Encapsulation of a metal center inside the cavity of a cyclodextrin (CD) allows the control of the possible coordination modes for the metal depending on the nature and size of the cavity. We show here that the formation of encapsulated square planar Au III and Pd II complexes with CD-Nheterocyclic carbene (NHC) ligands, is only possible in the largest band g-CD cavities. In the case of a-CD-derived ligands and Pd II , an unexpected reversal of the NHC ligand was observed. These extraverted or introverted conformations of metal complexes were carefully studied by NMR and their different behaviors depending on the cavity could be revealed. The size of the CD cavity was also found to have a significant effect on the ability of Au I to be oxidized into Au III. Furthermore, in the Pd II-catalyzed nucleophilic allylation of aldehydes, the b-CD-derived ligand was able to discrimate different substrates from a mixture according to their size, leading to a significantly favored reaction with the smallest substrate.