Dissociative Ligand Exchange at Identical Molecular and Carbon Nanoparticle Binding Sites

Ligand exchange reactions at nanoparticle surfaces are critical to the formation and function of nanomaterials. The kinetics of surface ligand exchange derive from a combination of factors related to local binding site structure and the surface reaction environment. Here, we isolate the contributions of the surface reaction environment by comparing the ligand exchange kinetics of a carbon nanoparticle binding site to that of a molecular analogue with identical binding site structure. Specifically, we synthesize a graphite-conjugated pseudo-octahedral ruthenium complex, GCC-Ru, bearing a single exchangeable phosphine ligand and compare its kinetics of ligand exchange to that of the identical molecular Ru complex. Using a combination of spectroscopies, we establish common molecular coordination environments and oxidation states for GCC-Ru and the molecular analogue and use 19F NMR to interrogate the kinetics and mechanism of ligand exchange. We find that surface conjugation results in a 2- to 3-fold rate enhancement, which derives from compensating changes to ΔH‡ and ΔS‡ for a common dissociative mechanistic pathway. Based on these data, we develop a model that explains these changes to the activation parameters through charge screening by the carbon and its impact on the local solvent environment at the surface binding site. This work highlights the key role of the solvent environment at a conductive surface in facilitating ligand exchange reactions.