarez-Hernández, Alejandro, Mendoza-Espinosa, Daniel
• Format: Article
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d4nj02392g

The preparation of a 1,3-bis-imidazolium functionalized 2,4-dihydroxyl p-tert -butylcalix[4]arene ligand [ t BuC4(OH) 2 (NHC) 2 ]Br 2 ( 1 ) is reported. Treatment of ligand 1 with excess of silver oxide allows for the straightforward preparation of the silver complex [ t BuC4(OH) 2 (NHC·AgBr) 2 ] ( 2 ) which is successfully employed as a transmetallation agent for the synthesis of a series of bimetallic complexes ( 3-5 ) of the type [ t BuC4(OH) 2 (NHC·M) 2 ] [M = Ru(cymene)Cl, Rh(COD)Cl, Pd(allyl)Cl]. Furthermore, the selective deprotonation of proligand 1 with KHMDS in the presence of AuCl(SMe 2 ) permits the isolation of the gold derivative [ t BuC4(OH) 2 (NHC·AuBr) 2 ] ( 6 ) in moderate yields. Characterization of the new complexes 3-6 was determined by spectroscopic methods and by elemental analysis. Complex [ t BuC4(OH) 2 (NHC·Ru(cymene)Cl) 2 ] demonstrated good catalytic efficiency for the transfer hydrogenation of ketones and aldehydes under low catalyst loadings, while complex [ t BuC4(OH) 2 (NHC·Pd(allyl)Cl) 2 ] performs well in the Suzuki coupling of aryl chlorides and boronic acids for the generation of di- and tri- ortho substituted biaryls. We report the synthesis, characterization, and catalytic performance of group 8-11 metal complexes supported by hybrid NHC-calix[4]arene ligands.