Heterogeneous catalysis is central to industrial processes and sustainable development. While advantageous in terms of process intensification, they usually suffer from having ill-defined active sites, preventing the implementation of rational design strategies. While they are thus typically developed via empirical approaches, Surface Organometallic Chemistry (SOMC) has emerged as a powerful and reliable approach to synthesize well-defined catalysts, including supported nanoparticles with tailored composition and interfaces. In SOMC, a molecular precursor is grafted (reaction with the surface functionalities of a support), on isolated OH groups, to first generate well-defined surface sites via protonation of one of the anionic ligands (Figure ). This step can be followed by a thermal treatment under vacuum or a reactive atmosphere to yield isolated metal sites or supported nanoparticles. By avoiding halide precursors, often employed in classical synthetic approaches used in heterogenous catalysis, and circumventing dissolution-precipitation processes encountered in aqueous media, the amount of spectator species can be minimized. Consequently, the materials are more easily characterized, hence meaningful structure-activity relationships can be established. One of the defining ingredients to a successful SOMC protocol is the choice of molecular precursor, MXxLn (X and L = anionic and neutral ligands in the Green classification, respectively). While very much investigated for early transition-metals, the number of reactive precursors for late transition metals remains scarce since their M-X bonds are less reactive towards surface OH groups. 4 In that context, our group has explored a number of late transition-metal complexes with ligands reactive towards surface O-H groups for facile grafting. We have found that molecular precursors with amidinate ligands constitute a robust platform, 8 paralleling their success in the related field of atomic layer deposition (ALD). 9,10 These precursors enable the synthesis of narrowly dispersed metallic nanoparticles of group 9 and 10 metals -Rh, Ir, Ni, Pd, Pt -on various supports (SiO2, Al2O3, C). This approach also enables to access more complex bimetallic compositions. As discussed above, the synthesis relies on a two-step approach involving first the grafting on the support to generate isolated metal sites stabilized by the remaining ligands followed by a thermal treatment under H2 that removes all organic residues and reduces the metal site to generate nanoparticles. Notably, the grafting process of amidinate precursors occurs without liberation of the protonated amidine ligand, which remains coordinated to the immobilized metal center. This sharply contrasts with what is observed with other anionic ligands (alkyl, alkoxide and amides), where the corresponding protonated ligands is liberated upon immobilization. In this work, we set out to investigate the grafting step of aminidate precursors in more detail, focusing on Ir(COD)(DIA) (COD = 1,5-Cyclooctadiene, DIA = N,N'-diisopropylacetamidinate) (1-Ir) as a prototypical example. In short, we uncover an unusual reversible grafting mechanism upon reaction of 1-Ir with surface and molecular silanols.