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Two independent pathways to Ag(I)-N-heterocyclic-calix [4]arene complexes (5a,b and 6-8) starting from three calix [4]arenes bearing one or two (distal or proximal) imidazolium substituents attached at the upper rim via a methylene linker are described. Complexes 5 were synthesized using the free carbene route, and complexes 6-8 were obtained via in situ formation of the N-heterocyclic carbene by deprotonation and reaction with Ag 2 O. The structure of 5a could be verified by an X-ray single-crystal structure determination. 1 H NMR studies of the compounds 5a,b showed dynamic behavior in solution, similar to a conformational change observed for known phosphine-based calixarene ligands. Using the imidazolium-calixarenes as precursors, NHC complexes of mercury, iridium, platinum, and ruthenium have been prepared and characterized. Additionally, cis and trans Pd(II)-N-heterocyclic-calix[4]arene complexes (3 and 13) were synthesized independently by in situ deprotonation of 2 with Pd(OAc) 2 and by transmetalation using Ag(I) complex 6 as a supramolecular carbene transfer reagent, respectively. Both isomeric complexes 3 and 13 were tested as catalysts in the Suzuki-Miyaura reaction and compared to previously reported in situ systems. Both isolated complexes exhibit, independently of their geometry, the same catalytic activity, which is superior to the in situ system used for comparison.

Supramolecular, water-soluble additives based on calix[n]arenes exhibit a beneficial influence on the ring-closing and cross metathesis of non-polar substrates in pure aqueous medium using standard Grubbs-II and Hoveyda-II catalysts. The catalytic activity observed in water is virtually the same as that in pure methanol. Quantitative yields of metathesis product can be achieved under mild aerobic conditions in/on water by (micro)solubilization of both the catalyst and starting materials by the macrocycles.

The deprotonation of imidazolium salts to N-heterocyclic carbenes is often a decisive step in modern catalytic reactions. Therefore, we studied the H/D exchange of the C2 H of 15 imidazolium-substituted calix[4]arenes and 11 nonmacrocyclic model compounds in methanol/water (97:3). The influence of the counterion, substitution directly on the imidazolium unit or on the preorientating calixarene backbone could be studied. The observed exchange rates might give a rational for the suitability of the imidazolium salts as precursors in the Suzuki coupling.

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